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6.1.7. Closing the Servo Loop

The following steps will close the servo loop and make all ofthe servo circuitry active. Again, it

is stiessed that the following steps be read and understood thoroughly before proceeding!

The purpose of this procedure is to adjust the servo loop trimpots so that the scanner/mirror

system yields the fastest critically damped step response to a square wave input. Once this is

obtained, the system will yield the best overall performance for any given input waveform. Only

tune the system up as fast as is needed for the specific application. Excessive speed or "loop

gain" will cause the system to have undesirable resonances which increase settling time.

As mentioned earlier, there are two servo configurations, class 1 and class 0. To determine if

your system is set up for class

or for class 0, look on the 670 board at jumper Wl. If the jumper

is connecting pins 2 and

the system is set up for class 1. If the jumper is connecting pins

and

it is set up for class 0 operation. The tune-up procedure for each is different, so each

procedure will

discussed separately below.

If it is only desired to verify the system tuning, skip down to section 6.1.7.1.2. or to section

6.1.7.2.2. Do not tum all the pots back to ground or the entire tuning procedure will have to be

followed.

6.1.7.1.

Class 1

The object of this procedure is to bring the servo gain up slowly so that confrol ofthe scanners is

maintained at all times. Move all the trimpots in small increments until experience with this

system is obtained. If at any time during this procedure the scanners start to move erratically and

make a loud buzzing noise, shut off the input power immediately, set all trimpots to zero and

restart the procedure.

6.1.7.1.1.

Coarse Tuning

Perform steps

- 7 in section

4.2.

above.

Initialize tiie following

timing

pots. Tum

R25,

R28,

R31,

and R59 counter-clockwise, CCW,

at least

tums or until they begin to click. Do not touch

R107.

It has been factory set and

should not need adjusting at this time. Tum R78 fiilly CW

tums.

Tum R25, R28 and R59 2-3 full tums CW. This should allow botii scanners to center

themselves with a slight amount of loop gain once the power is applied.

Attach a scope probe to the input signal at W4 to monitor the input signal. Use the rising

edge of this signal as the trigger source for tiie scope. Attach another scope probe to TPl to

monitor the Position Output signal, VP. Use TP2 or W7.2 as the ground reference for both

signals. Set the vertical gain to 0.2V/div for both channels on the scope.

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