Electro Cam PS-6144 Series - Manual (Page 64)

4-6 Speed Compensation
Speed Comp 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. See Figure 27 for 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 Section 5, be aware of the effects of
speed compensation on the relationship between the setpoints, the Group Input signal,
and the pulse programmed into the Group Channel. Speed compensation will not
affect Group Channels 91 through 96.
Figure 27—Product Speed Should be Constant Past Controlled Device
Negative Speed Compensation
Negative Speed Comp Normal speed compensation advances the setpoints in an output channel to compen-
sate for a fixed response time in the device being controlled. In some applications,
however, negative speed compensation is required to retard the setpoints 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. Figure 26 illustrates 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 PS-6144’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 Section 3 for details.
Figure 26—Simple Sensor Gating Scheme