A motion controller is similar to a PLC in that certain inputs trigger outputs that cause a desired movement or motion on a machine. With a motion controller, the inputs are typically electronic signals or pulses generated by encoders within servo motors. (An encoder is attached to the shaft of a motor that transmits signals that represent the shaft position back to the motion controller.) Precision timing is the key reason that Goetze's moved to digital motion control. The motors that power the feeding/collating system's conveyors and collating belts, timed one against another in a delicate balance, all follow the lead of the main drive on the wrapper, thanks to an encoder placed on the shaft of that motor. Indeed, the difference between digital and analog controls is one of precision. With an analog system, a motion controller sends a low-level voltage signal to the drive. As the voltage of the signal increases or decreases, so does the speed of the motor. The drawback: The controller must rely on analog conversion circuitry in the drive--which itself must be "tuned" or adjusted by the drive manufacturer--to accurately translate the signal into the desired speed. That means, for example, that a motion controller sending a 2.873-volt signal might be translated by the drive as 198 rpm, or maybe 201 rpm, depending on how that particular drive has been adjusted. With a digital motion control system, the motion controller literally instructs the drive--via instructions, speeds and other parameters represented as a code of 1's and 0's--to spin the motor at exactly 200 rpm.
Collating candy at 3,000/min (sidebar)
How digital motion control works
Feb 28, 1999
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