User's Manual

PMAC User Manual
Synchronizing PMAC to External Events 219
SYNCHRONIZING PMAC TO EXTERNAL EVENTS
Features to Help Synchronize Motion
PMAC has several powerful features to help in synchronizing the motion under PMAC control to external
events. These include position following, commonly known as electronic gearing; time-base control,
commonly known as electronic cams; position capture, which is very useful for registration applications;
and position compare, which can be used for precision scanning and measurement applications. Each of
these areas is covered in this section.
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 the
PMAC control) is fed into one of the PMAC encoder inputs. Typically this master signal is either from
an open-loop drive or a handwheel knob.
Position Following I-Variables
One or more of the PMAC motors is told that this encoder register is the master (with Ix05). Ix05 is an
address I-variable; that is, its value contains the address of the register holding the master position
information. Typically, this register is that of some processed position data in the Encoder Conversion
Table. It is helpful to have done the 1/T interpolation or similar to reduce the quantization noise in the
sampling of the master encoder (this is done automatically in the default setup).
The following ratio for each motor is set by Ix07 and Ix08, which can be analogized to the number of gear
teeth on master and slave in a mechanical following application. The following function is turned on and
off with Ix06. When it is on, the input stream from the master acts just like a trajectory generator,
creating a series of commanded positions to which the following axis controls.
I11
1
2 3
4 5 6
1
2
3 4
time
"R"
Execute
Calculate
A. Two moves ahead
LINEAR with I13=0
SPLINE1
B. One move ahead
LINEAR with I13>0
CIRCLE, PVT
I11
1
2
3 4 5
1
2
3
4
time
"R"
Execute
Calculate
C. No moves ahead
Ix92=1, RAPID,
HOME, DWELL,"S"
I11
1
2 3
1
2
3
time
"S"
"R"
Execute
Calculate
I11
DWELL
time
I11
2a
2a
Figure 51 PMAC Motion Program Recalculation