Traditional stiffness modeling methods do not consider all factors comprehensively, and the modeling methods are not unified, lacking a global stiffness model. Based on screw theory, strain energy and the virtual work principle, a static stiffness modeling method for redundant over-constrained parallel mechanisms (PMs) with clearance was proposed that considers the driving stiffness, branch deformation, redundant driving, joint clearance and joint contact deformation. First, the driving stiffness and branch deformation were considered. According to the strain energy and Castiliano’s second theorem, the global stiffness matrix of the ideal joint mechanism was obtained. The offset of the branch was analyzed according to the restraint force of each branch. The mathematical relationship between the joint clearance and joint contact deformation and the end deformation was established. Based on the probability statistical model, the uncertainty of the offset value of the clearance joint and the contact area of the joint caused by the coupling of the branch constraint force was solved. Finally, taking a 2UPR-RR-2RPU redundant PM as an example, a stiffness simulation of the mechanism was carried out using the finite element method. The research results show that the high-precision stiffness modeling method proposed in this paper is correct, and provides an effective method for evaluating the stiffness performance of the PM. The stiffness reflects the displacement of the end of the mechanism relative to the expected position under external forces. The stiffness of the parallel mechanism (PM) often determines the kinematic positioning accuracy and kinematic characteristics of the end effector. In addition, insufficient stiffness may reduce the natural frequency and dynamic performance of the system. Therefore, the stiffness performance should be evaluated in the product design phase.In terms of stiffness modeling methods of PM, the main methods include screw theory , the semWhen the mechanism has clearance joints, the end position depends on the attitude, load, geometric parameters of the joint and the joint force, and the relative position inside the joint is uncertain. In order to solve this problem, the commonly used methods are the worst-case method, probability statistical model, interval analysis method, virtual connection method and hybrid dimension reduction method. Choi et al.  put forwThe static stiffness model that considers the joint clearance needs to study the linear deformation and angular deformation of the end in all directions. In particular, the deformation of the end constraint direction needs to be considered. In order to establish a static stiffness model of the mechanism considering hinge clearance, it is necessary to study the line deformation and angular deformation in each direction of the end, considering the deformation in the direction of the end constraint in particular. Most of the existing error models are based on inverse kinematics, which can only obtain the deformation in the direction of the end output DOF, and they are not suitable for stiffness models. The over-constrained PM is affected by the coupling of the constraint force and constraint couple at the joint. The line deflection and angular deflection of the joint with clearance in the branch is coupled. The offset/deflection of the joint with clearance is affected by multiple factors; for example, the clearance size, external load, mechanism attitude, redundant branch and the constraint force/torque amplitude of the branch. This makes the modeling and analysis of its clearance model more difficult. For PMs used in a heavy-load field, the constraint force between joints is large. According to Hertz contact theory, the greater the contact force between two objects in contact, the greater the contact deformation of the hinge.To summarize, previous stiffness studies focused on local factors, resulting in inaccurate stiffness modeling. This paper studied the position distribution of the clearance joints under the branch-coupling constraint of redundant over-constrained mechanisms under different external loads. The mathematical relationships between the driving stiffness, branch deformation, redundant driving, joint clearance, joint contact deformation and end stiffness of the mechanism were established. The influence of each factor on the stiffness of the mechanism was analyzed. A novel 2UPR-RR-2RPU redundant over-constrained PM was taken as an example to verify the correctness of the proposed model.(1)According to the screw theory, the drive screw and constraint screw of a redundant branch and non-redundant branch are analyzed. Then, the drive Jacobian matrix and constraint Jacobian matrix are constructed.(2)The driving stiffness is analyzed from the perspective of material mechanics. The strain energy of each branch under the constraint force is calculated and the functional relationship between the strain energy of the branch and the constraint force of the branch is derived.(3)Based on Castigliano’s second theorem, the partial derivatives of the strain energy of each branch on the constraint force of the branch are calculated, respectively. The functional relationship between the deformation of the end of the branch and the constraint force of the branch is obtained, namely the flexibility matrix of the branch.(4)According to the deformation compatibility equation of the mechanism and virtual work principle, the stiffness matrix of the whole mechanism and the constraint force of each branch are solved and the end deformation caused by the driving stiffness and branch deformation is obtained.(5)Based on the constraints of each branch, the position distribution of the clearance joints and the contact area of the joints are predicted by the probability statistical model. It solves the problem of the modeling error caused by coupling constraints of over-constrained mechanisms. The deformation caused by the joint clearance and joint contact deformation along the constraint direction at the connection between each branch and the moving platform end is analyzed. Based on the principle of virtual work, the end deformation interval caused by joint clearance and joint contact deformation is obtained.(6)Assuming that there is no coupling between rigid body displacement and elastic deformation, the four factors are regarded as mutually independent and can be linearly superposed. A high-precision static stiffness model considering multiple factors is obtained.High-precision stiffness modeling method of redundant over-constrained PMs considering multiple factors:Based on the above assumptions and modeling process, the high-precision static stiffness model considering multiple factors can be expressed asIn the Equation, In the Equation, The force analysis of over-constrained PMs is statically indeterminate, and the structural stiffness of each branch needs to be considered. In this paper, the moving platform was assumed to be rigid, and the spatial composite elastic deformation of the branch bending, stretching and torsion was considered. The driving force/restraint stiffness matrix of the branch is defined as the mapping relationship between the driving force/restraint amplitude and the elastic deformation of the end along the driving force/restraint direction. w. According to the static equilibrium equation of the moving platform, we can obtainThe moving platform of the mechanism is acted on by a six-dimensional external force i acting on the moving platform, and i acting on the moving platform. n represents the number of all constrained screws of non-redundant branches in the mechanism, m, and i represents the number of all constraint forces of redundant branches in the mechanism.In Equations (4) and (5), Assuming that the branch driving force In Equation (8), Sorting Equation (3) and Equations (6)–(8) simultaneously, we can obtainIn order for Equation (9) to be established, it is necessary to satisfyCombining Equations (3), (6), (7), (10) and (11), the relationship between the external force on the moving platform and the micro-deformation of the moving platform when considering the driving stiffness and the deformation of the branch can be obtained.In the Equation,a represents the driving force, c represents the constraint force , n represents a basic branch and r represents a redundant branch. Combining Equations (5), (6) and Equations (9)–(11), the expressions of the driving force, constraint force and external force of the moving platform can be obtained.Rearranging the above equation can obtain(1)Firstly, the drive force (2)It is assumed that the additional motion of the branch with clearance is in the same direction as the restraint force of the branch. According to the size and direction of the restraint force of each branch, the additional motion direction of the branch with gaps can be determined. The static stiffness modeling process of redundant over-constrained PMs when considering joint clearance is shown in (3)First, the coupling effect of the constraint and constraint couple is ignored and the constraint is considered as a pure force or a pure couple. In most working conditions, the drive force of each branch is much greater than the constraint force, so it is assumed that the clearance joint offset/deflection and joint contact area in the drive force direction reach the maximum. It is also assumed that the ratio of the drive force The offset/deflection of a branch with joint clearance under an external force is affected by multiple factors, such as the clearance size, attitude of mechanism, redundant branch and branch constraint force/couple. Over-constrained redundant PMs generally belong to statically indeterminate structures, and the constraints between branches are complex. Under a certain static attitude and load, the joint with clearance will produce tiny line deflection/angular deflection in its constraint direction under the action of constraint force/torque. It is difficult to judge the joint contact area caused by the branch compound constraint, and it is difficult to establish an accurate mathematical model. In this section, based on certain assumptions, the approximate change interval of the mechanism end is obtained when the joint clearance and joint contact deformation are considered. The specific process is as follows:Therefore, the offset of each branch along the constraint direction is(4)i, i and i.).The offset/deflection of the end of each branch caused by the joint clearance and joint contact deformation is mapped to the deformation of the moving platform by the principle of virtual work. When the deviation of the restraint direction of the clearance joint does not reach the maximum value, the direction also does not reach the contact state and there is no contact deformation between the joints. The static stiffness modeling process of the redundant PM when considering the contact deformation of the joint is shown in (5)In order to solve the uncertainty of the gap joint offset value and joint contact area caused by the branch-coupling force, a random method can be used to describe the variation characteristics of the gap and contact area. In this paper, a 2UPR-RR-2RPU redundant over-constrained PM was taken as an example to verify the accuracy of the proposed stiffness modeling method. The mechanism is a loop decoupled PM that adopts the method of adding two redundant branches to improve the overall bearing capacity and deformation resistance of the output end.x0 axis along the oA4 direction, the y0 axis along the