THORLABS LNR502E, Руководство пользователя

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Page 22 ETN053047-D02
LNR502E Encoded Long Travel, Linear Stage with Stepper Motor Actuator
change of 10000. To display position values, the software will convert the encoder count into a 'real world' position by dividing by
10000.
6.2.2 Encoder Calibration Table
For a perfect 1mm pitch lead screw, a microstep count of 409600 would equate exactly to an encoder count of 10000.
However, due to lead screw pitch, non-linearity and other cyclic errors, this is not achievable in the ‘real world’. It is the purpose
of the encoder feedback handling within the APT software to accommodate for this and achieve the required encoder position
(the more accurate position reading).
One way to accommodate for this lead screw non-linearity is for the system to acquire a look up table of microstep count verses
encoder count readings. Using this 'calibration' table the system is then able to adjust the microstep count required (to drive
the motor) to achieve the required encoder count.
Setting Up a Calibration Table
There are various user settings which relate to encoder calibration table acquisition.
1) Click the ‘Settings’ button on the motor GUI, and select the ‘Encoder’ tab.
Fig. 6.3 Motor settings - Encoder tab
2) The upper collection of settings on this panel relate to Calibration Table functionality (see Section 6.2.3. for details on the
lower collection of settings).
Encoder Calibration - Sets the overall encoder calibration factor in counts/mm or counts/degree. On encoder equipped
stages currently available, this factor is factory set to 10000 (i.e. 10000 counts/mm or 0.1micron per count).
Calibration Sequence Step Size (mm or degrees)
- Specifies the stepping distance to use when a calibration table is
acquired. For example, a stepping distance of 0.2mm instructs the system to stop every 0.2mm, to read the encoder count
during a calibration sequence.
Calibration Sequence Sample Dwell (ms)
- In many cases it is good practise to allow the stage mechanics to settle for a
short period (allowing vibrations and other transients to die down) before sampling the encoder reading.
This parameter specifies the dwell time (in ms) to wait at each position point visited during an encoder calibration sequence,
before reading the encoder count.
Encoder QEP Sense
- Specifies the sense of the encoder signals being read by the controller electronics, i.e. positive or
negative. There is one setting applicable for a particular stage/encoder system and when set should not be altered.
Acquiring a Calibration Table
Note
The position values returned by the GetPosition and GetPositionEx methods are
derived from the microstep count in 'Microstep Positioning' mode and from the
encoder count in 'Encoder Positioning' mode - see the APTServer helpfile for more
details
Note
These settings are set to suitable defaults automatically when an encoded stage
type has been associated with the motor channel (using the APT Config utility).