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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 after following the troubleshooting instructions below contact your system integrator.

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 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.

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”). 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

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.

Trace: • piezos