as) United States
`a2) Patent Application Publication (0) Pub. No.: US 2007/0056176 Al
`(43) Pub. Date: Mar. 15, 2007
`
`Matsumiyaetal.
`
`US 20070056176A1
`
`(54) SURFACE PROFILE MEASURING
`INSTRUMENT
`
`(52) US. Ch cece esscsssnetsssssneeeseesnemesessesneeesea 33/551
`
`(75)
`
`Inventors: Sadayuki Matsumiya, Kawasaki-shi
`(JP); Shiro Igasaki, Kawasaki-shi (JP);
`Masaoki Yamagata, Kawasaki-shi (JP)
`
`Correspondence Address:
`RANKIN, HILL, PORTER & CLARK LLP
`4080 ERIE STREET
`
`WILLOUGHBY, OH 44094-7836 (US)
`
`(73) Assignee: MITUTOYO
`Kawasaki-shi (JP)
`
`CORPORATION,
`
`(21)
`
`Appl. No.
`
`11/469,076
`
`(22)
`
`Filed:
`
`Aug. 31, 2006
`
`(30)
`
`Foreign Application Priority Data
`
`Sep: 1;.2005
`
`(IP) cmesmssascmmann 2005-254016
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`GOIB 5/20
`
`(2006.01)
`
`(57)
`
`ABSTRACT
`
`Provided are a measuring section (210) including a vibrating
`contact-type probe having a measuring force detection cir-
`cuit (219) which detects a measuring force acting to the
`contact portion (212); a moving unit (a three-dimensional
`drive mechanism (300), a vertical movement drive mecha-
`nism (220)) that moves the measuring section (210) relative
`to a workpiece surface(S); and a drive control unit (400) that
`controls the moving unit based on the magnitude of the
`measuring force output from the measuring force detection
`circuit (219). The drive control unit (400) includes: a scan-
`ning-measurement control section (410) that moves for
`scanning the contact portion along the workpiece surface(S)
`with the measuring force maintained at
`the designated
`scanning measuring force; and a touching-measurement
`control section (420) that conducts touching-measurements
`on the workpiece surface (S) in a repeated manner, in the
`measurements the contact portion (212) being adapted to
`intermittently contact the workpiece surface (S) at a touch
`detecting measuring force.
`
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`Patent Application Publication Mar. 15,2007 Sheet 6 of 12
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`US 2007/0056176 Al
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`FIG.6
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`SCANNING-MEASUREMENT
`
`TOUCHING-
`MEASUREMENT
`
`MEASURING
`FORCE
`SIGNAL
`
`TOUCH
`SIGNAL
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`7
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`

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`US 2007/0056176 Al
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`Patent Application Publication Mar. 15,2007 Sheet 7 of 12
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`Patent Application Publication Mar. 15,2007 Sheet 8 of 12
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`Patent Application Publication Mar. 15,2007 Sheet 9 of 12
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`FIG.9
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`Patent Application Publication Mar. 15,2007 Sheet 10 of 12
`
`US 2007/0056176 Al
`
`FIG.10
`
`VIBRATION \
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`
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`CIRCUIT
`
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`

`Patent Application Publication Mar. 15,2007 Sheet 11 of 12
`
`US 2007/0056176 Al
`
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`Patent Application Publication Mar. 15,2007 Sheet 12 of 12
`
`US 2007/0056176 Al
`
`FIG.12
`
`(A)
`
`(B)
`
`(0)
`
`NON-
`CONTACTING
`
`REFERENCE
`LEVEL
`
`PRESSED-IN AMOUNT[um]
`
`13
`
`13
`
`

`

`US 2007/0056176 Al
`
`Mar. 15, 2007
`
`
`
`SURFACE PROFILE MEASURING INSTRUMENT
`
`BACKGROUNDOF THE INVENTION
`
`1. Field of the Invention
`
`[0001]
`
`[0002] The present invention relates to a surface profile
`neasuring instrument.
