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Author Topic: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)  (Read 24930 times)

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Re: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)
« Reply #30 on: March 30, 2011, 07:42:51 AM »
So are my differential encoders truly 1000 count encoders, giving me 4000 pulses per revolution or 1000 pulses per rev encoders (really 250 count encoders x 4 quadrature). The wording on there website is slightly tricky...

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Re: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)
« Reply #31 on: March 30, 2011, 07:43:11 AM »
Could be both. I never really like using the steps per calculator in Mach as it will only ever be as accurate as you can measure. Using longer distances to measure over will reduce the error but you still need an accurate way to measure that distance. Gauge blocks are good and usually accurate. DTI's are usually accurate but are only measuring over small distances.
Hood

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Re: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)
« Reply #32 on: March 30, 2011, 07:45:31 AM »
I would say they are 250 line encoders giving 1000 PPR
This seems to be borne out by the Z Axis as that is the one we know all the facts about, ie no gearing and 0.1 pitch screw.
Encoders have always been a PITA as some quote the PPR some the line count etc.

Hood
Re: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)
« Reply #33 on: March 30, 2011, 07:47:35 AM »
According to the manual i have my multiplier set to 1x. If i turned it to 4x would that give me the right numbers?

I found this in my viper driver manual:
"-  4 X  o r  1 X  q u ad ra tu re   e nc o d e r  c o u ntin g"

"Encoder Line count is the number of lines per turn.  With-in the viper drive the line
count is decoded 4 times finer(quadrature), so with a 1000 line encoder, the viper drive
sees 4000 counts/turn.  This is not to increase machine resolution, but to give the drive
more counts to reduce error.
The Step Multiplier setting in the viper sets the ratio of incoming Step/direction pulses
from the control software to the 4X encoder counts.
 So with a 1000 line encoder and a step-multiplier of 4 you would have 1000 steps/turn.
With a step multiplier of 8 you would have 500 steps/turn.
 With a step multiplier of 1 you would have 4000 steps/turn, but don’t be fooled thinking
your machine will be more accurate. A servo system always runs with a error of at least
a few encoder counts. Also it would require a very high input step rate to make the
motor spin fast.
  We recommend a 1000 line differential encoder for most applications. Encoders with
less than 400 counts/turn should be avoided. The viper can handle up to 625Khz
encoder frequency (assuming good cableing )"
Re: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)
« Reply #34 on: March 30, 2011, 07:51:42 AM »
Also he recommended 1000 line encoders. "anything less than 400 counts per turn should be avoided!."

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Re: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)
« Reply #35 on: March 30, 2011, 07:56:01 AM »
1xI would imagine means no electronic gearing so that would mean if the steps per you have set are moving the correct distance then your encoders are 250 line count and thus 1000 pulses per rev needed from Mach for 1 rev of motor.
If you increased the drives gearing to 4x then that would mean only 250 pulses from Mach would be needed, but you dont want to do that as it reduces the resolution as each step sent by Mach would move the motor 4 encoder pulses.

The higher encoder count would be better for accuracy and resolution but really I wouldnt worry too much unless you are not getting the accuracy that you are requiring with the encoders you have.
Hood
Re: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)
« Reply #36 on: March 30, 2011, 08:04:34 AM »
I guess we need to figure out what they mean by "CPR" or counts per revolution. They only offer 64-2500 CPR wheels. I picked 1000 CPR because i read the viper manual and took his suggestion of 1000 lines per rev.
Re: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)
« Reply #37 on: March 30, 2011, 08:11:52 AM »
I figured 1000 lines per revolution = 1000CPR. I wonder if they automatically calculate quadrature into the "CPR" really giving me, as you suggested a 250 line wheel.

But then again they offer a 2500CPR wheel. If they did in fact count quadature in there "CPR" then it would really only be a 625 line encoder, which doesn't sound right since thats there biggest model.

Also there 64 count encoder would only really be a 16 line encoder on a 1" disk.

I will call them tomorrow and let you know what they say. Should be interesting now that im fully confused! haha

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Re: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)
« Reply #38 on: March 30, 2011, 08:12:14 AM »
CPR and PPR can mean the same, I have seen all sorts from different places and it can get quite confusing.
As I said your Z we know has no gearing and you know the pitch is 0.1inch
So to move 1 Inch you need to rotate the motor(and screw) 10 times.
As you have the Steps per in Mach at 10,000, and I presume when you command a move of 1 inch it moves 1 inch, then that means your encoders are 1000 pulses per rev or 250 line. The only other factor would be the drive, if you had it set to 4x that would divide the pulses required from Mach by 4 so that would mean your encoders are actually 1000 line 4000pulses per rev.

So double check the drive setting and make sure you dont have it set to 4x.
Hood
Re: Mach 3 Driver test. Results for 3 computers, which is best? (PICS)
« Reply #39 on: March 30, 2011, 08:23:37 AM »
Awesome i will let you know asap tomorrow. Thanks for helping me out, its 5am time for bed haha.