Method for calibrating parameter of articulated coordinate measuring apparatus

1. A method of calibrating a group of parameters in an articulated coordinate measuring apparatus, the group of parameters including primary calibration parameters and secondary calibration parameters, wherein an articulated measuring arm of the apparatus is operated and a probe mounted to one end of said measuring arm is brought into contact with a measurement point on an object to be measured in order to measure a space coordinate of said measurement point, the method comprising:

placing a primary standard unit having a plurality of primary calibration reference portions in an operation space of said measuring arm;

operating said measuring arm to bring said probe into contact with each of said plurality of primary calibration reference portions in order to measure a space coordinate of each primary calibration reference portion at a plurality of arm positions, said plurality of arm positions corresponding to said primary calibration parameters, said primary calibration parameters being parameters in which parameter errors increase more than a predetermined reference when a predetermined time period passes;

performing a parameter calibration process of said primary calibration parameters based on measurement results of said plurality of primary calibration reference portions;

placing a secondary standard unit having a secondary calibration reference portion smaller in number than said plurality of primary calibration reference portions in the operation space of said measuring arm;

operating said measuring arm to bring said probe into contact with said secondary calibration reference portion in order to measure a space coordinate of said secondary calibration reference portion at a smaller number of arm positions than said plurality of arm positions, said smaller number of arm positions corresponding to said secondary calibration parameters, said secondary calibration parameters being parameters in which parameter errors increase more than a predetermined reference when a shorter time period than said predetermined time period passes; and

performing a parameter calibration process of said secondary calibration parameters based on measurement results of said secondary calibration reference portion.

2. The method according to claim 1 , wherein said articulated measuring arm comprises a probe mounting member having one end to which said probe is mounted, a first link connected to said probe mounting member, a first joint that provides a bending operation of said probe mounting member with respect to said first link, and a second joint that provides a twisting operation of said probe mounting member with respect to said first link, and

the method comprises measuring, when said second joint is rotated in a twisting direction to twist said first link with said probe being brought into contact with said primary calibration reference portions or said secondary calibration reference portion in a state where said probe mounting portion is vertically placed, space coordinates of said primary calibration reference portions or said secondary calibration reference portion at a plurality of arm positions.

3. The method according to claim 1 , wherein said articulated measuring arm comprises a probe mounting member having one end to which said probe is mounted, a first link connected to said probe mounting member, a first joint that provides a bending operation of said probe mounting member with respect to said first link, and a second joint that provides a twisting operation of said probe mounting member with respect to said first link, and

the method comprises measuring, when said first joint is rotated in a bending direction to rotate said probe mounting member along a vertical plane with said probe being brought into contact with said primary calibration reference portions or said secondary calibration reference portion from a state where said probe mounting portion is horizontally placed, space coordinates of said primary calibration reference portions or said secondary calibration reference portion at a plurality of arm positions.

4. The method according to claim 1 , wherein said articulated measuring arm comprises a probe mounting member having one end to which said probe is mounted, a first link connected to said probe mounting member, a first joint that provides a bending operation of said probe mounting member with respect to said first link, and a second joint that provides a twisting operation of said probe mounting member with respect to said first link, and

the method comprises measuring, when said second joint is rotated in a twisting direction to rotate said probe mounting member along a horizontal plane with said probe being brought into contact with said primary calibration reference portions or said secondary calibration reference portion from a state where said probe mounting portion is horizontally placed, space coordinates of said primary calibration reference portions or said secondary calibration reference portion at a plurality of arm positions.

5. The method according to claim 1 , wherein said articulated measuring arm comprises a probe mounting member having one end to which said probe is mounted, a first link connected to said probe mounting member, a second link connected to said first link and mounted to a support member, a fourth joint that provides a twisting operation of said first link with respect to said second link, a fifth joint that provides a bending operation of said second link with respect to said support member, and a sixth joint that provides a twisting operation of said second link with respect to said support member, and

the method comprises measuring, when said fourth joint and said sixth joint are rotated in a twisting direction to horizontally tilt said first link with said probe being brought into contact with said primary calibration reference portions or said secondary calibration reference portion in a state where said probe mounting portion is vertically placed, space coordinates of said primary calibration reference portions or said secondary calibration reference portion at a plurality of arm positions.

6. The method according to claim 1 , Wherein said parameter calibration process performs a parameter estimation process by a least squares method using a matrix with a P-matrix and an R-matrix as a design matrix, wherein

said P-matrix includes a component of a partial differential value in which a coordinate value obtained by measurement is partially differentiated by said primary calibration parameters or said secondary calibration parameters, and wherein

said R-matrix includes a component of a partial differential value in which a coordinate value obtained by measurement is partially differentiated by a vector component of a coordinate transformation vector which converts a coordinate system of the measuring arm into a coordinate system of the standard unit.

7. A non-transient computer readable medium encoded with a guide program which guides a user to perform calibration of a group of parameters in an articulated coordinate measuring apparatus, the group of parameters including primary calibration parameters and secondary calibration parameters, wherein the program causes a computer to execute the steps of:

guiding said user to place a primary standard unit having a plurality of primary calibration reference portions in an operation space of a measuring arm;

guiding said user to operate said measuring arm to bring a probe into contact with each of said primary calibration reference portions in order to measure a space coordinate of each primary calibration reference portion at a plurality of arm positions, said plurality of arm positions corresponding to said primary calibration parameters, said primary calibration parameters being parameters in which parameter errors increase more than a predetermined reference when a predetermined time period passes;

performing a parameter calibration process of said primary calibration parameters based on measurement results of said plurality of primary calibration reference portions;

guiding said user to place a secondary standard unit having a secondary calibration reference portion smaller in number than said plurality of primary calibration reference portions in the operation space of said measuring arm;

guiding said user to operate said measuring arm to bring said probe into contact with said secondary calibration reference portion in order to measure a space coordinate of said secondary calibration reference portion at a smaller number of arm positions than said plurality of arm positions, said smaller number of arm positions corresponding to said secondary calibration parameters, said secondary calibration parameters being parameters in which parameter errors increase more than a predetermined reference when a shorter time period than said predetermined time period passes; and

performing a parameter calibration process of said secondary calibration parameters based on measurement results of said secondary calibration reference portion.