How to setup gearbox/reducer

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15 Aug 2024 10:45 #307791 by DPFlex
Hello,
I have AC servo motor which has harmonic gearbox with ratio is 80:1
How can I setup LCNC to work correctly with the gearbox ratio ?.
Thank you.

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15 Aug 2024 19:55 #307835 by Todd Zuercher
Depending on if your a controling your servo closed loop or open loop in Linuxcnc. You have to calculate the encoder counts or steps per unit of measure that you wish to use with this joint. The units could be inches, mm or other if the joint is linear, or if the joint is rotary the units would be degrees, radians, revolutions, or other.

If for example this joint is for a rotary C-axis in degrees and your servo motor is closing the loop to Linuxcnc with a 2000 line encoder directly coupled to the motor and the motor is directly connected to your 80:1 gearbox. You would use 2000(4)*80/360=1777.777778 counts/degree. So in your ini file you'd put ENCODER_SCALE = 1777.777778
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16 Aug 2024 00:46 #307856 by tommylight
You did not give us enough info to be able to help:
-what is the motor driving
-how is that motor coupled to the machine
-how much does the machine move for one turn of the reduction
etc.
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16 Aug 2024 07:16 #307889 by DPFlex
Replied by DPFlex on topic How to setup gearbox/reducer
Hi Tommylight,
My system is:
- Drive: AC Servo EtherCAT drive
- Motor is installed in SCARA robot
- The encoder: 17 bit optical absolute multi-turn. Its resolution is 131072, so I understand it has 131072 counts for one turn.
- The mechanical gearbox ratio is 80:1, fixed with motor.
Hope it is all you need :) Thank you.

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16 Aug 2024 07:27 #307890 by DPFlex
Replied by DPFlex on topic How to setup gearbox/reducer
Hello Todd,
I understand that you make example of "incremental encoder" with quadrature.
My encoder is 17 bit absolute multi-turn type, so the counts for one turn is huge value 131072.
I calculate: 131072*80/360 = 29127.111111. Is it still correct to apply ?.

I put ENCODER_SCALE = 29127.111111 to INI file, but nothing happen.
I understand need to revise HAL file to use ENCODER_SCALE, but it seem encoder component is only suitable to incremental encoder type.
linuxcnc.org/docs/devel/html/man/man9/encoder.9.html

Please advise :) Thank you.

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16 Aug 2024 08:59 #307895 by Aciera
Replied by Aciera on topic How to setup gearbox/reducer
Looking at my notes on my Melfa robot config using absolute encoders it seems that the value in [Joint_n] SCALE is
360/gearbox_ratio
So for my 80:1 geared J0 I have SCALE = -4.5
for my 120:1 J1 I have SCALE = -3

And so on.

I'm not sure how I came up with that idea but it certainly works for me.
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16 Aug 2024 13:49 #307917 by DPFlex
Replied by DPFlex on topic How to setup gearbox/reducer
Hello Aciera,
Can you share your note here ?.
I searched in DH-parameters for Genserkins and Vismach/Melfa-sim, could not find your note or anything mentioned about absolute encoder :)
Thank you.

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16 Aug 2024 14:08 - 16 Aug 2024 14:26 #307919 by Aciera
Replied by Aciera on topic How to setup gearbox/reducer
Actually, looking at this more closely, it's probably specific to dmitrys Mechatrolink hardware as 'nyx' refers to his hardware driver:
setp nyx.0.servo-00.pos-scale [JOINT_0]SCALE

Looks like you have an EtherCAT setup so my input is not really relevant after all.

[edit]
I would expect that you need set the gear ratio in the motor drives.
Last edit: 16 Aug 2024 14:26 by Aciera.

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19 Aug 2024 09:46 #308125 by DPFlex
Replied by DPFlex on topic How to setup gearbox/reducer
Hello Aciera,
I have no "nyx" hardware to test, so I chose other option.
I revise "pos-scale" of cia402: "gear ratio" * "encoder counts" / 360 degree
 setp cia402.0.pos-scale 29127.111111
It runs well this moment.

Have you tried
<modParam name="encoderResolution" value="xxx" />
in EtherCAT option ?.
I think it is better solution. My drive does not support, so I could not try. Please share your experience.
Thank you.

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19 Aug 2024 14:52 #308141 by Todd Zuercher

Hello Todd,
I understand that you make example of "incremental encoder" with quadrature.
My encoder is 17 bit absolute multi-turn type, so the counts for one turn is huge value 131072.
I calculate: 131072*80/360 = 29127.111111. Is it still correct to apply ?.

I put ENCODER_SCALE = 29127.111111 to INI file, but nothing happen.
I understand need to revise HAL file to use ENCODER_SCALE, but it seem encoder component is only suitable to incremental encoder type.
linuxcnc.org/docs/devel/html/man/man9/encoder.9.html

Please advise :) Thank you.
 


This is a little bit of late reply, the encoder component documentation you referenced is a software encoder counting component applicable for reading an encoder via gpio such as through a parallel port. This would not be applicable to your situation with Ether CAT. But it sounds like you are on the right track now.
(I have no experience with Ether CAT.)
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