Simultaneous Positive and Negative Pressure Control Using Disturbance Observer Compensating Coupled Disturbance Dynamics

This letter introduces a simultaneous positive and negative pressure controller for a pneumatic pump. For precise position or force control of the pneumatic soft actuator, the pressure from the source has to be regulated. When the positive and negative pressures are regulated, coupled dynamics caused by the pressure change affect the controller performance. In other words, changes in the positive or negative pressure concurrently act as disturbances in the opposite pressure controller. Therefore, a disturbance observer is designed to compensate for the coupled pressure dynamics. A nominal model of the system is obtained based on the output-error model used in the MATLAB System Identification Toolbox. A simulation study is also performed to design a controller when the demand for the positive and negative pressures varies. Finally, a verification of the effectiveness of the controller is done through a series of experiments. In the step response test, the maximum pressure error of the positive and negative pressure was reduced from 0.159 to 0.152 kPa and from 0.3297 to 0.2334 kPa with the disturbance observer. Where positive and negative pressures change at the same time, the root mean square of the positive and negative pressure error decreased from 0.9701 to 0.4457 kPa and from 0.9848 to 0.4634 kPa applying the proposed pressure controller.