Chapter 3
Theory of Operation
Focus 30/35 Service Manual 3 - 30 P/N 79000035_SM, Version 1.5
Functional description
A simplified drive motion concept was realised by the combination of an coarse and fine stepper
motor. The same principle is used for Hz and V- drive except the design of the axises.
Coarse drive
The stepper motor with the pinion drives the cogwheel on the axis. The first gear stage with a ratio
of 9,25:1 allows a fast but imprecise coarse movement (green arrow). To avoid backlash the cogwheel
is preloaded by two extension springs.
Fig. 3-29 Coarse drive
Fine drive
The fine drive allows slow precise movement (red arrow). The fine drive stepper motor moves the
lever arm by a threaded spindle. Therefore the coarse drive stepper motor is switched off and
clamped.
The lever arm is connected to the coarse stepper motor housing by the clamp disc. The motion of the
spindle is transmitted over the lever arm to the coarse stepper motor housing. The rotation axis of the
lever arm is the motor axis of coarse drive stepper motor.
The right and the left light barriers of the MCB board limits the motion of the spindle.The return of
the lever arm to the centre position,reaching the end stops, will be done automatically by the
Cogwheel
Pinion
Coarse stepper motor
Extension spring
Vertical axis
Extension spring
Coarse movement
Fine movement
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