Scaling of axis

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9 years 7 months ago #88802 by Nondepietjes
Scaling of axis was created by Nondepietjes
Hi,

I have a litle question about getting the right movement on my lathe.
When i'm asking to move my axis 1mm, the axis moves 3 to 6 times more than that.
My DRO say's i'm at 1 mm but when i'm measureing it, its not the case.

whatever i'm doing and trying, nothing helps. i'm out of options and i don't know what to do.
I'm working with 2 servo's belt driven and a 5i25 and 7i777 mesa card.
Please i nead some help

Thanks in advance

OUTPUT_MIN LIMIT = 30
OUTPUT_MAX_LIM = -30
OUTPUT_SCALE = 30

MAX_OUTPUT = 9V at 2000rpm

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9 years 7 months ago #88815 by Todd Zuercher
Replied by Todd Zuercher on topic Scaling of axis
I believe that you need to make changes to
ENCODER_SCALE = ???
to fix your scaling problem. (The output scale has nothing to do with it.)
But you should not need to be guessing this number. It should be easily calculated if you know your encoder counts/rev and screw pitch and any reduction (from belts or gears).

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9 years 7 months ago #88860 by Nondepietjes
Replied by Nondepietjes on topic Scaling of axis
Hi,

Thanks for the reply.
I know the count /rev, there is a reduction but i don't know the reduction because i can't see al the gears.
But when i'm pressing the buttons 1mm on the AXIS program, my DRO says 1mm but m machine move always more.
regardles of my encoder scale because if i change that only the number on the DRO changes and not my movement of the machine.

kind regard koen

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9 years 7 months ago #88861 by rodw
Replied by rodw on topic Scaling of axis
I had a similar problem recently because the rack and pinion has some non standard module size. I was not using an encoder though. What I did was lay a 1 metre steel rule beside the linear rail and measure the error over a gcode 1m long movement. Then I adjusted the steps per mm (or steps per inch) up or down by that percentage and try again. After a number of iterations of this I was pretty happy with the result so I then ran some Gcode that ran up and down the axis 20 times (20 metres) using relative coordinates. I set a dial indicator up at one end as shown here



It worked out well within the required accuracy..... as the video shows.

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9 years 7 months ago #88868 by Nondepietjes
Replied by Nondepietjes on topic Scaling of axis
hi,

I'm working with servo's. And i set my encoder scale on the right amount. But the porblem is for example when i ask the machine to move 8mm, it moves mutch more than that. so i reset my encoder but the position it moves still stays the same.

PS:i'm sorry for my english.

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9 years 7 months ago #88878 by Todd Zuercher
Replied by Todd Zuercher on topic Scaling of axis
Ok, lets start with the basics.
What is your encoder counts per revolution? Is that the line count or quadrature count?
What is your screw pitch (distance traveled/turn of the screw)?
Is the encoder mounted on the motor or on the screw?
What is the gear reduction (if any) between the motor and the screw? In other words how many times must the motor turn in order to turn the screw one full revolution?

Where were you "setting" the encoder scale?
If you post a copy of the ini file in your config directory, we can help point out where this needs changed.

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9 years 7 months ago #88890 by Nondepietjes
Replied by Nondepietjes on topic Scaling of axis
The encoder count per rev is 2500. The rotary encoder is a ROD426 A2500.
the encoder from the z-axis is mounted on the screw and the encoder from the y-axis is a lineair encoder.
All the other things are unknown because it's a second hand machine with an old stearing.
and the company that bought the machine has non of this information. Al the components are verry hard to reach or not visibal. I think as far i can see the pitch of the screw is 5 mm.

I will upload a copy af the ini. file tommorow.

it's a verry difficuld job

kind regards

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9 years 7 months ago #88892 by Todd Zuercher
Replied by Todd Zuercher on topic Scaling of axis
That would be a line count of 2500, so the quadrature count will be 10000/rev. for the rotary encoder.
If the Z has that encoder mounted directly on a 5mm pitch screw. Then the encoder scale for AXIS_2 (or JOINT_2 in Master) should be 2000 for a mm configured machine (or 50800 for inches)

If your Y axis is using a linear encoder then the encoder scale will just be equal to the quadrature count of your linear scale for 1 unit of measure (or the inverse of the resolution of the linear scale if you know what that is.) If you don't know the specs of the linear scale you will probably need to measure and calculate it. It will likely be a factor of 10 (or even 40) if you guess the base units corrrectly.

What about your X axis you didn't mention it?

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9 years 7 months ago #88917 by Nondepietjes
Replied by Nondepietjes on topic Scaling of axis
Hi,

I thought i mentiont it but it's a lathe. i'm sorry!! :)
My linear encoder is a LS 703 from heidenhein. 700mm long.
I'm using TDM 1 indramat drives and 9v is 2000 rpm

Here is alsow my INI.file.

Attachment not found

Attachment not found

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9 years 7 months ago #88928 by Todd Zuercher
Replied by Todd Zuercher on topic Scaling of axis
I don't know much of anything about those Linear scales, and a quick Google search isn't telling me anything. I have seen a lot of people talk about Heidenhein scales, saying that they output an analog sine-wave signal and they have to be used with some sort of conversion box that into an incremental encoder signal. But I have no idea if that is the case with that one, or what it's resolution is or would be after interpolation. (It mght be 20um plus another 5X or 10X from interpolation.) I would think some experimentation should easily tell.

The important bits are here in your ini file
Code:
#******************** # Axis X #******************** [AXIS_0] TYPE = LINEAR HOME = 0.0 FERROR = 150 MIN_FERROR = 150 MAX_VELOCITY = 33.33333333 MAX_ACCELERATION = 10 P = 10 I = 0 D = 0 FF0 = 0.0 FF1 = 0 FF2 = 0.0 BIAS = 0.0 DEADBAND = 0.0 MAX_OUTPUT = 8 ENCODER_SCALE = 5000 #Change this to match the linear scale resolution OUTPUT_SCALE = 0.6 OUTPUT_MIN_LIMIT = -9 OUTPUT_MAX_LIMIT = 10009 MIN_LIMIT = -500 MAX_LIMIT = 500 HOME_OFFSET = 0.000000 HOME_SEARCH_VEL = -1.000000 HOME_LATCH_VEL = -0.500000 HOME_FINAL_VEL = 0.000000 HOME_USE_INDEX = NO HOME_SEQUENCE = 0 HOME_IGNORE_LIMIT = NO #******************** # Axis Z #******************** [AXIS_2] TYPE = LINEAR HOME = 0.0 FERROR = 2 MIN_FERROR = 1.5 MAX_VELOCITY = 33.333333 MAX_ACCELERATION = 20 P = 5 I = 0.0 D = 0.0 FF0 = 0.0 FF1 = 0.01 FF2 = 0.0 BIAS = 0.0 DEADBAND = 0.00001 MAX_OUTPUT = 0 ENCODER_SCALE = 500 #Change this to 2000 OUTPUT_SCALE = 10 OUTPUT_MIN_LIMIT = -10 OUTPUT_MAX_LIMIT = 10 MIN_LIMIT = -1000.0 MAX_LIMIT = 1000 HOME_OFFSET = 0.000000 HOME_SEARCH_VEL = 1.000000 HOME_LATCH_VEL = 0.500000 HOME_FINAL_VEL = 0.000000 HOME_USE_INDEX = NO HOME_SEQUENCE = 1

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