Patent Publication Number: US-2019176157-A1

Title: Measurement apparatus and sample holder used in the same

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present technique relates to a measurement apparatus configured to measure a sample held by a sample holder and the sample holder used in the measurement apparatus. 
     Description of the Background Art 
     For conducting an X-ray analysis or a measurement/an inspection by an optical system, a sample held by a sample holder for a measurement apparatus is measured and inspected. There are proposals of sample holders each configured to be capable of holding samples having various shapes. For example, Japanese Patent Laying-Open No. 2010-249760 proposes a sample holder including a circular block-shaped member provided with a holding recess portion formed in a V-shaped groove so as to be capable of reliably and stably holding a columnar sample, a cylindrical sample and a spherical sample. 
     Furthermore, Japanese Patent Laying-Open No. 2001-289753 proposes a sample holder including a substrate provided with an aperture changing mechanism, a sample holding mechanism and the like, in which the aperture changing mechanism is caused to pivot such that variously-sized samples can be moved to the measurement center position. 
     SUMMARY OF THE INVENTION 
     The sample holder disclosed in PTD 1 can hold only one sample. Accordingly, in order to measure one sample and thereafter measure another sample, it is necessary to perform the operation of exchanging the held sample. Specifically, when a sample is measured using the sample holder disclosed in PTD 1, it is necessary to repeatedly perform the operation of holding one sample with the sample holder and measuring the held sample, then removing the sample from the sample holder after the measurement, and then, again holding another sample with the sample holder and measuring the held another sample. 
     Furthermore, the sample holder disclosed in PTD 1 requires a sample to be held in a holding recess portion formed in a V-shaped groove, which requires the sample to be held at any one position in the direction along the V-shaped groove. Accordingly, depending on the size of the sample, it is necessary to perform the operation of determining the position of the sample such that the sample is held at the center position of the sample holder. 
     Furthermore, the sample holder disclosed in PTD 2 requires the operation of adjusting the aperture changing mechanism according to the size of the sample to be held by the sample holding mechanism. Also, the sample holder disclosed in PTD 2 requires the operation of, each time a sample having a different shape is held, adjusting the aperture changing mechanism such that the sample is located at the measurement center position. 
     The present technique aims to provide: a sample holder that can reduce the operations of holding and removing a sample during measurement of a plurality of samples to thereby facilitate alignment of the held sample; and a measurement apparatus configured to use the sample holder. 
     A measurement apparatus according to an aspect of the present invention is configured to measure a sample. The measurement apparatus includes: a sample holder on which a plurality of samples can be placed; a measurement unit configured to measure the plurality of samples placed on the sample holder; and a control unit configured to control a position of the measurement unit relative to a sample to be measured. The sample holder includes a substrate, and a holding unit configured to hold a sample. The substrate is provided with a plurality of holding units. The holding unit is configured to hold each of a plurality of samples having different shapes at a center position of the holding unit. 
     A sample holder according to another aspect of the present invention is used in a measurement apparatus configured to measure a sample. The sample holder includes: a substrate; and a holding unit configured to hold a sample. The substrate is provided with a plurality of holding units. The holding unit is configured to hold each of a plurality of samples having different shapes at a center position of the holding unit. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic diagram showing the configuration of a sample holder according to the present embodiment. 
         FIG. 1B  is a schematic diagram showing the configuration of the sample holder according to the present embodiment. 
         FIG. 2  is a schematic diagram showing the apparatus configuration of a measurement apparatus according to the present embodiment. 
         FIG. 3A  is a schematic diagram showing a sample holder on which a tablet is placed. 
         FIG. 3B  is a schematic diagram showing the sample holder on which a tablet is placed. 
         FIG. 4  is a flowchart for the measurement apparatus according to the present embodiment. 
         FIG. 5A  is a schematic diagram for illustrating the distance between measurement points. 
         FIG. 5B  is a schematic diagram for illustrating the distance between measurement points. 
         FIG. 5C  is a schematic diagram for illustrating the distance between measurement points. 
         FIG. 5D  is a schematic diagram for illustrating the distance between measurement points. 
         FIG. 6  is a schematic diagram showing a display example of measurement results. 
         FIG. 7  is a schematic diagram of an example showing different arrangement patterns of measurement points. 
         FIG. 8A  is a schematic diagram showing a sample holder formed of a circular substrate. 
         FIG. 8B  is a schematic diagram showing the sample holder formed of a circular substrate. 
         FIG. 9A  is a schematic diagram showing a sample holder formed of a circular substrate. 
         FIG. 9B  is a schematic diagram showing the sample holder formed of a circular substrate. 
         FIG. 10A  is a schematic diagram showing a sample holder including a different number of holding units. 
         FIG. 10B  is a schematic diagram showing the sample holder including a different number of holding units. 
         FIG. 10C  is a schematic diagram showing a sample holder including a different number of holding units. 
         FIG. 10D  is a schematic diagram showing the sample holder including a different number of holding units. 
         FIG. 10E  is a schematic diagram showing a sample holder including a different number of holding units. 
         FIG. 10F  is a schematic diagram showing the sample holder including a different number of holding units. 