`
`the invention relates to a surface
`[0003] For example,
`profile measuring instrument that detects a workpiece sur-
`face using a contact-type probe to measurethe profile of the
`workpiece surface.
`
`[0004]
`
`2. Description of Related Art
`
`[0005] There has been known a measuring instrumentthat
`scans the workpiece surface to measure a surface texture and
`a three-dimensional profile of the workpiece such as a
`roughness tester, a contour measuring machine, a roundness
`neasuring machine and a coordinate measuring machine.
`
`[0006] For such a measuring instrument, a probe is used as
`a displacement sensor that detects the workpiece surface
`based on small displacements of a contact portion that is in
`contact with the workpiece surface (Document: JP-A-2004-
`61322).
`
`FIG. 9 showsa profile measuring instrument 100
`[0007]
`sing a probe.
`
`[0008] The profile measuring instrument 100 includes: a
`probe 200; and a three-dimensional drive mechanism 300 as
`a movement mechanism that moves the probe 200 in the
`hree dimensions along a workpiece surface S.
`
`[0009] As shownin FIG. 10, the probe 200 is a vibrating
`contact-type probe that
`includes: a stylus 211 having a
`contact portion 212 at a tip end thereof; a stylus holder 213
`hat supports the stylus 211; a vibrator 214 provided for the
`stylus holder 213, the vibrator constantly vibrating the stylus
`211 at a natural frequencyin an axial direction of the stylus
`211; and a detector 217that detects a change inthe vibration
`of the stylus 211 to output a detection signal.
`
`
`
`
`
`[0010] The vibrator 214 includes: a piezoelectric element
`215 provided to the stylus holder 213 to vibrate the stylus
`211; and a vibration circuit 216 that applies to the piezo-
`electric element 215 an output signal (such as a pulse and a
`sinusoidal wave signal) at a predetermined frequency.
`
`[0011] The detector 217 includes: a piezoelectric element
`218 that converts the vibration of the stylus 211 to voltage;
`and a detection circuit 219 that detects the voltage from the
`piezoelectric element 218 to output a detection signal.
`
`[0012] The three-dimensional drive mechanism 300 is a
`hree-dimensional drive mechanism that includes an X, Y
`and Z direction slide mechanism generally used in coordi-
`ate measuring machines.
`
`[0013] Each of the axes of the three-dimensional drive
`nechanism 300 is provided with a linear encoder that
`detects a drive amount.
`
`In the arrangement described above, when the
`[0014]
`contact portion 212 is moved along the workpiece surface S
`as shown in FIG. 11, the detection signal changes as shown
`in FIG. 12 (D) by the positional relationship between the
`contact portion 212 and the workpiece surface S. From a
`state where the contact portion 212 is free (FIG. 12 (A)), the
`
`contact portion 212 is brought into contact with the work-
`piece surface S (FIG, 12 (B)). Whenthe contact portion 212
`contacts to the workpiece surface S at a predetermined
`measuring force (FIG. 12 (C)), the vibration of the contact
`portion 212 is suppressed,
`so that
`the detection signal
`reaches a predeterminedreferencelevel.
`
`[0015] The reference level is set in advance as a level
`obtained by subtracting from a detection signal value
`detected in the free state (the non-contacting state) of the
`contact portion 212 a change amount in signal generated
`when the contacting portion 212 is pressed at the predeter-
`mined measuring force.
`
`[0016] Note that the measuring force is a force at which
`the contact portion 212 is pressed to the workpiece surface
`S when
`the contact portion 212 is broughtinto contact with
`the workpiece surface S for detection of the workpiece
`surface S.
`
`
`
`[0017] The contact portion 212 is moved for scanning
`along the workpiece surface S while being pressed to the
`workpiece surface S such that the detection signal value is
`at the reference level. When the detection signal reaches the
`reference level, positional information of the probe 200 is
`sampled from slide amounts of the X, Y and Z axes of the
`three-dimensional drive mechanism 300. A contact point
`between the contact portion 212 and the workpiece surface
`S is calculated from the sampled position information of the
`probe 200, whereby theprofile of the workpiece surface S is
`illustrated.
