Abstract:
A surface texture measurement device capable of resolving errors for each entire display range, a controller for the surface texture measurement device, and a method for controlling the surface texture measurement device that includes selecting any one of the display ranges as a reference range and defining a calibration measurement value for each display range; sequentially inputting the calibration measurement values in place of the measurement values to the range amplifier corresponding to the reference range to obtain a reference display value rDATAi; inputting the calibration measurement values to the range amplifiers corresponding to each display range, then obtaining an AD-converted value ADi and a display value DATAi; computing a gain error rate ki=rDATAi/DATAi, a display resolution DIVi=DATAi/ADi, and a corrected display resolution cDIVi=DIVi×ki; and displaying the corrected display value cDIVi=DIVi×ki.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. §119 of Japanese Application No. 2012-051976, filed on Mar. 8, 2012, the disclosure of which is expressly incorporated by reference herein in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a surface texture measurement device, a controller for the surface texture measurement device, and a method for controlling the surface texture measurement device. In particular, the present invention relates to a surface texture measurement device having a plurality of display ranges and to a method for controlling the surface texture measurement device. 
         [0004]    2. Description of Related Art 
         [0005]    Conventionally, a surface texture measurement device is known in which a surface of a work piece is scanned by a stylus to measure a surface texture thereof (surface roughness, undulations, shape in outline, and the like). In the surface texture measurement device, the stylus is moved in a fixed direction (X-axis direction) and is displaced in a vertical direction (Z-axis direction) of the stylus due to unevenness in the surface of the work piece. Amplification or A/D conversion of a detection signal is performed, then the signal is displayed on a display as a function of movement distance. In addition, in a roundness measurement device, which is a type of surface texture measurement device, the stylus is in stationary contact with an outer peripheral surface of a work piece having a rotational form. By then rotating the work piece, the outline shape is detected for one rotation of the work piece. 
         [0006]    A displacement sensor used in the surface texture measurement device has a high level of sensitivity in general; however, a detection stroke (measurable range) of the displacement sensor is not large. In addition, a detection resolution is limited due to a performance of an A/D converter or due to a noise level of an amplifier, and thus the detection resolution cannot be made indefinitely larger. Thus, an amplification factor of the amplifier is switched to a plurality of levels and an appropriate selection can be made for display from a range with a high resolution and a short stroke through a range with a low resolution but a long stroke. 
         [0007]    In a surface texture measurement device  90  in  FIG. 7 , when a driver  92  moves an arm  93  in the X-axis direction with a command from a controller  91 , a stylus  94  displaces in the Z-axis direction according to unevenness in a surface of a work piece  95 . The displacement is detected by a displacement sensor  96  and is sent to the controller  91 . In the controller  91 , a detection signal from the displacement sensor  96  is amplified by a range amplifier  97 , and is then displayed on a display  98  as a graph of displacement amount corresponding to a scan position. For example, even in a case where the unevenness is unclear when the range amplifier  97  is set to a 1× range, as in a display  98 A, by setting the range amplifier  97  to a 10× range, the unevenness can be clearly identified, as in a display  98 B. 
         [0008]    As a surface texture measurement device having a plurality of display ranges as described above, Japanese Patent Laid-open Publication Nos. 2000-310529 and H05-34145 are known. In Japanese Patent Laid-open Publication No. 2000-310529, displays in a plurality of display ranges are automatically switched in response to measurement data, thus improving appropriateness and efficiency of a measurement operation. In Japanese Patent Laid-open Publication No. H05-34145, for displays in a plurality of display ranges, an offset amount for each range can be automatically controlled for measured data, thus improving appropriateness and efficiency of a measurement operation. 
         [0009]    In a surface texture measurement device, when switching between a plurality of display ranges to perform display, display errors may arise due to characteristics of a processing system for each display range or the like. Specifically, in each of the display ranges of the surface texture measurement device, one measurement value is converted to a display value with gain for each range. However, when there is an error in an amplifier for each range, there is a possibility that even when the measurement value is the same, a different display value will result for each display range. For example, at a 10 μm range, a display is 0.60 μm; however, at a 1 μm range, a display is 0.61 μm. 