         FIG. 11  is a schematic diagram of a sample holder including a holding unit configured to hold a sample by a movable pawl portion. 
         FIG. 12A  is a schematic diagram of a sample holder including a holding unit configured to hold a sample with a plurality of holding pins. 
         FIG. 12B  is a schematic diagram of the sample holder including the holding unit configured to hold a sample with a plurality of holding pins. 
         FIG. 13A  is a schematic diagram of a holding unit configured to hold a sample with a holding pin. 
         FIG. 13B  is a schematic diagram of a holding unit configured to hold a sample with a holding pin. 
         FIG. 13C  is a schematic diagram of a holding unit configured to hold a sample with a holding pin. 
         FIG. 13D  is a schematic diagram of a holding unit configured to hold a sample with a holding pin. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will be hereinafter described in detail with reference to the accompanying drawings, in which the same or corresponding components are designated by the same reference characters, and description thereof will not be repeated. 
     &lt;A. Sample Holder&gt; 
     A measurement apparatus according to the present embodiment employs the structure capable of measuring a plurality of samples having different shapes (hereinafter also referred to as a sample) placed on a sample holder.  FIGS. 1A and 1B  each are a schematic diagram showing the configuration of a sample holder  10  according to the present embodiment.  FIG. 1A  is a plan view of sample holder  10 .  FIG. 1B  is a cross-sectional view of sample holder  10  taken along an I-I plane. Sample holder  10  includes a substrate  1  and a holding unit  2  configured to hold a sample. Substrate  1  is provided with a plurality of holding units  2 . 
     Substrate  1  is formed of a rectangular flat plate and made of aluminum, for example. Substrate  1  may be formed of other materials such as metal (stainless steel and the like) other than aluminum, resin materials (plastic and the like), and a glass material. Substrate  1  is provided with a total of nine holding units  2  including: three holding units arranged in the lateral direction in  FIG. 1A ; and three holding units arranged in the longitudinal direction in  FIG. 1A . It is to be noted that the number and the size of holding unit  2  provided in substrate  1  are not limited to those shown in  FIGS. 1A and 1B . Although a plurality of holding units  2  are arranged in a lattice shape on substrate  1 , arrangement of holding units  2  is also not limited to those shown in FIGS.  1 A and  1 B. Sample holder  10  may be formed of a combination of a plurality of types of materials such as metal for substrate  1  and a resin material for the surface of holding unit  2  that comes into contact with a sample. 
     Holding unit  2  is formed as a recess portion having a truncated conical shape as shown in  FIG. 1B  and structured to hold a sample in the state where a part of the sample is in contact with the inside of the recess portion. In other words, holding unit  2  is formed in a grinding bowl shape so as to have a surface inclined from outside toward its center. Accordingly, various sizes and shapes of samples can be held by holding unit  2  since each of these various samples can partially come into contact with the inside of holding unit  2  at any one position. The inside shape of holding unit  2  is not limited to the shape having a surface continuously inclined from outside toward the center, but may be a shape inclined in a step-like pattern from outside toward the center. In other words, holding unit  2  may have an inner surface formed in a step-like pattern as long as holding unit  2  is entirely formed in a truncated conical shape. Furthermore, holding unit  2  does not need to be formed in a complete truncated conical shape, but may have an outer surface and a center portion that are formed perpendicular to the surface of substrate  1  for ease of processing and the like. Furthermore, the inclination of the surface of holding unit  2  from outside toward the center is not limited to the inclination shown in  FIG. 1B . 
     Holding unit  2  has a center portion formed as a bottom (the underside of  FIG. 1B ) that has a hole  3  penetrating through sample holder  10 . Hole  3  is formed in a circle that is concentric with the outer shape of holding unit  2 . The shape of hole  3  is not limited to a circle but may be other shapes. Hole  3  provided in holding unit  2  prevents dust from accumulating on the bottom of holding unit  2 . Thus, holding unit  2  exhibits excellent drainage also when sample holder  10  is washed with water. 
     Holding unit  2  does not need to have hole  3  at its bottom, but may have a recess portion having a truncated conical shape with a closed bottom. Furthermore, when holding unit  2  is not provided with hole  3  at its bottom, holding unit  2  does not have to have a flat bottom but may be formed as a recess portion having a conical shape. 
     Representative examples of the sample may be a tablet, a small-sized optical component such as a lens and a concave mirror, and the like. More specifically, a tablet may be formed in a circular shape, a triangular shape, a quadrangular shape, an elliptical shape, a rugby-ball shape, a hexagonal shape, an octagonal shape, and the like, and may be a hard capsule and the like. 
     &lt;B. Measurement Apparatus&gt; 
     In the following description, a measurement apparatus configured to measure a sample placed on sample holder  10  is a confocal microscope, for example.  FIG. 2  is a schematic diagram showing the apparatus configuration of a measurement apparatus  100  according to the present embodiment. As shown in  FIG. 2 , in measurement apparatus  100 , light emitted from lamp  20  formed as a point light source by a pinhole  30  is applied to a sample placed on sample holder  10 . In measurement apparatus  100 , when pinhole  40  is located at the position that is optically conjugate with the focal plane (confocal plane), the light returned from the focal plane reaches a detector  60 . The focal plane shown in  FIG. 2  coincides with the surface of the sample placed on sample holder  10 . Thus, the light returned from the sample reaches detector  60 , but most of the light returned from a non-focal plane  11  and displaced from the surface of the sample does not reach detector  60  (the confocal effect). By means of this effect referred to as a confocal effect, measurement apparatus  100  as a confocal microscope can achieve a high-resolution and high-contrast microscopic image. 