`
`
`[0018] The detection signal is dampeddifferently depend-
`ing on an angle at whichthe contact portion 212 contacts the
`workpiece surface S.
`
`
`
`Specifically, since the stylus 211 is vibrated in the
`[0019]
`axial direction thereof, the vibration of the stylus 211 is
`suppressed to different extents depending on whether the
`contact portion 212 abuts on the workpiece surface S in the
`axial direction of the stylus 211 or in a direction deviated
`from the axial direction of the stylus 211.
`
`[0020] Accordingly, for the vibrating contact-type probe
`200, the reference level of the detection signalis set on the
`premisethat the contact portion 212 contacts the workpiece
`in the axial direction of the stylus 211.
`
`[0021] Hence, in the case where the contact portion 212
`contacts the workpiece surface S in the axial direction of the
`stylus 211,
`the vibrating contact-type probe 200 can be
`moved for scanning such that the detection signal becomes
`the reference level in order to scan the workpiece surface S
`at a constant measuring force.
`
`[0022] However, depending on howthe workpiece surface
`Sis slant, the contact portion 212 mayabut on the workpiece
`surface S not in the axial direction of the stylus but in a
`direction deviated from the axial direction of the stylus 211.
`
`In this case, only a force component(in the axial
`[0023]
`direction of the stylus) out of the force acting from the
`workpiece surface S to the probe 200 can exert an influence
`on the detection signal change. Accordingly,
`the contact
`portion 212 is pressed too strongly to the workpiece in
`controlling the defect signal to the reference level, so that the
`measuring force cannot be maintained constant.
`
`[0024] Thus, when the measuring force cannot be main-
`tained constant, the workpiece surface S may be damaged
`
`14
`
`14
`
`

`

`US 2007/0056176 Al
`
`Mar. 15, 2007
`
`due to the too strong pressing and the stylus 211 maybend,
`preventing an accurate detection of the workpiece surfaceS.
`Therefore, the workpiece of which workpiece surface S can
`be measured by the vibrating contact-type probe 200 has
`been limited to a workpiece having a substantially flat
`surface.
`
`SUMMARYOF THE INVENTION
`
`[0025] An object of the present invention is to provide a
`surface profile measuring instrument which measures a
`profile of a workpiece surface, the surface including a slant
`portion, by using a contact-type probe.
`
`[0026] A surface profile measuring instrument according
`to an aspect of the present invention includes: a measuring
`section includinga stylus having a contactportionto contact
`a workpiece surface at a tip end and a measuring force
`detecting unit which detects a measuring force when the
`contact portion abuts on the workpiece surface; a moving
`unit which moves the measuring section relative to the
`workpiece surface; and a drive control unit which controls
`the moving unit based on the magnitude of the measuring
`force detected by the measuring force detecting unit. The
`contact portion is brought into contact with the workpiece
`surface to measure the workpiece surface. The drive control
`nit includes: a scanning-measurement control section that
`controls the moving unit such that the moving unit conducts
`a scanning-measurement in which the measuring force is a
`preset designated scanning measuring force and the contact
`portion is moved for scanning along the workpiece surface;
`and a touching-measurement control section that controls
`he moving unit such that the moving unit repeatedly con-
`ducts touching-measurements on the workpiece surface. In
`he touching measurements, the contact portion is brought
`into and then out of contact with the workpiece surface and
`he contact portion contacts the workpiece surface at a touch
`detecting measuring force set smaller than the designated
`scanning measuring force. The measuring force detecting
`nit has a predetermined measuring force detecting direc-
`ion. The measuring force detecting unit detects the mea-
`suring force acting in the direction. When the contactportion
`contacts the workpiece surface in a direction along the
`neasuring force detecting direction, the scanning-measure-
`nent contro] section conducts the scanning-measurement.
