Length measurement using rotary encoder
Length measurement using rotary encoder
(OP)
We have a sheet metal roll forming machine that performs various operations before finally shearing to length, the component length is required to vary, however the component length should be within +/- 0.5mm max. The drive is hydraulic and the encoder is driven by a wheel (rubberized) mounted on a common shaft with the encoder, contact between the wheel and metal is good. We have found that the steps/mm have to be changed regularly to keep the length within tolerance, the encoder has been changed and the system checked as much as possible.
Any suggestions?
Any suggestions?





RE: Length measurement using rotary encoder
A high speed or 'flying' shear requires a fixed relation between the shears inertial speed and that of the part speed.
RE: Length measurement using rotary encoder
RE: Length measurement using rotary encoder
Does it appear that the encoder is dropping steps? You might want to check data cables or reduce cable length if possible. Is the encoder experiencing a "reset" periodically (power loss or shut downs"?
Could the process be changed to utilize proximity sensors for establishing fixed positions instead?
Regards,
RE: Length measurement using rotary encoder
RE: Length measurement using rotary encoder
We have checked the encoder and the rest of the electronics associated and we found nothing wrong.
We tried with a new encoder and encoder module on the plc.
The encoder cable is the original with no extensions (under 800mm), properly shielded, far away from any power cables or any other source of electromagnetic noise, connected in differential mode.
There is no power loss or shut downs
We also tried a second stand alone plc with an encoder connected to the same encoder shaft running at the same time to compare the encoder values and they are almost identical.
It does go backward a fraction of mm every time stops to punch or shear but we can also see the encoder values decreasing, and when using the additional encoder we can see exactly the same encoder values.
Finally, unfortunately we can not use any other sensor for stabilising fixed positions because the distance between punches could be anything from 200mm up to 2500mm.
Regards
RE: Length measurement using rotary encoder
RE: Length measurement using rotary encoder
Thank you to every one for your suggestions.
Mike
RE: Length measurement using rotary encoder
Sounds like there could be a slight amount of slippage between the drive roll and the metal sheet. From the looks of it you have covered most if not all of any electrical issues.
Steve