[dynamo15]

Hello all.

We have a Fanuc Powermate i D with two servo motors used to position two ballscrews which control a table to dispense sealer on to a part.
The part has many holes we must go around.
We've generated a path offline and the resultant code gives us lines such as this (I'm not sure what the software was that created the G-Codes, something like MasterCAM???):

N114 G2 X9.2921 Y3.4506 I-5.2351 J-.2028
N116 Y3.4371 I-5.239 J0.
N118 X9.063 Y3.1886 I-.25 J.0006
N120 G3 X8.7195 Y2.815 I.0315 J-.3737
N122 X9.0386 Y2.4441 I.375 J0.
N124 G2 X9.2513 Y2.1969 I-.0373 J-.2472
N126 X9.2512 Y2.1882 I-.25 J0.

The existing parts run using code such as this:

N80G03X-2.000R0.42 
N90G02X-4.155Y1.17R2.53
N100G03X-4.455Y1.89R0.42 
N110G01X-5.33Y4.033
N120G03X-5.63Y4.776R0.42

Basically, what I'm asking is if the Powermate will recognize the code with the I,J instead of the R and react the same?
What, if any, are the differences/advantages between the 2 methods?

Thanks for any ideas and my apologies for being rather vague but this is relatively new to me.

[angelw]

The differences are as follows:

1. I and J arguments used in circular interpolation blocks define the centre of the arc/circle via signed, incremental values relative to the start point of the arc/circle. The start point will be the position in X and Y the slides are sent to by the motion block prior to the block containing the circular interpolation move, and the end point is defined by the X,Y coordinates expressed in the circular interpolation block.

2. When an R argument is used in a circular interpolation block, the control calculates the centre of the arc/circle from the Start/End point and Radius passed to it from the part program.

The "R" format circular interpolation is thought to be easier to program than the I,J,K format in that you only have to supply the Start/End point and Radius without the need to calculate the I,J,K values using trigonometry. If when using the "R" format, if either, or both the Start/End coordinates passed to the control are wrong, then the control calculates the arc/circle centre based on this wrong data so that the circular trajectory passes through the two points. Accordingly, if the profile shape is important, you may end up with the profile being out of tolerance without it being immediately obvious. When I,J,K format is used, if the End point is not on the circular trajectory of an arc described by the Start Point and the Centre defined by the I,J,K addresses, then an alarm will be raised by the control if the error exceeds a stored parameter value. Accordingly, the error in the profile is immediately obvious, and steps can be taken to remedy the problem.

With regards to the "R" format being easier than the I,J,K format, I don't see it that way. If the "R" format is to be used to produce an accurate profile according to a parts drawing where often the Start and End points of arcs are not given and need to be calculates based on other geometry, then I,J,K values are nearly always by-products of the calculations. Accordingly, when making these calculations manually, neither format is more difficult that the other, and when a CAM package is used to create the program there is clearly no argument that "R" format is easier than I,J,K.

In all Fanuc manuals the following warning is made:

"When an arc having a center angle approaching 180° is specified, the calculated center coordinates may contain an error. In such a case, specify the center of the arc with I, J, and K."

If you need to know how to program both ways to accommodate this possible error situation, I see no argument for not just programming using I,J,K format. The exception to this is when having to program out taper in a turning operation due to part deflection. In this case, wrong values in relation to the part drawing will be used to counteract the taper. Accordingly, its easier to use "R" format and allow the control to shift the arc centre to accommodate the varying Start/End points being edited at the control.

The math behind calculating an arc centre from two points and a radius yields accurate results if high precision, real numbers are used. Accordingly, the only reason I can see for the error that Fanuc warns of, is that the calculations are being made by the control using data passed to it by the program that has already been rounded to the least programmable increment set for the control.

The other big difference between "R" and I,J,K format is that a full circle can't be programmed in one block using "R" format, as can be using I,J,K format.

Regards,

Bill

[dynamo15]

Thank you Bill for the great information, much obliged!

One thing I noticed when using a simulator with my part programs was that cycle time using "R" seems to be shorter.
I'm not sure if this is just a function of the simulator; I'll find out when I actually get to use the Powermate and will post back.
Again, many thanks,

George.