Electro Cam PL-1746 Series - Manual (Page 97)

5-6 Speed Compensation
Speed Compensation Guidelines
Device Placement For speed compensation to work most effectively, the device being controlled by the
output channel should be located on the machine in a position where the product is
moving past the device at a constant speed. The illustration below is an example. In the
case of a glue gun, if the gun is ON when the speed is changing, the glue distribution
may be inconsistent from carton to carton at varying machine speeds.
Speed Comp & Modes When using Operating Modes as discussed in Chapter 6, be aware of the effects of
speed compensation on the relationship between the pulse edges, the Group Input
signal, and the pulse programmed into the Group Channel. Speed compensation will
not affect Group Channels (channels 91-96).
Product Speed Should be Constant Past Controlled Device
Negative Speed Compensation
Negative Speed Comp Normal speed compensation advances the pulse edges in an output channel to com-
pensate for a fixed response time in the device being controlled. In some applications,
however, negative speed compensation is required to retard the edges in an output
channel. Negative speed compensation is usually found in two situations:
“Wrap-Up” As some machines increase in speed, the drive train at some point between the re-
solver and the product “wraps-up,” or shifts with respect to the resolver. If the wrap-up
is proportional to machine speed, negative speed compensation can be used to retard
an output channel’s setpoints from the true resolver position, thus maintaining output
accuracy.
Sensor Lag While output channels are usually used to switch devices on and off, another use is to
“gate” a sensor into a PLC or other computer. The illustration below shows a basic
sensor gating scheme. In the illustration, the signal from the sensor reaches the PLC
only when the output channel from the PLS is turned on.
Most sensing devices have very fast response times. However, if a sensor’s response
time is slow, its signal will appear later and later in the machine cycle as the machine
speeds up. Eventually, the sensor may lag the resolver so much that its signal fails to
appear during the window programmed into the PL-1746’s output channel.
Negative speed compensation will correct this problem by causing the output channel
to lag its programmed machine position by a specified number of milliseconds. Nega-
tive speed compensation is calculated using the same method as standard speed com-
pensation. See SPEED COMP in Chapter 4 for details on programming negative speed
comp.
Simple Sensor Gating Scheme