CHAPTER 2. INSTALLATION 23
A
B
C
D
E
F G
K
J
H
S
R
P
SLOW
SPEED
FAST
SPEED
HOME
SPEED
SPEED
POSITIVE
DIRECTION
NEGATIVE
DIRECTION
DIRECTION REQUEST
+LIMIT
DECELERATION COMPLETE
MOTOR DIRECTION
MOTION REQUEST
FAST SPEED
HOME SPEED
SLOW SPEED
L
M
Figure 2-7. Ramped Clock Waveforms
When the Fast input is removed, the deceleration current generator
is turned on and this discharges the capacitor at a controlled linear
rate. There will be a corresponding fall in the output frequency from
the oscillator until the capacitor voltage reaches a preset clamp
level, at which point the motor will be running at Home Speed since
the only remaining input current to the oscillator is that from the
Home Speed current generator. This current generator is now
switched off and the motor stops.
The remaining circuitry on the board is for controlling motor direction
in conjunction with the limit interlock circuit. The Direction Request
input is taken to the direction latch which is only permitted to change
its state when deceleration is complete, in other words when the
ramping circuit is in its quiescent state. Under these conditions the
motor is either stationary or running within the start/stop range and
so can be instantly reversed. If the direction request is changed
whilst the ramping circuit is in operation (i.e. motor running in the
slew region) the Fast input is removed so that the motor decelerates
to Home Speed before reversing. The Fast input is then
reconnected so that the motor accelerates back up to speed in the
opposite direction.
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