Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> The development of a lightweight piezoelectric end-effector (multifinger type) for robotic applications is reported. The fundamental configuration of each finger is a simple piezoelectric bimorph structure made of a piezoelectric polyvinylidene fluoride material. Injection of a controlled high voltage into the finger can induce a deformation in a prescribed direction. Depending on the applied voltage, the effector can hold an object from outside or inside. The theoretical predictions are verified by the experimental and finite-element simulation results. This end effector is designed for lightweight objects such as electronic chips, and for high-precision (or even micro-precision) operation. Gripping force can always be enhanced by injecting higher voltage. Coordinating the applied voltage in two fingers can also compensate the position offset if misalignment exists in the setup. > <s> BIB001 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> A robotic manipulator with active members made of a piezoelectric material (PZT piezoceramics) has been designed and assembled. It features lower self-weight, more flexibility and better performance due to some new approaches in the design. First, an unconventional piezoelectric motor is designed as a light-weight, quick-response driver of the manipulator. The piezo-motor is integrated into a servo system to drive the robotic arm. Second, the linkage design is a light-weight and flexible structure. In order to control the undesired vibration interferences to the robotic arm, an active vibration control system is used having small wafer type piezoelectric sensors and actuators embedded in the linkage structure. The robotic arm is modeled as a simple cantilever beam, and a linear velocity feedback controller is designed targeting the fundamental bending mode. The experimental manipulator can move to a programmed destination very quickly and smoothly, with much less settling time compared to the passive linkage structure. <s> BIB002 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> The design of a microassembly desktop station is a major challenge for microsystem technology. This paper presents several piezoelectric micromanipulation robots, which have been developed to be used in a microassembly station. These robots are of different design and use different actuation principles so that each robot serves for a specific task. They are capable of travelling over long distances and of manipulating in the range of a few nanometers. Several robots of this kind can be accommodated in a microassembly station and can cooperate and perform microassembly tasks as a team. They can also be used for other operations such as online testing of microelectronic chips or manipulating biological cells. <s> BIB003 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> Using the Darwin2k development software, a genetic algorithm (GA) was used to design and optimize a pipe-crawling robot for parameters such as mass, power consumption, and joint extension to further the research of the Miniature Inspection Systems Technology (MIST) team. In an attempt to improve on existing designs, a new robot was developed, the piezo robot. The final proposed design uses piezoelectric expansion actuators to move the robot with a ‘ chimneying’ method employed by mountain climbers and greatly improves on previous designs in load bearing ability, pipe traversing specifications, and field usability. This research shows the advantages of GA assisted design in the field of robotics. <s> BIB004 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> In this paper, a novel miniature-step mobile robot with three degrees of freedom (DOFs) is developed based on the inchworm principle. This device, driven by a piezo stack actuator, utilizes a rhombic flexure hinge mechanism and four electromagnetic legs to achieve large stroke translation and rotation with high resolution on a platform. The design process of the rhombic flexible frame and the electromagnetic legs is described. The electric circuits for generating appropriate voltage signals are designed to control the legs to clamp to and release from the platform. In order to investigate the motion characteristics of the device, a series of experiments was carried out. The experimental results confirm that the device is capable of performing a 3-DOFs motion with a high resolution on a platform. Furthermore, the platform loading capacity allows some additional devices like a gripper or any other device for a particular application to be mounted on board. This enables the device's potential in a wide variety of applications. <s> BIB005 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> In this paper we present the design and prototype of a six-legged walking robot which uses Lightweight Piezoceramic Composite curved Actuator (LIPCA) as its actuator. LIPCA