Westamp A651 Series overview
Westamp 651 Series Servo Drive ControllersThe A651 amplifier consists of a closed loop feedback amplifier which has a second closed loop within the outer loop. ...
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Manufactured byWestamp
Product groupServo Amplifier
DescriptionWestamp 651 Series Servo Drive ControllersThe A651 amplifier consists of a closed loop feedback amplifier which has a second closed loop within the outer loop. Referring to the Block Diagram, analysis may begin at the signal input point at the left side of the page. The signal input comes to a summing point designated as a circle with a cross in it. The signal input and the tachometer input are of opposite polarity and are normally almost equal in magnitude. The difference between the signal input and the tachometer input becomes an error signal which is amplified in the amplifier designated Al gain. At the output of Al gain is a peak current control which limits the maximum output swing. This network has another function, that is, a shut-down capability by the RMS current limiter. The bandpass shaping components couple part of the peak current control output back to the first summing point. These components are usually necessary to accomplish a stable servo system.The above output is a command to the inner loop. The feedback to the inner loop summing point is from a motor current sense circuit which is sensing output current to a motor. Again, there is an error signal which is the difference between the command and feedback signal. This error signal is amplified in the A7 amplifier. Shaping components are included around this amplifier to accomplish a stable loop.The amplifier error signal from A7 goes to two comparator modulators having inputs from a triangle wave generator. If the Al output goes positive, one comparator modulator puts out wider and wider pulses at the frequency of the triangle wave generator. If the Al output goes negative, the other comparator modulator puts out wider and wider pulses. LLM and RLM input commands from external right or left limit switches are capable of inhibiting the modulators.One comparator modulator causes the motor to run in one direction. The other comparator modulator causes the motor to run in the second direction. Each comparator modulator goes to an AND gate and bridge driver circuit which, in turn, drives the output bridge. A polarity change box senses the action of each bridge driver and prevents turn on of the opposite bridge driver.The output bridge delivers rectangular voltage pulses to an external choke which, in turn, is connected to a motor. Because the choke has inductance, the current which flows to the motor increases while the voltage pulse is present and decreases while the voltage pulse is missing.The motor current sense circuit senses motor current through a very low value resistor. The fault current sensor measures current to the bridge from the power supply through another low value resistor. If excessive current is sensed, the fault current sensor shuts down the AND gates to turn off the bridge. Excess bus voltage or motor shorts can also trip the shut-down latch to turn off the gates.
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Westamp
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Product group
Servo Amplifier
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