information provided on this site is not guaranteed in any way. All
informations here are provided for
educational purposes only, USE THEM AT YOUR OWN RISK ! If you blow up your galvos, home, computer,
or anything else -- it's not my fault, use good judgement and play nice.
Assemble the board except resistor R19. This resistor will be soldered to board after position gain (P4) and offset (P6)
is correctly adjusted. Ensure that all trim pots (P1 to P6) are turned fully counter clockwise (CCW).
P1 should be always turned fully CCW. HFD path is not used.
Remove jumper JP2. This ensures that relay K1 will be OFF after power up. Connect your galvo to connector J1.
Connect regulated power supply +/- 20VDC to connector J2 (-20V to pin 1, GND to pin 2, +20V to pin 3).
Now turn on power supply. Measure voltage on C32. It should be 12V +/- 5%. Check also reference voltages VREF+
and VREF- (it should be +6.9V and -6.9V). Also check voltage on pin 10 of U6 (should be -5V)
and on pin 6 of U6 (should be +5V). Now measure Vpos voltage (pin 4 of J2). Using P6 (Position Offset) adjust Vpos = 0V.
Turn off power supply, wait for a while and then insert jumper J2. Next time you turn your power supply on,
relay K1 will be switched ON, but only if both rails of your power supply are working correctly. If at least
one power supply rail fails (positive or negative), relay K1 remains switched OFF. This protects you galvo !
Normaly relay K1 is switching under "no load" condition. U2 is unmuted after K1 is switched ON
and muted before K1 is swithced OFF. That's why I decided to use such "small" relay.
When R19 is not connected and P3 is fully counter clockwise amp is working in open loop mode. This mode is used to adjust
position gain. Prepare simple optical test bench according Test1.jpg, so you can monitor your galvo excursions. Insert jumper JP1
to position 1&2 (pins 1 & 2 shorted => VIN- tied to AGND).
Connect sine wave input signal with amplitude 10V and f = 50Hz
to pin 7 (VIN+) and pin 6 (AGND) of J2. Reflect the laser beam according Test1.jpg. Monitor signal Vpos (pin 4 of J2)
with oscilloscope. Now turn on power supply. You should hear audible click when relay K1 switches ON. Directed laser spot
should be in zero position. Now turn slowly P5 (Input Scale) few
turns clockwise (CW). Directed laser spot should be still in zero
Turn P2 (Servo Gain) clockwise slowly too. Galvo should start traveling back and
forth. Adjust P5 and P2 so galvo is reflecting the beam
at 1/2 of
its rated angle. Maximum rated angle is +/- 20° mechanical (
= 40° optical). On oscilloscope you should see sine wave with f =
Now adjust P4 (Position Gain) so Vpos has amplitude of 2.5V. Now
you can slowly turn P5 resp. P2 clockwise to increase scanning angle
to maximum rated angle. Close to the maximum rated angle Overposition
Shutdown should react. Cycling should be observed as amp tries
to move galvo to commanded position but Overposition Shutdown is
avoiding it. Correctly working amp should be able to reach maximum
rated angle (+/- 20° mechanical) without reaction of Overpostion
Shutdown. Amplitude of Vpos should be equal to 5V at maximum rated
If galvo will try to go above maximum rated angle, Overposition Shutdown should react. Now you can switch off power supply.
Solder R19 to its position. Ensure that P5, P2, P1 and P3 are fully counter clockwise (CCW). Do not touch P4 and P6 as
they have been already adjusted. Connect square wave input signal with amplitude of 10V and f = 20Hz to pin 7 (VIN+)
and pin 6 (AGND) of J2. Monitor signal Vpos (pin 4 of J2) with
oscilloscope. Turn on power supply. Laser spot should be in zero
Turn P5 (Input Scale) few turns clockwise. Laser spot should be still
in zero position. Now turn P2 (Servo Gain) clockwise very carefuly
until galvo starts to move. Square wave with oscillations should be
observed on oscilloscope. Reduce these oscillations by turning slowly
P3 (LFD) clockwise. Increase input signal turning P5
(Input Scale) clockwise to get bigger scanning angle (aproximately 1/2
of rated angle),
increase servo gain by turning P2 (Servo Gain) clockwise and again
reduce oscillations by turning P3 (LFD) clockwise. Always monitor
signal using oscilloscope. Repeat all these steps until you reach
maximum rated angle with maximum servo gain and Vpos is best
to square wave (without oscillations). As servo gain is increased, input signal will need to be decreased to keep galvo rotating at maximum
rated angle. Of course if you try to go above maximum rated angle, Overposition Shutdown should react. Do not let Overposition Shutdown
to cycle too long ! P5 (Input Scale) should be adjusted in way
that input signal with amplitude of 10V will produce maximum rated