Author Topic: Problem with index homing  (Read 12449 times)

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Offline jofriedl

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Problem with index homing
« on: August 31, 2015, 08:36:01 PM »
Almost done with the Matsuura MC500v retrofit and I'm running into an issue with index homing. When I attempt to reference all axis, the machine moves until it triggers each reference switch, but while its backing off the switch to find the index pulse sometimes  I get an error that reads "Index distance not within allowed limit'. I'm not sure what this is about. Using the CSMIO/IP-A plugin, Ive counted the index pulses per revolution (2k in the Z and 3K in the X and Y), so I know thats not it.  Even more perplexing is the fact that it doesn't always happen and it won't always happen on the same axis twice. Am I missing something? Thanks for any and all help.

Jonathon

 

Offline Hood

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Re: Problem with index homing
« Reply #1 on: September 02, 2015, 03:40:08 AM »
Try moving the switch slightly or moving the motor belt a tooth or two, just thinking it may be the Index is too close to the switch.

The only other things I can think of are the index pulse is not being seen correctly due to noise or maybe you have the wrong encoder count set in the plugin?
Hood

Offline jofriedl

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Re: Problem with index homing
« Reply #2 on: September 03, 2015, 12:02:46 AM »
Thanks for your response, Hood. I disconnected the servo from the ball screw and turned the servo 90 degrees. No change in whatsoever. I looked at the wiring and I really don't have anything that would cause too much noise. I do have 12V to5V optocouplers between the encoders and the IPA; maybe the single pulse is getting lost in the opto-coupling. But there are LEDs on the optocouplers that light up on the pulses. I can see the index pulse flash when I pass it.

As far as having the right number of pulses per revolution, I used the readout from the CSMIO plugin window that displayed the encoder pulses in realtime. I set the encoder at 0 and used the mpg to complete one rotation of the servo. At the end of one rotation the display read 3000 pules for the y axis (I'm assuming the X and Y are the same) and 2000 pulses for the Z axis. Due to different gearing in the Z axis, it comes out to the same number of pulses per inch on all axis. I've also played with the numbers and put pulses per revolution in the tens of thousands so if the index pulse was getting lost it the ipa would simply assume that it hadn't reached it yet.

My only thought it this. Does the index pulse have to come after the axis has moved off of the homing limit switch? What happens if the switch is triggered but the axis decelerates past the index pulse a time or two? Ive played with speed and it seems the issues happens independent of any speed.


Offline Hood

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Re: Problem with index homing
« Reply #3 on: September 03, 2015, 03:23:57 AM »
 I do not think it has anything to do with gearing or steps per unit, from memory it it is simply encoder pulses per rev.
Set the encoder setting in the plugin to whatever pulses per rev it is.
For example if your encoder is 2500 line encoder then the pulses per rev will be 10,000, if it is a 1024 line encoder then it will be 4096  i.e. line count of encoder x 4.

Hood

Offline jofriedl

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Re: Problem with index homing
« Reply #4 on: September 03, 2015, 09:34:49 AM »
O have no way to telling how many lines the encoder has. I've contacted Yaskawa and they don't have any information on the encoders. Can I simply use the method I described above using the CSMIO plugin to count the pulses or should I keep trying to chase down literature on these encoders?

Offline Hood

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Re: Problem with index homing
« Reply #5 on: September 03, 2015, 09:43:10 AM »
What type of motors? AC or DC, what  year, roughly, are they?
Hood

Offline jofriedl

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Re: Problem with index homing
« Reply #6 on: September 03, 2015, 11:46:35 AM »
They are brushed DC and the machine was made in 1979 if that helps.

Offline Hood

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Re: Problem with index homing
« Reply #7 on: September 03, 2015, 12:10:06 PM »
Quite likely they are 500 or  1024 line then, try 2000 or 4096 and see.
Hood

Offline jofriedl

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Re: Problem with index homing
« Reply #8 on: September 03, 2015, 12:36:44 PM »
the plugin test indicates that they are 2000 pulses per rev so I've got the plugin configured for 2000 lines, but I'll try 4096 when I get to the shop later. Thanks hood.  I don't know what CS labs would do without you:)

Offline Hood

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Re: Problem with index homing
« Reply #9 on: September 03, 2015, 02:15:07 PM »
Ah ok, I thought you had said 3000 and that struck me as a weird number for an encoder.
Hood