     As a configuration for applying light emitted from lamp  20  onto a sample, measurement apparatus  100  includes a pinhole  30 , a collimator lens  31 , a beam splitter  32 , and an objective lens  33 . Furthermore, as a configuration for detecting the light from the sample, measurement apparatus  100  includes objective lens  33 , beam splitter  32 , a condenser lens  41 , and pinhole  40 . 
     Lamp  20  is a light source configured to emit light by it self, for example, and may be a laser that outputs light having a single wavelength, a light-emitting diode (LED) that outputs light having a wide wavelength width, an incandescent lamp, or the like. Furthermore, by using a laser that outputs light having a single wavelength as lamp  20 , measurement apparatus  100  can be configured as a confocal laser scanning microscopy (CLS) that allows a fluorescent observation in a sample plane. 
     Detector  60  is an optical sensor capable of detecting the light such as ultraviolet light, visible light and infrared light from a sample, a spectrophotometer configured to output a wavelength spectrum contained in the light from a sample, or the like. More specifically, the optical sensor is formed of a photomultiplier tube, a photodiode, a charged coupled device (CCD) sensor, a complementary metal oxide semiconductor (CMOS) sensor, or the like. Furthermore, the spectrophotometer includes a diffraction grating for separating the incident light into wavelength components, and a detection element for detecting each of the wavelength components separated by the diffraction grating (a photomultiplier tube, a photodiode, a photodiode array, a CCD or the like). 
     In addition, lamp  20 , pinholes  30  and  40 , collimator lens  31 , beam splitter  32 , objective lens  33 , condenser lens  41 , and detector  60  constitute a measurement unit for measuring a sample placed on the sample holder. 
     By performing various kinds of numerical analysis processes (representatively, a fitting process and a noise removing process) based on the detection results (detected values, wavelength spectra, and the like) obtained from detector  60 , an information processing apparatus  50  can identify the substance contained in the sample. Also, information processing apparatus  50  can calculate the size and the shape of the sample based on the position information of sample holder  10  obtained from a position controller  52 . 
     Based on the control information from information processing apparatus  50 , position controller  52  adjusts the position of sample holder  10  relative to objective lens  33 , and outputs the position information of sample holder  10  to information processing apparatus  50 . In other words, position controller  52  supplies a position instruction to a drive mechanism  54  based on the control information from information processing apparatus  50 . Drive mechanism  54  can move sample holder  10  in the direction parallel to the surface on which the sample is placed and in the direction perpendicular to this parallel direction. Thus, drive mechanism  54  can move the measurement point on sample holder  10  for detector  60  and also can change the focal position (image formation position) of objective lens  33  relative to sample holder  10 . 
     In measurement apparatus  100 , information processing apparatus  50 , position controller  52  and drive mechanism  54  constitute a control unit for controlling the position of the measurement unit relative to the sample to be measured. 
     Measurement apparatus  100  as a confocal microscope can measure various objects by using variously changed combinations of lamp  20  and detector  60 . For example, when lamp  20  is used as a laser configured to output light having a single wavelength and measurement apparatus  100  is used as a confocal laser scanning microscope, the light from lamp  20  is scanned in the XYZ direction of the sample, so that the surface shape of the sample can be measured. Furthermore, when the sample having a fluorescent marker added thereto is measured, measurement apparatus  100  can measure distribution of the fluorescent marker in the sample. 
     Furthermore, when detector  60  is used as a spectrophotometer and measurement apparatus  100  is used as a confocal spectral reflectance measuring microscope, the spectral reflection spectrum only at the focal position can be measured, so that the spectral reflectance on the surface of the sample can be measured. Based on the detected reflection spectrum, the confocal spectral reflectance measuring microscope allows measurements such as calculation of the film thickness of the thin film sample applied onto the sample surface, identification of substance, and the like. 
     Furthermore, when lamp  20  is used as an infrared light source and detector  60  is used as a spectrophotometer allowing spectral detection of infrared light so as to be used as a confocal infrared spectrometric microscope, the light from lamp  20  is scanned in the XYZ direction of the sample to detect the infrared spectrum, so that the substance in the sample at each measurement point can be identified, thereby obtaining a distribution of the substance in the sample. 
     Furthermore, when detector  60  is used as a spectrophotometer and lamp  20  is configured to output light having a single wavelength by using a combination of a laser or a incandescent lamp that outputs light having a single wavelength and a spectroscope so as to be used as a confocal fluorescence spectrometric microscope, the fluorescence spectrum of the sample is measured to compare the measured fluorescence spectrum with the fluorescence spectrum specific to the substance, so that the substance contained in the sample can be identified. 
