Abstract:
A particle distribution size measuring apparatus incorporates a detector array having a plurality of light detecting elements located on a substrate. A first group of detector elements have a plurality of sectors with a common sector angle, while at least one other detector element is positioned furthest from an optical axis and has a smaller sector angle. Each of the detector elements can be formed on a single substrate and their position and alignment have increased the efficiency of manufacturing the arrays.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a particle size distribution measuring apparatus, and more particularly to an array detector used in the measuring apparatus of a configuration to maximize production yield and a manufacturing method for forming a plurality of array detectors. 
     2. Description of Related Art 
     A particle size distribution measuring apparatus has been provided with a limited array detector having a plurality of light detecting elements (devices) for detecting an intensity of scattering light at various scattering angles when a laser beam from a laser beam source is irradiated onto dispersed particles. 
     FIG. 4 schematically shows the principal parts of a conventional particle size distribution measuring apparatus. A circulating type cell  1  (flow cell) comprising a transparent container, receive a sample solution  2  prepared by dispersing a particle group of a sample target for measurement in a proper dispersion medium. A laser beam source section  3  is located on one side (rear side) of the cell  1 . The laser beam source section  3  is composed of a laser beam source  5  comprising a He-Ne laser emitting a parallel laser beam  4 , towards mirrors  6  and  7  for changing a traveling direction of the laser beam  4  by an angle of 90°, and a beam expander  8  for properly enlarging the parallel laser beam  4  in a light (beam) flux direction. 
     A collective (condenser) lens  9  is located on the other side (front side) of the cell  1 , and a ring-like array detector  10  is arranged on a focal position. As shown in FIG. 5, the array detector  10  comprises a transmitted light detecting element  11  which is formed on a position corresponding to an optical axis of the collective lens  9 , and a scattering light detecting element group  12  for detecting scattered light  4 A. The scattering light detecting group  12  comprises a plurality of circular-arc scattering light receiving elements  12 ,  12   b , . . .  12   n , which are formed coaxially with the transmitted light detecting element  11  so as to have a wider width as they are positioned remote from the transmitted light detecting element  11 . Incidentally, a reference numeral  13  denotes an isolation gap between detecting elements. The aforesaid array detector  10  receives the light scattered/diffracted at a relatively small angle of the laser beam  4 A as it is diffracted or scattered by the particles in the cell  1  for various scattering angles, and then, measures their light intensity. The transmitted light detecting element  11  is used for adjusting a position optical axis and for measuring a concentration of the sample solution  2 . 
     A reference numeral  14  denotes a multiplexor which successively captures an output (scattering light intensity signal) of the array detector  10 , and successively transmits it to an A/D converter  15 , and a computer  16  which functions as a processor to which an output of the A/D converter  15  is inputted. The computer  16  stores a program for processing the output of the array detector, converted into a digital signal, on the basis of a Fraunhofer diffraction theory or a Mie scattering theory, and for determining a particle size distribution of the particle group. A reference numeral  17  denotes a color display for displaying the processed results or the like. 
     In the aforesaid particle size distribution measuring apparatus, where the sample solution  2  is supplied to the cell  1 , and the laser beam  4  from the laser beam source is irradiated to the sample cell  1 , the laser beam  4  is diffracted or scattered by the particles in the cell  1 . A diffracted or scattered laser beam  4 A is incident upon the array detector  10  by means of the collective lens  9 , and then, each output from the scattering light receiving elements  12   a ,  12   b  . . .  12   n  constituting the array detector  10 , is amplified by means of a pre-amplifier (not shown), and thereafter, is inputted to the multiplexor  14 . 
     In the multiplexor  14 , a light intensity data for each scattering angle obtained by the array detector  10 , that is, an analog electric signal is successively captured in a predetermined order. The analog electric signal captured by the multiplexor  14  is made into a serial signal, and then, is successively converted into a digital signal, and further, is inputted to the computer  16 . The computer  16  processes the light intensity data for each scattering angle obtained by the array detector  10  on the basis of a Fraunhofer diffraction theory or a Mie scattering theory, and thus, determines a particle size distribution of the particle in the sample solution  2 . Then, the result is displayed on the color display  17 , or is stored in a memory device (not shown). 