oA1 direction, and the z0 axis is determined according to the right-hand rule. The moving coordinate system x1 axis along the o1B4 direction, the y0 axis along the o1B1 direction, and the z1 axis is determined according to the right-hand rule. The middle branch of RR is a just-constrained branch and its axis of rotation connected to the fixed platform is along the direction of x-direction DOF of rotation of the moving platform around the axis. Its axis of rotation connected to the moving platform is along the direction y-direction DOF of rotation of the moving platform around the axis. Among them, the R pairs of the two UPR branches whose respective U pairs are connected to the fixed platform and the R pairs of the RR just-constrained branch that are connected to the fixed platform are coaxial. The respective R pairs of the two UPR branches are parallel to the R pairs of the RR just-constrained branch, which is connected to the moving platform. Among them, the R pair of the two RPU branches whose U pairs are connected to the moving platform is coaxial with the R pair that is connected to the RR just-constrained branch and moving platform, and the respective R pairs of the two RPU branches are, respectively, parallel to the R pairs that are connected to the RR just-constrained branches and fixed platform.As shown in In order to obtain the full Jacobian matrix of the mechanism, the constraint Jacobian matrix and the driving Jacobian matrix of the mechanism should be solved first.It can be represented by a screw asIn Equation (16), Let the rotation angle of the mechanism around the rotation axis According to the screw theory, the screw that is reciprocal to the non-redundant UPR branched motion screw is its constraint screw.Redundant UPR branches and non-redundant UPR branches are symmetrically arranged in the plane of the base coordinate system with respect to the RR just-constrained branch. In order to obtain the constraint screw According to the screw theory, the screw that is reciprocal to the non-redundant RPU branched motion screw is its constraint screwThe redundant RPU branches and the non-redundant RPU branches are symmetrically arranged on the base coordinate system The RR intermediate branch-constrained screw is expressed in the fixed coordinate system asFrom Equation (3), it can be obtained that the non-redundant constrained Jacobian matrix The following assumptions are made for the stiffness model: the weight of all components is ignored; all joint models are frictionless; the moving platform is assumed to be a rigid body; and the spatial composite elastic deformation of the branch is considered, including tensile, shear, bending and torsional deformation.The branch driving stiffness can be simplified as a series spring system, and the driving stiffness coefficient EA represents the tensile modulus of the pendulum rod, In the Equation, it is expressed as a U pair along the rod axial stiffness x-axis direction at the cross-section of the RR branch, y-axis direction at the cross-section, z-axis direction at the cross-section, x-axis direction at the cross-section, and z-axis direction at the cross-section.The force diagram of the UPR branch is shown in The internal force of the section where the In the Equation, The strain energy of UPR branches can be expressed asIn the Equation, In the Equation,According to Castigliano’s theorem, we can obtainArranging the above Equation into matrix form, we can obtainIn the EquationIt can be seen from the UPR branch compliance matrix that the compliance matrix is not a diagonal matrix. There is a coupling relationship between the constraint force x-axis direction at the cross-section of the RR branch, y-axis direction at the cross-section, z-axis direction at the cross-section, x-axis direction at the cross-section, and z-axis direction at the cross-section.The force diagram of the RPU branch is shown in The internal force of the section where the displacement from the RPU branch to the negative direction of the branch coordinate system In the Equation, The strain energy of RPU branches can be expressed asIn the Equation, According to Castigliano’s theorem, we can obtainIn the Equation,Arranging the above Equation into matrix form, we can obtainIn the Equation,The stiffness matrix of the RPU branch is the inverse of the compliance matrixIt can be seen from the RPU branch compliance matrix that the compliance matrix is not a diagonal matrix. There is a coupling relationship between the constraint force x-axis direction at the cross-section of the RR branch, y-axis direction at the cross-section, z-axis direction at the cross-section, x-axis direction at the cross-section, and z-axis direction at the cross-section.The force figure of the RR just-constrained branch is shown in The internal force of the section where the displacement from the RR just-constrained branch to the negative direction of the branch coordinate system In the Equation, The strain energy of the RR-constrained branch can be expressed asAccording to Castigliano’s theorem, we can obtainArranging the above Equation into matrix form, we can obtainIn the Equation,The stiffness matrix It can be known from the RR branched compliance matrix that the compliance matrix is a diagonal matrix and that there is no coupling relationship between the constraint force, constraint couple and their corresponding elastic deformation.The precise mathematical model of the over-constrained redundant PM with joint clearance is very complicated. The tiny deformation transmitted by each branch with joint clearance to the moving platform is affected by many factors, such as the driving force, posture and attitude, clearance size and external load. The position and attitude of the moving platform is not completely calculated by the inverse kinematic solution, so the moving platform has an active status in the tiny working space, resulting in an uncertain position of the moving platform. An excessive constraint force between joints under large-load conditions will lead to slight penetration deformation, and the penetration deformation of joints will also affect the stiffness of the moving terminal. This cannot be ignored in the field of high precision.(a)The R pair shaft and the U pair cross shaft are regarded as rigid bodies, and the shaft is in complete contact with the inner wall of the outer cylinder of the rod. (b)The friction force of the joint, the gravity of the rod and the deformation of the branch are ignored. The branch is regarded as a two-force rod.(c)The clearance of the driving pair is not considered.(d)It is assumed that the linear/angular displacement of the joint reaches the maximum value under the action of the constraint force/couple.(e)The clearance at the end of the branch is approximately equal to the linear superposition of the linear/angular displacements of each joint in the branch caused by the constraint force/couple.(f)Without considering the coupling effects of the constraint force and constraint couple on the joint with clearance, the linear displacement/angular displacement of the joint with clearance under the pure force/pure couple is calculated independently, and then a statistical probability model is used to modify the simplified gap stiffness model. Because most parallel robots have no large deformation during operation, it is assumed that there is no coupling between rigid body displacement and elastic deformation in the calculation. This assumption also ensures that the end stiffness changes caused by joint clearance can be calculated independently.Usually, the R pair consists of two parts: the rotating shaft and the outer cylinder of the clearance. It is assumed that there is an assembly clearance between the rotating shaft and the rod in the axial and radial directions of the rotating shaft. A local coordinate system y-axis, as shown in x-axis or z-axis, it can be inferred from the geometric relationship of the clearance modelWhen the constraint force is the pure constraint couple around the Solving the above equation, we can obtainWithout considering the coupling effect of the constraint force and constraint force couple, the simplified approximate clearance model of the R pair can be expressed asThe UPR branch is subject to the constraint couple Assuming that the radial and axial clearances of the two orthogonal R pairs in the U pair are The first lines of three represent the offsets along the three axes of the coordinate system Then, the offset/deflection of the U pair in the coordinate system In the Equation, The offset The R pair is acted on by the driving force Therefore, the total offset of the UPR branch in the direction of the driving force produced by the driving force The UPR branch is subjected to a constraint couple along the normal direction of the U axis. The deflection generated by the U pair can be equivalent to the superposition of the deflections of the two R pairs with mutually orthogonal axes around the direction of the constraint couple; that is, The RPU branch clearance model is the same and will not be introduced here.The RR intermediate branch clearance model can be equivalent to a U pair, and the branch terminal offset/deflection isWe can obtainThe method of the virtual work principle is suitable for the prediction of the position and attitude accuracy of the mechanism under complex working conditions, and it can achieve a more reasonable description between the joint clearance and the end position and attitude error. The virtual work principle is used to determine the relationship between the position error of each branch and the position error of the platform caused by the clearance. The superposition method is used to quantify the position and attitude error of the branch caused by the clearance of each joint. It is assumed that the offset/deflection of the end of the branch reaches the maximum under the constraint/couple of the branch. It can be obtained from the virtual work principle.Simplifying further, we can obtainIn the Equation, In the Equation,Due to the coupling effect between the restraint forces, the offsets of the clearance joint along the restraint force direction do not all reach the maximum value. Assuming that the probabilities of the position and attitude of the offset feature elements of all gap joints in the space of the gap joints are equal and meet the normal distribution, the gap joint offset value is given a specific probability distribution attribute on the basis of the maximum value. For the probability distribution of joint clearance, in most cases, it is less than 1. The correction coefficient of random physical variables is defined as the normal distribution coefficient In the Equation, The contact force is approximately equal to the constraint force and is much larger than the friction.Contact deformation is linear elasticity, regardless of the coefficient of restitution, contact deformation speed and initial impact speed.The contact force of the joint is approximately equal to the constraint reaction force.The influence of the coupling of the constraint force and constraint couple on the contact deformation is ignored. The contact deformation under the independent action of the restraint force/moment is calculated separately, and then the calculated results are superposed.When there is clearance, the restraint force of each branch is approximately equal to that obtained by solving the stiffness matrix of the mechanism when there is no clearance.There are three cases of the R-pair contact model: (a) plane–plane contact along the axis of