Method and apparatus for tracking the position and orientation of a stylus and for digitizing a 3-D object

A method for zeroing sensors of a probe apparatus of a three-dimensional coordinate measuring system, said probe apparatus including a linkage arm assembly having a probe positioned at a first end, a support base positioned at a second end, and at least five rotary joints positioned between said probe and said support base, said at least five rotary joints being coupled to a plurality of sensors, each sensor operative to measure an angle differential resulting from movement of an associated rotary joint, the method comprising:

• placing said probe in a receptacle positioned on said probe apparatus, said receptacle being positioned such that when said probe is positioned in said receptacle, four of said at least five rotary joints are substantially fixed in a known angular configuration and wherein a fifth of said at least five rotary joints may be positioned at any rotary position relative to a member coupled to said fifth rotary joint, said known angular configuration being a home position;
• receiving an indication to zero said sensors of said probe apparatus, wherein said fifth rotary joint is positioned at a particular rotary position relative to said member coupled to said fifth rotary joint when said indication to zero said sensors is received;
• and
• assigning a known angle to each of said at least five rotary joints when said probe is positioned in said receptacle, wherein said particular rotary position is considered a known angle for said fifth rotary joint.

A method for calibrating a three-dimensional probe apparatus having a probe moveable within a selected volume and a plurality of joints provided in a mechanical linkage coupled to said probe, the method comprising:

• retrieving calibration parameters from a storage device;
• sampling a plurality of orientations of said probe as said orientations of said probe are varied at an arbitrary location within said selected volume, wherein a position of a known point on said probe is maintained fixed at said arbitrary location while said orientation of said probe is varied to provide multiple configurations of angles of said joints of said probe apparatus, said sampled plurality of orientations of said probe being sampled from data provided by sensors that detect said joint angles and are coupled to said probe apparatus;
• using said sampled plurality of orientations of said probe to determine a set of spatial coordinates of said known point on said probe at each of said sampled plurality of orientations;
• comparing said set of determined spatial coordinates of said known point at each of said sampled plurality of orientations and determining differences between said set of determined spatial coordinates at each of said sampled plurality of orientations and at least one other set of said determined spatial coordinates;
• and
• adjusting said calibration parameters based on said determined differences between said set of determined spatial coordinates at each of said sampled plurality of orientations and at least one other set of said determined spatial coordinates such that said adjusted calibration parameters are used when determining a position and orientation of said probe during operation of said probe apparatus.

A method for zeroing sensors of a probe apparatus of a three dimensional coordinate measuring system, said probe apparatus including a linkage arm assembly having a probe positioned at a first end, a support base positioned at a second end, and a plurality of rotary joints positioned between said probe and said support base, said rotary joints being coupled to a plurality of relative sensors, each of said sensors operative to measure an angle differential resulting from movement of an associated rotary joint, the method comprising:

• providing an index mark at a predetermined position in a sensing range of each of said relative sensors such that each of said index marks corresponds to a known angle of an associated rotary joint;
• detecting said index mark for each of said sensors when a user grasps said probe and moves said probe within a workspace, said movement of said probe causing said rotary joints to rotate such that said index mark of each of said sensors is detected;
• and
• assigning a predefined reference angle to each of said rotary joints associated with said detected index mark of each of said sensors, wherein said predefined reference angle of each of said rotary joints associated with said detected index mark of each of said sensors is a reference zero angle.

A probe apparatus which provides three-dimensional position and orientation data to a computer system and determines calibration parameters, said probe apparatus comprising:

• a mechanical linkage assembly, including:
• a support base provided at a first end of said mechanical linkage assembly for supporting said mechanical linkage assembly;
• a probe provided at a second end of said mechanical linkage assembly and moveable within a selected volume;
• a plurality of joints provided between said probe and said support base;
• and
• a plurality of sensors coupled to said mechanical linkage assembly operative to sense joint angles related to a position and orientation of said probe and provide joint angle data to said computer system;
• means for determining a set of spatial coordinates for a known point on said probe at each of a plurality of sampled orientations of said probe when said probe is positioned at an arbitrary location within said selected volume and said orientation of said probe is varied while maintaining said known point on said probe at said arbitrary location;
• means for determining error values, each of said error values being between said set of spatial coordinates determined for each of said plurality of said sampled orientations and at least one other set of said spatial coordinates;
• and
• means for increasing the accuracy of position and orientation data provided by said probe apparatus by determining calibration parameters based on said error values, said calibration parameters being used when determining said position and orientation of said probe in normal usage.

A probe apparatus which provides three-dimensional position and orientation data to a computer system and zeroes transducers of the apparatus, the probe apparatus comprising:

• a mechanical linkage assembly, including:
• a support base provided at a first end of said mechanical linkage assembly for supporting said mechanical linkage assembly;
• a probe provided at a second end of said mechanical linkage assembly and moveable within a selected volume;
• N rotary joints positioned between said probe and said support base, wherein N is an integer;
• and
• a plurality of sensors coupled to said mechanical linkage assembly, each sensor operative to measure an angle differential resulting from movement of an associated rotary joint;
• a receptacle positioned on a joint member rotatably coupled to said support base of said probe apparatus such that when said probe is positioned in said receptacle, N-1 of said rotary joints are substantially fixed in a known angular configuration, and an Nth rotary joint is substantially free to be positioned at any angular position;
• and
• a device that provides a known zero angle reference for said sensors when said N-1 rotary joints are in said known angular configuration.

A method for zeroing sensors of a probe apparatus of a three-dimensional coordinate measuring system, said probe apparatus including a linkage arm assembly having a probe positioned at a first end, a support base positioned at a second end, and at least five joints positioned between said probe and said support base, said at least five joints being coupled to a plurality of sensors, each sensor operative to measure an angle differential resulting from movement of an associated joint, the method comprising:

• placing said probe in a receptacle positioned on said probe apparatus, said receptacle being positioned on a joint member rotatably coupled to a grounded joint member of said probe apparatus such that when said probe is positioned in said receptacle, four of said at least five joints are substantially fixed in a known angular configuration and wherein a fifth of said at least five joints may be positioned at any angular configuration, said known angular configuration being a home position;
• receiving an indication to zero said sensors of said probe apparatus;
• and
• assigning a known angle to each of said at least five joints when said probe is positioned in said receptacle.