path-following axis out of control with kerf on

[lukewang]

Hi,

 

I am running this NC proggram with a kerf:

ABS

CCR(1)

CC1

Linear X-172.646 Y-505.895 C-200

Linear C30 (path following axis C runs away here)

Linear X0 Y-400 C30

CC4

 

if I turn off kerf now:

ABS

CCR(0)

CC1

Linear X-172.646 Y-505.895 C-200

Linear C30 (path following axis C is fine here)

Linear X0 Y-400 C30

CC4

 

or if I add a zero-distance move after Linear C30:

ABS

CCR(1)

CC1

Linear X-172.646 Y-505.895 C-200

Linear C30 (path following axis C is fine here)

Linear X-172.646 Y-505.895

CC4

 

It seems kerf affects path-following axis control? why?

 

Thanks for your help.

 

Luke

[JeffLowe]

Do you have lookahead turned on and have you set a reasonable Aux axis feetrate limit (Isx86)?

 

Hi,

 

I am running this NC proggram with a kerf:

ABS

CCR(1)

CC1

Linear X-172.646 Y-505.895 C-200

Linear C30 (path following axis C runs away here)

Linear X0 Y-400 C30

CC4

 

if I turn off kerf now:

ABS

CCR(0)

CC1

Linear X-172.646 Y-505.895 C-200

Linear C30 (path following axis C is fine here)

Linear X0 Y-400 C30

CC4

 

or if I add a zero-distance move after Linear C30:

ABS

CCR(1)

CC1

Linear X-172.646 Y-505.895 C-200

Linear C30 (path following axis C is fine here)

Linear X-172.646 Y-505.895

CC4

 

It seems kerf affects path-following axis control? why?

 

Thanks for your help.

 

Luke

[curtwilson]

There are several things to look at, and Jeff has pointed some out. First, assuming your "vector feedrate axes" are the default set of (X, Y, Z), the commanded speed of your C-axis move is not governed by your F-code value (which is a linear speed), but rather by Isx86 (which can be a rotary speed). Have you checked your setting of Isx86? Second, if lookahead is active, you can have the speed limited by Ixx16 for the motor assigned to the C-axis.

 

The next issue is the the cutter comp (kerf) algorithm must be able to buffer and look through the C-axis move to properly compute the compensated intersection point between the incoming XY move and the outgoing XY move. Have you set up a buffer for this type of move with the DEFINE CCBUF command?

[lukewang]

I did the test with Isx86. Yes, my rotary C axis is affected by this variable. My problem is solved.

 

Then another problem is coming. I have 2 rotary axes, both of them seem to be controlled by Isx86, which is not ideal. I prefer each of them being controlled by separate feedrate limits, anyway I can do it?

 

Thanks Jeff and Curt.

[curtwilson]

There is only one Isx86 alternate feedrate value per coordinate system, so what you want cannot be done directly. However, for these rotary-axis-only moves, you could go into RAPID mode, where each motor's speed is controlled separately. And if you want, you could specify the use of the jog speed parameter Ixx22 for these moves rather than the default maximum speed parameter Ixx16.

 

Or, if lookahead is active, the speed of LINEAR mode moves for these axes is limited by the underlying Ixx16 motor maximum speed parameters.