the shaft caused by axial restraint; (b) cylinder–cylinder contact along the radial direction of the shaft caused by radial restraint; (c) line–plane contact caused by the radial restraint couple. The kinematics pair has two parallel contact surfaces. The contact areas of the contact surface are known. The contact force model is expressed asThe corrected elastic modulus can be expressed asIn the Equation, the elastic modulus and Poisson’s ratio of one contact body are It can be obtained that the contact deformation caused by the axial constraint force isTwo cylinders whose axes are parallel to each other are in contact, and the contact force can be expressed asThe contact deformation caused by the radial constraint force isFor the contact deformation caused by the constraint couple in the radial direction, the contact force can be expressed asThe functional relationship between the contact force and the deformation at the contact point isR is the equivalent radius of the two contact bodies, and is shown as follows:It can be seen from the above Equation that the functional relationship between the contact angle deformation of the joint and the constraint couple is not linear. In order to simplify the contact deformation model, the constraint couple within a certain range of the contact deformation model is universal. A correction factor The R pair approximate contact deformation model can be defined asIn the Equation, The U pair joint contact deformation model can be equivalent to the U pair joint clearance model, and the approximate contact deformation model in the U-axis coordinate system In the Equation, Assuming that each clearance joint of the mechanism reaches a permanent contact state under a static large load, the contact force is approximately equal to the constraint force. Taking the UPR branch as an example, the contact deformation of the driving pair is ignored. Firstly, the contact deformation caused by the driving force In order to analyze the contact deformation of U pair axis 1 in the direction of the driving force In the Equation,According to Equation (77), the six-dimensional contact deformation of the U pair shaft 1 in the coordinate system The contact deformation Therefore, the total contact deformation of the U pair in the direction of the driving force In the Equation, When the UPR branch is only subjected to the driving force The contact offset of the UPR branch in the direction of the driving force caused by the driving force The UPR branch is subject to a constrained couple Then, the total angular contact deformation of the UPR branch along the direction of the constraint couple The UPR branch is subjected to a constraint force The RPU branch clearance model is the same and will not be introduced here.The contact model of the RR intermediate branch is equivalently analyzed as the U pair, and it can be obtained thatThe terminal 6-DOF directional deformation is quantified as the joint contact deformation and the load function acting on the platform by the principle of virtual work.Simplifying further, we can obtainIn the Equation,In the Equation,Because of the coupling effect between the restraint forces, the contact areas of the joint along the restraint force direction do not all reach the maximum value. This will cause a stiffness modeling error. In order to achieve the high-precision stiffness modeling of the mechanism, it is assumed that all the characteristic elements of the joint contact area are located in all the contact areas within the joint with equal probability and meet the normal distribution. Therefore, the joint contact area is given a specific probability distribution attribute on the basis of the maximum value. For the probability distribution of the joint contact area, in most cases, it is distributed at around less than 1. The correction coefficient In order to reflect the end deformation of a 2UPR-RR-2RPU redundant PM when driving stiffness and branch deformation are considered, the square root of linear deformation in three directions is taken as the stiffness evaluation index.x axis, y axis and z axis, respectively.x, y and z axes, respectively.In the Equation, z-direction actuator cylinder to simulate the force acting on tires on rough, potholed and inclined roads. It compensates for the deficiency of a four-channel road simulation platform that can only provide z-direction excitation. The quarter vehicle load is 7500. Through the above stiffness performance evaluation indicators, the global performance distribution of a 2UPR-RR-2RPU redundant PM under four factors was studied, respectively, as shown in The structural parameters of the 2UPR-RR-2RPU redundant PM are as follows: the external diameter of the swing rod is 40 mm; the internal diameter of the swing rod and the external diameter of the push rod are 25 mm; the length of the swing rod is 205 mm; the diameter of the intermediate restraining chain is 45 mm and its height is 320 mm; the radius of the fixed platform is 260 mm; the radius of the moving platform is 210 mm; the elastic modulus is 200 GPa; and the Poisson’s ratio is 0.3. In the analysis of joint clearance, it is assumed that the axial clearance of the joint is 0.1 mm and the radial clearance is 0.05 mm. In the analysis of joint contact deformation, the length of the joint outer cylinder is 105 mm, and the diameter of the joint outer cylinder inner wall is 25 mm given a 7500 N external load downward along the normal direction of the moving platform. This parallel mechanism is applied in the field of wheel coupling fatigue durability testing. The mechanism is connected in series with the Through the defined stiffness index in this paper, the following conclusions can be drawn.After the introduction of redundant branches, the stiffness characteristic distribution of the PM is improved. The structural stiffness has good symmetry in the workspace. The linear stiffness and angular stiffness are obvious. The stiffness of the mechanism is less affected by the rotation angle In order to verify the correctness of the theoretical model under the ideal joint, the Solidworks model was imported into the Ansys Workbench. The material performance parameters were defined as follows: density The deformation cloud diagram obtained by finite element simulation is shown in The given load of the moving platform is as follows:The revised stiffness model considering the clearance and joint contact deformation was calculated 5000 times. The 32 random variables involved in the calculation each time meet the normal distribution. A histogram was drawn and the distribution was fitted for the 5000 groups of final end deformations—that is, the distribution shape of the end stiffness—taking 50 sample spaces within the maximum and minimum range of linear deformation/angular deformation at the end of the 2UPR-RR-2RPU redundant PM. The stiffness distribution of the initial position and attitude considering joint clearance and joint contact deformation is shown in According to the stiffness distribution diagram, the following conclusions are drawn.The fluctuation range and probability distribution of the output end stiffness caused by the random parameters related to 16 joint gaps and 16 joint contacts are clearly shown. According to the law of large numbers, although the linear stiffness/angular stiffness distribution in each direction is slightly different, it basically conforms to the normal distribution.The shape of the stiffness distribution is determined by the predetermined pose and given parameters .In order to facilitate the convergence of the model, the calculation time was saved. In the simplified model, the connecting rod was set as a rigid body, and the clearance joint was set as frictionless contact. The mesh of the contact area was refined, the contact parameters and iteration steps were set reasonably and the fixed constraints were added to the fixed platform. The deformation of the moving platform with clearance joints under two different loads in the attitude Load 1:Load 2:x, y, z axis tends to zero under the given boundary conditions. Therefore, only the line deformation along the x, y, z direction was analyzed. When the standard deviation is 1/16, the finite element simulation of the stiffness prediction interval at the output end of the attitude and the center of the moving platform is obtained. The simulation results are shown in The above load on the moving platform was applied and the contact parameters of the clearance joint  were set. The angular deformation around the As shown in z direction is far greater than that along the x, y directions, whereas the force amplitude of load 2 along the x, y, z directions is equal. Taking t as the step size, the simulation time is given as 2 s, and the output motion law and applied dynamic load of the PM are as follows:In order to evaluate the accuracy of the joint clearance model and joint contact deformation model under different external loads, the deformation of the end under two different external loads is discussed. The force amplitude of load 1 along the Plan attitude and load 1:Plan attitude and load 2:Based on the analysis method proposed in this paper, the driving stiffness, bar deformation, joint clearance and joint contact deformation were considered. Using Matlab software to calculate the 2UPR-RR-2RPU redundant PM, the deformation of the PM output end in the six-DOF direction is caused by various factors under the above load conditions and given motion laws. Statistical analysis was carried out on the modified clearance model and joint contact deformation model. The stiffness performance considering clearance and joint contact deformation was evaluated by means of sample mean and the quality of the statistical simulation results was evaluated. The maximum/minimum values of the samples were used to judge the stiffness fluctuation range considering the clearance and joint contact deformation. The approximate linear/angular stiffness interval of the mechanism in each direction can be determined. The maximum, minimum and average values of line deformation/angular deformation in each direction considering different factors under two different planning attitudes and loads are shown in Firstly, a high-precision stiffness modeling method of an over-constrained redundant PM was proposed. Taking a 2UPR-RR-2RPU over-constrained redundant PM as an example, the ideal joint was derived by using strain energy and Castigliano’s second theorem. The stiffness matrix of the mechanism with its driving stiffness and branch deformation and the restraint force of each branch should be considered.Based on the principle of virtual work, a stiffness modeling method considering the joint clearance and joint contact deformation was proposed. The probabilistic model was used to predict the position distribution of the clearance joints, and the problem of the modeling error caused by coupling constraints of over-constrained mechanisms was solved. The stiffness variation interval considering the joint clearance and joint contact deformation under different external loads was obtained, and the influence degree of each factor  on the end deformation was analyzed.Finally, the correctness of the proposed stiffness model was verified using the finite element method. This method can help robot designers and manufacturing engineers to fully consider the influence of multiple factors  on the static stiffness of the mechanism. Through this method, a high-precision static stiffness model can be established to achieve the best performance of the mechanism.


