Performance improvements for stick-slip positioners

Stick-slip actuators are frequently used systems for micro- and nano positioning because of their high dynamics and simple design. Driving at high velocities however is restricted, as either the actuators are very stiff and have a short stroke, or they have a large deformation but low natural frequencies. Beyond a certain frequency, which is determined by the actuators' natural frequency, the masses to be moved, and the damping ratios, the system cannot be driven in a controlled manner any more, as the velocity no longer increases linearly with the driving frequency and presents a "chaotic" behavior. This behavior is a result of a vibration after one step not being completely damped out before the next step occurs. In this paper, we propose a method to actuate stick-slip actuators with low natural frequencies at comparatively high driving frequencies, which permits to increase the velocity compared to the velocity obtained with a simple saw tooth signal of the same frequency. The driving signal for the actuators is convolved with a pulse sequence that cancels occurring vibration, a method that is commonly called "input shaping". Particular aspects of signal shaping for stick-slip drives will be discussed, simulation as well as measured experimental results are given.