# US 2008/0184579 A1 · Measuring methods for use on machine tools > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2008/0184579 A1 - Document ID: US20080184579A1 - Status: Published application - Kind: A1 - Application number: 12/078,445 - Filed: 2008-03-31 - Published: 2008-08-07 - Earliest claimed: 2003-09-24 - Assignees: Renishaw PLC - Inventors: Geoffrey McFarland - Web page: https://patentgrep.com/patent/US20080184579A1 ## CPC - G05B 19/19: characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path - G01B 21/04: by measuring coordinates of points - G05B 2219/36503: Adapt program to real coordinates, software orientation - G05B 2219/37097: Marker on workpiece to detect reference position - G05B 2219/50049: Control machine as function of position, angle of workpiece - G05B 2219/50063: Probe, measure, verify workpiece, feedback measured values - G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G) - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS ## Abstract On a machine tool, a program receives data from a scanning or analogue probe, measuring a feature of a workpiece. This data is combined with assumed machine position data during the scanning movement. This avoids having to break into the servo feedback loop to get actual measured machine position data. The assumed machine position data can be derived from a part program which controls the scanning movement. Several ways are described for compensating for errors between the assumed machine position values and the actual values. ## Claims ### Claim 1 A method of measuring workpieces on a machine tool, comprising the steps of: causing relative movement between an analogue or scanning probe and a workpiece, along a pre-defined path comprising nominal positions of the probe relative to the workpiece, under control of a part program; during the movement, taking measurements of a position of a surface of the workpiece relative to the probe, using an output of the probe; and combining said measurements from the output of the probe with assumed data derived from said part program. ### Claim 2 (depends on 1) A method according to claim 1, wherein a result of said combining step gives a dimension of the workpiece. ### Claim 3 (depends on 1) A method according to claim 1, wherein the assumed data derived from said part program comprises at least one target or nominal probe output reading. ### Claim 4 (depends on 1) A method according to claim 1, wherein a result of said combining step gives an error value for a dimension of the workpiece. ### Claim 5 (depends on 1) A method according to claim 1, including a step of compensating for a difference between the assumed data derived from the part program and an actual position of the probe relative to the workpiece. ### Claim 6 (depends on 5) A method according to claim 5, wherein the compensating step uses data from an artifact of known dimensions and form. ### Claim 7 (depends on 6) A method according to claim 6, wherein the artifact has similar dimensions to a feature of the workpiece being measured. ### Claim 8 (depends on 6) A method according to claim 6, wherein the artifact has a dissimilar dimension to the feature being measured, or is measured at a dissimilar speed, and the compensation includes interpolation to correct for such dissimilar dimension or speed. ### Claim 9 (depends on 5) A method according to claim 5, wherein the compensating step uses data from reference points measured on the surface of the workpiece. ### Claim 10 (depends on 5) A method according to claim 5, wherein the compensating step uses an error map determined by comparing scans of the surface of the workpiece at slow and fast speeds. ### Claim 11 (depends on 1) A controller or probe interface for a machine tool, programmed to perform a method according to claim 1. ### Claim 12 (depends on 3) A controller or probe interface for a machine tool, programmed to perform a method according to claim 3. ### Claim 13 A method of measuring workpieces on a machine tool, comprising the steps of: causing relative movement between an analogue or scanning probe and a workpiece, along a pre-defined path comprising nominal assumed first positions of the probe; during the movement, taking measurements of a workpiece surface relative to the probe, using an output of the probe; and combining said measurements from the output of the probe with data derived from the assumed first positions of the probe. ### Claim 14 (depends on 13) A method according to claim 13, wherein a result of said combining step gives a dimension of the workpiece. ### Claim 15 (depends on 13) A method according to claim 13, wherein data derived from the pre-defined path comprises at least one target or nominal probe output reading. ### Claim 16 (depends on 13) A method according to claim 13, wherein a result of said combining step gives an error value for a dimension of the workpiece. ### Claim 17 (depends on 13) A method according to claim 13, including a step of compensating for a difference between a nominal assumed position in the pre-defined path and an actual position of the probe relative to the workpiece. ### Claim 18 (depends on 17) A method according to claim 17, wherein the compensating step uses data from an artifact of known dimensions and form. ### Claim 19 (depends on 18) A method according to claim 18, wherein the artifact has similar dimensions to the feature of the workpiece being measured. ### Claim 20 (depends on 18) A method according to claim 18, wherein the artifact has a dissimilar dimension to the feature being measured, or is measured at a dissimilar speed, and the compensation includes interpolation to correct for such dissimilar dimension or speed. ### Claim 21 (depends on 17) A method according to claim 17, wherein the compensating step uses data from reference points measured on the workpiece surface. ### Claim 22 (depends on 17) A method according to claim 17, wherein the compensating step uses an error map determined by comparing scans of the workpiece surface at slow and fast speeds. ### Claim 23 (depends on 13) A controller or probe interface for a machine tool, programmed to perform a method according to claim 13. ### Claim 24 (depends on 13) A method according to claim 13, wherein: the causing relative movement is under control of a part program; and the assumed first positions of the probe are derived from the part program.