Geomagic Geomagic Phantom Premium 1.56DOF, Руководство по эксплуатации устройства

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Premium 1.56DOF/1.5HF6DOF Device Guide D-1
Appendi x
Appendix: Maximizing
Positioning Accuracy
The objective of this technical note is to help you achieve a high level of positioning
accuracy in the Phantom devices as specified in our product literature.
Phantom devices have excellent inherent repeatability under no-load conditions. However,
they can only be accurate if they have been initialized properly. The proper procedure for
initialization is outlined in this note.
Why initialization matters
All Phantom devices are equipped with incremental rotary encoders, which measure the
joint angles of the Phantom mechanism. These measurements are then used to calculate
the endpoint position in Cartesian space, based on the linkage structure, link lengths and
other such parameters.
This method of arriving at the endpoint position
implies an absolute knowledge of the joint
angles. However, incremental encoders can
only provide angular measurements relative to
the joint angles at which the system “woke up”
at initialization time. To obtain absolute angular
measurements, the system must initialize at a
known position and orientation, often referred
to as neutral position.
Initialization position for Phantom Devices
To keep the initialization procedure simple, we have chosen an easily recognized point in
the center of the workspace of the Phantom as neutral position. Roughly speaking, the
optimal startup position involves keeping the first link horizontal and perpendicular to the
front face of the base, and the second link vertical and pointing down from the first. If
there is an encoder gimbal, the face of the gimbal with a label indicating “This side faces
the Phantom” should be vertical and it should face the base of the Phantom. The thimble
or stylus should be horizontal in the plane of the first and second linkages.