     Furthermore, when detector  60  is used as a spectrophotometer and lamp  20  is used as a laser configured to output light having a single wavelength so as to be used as a confocal laser Raman microscope, the Raman scattering light from the sample can be measured. The confocal laser Raman microscope is configured to compare the Raman spectrum of the sample with the Raman spectrum specific to the substance, so that the substance contained in the sample can be identified. 
     Measurement apparatus  100  is not limited to the confocal microscopes as described above but may be: a microspectroscopic apparatus configured to measure the spectral reflectance and the spectral transmittance of a sample using illumination light as a light source; a microscopic FTIR employing the Fourier conversion scheme (an infrared microscope); an FT Raman microscope; a three-dimensional (3D) shape measuring apparatus; a light interference microscope; a digital holographic microscope (DHM); and the like. 
     &lt;C. Measuring Method&gt; 
     The following is an explanation about a method of measuring a sample by measurement apparatus  100 . In measurement apparatus  100 , detector  60  can be switched between the optical sensor and the spectrophotometer. Also, in measurement apparatus  100 , when lamp  20  is used as a laser configured to output light having a single wavelength, detector  60  is uses as an optical sensor to measure the shape of the sample by utilizing a confocal point, and detector  60  is also used as a spectrophotometer so as to be employed as a confocal laser Raman microscope, the component (substance) contained in the sample can be measured, which will be specifically described below. 
     First, a tablet (sample) as an object to be measured is placed on sample holder  10 .  FIGS. 3A and 3B  each are a schematic diagram showing sample holder  10  on which a tablet is placed.  FIG. 3A  shows a plan view of sample holder  10 .  FIG. 3B  shows a cross-sectional view of sample holder  10  taken along an I-I plane. 
     In sample holder  10  shown in each of  FIGS. 3A and 3B , an alignment mark  4  is provided on substrate  1 . Thus, when sample holder  10  is placed on measurement apparatus  100  in the state where alignment mark  4  is located at the upper left in the figure, holding units  2  are arranged in the A column, the B column and the C column from the left, and also arranged in the first row, the second row and the third row from the top. In other words, holding unit  2  at the upper left in sample holder  10  can be identified as holding unit  2  at A 1 , and holding unit  2  in the center can be identified as holding unit  2  at B 2 . The alignment of the sample holder does not have to be set based on an alignment mark. For example, sample holder  10  may be aligned in the following manner. Specifically, sample holder  10  is placed such that a pin placed upright on the measurement apparatus at the position of the sample holder to be located is inserted into a hole provided at the position of alignment mark  4  on sample holder  10  (pin alignment). 
     In sample holder  10 , for example, a tablet  5   a  having a diameter of 18 mm is held in holding unit  2  in the A column, a tablet  5   b  having a diameter of 5 mm is held in holding unit  2  in the B column, and a tablet  5   c  having a diameter of 10 mm is held in holding unit  2  in the C column. In other words, three types of different tablets  5   a  to  5   c  can be placed on sample holder  10 . Accordingly, by using the above-mentioned sample holder  10  in measurement apparatus  100 , measurement apparatus  100  can measure three types of different tablets without having to perform the operations of holding/removing a sample. 
     Furthermore, sample holder  10  includes holding unit  2  formed in a truncated conical shape. Accordingly, even when tablets  5   a  to  5   c  have different diameters, each of these tablets  5   a  to  5   c  can partially come into contact with the inside of a corresponding one of holding units  2  at any position, so that tablets  5   a  to  5   c  can be reliably held in holding units  2 . As shown in  FIG. 3B , tablet  5   a  having a larger diameter is held in contact with holding unit  2  at a position farther away from the center position of holding unit  2  while tablet  5   b  having a smaller diameter is held in contact with holding unit  2  at a position closer to the center position of holding unit  2 . Tablet  5   c  that is larger in diameter than tablet  5   b  is held in contact with holding unit  2  at a position farther away from the center position of holding unit  2  as compared with tablet  5   b.    
     Also as shown in  FIG. 3A , the center position of holding unit  2  (the vertex of the truncated cone) coincides with the center position of each of tablets  5   a  to  5   c  held in a corresponding one of holding units  2 . Specifically, even when tablet  5   a  has a larger diameter and tablet  5   b  has a smaller diameter, the center position of holding unit  2  similarly coincides with the center position of each of tablets  5   a  and  5   b  held in their respective holding units  2 . Thus, without having to measure and calculate the center position of each tablet, measurement apparatus  100  can set the predetermined center position of each holding unit  2  as the center position of the tablet held in each holding unit  2 . By setting sample holder  10  in the state where alignment mark  4  is positioned in alignment, measurement apparatus  100  can measure the center position of holding unit  2  as the center position of each of tablets  5   a  to  5   c , so that the position of each tablet can be readily aligned. 
     The following is an explanation about the flowchart in the case where the sample placed on sample holder  10  is measured with measurement apparatus  100 .  FIG. 4  is a flowchart for measurement apparatus  100  according to the present embodiment. The flowchart shown in  FIG. 4  will be described below with reference to an example of the configuration in which tablets  5   a  to  5   c  are placed on sample holder  10  shown in each of  FIGS. 3A and 3B . Furthermore, in measurement apparatus  100 , information processing apparatus  50  (see  FIG. 2 ) controls the position of the measurement unit relative to tablets  5   a  to  5   c  to be measured; calculates the result detected by detector  60 ; and the like, which will be described below. 
