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circularity test 840D

Created by: owenfred at: 9/3/2013 9:14 PM (8 Replies)

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9/3/2013 9:14 PM	Rate (0)
owenfred Posts: 30 Rating: (1)	We have replaced the ball screw and linear guideways on x and z axis. The machine is a 5 axis mill with glass scales and rotary encoders. We are having some troubles tuning the machine with the new X axis parts. Z seems to be just fine. X has the same rough motion it did before we replaced the parts. Sounds and feels tlike a bearing that has bumps in it on the ball screw, but it is brand new. I have attached a 2 circularity test from the machine: Test1 is the test with G3 direction at 4.8 on the pos_ctrl_gain for X and Y axis TestG2 is the test with G3 direction at 3.0 on the pos_ctrl_gain for X and Y axis Can anyone offer some input as to what can be done to reduce the error or what the tuning/noise issue could be? Thanks Attachment TEST1.jpg (546 Downloads)
owenfred Posts: 30 Rating: (1)
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9/3/2013 9:14 PM	Rate (0)
owenfred Posts: 30 Rating: (1)	testg2 Attachment TESTG2.jpg (330 Downloads)
owenfred Posts: 30 Rating: (1)
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9/3/2013 10:23 PM	Rate (0)
owenfred Posts: 30 Rating: (1)	Here is a plot with X pos control gain at 10 and Y pos control gain at 5 and a G2 30mm radius at 1500 mm/min. Attachment X10Y5G2T.jpg (342 Downloads)
owenfred Posts: 30 Rating: (1)
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9/4/2013 11:01 AM	Rate (0)
OvidiuNastac Silver Member Joined: 1/29/2008 Last visit: 7/26/2022 Posts: 419 Rating: (19)	Hi It is not very clear from your posting if you have done the crcularity test both with G2 and G3. I assume that the first test is with G3 and the second one is with G2.From the crcularity error from what I see in your pictures, it seems that you must reduce the X axis gain a litle bit. I know that ussualy the gain must be the same but in reality it depends on the mechanics of the machine. If you didn't done the test both with G2 and G3 I sugest you to do them and if you see that the elipse is inclined in oposite directions than you must reduce the gain on one of the axis. If the elipse is inclined in the same direction than you have a perpendiculatity error between the axis. As about the noise, try to increase the gain until the axis becomes instable and than reduce the gain at about 70% of the previous value. Good luck Nin

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9/4/2013 5:29 PM	Rate (0)
James N. Posts: 8 Rating: (0)	I am working with Owen on this machine. The circle test has been run in g2 and g3, and the elipse does indeed reverse direction of incline between the two. I tried lowering the position control gain of the x axis, resulting in more of a peanut shape than an elipse and it is deviating over 200 microns from a nominal circle. If I increase the position control gain of the X axis, the elipse becomes more and more circular however the axis becomes unstable before the machine can trace a circle within a +- 100 micron range. At one point I had the gain so high it made a circle that deviated only +-25 microns, but when that X axis went unstable it made such a loud violent noise that people were coming over to see if the machine crashed!
James N. Posts: 8 Rating: (0)
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9/4/2013 9:53 PM	Rate (0)
pierre_g Posts: 67 Rating: (5)	Hello, Set gain correctly for each axis and after that to obtain a good circularity test you can enable MD32900 $MA_DYN_MATCH_ENABLE on all axis and set a value in MD32910 $MA_DYN_MATCH_TIME. Ex: $MA_POSCTRL_GAIN[0,AX1]=6 $MA_DYN_MATCH_ENABLE[AX1]=1 $MA_POSCTRL_GAIN[0,AX2]=6.72 $MA_DYN_MATCH_ENABLE[AX1]=1 $MA_DYN_MATCH_TIME0,AX2]=0.00065 Do reset each time you change value in MD32910. Look in manual extended functions K3. Pierre
pierre_g Posts: 67 Rating: (5)
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9/5/2013 8:28 AM	Rate (0)
OvidiuNastac Silver Member Joined: 1/29/2008 Last visit: 7/26/2022 Posts: 419 Rating: (19)	Hi Instead of increasing the X axis gain, which lead to vibrations, try to decrease the Y axis gain until you obtain a good circularity value. You must first establish the less stable of the two axis by increasing the gain until the machine becomes instable. Write down the values and then reduce the gain at about 70% of the value. After that you must compare the gain and put the minimum value for both axis and perfom circularity test with G2 and G3. After that you must perform also the circularity tests in all other planes in which the gain is diferent or you can proceed with the sugestion from Pierre. Good luck Nit
	Last edited by: OvidiuNastac at: 9/5/2013 8:35 AM
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9/5/2013 5:21 PM	Rate (0)
owenfred Posts: 30 Rating: (1)	As it turns out... Problem #1: changing speed_cntrl_integrator_time to 500ms doesn't get rid of the effects of the speed control gain. Therefore when I adjusted the pos_cntrl_gain to have a steep slope to position without overshoot it was set way to high... 4.8 or so. Problem #2 when I use the automatic configuration the speed ctrl gain and integrator time are also set way to aggressive... I.E. speed ctrl gain =12 integrator time=25ms The answer was to adjust the values manually to achieve a mildly agressive tuning curve. 1) integrator time to 500ms and speed ctrl gain as low as it would go without alarming out the setpoint step test. 2) adjust pos_cntrl_gain to achieve a steep ramp, no overshoot, no oscillation, and responable "feel" from the mechanical system around 1.9 or 2.2 or so. 3) Adjust speed ctrl gain up to 5 or so and adjust the integrator time to approximately effect the response curve just after the mild over shoot. around 60 to 85ms. 4) Adjust the speed ctrl gain up/down in tandem with integrator time to achieve the shortest settling time with minimal overshoot. The circularity test now shows .016mm circularity. Much better than the .2mm we had before.
owenfred Posts: 30 Rating: (1)
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9/5/2013 7:37 PM	Rate (0)
owenfred Posts: 30 Rating: (1)	Oh by the way. Here is the updated circularity test after adjusting the friction time constant. Owen Attachment CIRC.jpg (490 Downloads)
owenfred Posts: 30 Rating: (1)
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This contribution was helpful to 1 thankful Users rmb_cardoso

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