         [0010]    In response to such errors between ranges, a user can resolve the errors by controlling a device for each display range. Meanwhile, when switching between display ranges is performed automatically as in Japanese Patent Laid-open Publication No. 2000-310529, when a user controls each of the switches, the benefit of automation is undermined. Thus, a technology capable of automating even error control, as in Japanese Patent Laid-open Publication No. H05-34145, is very meaningful. The errors between ranges that Japanese Patent Laid-open Publication No. H05-34145 attempts to resolve are chiefly errors in an offset amount for each range. Offset errors are representative of errors between ranges; however, it has become clear that simply resolving offset errors is insufficient for resolving errors between ranges. 
         [0011]    In  FIG. 8 , the display values are shown on the vertical axis with respect to the measurement values on the horizontal axis. The relationship between each value is basically a proportional relation having a positive slope. In conventional switching between display ranges, when the measurement value is small, a display range R 1  having a high amplification factor is used. As the measurement value becomes larger, display is performed by switching to display ranges R 2  and R 3 . Errors between ranges arise in each of the display ranges R 1  to R 3 . As mentioned previously, the offset error is representative of the error between ranges and appears in the graph of  FIG. 8  as a step between each display range. The offset error corresponds to parallel translation on the graph; however, actual errors between ranges also appear as an inclination in the graph. Accordingly, simply resolving the offset error described above stalls at a partial resolution of the error between ranges. Thus, development of a technology capable of resolving errors for each entire display range is desired. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides a surface texture measurement device, a controller for the surface texture measurement device, and a method for controlling the surface texture measurement device capable of resolving errors for each entire display range. 
         [0013]    In addition to an offset error (representative of an error between ranges), the present invention also corrects a gain error (a different representative error between ranges) and thus achieves resolution of errors for each entire display range. Specifically, in  FIG. 8 , a change in amplified gain for each display range is shown as an incline in the graph for each display range. By correcting this gain error, the present invention attempts to resolve errors in each entire display range. To this end, the present invention includes structures as indicated hereafter. 
         [0014]    The surface texture measurement device of the present invention includes a displacement sensor detecting displacement of a surface of a work piece; a display displaying measurement results; and a controller processing a detection signal from the displacement sensor and displaying the measurement results on the display. The controller includes a sensor circuit, a range amplifier circuit, an AD converter, and a digital converter. The sensor circuit processes the detection signal from the displacement sensor and outputs the detection signal as the measurement value. The range amplifier circuit includes a plurality of range amplifiers amplifying the measurement value at different amplification factors. The AD converter performs digital conversion of an analog signal amplified by the range amplifier circuit. The digital circuit processes an AD-converted value converted by the AD converter and displays the AD-converted value on the display in a plurality of display ranges corresponding to the range amplifiers. In the surface texture measurement device, the digital circuit displays a product of the AD-converted value converted by the AD converter and a corrected display resolution corresponding to the display range as a corrected display value on the display. For the corrected display resolution, any one of the display ranges is selected as a reference range and a calibration measurement value is defined for each of the display ranges. The calibration measurement values are sequentially input in place of the measurement values to the range amplifier corresponding to the reference range to obtain as a reference display value a display value displayed on the display. The calibration measurement values corresponding to each of the display ranges are input in place of the respective measurement values to the range amplifiers corresponding to each of the display ranges, then the AD-converted value and the display value displayed on the display is obtained for each of the display ranges. For each of the display ranges, the gain error rate is computed by dividing the reference display value by the display value; the display resolution is computed by dividing the display value by the AD-converted value; and the product of the display resolution and the gain error rate is recorded as the corrected display resolution. 
