Delta Tau GEO BRICK LV Manual De Usuario
Turbo PMAC User Manual
184
Setting Up the Servo Loop
PMAC Compensation Tables
Standard leadscrew compensation
e.g.
∆x = f(x)
y
Get linear encoder accuracy (almost!) with rotary encoder
y
Characterize system with linear sensor
y
Enter errors in PMAC
M
E
∆x
∆x
∆x
∆x
∆x
DEFINE COMP 200, #1, #1, 100000
Table Length
Source Motor
Table Span in Counts
Target Motor
Target Motor
Uses of Cross-Axis Compensation
The ability to have separate source and target motors for a table has several uses. The first is the
traditional compensation for imperfect geometry, as in a bowed leadscrew. For instance, on an XY table,
if the X-axis leadscrew is bowed, the Y-axis position should receive a correction as a function of X-axis
position. If motor #1 is the X-axis, and motor #2 is the Y-axis, the table holding this correction would
have motor #1 as the source motor, and motor #2 as the target motor.
traditional compensation for imperfect geometry, as in a bowed leadscrew. For instance, on an XY table,
if the X-axis leadscrew is bowed, the Y-axis position should receive a correction as a function of X-axis
position. If motor #1 is the X-axis, and motor #2 is the Y-axis, the table holding this correction would
have motor #1 as the source motor, and motor #2 as the target motor.
PMAC Compensation Tables
Cross-axis compensation
e.g.
∆y = f(x)
y
Useful for bowed leadscrews
y
Can be used to build electronic cam tables
DEFINE COMP 100, #1, #2, 100000
Table Length
Source Motor
Table Span in Counts
Target Motor
Target Motor
∆y
∆y
∆y
∆y
∆y
∆y
M
E
A second use for cross-axis compensation is what is often known as the electronic cam. In this case, the
entire movement of the target motor is caused by the entries in the compensation table, not just the
corrections. This method of implementing electronic cam operation has two significant advantages over
Turbo PMAC’s time-base following, the other method of creating electronic cams: the compensation
table is bidirectional – the master can turn in either direction – and it is absolute, so the phasing in is
simply a matter of homing the axes.
entire movement of the target motor is caused by the entries in the compensation table, not just the
corrections. This method of implementing electronic cam operation has two significant advantages over
Turbo PMAC’s time-base following, the other method of creating electronic cams: the compensation
table is bidirectional – the master can turn in either direction – and it is absolute, so the phasing in is
simply a matter of homing the axes.
The time-base method, in which the motion program of the slave motors defines the motion, retains the
advantage of being able to change on the fly through math and logic in the program, and of second or
third order interpolation between points, rather than the compensation table’s 1
advantage of being able to change on the fly through math and logic in the program, and of second or
third order interpolation between points, rather than the compensation table’s 1
st
-order interpolation.
Refer to the Synchronizing Turbo PMAC to External Events section of this manual for details.
Dimension of the Table
Turbo PMAC presently supports one-dimensional (1D) and two-dimensional (2D) position compensation
tables. Three-dimensional (3D) tables may be supported in the future. 1D tables have a single source
motor; 2D tables have two source motors. Note that a table with a single source motor that is different
from the target motor (a cross-axis compensation table) is still a 1D table.
tables. Three-dimensional (3D) tables may be supported in the future. 1D tables have a single source
motor; 2D tables have two source motors. Note that a table with a single source motor that is different
from the target motor (a cross-axis compensation table) is still a 1D table.