Reference Manual

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Turbo PMAC/PMAC2 Software Reference

Turbo PMAC Program Command Specification 408

Alternatively, just the magnitude of the vector to the center can be specified with R{data} on the

command line. If this is the case, Turbo PMAC will calculate the location of the center itself. If the value

specified by {data} is positive, Turbo PMAC will compute the short arc path to the destination (<=

180

); if it is negative, Turbo PMAC will compute the long arc path (>= 180

). It is not possible to

specify a full circle in one command with the R vector specifier.

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 only define 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 direction of the arc to the destination point – clockwise or counterclockwise – is controlled by

whether the card is in CIRCLE1 (clockwise) or CIRCLE2 (counterclockwise) mode. The sense of

clockwise in the plane is determined by the direction of the NORMAL vector to the plane.

If the destination point is a different distance from the center point than is the starting point, the radius is

changed smoothly through the course of the move, creating a spiral. This is useful in compensating for any

round off errors in the specifications. However, if the distance from either the starting point or the

destination point to the center point is zero, and error condition will be generated and the program will stop.

If the vector from the starting point to the center point does not lie in the circular interpolation plane, the

projection of that vector into the plane is used. If the destination point does not lie in the same circular

interpolation plane as the starting point, a helical move is done to the destination point.

If the destination point (or its projection into the circular interpolation plane containing the starting point)

is the same as the starting point, a full 360

arc is made in the specified direction (provided that IJK

vector specification is used). In this case, only the vector needs to be specified in the move command,

because for any axis whose destination is not specified, the destination point is automatically taken to be

the same as the starting point.

If no vector, and no radial magnitude, is specified in the move command, a linear move will be done to

the destination point, even if the program is in circular mode.

Note:

Turbo PMAC performs arc moves by segmenting the arc and performing the best

cubic fit on each segment. I-variable Isx13 determines the time for each segment.

Isx 13 must be set greater than zero to put the coordinate system into this

segmentation mode in order for arc moves to be done. If Isx13 is set to zero,

circular arc moves will be done in linear fashion.

Examples:

X5000 Y3000 I1000 J1000

X(P101) Z(P102) I(P201) K(P202)

X10 I5

X10 Y20 C5 I5 J5

Y5 Z3 R2

J10 ; Specifies a full circle of 10 unit radius