         [0015]    A controller of a surface texture measurement device of the present invention is provided to the surface texture measurement device including a displacement sensor detecting displacement of a surface of a work piece and a display displaying measurement results. The controller processes a detection signal from the displacement sensor and displays the measurement results on the display. The controller includes a sensor circuit, a range amplifier circuit, an AD converter, and a digital circuit. The sensor circuit processes the detection signal from the displacement sensor and outputs the detection signal as a measurement value. The range amplifier circuit includes a plurality of range amplifiers amplifying the measurement value at different amplification factors. The AD converter performs digital conversion of an analog signal amplified by the range amplifier circuit. The digital circuit processes an AD-converted value converted by the AD converter and displays the AD-converted value on the display in a plurality of display ranges corresponding to the range amplifier. In the controller, the digital circuit displays a product of the AD-converted value converted by the AD converter and a corrected display resolution corresponding to the display range as a corrected display value on the display. For the corrected display resolution, any one of the display ranges is selected as a reference range and a calibration measurement value is defined with respect to each of the display ranges. The calibration measurement values are sequentially input in place of the measurement values to the range amplifier corresponding to the reference range to obtain a display value displayed on the display as a reference display value. The calibration measurement values corresponding to each of the display ranges are input in place of the respective measurement values to the range amplifiers corresponding to each of the display ranges, then the AD-converted value and the display value displayed on the display are obtained for each of the display ranges. For each of the display ranges, a gain error rate is computed by dividing the reference display value by the display value; a display resolution is computed by dividing the display value by the AD-converted value; and a product of the display resolution and the gain error rate is recorded as the corrected display resolution. 
         [0016]    A method for controlling a surface texture measurement device controls the surface texture measurement device including a displacement sensor detecting displacement of a surface of a work piece, a display displaying measurement results, and a controller processing a detection signal from the displacement sensor and displaying the measurement results on the display. The controller includes a sensor circuit, a range amplifier circuit, an AD converter, and a digital circuit. The sensor circuit processes the detection signal from the displacement sensor and outputs the detection signal as the measurement value. The range amplifier circuit includes a plurality of range amplifiers amplifying the measurement value at different amplification factors. The AD converter performs digital conversion of an analog signal amplified by the range amplifier circuit. The digital circuit processes an AD-converted value converted by the AD converter and displays the AD-converted value on the display in a plurality of display ranges corresponding to the range amplifiers. The method for controlling the surface texture measurement device includes selecting any one of the display ranges as a reference range and defining a calibration measurement value for each of the display ranges; sequentially inputting the calibration measurement values in place of the measurement values to the range amplifier corresponding to the reference range to obtain a display value displayed on the display as a reference display value; inputting the calibration measurement values corresponding to each of the display ranges in place of the respective measurement values to the range amplifiers corresponding to each of the display ranges, then obtaining the AD-converted value and the display value displayed on the display for each of the display ranges; computing a gain error rate by dividing the reference display value by the display value, computing a display resolution by dividing the display value by the AD-converted value, and recording a product of the display resolution and the gain error rate as the corrected display resolution for each of the display ranges; and displaying as the corrected display value a product of the AD-converted value converted by the AD converter and the corrected display resolution corresponding to the display range on the display, using the digital circuit. 
         [0017]    In the present invention as described above, when displaying measurement results on the display with the controller, display with a plurality of display ranges can be performed. In addition, gain error for the range amplifier performing display in each of the display ranges can be corrected (gain error correction) and the measurement results displayed by each display range can be made accurate. Specifically, one of the plurality of display ranges is used as the reference range to compute the gain error rate between the reference range and the other display ranges. The display resolution of each display range is then controlled based on the gain error rate. Accordingly, the gain can be controlled for each display range using the reference range as a reference. As a result of this gain error correction, display at the corrected display resolution using the reference range as the reference as well as resolution of a range error for the reference range become possible in all display ranges. The gain error correction also enables resolution of errors for each entire display range. 
         [0018]    In the present invention, obtaining the AD-converted value and the display value for the range amplifier corresponding to each display range and recording the corrected display resolution for each display range can be performed sequentially for each of the display ranges. Alternatively, after the AD-converted values and the display values are obtained for all display ranges, the corrected display resolutions for all display ranges may be recorded collectively. In the present embodiment, obtaining the reference display value with the range amplifier corresponding to the reference range can be performed prior to obtaining the AD-converted value and the display value for the range amplifier corresponding to each display range, or can be performed thereafter, or in parallel. In short, the order is determined such that data required for recording the corrected display resolution for each of the display ranges is available. 
