No abstract

Successful control of a dielectric elastomer actuator (DEA) can be a challenging task, especially if no overshoot is desired. The work presents the first use of the PIλDμ control for a dielectric elastomer actuator to eliminate the overshoot. The mathematical model of the dielectric elastomer was established using the fractional Kelvin-Voigt model. Step responses are first tested in the Laplace domain, which gave the most satisfactory results. However, they did not represent the real model. It cannot have negative force acting on the dielectric elastomer actuator. Simulations in Matlab/Simulink were performed to obtain more realistic responses, where output of the PIλDμ controller was limited. Initial parameters for a PID control were obtained by the Wang–Juang–Chan algorithm for the first order plus death time function approximation to the step response of the model, and reused as the basis for the PIλDμ actuator control. A quasi-anti-windup method was introduced to the final control algorithm. Step responses of the PID and the PIλDμ in different domains were verified by simulation and validated by experiments. Experiments proved that the fractional calculus PIλDμ step responses exceeded performance of the basic PID controller for DEA in terms of response time, settling time, and overshoot elimination.

No abstract

Workpiece positioning into a machine's workspace has become a simple task. Advanced CNC machines are equipped with standardized clamping systems, allowed workpiece dimensions are listed in the machine's documentation and tolerance levels of the end produced parts are known. This gives users plenty of information and good confidence that they are choosing the best machine for a specific task. For more universal machines like industrial robots this is not the case. Due to their flexibility industrial robots can be an alternative to specialized CNC machines, but when a specific task should be executed, important information is missing. For a standard industrial robot the mechanisms layout, its dimensions and its reachable workspace is known, but accuracy levels over the robot's workspace are not. If a workpiece should be milled within certain accuracy limits the robot's documentation offers no information on how close it can be located to the borders of the robot's workspace. This article deals with the mentioned problem with a novel methodology. Based on experimental data we found that a standard 6 DOF industrial robot's reachable workspace can be divided into two regions, one with suitable milling accuracy and another with rapidly decreasing milling accuracy. To isolate the suitable accuracy region a regional non-dominated sorting algorithm was developed and an accuracy contour separating the regions was extracted. In the second part of the article a genetic search algorithm based on regional non-dominated sorting was applied to find the biggest arbitrary shaped workpiece's size, position and orientation in the suitable milling accuracy region of the robot's workspace.

Dielectric elastomer actuators also known as DEAs are widely used as soft actuators. In order to control such actuators its mechanical properties are needed. Since viscoelastic materials are mainly used as a base for DEAs, an appropriate mathematical model is needed to get appropriate control parameters. Viscoelastic elastomers have very complex mechanical characteristics. They exhibit a combination of behaviors of solid material and liquid. Usually, solid materials exhibit elasticity up to a certain point. Liquids exhibits viscosity. They change their shape regardless on the stress applied on it and do not regain their original shape. Viscoelastic materials exhibit both behaviors at once. However, the ratio between elasticity and viscosity depends on the material being used. The use of fractional Kelvin-Voigt model can be of great help in determining the elastic and/or viscous material properties. Even more, a comparison between single and double fractional Kelvin-Voigt models will be given for low frequency strain ranges. It will be shown that viscoelastic mechanical properties are frequency dependent. At the end a least-square method is introduced for determination of optimal parameters for both models. This study can be used as a guidance for viscoelastic material parameter identification either for single or double fractional Kelvin-Voigt model. Both models can be further used in control theory with fractional derivatives to obtain proper control parameters since they are easily transferable to Laplace domain.