Design and analysis of pneumatic force generators for mobile robotic systems

Pneumatic components are rather rugged and suitable for harsh environments and therefore are an attractive alternative for mobile robots. Many robotics control algorithms require that the robot actuators be force or torque generators, so the robot controller can impose proper torque levels onto the robot joints as required by the control algorithm. While creating a torque generator using electric actuators is relatively straightforward using current feedback, there are challenges in transforming pneumatic actuators into pure force generators. This paper develops a control algorithm to convert pneumatic actuators into force generators. Because delivered work from a pneumatic actuator is product of the actuator force and the piston's displacement, the actuator force can be effectively controlled through precise measurement of the piston's displacement and robust control of the actuator's work. This paper first develops an exact model of a pneumatic system consisting of a double-acting cylinder and a servo-valve, with the goal of providing an insight into the design and control requirements for pneumatically actuated systems. Using the model, two subjects are presented in detail: 1) derivation of a control algorithm that converts a pneumatic actuator into a force generator for robotics control applications and 2) derivation of equations that can be used to design or size the power source for mobile robotic systems, where continuous source of power is unavailable.