         [0019]    The surface texture measurement device of the present invention preferably includes a level shift circuit between the sensor circuit and the range amplifier circuit, the level shift circuit adding a level shift amount to the measurement value from the sensor circuit. The level shift amount is preferably designated by the offset amount for each of the display ranges, received from the digital circuit. The offset amount is preferably treated as the level shift amount at a point when the level shift amount is controlled such that the AD-converted value is equal to a predetermined value in a state where the measurement value output from the sensor circuit is a predetermined reference voltage. 
         [0020]    The controller for the surface texture measurement device of the present invention preferably includes the level shift circuit between the sensor circuit and the range amplifier circuit, the level shift circuit adding the level shift amount to the measurement value from the sensor circuit. The level shift amount is preferably designated by the offset amount for each of the display ranges, received from the digital circuit. The offset amount is preferably treated as the level shift amount at a point when the level shift amount is controlled such that the AD-converted value is equal to a predetermined value in a state where the measurement value output from the sensor circuit is a predetermined reference voltage. 
         [0021]    In the method for controlling the surface texture measurement device of the present invention, the surface texture measurement device preferably includes the level shift circuit between the sensor circuit and the range amplifier circuit, the level shift circuit adding the level shift amount to the measurement value from the sensor circuit. The level shift amount is preferably designated by the offset amount for each of the display ranges, received from the digital circuit. The method for controlling the surface texture measurement device preferably includes, in each of the display ranges, the measurement value output from the sensor circuit being a predetermined reference voltage; controlling the level shift amount such that the AD-converted value is equal to a predetermined value in such a state; and treating the level shift amount at this point as the offset amount. 
         [0022]    In the present invention as described above, offset control can be performed for circuits ranging from the range amplifier circuit to the AD converter. In particular, by defining the offset amount for each display range (i.e., for each range amplifier), when the display range is switched, the corresponding offset amount can be defined. 
         [0023]    In the present invention, 0 volts, for example, can be employed as the predetermined reference voltage and the reference voltage can be easily obtained by grounding the device. In such a case, the predetermined value of the AD-converted value may also be set to 0 (i.e., the level shift amount may be controlled such that the AD-converted value is equal to 0). This offset control is preferably performed before gain error correction in the present invention. However, the offset control may be after the gain error correction or may be performed in parallel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
           [0025]      FIG. 1  is a block diagram illustrating an embodiment of a surface texture measurement device according to the present invention; 
           [0026]      FIG. 2  is a flow chart illustrating control procedures in the embodiment; 
           [0027]      FIG. 3  is a graph illustrating information controlled in the embodiment; 
           [0028]      FIG. 4  is a graph illustrating information controlled in the embodiment; 
           [0029]      FIG. 5  is a graph illustrating information controlled in the embodiment; 
           [0030]      FIG. 6  is a graph illustrating control results in the embodiment; 
           [0031]      FIG. 7  is a frame view illustrating a schematic configuration of a conventional surface texture measurement device; and 
           [0032]      FIG. 8  is a graph illustrating measurement results in the conventional surface texture measurement device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description is taken with the drawings making apparent to those skilled in the art how the forms of the present invention may be embodied in practice. 
         [0034]    Hereafter, an embodiment of the present invention is described with reference to the drawings. In  FIG. 1 , a surface texture measurement device  10  according to the present embodiment is provided with a configuration similar to a conventional surface texture measurement device  90  (see  FIG. 7 ) described above. Specifically, as described by  FIG. 7 , in the surface texture measurement device  90 , a driver  92  moves an arm  93  in an X-axis direction. A stylus  94  is displaced in a Z-axis direction according to unevenness in a surface of a work piece  95 . This displacement is detected by a displacement sensor  96  and is then sent to a controller  91 . A detection signal from the displacement sensor  96  is amplified in the controller  91  by a range amplifier  97  and is displayed on a display  98  as a graph of displacement amount corresponding to a scan position. The surface texture measurement device  10  of the present embodiment has a similar configuration to that described above. Accordingly, in  FIG. 1  and in the following description, the same reference numerals are used for elements similar to those of  FIG. 7  and duplicative descriptions are omitted. 