     First, when sample holder  10  is placed on measurement apparatus  100  in the state where alignment mark  4  is positioned in alignment, information processing apparatus  50  sets the center position of each holding unit  2  at the center position of each of tablets  5   a  to  5   c  (step S 10 ). 
     Then, based on the center position of each of tablets  5   a  to  5   c  set in step S 10 , information processing apparatus  50  moves the measurement unit to the position of holding unit  2  to be measured (step S 11 ). When holding unit  2  at A 1  on sample holder  10  shown in each of  FIGS. 3A and 3B  is first measured, information processing apparatus  50  moves the measurement unit to the center position of holding unit  2  at A 1 . In the above explanation, information processing apparatus  50  moves the measurement unit to sample holder  10 , but information processing apparatus  50  may move sample holder  10  to the measurement unit. 
     Then, information processing apparatus  50  measures the end position of tablet  5   a  and the center position of tablet  5   a  (step S 12 ). Specifically, in order to measure the shape of tablet  5   a , information processing apparatus  50  measures the coordinates (x 1 , y 1 , z 1 ) at the end position of tablet  5   a  and the coordinate (z 2 ) at the center position of tablet  5   a . The measured coordinates x and y each indicate the position in the plane of sample holder  10  while the measured coordinate z indicates the height of the sample in the direction perpendicular to the surface of sample holder  10 . Furthermore, the x and y coordinates at the center position of tablet  5   a  are not measured since these coordinates are previously set in step S 10 . 
     Then, information processing apparatus  50  calculates the size and the curvature of tablet  5   a  (sample) based on the measurement results obtained in step S 12  (step S 13 ). Specifically, based on the coordinates at the center position of tablet  5   a  set in step S 10  and the measured coordinates (x 1 , y 1 ) at the end position of tablet  5   a , information processing apparatus  50  can calculate the size (diameter) of tablet  5   a . Furthermore, information processing apparatus  50  calculates the curvature of tablet  5   a  based on the height (z 2 ) in the center position of tablet  5   a  and the height (z 1 ) in the end position of tablet  5   a.    
     Then, information processing apparatus  50  sets the distance between the measurement points based on the size of tablet  5   a  (sample) calculated in step S 13  (step S 14 ). Measurement apparatus  100  can set a plurality of measurement points for one sample and measure, for example, the Raman scattering light for each measurement point to thereby identify the substance. The measurement points can be arranged at a fixed distance form each other irrespective of the size of the sample, and also arranged at a distance from each other such that each sample includes the same number of measurement points irrespective of the size of the sample.  FIGS. 5A to 5D  each show a schematic diagram for specifically illustrating the distance between the measurement points.  FIG. 5A  is a diagram showing the measurement points arranged at a fixed distance from each other irrespective of the size of the sample.  FIGS. 5B to 5D  each are a diagram showing the measurement points arranged at a distance from each other such that each sample includes the same number of measurement points irrespective of the size of the sample. 
     In holding unit  2  shown in  FIG. 5A , measurement points  12  are arranged at regular intervals. Accordingly, the number of measurement points  12  at which each tablet is measured is different among the cases where: tablet  5   a  is held; tablet  5   b  is held; and tablet  5   c  is held. In other words, measurement apparatus  100  can obtain the measurement results from more measurement points  12  in the case of larger tablet  5   a , but can obtain the measurement results only from less measurement points  12  in the case of smaller tablet  5   b . However, since each measurement distance is fixed, the control for moving the measurement unit can be readily done. 
     On the other hand, the same number of measurement points  12  are included in each of tablet  5   a  shown in  FIG. 5B , tablet  5   b  shown in  FIG. 5C , and tablet  5   c  shown in  FIG. 5D . Thus, measurement apparatus  100  obtains the measurement results from the same number of measurement points  12  irrespective of the size of the each tablet. However, since the measurement distance is different depending on the size of each tablet, the control for moving the measurement unit becomes complicated. 
     Then, information processing apparatus  50  measures measurement points  12  set in step S 14  (step S 15 ). Specifically, information processing apparatus  50  moves the measurement unit to the previously-set measurement point  12  and measures, for example, the Raman scattering light from each measurement point  12  with detector  60  to obtain the results. 
     When the measurement of tablet  5   a  held in holding unit  2  at A 1  on sample holder  10  ends, measurement apparatus  100  measures tablet  5   a  held in next holding unit  2  at A 2 . Thus, information processing apparatus  50  moves the measurement unit located in holding unit  2  at A 1  to the position of holding unit  2  at A 2 . Information processing apparatus  50  determines whether or not the current holding unit  2  is the last holding unit  2  to be measured (step S 16 ). In sample holder  10  shown in each of  FIGS. 3A and 3B , holding unit  2  at C 3  is assumed to be the last holding unit  2 . 