`Whenthe contact portion contacts the workpiece surface in
`a direction deviated from the measuring force detecting
`direction,
`the touching-measurement control section con-
`ducts the touching-measurement.
`
`
`
`In the above-described arrangement, the contact
`[0027]
`portion is adapted to contact the workpiece surface bythe
`moving unit in order to measure the workpiece surface.
`Herein, the measurement is conducted while switching a
`measuring mode between the scanning-measurement
`in
`which the contact portion is moved to scan the workpiece
`surface and the touching-measurement in whichthe contact
`portion is movedto and from the workpiecesurface to detect
`the workpiece surface. Specifically, when the workpiece
`surface is substantially perpendicular to the measuring force
`detecting direction and the contact portion contacts the
`workpiece surface in the measuring force detecting direc-
`tion,
`the scanning-measurement
`is conducted. When the
`workpiece surface is deviated from a direction substantially
`perpendicular to the measuring force detecting direction and
`the contact portion contacts the workpiece surface in the
`
`direction deviated from the measuring force detecting direc-
`tion, the touching-measurement is conducted.
`
`to maintain the
`In the scanning-measurement,
`[0028]
`deformation amounts of the stylus and the workpiece con-
`stant in order to ensure the measuring accuracy, the contact
`portion needs to be moved along the workpiece surface such
`that the measuring force between the contact portion and the
`workpiece surface becomesconstant at the preset designated
`scanning measuring force.
`
`[0029] Note that the measuring force detecting unit that
`detects the measuring force between the contact portion and
`the workpiece surface can only detect the measuring force in
`a certain direction. When the contact portion abuts on the
`workpiece surface in the direction that the measuring force
`is detectable, the measuring force detecting unit can reliably
`detect the measuring force acting on the contact portion.
`Accordingly, the scanning-measurement in which the mea-
`suring force can be maintained constant at the designated
`scanning measuring force can be conducted based on the
`detected measuring force.
`
`[0030] However, when the workpiece surface has a slant
`portion, it becomes impossible to cause the contact portion
`to contact the workpiece surface in the measuring force
`detecting direction.
`
`In this case, only a force component in the mea-
`[0031]
`suring force detecting direction out of the measuring force
`generated between the workpiece surface and the contact
`portion is detectable. Accordingly,if the detected measuring
`force is adjusted to be the designated scanning measuring
`force, the contact portion is pressed too strongly into the
`workpiece surface, which prevents the scanning-measure-
`mentthat requires the constant measuring force. Up to now,
`in the case in which the direction in which the contact
`
`portion contacts the workpiece surface is deviated from the
`measuring force detecting direction, the surface profile can-
`not be measured with high accuracy,
`thereby limiting a
`measurable surface profile of the workpiece.
`
`In contrast, according to the aspect of the inven-
`[0032]
`tion, when the direction in which the contact portion con-
`tacts the workpiece surface is deviated from the measuring
`force detecting direction due to the slant portion of the
`workpiece surface, the measuring modeis switched from the
`scanning-measurementto the touching-measurement.In the
`touching-measurement, the touch detecting measuring force
`is set to be a value smaller than the designated scanning
`measuring force, so thatit is possible to detect the contact of
`the contact portion to the workpiece surface bydetecting the
`small measuring force. When the direction in which the
`contact portion contacts the workpiece surface is deviated
`from the measuring force detection force, only the force
`component in the measuring force detecting direction out of
`the total measuring force can be detected by the measuring
`force detecting unit. However,
`the touch of the contact
`portion to the workpiece surface can be detected when the
`force component reaches the touch detecting measuring
`force that is set as the small value, thereby preventing the
`contact portion from being pressed too strongly into the
`workpiece surface. In the touching-measurement, since the
`contact portion and the workpiecesurface are not abutted to
`each other too strongly, deformations of the contactportion
`and the workpiece can be quite small, so that the workpiece
`surface can be accurately detected.
