EP 1 998 137B12510152025303540455055Description[0001] The present invention relates to an abnormalitydetecting method for a form measuring mechanism anda form measuring mechanism using various probes suchas a scanning probe, a touch signal probe, a probe for asurface roughness measuring machine, a probe for ancontour measuring machine, etc., and more specifically,to an abnormality detecting method for a form measuringmechanism which is preferably used in a formmeasur-ingmechanism that measures changes of a measuredobject by bringing a probe into direct contact with theobject to be measured, and makes it possible to easilyjudge contamination and wearing when the contamina-tion and wearing occur on the probe and properly cleanor replace the probe, and the form measuring mecha-nism.[0002] In a measuring mechanism which measures aform of an object to be measured, during repetition ofmeasurements of the objects, the tip end of a contacttype probe (hereinafter, simply referred to as a probe,)is gradually contaminated by several-micrometer to 0.1millimeter orders of dust and oil on the obj ect. Then, thecontact sensitivity changes or foreign bodies such as dustare caught between the probe tip end and an object, re-sulting in a measurement abnormality. To avoid this, ob-jects and the probe are soaked in a cleaning liquid andcleaned. However, only soaking in a cleaning liquid can-not sufficiently remove contamination, and removed con-tamination may adhere again, so that as shown in Jap-anese Laid-Open Patent Publication No. 2000-35325(Patent document 1), it has been proposed that air isblown to the probe tip end to clean it as appropriate.[0003] Further, the tip end of the probe is worn anddeformed through use. Therefore, to enable accuratemeasurement even if the tip end of the probe is deformeddue to wearing, as shown in Japanese Laid-Open PatentPublication No. 2001-280947 (Patent document 2), it hasbeen proposed that a reference sphere for calibrating theprobe form is provided and the probe is calibrated.[0004] However, as shown in Fig. 13(a), assuming thatmeasurement is made by using the reference sphere 30shown in Patent document 2 in a state that dust 2, etc.,adheres to the reference sphere 30 and/or probe 24, aform measured in this case is not the form that shouldbe measured as shown in Fig. 13 (b) but is the formmeas-ured in actuality as shown in Fig. 13(c). Therefore, fromonly the result of Fig. 13(c), it cannot be judged whetherthe measurement abnormality was caused by contami-nation on the tip end of the probe 24 or contamination onthe reference sphere 30. Therefore, this requires extralabor of randomly repeating cleaning and measurementof the tip end of the probe 24 and the reference sphere 30.[0005] Even when the contamination can be judged ascontamination on the reference sphere 30 or the tip endof the probe 24, if the location thereof is not sufficientlyidentified, cleaning must still be repeated a plurality oftimes.[0006] Further, when the probe 24 is used over a longperiod of time, even if it is calibrated by using the refer-ence sphere 30, desired measurement accuracy cannotbe secured when the probe is extremely worn out, so thatthe probe 24 needs to be replaced. However, due to in-fluence from the contamination, it is difficult to judgewhether the probe 24 has been worn out, and the timeof replacement of the probe 24 cannot be judged.US2002/0189319 A1 describes a method of calibratingmeasuring machines by measuring three referencespheres with the probe and calibrating the probe basedon the measured values. The present invention wasmade to solve the conventional problems describedabove, and an object thereof is to provide an abnormalitydetecting method for a form measuring mechanism anda form measuring mechanism which make it possible tojudge contamination on the tip end of the probe 24, de-formation due to wearing on the tip end of the probe 24,or contamination of the reference sphere 30, deformationdue to wearing of the reference sphere 30, and make itpossible to at least identify a location of contamination inthe case of contamination on the tip end of the probe 24or on the reference sphere 30, judge a state of a wornregion in the case of wearing on the tip end of the probe24 or on the reference sphere 30, or judge whether theprobe 24 or on the reference sphere 30 needs to be re-placed.[0007] According to the present invention as definedin the appended claims, when detecting an abnormalityof a form measuring mechanism which brings a probeinto direct contact with an object to be measured to meas-ure the form of the object, a plurality of reference spheresfor calibrating the form of the probe are measured, andform abnormal values which are common (correspond)in position and size to each other and form abnormalvalues which are not common (correspond) to each otherobtained through measurement of the referencespheres, are judged, and at least any one of a worn stateand a contamination including dust adhering of the probejudged from the common form abnormal values and wornstates and a contamination including dust adhering ofthe reference spheres judged from the form abnormalvalues not common to each other are notified, wherebythe problems are solved.[0008] The principle of the solution means of thepresent invention will be described with reference to Fig.1. A plurality, for example, two of reference spheres 130aand 130b are prepared and the reference spheres 130aand 130b are measured with the probe 124. At this time,assuming that dust 4 adheres to the surface of the probe124, dust 6 adheres to the surface of the reference sphere130, and dust 8 adheres to the surface of the referencesphere 130b, the measurement results of the referencespheres 130a and 130b are as shown in the lower stageof Fig. 1. At this time, dust 4 of the probe 124 is measuredas form abnormal values with an inclination angle θ com-mon in both measurement results. On the other hand,the dust 6 appears only in the measurement result of the1 2