         [0035]    In  FIG. 1 , the surface texture measurement device  10  of the present embodiment includes a controller  11  based on the present invention. The driver  92 , the displacement sensor  96 , and the display  98  are connected to the controller  11 . In addition, an operator  12  and a high-capacity exterior memory  13  are connected to the controller  11 . The operator  12  serves to perform operations such as operation instruction and definition and the high-capacity exterior memory  13  stores information. The controller  11  includes an analog circuit  20  and a digital circuit  30 . An AD converter  41  and a DA converter  42  are provided between the analog circuit  20  and the digital circuit  30 . The AD converter  41  performs digital conversion of an analog signal output from the analog circuit  20  and passes the signal to the digital circuit  30 . The DA converter  42  performs analog conversion of a digital signal output from the digital circuit  30  and transmits the signal to the analog circuit  20 . 
         [0036]    The analog circuit  20  includes a sensor circuit  21  performing a process to, for example, amplify a detection signal SS from the displacement sensor  96  and outputting the detection signal SS as a measurement value SA. The measurement value SA is obtained by, for example, the detection signal SS being amplified by an amplifier  211  and rectified by a synchronous rectifier  212 , after which the detection signal SS passes through a filter circuit  213 . In addition, the analog circuit  20  includes a level shift circuit  22  and a range amplifier circuit  23 . The level shift circuit  22  performs level shifting (offset control or bias control) on the measurement value SA output from the sensor circuit  21  with a predetermined level shift amount LS. The range amplifier circuit  23  includes a plurality of range amplifiers  231  to  233  amplifying the level-shifted measurement value SA at different amplification factors. Moreover, the analog circuit  20  includes a drive control circuit  24  controlling the driver  92  based on an operation command from the digital circuit  30 . 
         [0037]    In order to perform display in a plurality n of display ranges Ri (i=1 to n), the range amplifier circuit  23  includes n range amplifiers. In the present embodiment, n=3 and three range amplifiers  231  to  233  are provided to correspond to display ranges R 1  to R 3 . A range amplifier corresponding to each display range Ri (i=1 to n) has an amplification factor of βi. In the present embodiment, the amplification factors of the range amplifiers  231  to  233  corresponding to the display ranges R 1  to R 3  are β 1  to β 3 , respectively. Moreover, when an output from the range amplifier for each display range Ri is an amplified measurement value AAi, the amplification factor βi of each range amplifier Ri equals the amplified measurement value AA divided by the sum of the measurement value SA and the level shift amount LS. The amplified measurement value AAi undergoes digital conversion by the AD converter  41  and is passed to the digital circuit  30  as an AD-converted value ADi. In the present embodiment, the amplified measurement values AA 1  to AA 3  for each of the display ranges R 1  to R 3  are passed to the digital circuit  30  as AD-converted values AD 1  to AD 3 . 
         [0038]    The digital circuit  30  includes a CPU  31  using a microprocessor or the like. The CPU  31  is connected to the display  98 , the operator  12 , and the exterior memory  13  via an input/output interface (I/O)  32 . A non-volatile memory  33  such as a flash ROM can be connected to the CPU  31  and can appropriately store data used in processing. The CPU  31  operates using an operation program written to a program area not shown in the drawings and performs the following operation. 
         [0039]    The operation command is output based on the operation program. This command is transmitted to the drive control circuit  24  via the DA converter  42  and causes the driver  92  to execute a designated measurement. Thereby, the surface texture of the work piece  95  is detected by the displacement sensor  96  and is transmitted to the sensor circuit  21  as the detection signal SS. The AD-converted value ADi is passed from the range amplifier circuit  23  in the analog circuit  20  through the AD converter  41 . The AD-converted value ADi then undergoes a predetermined process and a graph of the measurement results (graph of an X-axis movement position and a Z-axis displacement) is displayed on the display  98  with any of the display ranges Ri. At this point, when a display value DATA for a length of the graph on a screen is the measurement result for the AD-converted value ADi in the graph displayed on a display screen of the display  98 , a display resolution DIVi for the display range Ri on the display  98  is in a relationship where the display value DATA=ADi×DIVi. 