     When it is determined that the current holding unit  2  is not the last holding unit  2  (NO in step S 16 ), information processing apparatus  50  moves the measurement unit to the position of the next holding unit  2  (step S 17 ). When it is determined that the current holding unit  2  is the last holding unit  2  (holding unit  2  at C 3 ) (YES in step S 16 ), information processing apparatus  50  displays the measurement results on a monitor connected thereto (step S 18 ). 
       FIG. 6  is a schematic diagram showing a display example of the measurement results. Display screen  5   l  shown in  FIG. 6  shows sample  1  exhibiting the component ratio of tablet  5   a  held in holding unit  2  at A 1 . Specifically, tablet  5   a  placed at A 1  contains 40% of component A, 35% of component B, 15% of component C, and 10% of component D. Similarly, display screen  5   l  shown in  FIG. 6  shows sample  2  exhibiting the component ratio of tablet  5   a  held in holding unit  2  at A 2 , and sample  3  exhibiting the component ratio of tablet  5   a  held in holding unit  2  at A 3 . Specifically, tablet  5   a  placed at A 2  contains 45% of component A, 30% of component B, 16% of component C, and 9% of component D. Tablet  5   a  placed at A 3  contains 50% of component A, 25% of component B, 10% of component C, and 15% of component D.  FIG. 6  further shows the total component ratio obtained by summing the component ratios of sample  1  to sample  3 . Tablet  5   a  contains the average component including: 45% of component A, 30% of component B, 14% of component C, and 11% of component D. In this way, sample holder  10  can hold a plurality of tablets (samples). Thus, measurement apparatus  100  can measure the same type of samples several times in one sample placement. Accordingly, measurement apparatus  100  can performs a statistical process for component variations and the like based on the plurality of measurement results obtained from the same type of samples. 
     As described above, measurement apparatus  100  according to the present embodiment includes: a sample holder  10  on which a plurality of samples can be placed; a measurement unit configured to measure the plurality of samples placed on sample holder  10 ; and a control unit configured to control the position of the measurement unit relative to the sample to be measured. Furthermore, sample holder  10  includes a substrate  1  and a holding unit  2  configured to hold the sample. Substrate  10  is provided with a plurality of holding units  2 . Holding unit  2  is configured to be capable of holding each of the plurality of samples having different shapes at the center position of holding unit  2 . By providing such a configuration, when measurement apparatus  100  measures a plurality of samples using sample holder  10  on which a plurality of samples having different shapes can be placed, the operations of holding and removing each sample can be reduced. 
     Particularly, in sample holder  10  according to the present embodiment, holding unit  2  is formed as a recess portion having a conical shape or a truncated conical shape, and structured to hold a sample in the state where a part of the sample is in contact with the inside of the recess portion, so that holding unit  2  can hold each of a plurality of samples having different shapes at its center position. By providing such a configuration, even when a plurality of samples having different shapes are placed on holding units  2  each having a conical shape or a truncated conical shape, the plurality of samples can be held at the center positions of their respective holding units  2 . 
     Furthermore, the control unit may control the position of the measurement unit relative to the sample with respect to the center position of holding unit  2  as the center position of the sample held in holding unit  2 . By providing such a configuration, measurement apparatus  100  does not have to calculate the center position of the sample by measurement, so that the position of the held sample can be readily aligned. 
     Furthermore, the control unit can calculate the size of the sample based on at least one sample end position measured by the measurement unit and the center position of the holding unit. Since the center position of the holding unit coincides with the center position of the sample, measurement apparatus  100  can calculate the size of the sample only by measuring the position of the sample end. 
     Furthermore, the control unit can set the number of measurement points, at which the sample is measured, based on the calculated size of the sample (i) such that each sample includes the same number of measurement points irrespective of the size of the sample, or (ii) such that the measurement points are arranged at a fixed distance from each other irrespective of the size of the sample. Measurement apparatus  100  can change the distance between the measurement points according to the sample. 
     Furthermore, the measurement unit can optically measure the sample to measure the height of the sample in the direction perpendicular to sample holder  10 . For example, the measurement unit can measure the height of the sample utilizing a confocal point by means of a lamp used as a white light source. 
     Furthermore, the control unit can calculate the curvature of the sample based on (i) the height of the sample in at least one sample end position measured by the measurement unit and (ii) the height of the sample in the center position of the holding unit. For example, information processing apparatus  50  calculates the curvature of tablet  5   a  based on the height (z 2 ) in the center position of tablet  5   a  and the height (z 1 ) in the end position of tablet  5   a.    
     Furthermore, holding unit  2  has a hole  3  provided in a part of the recess portion and penetrating through sample holder  10 . Such a configuration can prevent dust from accumulating on the bottom of holding unit  2 . Thus, holding unit  2  exhibits excellent drainage also when sample holder  10  is washed with water. 
