May
18, 1998 Design News
FEATURED PRODUCT
Midrange servoamplifier takes up the
slack
by John Lewis, Northeast Technical
Editor
Automated fastening machines require precise velocity
and torque control. Winding machines need high-speed
wire take up, and precise tension control. That's where
Copley Control's Model 5424AC could simplify controls
on fastening or winding machines--as well as pick-and-place,
robots, automated assembly equipment, and material testing
machines.
It features remote speed/torque mode switching, and
drives brushless dc servomotors (to 2.5 hp continuous)
with power direct from AC mains.
The servoamplifier's current monitor provides feedback
to the controller. As fasteners take up toward the end
of travel, sensors detect increasing winding current
and signal the controller which then cues the amplifier
to switch from velocity to torque mode. In the torque
mode maximum current settings prevent the motor from
applying excessive torque to delicate loads, and from
overheating.
Three velocity loops add to the servoamplifier's flexibility.
A frequency-to-voltage (F/V) converter emulates traditional
motor-driven tachogenerators. Result: speed feedback
without a separate motor-driven tachometer. Another
velocity mode uses the F/V converter to transform digital
shaft encoder signals to analog velocity feedback. The
third mode uses IR compensation to control the motor
back emf and maintain constant velocity as the load
changes. Adjustable soft start capability smoothes mechanical
operations.
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