This research explored a new linear hybrid actuator, which consists of a pneumatic cylinder with a magnetorheological brake embedded in its piston. Magnetorheological brakes are promising actuators since they can apply large forces in a small actuator size, but they can only oppose motion, as they are passive actuators. Pneumatic cylinders are desirable actuators due to their high force-to-weight ratio and ability to apply active forces. However, they require expensive servo valves for precise position control. The new hybrid actuator benefits from the advantages of magnetorheological brakes and pneumatic cylinders. It can apply forces using compressed air and can resist external forces using the magnetorheological brake. The embedded brake also eliminates the undesirable side effects of using compressed air and allows precise positioning of the piston anywhere in its stroke with simple solenoid valves. Fields such as haptics and robotics might benefit greatly from the use of the hybrid actuator where a high force-to-weight ratio could be employed. The study contributes (1) a triple helix flux guide for the linear magnetorheological brake, (2) serpentine flux path to enable larger braking forces, (3) shear mode activation, and (4) control algorithms that enable use of simple solenoid valves and improved power efficiency. When compared to an existing purely pneumatic control algorithm, the hybrid actuator exceeded the performance in position tracking and force disturbance rejection. A power management algorithm demonstrated that disabling the brake when the piston was in position vastly decreases the power consumption.
Adaptive Position Control of a Pneumatic Cylinder.