C. albicansis an important human fungal pathogen and filamentation is essential for its virulence. Ume6 is a transcription factor critical for filamentation. Ume6 is composed of three domains, a long N terminal domain, Zn-finger domain, and a C-terminal domain. Previously, it was shown that the Zn-finger domain is essential for filamentation, as removal of this domain led to a lack of filamentation. However, the role for the C-terminal domain has not been defined. We find deletion of the C-terminal domain leads to a filamentation defect and the defect is not as severe as removal of the Zn-finger orume6deletion. We mutated a number of residues in the C-terminal domain to try to identify specific residues important for filamentation, but all of our mutants displayed wild type filamentation. Alpha fold predictions suggest the C-terminal domain forms a single alpha helix that is predicted to interact with the Zn-finger domain via hydrogen bond. Our data suggests the C-terminal domain binds the Zn-finger domain and through this interaction is important for filamentation. C. albicansis the most prevalent human fungal pathogen (Beck-Sague and Jarvis 1993). As a commensal,C. albicans asymptomatically colonizes gut mucosal tissue, however, immunosuppression can lead toC. albicans becoming an opportunistic pathogen.C. albicans can infect a wide range of host tissues including the mouth, genitourinary tract, heart, and kidneys. Infections range in severity from irritating mucosal infections, such as thrush, to candidemia, a life-threatening systemic infectionC. albicans, like many human fungal pathogens, can undergo morphological changes and these changes are critical for virulence. One of the most pronounced morphological changesC. albicansundergoes is the process of filamentation. During filamentation,C. albicansproduces long extensions that can invade agar or tissueIn response to stress,C. albicansUme6 is a transcription factor that is over 800 amino acids in length. It is composed of a 760 amino acid long but poorly conserved N-terminal domain. The Zinc-finger is critical for function as truncation of this domain leads to loss ofC. albicans'ability to form filaments. C-terminal to the Zinc-finger domain is a poorly conserved C-terminal domain for which little is known. Given its lack of conservation, we hypothesized the C-terminal domain was dispensable for wild type filamentation and growth. To test this hypothesis, we used CRISPR mediated genome editing to generateume6-822which truncated Ume6 after the Zinc-finger domain. We next tested if our mutant strain had a defect in growth rate or filamentation. We found that whileume6-822 grew at an equivalent rate to wild type at both 30 and 37 C°it had a severe defect in filamentation at both temperatures when grown on Spider media. We observed a wrinkled colony phenotype at 37 but not 30 C°, and we never detected agar invasion even after 9 days of incubation at either temperature. This is similar the phenotype observed when we removed the entire Zinc-finger domain and in the deletion mutantsume6-822filamented at wild type levels suggesting a specific defect in agar invasion, but not filament formation.ume6-833,ume6-838, andume6-840, each of which replaced two C-terminal tail residues with alanine. We found these mutants did not changeC. albicansgrowth rate and did not have profound effects on filamentation.ume6-840 appeared to have a minor effect on filamentation, but we are hesitant to place high significance on this change as it was not nearly as severe asume6-822.Attempts to create further truncations and additional mutants were unsuccessful suggesting this region of DNA is not readily accessible to genome editing machinery. Another formal possibility is that these residues are essential in the context of the rest of the protein. Ume6 is not essential, as much more severe truncation and deletion mutant strains are viableNext, we wanted to determine if particular C-terminal tail residues were important for function. We used CRISPR to generate 3 strains;UME6deletion onC. albicansbiology have been thoroughly characterized, little is known about how the underlying biochemistry of the Ume6 protein leads to these phenotypes. To further understand why the truncation of the poorly conserved Ume6 C-terminal tail had such a profound effect on filamentation, we examined structural predictions for Ume6. Alphafold structural predictions are provided on theCandidagenome database (CGD) for all predicted open reading frames in the annotated genomesC. albicansUme6 provided little insight into the function of the N-terminal domain as almost the entire domain had confidence scores below 50 which is indicative of a protein region that either lacks structure or is labileC. dubliniensis,C. parapsilosis, andC. auris Ume6 homologs. The Zinc-finger and C- terminal domains however are predicted with high confidence with the Zinc-finger forming a classic Zinc-finger fold and the C-terminal domain predicted to form a single alpha helix. Furthermore, Asn825’s side chain amine is predicted to hydrogen bond to the carboxylic acid backbone of residues Phe791 and Gly792 located in the Zinc-finger domain. Analogous interactions are predicted inC. dubliniensisandC. parapsilosisUme6 homologs.C. auris, the only other Ume6 homolog for which Alphafolds predictions are given on the CGD is predicted to form a C-terminal alpha helix, but the residues that theC. aurishelix uses to interact with the Zinc-finger domain are distinct from the predictions forC. albicans,C. dubliniensisandC. parapsilosis.While the ramifications ofC. albicans, elimination of the C-terminal tail leads defects in filamentation. While none of the point mutants we made led to an observable defect in filamentation, Alphafold predictions suggest hydrogen bonds between the Asn825 side chain and the Zinc-finger motif could be important for orienting the Zinc-finger motif. In addition, Zn-finger proteins have been shown to dimerize and the C-terminal tail interactions could play a role in orienting the Zinc-finger domain so that dimerization can take place2+ion. The interaction between Asn825 and both Phe791 and Gly792 or an analogous interaction is predicted to occur in a number of other CTG species suggesting a shared structural theme of a C-terminal alpha helix that interacts with the Zinc-finger domain via hydrogen bonds. Interestingly,C. glabrata’sUme6 C-terminal tail is predicted to form an alpha helix but no hydrogen bonds are predicted to interact with the Zinc-finger domain. Alphafold was not able to predict the structure of the vast majority ofC. albicansUme6, suggesting these regions are either unstructured or highly labile. To our knowledge, there are no known structures of the Ume6 protein family in the protein data bank, but many budding yeast species encode Ume6 homologs. The effect of Ume6 on phenotype differs between species, with theS. cerevisiaehomolog thought to be important for mating andC. albicansessential for filamentation. Furthermore, while Ume6 has been shown to play a role in filamentation in a number of CTG clade species, the process and significance of filamentation to virulence varies amongst members of the CTG clade.Taken together our data suggests an important conserved role for the Ume6 C-terminal tail in the CTG fungal clade. InC. albicans Strain Creation:UME6were cloned into pV1093. Vectors were linearized via digestion with KpnI and SacI. Repair templates encoding premature stop codons or point mutations inUME6were synthesized. Repair templates and linearized vector were co-transformed intoC. albicans SC5314 via lithium acetate transformation. Transformations were plated on YPD supplemented with 200 µg/ml nourseothricin for 3 days at 30°C. Single colonies were isolated on YPD supplemented with 100 µg/ml nourseothricin and grown for 3 days at 30°C. Mutants were identified via restriction digest screening and DNA sequencing.Guide RNA primers targetingGrowth and Filamentation Assays:600. 4-fold serial dilutions were plated on YPD and Spider. Plates were incubated at 30 and 37°C. Images were taken from 24 hours to 9 days. For liquid filamentation strains were grown in spider media for 24 hours at 37 °C and visualized using a Leica DMIL microscope.Strains were grown overnight in YPD at 25°C. Each strain was diluted to 0.1 OD


Vitis vinifera) worldwide. In Chile, Phaeomoniella chlamydospora is the major fungal trunk pathogen associated with GTDs. In the vineyards, the natural infections by P. chlamydospora are associated with air-borne conidia dispersed onto fresh pruning wounds from pycnidia. These pruning wounds are considered an important entrance for fungal trunk pathogens such as P. chlamydospora in the host in the field. However, the duration of the susceptibility of grapevine annual pruning wounds to P. chlamydospora is still unknown in Chile. Therefore, this study aimed to evaluate the period of susceptibility of pruning wounds of different ages to artificial infection of P. chlamydospora on grapevine cv. Cabernet Sauvignon, Central Chile. Artificial inoculations of a conidial suspension (105 conidia/mL) of P. chlamydospora were used to determine the susceptibility of pruning wounds of different ages, from 1, 15, 30, and 45 days after pruning. The experiments were conducted on lignified cuttings in a greenhouse, and on vine spurs in two vineyards  during two consecutive seasons. The results indicated that the pruning wounds of grapevine cv. Cabernet Sauvignon were very susceptible to infections by P. chlamydospora, with a percentage of pruning wounds infected from 97 to 71% for cuttings, and 96% to 60% for spurs, during the first 15 days after pruning. However, the susceptibility of pruning wounds of different ages in cuttings and spurs of grapevine, generally decreased as the time from pruning to inoculation increased. Moreover, the pruning wounds the pruning wounds remained susceptible to artificial inoculation by P. chlamydospora for up 45 days after pruning with percent of wounds infected from 8.0 to 12.2, and 8.3 to 18.8% on cuttings and spurs of grapevine, respectively. Finally, this study constitutes study constitutes the first research focalized on the susceptibility of pruning wounds of various ages of grapevine cv. Cabernet Sauvignon to artificial inoculations by P. chlamydospora in Central Chile.Grapevine trunk diseases (GTDs) are one of the most important phytosanitary problems that affect grapevines ( Vitis vinifera L.) is a crucial fruit crop that is cultivated in several countries in both hemispheres (www.fao.org/faostat). Chile is one of the leading exporters of wines with over 136,166 ha dedicated to wine production, which