Aerotech UNIDEX 600 Series, User Manual

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Getting Started U600 User’s Guide
2-10
Aerotech, Inc.
Version 1.4
2.4. Motor Units (Resolution and Direction)
Configuration defines the number of counts or machine steps per motor revolution.
However, after configuration, the user must set two machine parameters that instruct the
software how to convert from motor counts into user units (inches, degrees, or
millimeters) and vice versa. In the U600MMI these can be set through the Machine
Parameters page. In AerDebug they can be set via the “PARMSET M <name>”
command, where <name> is the name of the parameter as described below.
2.4.1. Linear vs. Rotary type
An axis may be a type that produces linear or rotary motion. A linear axis is defined by
setting the Type task parameter to zero. Linear axes use inches or millimeters as units, and
are appropriate for stages.
There are two types of rotary axes, both use degrees as their distance units. The first,
Type 1, is a rotary axis with modulo position. It is the appropriate type for stand-alone
motors. An axis with modulo position displays 0 through 359 degrees, and rolls over its
position display back to 0 when it reaches 360 degrees. This will repeat for each
revolution in either direction. Also, when programming in absolute units (specifying a
particular target in degrees), a modulo position rotary axis always chooses the direction to
move (clockwise or counter-clockwise) in order to move the shortest distance to its
angular destination. When there is no short distance (e.g., a move of 180 degrees), it
always causes clockwise (CW) rotation to the destination. This behavior does not apply
when programming in relative mode (specifying a distance relative to the current
position), in which case the arithmetic sign of the target determines the direction, similar
to a linear type motors. A modulo rotary axis is defined by setting the Type parameter
to 1.
A non-modulo rotary axis uses degrees as its distance units, but does not turnover like the
modulo rotary axis, nor will it pick the shortest distance to its angular destination in
absolute mode. It is appropriate for motors operating in helical coordinate systems. A
non-modulo rotary axis is defined by setting the Type parameter to 2.
2.4.2. Motor Resolution
An axis must also have its scaling defined, so the motor counts (or machine steps) can be
converted to user program units (millimeters, inches or degrees). This is done by the
CntsPerDeg and CntsPerInch machine parameters. Use the respective parameter based on
the type of axis defined by the Type machine parameter (see 2.4.1.). These parameters
indicate the number of machine counts per inch or degree.
For linear type motors, users must enter the counts per inch, even if doing all the
programming in millimeters (using G71).
For axes using brushless linear motors, the value entered into the CntsPerInch parameter
is the number of counts equal to one electrical cycle of the motor.
2.4.3. Motor Direction
Regardless of the motor type, the user must specify which rotational direction of the
motor corresponds to a positive units value. This is done with the arithmetic sign of the
CntsPerDeg or CntsPerInch task parameters. A positive sign indicates that a positive
units value (degrees/inches/millimeters) as measured from zero units, is reached by a
clockwise rotation of the motor. A negative sign indicates that a negative units value
(degrees/inches/millimeters) as measured from zero units, is reached by a counter
clockwise rotation of the motor.