`
`15
`
`15
`
`

`

`US 2007/0056176 Al
`
`[0033] As described above, the aspect of the invention
`ensures not only the scanning-measurement of the work-
`piece surface but also the touching-measurement of the
`workpiece surface including a portion immeasurable in the
`scanning-measurement with high accuracy.
`
`[0034] Note that the measuring force detecting unit may
`vibrate the stylus in the axial direction of the stylus at a
`atural frequency and may detect the measuring force based
`on the change in the vibration level generated at the time
`when the contact portion abuts on the workpiece surface. In
`his case, the measuring force detecting direction becomes
`parallel to the axial direction of the stylus. Alternatively, the
`neasuring force detecting unit may include a strain gauge
`for detecting distortion of the stylus and maydetect the
`neasuring force based onthe detected distortion amount by
`he strain gauge.In this case, the measuring force detecting
`direction becomes the direction in which the strain gauge
`detects the distortion.
`
`[0035] Accordingto an aspect ofthe invention, the surface
`profile measuring instrument may preferably further
`includes: a displacement detector which detects a displace-
`nent of the contact portion to output a displacement detec-
`ion signal. The touching-measurementcontrol section may
`preferably include a contact detecting section which outputs
`a touch detection signal when the measuring force reaches
`he touch detecting measuring force. The drive control unit
`naypreferably include: a counter which counts the displace-
`nent detection signal to calculate a position of the contact
`portion; a latch counter which receives the touch detection
`signal and latches the position of the contact portion which
`is counted by the counter; and a profile analyzing section
`which calculates a surface profile of the workpiece based on
`heposition of the contact portion calculated by the counter
`and the position of the contact portion latched by the latch
`counter.
`
`
`
`In the above-described arrangement, the displace-
`[0036]
`nent of the measuring section is detected by the displace-
`nent detector and the counter counts the displacement
`detection signal from the displacementdetector to obtain the
`actual position of the measuring section. In the touching-
`neasurement of the workpiece surface, the contact portion
`is brought from a position apart from the workpiece surface
`oward the workpiece surface into contact with the work-
`piece surface and when the measuring force detected bythe
`neasuring force detecting unit reaches the touch detecting
`neasuring force, the contact detecting section outputs the
`ouch detection signal. And, whenthe latch counterreceives
`he touch detection signal, the latch counter latches the count
`value by the counter.
`
`In such an arrangement, since the position of the
`[0037]
`contact portion at the time when the touch detecting mea-
`suring force is detected by the contact of the contact portion
`0 the workpiece surface, the surface profile of the work-
`piece can be obtained based on the latched data.
`
`in the
`[0038] According to an aspect of the invention,
`surface profile measuring instrument, the drive control unit
`naypreferably include a switching section for selecting the
`scanning-measurementcontrol section or the touching-mea-
`surement control section as the one to be operated. The
`switching section maypreferably be switched in accordance
`with a selection by a user depending on the profile of the
`workpiece surface.
`
`Mar. 15, 2007
`
`the user
`In the above-described arrangement,
`[0039]
`selects which portion of the workpiece surfaceis to receive
`the scanning-measurement and which portion thereofis to
`receive the touching-measurement by judging from the tilt
`angle and the curvature of the workpiece surface. In addi-
`tion, the user can select the measuring mode byarbitrarily
`switching the switching section. Hence, as compared with,
`for example, a case in which the profile measuring instru-
`mentis adapted to repeat the scanning-measurementand the
`touching-measurementto automatically select the most suit-
`able measuring mode, the measuring mode can beselected
`more speedily and appropriately, thereby ensuring an effec-
`tive measurement.
