Dumb question

I have an Incemental Linear encoder that has a resolution of 2 microns. I have a 1756-HSC card that will read the pulses. I know 3175 counts = 1 inch. I also know 25400 microns = 1 inch or .0000394 inches in a micron. But how do I know how many 1 count equals in the HSC.

The machine need to measure and control a gap between 2 rolls. Thanks for your help

DBLD99 said:

I have an Incemental Linear encoder that has a resolution of 2 microns. I have a 1756-HSC card that will read the pulses. I know 3175 counts = 1 inch. I also know 25400 microns = 1 inch or .0000394 inches in a micron. But how do I know how many 1 count equals in the HSC.

The machine need to measure and control a gap between 2 rolls. Thanks for your help

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25400 Microns divided by 3175 counts = 8 microns per count.

You will have to scale the HSC count register. You can use a CPT instruction to do this. It's just cross multiplication to find X

3175 CPI = 25400 MPI

25400M / 3175C = 8M per Count

It looks you have a quadrature encoder with a base rate of 3175 pulses per inch on both channel A and channel B. When the high speed counter is configured for quadrature, it changes by one count for each of four events: Channel A going high, Channel B going high, Channel A going low, Channel B going low. So you have 12700 events per inch of travel which is the same as saying that each event represents 2 microns of travel since the previous event.

The accumulated value in the HSC represents distance in steps of 2 microns. An accumulated value of 123456 represents 246912 microns or 9.7209449 inches. To convert the accumulated count to inches, divide it by 12700, which is the number of 2-micron units per inch.

Steve,

Is it possible to set the read factor to X1, X2, or X4? If so, wouldn't the counts also reflect the different resolutions?

Bryan

sorry, Yeah I knew it was 8microns, for 1 count. But if the customer wants to move these rolls within 2 microns it cant be done then, Because the HSC wont give me that resolution.

Bryan,

You're right, I'm sure you can set up the HSC for X1, X2, or X4 although I'm not up to speed on the details of exactly how to do it. You have to write the correct data to the M file.

My comment was intended to resolve the apparent conflict between these two statements in the original post.

resolution of 2 microns

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and

3175 counts = 1 inch

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DBLD99,

You stared that the customer wants to have 2 micron resolution. If you follow Steve's 1st post, by utilizing 4X resolution on the HSC, it looks like you can attain 2 micron increments in the count register.

Bryan

right, thanks guys

DBLD99,

You're right. You can't position the rolls to within 2 microns. Even if you could reliably position to within +/- 1 count, that's still a 4 micron range. And that's assuming no other sources of error (backlash, torsional windup, encoder alignment, etc). Remember also that the HSC only reports its data to the PLC once per scan. If the PLC is involved in controlling the actuator that's positioning the rolls, you have to factor in the difference between the PLC's value and the HSC's value.

To get better positioning accuracy, you're going to need better encoder resolution. Then you have to make sure that the HSC will be able to count the higher resolution pulses at the speeds you need to run the positioning system. If not, you'll need to move to a dedicated motion controller.

DBLD99 said:

sorry, Yeah I knew it was 8microns, for 1 count. But if the customer wants to move these rolls within 2 microns it cant be done then, Because the HSC wont give me that resolution.

Click to expand...

You must be using hydraulics, in which case to get this accuracy you need a hydraulic servo controller and associated linear transducer such as a Temposonic with a USS interface. A PLC isn't up to this sort of control without a servo controller card.

Is this a plastics or rubber application?

None of them. We actually just ordered a MO8SE card and some Kinetex servos. There is 4 rolls and customer wants to control the gap between the rolls and is running some paper through it and coating it with something. Thanks for all your help