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Reg: circularity error

Created by: badhrisen at: 11/26/2009 5:00 AM (6 Replies)

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11/26/2009 5:00 AM	Rate (0)
badhrisen Posts: 3 Rating: (0)	Dear Friends, We are using 840D system in Horizontal boring machine to make a spicot step boring with circular interpolation. in this case we are facing in circularity error problem 0.4 mm. Action taken, we adjusted gain for the corresponding axis . and we checked the mechanical parameters also with in the tolerance. 1. If any possiblity to reduce circularity error with adjustment in electrical parameters. Regards Badhri sen.
badhrisen Posts: 3 Rating: (0)
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11/26/2009 9:40 AM	Rate (0)
Pee Ell Sea Posts: 672 Rating: (57)	Hi, Axis gain and hence axis following error must be identical for each axis. Following error can be viewed in the Diagnosis pages and checked at various speeds. If you have analog drives then it may require trimming with a tacho feedback pot. If all is correct then increase the position loop gain of all axes to reduce the following error and improve accuracy. This assumes that your machine is capable of responding mechanically. Check the bore and see if the errors occur on the circle quadrants which suggests backlash as the axis reverses.
Pee Ell Sea Posts: 672 Rating: (57)
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11/27/2009 1:34 PM	Rate (0)
OvidiuNastac Silver Member Joined: 1/29/2008 Last visit: 7/26/2022 Posts: 419 Rating: (19)	Hi There are many ways to improve the circularity error but the real issue is to detect the cause of the errors because could be various causes such: reversal spikes (at the turnover point the axis is stopped for a short time due to mechanical problem) , scaling error (pitch error of the ball screw), servo mismatch (unequal load of the axis or unequal servo gain) , squareness error of the pair axis, stick slip , straightness of the guideways, vibration, cyclic error (unequal wear of the ball screw), lateral play between guideway and closing plates, backlash. Ones of them can be reduced by adjusting some of the machine data or by introducing some functions that 840D have it (friction compensation). If you have a Ballbar kit (see the attachment) or if you have Advanced HMI you can trace the circle. Only than you can decide if or where you must change something or to repair something (if it's a mechanical problem). You can try to increase servo gain for both axis involved in the interpolation movement and use FFWON function in the part program and/or reduce the feed. Good luck Nit Attachment New Picture.gif (265 Downloads)

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11/30/2009 10:50 AM	Rate (0)
badhrisen Posts: 3 Rating: (0)	Dear Friends, Thank you for your reply. i will try and do necessary points in your suggestion on machine.
badhrisen Posts: 3 Rating: (0)
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12/3/2009 10:49 AM	Rate (0)
Keyan Posts: 13 Rating: (0)	Hi, Nit is correct, we are also facing the same problem. we tried to bore 2000mm bore by circular interpolation by HMC. but we got 0.3mm circularity error. if your machine is not having the scale, and running with motor encoder, servo loop is only between your Encoder and NCK. but what about physical movement?. so if you tune your servo you can not expect the great result.so you have to consern with your mechanical system. you have also think about your acclearation and deceleration of your moving masses during your circular interpolation . i want to know your transmission system for X-axis ( Rack or Ball screw). Regards, keyan
Keyan Posts: 13 Rating: (0)
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12/3/2009 10:53 AM	Rate (0)
CraigSimpson Posts: 159 Rating: (1)	I can't see any spec of linear measurement; are you using heidenhain scales or just simply rotary encoder feedback?
CraigSimpson Posts: 159 Rating: (1)
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9/10/2010 8:15 PM	Rate (0)
CraigSimpson Posts: 159 Rating: (1)	You can force the machine to compensate for any mechanical misalignment using the CEC tables (sag and angularity errors) if required. Within reason obviously!!
CraigSimpson Posts: 159 Rating: (1)
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