`
`[0040] According to an aspect of the invention, in the
`surface profile measuring instrument, the drive control unit
`may preferably include: a switching section for selecting the
`scanning-measurementcontrol section or the touching-mea-
`surement control section as the one to be operated; and a
`switching control section which controls the switching ofthe
`switching section. The switching control section may pref-
`erably switch and control the switching section based on a
`change in the measuring force detected by the measuring
`force detecting unit.
`
`[0041] Herein, the measuring force detecting unit may be
`adapted, for example,
`to vibrate the stylus in the axial
`direction thereof and to detect the measuring force between
`the contact portion and the workpiece surface in accordance
`with change in vibration level in the axial direction of the
`stylus.
`
`Inthe above-described arrangement, when the con-
`[0042]
`tact portion contacts the workpiece surface and the vibration
`of the stylus is suppressed,
`the vibration level becomes
`small. Due to the difference in the vibration, the measuring
`force acting to the contact portion from the workpiece
`surface can be detected. Note that since the stylus is vibrated
`in the axial direction thereof, when the contact portion
`contacts the workpiece surface in the axial direction of the
`stylus, the vibration of the stylus is suppressed bythe force
`acting to the contact portion from the workpiece surface.
`However, when the contact portion contacts the workpiece
`in a direction deviated from the axial direction ofthe stylus,
`only a force component in the axial direction ofthe stylus
`out of the force acting to the contact portion from the
`workpiece surface contributes the suppression of the vibra-
`tion of the stylus.
`
`[0043] Accordingly, when the contact portion contacts the
`workpiece surface in a direction deviated from the axial
`direction of the stylus,
`the measuring force between the
`contact portion and the workpiece surface cannot be accu-
`rately detected and the detected vibration level of the stylus
`becomes weak. Hence, when the contact portion contacts the
`workpiece surface in the axial direction of the stylus, where
`the measuring force can be accurately detected, the scan-
`ning-measurement can be conducted. While, when the con-
`tact portion contacts the workpiece surface in a direction
`deviated from theaxial direction of the stylus, the scanning-
`measurement cannot be conducted, so that the touching-
`measurement needsto be alternatively employed.
`
`In contrast, according to the aspect of the inven-
`[0044]
`tion, since the switching control section controls the switch-
`ing section based on the measuring force detected by the
`measuring force detecting unit, it is not necessary for the
`
`16
`
`16
`
`

`

`US 2007/0056176 Al
`
`Mar. 15, 2007
`
`user to judge and switch, which simplifies the measurement.
`Owing to the automatic switching, even when the surface
`profile cannot be measured in the scanning-measurement,
`the profile measurement can be automatically conducted in
`the touching-measurement.
`
`in the
`[0045] According to an aspect of the invention,
`surface profile measuring instrument, the drive control unit
`maypreferably include: a switching section for selecting the
`scanning-measurementcontrol section or the touching-mea-
`surement control section as the one to be operated; and a
`switching control section which controlsthe switching of the
`switching section. The switching control section may pref-
`erably switch and control the switching section based on the
`surface profile of the workpiece.
`
`deviated from the measuring force detecting direction, the
`force component in the measuring force detecting direction
`out of the force acting to the contact portion from the
`workpiece surface can be detected as the measuring force.
`Hence,if the pressing amountofthe probeis controlled such
`that the force component in the measuring force detecting
`direction becomesthe designated scanning measuringforce,
`the force acting between the contact portion and the work-
`piece surface becomeslarger than the designated scanning
`measuring force, so that
`the scanning-measurement that
`requires a constant measuring force cannot be conducted.
`
`In contrast, according to the aspect of the inven-
`[0051]
`tion, the designated scanning measuring force 1s changed in
`accordance with the angle between the workpiece surface
`and the measuring force detecting direction, so that the
`measuring force acting between the contact portion and the
`workpiece surface is maintained constant, thereby ensuring
`a scanning-measurement in which the measuring force is
`accurately maintained constant.
`
`[0052] According to an aspect of the invention and based
`on the same principle as described above,
`the touching-
`measurement control section may preferably change the
`touch detecting measuring force in accordance with the
`angle formed by the workpiece surface and the measuring
`force detecting direction.
