Recognizing End Of Range; Travelling To The Mid-Position - Leica WILD M695 Service Manual

Description microscope M695
09/93 3077-HWE
Motorized focusing

Recognizing end of range

Presetting the focus
displacment speed
Travelling to the
mid-position
7-12
The control signals (0V/5V) for A/B FOCUS UP and A/B FOCUS DOWN
pass through the swingarm cable and the Lamp Servo to reach Zoom Servo
at the microscope. ZOOM UP/DOWN activates the end-stage transistors in
the zoom servo board. The end-stage consists of a bridging circuit of transi-
stors, and so the motor can drive the focusing mechanism in both senses of
rotation.
Reflexive light barriers sense 2 encoder tracks at the circumference of the
focus gear: UP/DOWN+CENTER and LIMIT.
With the light barrier UP/DOWN, through gate 2 or 5, the direction of the
arrived limit position is decoded. Through gate 2 or 5 LIMIT blocks FOCUS
UP or DOWN at the following NAND-gate. The final stage is then blocked
for that direction.
The displacement speed is altered with the supply voltage for the focus motors.
The final stage only has a switching function. The FOCUS SPEED level is
the reference for the voltage regulator on the focus servo board.
The current through the final stage is limited to about 140mA.
Triggered by:
• Pressing key "Center Position" at the focusing unit
• Switching on the microscope.
• 30ms-pulse to FOCUS SPEED from control unit. The comparator recog-
nizes when FOCUS SPEED is at GND potential.
The following functions are activated as a result:
1. The selflock circuit is triggered. Gate 2 and 5 block FOCUS UP and
DOWN to the final stage. The voltage supply for the focusing motor is
switched to maximal speed.
2. Lightbarrier UP/DOWN+CENTER senses, at which side from mid-posi-
tion the focus gear is staying. Through gate 3 or 4 the final stage is
controlled - the motor drives the focus gear toward mid-position...
3. ...until the light barrier on the sensor board detects the crossing from dark
to bright at mid-position. The selflock cicuit is reset (Clr) - the motor stops.
Service manual M695
Doc code 636 718