CNC Sewing machine question

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15 Jan 2020 16:04 #154929 by jmelson
Replied by jmelson on topic CNC Sewing machine question

ahmetbm wrote: I designed the needle as an axis which made it easy to manage the sewing steps. However when it comes to moving backward or forward, it rotates the needle. So i am confused to change back the needle to spindle.

Yes, I think this is the wrong approach. You could configure the sewing machine as a "spindle", with a spindle on/off
and a speed setting. And, you'd need to come up with a way to "index" the sewing motor to the needle-up position.
So, when the program does M03, the sewing motor starts. When the program does M05, the motor slows to a lower
speed and then stops when a sensor detects needle up. Every M05 would be followed by a wait command (dwell G04 Pnnn) to allow for the needle to come to a stop. During sewing, the X-Y feedrates would be slow enough that the moves would be accomodated by material stretch. Only after the M05 and dwell would the X-Y axes move faster to move
to a new part of the embroidery pattern. I'm pretty sure a number of people have done this before.


Jon

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15 Jan 2020 16:34 #154931 by tommylight
Search for RugBot.

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15 Jan 2020 18:26 #154944 by Badger
Replied by Badger on topic CNC Sewing machine question
Is this part of the conversation about "sewing" a consistent stitch length such as making clothing, or a variable stitch length such as for embroidery?

The Rugbot needs consistent stitch length so I run the needle in velocity mode, without any gcode instructions, and it works flawlessly. This would not work for variable length embroidery type of stitches.
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16 Jan 2020 08:04 #154999 by ahmetbm
Replied by ahmetbm on topic CNC Sewing machine question
I have seen Rugbot, however my configuration has a difference. I have two motors(yaskawa) that run sewing machine's needle and hook seperately. With step control mode i was able to run the motors synchronously with no problem. When i faced going back problem, i searched and found two solution, one is to use spindle mode, other is to manage coordinates through linuxcnc. Since i am new on linuxcnc, i asked to yaskawa tech service, if it is possible to run two motors in velocity control mode synchronously. They did not give a clear yes, i think i will have to test it my self, if i can not find an easier way through linuxcnc.

Is this part of the conversation about "sewing" a consistent stitch length such as making clothing, or a variable stitch length such as for embroidery?

Stitch length is about 2.5mm and in some places between 1-2mm for tightening, it is not embroidery machine, it will sew only gloves.

I can lift up the needle part about 100mm, so it is not necessary to stop needle at the top position, but it would be better if i can. Because i don't waste time for the needle part to come to upper position.

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16 Jan 2020 10:32 #155009 by andypugh

ahmetbm wrote: Since i am new on linuxcnc, i asked to yaskawa tech service, if it is possible to run two motors in velocity control mode synchronously. They did not give a clear yes,


Yaskawa wouldn't know what LinuxCNC can do, but it is fairly easy to force one motor to move in synch with another (and to alter the phase between them). What you do is to use a PID module where the command is the phase difference between the motors and the feedback is the difference between the two encoder positions.

(For testing it will be fine to use the difference between the two floating-point position, but if long run-times are anticipated it might be better to scale the difference between the encoder counts. Encoder counts are stored internally as 64 bit numbers so will never overflow.
Floating point positions will, after a long time, start to be large, and subtracting one large number from another to return a difference close to zero will eventually become imprecise. This is because floating-point only has 52 bits of precision, but 52 bits is still a very long run-time for most machines.)
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16 Jan 2020 11:06 - 16 Jan 2020 11:06 #155013 by ahmetbm
Replied by ahmetbm on topic CNC Sewing machine question

andypugh wrote: (For testing it will be fine to use the difference between the two floating-point position, but if long run-times are anticipated it might be better to scale the difference between the encoder counts. Encoder counts are stored internally as 64 bit numbers so will never overflow.
Floating point positions will, after a long time, start to be large, and subtracting one large number from another to return a difference close to zero will eventually become imprecise. This is because floating-point only has 52 bits of precision, but 52 bits is still a very long run-time for most machines.)


I need about 10K revolution and then the proces will start over. Can this be considered as long run?

I am using general mechatronics pci 6 control card.
Last edit: 16 Jan 2020 11:06 by ahmetbm.

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16 Jan 2020 11:57 #155017 by andypugh

ahmetbm wrote: I need about 10K revolution and then the proces will start over. Can this be considered as long run?


Not really. (And I was wrong anyway)

What I said would make sense if the HAL version of the encoder counts was 64 bit, but it is 32 bit, so rolls over at about 2,000,000,000 counts. The floating-point position is 52 bits resolution, so starts to have 1-count position errors after 4,000,000,000,000,000 counts.

This really is only likely to be a practical problem with very fast spindles and very high encoder counts.

I am using general mechatronics pci 6 control card.

Can you attach a pin listing of all the General Mechatronics pins?

A command something like "halcmd show pin *gm* " should give a list that can be copied and pasted to a text file.
Then the same with "show param"

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16 Jan 2020 12:37 #155020 by ahmetbm
Replied by ahmetbm on topic CNC Sewing machine question

andypugh wrote: Can you attach a pin listing of all the General Mechatronics pins?


Here is parameters list. i will try to use one driver slave and other as master.

File Attachment:

File Name: hal_params.txt
File Size:14 KB
Attachments:

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16 Jan 2020 13:12 #155021 by andypugh
Do you need to be able to alter the relative phase?
If not, then a PID controller with feedback from the slave motor position, and command directly from the master motor encoder position will do what you want.

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16 Jan 2020 14:09 #155023 by ahmetbm
Replied by ahmetbm on topic CNC Sewing machine question
Master encoder will run in velocity control mode, and slave will run in step control mode, i am preparing test setup.

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