Re: [CAD_CAM_EDM_DRO] older encoders safe to use?

scyvt wrote:

> My first look at a BEI encoder circa 1997 surprised me with the amount of circuitry inside it -
> quite unlike the US Digital ones that I had been looking at up to this point, which contain
> little more than the disc and the led/phototransistor module. This makes me wonder what
> the expected service life for used industrial encoders might be, and if they can be relied
> upon. It seems likely that many of the rotary encoders on ebay are around that vintage, or
> quite possibly older.
>
> Encoder failure could create quite a bit of havoc, no? Can anyone comment on their
> experience with older used encoders - good or bad?

I am using 3 Sumtak encoders that say they were made in 1987, so
they are 20 years old. I'm sure they were in some piece of gear
before I got them in 1996 or so. They've been in my shop
Bridgeport conversion since then, without any trouble. These
industrial-grade encoders cost $300 and up, and they use very
conservative design practices, the same as your BEI units. US
Digital encoders are not made to the same standards, but
probably other than dirt getting in them, they are quite
reliable, too.

Most simple servo systems do have a problem with loss of encoder
feedback, and will run away. In the bad old days when encoders
had incandescent light bulbs in them, CNC controls had elaborate
schemes to detect failure of the bulb. For instance, the
Allen-Bradley 7320 used differential encoders that went into
shutdown when the bulb failed, and the signals were no longer
complementary. If the control sensed a violation of the
complementary nature of the A, B or Z signals from the encoder
that lasted more than one microsecond, the control went to
Estop. If the velocity tachometer for the servo amp showed a
velocity that was 20% greater than the velocity shown by the
encoder, it also went to E-stop. I don't know of too many
systems that go to these lengths today.

Jon