PMAC Product Guide Circular Interpolation PMAC allows circular interpolation on the X, Y, and Z axes in a coordinate system. As with linear blended moves, TA and TS control the acceleration to and from a stop and between moves. Circular blended moves can be feedrate-specified ( F ) or time-specified ( TM ), just as with linear moves. It is possible to change back and forth between linear and circular moves without stopping. This is accomplished by entering the LINEAR command when linear interpolation is needed and the CIRCLE1 or CIRCLE2 command for circular interpolation. 1. PMAC performs arc moves by segmenting the arc and performing the best cubic fit on each segment.
I-Variable I13 determines the time for each segment. I13 must be set greater than zero to put PMAC into this segmentation mode in order for arc moves to be done. If I13 is set to zero, circular arc moves will be done in linear fashion. The practical range of I13 for the circular interpolation mode is 5-10 msec. A value of 10 msec is recommended for most applications. A lower than 10 msec I13 value will improve the accuracy of the interpolation (calculating points of the curve more often) but will also consume more of the PMAC’s total computational power. 2.
When PMAC is segmenting moves automatically (I13 > 0) which is required for Circular Interpolation, the Ix17 accelerations limits and the Ix16 velocity limits are not observed. 3. Any axes used in the circular interpolation are automatically feedrate axes for circular moves, even if they were not so specified in an FRAX command. Other axes may or may not be feedrate axes. Any non-feedrate axes commanded to move in the same move command will be linearly interpolated so as to finish in the same time. This permits easy helical interpolation. 4. The plane for the circular arc must have been defined by the NORMAL command (the default -- NORMAL K-1 -- defines the XY plane).
This command can define only planes in XYZ-space, which means that only the X, Y, and Z axes can be used for circular interpolation. Other axes specified in the same move command will be interpolated linearly to finish in the same time. The most commonly used planes are: NORMAL K-1 ; XY plane -- equivalent to G17 NORMAL J-1 ; ZX plane -- equivalent to G18 NORMAL I-1 ; YZ plane -- equivalent to G19 5. To put the program in circular mode, use the CIRCLE1 command for clockwise arcs (G02 equivalent) and CIRCLE2 for counterclockwise arcs (G03 equivalent). LINEAR will restore it to linear blended moves.
Once in circular mode, a circular move is specified with a move command specifying the move endpoint and either the vector to the arc center or the distance (radius) to the center. The endpoint may be specified either as a position or as a distance from the starting point, depending on whether the axes are in absolute ( ABS ) or incremental ( INC ) mode (individually specifiable). Motion Programs 79