| This research presents nonlinear pneumatic controllers which, unlike many previous controllers, more fully account for the nonlinear dynamic properties of pneumatic systems. The nonlinear dynamics for the pneumatic systems include the servovalve flow characteristics and the thermodynamic properties of air compressed in a cylinder. Originally discounted as not being suitable for anything other than stop to stop control, we have shown with theory and experiments that these actuators can rival the performance of more common electric actuators. To demonstrate this, several control algorithms were developed and tested. In one approach a standard joint torque controller with a Lyapunov-like stability proof is extended to include the additional actuator dynamics of an air powered system. Another approach, based on hierarchical system stability theory, is presented and demonstrated which allows most existing control laws that have been developed for electric motor driven robots to be extended to pneumatically actuated robots. All the controllers tested exhibited good trajectory tracking characteristics for the multiple degree of freedom robot used in the experiments. In addition to these trajectory tracking control laws, a hybrid position/force control algorithm was developed. The experimental results indicate that the tip forces on the robot can be controlled without the need for the expensive force/torque sensor that is usually required by electric motor driven systems. |
