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Unread January 29th, 2013, 11:08 AM   #1
TimothyMoulder
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Encoder Output Scaling

Hi all!

I'm looking to check my math on some calculations, and I'd appreciate any feedback:

I've got a Yaskawa sigma-5 servo setup. I've connected the encoder output from the drive to a Trio 405 motion controller.

The motor is connected by a 15:1 gearbox to a 10mm pitch ball screw. I am scaling to inches, so I'd like to get 25400 pulses at the Trio per inch of mechanical travel.

The Yaskawa drive allows you to assign a number of output pulses per motor revolution. So here are my calculations:

One inch of travel on the screw is 2.54 revolutions. With the gearbox, that means 38.1 revolutions on the motor shaft per inch of travel.

Pn212 in the Sigma5 drive is the number of output pulses per revolution of the motor. I calculate this as:

25400 / 38.1 = 666.66667 pulses per revolution to achieve scaling of 25400 pulses per inch.

Question 1 is my math right?

Question 2 = can anyone recommend how should I handle a repeating number like this? Round up or round down?

Question 3 should I instead go to 667 pulses and change my Trio parameter to 25412?

Or should I be looking at a different approach?

Thanks,

TM
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Unread January 29th, 2013, 05:45 PM   #2
Eric Nelson
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Been a while since I played with a Trio, but if memory serves, you can just use an equation as the UNITS value in the Trio.

Suppose you set the drive to output 'n' pulses per revolution... You know that 1" of travel is exactly 38.1 revolutions, so 38.1 x 'n' = pulses per inch

In the Trio, just enter the equation:

UNITS=38.1*n/1

Then you should be able to enter distances directly as inches in the Trio program. A value of 1.375" should move exactly 1-3/8".



-Eric
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Unread January 31st, 2013, 09:47 AM   #3
TimothyMoulder
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Thanks Eric, got it worked out.

In case anybody else looks at this - I forgot the quadrature Luckily, I caught it before downloading.

TM
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