Market: Machine Tool industry - Lathe
Product: DGS20

A company in the machine tool industry came to us with a need for an encoder on a new lathe project. The encoder would be used to keep track of speed and position of the tool head. Initial requirements included: a rugged package with a mil spec. connector; heavy duty bearings capable of 20# radial loads; environmental protection to IP65 (to protect the unit form cutting oil, metal chips and other common factory contaminants); 1024 PPR; flange mounting; and a 5 volt differential line driver output (dictated by the control they selected).

The DGS20 was chosen as the best solution. The DGS20 is designed to meet an IP65 rating when the optional shaft seal is selected. The DGS20 has an aluminum sleeve with bearings capable of 35# radial and 40# axial loading which was adequate for this application. The standard, rugged aluminum cover with a side exit 10 pin connector was chosen to provide the rugged package they desired. The initial model selected was a standard catalog item; DGS20 DM-1024-5LD-F10S-1A.

In this application the encoder shaft was designed to be driven via a belt and pulley. This method of driving the encoder shaft is what created the high radial loading specification. During evaluation testing it was determined that the encoder shaft would have to be lengthened in order for the pulley to seat properly without cocking to one side. This change would also eliminate any possibility of the shaft seal and bearing pilot interfering with the pulley - especially in cases where the pulley might be assembled too far onto the shaft. Since the pulley specified was to be attached to the encoder shaft by two set screws 90? apart, the customer felt that they wouldn't need a flat on the shaft. However, the customer was made aware of the fact that the additional shaft length, would in effect increase the moment arm of the load on the encoder shaft. The end result would be higher shaft loading on the encoder bearings. This tradeoff was discussed and found acceptable.

The solution to this problem was to increase the shaft length of the standard model they had specified from 0.80 to 1.25 inches. This modification allowed the pulley to be fully seated on the shaft with extra room between the pulley and the bearing pilot.