Homing the ID Primary Adjustable Aperture

The 22-ID adjustable primary aperture has a coupled motor drive system controlled by a PMAC coordinate system. In this coordinate system, X is center position and Y is size, with the origins of the motors to be defined as the most open position that does not trigger a limit. Motors 1 and 2 control the vertical aperture size and center, and motors 3 and 4 the horizontal size and center. The vertical aperture is defined in coordinate system 1, and the horizontal in coordinate system 2. Two PLC programs are required, #3 and #4, to calculate the coordinate system position from the encoder positions. Motion program 6 is used by both coordinate systems for rapid mode drives to destinations stored in q variables Q51 and Q52 for X and Y respectively. The positions for each coordinate system are stored in Q31 (X) and Q32 (Y).

1. Hook up PMAC tuning computer to PMAC upstream of the Aperture stand.

2. Back up the coordinate systems, if it has not already been done, using the executive backup command.

3. Undefine the coordinate system with the following commands in the PMAC executive terminal window:

&1#1->0#2->0
&2#3->0#4->0

4. Ensure that motor 1 is not on a limit. Drive motor 2 positive until it goes into the positive limit. Motor 2 moves negative from its home position, so the most positive position is the home position. Home the motor with homez. Move motor 2 -50,000 steps to clear limit hysteresis, and then to -30,000, and again home the motor with homez.

5. Drive motor 1 to its negative limit, home it with homez, move it to 50,000 steps, move it back to 30,000 steps, and home it again with homez.

6. Restore the coordinate systems, using the executive restore command.

7. Drive the motors using the coordinate system to center the aperture with an opening of 2mm x 4mm. This is done with the following commands:

&1 Q51=0 Q52=2000 b6r
&2 Q51=0 Q52=4000 b6r

Positions after the drive, in steps:

#1      713467
#2     -356734
#3      426933
#4     -213467

Note that since the resolution of the drive is 123 steps per micron, there may be a slight discrepancy in these positions.

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