         [0040]    In the surface texture measurement device such as that in the present embodiment, as described previously, an error in the amplification factor βi of the range amplifier for each display range Ri, for example, affects the AD-converted value ADi. As a result, the error between ranges is reflected in the display value DATA displayed on the display  98 , as well. In order to resolve such errors between ranges, a control procedure based on the present invention is performed before the measurement operation. 
         [0041]    In  FIG. 2 , the control procedure based on the present invention includes an offset control stage P 1 , a gain error correction stage P 2 , and a test display stage P 3 . The offset control stage P 1  is not necessary for the present invention, but is preferably executed in order to improve control results. The gain error correction stage P 2  is a necessary procedure based on the present invention. The test display stage P 3  is a procedure used when verification of results is desired, and may be omitted as appropriate.  FIG. 2  is generalized using n number of display ranges. However, as described previously, in the present embodiment, n=3 (i.e., the number of display ranges i=1 to 3) in order to apply the configuration of  FIG. 1 . 
         [0042]    In the offset control stage P 1 , steps P 11  and P 12  are executed. In the step P 11 , a reference voltage of 0 V is input to the level shift circuit  22  for each display range Ri (i=1 to n) as a calibration measurement value SAi in order to control the level shift amount LS where the AD-converted value ADi=0.In the step P 12 , the controlled level shift amount LS is recorded as an offset amount ADofsi in each display range Ri. 
         [0043]    Specifically, first, the range amplifier  231  for the display range R 1  is selected and the reference voltage of 0 V is input to the level shift circuit  22  as the calibration measurement value SA 1  in order to control the level shift amount LS where the AD-converted value AD 1 =0. When the control is complete, the level shift amount LS is recorded as the offset amount ADofs 1  for the display range R 1 . Next, the range amplifier  232  for the display range R 2  is selected and the level shift amount LS is similarly recorded as an offset amount ADofs 2 , then an offset amount ADofs 3  is recorded for the display range R 3 . 
         [0044]    For example, in  FIG. 3 , with respect to a range input (the calibration measurement value SA 1  input to the level shift circuit  22 ), a range output for each display range R 1  to R 3  (amplified measurement results AA 1  to AA 3 , which are outputs of the range amplifiers  231  to  233 ) form respective straight lines having positive slope. When the range input for each of the display ranges R 1  to R 3  is 0, the range output for the display range R 1  is 0. However, the range outputs for the display ranges R 2  and R 3  are not 0. For the display ranges R 2  and R 3 , the range outputs can be made 0 by adding the level shift amount LS. This level shift amount LS is recorded as the offset amounts ADofs 2  and ADofs 3 . 
         [0045]    The offset amount ADofsi (i=1 to 3) obtained in this way is an offset amount for aligning outputs when each input is the same. By level shifting the actual measurement value SAi with this offset amount, correction of the offset error between each of the display ranges 1 to 3 can be performed. 
         [0046]    In the gain error correction stage P 2 , steps  21  through  24  are executed. In the step P 21 , any one of the display ranges Ri (i=1 to n) is selected as a reference range Rr. Then the calibration measurement value SAi is defined for each of the display ranges Ri (i=1 to n). At this point, the calibration measurement value SAi is preferably defined as a value close to the greatest range value for a range having the greatest amplification factor among each of the display ranges Ri and the reference range Rr. 
         [0047]    For example, in  FIG. 4 , the display range R 2  is selected as the reference range. The calibration measurement value SAi for the display range R 1  is defined with respect to the display range R 2 , which is the reference range. In such a case, when the calibration measurement value SA 1  is used as the range input (input to the level shift circuit  22 ), the AD-converted value of the range output for the display range R 1  (i.e., the amplified measurement value AA 1 , which is the output of the range amplifier  231 ) is the AD-converted value AD 1  and the AD-converted value of the range output for the display range R 2  (i.e., the amplified measurement AA 2 , which is the output of the range amplifier  232 ) is the AD-converted value AD 2 . In such a case, an incline of the graph for the display range R 1  (amplification factor β 1 ) is greater than the incline of the graph for the display range R 2  (amplification factor β 2 ). Therefore, the calibration measurement value SA 1  may be selected that gives the AD-converted value AD 1  close to the greatest range value for the display range R 1 . 
