Phidgets Forums

Hi

I have HKT22 optical encoder (3531_0) attached to stepper 3331 which is driving a leadscrew. I am trying to do a reliability test by stepping e.g. 60,000 steps in one direction and then another to test repeatability of positioning.

The positioning repeatability/accuracy as measured by a Vernier is less than 0.1mm (great!). But, when I read the encoder Position value before moving and after stopping the motor I get large error. For example, I get up to 1,000 pulses error on a 60,000 steps move which in my case equates to approximately 8mm error. Note, this error actually does not exist - Vernier shows less than 0.1mm error, this 'error' is just reported by the encoder. I was hoping to use the encoder for closed loop control but with such a large discrepancy between reality and what the encoder reports it appears to be useless for it's purpose.

I have run my software in debug mode so to make sure I know when the encoder readout is taken and that the motors are stationary and the encoder really returns values that are not correct. I also introduced a pause in between moving and reading the encoder for when I am not in the debug mode. The encoder is firmly attached to the shaft too so the disc is not slipping and there is no dust etc on it either.

Is this normal, am I missing something??

I figured out what it was, so I have question on guarantees and also posting for posterity in case it's useful for someone else.

After much checking, testing, and swaping components out - it appears two things have happened:

1. The optical disc is not working well, when I replaced with another disc it started working as expected.

2. The bad disc was also getting easily undone from the shaft (e.g. after 10 moves). I didn't spot that previously but have managed to do a run of 10 moves without disc getting loose so to confirm the disc was at fault.

When optical disc is broken, is that covered by the warranty, should I ask the local distributor to replace the faulty HKT22?

If the encoder disk was not working properly or broke within a year of purchase, it is eligible for warranty replacement. If you bought it from a distributor, you should get the replacement from them and they will ask us to reimburse their stock on their next order.