     &lt;D. Modification&gt; 
     (1) Measurement apparatus  100  according to the present embodiment has been described with reference to an example of the arrangement pattern in which the measurement points are arranged at regular intervals as shown in  FIGS. 5A to 5D . However, the arrangement pattern of the measurement points is not limited to the above, but another arrangement pattern may be employed or different arrangement patterns may be employed for each holding unit  2 .  FIG. 7  is a schematic diagram of an example showing different arrangement patterns of measurement points  12 . As in sample holder  10  shown in each of  FIGS. 3A and 3B , in sample holder  10  shown in  FIG. 7 , when sample holder  10  is set in measurement apparatus  100  in the state where alignment mark  4  is located at the upper left in the figure, holding units  2  are arranged in the A column, the B column and the C column from the left and also arranged in the first row, the second row and the third row from the top. In other words, holding unit  2  at the upper left in sample holder  10  is identified as holding unit at A 1 , and holding unit  2  in the center is identified as holding unit  2  at B 2 . Also in sample holder  10  shown in  FIG. 7 , for example, tablet  5   a  having a diameter of 18 mm is held in holding unit  2  in the A column, tablet  5   b  having a diameter of 5 mm is held in holding unit  2  in the B column, and tablet  5   c  having a diameter of 10 mm is held in holding unit  2  in the C column. 
     As shown in  FIG. 7 , measurement apparatus  100  sets the arrangement pattern of measurement points  12  so as to be arranged radially on the tablet in the first row, and sets the arrangement pattern of measurement points  12  so as to be arranged in a cross shape on the tablet in the A column in each of the second and third rows, and on the tablet in the C column in each of the second and third rows. Also, measurement apparatus  100  sets the arrangement pattern of measurement points  12  so as to be arranged in a concentric manner on the tablet in the B column in each of the second and third rows. 
     In this way, for each holding unit  2 , the control unit can change the arrangement pattern of measurement points  12  at which the sample is measured. By providing such a configuration, measurement apparatus  100  can conduct a measurement in accordance with the sample characteristics such as the shape of the sample. 
     (2) Measurement apparatus  100  according to the present embodiment has been described with reference to an example of sample holder  10  formed of substrate  1  having a rectangular shape as shown in  FIGS. 1A and 1B . However, the shape of the sample holder is not limited to a rectangular shape, but the sample holder may be formed of a substrate having another shape. For example, the sample holder formed of a circular substrate will be hereinafter described. 
       FIGS. 8A, 8B, 9A, and 9B  each are a schematic diagram of a sample holder  10 A formed of a circular substrate.  FIG. 8A  is a plan view of sample holder  10 A.  FIG. 8B  is a cross-sectional view of sample holder  10 A taken along an A-A plane.  FIG. 9A  is a bottom view of sample holder  10 A.  FIG. 9B  is a front view of sample holder  10 A. The left side view, the right side view and the rear view of sample holder  10 A each are the same as the front view shown in  FIG. 9B , and therefore, not shown. In sample holder  10 A shown in each of  FIGS. 8A, 8B, 9A, and 9B , the outline of each characterizing portion for design is drawn with a solid line, and the outline of each non-characterizing portion is drawn with a dashed line. 
     Sample holder  10 A includes circular flat plate-shaped substrate  1  provided with a plurality of holding units  2 . Substrate  1  is not provided with a plurality of holding units  2  arranged in a lattice shape as shown in  FIGS. 1A and 1B  but provided with eight holding units  2  arranged in a circumferential shape. Holding units  2  may be arranged to form two or three concentric circumferences as long as sample holder  10 A has enough diameter. Furthermore, holding units  2  may be arranged to form a swirl shape. 
     When sample holder  10 A is rotatably fixed at the center of substrate  1 , measurement apparatus  100  can rotate sample holder  10 A to move the sample to be measured toward the measurement range. 
     In sample holder  10 A shown in each of  FIGS. 8A, 8B, 9A, and 9B , the outline of each characterizing portion for design is drawn with a solid line while the outline of each non-characterizing portion is drawn with a dashed line. When the present application is changed to the application for design registration, the partial design of the portion shown by a solid line in each of the figures can be specified as the “design for which registration is requested”. Also, an optional design portion in the region surrounded by the outline drawn with a dashed line, and the design portion including a combination of the optional portion and the portion surrounded by the outline drawn with a solid line can be specified as the “design for which registration is requested”. Furthermore, the design of the entire shape of sample holder  10 A may be changed to the application for design registration as the “design for which registration is requested”. In other words,  FIGS. 8A, 8B, 9A, and 9B  show designs in every manner that can be specified in each of the figures. 
     (3) Measurement apparatus  100  according to the present embodiment has been described with reference to an example of sample holder  10  including rectangular substrate  1  provided with nine holding units  2  as shown in  FIGS. 1A and 1B . However, the number of holding units  2  provided in the sample holder is not limited to nine but another number of holding units  2  may be provided in the substrate. 
       FIGS. 10A to 10F  are schematic diagrams of sample holders that are different in number of holding units  2 .  FIG. 10A  shows a sample holder  10 B including rectangular substrate  1  provided with two holding units  2 .  FIG. 10B  is a cross-sectional view of sample holder  10 B taken along a B-B plane.  FIG. 10C  shows a sample holder  10 C including rectangular substrate  1  provided with four holding units  2 .  FIG. 10D  is a cross-sectional view of sample holder  10 C taken along a C-C plane.  FIG. 10E  shows a sample holder  10 D including rectangular substrate  1  provided with six holding units  2 .  FIG. 10F  is a cross-sectional view of sample holder  10 D taken along a D-D plane. 