         [0048]    Meanwhile, in  FIG. 5 , the calibration measurement value SA 3  for the display range R 3  is defined with respect to the display range R 2  (the reference range). In such a case, similarly, the AD-converted value of the range output for the display range R 2  (i.e., the amplified measurement value AA 2 , which is the output of the range amplifier  232 ) is the AD-converted value AD 2  and the AD-converted value of the range output for the display range R 3  (i.e., the amplified measurement AA 3 , which is the output of the range amplifier  233 ) is the AD-converted value AD 3 . In such a case, the incline of the graph for the display range R 2  (amplification factor β 2 ) is greater than the incline of the graph for the display range R 3  (amplification factor β 3 ). Therefore, the calibration measurement value SA 3  may be selected that gives the AD-converted value AD 2  close to the greatest range value for the display range R 2 . 
         [0049]    In the step P 22 , the reference range Rr (i.e., the range amplifier corresponding to the reference range Rr) is selected. Then, with the reference range RR selected, the calibration measurement value SAi (i=1 to n) is sequentially input to the level shift circuit  22 . Then, a reference display value rDATAi (i=1 to n) is obtained from the length of the graph in a displayed image on the display  98 . The obtained reference display value rDATAi (i=1 to n) is obtained by inputting each of the calibration measurement values SAi (i=1 to n) to the range amplifier corresponding to the reference range Rr (shared reference range amplifier). The obtained reference display value rDATAi (i=1 to n) reflects characteristics of the reference range Rr with respect to each of the calibration measurement values SAi (i=1 to n). 
         [0050]    In the step P 23 , each calibration measurement value SAi for each of the display ranges Ri (i=1 to n) is input to the level shift circuit  22  and the AD-converted value ADi output for the calibration measurement value SAi is obtained. In addition, the display value DATAi is obtained from the length of the graph in the displayed image on the display  98 . The obtained AD-converted value ADi and display value DATAi reflect the characteristics of the range amplifier corresponding to each of the display ranges Ri (i=1 to n) with respect to each of the calibration measurement values SAi. 
         [0051]    In the step P 24 , each of the following values is computed for each of the display ranges Ri (i=1 to n). A gain error rate ki is found by ki=rDATAi/DATAi. The gain error rate ki is a ratio of the reference display value rDATAi (after amplifying the same calibration measurement value SAi in the range amplifier for the reference range Rr) and the display value DATAi (after amplifying the same calibration measurement value SAi in the range amplifier for each of the display ranges Ri). The effect of an error between ranges for each of the display ranges Ri that include the amplification factor fix is bundled and can be measured as a ratio with respect to the reference range Rr. 
         [0052]    The display resolution DIVi is a display resolution for the display range Ri displayed on the display  98  and is computed by DIVi=DATAi/(ADi−ADofsi). At this point, the display value DATAi still includes errors between ranges for each of the display ranges Ri and the display resolution DIVi also includes errors between ranges. A corrected display resolution cDIVi is found by cDIVi=DIVi×ki. As previously described, the display resolution DIVi includes errors between ranges; however, the effect of errors between ranges in each of the display ranges Ri is bundled and corrected by the gain error rate ki, which is measured as a ratio with respect to the reference range Rr. Thereby, the errors between ranges can be resolved in the corrected display resolution cDIVi. 
         [0053]    In the test display stage P 3 , as in a step P 31 , the actual measurement value SA is input for each of the display ranges Ri (i=1 to n), then a corrected display value cDATAi=(ADi−ADofsi)×cDIVi is displayed. In the present embodiment, by using the corrected display resolution cDIVi to perform calculations with the AD-converted value ADi and the offset amount ADofsi and to display on the display  98 , the corrected display value cDATAi=(ADi−ADofsi)×cDIVi that does not include the errors between ranges can be obtained. In addition, by performing display using the corrected display value cDATAi, the errors between ranges can be resolved between each of the display ranges Ri (i=1 to n) on the display  98 . 
