Losing steps with servos and Mach 3

[tjs88yj]

I am having trouble with my mill, it seems that I am losing steps. The mill is set up as follows...

1986 Hurco SM1 Stock ElectroCraft Servos and encoders, Larkin Viper 200 drives, Smoothstepper, CNC4PC C23 BOB, Dura Pulse GS3 VFD, Mach 3

I am using an indicator mounted in the spindle, I zero out the indicator on a bar clamped to the table parallel to the Y axis, making sure to remove any possible backlash. I then make a G1 move in the X axis of -2.953" (75mm) and then insert a 75mm Jo block. With the feed rate set to 4 IPM the indicator reads .000. I then remove the backlash and rezero my indicator on the Jo block, remove the block and make a g1 move in the X axis back to 0. The indicator will read -.0015. I did this 3 time at this feed rate and had the same results. When I increase the feed rate to 6 IPM, I get an indicator reading of .001 on th first negative X axis move, but it is off -.035" on the move back to 0. If I increase the feedrate to 10 IPM I get .006" on the negative move and .067" on the move back to 0. If I do a G0 move it is off almost .185" on the move back to 0.

I've do some limited testing in the Y and Z axis and don't seem to have any issue, the indicator reads within .0005" both directions.

Any idea what might be happening?

Thanks

Tom

[Runner4404spd]

i had a similar problem but i was running geckos. what i found was that the servo drive would fault, but not enough to trigger the fault light and then, mach kept going so my tool ended up out of position. mine was more intermittent than yours and it really drove me nuts. i finally broke down and had to retune the drives and make sure all the axes had way oil on them with a one shot oiler.

[sandefuj]

Hi tjs88yj:
I have a very similar setup to yours, same motors and the viper 200’s different BB though. If you want to see how many steps of error your move from X=75mm to X=0 is, use the e command from hyper terminal. As the axis’s is moving press the e key over and over and you will see the error’s in HEX, then convert to decimal. If you are using a step multiplier of 4 then divide your converted decimal values by 4 to get the actual steps of error. On the Viper does the yellow LED ever blink during the move? The yellow LED tells you that you are losing position (steps) greater than your R value assigned for the drive. Also something to check is in Mach3 under motor tuning for the bad axis’s to make sure you have your Steps Per correct; when you try and move one inch do you get one inch of travel? After you get things working, make sure you setup the f (feed forward), it’s really cool, you can dial in your drive to almost no error as you move your table around.
Jay

[tjs88yj]

Hi tjs88yj:
I have a very similar setup to yours, same motors and the viper 200’s different BB though. If you want to see how many steps of error your move from X=75mm to X=0 is, use the e command from hyper terminal. As the axis’s is moving press the e key over and over and you will see the error’s in HEX, then convert to decimal. I tried this and whenever I entered the 'e' key it returned all 0's. If you are using a step multiplier of 4 then divide your converted decimal values by 4 to get the actual steps of error. I am not using a step multiplier. Should I be? If so how large of a multiplier? On the Viper does the yellow LED ever blink during the move?No just stays solid yellow. The yellow LED tells you that you are losing position (steps) greater than your R value assigned for the drive. I have the R value set at 150 is this too large? Also something to check is in Mach3 under motor tuning for the bad axis’s to make sure you have your Steps Per correct; when you try and move one inch do you get one inch of travel? Yes, as long as I have the feed rate set below 4 IPM. After you get things working, make sure you setup the f (feed forward), it’s really cool, you can dial in your drive to almost no error as you move your table around.
Jay

Tom

[sandefuj]

Yes, I think you do need a step multiplier.
This is what the Viper manual says about step multiplier:

“The Step Multiplier setting in the viper sets the ratio of incoming Step/direction pulses
from the control software to the 4X encoder counts.
So with a 1000 line encoder and a step-multiplier of 4 you would have 1000 steps/turn.
With a step multiplier of 8 you would have 500 steps/turn.

With a step multiplier of 1 you would have 4000 steps/turn, but don’t be fooled thinking
your machine will be more accurate. A servo system always runs with a error of at least
a few encoder counts. Also it would require a very high input step rate to make the
motor spin fast.”

So you have to put a jumper on whatever bank you are tuning to set the step multiplier, I used 4.

The LED should not be solid yellow, which is the Current Warn indicator, meaning your motor is in a continuous over current state, can’t be good.
Your R value is set at the default, what encoder count are you using? The higher the encoder count the higher the R sort of.

I’m no expert on this stuff, but I have gone through some of the same problems you are having, and with Larkin’s support, got it all sorted out. So you might want to email Larkin support, they have always helped me.

Jay