consists of multiple layers of glass/epoxy and carbon/epoxy that encapsulate a unimorph piezoelectric ceramic actuator. It uses lightweight fiber-reinforced plastic layers, and it is a lighter structure and generates a higher force and a larger displacement than other conventional piezo-composite type actuators. Like most six-legged walking insects including cockroaches, our robot uses the alternating tripod gait where the front and rear legs on the same side move together with the middle leg on the other side for its locomotion. Two LIPCA strips in different phases are used for actuating each tripod so that only one tripod may touch the ground. All the experiments with the prototype show that LIPCA can be used as an alternative actuator for small and light mobile robots. <s> BIB006 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> Recent biological studies on water strider insects revealed how they maintain stability and maneuver on the surface of water. While macroscale bodies use buoyancy, these very small insects use surface tension force to balance their weight on water. This paper proposes a biologically inspired miniature robot that utilizes the unique scaling advantage of these insects. The paper focuses on understanding the physics of the interaction between the insect and the surface of water and on designing a robot that mimics their key features. Hydrophobic Teflon coated wire legs optimized to take the most advantage of the surface tension force are used to support the weight of the 1-g robot. It is shown that twelve of these legs can support up to 9.3 g of payload. A T-shape actuation mechanism with three piezoelectric unimorph actuators is designed and studied to enable controlled locomotion. Static and dynamic properties of the robot are analyzed and compared with the experimental results. The tethered robot can successfully make both linear and rotational motions. Maximum forward speed is measured to be 3 cm/s, and the rotational speed is 0.5 rad/s. This robot proposes a new way of locomotion on water surface for future robots and devices. <s> BIB007 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> This paper addresses the design of a biomimetic fish robot actuated by piezoceramic actuators and the effect of artificial caudal fins on the fish robot’s performance. The limited bending displacement produced by a lightweight piezocomposite actuator was amplified and transformed into a large tail beat motion by means of a linkage system. Caudal fins that mimic the shape of a mackerel fin were fabricated for the purpose of examining the effect of caudal fin characteristics on thrust production at an operating frequency range. The thickness distribution of a real mackerel’s fin was measured and used to design artificial caudal fins. The thrust performance of the biomimetic fish robot propelled by fins of various thicknesses was examined in terms of the Strouhal number, the Froude number, the Reynolds number, and the power consumption. For the same fin area and aspect ratio, an artificial caudal fin with a distributed thickness shows the best forward speed and the least power consumption. <s> BIB008 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> Biology is a useful tool when applied to engineering challenges that have been solved in nature. Here, the emulous goal of creating an insect-sized, truly micro air vehicle is addressed by first exploring biological principles. These principles give insights on how to generate sufficient thrust to sustain flight for centimeter-scale vehicles. Here, it is shown how novel manufacturing paradigms enable the creation of the mechanical and aeromechanical subsystems of a microrobotic device that is capable of Diptera-like wing trajectories. The results are a unique microrobot: a 60 mg robotic insect that can produce sufficient thrust to accelerate vertically. Although still externally powered, this micromechanical device represents significant progress toward the creation of autonomous insect-sized micro air vehicles. <s> BIB009 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> This paper presents the development of a mesoscale self-contained quadruped mobile robot that employs two pieces of piezocomposite actuators for the bounding locomotion. The design of the robot leg is inspired by legged insects and animals, and the biomimetic concept is implemented in the robot in a simplified form, such that each leg of the robot has only one degree of freedom. The lack of degree of freedom is compensated by a slope of the robot frame relative to the horizontal plane. For the implementation of the self-contained mobile robot, a small power supply circuit is designed and installed on the robot. Experimental results show that the robot can locomote at about 50 mm·s−1 with the circuit on board, which can be considered as a significant step toward the goal of building an autonomous legged robot actuated