New Compliant Mc-Kibben Actuator Driven by Pneumatic Actuators as a Hexapod Platform in Robotic Applications

This paper presents the design and implementation of a parallel-kinematic hexapod tool driven by pneumatic actuators. It consists of six discrete linear actuators, each of which is assembled as an antagonistic setup of McKibben pneumatic muscles with pressure and position sensors. Thanks to the antagonistic principle of the units together with the inherently nonlinear behaviour of Mc-Kibben actuators, the stiffness of the hexapod can be adjusted and thus selected within a wide range. As a whole, the hexapod can be considered as a simple adjustable passive damping and uncoupling unit that can be mounted at the TCP of a serial industrial robot, for example. As second application, the unit can be used as a combined sensor/actor device with the ability to give a force feedback to the user. The unit can therefore be used as a stand-alone device where the forces applied to the hexapod’s TCP can be measured and the TCP’s position can be altered corresponding to the desired force of the respective application. The main targeted area of application is warm compact-forging assisted by industrial robots. This process is characterized by high impulse forces. In case of a conventional robot holding the workpiece in-process, these force impulses are lead from the workpiece through the endeffector and the gears into the robot’s electrical drives. Since the stiff mechanical structure of the gears is not well-designed for high impulse forces, today the parts have to be released during the process. Introducing a lightweight compliant structure designed as a hexapod attached to the endeffektor, force impulses can be considerably attenuated and robot-based holding and manipulating parts during forging becomes possible. This tool has been realized with the help of compliant pneumatic actuators.