     The aforesaid array detector  10  is manufactured by cutting a wafer into a predetermined shape. In the conventional case, an open (sector) angle of each element  12   a  to  12   n  constituting the scattering light detecting element group  12  has been set to a fixed angle, for example, an angle of 90°. For this reason, the array detector  10  has the following problems. More specifically, in the array detector  10 , there is a need to mutually make equal the scattering light detecting characteristics of the scattering light detecting elements  12   a  to  12   n . For this reason, as shown in FIG. 5, the array detector  10  is formed in a manner that a dimension of the respective scattering light detecting elements  12   a  to  12   n  is gradually increased in its radius direction and circumferential direction from the transmitted light detecting element  11 , and also, an area thereof is increased in an exponential function. In this case, if each open (sector) angle of the scattering light detecting elements  12   a  to  12   n  is held constant, as a radius distance from the transmitted light detecting element  11  gradually becomes larger, an area of each effective light collection portion (portion shown by a symbol “a” in FIG. 5) of the scattering light detecting elements  12   a  to  12   n  is increased. For this reason, the array detector  10  is required to be of a relatively large size, and also, any equipment for holding the array detector  10  becomes large, as a result, the particle size distribution measuring apparatus will be of a large size. 
     Moreover, the number of the array detectors  10  capable of being manufactured from a single wafer  18  is four (4) as shown in FIG. 5, in the case where the detector element sector angle is 90°. Therefore, the number of array detectors  10  capable of being manufactured from a single wafer is limited as number; for this reason, there is an increase in cost, and as a result, the particle size distribution measuring apparatus becomes expensive. 
     Examples of conventional array detectors can be seen in U.S. Pat. No. 5,164,787 and U.S. Pat. No. 5,185,641. 
     The prior art is still seeking improved and cost efficient array detectors. 
     SUMMARY OF THE INVENTION 
     The present invention has been made taking the aforesaid problems of the prior art into consideration. It is, therefore, a first object of the present invention to provide a small and compact particle size distribution measuring apparatus which includes a compact array detector section on an improved configuration. 
     A second object of the present invention is to provide a compact array detector to be used in a particle size distribution measuring apparatus, which can reduce an occupancy area in the measuring apparatus. 
     A third object of the present invention is to provide a manufacturing method of making an array detector, which can optimize the number of array detectors from a single wafer. 
     To achieve the above first object, the invention defined in a first aspect provides a particle size distribution measuring apparatus which includes an array detector having a plurality of scattering light detecting elements for detecting an intensity of scattering light generated when a laser beam is irradiated from a laser beam source to a dispersed particle group for each scattering angle, and measures a particle size distribution of the particle group on the basis of a scattering light intensity signal from each scattering light detecting element. 
     The array detector being formed so that a plurality of scattering light detecting elements are located on one detection plane in one radius direction with the use of an optical path as the center, and so that the maximum sector angle is obtained within a width previously set, and individual detector elements can have different sector angles. 
     The array detector include a first plurality of detector elements having a constant sector angle, e.g. 90° and a second plurality of detector elements having sector angles that are reduced in size With detector areas that are increased in size as they are further positioned from an optical axis. 
     To achieve the above second object, the invention provides an array detector which has a plurality of scattering light detecting elements for detecting an intensity of scattering light having a small scattering angle for diffraction/scattering light generated when a laser beam is irradiated from a laser beam source to a dispersed particle group for each scattering angle. The plurality of scattering light detecting elements being located on one detection plane in one radius direction with the use of an optical axis of the irradiating light source as the center, and being formed so that a maximum sector angle is obtained within a width previously set, and their sector angles are not set so as to become constant. 
     To achieve the above third object, the invention provides a manufacturing method for an array detector which is formed so that a plurality of scattering light detecting elements are cut out of a single wafer, the plurality of scattering light detecting elements being located on one detection plane in one radius direction with the use of an optical axis as the center, and being deposited on the wafer so that the maximum sector angle is obtained within a maximum width previously set, and their sector angle is not set so as to become constant. 
