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6.1.9. Matching Two Servo (X and Y) Channels

The purpose of this section is to match the dynamic performances of a dual axis X and Y system

over all angles and frequencies. This system would consist of two 670 boards and two scanners.

If the two channels are not closely matched, the system will not make sfraight lines when both

channels are moved simultaneously. They also will not retrace a pattem when the beam is

traveling in the opposite direction. Thus, it is cmcial for optimum performance to perform this

procedure whenever either servo channel has been retimed. This matching is done standard at

(Zlambridge Technology and should not need to be repeated during the normal operating life of

the system.

Set up the system by following steps 1 - 7 in section 4.2. The system must have had its

Command Input Scale Factor, Position Output Scale Factor, and Closed Loop Response

adjusted properly to perform this. Ensure the mirrors are aligned by following the procedure

in section 7.1.8., to eliminate the chance of their hitting.

Input a 30 Hz square wave signal such that the scanners move 2° mechanical peak-to-peak.

For larger systems a slower square wave can be used. It is very important that the two

channels receive the information simultaneously, or this procedure cannot be performed

properly. For analog input systems, this is easily done by using a BNC "T" connector and

hooking up to both inputs simultaneously. If

the

system is digital, do not let a timing skew

occur between the X and Y channels. Let both channels' CS lines go low simultaneously. If

this is not possible, convert the 670 for analog input operation for the purpose of this

procedure.

Tum on the system power. Monitor both channels' position out signals, Vp on TPl, on an

oscilloscope while extemally triggering the scope on the input signal at W4. Monitor the

channel with the greater inertia first. This is usually the slower system. In most cases this is

the Y-channel. Ensure the step response is at the required speed for the application and that

it looks critically damped. Refer to the timing procedure above in section 7.1.7. for specific

instmctions. If it is not tuned as required, retune this channel now.

Input a full-field signal. Monitor the same channel and ensure that the large signal step

response is also as desired. Once this is accepted, do not tum any ofthe pots associated with

this channel or this procedure must be started over again.

Input a 2° signal again. Now monitor both channels' Position Out signals superimposed on

one another on the oscilloscope. Increase the vertical gain and sweep speed on the

oscilloscope until the speed difference between the two channels is noticeable. See Figures

30 and

31.

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Axis 670 Bedienerhandbuch Seite 50