         [0054]    The gain error correction stage P 2  (steps P 21  through P 24 ) was described using a specific example of the present embodiment, which includes three display ranges R 1  to R 3 . First, based on the step P 21 , the middle display range R 2  was selected as the reference range from among the display ranges R 1  to R 3 . Then, as shown in the specific example of  FIGS. 4  and  5  above, the calibration measurement values SA 1  and SA 3  are defined for the display ranges R 1  and R 3 , which are not the reference range. Next, based on the step P 22 , in a state where the display range R 2  (the reference range) is selected, the calibration measurement value SA 1  is input to measure the reference display value rDATA 1  and the calibration measurement value SA 3  is input to measure the reference display value rDATA 3 . 
         [0055]    Then, based on the step P 23 , in a state where the display range R 1  (a display range other than the reference range) is selected, the calibration measurement value SA 1  is input to measure the AD-converted value AD 1  and the display value DATA 1 . Similarly, in a state where the display range R 3  is selected, the calibration measurement value SA 3  is input to measure the AD-converted value AD 3  and the display value DATA 3 . Moreover, based on the step P 24 , the gain error rates k1 and k3,the display resolutions DIV 1  and DIV 3 , and the corrected display resolutions cDIV 1  and cDIV 3  are computed for the display ranges R 1  and R 3 , which are not the reference range. 
         [0000]        k 1 =r DATA1/DATA1 
         [0000]        k 3 =r DATA3/DATA3 
         [0000]      DIV1=DATA1/( AD 1 −ADofs 1) 
         [0000]      DIV3=DATA3/( AD 3 −ADofs 3) 
         [0000]        c DIV1=DIV1 ×k 1 
         [0000]        c DIV3=DIV3 ×k 3 
         [0056]    Moreover, because the display range R 2  (the reference range) is itself the reference, the gain error rate k2=rDATA 2 /DATA 2 =1 and the corrected display resolution cDIV 2 =DIV 2 ×1=DATA 2 /(AD 2 −ADofs 2 ). 
         [0057]    Following these calculations, the errors between ranges for the display ranges  1  to  3  can be resolved by using the corrected display values cDATAi to perform the display. 
         [0000]        c DATA1=( AD 1 −ADofs 1)× c DIV1
 
         [0000]        c DATA2=( AD 2 −ADofs 2)× c DIV2
 
         [0000]        c DATA3=( AD 3 −ADofs 3)× c DIV3
 
         [0058]    By performing display employing these corrected display values cDATAi, the gain error in the incline can be resolved with the corrected display resolution cDIVi and correction using the ADofsi can be performed on the offset error. Thereby, according to the surface texture measurement device  10  of the present embodiment, as shown in  FIG. 6 , a smooth, continuous graph can be obtained between each of the display ranges R 1  to R 3  and the errors between ranges arising from switching between the display ranges R 1  to R 3  can be resolved. 
         [0059]    Moreover, the present invention is not limited to the embodiment described above, but may include modifications within a scope not departing from the object of the present invention. In the above-described embodiment, three display ranges R 1  to R 3  are used and the middle display range R 2  is used as the reference range Rr. However, the display range R 1  may also be used as the reference range, for example, and gain error rates k2 and k3 may be computed for the other display ranges R 2  and R 3 . In the present embodiment, three display ranges Ri were used, but four or more may also be used. 
         [0060]    In the above-described embodiment, in order to correct the offset error as well, the offset amount ADofsi is computed in the offset control stage P 1 . By taking the offset amount ADofsi into account in the gain error correction stage P 2 , the resolution DIVi is calculated by DIVi=DATAi/(ADi−ADofsi). In addition, the corrected display value cDATAi=(ADi−ADofsi)×cDIVi is used for display. However, the computation of the offset error may be omitted. In such a case, the resolution DIVi=DATAi/ADi may be computed in the gain error correction stage P 2  and the corrected display value cDATAi=ADi*cDIVi may be displayed. Other configurations in the surface texture measurement device  10 , such as the configurations of the analog circuit  20 , the digital circuit  30 , or the driver  92 , the displacement sensor  96 , and the display  98  which are connected to the controller  11  may be modified as appropriate. 
         [0061]    It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular structures, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. 
         [0062]    The present invention is not limited to the above described embodiments, and various variations and modifications may be possible without departing from the scope of the present invention.