Quasi Time-Optimal Path Tracking for Pneumatic Robots Considering Third-Order Actuator Constraints

The class of pneumatic robots with rigid links and pneumatic actuators is well suited as collaborative robots because, unlike electric robots, they have direct drives. The low inertia of direct drives results in less energy having to be transferred in the event of a collision. However, pneumatic direct drives come with their own challenges. Due to the compressibility and the flow characteristics of air, the pressure build-up in such a drive has its own dynamics, depending on the current state of motion of the robot. These dynamics are not negligibly fast compared to the kinetics of the robot and need to be taken into account when generating trajectories for the robot to ensure their feasibility. This paper presents a model of a pneumatic actuator to account for the dynamics of its pressure build-up. Based on this model, a solution to the quasi time-optimal path tracking problem, i. e. generating trajectories to a given path, is given for a robot driven by such pneumatic actuators. The proposed approach to the quasi time-optimal path tracking problem is evaluated by executing the generated trajectory on a real pneumatic robot. From this experiment, it was found that the robot can execute the trajectory precisely, confirming its feasibility.