Design optimisation of industrial robots using the Modelica multi-physics modeling language
Superior performance of industrial robots can only be achieved if the interaction of mechanics, electronics and software is taken into account already in the design phase. Conventional approaches to modelling, however, cannot cope with such multi-physics systems. The new Modelica modelling language has been specifically developed for this purpose. It also significantly increases re-usability of model components, since components adapt to the connection structure in which they are used. In the European resarch project “Real-time Simulation for Design of Multi-physics Systems“ (RealSim), efficient tools for modelling, simulating and optimising industrial robots are developed. A general Modelica MultiBody library (freely available from [1] or [2]) formed the basis for the development of a specific robot component library. A development environment for creating robot models out of the available components was provided, in which initial calculations to verify the first rough design can also be performed. Tools for automated optimisation were developed that take the initial design as the starting point. Afterwards, the performance of a design can than be verified in a real-time simulation before investing in building a real prototype. These powerful development tools provide the basis for an even more efficient development process and superior robot performance in the future.
Mixed-mode Integration for Real-time Simulation
The new possibilities of multi-domain hierarchical modelling often lead to models with both fast and slow parts. In this paper a new approach to simulate such systems is discussed that is especially useful in real-time applications. Mixed-mode integration represents a middle course between implicit and explicit integration. The main idea is to split up the system into a fast and a slow part and to apply implicit discretization only to the fast part. The partitioning of the system can be performed offline using a newly developed automatic selection routine, before real-time simulation starts. Mixed-mode integration was applied to several Modelica models from different fields, e.g. models of a diesel engine and an industrial robot and tested using Dymola. Speedup factors from about 4-16 were recorded. In this paper, mixed-mode integration is introduced, the selection routine is described and numerical results are presented.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.