9600 Service Manual - gmecorp-usa.com

10 Image System
IRIS MOTOR
The collimator iris motor is driven by the Image Function PCB when the field size (e.g.
NORM, MAG, MAG2) is changed or when the iris size is adjusted with the iris control
switch (see Figure 6). U17 on the Image Function PCB receives the commands from the
Technique Processor. Microcontroller U16 receives the instructions and communicates
the data to U11, the Motor Driver PLD (programmable logic device).
U11 then enables and drives the iris motor in the desired direction via U18, the motor
driver IC for the collimator iris motor. See Table 2 and Figure 7 for details of the drive
logic.
Motor speed is varied by pulse width modulation (PWM), output from microcontroller
U16, pin 39 (PWM0) to the Motor Driver PLD, U11 pin 11. Pulse width modulation is
used instead of direct DC driving so that collimator iris sizing is accomplished more
efficiently without “hunting” by overcorrecting and then re-correcting.
The iris motor has a potentiometer mechanically linked to it (see Figure 7) that provides
feedback for indication of iris size. Micro-controller U16 pin 9 samples the iris position
voltage every 10 ms and compares it with values contained in EEPROM U7 on the
Image Function PCB. The values stored in EEPROM U7 reflect the iris potentiometer
values for the iris field sizes acquired during calibration of the iris (see Collimator Iris
Calibration below). When a field size is selected the iris motor is driven until the value of
the potentiometer and the value in the EEPROM match for the selected field size.
If an error, such as the iris size being too large for the selected field, is detected the
micro-controller sets the IF_FAULT signal U6-18 high. If U6-18 is high then DS2
illuminates indicating an error condition. In addition a status word sent via RS-232 serial
communication to the Technique Processor PCB every second by the Image Function
PCB will indicate there has been an error. The fault line from U5 pin 8 to PIO U38 on the
Analog Interface PCB is no longer used by software because of the serial
communications.
Collimator Iris Calibration
The collimator iris field sizes are calibrated by using collimator calibration software
available on the Mainframe Menu. Jumper E5 is installed and the collimator field sizes
are set using the collimator iris controls on the control panel. The calibration information
obtained from the voltages from the iris potentiometer (IRIS SIGNAL) are stored in
EEPROM U7 on the Image Function PCB. See the Image System Calibration section
of this manual for the procedure to perform this calibration.