     According to the present invention, the array detector is manufactured so that the width W n  of the scattering light detecting element situated on the farthest position from the center of the transmitted light detecting element does not exceed the maximum width W previously set. Thus, in the case of the same number of elements, an occupancy area of the array detector is made small on a single wafer, and therefore, a compact and cheap array detector can be obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings. 
     FIG. 1 is a view schematically showing a construction of principal parts of a particle size distribution measuring apparatus of the present invention; 
     FIG. 2 is a top plan view schematically showing a construction of an array detector of the present invention; 
     FIG. 3 is an explanatory view for manufacturing array detectors from a single wafer; 
     FIG. 4 is a view schematically showing a construction of a conventional particle size distribution measuring apparatus; and 
     FIG. 5 is a view to illustrates a problem in a conventional array detector. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventors of carrying out their invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the general principles of the present invention have been defined herein specifically to provide an improved particle measuring apparatus with a detector array and method of manufacturing the same. 
     FIG. 1 to FIG. 3 show one embodiment of the present invention. FIG. 1 is a view schematically showing a construction of the principal parts of a particle size distribution measuring apparatus of the present invention. Reference can be made to “Light Scattering By Small Particles” by H. C. van de Halst, Dover Publications 1981 as background reference for scattering theory. 
     In FIG. 1, like reference numerals are used to designate the same components as shown in FIG. 4, and therefore, their details are omitted. An array detector  21  is attached to a detector retaining member  22  and is vertically located thereon. The array detector  21  is different from the conventional array  10  shown in FIG.  4  and FIG. 5 in the following points. More specifically, a plurality of scattering, light detecting elements are located on one detection plane of a substrate in one radius direction around an optical axis, and these scattering light detecting elements are formed so that their maximum sector angles are obtained within a preset width, and all of the angles are not set to be constant or equal. The manufacturing method of the above array detector will be described below with reference to FIG.  2  and FIG.  3 . 
     FIG. 2 is a top plan view schematically showing a construction of an example of an array detector  21  of the present invention. In FIG. 2, a reference numeral  23  denotes a transmitted light detecting element for adjusting an alignment of the detector array with an optical axis of an irradiating light source and for measuring a sample fluid concentration. The transmitted light detecting element  23  when aligned corresponds to a position on an optical axis of the particle measuring apparatus. Reference numerals  24   a  to  24   n  denote a plurality of circular-arc scattering light detecting elements which are formed concentrically with the transmitted light detecting element  23  so as to have a radius wider width when located further from the transmitted light detecting element  23 . These scattering light detecting elements  24   a  to  24   n  are formed so that their dimensional sizes are gradually increased in their radius direction, and their sector area is increased as they extend outward far from the transmitted light detecting element  23 . A reference numeral  25  denotes an isolation gap formed between the transmitted light detecting element  23  and an upper arc boundary and lower arc boundary of each of the scattering light detecting elements  24   a  to  24   n . The construction described thus far is almost the same as the conventional array detector  10 . 
     In the array detector  21  of the present invention, each sector angle of the scattering light detecting elements  24   a  to  24   n  is not set so as to become constant (e.g., angle of 90°) like the conventional case, but is set so that the maximum sector angle can be obtained in a preset width. More specifically, as seen from FIG. 2, in a first group of scattering light detecting elements, that is, reference numerals  24   a  to  24   d  in illustration, which are near the transmitted light detecting element  23  situated on the center of the sector, their sector angle Θ is mutually equal, and is set so as to become an angle of 90°, for example. 
     In a second group of scattering light detecting elements  24   e  to  24   n  which are situated outside the scattering light detecting element  24   d , a width shown by a symbol W in FIG. 2 is previously set. Thus, their sector angle of the scattering light detecting elements  24   e  to  24   n  is set so as to gradually become smaller. For example, there is the case where a sector angle Θn of the farthest scattering light detecting element  24   a  becomes less than 30°. Additionally, a medium circumferential distance of the sectors of the second group approximate an outermost edge distance, e.g. corner points, between the respective comers of the most radial sector,  24   d , of the first group of detector elements. 
