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Encoders

How encoders can be used to assist in the labeling system use.

“Square wave” pulses are produced from encoders placed on the motor shaft. This is why encoders are also known as pulse generators. With a PLC, the pulses generated by an encoder can do more than control the motor it is mounted to, but they can also control other motor speeds, as well as give input to counters (used instead of timers). They can even provide a base line for stepper motors if the pulse train rate is high enough. Accurate labeling requires high resolution and counting speeds, which can not be met by all encoders or PLCs. There is a big variation in the amount of pulses per revolution provided by encoders, with some delivering as many as 360 and some delivering as little as 6.

Here is an example of a labeling system using an encoder. You have a gear motor that has 1800 rpm as its top speed of operation and a top output speed of 30 rpm; this is accomplished with a conveyer driven by a 6” pulley. In one minute the conveyer could travel 565 inches and deliver 10,800 pulses (assuming you were using a model that delivered 6 pulses per revolution). While that may sound good, further inspection would reveal that if you have +/- one pulse accuracy your label accuracy could be off by almost 1/8 inch in this minute alone.

What is the answer to this dilemma? High Frequency Response Encoders.

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