Linear encoders can do a lot to improve factory automation. When used as secondary feedback they can greatly enhance the precision of motion control systems. They can act as a feedback device for automatic size change, and they can be used in gauging applications.
However, they can be troublesome to maintain. Most linear encoders are made from a glass strip or rod that is etched with index marks and read optically. These kinds of encoders can achieve very high accuracy…with high price points to match. However, a consistent problem in many factory automation environments is the mechanical fragility of the glass scale encoder. They can be easily broken by shock, vibration, or impact. The presence of dirt and liquids can also interfere with proper operation. Repair costs can become a problem, not to mention the cost of carrying the spare parts needed to cope with long lead times for replacements.
Depending on the resolution and accuracy class required, one alternative to these issues is the magnetic linear encoder. Today’s magnetic encoders can achieve resolution to 1 μm and accuracy to ±5 μm. Rather than index marks on glass, the scale consists of magnetic poles precisely located on a ferromagnetic strip of tape. A magnetic read head glides over the tape and outputs digital position signals. The magnetic system is much more tolerant of shock and vibration, and can tolerate most kinds of liquids and dirt. The main caveat is ferrous particles or chips; these can accumulate on the magnetic strip and cause position deviations.
Most magnetic linear encoders offer incremental signals, but a new option is absolute position over an SSI or BiSS-C serial interface. This allows the encoder to report position upon power-up, without the need for a time-wasting homing or reference run. This can be helpful in situations like a power outage, where it may not be possible to re-home the machine without damaging work in process and/or breaking tooling.
To learn more visit www.balluff.us.