are concentrated in the central zone between the Metropolitana  and Maule regions . The export of wine reached 908 million liters during the 2021 growing season, representing an important agricultural activity for the economy in terms of productivity and employment creation, and accounting for USD$ 2,037 million . The main cultivars planted were Cabernet Sauvignon and Sauvignon Blanc, representing 29.4% and 11.2% of total grapevines, respectively . Central Chile is characterized by a Mediterranean climate (Csb) with a warm and dry summer and cold, wet winters with main annual rainfall between 342 and 676 mm  Crous & W. Gams, Phaeoacremonium spp., and species belonging to families of Botryosphaeriaceae as Diplodia seriata De Not. and Neofusicoccum parvum (Pennycook & Samuels) Crous, Slippers & A.J.L. Phillips., and Diatrypaceae such as Eutypa lata (Pers.) Tul. & C. Tul., and Cryptovalsa ampelina (Nitschke) Fuckel., among others (Grapevine trunk diseases (GTDs) such as Botryosphaeria dieback, Eutypa dieback, Petri disease, Esca disease, and Esca-like disease, which are caused by fungal pathogens, are one of the most important phytosanitary problems that affect in Chile . GTDs cain Chile . Severalg others .P. chlamydospora is one of the main fungal trunk pathogens associated with Petri and Esca-like diseases. It is consistently involved with black-wood streaking symptoms and characterized by the presence of dark-brown to black discoloration of xylem tissue in the wood , and pycnidia developed on the surface of plantlets, shoots, and vines inoculated with P. chlamydospora (P. chlamydospora on the surface of pruning debris (ground) and diseased tissues (cordons and old spurs) in the vine  and healthy vineyards (10 years old), with 21 and 0% of grapevines showing GTDs symptoms, respectively, in Catalonia, Spain , but the susceptibility decreased on the wounds when the time between pruning wounds and inoculation increased  that were aseptically placed onto 2% water agar (WA). Mycelium plug (5-mm diameter) of 15 days-old culture of Pach-3 was placed in both extremes of wood chips on WA and incubated for 21 days at 25°C under near UV light with a regime of 12 h of photoperiod, and then another 21 days incubated at 10°C  cv. Cabernet Sauvignon were collected during the second week of June (dormant seasons 2014 and 2015) from an apparently healthy commercial vineyard located in Buin , Central Chile. Cuttings were transported to the laboratory and maintained at 5°C. The dormant cuttings were washed with sterile distilled water, and then 10 dormant cuttings were placed at a 90° angle at 10 cm in depth in a polyethylene box (35 x 30 x 15 cm) containing humid perlite .Healthy lignified dormant canes (50 cm long) of one-year-old of grapevine  of necrotic tissues from inoculated cuttings were surface disinfected, sprayed with ethanol (75°), dried under a flow hood, and placed on Petri dishes containing modified PDA (2%) with 0.005% tetracycline, 0.01% streptomycin, and 0.1% Igepal CO-630 (Sigma-Aldrich) . Plates P. chlamydospora was positive in 0.4 and 2.1% of grapevine showing symptoms of Esca-like in vineyards located in Maipo and Cachapoal, respectively.Field studies were performed in the 2014 and 2015 dormant seasons in two irrigated commercial vineyards of 12- and 15-year -old cv. Cabernet Sauvignon located in Maipo Valley and Cachapoal Valley, in Central Chile, respectively. Vines were trained as bi-lateral cordons and spur prune during the experiments. Both vineyards were considered of low prevalence, with values estimated between 3 and 7% of grapevines with symptoms of Esca-like disease . The det5 conidia/mL) placed with a micropipette on each pruning wound  using SigmaStat 12.0 .The experiments of dormant cuttings were arranged using a completely randomized design. Vascular discoloration (mm) data and percent of infection (%) were analyzed separately as a two x four factorial (years x age of pruning wounds), with four replicates and ten dormant canes as the experimental units. Percent of wounds infected (%) data were transformed using the arcsine of the square root of the proportion prior to analyses. Data were studied for an analysis of variance (ANOVA), and means were subjected to a pairwise multiple comparison test of Tukey (P < 0.05) using SigmaStat 12.0 .In the vineyard experiments, the inoculation treatments were arranged as a randomized complete block design, where each year was analyzed separately. Vascular discoloration (mm) and percent of wounds infected (%) data were analyzed independently, as a two x four factorial (locations x age of pruning wounds), with eight replicates and eight spurs in two consecutive vines as the experimental units. Percent of wounds infected (%) data were transformed using the arcsine of the square root of the proportion before analysis. Data were studied for an analysis of variance (ANOVA), and means were subjected to a pairwise multiple comparison test of Tukey .P. chlamydospora (Pach-3). The analysis of the variance of vascular discoloration data showed no significant year x age of pruning wound interaction . The extent of vascular discoloration was significant according to the age of the pruning wound , with an extent of vascular discolorations of 31.6 and 25.9 mm for 2014 and 2015, respectively , with the mean percentage of wounds infected decreasing from 96.9 to 18.8%. However, the year factor  and the interaction between year x age of pruning wounds  had no significant effect on the percentage of wounds infected   and 47.2 mm (Buin), with significantly more extensive lesions than the other ages of pruning wounds (P. chlamydospora on fresh pruning wounds (one day of age of pruning wounds) produced significantly more extensive vascular discoloration, with values of 58.2 mm (Nancagua) and 49.1 mm (Buin), than the vascular discoloration obtained from spurs inoculated at 15, 30, and 45 days after pruning, with values of 34.4 mm (Nancagua) to 8.1 mm (Buin)  in 2014 and  in 2015 (P=0.011 (F=6.91) and P<0.001 (F=49.31) on the % infected pruning wounds, respectively  of  pruning Figure 6As shown in P. chlamydospore by evaluating rooted cuttings and spurs in two vineyards in Central Chile. Data obtained from two consecutive seasons of artificial inoculations showed that pruning wounds remained susceptible to P. chlamydospora for up 45 days after pruning. Natural infection was not detected in the non-inoculated controls. However, this pathogen was detected in very low prevalence at the sites of experimentation from previous work . The absence of P. chlamydospora from non-inoculated pruning wounds in the present work may possibly be due to their low prevalence in these vineyards, and to there being fewer opportunities for this low level inoculum to infect non-inoculated spurs in both vineyards. To determine the presence of conidia of P. chlamydospora, it is necessary to monitor these airborne spores using spore traps in the vineyards during the season and find the presence of pycnidia on the diseased vines  and germination (15 to 35°C) of P. chlamydospora is very wide  obtained from 1 to 15 days are epidemiologically important for the dissemination of P. chlamydospora in the vineyard over time  coincides with the peak of spore release and the presence of the first rains of the season that generally occur in California .The authors declare that the study was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


A domain in the ORF1 polyprotein of the hepatitis E virus that was previously thought to be a protease is actually a zinc-binding domain. Related research article LeDesma R, Heller B, Biswas A, Maya S, Gili S, Higgins J, Ploss A. 2023. Structural features stabilized by divalent cation coordination within hepatitis E virus ORF1 are critical for viral replication. eLife12:e80529. doi: 10.7554/eLife.80529.Hepatitis E virus (HEV) is a single-stranded, positive-sense RNA virus that is spread by fecal-oral transmission. Although infection is usually self-limiting, it can result in death via acute liver failure. The World Health Organization estimates that HEV causes 20 million infections and 44,000 deaths per year, particularly among expectant mothers . The genIn HEV, translation of the first open reading frame (ORF1) produces a polyprotein that contains seven domains. Multi-domain polyproteins are also made by other viruses, including HIV, hepatitis C virus, Chikungunya, Dengue, SARS coronavirus, rubella, influenza, and polio. In most other viral families, this polyprotein is then cleaved into individual proteins by enzymes called proteases that derive from the virus or its host . AlthougNow, in eLife, Alexander Ploss and colleagues at Princeton University – including Robert LeDesma as first author – report the results of experiments which shed light on the role of the pPCP domain . Their rIf the pPCP domain were a protease, LeDesma et al. hypothesized that it would be possible to rescue protease-defective mutants by expressing pPCP in trans, so they generated cell lines that expressed either the wild-type ORF1 polyprotein, two mutant ORF1 polyproteins ), or the wild-type pPCP domain alone. The next step was to transfect each of these cell lines with a reporter RNA in which ORF1 was either wild type or one of the mutants. Their results suggest that the pPCP domain is either not a protease or not proteolytically active in isolation.The researchers then turned their attention to the residue Cys483. If this residue were part of a protease catalytic site then it, and no other cysteines in the pPCP domain, would support replicase activity. However, alanine and triple-alanine mutation indicated that six of the eight cysteines in the PCP domain are critical for replicase activity.Since there is no protease, they investigated what the pPCP domain and the residue Cys483 might do. LeDesma et al. noticed that a six-cysteine motif within the domain was similar to other proteins that may bind bivalent metal cations. Using inductively coupled plasma mass spectrometry and confocal microscopy, the researchers observed that the mutation C483A reduced the ability of the domain to bind zinc ions, and also resulted in ORF1 being unable to localize in the nucleus.Like all the best science, this work raises more questions than it answers. Zinc-binding domains with unique folds have been identified in a number of positive-sense RNA viruses , and if In Chikungunya, a viral protease digests the polyprotein to generate a functional replication complex . In the Given the significant effect that HEV infection has on human health, more information about ORF1 domain organization and function can assist in the development of drugs to combat disease.


