Zeiss Axio-Series Microscopes use a ball race mechanism to transfer the rotation of the fine-focus shaft to the coarse focus shaft of the microscope. The coarse focus shaft connects to the rack and pinion focusing mechanism on the microscope. The ball race mechanism is a friction drive transfer mechanism with no rigid connection (i.e., no gears) in the drive train. Hence, accurate position information can only be obtained from the coarse focus shaft of the microscope. ASI Z-drives use an anti-backlash gear screwed onto the coarse focus shaft to provide positional information to the gear-driven rotary encoder. Motor drive power is applied to the fine focus shaft of the microscope and transmitted to the focusing mechanism through the Zeiss ball race mechanism.
Potential pit falls:
If there is excessive friction on the coarse focus knob, either because the anti-backlash gear and the encoder are positioned incorrectly, or because of problems with the microscope, then turning the fine focus knob will fail to transmit sufficient force through the ball race mechanism to turn the coarse focus knob. Under these circumstances, the ASI Z-drive will not work. The motor will spin until it "gives up" after a second or so. And then it will likely try again, perhaps in another direction.
Fine mechanical adjustment of the drive is the key to optimum performance
Once the drive is attached, the adjustment screws have been tightened, and the shaft clamp has been tightened, perform the following tests before powering up the unit:
- Using the right-side knobs – rotate the coarse focus knob from one focus extreme to the other. It should feel smooth and uniform throughout the range. You should be able to "feel" the teeth of the anti-backlash gear, but only barely.
- Next, with the coarse focus somewhere in the middle of the focus range, rotate the fine-focus knob and be sure that doing so actually causes the anti-backlash gear (i.e., the coarse knob) to rotate as well. Rotate the fine-focus through one complete revolution of the anti-backlash gear to be sure that there are no "tight spots".
If either of these checks are unsatisfactory:
- Loosen the shaft clamp and the top adjustment bar allen-head screw (horizontal adjustment). Slide the drive back or forth slightly – looking for more favorable alignment, then retighten.
- Repeat steps 1 and 2 above. If still unsatisfactory, try loosening the vertical adjustment screw on the side of the drive and move the drive up or down a little bit – again looking for more favorable alignment.
- Continue this process until satisfactory results are obtained.
Troubleshooting
A properly-adjusted drive will quickly move to the desired position and settle to the exact value commanded. Several circumstances can cause the motor to run unexpectedly:
- Focus mechanism is at the end of its travel range: Motor tries to get to position but is unable, so it shuts down after short period.
Solution: Keep within its focus range.
- On linear encoder models: the linear encoder is selected with the back panel switch, but the linear encoder is not installed or not correctly installed.
Solution: Switch to rotary encoder mode, or correctly install linear encoder.
- Excessive friction is not allowing the coarse knob to be turned via the ball race mechanism of the Zeiss Axio-series microscope:
Solution: Adjust the Z-drive mechanical alignment. Be sure the microscope is up to Zeiss specifications.
If the drive is unstable, or spends to much time "seeking", check the following:
- Anti-backlash gear is under spring tension and engaged properly.
- Shaft clamp is tight.
- Encoder gear is tight (mates with the anti-backlash gear).
