Need synchronization of X and Y axis by offset
- james higgs
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14 Mar 2012 19:17 #18604
by james higgs
Need synchronization of X and Y axis by offset was created by james higgs
I have a tape library XY assembly with two servo motors onboard (I am using two open-source Elm servo boards with step-dir input). The servos are both fixed to the base, meaning the x axis does not have a servo moving around with it, and therefore whenever the Y axis moves, the X axis also moves, because it is riding along a stationary belt. In other words, the X servo must compensate for any Y axis movement, approximately 1 step X for every 6 steps Y. I understand that software compensation is not a perfect solution for this, but I think EMC2 or LinuxCNC as it is now called should have a compensation feature somewhere, right?
How could I fix this problem with LinuxCNC?
How could I fix this problem with LinuxCNC?
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14 Mar 2012 20:22 #18605
by BigJohnT
Replied by BigJohnT on topic Re:Need synchronization of X and Y axis by offset
You might want to create a non-trivial kinematics for that machine like you would with robot arms and things that don't follow the simple XYZ movements.
linuxcnc.org/docview/2.5/html/motion/kinematics.html
John
linuxcnc.org/docview/2.5/html/motion/kinematics.html
John
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- james higgs
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14 Mar 2012 20:38 - 14 Mar 2012 20:39 #18606
by james higgs
Replied by james higgs on topic Re:Need synchronization of X and Y axis by offset
Are there any examples of something like this that come with LinuxCNC so they can be directly experimented with?
Last edit: 14 Mar 2012 20:39 by james higgs.
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15 Mar 2012 08:51 #18608
by Rick G
Replied by Rick G on topic Re:Need synchronization of X and Y axis by offset
It seems to me that something like this came up before on this forum, a machine was built with the x and y motors mounted to the frame and the carriage was moved by cables.
All moves required both motors to compensate for the other.
I believe the idea was to keep the mass of the carriage as light as possible for fast acceleration.
Unfortunately I cannot provide a link for that, perhaps someone will chime in with it.
But it may give you a starting point.
Rick G
All moves required both motors to compensate for the other.
I believe the idea was to keep the mass of the carriage as light as possible for fast acceleration.
Unfortunately I cannot provide a link for that, perhaps someone will chime in with it.
But it may give you a starting point.
Rick G
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15 Mar 2012 11:00 #18609
by BigJohnT
Replied by BigJohnT on topic Re:Need synchronization of X and Y axis by offset
There are a few sample configurations for scara and puma type of non trivial kinematics. Take a look at those and see if you can see how they work so you might modify one to suit your machine. It does sound like a very interensing machine do you have any photos of the machine?
John
John
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- james higgs
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15 Mar 2012 20:46 #18610
by james higgs
Replied by james higgs on topic Re:Need synchronization of X and Y axis by offset
Here are photos of the device, your forum is way too slow to upload anything.
s9.postimage.org/mfy3gtupb/image.jpg
s13.postimage.org/68l3kdznb/image.jpg
There is actually one left for sale,
hxxp://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380375049171&ssPageName=ADME:X:RTQ:US:1123
I am 90% sure they will take an offer of $80. They have been trying to sell it for a long time. It will probably be gone shortly with this posted here.
There are problems with the assembly. It cannot be used as a precision positioning device, the backlash is awful. I had to disassemble it and use PL polyurethane (find some PL premium at the Home Depot in the large 29oz size tubes) to form a more rigid connection between the acetal nuts and the carriages. Nothing really sticks to acetal but the polyurethane at least expands to fill in all gaps. Even so, the nuts have some pretty bad backlash. This is good for fast positioning but the the assembly is not rigid enough for anything most CNC people would be interested in. It is good only as an educational tool until the problems are ironed out.
In case anyone is interested, here is the pinout of the tiny servos on the device:
With the gear end of the motor facing up, the motor at the top and the connector below it,
1 3 5 7 9 11 13
. . . . . . .
. . . . . . .
2 4 6 8 10 12 14
1 Motor -
2 Motor -
3 Motor +
4 Motor -
5 Motor +
6 Motor +
7 Encoder -
8 N/C
9 Encoder -
10 Encoder +: 3.3V to 5V
11 Encoder -
12 Encoder Channel A quadrature output
13 Encoder -
14 Encoder Channel B quadrature output
s9.postimage.org/mfy3gtupb/image.jpg
s13.postimage.org/68l3kdznb/image.jpg
There is actually one left for sale,
hxxp://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380375049171&ssPageName=ADME:X:RTQ:US:1123
I am 90% sure they will take an offer of $80. They have been trying to sell it for a long time. It will probably be gone shortly with this posted here.
There are problems with the assembly. It cannot be used as a precision positioning device, the backlash is awful. I had to disassemble it and use PL polyurethane (find some PL premium at the Home Depot in the large 29oz size tubes) to form a more rigid connection between the acetal nuts and the carriages. Nothing really sticks to acetal but the polyurethane at least expands to fill in all gaps. Even so, the nuts have some pretty bad backlash. This is good for fast positioning but the the assembly is not rigid enough for anything most CNC people would be interested in. It is good only as an educational tool until the problems are ironed out.
In case anyone is interested, here is the pinout of the tiny servos on the device:
With the gear end of the motor facing up, the motor at the top and the connector below it,
1 3 5 7 9 11 13
. . . . . . .
. . . . . . .
2 4 6 8 10 12 14
1 Motor -
2 Motor -
3 Motor +
4 Motor -
5 Motor +
6 Motor +
7 Encoder -
8 N/C
9 Encoder -
10 Encoder +: 3.3V to 5V
11 Encoder -
12 Encoder Channel A quadrature output
13 Encoder -
14 Encoder Channel B quadrature output
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16 Mar 2012 03:12 #18611
by PCW
Replied by PCW on topic Re:Need synchronization of X and Y axis by offset
OT but the good news is that the forum slowness (its been bad for about 2 days) is fixed!
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16 Mar 2012 11:32 #18616
by BigJohnT
Replied by BigJohnT on topic Re:Need synchronization of X and Y axis by offset
So are you saying that when you turn the short axis motor (the one with the motor on the left in the second photo) that the long axis screw turns because of slop in the double reversing belt?
Interesting machine for sure, thanks for sharing the photo.
John
Interesting machine for sure, thanks for sharing the photo.
John
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