Hologic DISCOVERY A, Technical Manual

Page: 137 / 274

Discovery QDR Series Technical Manual
4-15
8. If the position limits are within specifications, Type
Y<Enter>
to accept the cal-
ibration values.
4.6.0.2.1 Calibration Parameters
The motor_direction field determines whether the positive step direction is the reverse of
the direction of increasing encoder values ('0' if the direction is not reversed, '1' if it is).
This value is set from the corresponding parameter in the MOTOR_AY.PRO file and is a
constant for each motor (i.e., the direction of increasing encoder values must agree with
the system coordinates and the positive step direction is set by the wiring harness for the
stepper motor).
The eight calibrate_position fields are:
1) 1 (Tolerance). The
±
position tolerance, in encoder ticks, for absolute moves. The
calibration program sets this field to the value found in the corresponding
calibrate_position field in the MOTOR_AY.PRO file.
2,3) 2288,41187 (NumberOfSteps,StepDistance). The number of motors steps
corresponding to the step distance in microns. The ratio of these two numbers
determines the step size (41187/2288
≅
18 microns). The calibration program sets
these fields to the values found in the corresponding calibrate_position fields in
the MOTOR_AY.PRO file. Since these values are a property of the mechanical
design of the system, they should never change.
4,5) 209,61339 (NumberOfTicks,TickDistance). The number of encoder ticks
corresponding to the tick distance in microns. Again, it is the ratio of these two
numbers (61339/209
≅
293 microns) that determines the encoder calibration.
These numbers will generally change from calibration to calibration (although the
ratio should remain approximately the same).
6) 363 (EncoderOffset). The value subtracted from the encoder readback to set the
origin of motion. The origin of AY motion is the extreme right mechanical stop, so
this value should be the same as the first field below.
7,8) 363,3719 (NegLimit,PosLimit). The encoder readings for the negative (right) and
positive (left) mechanical stops.
The pos_limit_position and the neg_limit_position are the limits of motion, in microns,
in the positive and negative direction.
Note: The PosLimitOffset and NegLimitOffset entries in the [AyMotor] section of the
SQDRIVER.INI file determine the motion limits relative to the mechanical stops.
If these entries are not present, or are zero, the motion limits are set to the
mechanical limits, as in the above example).
Note: The last calibration scan data is saved in the file MOTOR_AY.DAT. You can
reanalyze the data–e.g., after editing SQDRIVER.INI by typing the command
CALIBRATE @MOTOR_AY.DAT
at the
MOTOR$AY>
prompt in SQDRIVER.