User`s manual

5.0 - Motion Programs
Page - 55
5.10.4 - Position Following (Electronic Gearing)
PMAC has several methods of coordinating the axes under its control to axes not under its control. The simplest method is
basic position following. This is a motor-by-motor function, not a coordinate system function as time-base following is. An
encoder signal from the master axis (which is not under PMAC's control) is fed into one of PMAC's encoder inputs. This
master signal is typically either from an open-loop drive or a handwheel knob. Ix05 and Ix06 control this function.
5.10.5 - Cutter Radius Compensation
PMAC provides the capability for performing cutter (tool) radius compensation on the moves it performs. This
compensation can be performed among the X, Y, and Z axes, which should be physically perpendicular to each other. The
compensation offsets the described path of motion perpendicular to the path by a programmed amount. Cutter radius
compensation is valid only in LINEAR and CIRCLE move modes. The moves must be specified by F (feedrate), not TM
(move time). PMAC must be in move segmentation mode (I13 > 0) to do this compensation (I13 > 0 is required for
CIRCLE mode anyway.). Program commands CC0, CC1, CC2, CCR and NORMAL control this feature.
5.10.6 - Synchronous M-Variable Assignment
The scan of a motion program and execution of the commands in it are governed by the lookahead feature. PMAC will
calculate move commands ahead of time for a proper blending and will execute every instruction in between immediately.
This ahead-of-time situation would make an M-variable assignment asynchronous to the motion profiles unless a double
equal sign is used instead. M1==1, for example, will indicate PMAC that the assignment have to take place at the blending
point between the previous move encountered and the next. In LINEAR and CIRCLE mode moves, this blending occurs
V*TA/2 distance ahead of the specified intermediate point, where V is the commanded velocity of the axis, and TA is the
acceleration (blending) time. This is only available for M-variables and that are not in the form TWB, TWD, TWR, TWS.
5.10.7 - Synchronizing PMAC to Other PMACs
When multiple PMACs are used together, inter-card synchronization is maintained by passing the servo clock signal from
the first card to the others. With careful writing of programs, this permits complete coordination of axes on different cards.
5.10.8 - Axis Transformation Matrices
PMAC provides the capability to perform matrix transformation operations on the X, Y, and Z axes of a coordinate system.
These operations have the same mathematical functionality as the matrix forms of the axis definition statements, but these
can be changed on the fly in the middle of programs; the axis definition statements are meant to be fixed for a particular
application. The matrix transformations permit translation, rotation, scaling, mirroring, and skewing of the X, Y, and Z axes.
They can be very useful for English/metric conversion, floating origins, making duplicate mirror images, repeating
operations with angle offsets, and more. The matrices gets implemented by the use of Q-variables and the commands
DEFINE TBUF, TSEL, TINIT, ADIS, IDIS, AROT and IROT.
5.10.9 - Position-Capture and Position-Compare Functions
The position-capture function latches the current encoder position at the time of an external event into a special register. It is
executed totally in hardware, without the need for software intervention (although it is set up, and later serviced, in
software). This means that the only delays in the capture are the hardware gate delays (negligible in any mechanical
system), so this provides an incredibly accurate capture function. The move-until-trigger functions (either jog or motion
program) conveniently use the position capture feature for continuous motions until a trigger condition is reached.
The position-compare feature is essentially the opposite of the position-capture function. Instead of storing the position of
the counter when an external signal changes, it changes an external signal when the counter reaches a certain position.
5.10.10 - Learning a Motion Program
It is possible to have PMAC “learn” lines of a motion program using the on-line LEARN command. In this operation, the
axes are moved to the desired position and the command is given to PMAC. PMAC then adds a command line to the open
motion program buffer that represents this position. This process can be repeated to learn a series of points.
The motors can be open-loop or closed-loop as they are moved around.