by piezoelectric actuators. <s> BIB010 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> Abstract Ultrasonic motor is one of the most promising candidates for arranging the joints of robot arms or fingers. In this work, a novel robot finger joint based on a hybrid multi-DOF piezoelectric ultrasonic motor is designed and fabricated. The motor's stator is assembled by a multi-layered piezoelectric longitudinal vibrator and a sandwich bending vibrator. The multi-layered vibrator can produce large longitudinal vibration velocity in the z direction at low driving voltage. The sandwich vibrator composed by two PZT rings and four-divided bronze electrodes can excite the bending vibration in two orthogonal directions under phased voltages. The combination of the longitudinal and bending vibrations enable a ball rotor rotate in three directions. In our designed model, a stainless steel layer is adhered on the stator's surface to improve the rotation torque, and the maximum torque about 23.5 mNm is obtained. An orthogonal bearing holding mechanism is introduced to hold the ball rotor without preventing the multi-DOF motions of the robot finger joint. The motions of the finger are demonstrated and evaluated experimentally. <s> BIB011 </s> Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review <s> Piezoactuator-Based Robots <s> Recently, many challenges are being made toward the realization of flight motions like insects, birds and so on. The purpose of this work is to develop flapping robots using a new type of piezoelectric material, that is, piezoelectric fiber composites. By using the composites, actuating as well as energy-harvesting fibers and sensing fibers can be embedded in the structure and it makes flapping robots with compact and light structure. This paper proposes a new flapping mechanism for the flapping robots using piezoelectric fiber composites to improve the performance of the robot developed in our previous work, which is inspired from insects with indirect flight muscle. A prototype of flapping robot using the new flapping mechanism has been made and experimental results show the improvement of the performance. <s> BIB012
The piezoelectric robot research works can be classified as robot arm and finger, inchworm robot, underwater robot legged robot, and flying robot. They are summarized in Table 1 . The early research on piezoelectric robots was focused on control of the robot arm and manipulator. In 1989, Tzou developed a lightweight robot endeffector using a bimorph structure based on a PVDF material BIB001 . Depending on the applied voltage, the effector could hold an object from outside or inside. The theoretical prediction was verified with the experimental and finite element simulation results. This endeffector can be used for pick up lightweight objects, such as electronic chips. Varadan et al. proposed a lightweight robot using a piezoelectric motor and a piezoelectric ceramic actuator BIB002 . The piezoelectric sensor and actuator were attached on the surface of the lightweight flexible arm, and the piezoelectric motor was designed and installed as a quick response driver of the robotic arm. The diameter of the piezoelectric motor was 40 mm, with a maximum speed of 520 r/min and a maximum torque of 0.07 Nm. The total weight of the manipulator was only approximately 0.1 kg. Fatikow et al. developed three different piezoelectric micro-manipulation robots BIB003 . First, a one-leg robot was designed as a positioning unit by using a stacked piezoelectric actuator. A three-leg robot, called SPIDER-1, was also designed as a positioning unit by using bimorph-type piezoelectric ceramic actuators. Finally, a manipulator driven by three piezoceramic actuators was designed. The bimorphic actuator that is fastened to the robot's body was used to raise and lower the manipulator arm, while the other two actuators work as a two-fingered gripper. Zhang et al. proposed a robot finger involving two joints with four DOF, based on two hybrid multi-DOF piezoelectric ultrasonic motors BIB011 . The motor's stator was assembled by a multi-layered piezoelectric vibrator for longitudinal motion and a sandwich type bending vibrator. The multi-layered vibrator can produce a large longitudinal vibration velocity in the z direction at low driving voltage. The sandwiched vibrator, composed of two PZT rings and four divided bronze electrodes, can excite the bending vibration in two orthogonal directions under phased voltages. By combining the longitudinal and bending vibrations, rotation of the ball rotor can be generated in three directions. This method is illustrated in Figure 1 . Many research works have been conducted for inchworm type robots driven by a piezoelectric actuator. Holinger and Briscoe carried out an optimization, based on a genetic algorithm and numerical performance evaluation, for a piezoelectric pipe-crawling inspection locomotion BIB010 . The