Combined PWM- and Hysteresis Switching Control for a Digital Hydraulic Actuator

The so called Digi-Actuator is a positioning actuator based on two fast switching valves and a special hydraulic circuitry. It is designed as a special valve block with a nominal size 6 interface. The hydraulic behavior of the Digi-Actuator is comparable to a fast proportional 4/3 way valve. The proportional valve can be replaced without any hydraulic modifications. In this paper an advanced Digi-Actuator, its main components, and hydraulic circuit are presented. It enables a more precise positioning, smoother motions, and low as well as high actuation speeds. Its performance is demonstrated by an autonomous test rig. It also serves for the testing of different control techniques. A combined PWM- and hysteresis control is investigated by simulations as well as by experiments. With this technique a repeatable accuracy of < 100 μm was achieved. An outlook is given in which way the performance of the Digi-Actuator can be further improved. This outlook comprises other control methods, like sliding mode control, and modified hydraulic circuitries.