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Piezos

The piezo objective movers are the most fragile part of the system you should exercise caution with them both mechanically and electrically. If you think you have a failure, first follow the troubleshooting instructions below and then contact your system integrator for further help.

Caring For Your Piezo Objective Movers

Mechanically, avoid applying external force to the piezos. When assembling or disassembling the microscope, be sure not to set down the SPIM head resting on the piezos. With pre-2015 piezos (not on dovetail), exercise caution not to screw in the bushings too tightly, and note the manual's instructions regarding inserting/removing the objectives. As of 2015, the piezos can be removed from the SPIM arm mount on dovetail easily (see manual) and it is impossible to over-tighten the bushings.

Electrical stresses on the piezo objective movers are inevitable during normal use. However, applying extreme and/or static voltages to the piezo actuators for long periods can pre-maturely degrade performance and ultimately can lead to actuator failure.1) To maximize piezo lifetime they should to be turned off when not in use, or else apply only a small voltage across them. Reducing the humidity of the operating environment will also prolong piezo lifetime.

The simplest way to turn off the piezo actuators is to power down the entire Tiger controller when not in use. Beginning in firmware v3.00 you can turn off the piezos using the MC <axis>- command to explicitly disable the axis and turn it back on with MC <axis>+ (in Micro-Manager use the property “MotorOnOff” to do this). For ADEPT Rev M cards or later (approx. August 2015 or later) the MC – command works whether in internal or external mode, but for earlier versions of the card it only has an effect in internal mode. Beginning in firmware v3.11 there is an auto-sleep function to automatically put the piezos in a good (low-voltage) position after a specified time being stationary; the auto-sleep function only works in internal input mode. In external input mode, 2 volts is a good input voltage to use when the piezos are resting for long periods.

Troubleshooting

If you need to know how to send serial commands see http://www.asiimaging.com/docs/tech_note_rs232_comm.

  1. Make sure the piezo is set to be internal closed-loop input mode (or external if you are using external control mode).
    1. Send the PM <axis>? command and note the response. It should be 0 (e.g. Q=0) for internal closed-loop.
  2. Use the PZINFO command to see if the high voltage supply is as expected.
    1. Send the command <Card Address> PZINFO, e.g. 4 PZINFO for P on a typical diSPIM and 5 PZINFO for Q on a typical diSPIM.
    2. Look at the line that says HV : and note the voltage, the voltage should be around 150 V (140 - 160 V are acceptable, usually with failures it is < 50 V)
    3. If the high voltage supply is low there can either be a problem with the card or with the actuator so proceed to the next step
  3. If you have a diSPIM, exchange the drive electronics to isolate a card vs. actuator problem
    1. Power the controller off.
    2. Exchange the two piezo cables on the front of the controller.2)
    3. Turn the controller back on.
    4. Use the PZINFO command as described above to see if the high voltage is still low on the original problem card/axis. If not, check the other one. If the problem stays with the card then the problem is likely with the card. If the problem moves with the actuator then the problem is likely with the actuator.
  4. Alternative to exchanging the drive electronics for single piezo systems
    1. Power the controller off
    2. Remove the actuator cable
    3. Turn the controller back on.
    4. Use the PZINFO command as described above to see if the high voltage is still low. If the measured high voltage remains low with the actuator unplugged the problem is likely with the card, but if it recovers then the problem is likely with the actuator.
  5. Remove the problem card/actuator from the system.
    1. If there is a problem, there is no sense in continuing to stress the card and/or actuator!
    2. Power off the controller.
    3. If the problem appears to be with the actuator, unplug that actuator.
    4. If needed, restore the other actuator to its original card.
    5. If the problem appears to be with the card, unscrew the faceplate screws and pull it out of the controller.
  6. If you have a problem with the card and/or actuator, contact the system integrator detailing the results of your testing.
1)
The piezo actuator is a stack of thin dielectric layers of piezoceramic material with alternating electrodes across which a voltage is applied (generally -20V to 120V). The main failure mechanism is electromigration of the electrode material through the piezoceramic leading to shorts. Electromigration is proportional to at least the square of the applied voltage and worsens with humidity. It is believed that fixed voltages are worse because self-heating during movement prevents the build-up of moisture.
2)
Each card has been calibrated or paired with the corresponding actuator for optimal performance, but any working card will drive any working actuator

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