Volumetric error compensation system with laser tracker and active target

An active target for a multi-dimensional measuring system having a tracking device and a source of laser light, comprising:

• an optical target adapted to communicate with the source of laser light;
• a first gimbal assembly supporting said optical target for rotation about a first rotational axis;
• a first motive means operative to cause rotational movement about said first rotational axis;
• a second gimbal assembly supporting said first gimbal assembly for rotation about a second rotational axis orthogonally disposed relative to said first rotational axis;
• and
• a second motive means operative to cause rotational movement of said first gimbal assembly about said second rotational axis,
• whereby said optical target is supported at the center of said first and said second gimbal assemblies.

A multi-dimensional measurement system having a laser tracker, a laser light source, a controller device and a remote target, said remote target comprising:

• an optical module adapted to communicate with the laser light source;
• a position sensitive detector operatively coupled with said optical module and operative to provide an indication of the orientation of said optical module relative to the laser light;
• first support means to rotatably support said optical module and said position sensitive detector for 360 degree rotation about a first rotational axis;
• first motive means coupled to said optical module to cause rotational movement of said optical module and said position sensitive detector about said first rotational axis;
• second support means to rotatably support said optical module and said position sensitive detector for 360 degree rotation about a second rotational axis;
• and
• second motive means operatively coupled to said optical module to cause rotational movement of said optical module and position sensitive detector about said second rotational axis,
• whereby said optical module is maintained facing the laser tracker at all times as the remote target is moved multi-dimensionally.

A measurement system for an multi-dimensional movable object, the system comprising a laser tracker having a source of laser light, a control device and an active target which can be attached to the movable object, the active target comprising:

• an optical module adapted to communicate with the laser light source;
• a first gimbal assembly supporting said optical module for rotation about a first rotational axis;
• said first gimbal assembly having a first motive means operative to cause rotational movement of said optical module about said first rotational axis;
• and
• a second gimbal assembly supporting said first gimbal assembly for rotation about a second rotational axis orthogonally disposed relative to said first rotational axis,
• said second gimbal assembly having a second motive means operative to cause rotational movement of said first gimbal assembly about said second rotational axis,
• whereby said optical module is supported at the center of said first and said second gimbal assemblies.

A method for compensating for positional errors of an object movable in three-dimensional space under control of a controller, the object having an active target and the position of the object being tracked by a laser tracker tracking on the active target, the method comprising the following steps:

• a. generate a set of command positions the object is to follow in moving in three-dimensional space;
• b. build a three-dimensional machine model to include a complex path for the laser tracker to follow for all positions the object may take;
• c. build a measurement plan to represent all of the possible positions in each axes the object may take;
• d. load measurement plan into controller controlling movement of the object;
• e. place laser tracker in a fixed position;
• f. make measurements of position of object as it is moved to each of the random points in the measurement plan;
• g. compare measurement data for the object with the set of command positions;
• h. develop error compensation model to reduce the differences between the measurement data and the set of command positions;
• i. validate error compensation model as correct and accurate for volumetric compensation;
• j. load error compensation model into the controller controlling movement of the object;
• and
• k. apply volumetric compensation model as object moves to each command position.