In closed loop mode, an additional daughter PCB is mounted on driver PCB (see figure). Feedback from an external optical encoder mounted on piezo motor is transmitted to the daughter board and used to close the loop. The position and speed of the motor can be controlled through an elaborate set of commands via either a USB port (through DTI’s GUI) or serial (RS 232) port commands.
Driver PCB with Installed Daughter Board
The daughter board performs two key functions. Firstly, it enables the communication between the optical encoder installed on piezo motor and the driver PCB microprocessor, which provides for precision linear or rotational closed loop control. Secondly, the daughter board’s communications unit allows piezo motor motion control via external devices using either USB or Serial Port (RS 232) interface.
During installation of the daughter Board, the microcontroller is factory-programmed with proprietary encoder motion control algorithms. Once the daughter board is installed the driver PCB will no longer work as a standalone driver. However, manual control of motor movement can still be achieved by pushing the Manual Control Buttons of the driver PCB (Note: speed of motion will be lower than observed when pressing these buttons in open-loop mode).
DTI currently uses two types of encoders depending on whether the motor is a rotary or linear model:
- The linear encoder has a resolution of 2.6 µm after interpolation and quadrature detection.
- The rotary encoder has a resolution of 196 µrad (32,000 PPR) after interpolation and quadrature detection.
Two output signals from the encoder (channel A and channel B, with phase difference of 90°) can be monitored on the pins of the Encoder Output connector.