     Namely, in the above array detector  21 , the first group of scattering light detecting elements  24   a  to  24   d  satisfy a condition such that their dimension is gradually increased in their radius direction and also in a circumferential direction, and their area is increased. The same sector angle is maintained. The scattering light detecting elements  24   e  to  24   n  are formed so that a maximum sector angle can be obtained within a preset width dimension W. In the array detector  21  constructed in the manner as described above, the whole dimension is set within a range of a rectangular shape having a width W and a length L; therefore, the occupancy area becomes considerably small as compared with the conventional array detector  10 . 
     In the case of manufacturing the above array detector  21 , for example, as shown in FIG. 3, a wafer  25  having a diameter 8 inches is sized to a rectangular portion  26  having the maximum width W and length L. And then, a portion equivalent to the transmitted light detecting element  23  is set at the center on one side in the width direction of the rectangular portion  26 , and thereafter, the plurality of scattering light detecting elements  24   a  to  24   n  are formed as described above with the use of the set transmitted light detecting element  23  as the center. According to the manufacturing method of the array detector  21  of the present invention, an occupancy area of the array detector  21  becomes small. Therefore, it is possible to manufacture the array detector  21  having the same performance as the conventional case from a single wafer, and to increase the number of array detectors by three to four times as much as the conventional case for the same size wafer, and thereby, a significant cost reduction can be achieved. 
     The array detector  21  formed as described above is attached to the detector retaining member  22  so that the transmitted light detecting element  23  coincides with an optical axis of the collective lens  9 . 
     As described above, according to the present invention, as shown in FIG. 2, the array detector  21  is manufactured so that the width W n  of the scattering light detecting element situated on the farthest position from the center of the transmitted light detecting element  23  does not exceed the maximum width W previously set. Thus, it is possible to solve the problem that the effective area of the scattering light detecting elements  24   a  to  24   n  is increased as a radius from the transmitted light detecting element  23  becomes large; therefore, a compact array detector can be manufactured. In the case of the same number of elements, an occupancy area of the array detector is made small in the single wafer  25 , and therefore, it is possible to manufacture the array detector  21  in quantities of several times the conventional case from a single wafer  25 , and to reduce manufacture cost. Moreover, the detector retaining member  22  for retaining the compact array detector  21  is made into a small size as compared with the conventional case. Therefore, this serves to also make small the particle size distribution measuring apparatus, and to achieve a cost reduction. 
     The provision of an increased number of detector elements on a single elongated rectangular substrate lowers the cost and improves the alignment in the measuring apparatus. 
     The present invention is not specially limited to the above embodiment, and various modifications may be carried out. For example, in the particle size distribution measuring apparatus, in addition to the array detector  21 , the following optical detecting group for wide-angle scattering light may be located in the vicinity of the cell  1 , more specifically, the optical detecting group for wide-angle scattering light detects each light scattered/diffracted at a relatively large angle of the laser beam  4 A diffracted or scattered by the particles in the cell  1  for each scattering angle, and thus, measures a particle size distribution of a further micro particle. 
     The laser beam  4  irradiated to the cell  1  does not always need to be a parallel beam. A semiconductor laser may be used as the laser beam source  5 , and the collective lens may be interposed between the semiconductor laser and the cell  1  so that a converged laser beam can be irradiated to the cell  1 . 
     Moreover, the cell  1  does not need to be a circulating type, and the target for measurement may be a powder or particle dispersed in a gas or solid, in addition to particles in a liquid. 
     According to the present invention, the width of the scattering light detecting element in the array detector is limited to a predetermined width; therefore, a compact array detector can be manufactured. Further, it is possible to manufacture many array detectors from a single wafer, and to reduce a manufacture cost of the array detector. Furthermore, the device for retaining the compact array detector is made into a small size, and therefore, it is possible to make small the particle size distribution measuring apparatus, and to achieve a cost reduction. 
     Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.