Viola epipsila Ledeb., V. palustris L.) are endangered because the ranges of both species are drastically decreased due to global climatic changes. Their disappearance might also be the result of the formation of interspecific hybrids which can replace the parent species. The study of such species is particularly important because they might be considered as indicators of anthropogenic changes occurring in peatlands and their disappearances. The taxonomic situation of studied species is intricate, and the presence of interspecific hybrids and putative introgressants [V. pubifolia (Kuta) G. H. Loos ] makes it even more complicated. The main goal of our study was to reconstruct the origin of V. pubifolia and its genetic relatedness to both putative parental species—V. palustris and V. epipsila—using advanced molecular methods. The taxonomic problem has been finally solved. We found no basis to separate V. pubifolia as a species in its own right because its morphological characters as well as genetic variation fall well within the range of variability of V. palustris. We have also concluded that the low genetic differentiation and heterozygosity of V. epipsila in Europe might be a cause of the reduced tolerance of this species to changing environmental conditions and can possibly lead to its extinction.The wetland violets of Central and Northern Europe  G. H. Loos , interspecific hybrids, and putative introgressants. The genetic affinity of V. pubifolia to V. palustris, and their shared origin via hybridization followed by polyploidization, were confirmed using inter simple sequence repeat (ISSR) markers, restriction site-associated DNA sequencing (RAD-Seq), and a low-copy nuclear gene, GPI, which encodes glucose-6-phosphate isomerase. The other taxa of subsect. Stolonosae were not identified as putative parents of V. pubifolia by GPI. Our analyses indicated that V. pubifolia can be included in the morphological and genetic variation of V. palustris. The ISSR, RAD-Seq, and genome size value separated well V. palustris from V. epipsila and hybrids. The results also reopen the discussion on intraspecific variation in the context of taxa ranks and species concepts. The reduced tolerance of V. epipsila in Europe to changing environmental conditions might result from low genetic differentiation and heterozygosity, as well as the increased number of interspecific hybrids , and eventually can possibly lead to its extinction. The disappearance of populations/individuals of this species may indicate anthropogenic changes occurring in peatlands.In Europe, the  Viola L. is one of the largest angiosperm genera, comprising ca. 658 recognized species; it consists of two sub-genera, 31 sections, and 20 subsections. It is distributed mainly in the temperate zones of both hemispheres and it occupies a high diversity of habitats and elevations .,30.ViolaV. pubifolia and V. palustris were harvested randomly from plants growing in natural sites. Thirty samples of V. pubifolia and one sample of V. palustris were taken from plants located in the experimental garden , three V. epipsila , three hybrids , and three V. pubifolia  samples were used from the previous research , V. occidentalis, V. macloskeyi, V. renifolia, V. principis, V. vaginata, V. selkirkii, V. mirabilis, V. rubella, V. pusilla, and V. congesta were taken from GenBank accessions , followed by genome duplication [V. palustris [V. palustris, is the result of the knockout or silencing of the B homoeolog. Polyploidization induces genetic and epigenetic processes, including DNA sequence elimination and gene silencing, contributing to the functional diversification or subfunctionalization of duplicated genes, and the genetic and cytological diploidization of allopolyploids. Epigenetic modifications may produce adaptive epimutations and novel phenotypes [This great morphological variability of lication . In sexualustris , new genenotypes ,75,76.V. pubifolia individuals observed at CH or CL blooming can lead to erroneous classification to V. epipsila or hybrid V. epipsila × V. palustris [The hairy lower leaf surface and the location of bracts in the middle or even above the middle of the pedicel of alustris ,10.V. palustris but not a hybrid, which is sterile. It should also be taken into account that the shape and hairiness of the leaf blade are seasonally variable; there are also differences between leaves developing on stolons and on rhizomes (stolon leaves are more acute and with a more open sinus). Herbarium specimens in the vegetative stage (only leaves and rhizomes) are impossible to be correctly identified in the V. epipsila—V. palustris group .It is recommended to describe and classify specimens in the field during the period of CH or CL fruiting. Normally developed, the seed-filled capsules indicate Viola as important for biodiversity and nature conservation. The increased number of interspecific hybrids , with a simultaneous reduction in the number of V. epipsila and/or V. palustris individuals or populations V. pubifolia fall well within the range of variability of V. palustris.Morphological characters of (2)V. pubifolia is V. palustris, based on ISSR, GPI, and RAD-Seq.Genetically, (3)V. epipsila confirmed by RAD-Seq might explain its low tolerance to changing environments and the risk of extinction.The low genetic diversity and heterozygosity of selected Central and Northern European populations of (4)V. epipsila populations and the disappearance of its natural habitats suggest that in some areas it might require effective conservation strategies.The declining number of


Covalent organic frameworks (COFs) stand for a class of emerging crystalline porous organic materials, which are ingeniously constructed with organic units through strong covalent bonds. Their excellent design capabilities, and uniform and tunable pore structure make them potential materials for various applications. With the continuous development of synthesis technique and nanoscience, COFs have been successfully combined with a variety of functional materials to form COFs‐based composites with superior performance than individual components. This paper offers an overview of the development of different types of COFs‐based composites reported so far, with particular focus on the applications of COFs‐based composites. Moreover, the challenges and future development prospects of COFs‐based composites are presented. We anticipate that the review will provide some inspiration for the further development of COFs‐based composites. In this review, we have summarized the development of different types of COFs‐based composites reported so far, with particular focus on the representative applications of COFs‐based composites, and the in‐depth insight into their current challenges and future development prospects. We anticipate that this review may provide some inspiration and insights for the further development of COFs‐based composites. To date, a large number of COFs based on various synthetic strategies, such as interface synthesis, mechanical synthesis, photoacoustic and room temperature synthesis and different covalent linkages, such as boronic acid bond, imine bond, triazine bond, boronate ester bond, hydrazone bond, azine bond, imide bond, carbon‐carbon bond, amide bond, azo bond have been rapidly reported.Covalent organic frameworks (COFs), are a new type of booming crystalline and organic porous materials, which have sprung up in materials science and synthetic chemistry by introducing various organic building units into the frameworks since the first ground breaking work was reported by Yaghi's group.1 COFs However, COFs also Have some weaknesses, including the microcrystalline state of COFs being difficult to dissolve in most solvents, low conductivity, and optical properties, which have limited their further applications. Various materials, including metal nanoparticles (NPs), metal oxides materials, MOFs, carbon materials, polymers, and others combined with COFs to fabricate COFs‐based composites to possess the advantages of both parent components, and exhibit new unique properties. Moreover, COFs‐based composites have mushroomed and attracted extensive attention in many areas. Check out the number of scientific publications in the field of COFs/COFs‐based composites, we can see the published papers in the COFs/COFs‐based composites field have increased significantly in recent years  can improve the efficiency of electron as well as hole transport.COFs play a certain limiting effect on the NPs covered on the surface, which has a role similar to that of surfactant and can effectively control the growth of NPs to prevent the aggregation of NPs.36 Amo The typical applications of COFs‐metal NPs composites also can be found as listed in Table Catalysis and sensing are the most important applicatiions for COF‐metal NPs, which means that the exploration in other application areas is still in a nascent stage.39 The2.1.1COFs have heterogeneity in which the ordered framework facilitates charge carrier transport and the open porous structure facilitates mass transport, while their insolubility as well as stability allow for recycling.54 This work promoted the catalytic application of functional COFs to a certain extent. In 