`
`[0053] According to an aspect of the invention, the mov-
`ing unit includes: a fine feed mechanism which finely moves
`the measuring section; and a coarse feed mechanism which
`movesthe fine feed mechanism and the measuring section
`more coarsely than the fine feed mechanism.
`
`[0054] Herein, the fine feed mechanism may bepreferably
`a feed mechanism that has high response speed. For
`example, the fine feed mechanism maybe a piezoelectric
`actuator using a piezoelectric element.
`
`[0055] The coarse feed mechanism maybe an electromag-
`netic actuator.
`
`In the above-describe arrangement, since the fine
`[0056]
`feed mechanism and the coarse feed mechanism are pro-
`vided, in the scanning-measurement, the fine feed mecha-
`nism, of which response speed is high, can finely move the
`contact portion for small ridges and valleys of the workpiece
`surface, and the coarse feed mechanism, which can process
`a large change, can process a large profile change of the
`workpiece surface (such as an undulation). Hence,
`the
`contact portion can be moved for scanning along the work-
`piece surface accurately and speedily.
`
`
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows an arrangement ofa first embodiment
`[0057]
`of a surface profile measuring instrument according to the
`present invention;
`
`FIG. 2 shows change in vibration level in a scan-
`[0058]
`ning measurement according to the first embodiment;
`
`FIG. 3 shows changein vibration level and output
`[0059]
`timings of touch detection signals in a touching-measure-
`ment accordingto the first embodiment;
`
`FIG. 4 shows a process of a measurement of a
`[0060]
`workpiece surface according to the first embodiment;
`
`
`
`17
`
`[0046] Herein, controlling of the switching section based
`on the surface profile of the workpiece by the switching
`control section may be, for example, a switching between
`the scanning-measurement and the touching-measurement
`which is made based on the curvature of the workpiece
`surface andthe angle between the workpiece surface and the
`measuring force detecting direction both obtained through
`the calculation of the surface profile of the workpiece based
`on the already-measured measuring data. Alternatively, the
`curvature and thetilt angle of the workpiece surface maybe
`obtained from the design data, specifically by obtaining the
`surface profile of the workpiece from the design data of the
`workpiece.
`
`
`
`
`
`In the above-described arrangement, when the sur-
`[0047]
`face profile of the workpiece includes a large curvatureor a
`large tilt angle, it means that the contact portion contacts the
`workpiece surface in the direction deviated from the axial
`direction of the stylus. Accordingly, the measuring force
`acting between the contact portion and the workpiece sur-
`face cannot be accurately detected by the measuring force
`detection unit, so that the scanning-measurement cannot be
`conducted with the measuring force maintained constantat
`the designated scanning measuring force.
`
`
`
`In contrast, according to the aspect of the inven-
`[0048]
`tion, since the surface profile of the workpiece is analyzed
`to switch to the touching-measurement based on,
`for
`example, the curvatures or the tilt angles of the workpiece,
`it 1s not necessary for the user to judge and switch, thereby
`simplifying the measurement. Owing to the automatic
`switching, even when the surface profile cannot be measured
`in the scanning-measurement, the profile measurement can
`be automatically conducted in the touching-measurement.
`
`in the
`[0049] According to an aspect of the invention,
`surface profile measuring instrument, the scanning-measure-
`ment control section may preferably change the designated
`scanning measuring force in accordance with an angle
`formed by the workpiece surface and the measuring force
`detecting direction.
`
`the desig-
`In the above-described arrangement,
`[0050]
`nated scanning measuring force in the scanning-measure-
`ment is changed in accordance with the angle between the
`workpiece surface and the measuring force detecting direc-
`tion. For example, when the contact portion contacts the
`workpiece surface in the direction deviated from the mea-
`suring force detecting direction,
`the designated scanning
`measuring force is changed to take a smaller value. W