SENSOR DESIGN, IDENTIFICATION AND CONTROL OF A DEFORMABLE PNEUMATIC ACTUATOR

In this paper the complete process of sensor design, modelling, identification and control for a prototypal pneumatic actuator is presented. The importance of pneumatic deformable actuators lies in their ability to manipulate delicate objects and to operate in hostile and dangerous environments, making them suitable to be employed for instance in agricultural or aerospace applications. The actuator under study is constituted by a rubber tube internally divided into three chambers in which the pressure can be independently controlled. The tube is encircled by several iron rings that prevent its radial deformation so that, when the pressure in the internal chambers is increased, the actuator grows longer and it also bows whenever the pressure in the three chambers is uneven. The actuator is equipped with simple and low cost sensing devices that enable to determine the changes of length along three generatrices of the tube. The sensor outputs allow to fully determine the position of the end effector. However, there exists a highly nonlinear relation between the three cartesian coordinates of the end effector and the sensor outputs, thus requiring a preliminary careful calibration process of the sensing equipment. The closed-loop position control is then implemented commanding the pressure in the three chambers of the device on the base of the signals collected at the three sensor outputs. Different control schemes (decoupled control, LQR, LQG) have been successfully applied using models of different complexity for representing the dynamic behavior of the actuator.