2014, Banerjee's group reported the incorporation of Pd(II) complex and Pd(0) nanoparticles on TpPa‐1 COFs. Impressively, the hybrids were suitable for heterogeneous catalysis under both highly basic and acidic conditions. However, the particle size of Pd NPs was much larger than the pore size of the COFs. The deposition of metal NPs on COFs surface increased the possibility of leaching of NPs in the catalytic cycling reaction and affected the reusability of the catalyst. In order to address the problem, carrier materials with strong interactions with Pd NPs, especially heteroatom‐doped materials, such as quaternary ammonium (QA) salt‐decorated COFs, were used to stabilize Pd NPs to prepare Pd@COF‐QA hybrid materials. Meanwhile, the average size (2.4 nm) of Pd NPs was smaller than the pore size (3.8 nm) of COF‐QA, demonstrating that Pd NPs could be deposited in the pores. A series of experimental results showed that the prepared Pd@COF‐QA material could be acted as an excellent phase transfer catalyst to improve aqueous Suzuki‐Miyaura coupling reaction under mild reaction conditions. In 2017, thioether‐containing COFs, have acted as catalyst supports to immobilize metallic Pt NPs and Pd NPs. Both Pd NPs and Pt NPs immobilized within the COFs cavity have narrow size (1.7 ± 0.2 nm) and high loading levels. A series of experiments show that the crystallinity of COFs as well as thioether group in the cavity play an important role in the controlled synthesis of metallic NPs. Meanwhile, it is found that the prepared material is an excellent asymmetric heterogeneous catalyst that effectively promotes Henry and reductive Heck reactions with strong stereoselectivity and high yield  was employed as a solid support for the confined growth of ultrafine mono‐ and bimetallic nanoparticles , it is demonstrated that the prepared Phos‐COF‐1‐supported NPs display high catalytic activities, good stability, and recyclability toward multiple coupling and reduction reaction @TpPa COFs using a template method @TpPa COFs achieved a high conversion at 0.05 mol% Pd loading and the size cutoff efficiency for aryl benzene amounting to 100%. Impressively, the catalyst showed good recyclability.In addition, a protective layer can be designed to overcome the etching of metal NPs. For example, a mesoporous ceria shell was introduced to hinder the Pd NPs leaching and block the Pd NPs aggregation.58 In d Figure .[51] oxygen evolution reaction (OER), as well as hydrogen evolution reaction (HER). Most reactions are highly efficient (80% to 99% yield) within 2 h.Exploration of COFs‐metal NPs catalysts involves various catalysis aspects. For example, NPs@COFs composites can also catalyze the oxygen reduction reaction,59 oxy2.1.2 COF‐metal NPs are endowed with unparalleled sensing properties due to their various constituent and collaborative functions.The development of nanoscience has driven innovation of all kinds of sensors by exploiting nanomaterials inimitable chemical and physical properties.64 COF In situ growth of Au NPs on COFs was reported as colorimetric sensors. Based on the stable peroxidase‐mimicking activity, when Hg(II) and H2O2 were present, the color of 3,3,5,5‐tetramethylbenzidine (TMB) changed from colorless to blue, and the color produced by TMB was proportional to the Hg(II) concentration . The electronic medium toluidine blue as well as Au NPs‐doped COF were used to achieve signal amplification. TB‐Au‐COF offered more active sites for fixing antibodies (Ab2). Under the best conditions, the limit of detection (LOD) of the designed electrochemical immunosensor was as low as 0.17 pg mL−1  as well as a low LOD (9.5 × 10−9 mol L−1). After 100 cycles, the sensor still maintained extreme stability and catalytic activity.At present, progress in developing electrochemical sensing based on COFs has been successfully established to detect environmental pollutants and biomedical analysis. An interesting example is the preparation of a novel sandwich electrochemical sensor from a composites of troponin.70 To 1 Figure . In addi−1. The detection of hydrazine in this material was further realized by amperometric technology. Compared with other hydrazine sensors (such as Fe3O4 and NiCo2O4), DQ‐COF/Ni has a lower LOD (0.07 μM). The performance is far superior to that of existing porous materials, which is attributable to the synergy of Ni matrix‐enhanced electron transfer and electroactive DQ‐COF.Based on the presence of ample anthraquinone sites as well as the high surface area, DAAQ‐TFP COF (DQ‐COF) exhibited a hydrazine removal capacity up to 1108 mg g−1.53 TheIn addition to hydrazine, other targets such as dopamine, catechol, hydroquinone, and resorcinol have also been detection using COFs‐metal NPs electrochemical sensors.742.1.3 photodynamic and photothermal therapy, pH‐responsice chemo/photothermal/chemodynamic synergistic therapy for cancer.Through continuous efforts, COFs‐metal NPs composites have been used to achieve targeted delivery of glucose oxidase,75 pho The photodynamic effect is significantly enhanced after the coordination of COF with CuSe NPs. Meanwhile, the obtained COF‐CuSe nanocomposite exhibits satisfactory PTT effect, and the photothermal conversion efficiency reaches 26.34%. Both in vivo and in vitro experiment data demonstrate that the COF‐CuSe nanoplatform is an ideal platform for PTT and PDT.The combination of photodynamic therapy (PDT) as well as photothermal therapy (PTT) has broad prospects in the treatment of tumors. In order to realize a satisfactory anti‐tumor effect, selecting an appropriate photosensitizer is a prerequisite. Hu et al. used CuSe as the ideal photothermal agent combine with photosensitizer COF to construct a bifunctional tumor therapeutic agent.77 The In addition, flower‐like hollow COFs loaded with Au NPs were successfully used for high‐efficiency, selective capture of ultratrace brain natriuretic peptide from human serum samples. This means that COFs‐Au NPs can act as a fascinating enrichment probe in biological as well as clinical analysis.A facile room‐temperature synthesis method was used to produce flower‐like COFs with controllable shapes.79 In  In the experiment, the zinc porphyrin COF (ZnCOF) was synthesized using MnO2 as a template, and then bovine serum albumin was selected as the reducing agent and stabilizer to adsorb on the MnO2/ZnCOF surface for the in situ preparation of Au NPs. The produced MnO2/ZnCOF@Au&BSA nanosystem could act as an effective nano‐therapeutic agent for FL‐enhanced tumor imaging and cancer therapy.Yuan et al. constructed a pH‐responsive COFs‐based organic/inorganic hybrid platform.80 In 2.2 COF‐metal oxide composites have made significant progress in catalysis, adsorption, PTT, lithium‐sulfur batteries, gas separation, absorption, and sensor fields.COFs‐metal oxides composites are one of the most reported COFs‐based composites.81 COF2.2.1Due to the excellent stability of COFs in most solvents, catalysts designed and synthesized on the basis of COFs can be easily recycled from different catalytic systems by centrifugation and drying steps.933+‐doped TiO2 NPs with an average particle size of 2.3 nm. The synthesized Fe‐TiO2@COF demonstrated excellent photocatalytic activity under ambient light and could degrade methylene blue. Among various types of COFs‐metal oxides composites, how to integrate COFs and metal oxides inorganic tightly is still a huge challenge. In another work, COFs and inorganic semiconductor material TiO2 were designed to form Z‐scheme hybrid (TiO2‐TpPa‐1‐COF) for the first time. Covalent bonds can act as a bridge in the heterostructure to enhance the catalytic performance by separating the electron‐hole and transferring photogenerated electrons in the photocatalytic process. Lan et al. constructed COF‐semiconductor Z‐type photocatalysts by integrating a variety of semiconductors  with COFs (COF‐316/318) and prepared different COF Z‐scheme semiconductor catalysts ,97 aro Table The first example of the use of magnetic triazine‐based COFs for magnetic separation was reported in 2011, subsequently, the field is growing rapidly.83 Tab3O4 as the carrier to build a magnetic COFs for MSPE. For example, Fe3O4@TbBd nanobeads as a new MSPE extractant can selectively isolate and enrich trace amounts of estrogens from human urine samples. High enrichment factors (75−197 fold) as well as wide linearity range (0.005–10 g L−1) were observed using MSPE and high performance liquid chromatography‐mass spectrometer (HPLC‐MS).In the above examples, most of them make use of FeHPLC‐MS).111 As expected to design, GSH‐functionalized magnetic COFs showed excellent size exclusion effect, good selectivity, excellent sensitivity, and excellent enrichment performance for endogenous N‐linked glycopeptide  ‐functionalized magnetic COFs microspheres by using magnetic crystal nanoclusters as the core, COFs as the shell, and GSH with good biocompatibility and high hydrophilicity as the surfactant.112 Ase Figure . Surpris3O4@[NH2]‐COF using a room temperature synthesis strategy. The prepared magnetic COFs showed outstanding extraction performance for nine types of perfluoroalkyl acids (PFAAs) due to the strong electrostatic interaction as well as hydrophobic interaction. The linearity of the