PDXC2 ORIC® Piezo Stage Controller Chapter 2: Overview
Rev A, July 25, 2023 page 3
Operation Principle
The PDXC2 controller mainly consists of 2 circuits: the control circuit and analog switch circuit. The control circuit
generates charge or discharge pulses to the analog switch circuit, then the analog switch circuit will generate
sawtooth waveforms (Figure 2). The waveforms are then exported to the 15-pin D-SUB connector on the front
panel to drive the different stages.
The stage uses a piezo inertial drive motor, which consists of three main parts: a flexure-coupled piezo actuator,
a friction element, and a slider (as seen in Figure 3). During the "stick" part of a cycle, the piezo slowly expands
under the ramp voltage, pushing the friction element and the slider forward in unison. During the "slip" part, the
drive voltage drops rapidly and the piezo element returns to its starting length, with the friction element "slipping"
backward. The slider does not move due to its inertia and the low coefficient of kinetic friction between the friction
element and the bottom surface of the slider. Figure 2 shows the piezo drive voltage during one "stick-slip" cycle.
Repeating this cycle produces continuous forward travel of the slider. To travel in the reverse direction, the
opposite drive voltage pattern is required, resulting in rapid piezo expansion and slower piezo contraction, or
"slip-stick". During operation, the stage makes a high-pitched noise and may generate some heat. This is normal
behavior in the performance of the device and does not indicate a faulty condition.
Due to several factors that include the application conditions, piezo hysteresis, component variance, and the axial
load, the achieved step size will vary and is not repeatable. To help overcome this variance and accurately control
the stage movement, an external feedback system is added for closed-loop control of the feedback slider position
to controller.
Figure 2 Sawtooth Waveform Figure 3 Stick-Slip Movement Illustration
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