design of the robot leg is inspired by legged insects and animals, and the biomimetic concept is implemented in the robot. The manufactured robot is presented in Figure 3 (b). The maximum payload of the bounding prototype was found to be approximately 100 g. The bounding prototype has the ability to carry an additional load, up to 100 g, at a speed of 67 mm/s. Song and Sitti developed a biologically inspired miniature water strider robot driven by the surface tension force BIB007 . To support the weight of the robot, optimized hydrophobic Teflon coated wire legs were adopted by taking the advantage of the surface tension force. A T-shape actuation mechanism, with three piezoelectric unimorph actuators, was designed to control the locomotion. The maximum forward speed obtained was 30 mm/s, and the rotational speed was 0.5 rad/s. Research works for biomimetic underwater robots have been carried out by many researchers, utilizing various piezoelectric actuators. Goo et al. proposed a biomimetic fish robot actuated by a LIPCA BIB008  . The limited bending displacement produced by a LIPCA was amplified and transformed into a large tail beat motion by using a linkage system. The fully assembled biomimetic fish robot was 270 mm long, 50 mm wide, and 65 mm high, with a total mass of 550 g including a dummy weight of 450 g. From the experimental results, and by adopting a variable thickness caudal fin, the swimming speed reached 25 mm/s at 0.9 Hz with applied input voltage of 300 Vpp. Zhao et al. developed a soft underwater robot by mimicking a cow nosed ray, based on MFC actuators  . The fabricated fish robot structure is presented in Figure 4 . The size of the proposed robot body was 110 mm long, 230 mm width, and the tail length was 20 mm long. The swimming speed of the manufactured robot, increased by rising the frequency of the input rectangular wave, was 53 mm/s at 1 Hz and 200 mm/s at 10 Hz. Aiguo et al. also developed a snakelike underwater robot as shown in Figure 5  . The whole length of the robot was 130 mm and the maximum swimming speed reached approximately 500 mm/s at 35 Hz square wave, with applied input voltage from -500 to 1500 V. Because the piezoelectric actuator has the inherent advantage of high actuating force per unit volume, many research works have been undertaken to develop a flapping wing for flying robots. In 2009, Ming et al. developed an active flapping wing with MFC actuators and investigated its characteristics through experiments  . The prototype of the proposed flapping wing is presented in Figure 6 (a). The weight, area, and span of one side single wing were 2.25 g, 4200 mm robot BIB004 . The proposed design used piezoelectric expansion actuators to move the robot with the 'chimneying' method employed by mountain climbers, and greatly improved on previous designs in load bearing ability, pipe traversing specifications, and field usability. The optimization was performed for total mass, power consumption, and joint extension, and then the robot design parameters were obtained. After optimization for power consumption, the center extension was increased from 3.0 mm for the initial configuration to 5.0 mm for the optimized configuration. However, the power consumption was decreased from 1514 W for the initial configuration to 584 W for the optimized configuration. Yan et al. developed a miniature-step mobile robot with 3-DOF driven by a piezoelectric actuator BIB005 . By utilizing a rhombic flexure hinge mechanism and four electromagnetic legs, large stroke translation and rotation with high resolution was achieved. The assembled mobile robot is presented in Figure 2 . In the last decades, many types of walking robots activated by piezoelectric actuators were proposed and developed. Lee et al. proposed a cockroach-inspired six-legged hexapod robot, which uses a lightweight piezoceramic composite curved actuator (LIPCA) BIB006 . The fabricated robot is presented in Figure 3 BIB012 . The flapping robot prototype is presented in Figure 6 (c). They designed the driving module by using two double-end supporting beams made of carbon fiber reinforced polymer (CFRP) with a surface-bonded MFC actuator. The mean lift and meat thrust forces reached 36.67 mN and 37.48 mN, respectively. In addition, compared to the previous ring-shaped module, the ratio of lift to weight increased from 0.0157 to 0.9355 and the ratio of thrust to weight increased from 0.0686 to 0.956, approaching to 1. Wood developed a biologically inspired flying-insect robot with a piezoelectric actuator and evaluated its performance through experiments BIB009 . The schematics and photograph of the proposed micro robot is presented in Figure 7 . The total mass was 60 mg with a wing span of 30 mm. The maximum wing velocity was 6 m/s and the resonant frequency was 110 Hz. From the experimental results, the average lift was 1.14 mN and the ratio of thrust to weight was approximately 2.