Power Brick Controller User Manual
Manual Motor Setup
121
Verifying Encoder Feedback, Scaling to User Units
Warning
The absence of encoder data is potentially a very dangerous condition
in closed-loop control, because the servo loop no longer has any idea
what the true physical position of the motor is – usually it thinks it is
"stuck" – and it can react wildly, often causing a runaway condition.
Verifying encoder feedback is typically performed in the configuration setup section of the various
feedback devices. The user should verify that:
The feedback device is reporting data. This is commonly done by moving the motor / encoder shaft
by hand and monitoring counts in the position window in the IDE software.
The feedback device is reporting the correct number of counts. These are the motor units per user
unit. Typically per revolution for rotary encoders (before gearing) or mm / inch for linear encoders.
This is a good point of the setup to consider scaling the motor to user engineering units using
Motor[].PosSf
, and
Motor[].Pos2Sf
. Scaling to user engineering units is advantageous because it
allows jogging the motor in user units instead of counts or motor units.
Care must be taken to all motor elements (e.g.
Motor[].JogSpeed
) using motor units as they will
be now in user engineering units.
Changing
Motor[].PosSf
, and
Motor[].Pos2Sf
also affects the servo loop gains which must be
tuned accordingly.
Coordinate system axis definition, if linear (non-kinematic) assignment, can be defined as 1 (plus
offset if applicable).
Examples:
o
A linear motor with 1 nm resolution yielding 1,000,000 counts/mm desired to be
programmed in millimeters. Both
Motor[].PosSf
and
Motor[].Pos2Sf
are set to 1 /
1000000.
o
A rotary motor with 131,072 counts per revolution desired to be programmed in degrees
requires
Motor[].PosSf
and
Motor[].Pos2Sf
to be set to 360 / 131072
.
o
A rotary motor with 1,0485,76 counts per revolution with a 10:1 inch gear reduction
desired to be programmed in inches requires
Motor[].PosSf
and
Motor[].Pos2Sf
to be set
to 10 / 1048576.
