Troubleshooting Z-Drive Problems

The ASI Z-drive is a fine precision device. If the drive shaft is not properly aligned with the focus shaft of the microscope, then binding of the gears may result, causing the system to operate improperly. To test for misalignment, disengaged the Z-drive (switch on front of controller), or turn power off on the controller. Once disengaged, gently turn the focus knob and insure that it has a smooth friction feel throughout the entire 360 degree rotation. If any binding or roughness, or grinding of gears is felt, then the drive needs to be realigned.

To realign the Z drive, use the instructions given in your manual on installing and aligning the Z-drive, and also refer to the video tape if one was provided with your system. In general, the procedure is to loosen one or both of the mounting screws on the adjustment bar, then position the drive slightly forward or back of where it sits while turning the fine focus knob. Search for the position where there is no "feel" of the gears - absolute smoothness. Then retighten the screws and check again to be sure nothing has shifted.

If the system still has problems after it has been determined that the Z-axis drive is installed and properly aligned, then the control electronics may need to be aligned.

The MS2000/MFC2000 controllers are aligned to a free-standing stage and z-axis motor. Under most circumstances, this alignment will give performance within ASI-specified tolerances. However, depending upon the particular microscope, software being used, and operating environment, it may be better to have the controller aligned with the stage and focus motor attached to the microscope.

Once you have verified that your Z-axis drive is properly installed and aligned, please refer to the following procedure to align the control electronics.

MS-2000 Calibration Procedure:

Motor Driver Calibration:

Step 1:

Opening the case:

• Turn off the power and remove all cables attached to the controller.
• Remove the six case screws located on the back top and bottom front of the controller.
• Remove the White Top from the Blue Case bottom. (Note: on older units a flat screwdriver may be required to pry the lid off by placing the screwdriver under the white lid along the sides on the back top.)
  (On older units, pry at arrows)




Control Electronics in an open case

Step 2:

After the case has been opened, connect the stage cable, the z-drive cable, serial cable, and power cord to the controller. Leave the top of the controller connected and set it aside so you can gain access to the control electronics, yet still read the LED display.

Step 3:

Establish serial communication with the control unit with a PC and a terminal program: Ensure the serial/USB cable is installed between the controller and the PC. Using a terminal program such as HyperTerminal, select the correct COM port (usually 1), and set up for the following parameters:

• Parity: None
• Data Bits: 8
• Stop Bits: 1
• Baud Rate: 9600 (or the appropriate speed – see dip switch settings in manual)
• Handshaking: None

Step 4:

Place the DIP Switch 1 (located on the back-panel) in the UP position, and Switch 2 in the DOWN position. You should now have two sets of numbers displayed on your LCD screen.
The upper card is the drive card. The card consists of 3 identical circuits. From left to right, the three circuits control the X, Y and Z axis motors.
Each Circuit has two Potentiometers or Pots. The Pot on the left controls the centering of the voltage that drives the motor. This pot is set so when the motor is not moving, the motor signal is as close to zero volts as possible. The pot on the right is a feedback adjustment that adjusts the low-speed performance of the circuit. To do the alignment, you first set the zero position. Then adjust the low-speed control for the correct velocity at low speeds to make the motor control linear. Finally, recheck the zero position.

Do Steps 5 - 13 for Z-axis drive (U10) located on lower left hand corner of driver board:

Step 5:

Attach a digital voltmeter (DVM) to measure the voltage between TPX1 and TPX2 on the drive card. (This is the voltage applied to the motor.)

Step 6:

Using the computer terminal program send an "AL" + <ENTER> command to the controller, i.e., type al and hit enter. This places the controller in calibration mode and allows you to directly control the DACs that set the voltage to the motor.

The display should now appear as shown below.

X128.00000> 0.00000 
Y128.00000> 0.00000
Z128.00000> 0.00000
Calibration Mode

The first number is the DAC setting, the second number is the linear velocity along the axis. A DAC count of 128 corresponds to zero motor voltage. DAC = 0 corresponds to maximum negative velocity, while DAC = 255 corresponds to maximum positive velocity.

The following table helps show which keys on the keyboard to press to affect the numbers on the LCD showing the DAC bits setting. Match the axis column with the change you would like to make (ROW). Notice the keypad is used as a direction controller for the X and Y axis, and the "5" key stops all motion.

X	Y	Z	Effect
6	8	.	Increase DAC by 1
4	2	,	Decrease DAC by 1
Following commands are not available on all older units
x	y	z	Set DAC = 0
w	r	q	Set DAC = 28
s	t	a	Set DAC = 118
S	T	A	Set DAC = 138
W	R	Q	Set DAC = 228
X	Y	Z	Set DAC = 255
5	5	5	Set DAC = 128 (ZERO VOLTAGE) or hit ZERO button on unit

Step 7:

With the DAC setting at 128, adjust the ZERO potentiometer so that the DVM registers less than ±0.010 volts.

Step 8:

Using the appropriate key, set the DAC to 28 and write down the speed (right column on LCD Screen). Note:  BE CAREFUL not to run into end of lead screw as there is no limit switch to stop the stage when in alignment-mode. Use the 5 key or ZERO button on controller to stop movement.

Step 9:

Using the appropriate key, set the DAC to 228 and write down the speed (right column on LCD Screen). See above note! Then stop movement by hitting 5 on keyboard or ZERO on controller.

Step 10:

Set the DAC to 118 and use the LOW SPEED CONTROL pot to adjust the speed to be 1/10th the speed written down in Step 8. CCW rotation increases the speed; CW rotation decreases the speed.

Note:  Due to encoder resolution, numbers may not exactly match – get as close as possible. In some cases the pot may have to be adjusted fully clockwise (as low as possible). It is normal for the number to flicker back and forth between two close speeds.

Step 11:

Set the DAC to 138 and use the LOW SPEED CONTROL pot to adjust the speed to be 10% of the speed written down in Step 9 (move the decimal point one digit to the left).

Step 12:

Repeat Steps 10 and 11 for the best balance.

If the motor buzzes without being instructed to move, turn the LOW SPEED CONTROL clockwise until the buzzing stops.

Step 13:

Repeat Step 7 for X and Y axis, if necessary.

Note:  If the zero voltage is too erratic and jumpy, turn the LOW SPEED CONTROL pot a quarter-turn in the clockwise direction until voltage reading becomes more stable.