     (4) Measurement apparatus  100  according to the present embodiment has been described with reference to an example of sample holder  10  including holding unit  2  that is formed as a recess portion having a conical shape or a truncated conical shape as shown in  FIGS. 1A and 1B  so as to hold a sample in the state where a part of the sample is in contact with the inside of the recess portion. However, holding unit  2  formed in the sample holder may have any configuration as long as holding unit  2  can hold each of a plurality of samples having different shapes at the center position of holding unit  2 . In other words, the configuration of the holding unit is not limited to a recess portion having a conical shape or a truncated conical shape, but the holding unit may have another configuration as long as the holding unit is configured to be capable of holding each of samples having various different shapes. 
     For example, the holding unit may be configured to hold each of the plurality of samples having different shapes at the center position of the holding unit by holding each of the plurality of samples with a plurality of pawl portions (movable members) provided in the substrate.  FIG. 11  is a schematic diagram of a sample holder having a holding unit configured to hold a sample with a movable pawl portion. As in sample holder  10  shown in each of  FIGS. 3A and 3B , in sample holder  10 E shown in  FIG. 11 , when sample holder  10 E is set in measurement apparatus  100  in the state where alignment mark  4  is located at the upper left in the figure, holding units  70  are arranged in the A column, the B column and the C column from the left and also arranged in the first row, the second row and the third row from the top. 
     Holding unit  70  shown in  FIG. 11  holds a tablet  5   d  (sample) while three pawl portions  73  attached to a frame  72  provided in substrate  1  are moved by an adjustment screw  71 . In other words, holding unit  70  holds tablet  5   d  at three points using three pawl portions  73 . Also, three pawl portions  73  can be moved by operating adjustment screw  71  to change the distance among three pawl portions  73  according to the size of the sample to be held. In addition, holding unit  70  is designed such that the center position of the sample is always located at the center position of the same holding unit when the sample is held by three pawl portions  73 . 
     (5) The holding unit may be configured to be capable of holding each of a plurality of samples having different shapes at the center position of the holding unit by holding each of the plurality of samples using a plurality of holding pins, each of the plurality of holding pins being inserted into a hole provided in the substrate for fixation.  FIGS. 12A and 12B  each are a schematic diagram of a sample holder having a holding unit configured to hold a sample with a plurality of holding pins.  FIG. 12A  is a plan view of a sample holder  10 F.  FIG. 12B  is a cross-sectional view of sample holder  10 F taken along an F-F plane. As in sample holder  10  shown in each of  FIGS. 3A and 3B , in sample holder  10 F shown in each of  FIGS. 12A and 12B , when sample holder  10 F is set in measurement apparatus  100  in the state where alignment mark  4  is located at the upper left in the figure, the holding units are arranged in the A column, the B column and the C column from the left and also arranged in the first row, the second row and the third row from the top. Each of the holding units shown in  FIGS. 12A and 12B  is provided with a through hole  82  at the position of substrate  1  corresponding to the center position of each holding unit, and also provided with holes  81  at regular intervals around through hole  82 . Each of the holding pins is inserted through a corresponding one of holes  81  so as to be placed upright. 
     The following is a specific explanation about the configuration for holding a sample with a plurality of holding pins.  FIGS. 13A to 13D  each are a schematic diagram of a holding unit configured to hold a sample with holding pins.  FIGS. 13A and 13B  show holding pins  83  and  84 , respectively, inserted through holes  81  so as to be placed upright. Holding pin  84  is designed such that a portion for holding a sample (a head portion) is larger in diameter than holding pin  83 . In  FIG. 13C , a tablet  5   e  is held with three holding pins  83 . In other words, the holding unit holds tablet  5   e  at three points using three holding pins  83 . The holding unit can hold each of samples having various shapes by using at least three holding pins.  FIG. 13C  shows the manner in which each of the holding units holds a corresponding one of tablets  5   f  to  5   i  having different diameters by using holding pins having head portions with different diameters even when each of these holding pins having head portions with different diameters is inserted through the same hole  81 . Specifically, the holding unit holds a tablet  5   j  using holding pin  83  and holds a tablet  5   k  smaller in diameter than tablet  5   j  using holding pin  84  having a head portion larger in diameter than holding pin  83 . 
     The shape that can be held by the holding unit is not limited to a circular shape, but may be a triangular shape, a quadrangular shape, a hexagonal shape, an octagonal shape, an elliptical shape, and the like.  FIG. 13D  shows the manner in which the holding unit uses three holding pins to hold each of triangular tablets  5   l  and  5   m  and hexagonal tablets  5   n  and  5   o , and also uses four holding pins to hold each of a quadrangular tablet  5   p , an octagonal tablet  5   q  and an elliptical tablet  5   r . Specifically, the holding unit uses four holding pins  83  to hold quadrangular tablet  5   p , and uses four holding pins  84  each having a head portion larger in diameter than holding pin  83  to hold octagonal tablet  5   q.    
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims.