Motion Control

Open-Loop

(Non-Feedback Control)

When an external control signal (logical TTL “0”) is applied continuously to the external input control of the driver board, the piezo motor will move in continuous mode at its maximum specified speed. Alternatively, control of speed of motion using PWM is implemented by varying the pulse duration and repetition rate (frequency) of the input signal. The size of each step is determined by the pulse duration, and the speed of travel is determined by the pulse repetition rate. The minimum pulse duration is approximately 30 µs (microseconds). The maximum repetition rate (F), measured in Hertz, for a selected pulse duration (T), measured in seconds, is determined by the formula F = 1/T. The range of speed variation in PWM mode can be up to 6 orders of magnitude.

Digital Control of piezomotor via PWM

Similar to DC motors, control of the piezo motor speed in continuous mode can be accomplished by adjusting the power supply voltage of the driver PCB within the range 5V DC to 12V DC (note: this requires custom programming of the driver PCB). This control can enable decreases in the maximum specified speed of the piezo motor at 5 V down to 1/5th of the speed at 12 V. In this mode, PWM can also be used in parallel to vary speed within a higher dynamic range.

Motion control of the piezo motor in this mode can be accomplished using virtually any standard commercially available DC driver/software (e.g. Arduino). However, when implementing this mode of control, it is necessary to consider the following points:

  • A supply voltage, with positive polarity, in the range of 5 V DC to 12 V DC must be applied to the 12 V DC input connector of the driver PCB. Providing the driver PCB has been custom programmed, then the speed of the motor will be proportional to the input voltage. If the driver PCB was not custom programmed and the input voltage is decreased from 12 V DC to 9 V DC, the motor will continue to hold a constant speed (due to an internal algorithm for speed stabilization). However, if the input voltage drops below 9 V DC, then the speed stabilization algorithm will not be able to hold the motor at constant speed and the motor will either slow down or stop.
    Note: In contrast to DC motors, negative input voltages to the driver PCB should NOT be used to change direction of motion as this may lead to failure and damage of the driver PCB. Change of the direction of movement is implemented through activation of the corresponding pins of the External Input Control pins (pin 1 and pin 2).
  • Due to the very high dynamic characteristics of the piezo motor, the minimum response time to a DC driver input will be substantially lower (e.g. 10 to 100 µsec) compared to a comparable DC motor.

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