six analytes was from 10 to 1000 ng L−1, and the LODs were between 0.05 and 0.38 ng L−1 by HPLC‐MS/MS. The applicability of this strategy was further studied by analyzing nine kinds of PFAAs in rain water, pond water, tap water, and waste water samples. The recoveries of 9 PFAAs were 72.1–113.3%, 74.7–115.1%, 74.8–115.4%, 78.5–113.7%, respectively. Cai et al. established a bouquet‐shaped magnetic TpPa‐1 and used it as an adsorbent for MSPE trace polycyclic aromatic hydrocarbons (PAHs) in environmental samples. Quantitative extraction of six analysts (10 ng) required only 5 mg magnetic TpPa‐1, and the recovery rate of most PAHs was above 90%, which showed a high extraction efficiency and excellent enhancement performance of magnetic TpPa‐1.The synthesis method of low‐cost COFs‐based composites is beneficial to further promote the practical application of COFs‐based composites. Zhao et al. prepared a new Feeraction.113 Th3O4 is prone to oxidation, agglomeration, and instability in acidic media. NiFe2O4, a heterotrophic photo‐Fenton catalyst for the degradation of organic pollutants, has arose much concern due to its outstanding chemical stability as well as magnetic properties. Herein, NiFe2O4 can be considered as one of the excellent substitutes for traditional magnetic Fe3O4 NPs. NiFe2O4@COFs nanocomposites were prepared by rapid room‐temperature synthesis. Owing to π–π, hydrophobic interactions as well as van der Waals forces, the adsorption capacity of NiFe2O4@COFs for brominated flame retardants was stronger than that of carbon nanotube materials. Under the optimal experimental conditions, NiFe2O4@COFs showed excellent adsorption properties with a low LOD (0.03–1.9 μg L−1), and a wide linear range (0.11–1000 μg L−1). In addition, the obtained magnetic material acted as an extractant to determine five brominated flame retardants in real samples, and the recovery rate was between 91.5% and 102%.Since traditional Feoperties.116 He2.2.3 The open structure of the conjugated microporous polymer is conducive to heat conduction. Hence, the use of COFs can be foreseen as a novel and attractive avenue for the development of organic photothermal agents. There have been some designs based on COFs‐metal oxides to achieve PTT for cancer cells. Wang's group further investigated the potential of Fe3O4@COF for PTT. In the work, a core–shell type Fe3O4@COF (TpBD) was synthesized using Fe3O4 as a template and modified with polyethylene glycol (PEG) in order to increase the stability of the material. The characterization data manifested that the pore size of TpBD was 1.3–2.0 nm, the specific surface area was 1346 m2 g−1, and the thickness of shell was 100 nm. The photothermal experiment displayed that the photothermal conversion efficiency of Fe3O4@COF‐100 was 21.5% at 785 nm, which was 2–3 times higher than that of Fe3O4 nanoclusters alone.PTT to ablate cancer cells by targeting radiation photosensitizer molecules to emit heat has been shown to be an effective approach to cancer treatment.118 Th That is, after the photosensitizer absorbs light energy, PDT kills cancer cells by exciting oxygen (O2) into ROS. Due to the limitation of the hypoxic microenvironment in tumor cells, many photodynamic therapies have certain limitations, and it is difficult to generate highly cytotoxic ROS against tumors. Here, COF was selected as a platform to combine with Au NPs, and then a layer of MnO2 was coated on this composite, finally introducing hyaluronic acid to increase biocompatibility  that result in oxidative damage to cellular components such as DNA, lipids, as well as proteins.122 Thy Figure . From the aspect of studies, a few attempts have been made to select COF as a new kind of stationary phase for HPLC separations. By fixing different COFs with irregular shape, inhomogeneity, and low density on the surface of SiO2 to form composite materials, good separation can be achieved at low column back pressure. Fan et al. constructed an in situ growth strategy, in which COF5 was modified onto SiO2 NPs as a stationary phase for HPLC to form a COF‐silica composites (SiO2@COF5), which overcame the disadvantages of irregular COF morphology and the low column efficiency of submicron‐level COF and promoted its application in the field of HPLC. In order to increase the separation performance, Zhang et al. fabricated core–shell SiO2@covalent triazine‐based organic polymer (CTP) microspheres for mixed‐mode chromatographic stationary phase. Multiple retention mechanisms  could be provided by this stationary phase due to the synergistic interaction of triazine and aromatic groups on CTP. Based on the above‐mentioned interaction mechanisms, the successful separation of several hydrophilic and hydrophobic analytes with high shape selectivity is achieved by performing different chromatographic conditions. COF‐LZU1 (Lan Zhou University‐1) is a “star” of imine bonded COFs. COF‐LZU1 is stable in water and most organic solvents, rich in multiple benzene rings, and providing a rich conjugated structure. Therefore, the SiO2@rLZU1 (reduced Lan Zhou University‐1) composites acted as a new reversed‐phase chromatographic stationary phase, which exhibited good reproducibility and high resolution in the separations of acidic, neutral, and basic compounds.The particle size distribution, morphology, and homogeneity of the COFs have a considerable impact on the separation performance of HPLC column.263 Fr In 2021, monodisperse chiral CTpBD@SiO2 microspheres were fabricated as a chiral stationary phase for enantioseparation via an in situ growth strategy. The chiral COF@SiO2 microspheres integrate the excellent column packing properties of silica and the unique chiral recognition ability of chiral COF. The results indicated that the CTpBD@SiO2‐coated columns had excellent chiral separation performance for ketones, phenols, alcohols, bases, amines, and other chiral compounds. In addition, a facile one‐pot method is reported to prepare a novel β‐CD‐COF@SiO2 chiral stationary phase for enantioseparation. The prepared β‐CD‐COF@SiO2 stationary phase exhibited high enantioselectivity and excellent separation performance for diverse racemic compounds.Chiral COFs are a fascinating separation medium in HPLC.264 In2‐NH2 spheres. The synthesized BtaMth@SiO2 composites exhibited excellent resolution for the separation of the cis‐trans isomers of β‐cypermethrin and metronidazole in normal‐phase mode and the positional isomers of nitrochlorobenzene and nitrotoluene in reversed‐phase mode.In another report, composites were prepared successfully by growing chiral COFs (BtaMth COFs) on the surface of SiO spheres.264 Th However, there remains a big challenge in improving the photochemical activity of COFs. Zhao et al. changed the ratio of β‐ketoenamine as well as imine, and successfully prepared diverse COFs for photocatalytic hydrogen production. Inspired by the appropriate HOMO energy of COFs, nonquenched excited state, and planar and moderately ordered structure, covalent coupling with NH2‐Ti3C2Tx enables the formation of COF/NH2‐Ti3C2Tx composites. The photocatalytic experiment and theoretical analysis showed that the more β‐ketoenamine groups, the better the photocatalytic performance.  The organic monomer used to synthesize COFs is relatively expensive, which makes the synthesis cost of COFs‐based composites high. (2) During the synthesis process, a series of preparation approaches have been established  for the preparation of diverse COFs and COFs‐based composites with high crystallinity and harsh reaction conditions , which makes it rather difficult to control the morphology and size of COFs‐based composites, let alone large‐scale production and practical applications. (3) In practical applications, many properties of COFs‐based composites are usually superior to those of single materials. However, in terms of hydrophilic and hydrophobic properties, most of these materials are poor in hydrophilicity, and the robustness and mechanism of the composites remain to be investigated. (4) The long‐term biotoxicity of COFs‐based composites in vivo has not been fully investigated. Besides, it has been shown that the current studies mainly focus on a few “classic” COFs. More alternative chemically and thermally stable porous COFs are urgently required.Of course, green, economical synthetic strategies as well as mild reaction conditions are still the main direction of research efforts. Meanwhile, more assisted techniques such as computer simulation, machine learning are expected to better provide theoretical data for the design, characterization, and application of COFs‐based composites. It is still essential to further study the mechanism between COFs and the corresponding functional materials in the reaction processes to obtain composites with better and more stable performance by combining specific materials with specific problems. In addition, it is also necessary to find new potential materials to construct COFs‐based composites with more practicability, biocompatibility, and low‐toxicity. Finally, we believe that COFs‐based composites will certainly continue to emerge, and the different properties they bring will be more widely used in various research fields.The authors declare no conflicts of interest.