Why rotary encoders instead of scales?

Cost, for the most part. Durability is also an issue.

Wes, Cost would be my guess. In a typical application the builder or retro-fitter gets a motor along with an encoder or resolver as a package. Saves mounting and aligning scales.

Just a guess, but cost is what usually drives decisions like this.

Best, Steve

Cost--especially nowadays where oftentimes your rotary encoder is using mylar disc instead of glass.

Wes,

There are lots of reasons and cost is one of them. Maintaining them is more trouble too. The table must have no side to side movement or the head spacing can get out of spec.

Another thing is that I can get the gain MUCH higher with a nice tight motor / encoder combination. Just a little lost motion (with scales) will force me to lower the gain, accel, and decel. If you need the accuracy, scales are certainly necessary. On a large boring mill, they are almost a necessity due to expansion of the screw during the course of the day. On smaller machines, we can get acceptable accuracy with good screw/thrust bearing preload and bi directional laser comp.

Warren

Cost. Since even if machine has scales, it still needs encoder in motor. This is needed for drive electronics to know what is rotation angle of motor. Because different phases of motor have to be "fed" accordingly to rotation angle.

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