Research → Mechatronic systems → Pneumatically actuated ball and beam system → Experimental system description


The beam with v-shaped profile is placed in the center of rotation of the pneumatic motor, which is used as an actuator. The beam is made to rotate in a vertical plane by applying a torque at a center of rotation generated with compressed air. The pneumatic rotary drive (swivel actuator with shock absorbers FESTO type DSM-25-270-P-CC) is used to tilt the beam with the objective of keeping the ball stationary at the center of the beam. A rotational servo potentiometer made by Spectrol, which is mounted at the rear of the actuator shaft is used to sense deviation angle on the beam. The electronic reference voltage card with a ref-chip reduces the measured signals from potentiometer to required values. When the angle of the beam is changed gravity causes the ball to roll along the beam. A metal ball with the radius 1.5 cm is free to roll (with one degree of freedom) along the beam. Two parallel wires are placed on the beam giving an end to end resistance of approximately 50 kOhm in the circuit. The ball then acts as a contact between the resistive wires and the voltage coming out from this measuring system will change. It is supposed that the ball remain in contact with the wires and the ball rolling occur without slipping. A plastic bumper is at each side of the beam so the ball can roll upon the beam within a distance of about 53 cm. The proportional 5/3 control valve (FESTO type MPYE-5 1/8 HF-010B) can adjust flow-rate by changing the spool position according to input voltage in the range 0 to 10 V. When input voltage is 5 V, all control edges are closed so that the flow rate to the actuator is zero. To detect differential pressure between two actuator chambers, and also the supply air pressure, three pressure transducers SMC ISE4-01-26 were employed. The measured signals are passed to the Intel-based PC through data acquisition and control board (Advantech PCL-812PG) with 12-bit A/D converter. A digital controller realized on a PC accomplishes the stabilization of the ball. Based on signal measurements, the controller generates a suitable control signal, which is passed to the proportional valve via 12-bit D/A converter. Control system design and experimental verification is performed in the Matlab/Real-Time Workshop program, which allows a rapid control system development and testing.