Standard drive electronics for Piezo LEGS® range from simple and low cost to advanced controllers for closed loop control. The motor is powered by signals below 50 V in amplitude, and custom drive circuitry can even run on battery.
Piezo LEGS motors can be used in different ways depending on the requirements of the particular application. Required resolution is always the key question. As its name implies, a Piezo LEGS motor takes steps to create motion and, just as in humans, it can walk in different ways. It can move fast or slow, take long steps, short steps or partial steps, and stop at any point. All accomplished by different movement patterns and frequencies of the legs.
If we study one of the piezoceramic legs in detail, the actuator is built like a bimorph (Figure 1). Left and right side of the leg can be independently activated (0-48V). When energized, the leg can extend and bend a few microns. The tip of the leg (i.e. the friction drive pad) can move to any point within the rhombic area as illustrated in Figure 1. When the leg is not energized, the tip of the leg will be at point a. When only activating one side of the leg, it will bend to the left or to the right (b or d respectively). With both sides of the leg fully activated, it will extend to its maximum height (at point c). A Piezo LEGS motor will have several actuator legs working together. The motion of the motor will be dependent of the input electrical waveform signals. To achieve motion, two legs (or more) are driven in parallel. In total, each motor will need four separate control signals. Each leg, however, is controlled with two voltages. In Figure 2 two different waveforms are depicted. Rhomb is a rudimentary waveform which will make the tip of the leg move in a rhombic pattern. A more advanced waveform is called Delta. The Delta waveform is optimized for smoothest walking, and is best for high precision positioning.
Voltage plots; waveform Rhomb (left), and waveform Delta (right). The two input signals (U1 and U2) will control each separate half of the bimorph leg. Resulting plots describe the motion of the tip of the leg for given waveform type.