Abstract:
The present invention provides a light scattering particle size distribution measuring apparatus, which does not require a burdensome optical axis adjustment of operator for every measurement and which is capable of maintaining a state most suitable for measuring. 
     In the present invention, the light scattering particle size distribution measuring apparatus irradiates a sample with light from a light source, detects the resulting scattered light from the sample by a photodetector. Thereafter, the present invention calculates the size distribution of particles in the sample on the basis of the scattered light intensity pattern obtained. In addition, an automatic adjustment mechanism aligns and maintains the central position of the foregoing photodetector with the central position of the foregoing light source.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a light scattering particle size distribution measuring apparatus, which irradiates a material sample with light from a light source, and measures the size distribution of particles in the sample on the basis of a scattered light intensity pattern obtained thereat. 
     DESCRIPTION OF THE PRIOR ART 
     Systems capable of measuring the size distribution of particles within a sample of material are useful in a plurality of fields. FIG. 7 shows a schematic of a prior art scattering particle size distribution measuring apparatus system. As shown in FIG. 7, the system comprises a light source  71 , capable of emitting laser light  72 . In addition, a shutter  73 , comprising a shutter member  73   a  and a shutter driving member  73   b , is used to modulate the laser light  72 . A beam expander  74  expands the laser light  72  prior to incurring a flow through cell  75  containing a material sample  76 . Thereafter, a condenser lens  77  is used to focus the light onto a photodetector  78  which detects the scattered and transmitted light from the condensor lens  77 . Commonly, a multiplexer  79 , which is in communication with a CPU  80 , captures the signal from the photodetector  78  upon the detection of light. The CPU  80  may be programmed with various algorithms and other mathematical formulae to permit arithmetic computations of scattering based on the light intensity pattern received at the photodetector  78 . A personal computer  81 , in communication with a display terminal  82 , may be used to control the overall system. 
     In the foregoing system, when a cell  75  containing a material sample  76  is irradiated with laser light  72 , a portion of light is scattered by particles within the material sample  76 , and a portion of the light is transmitted through the material without a scattering effect. 
     A problem associated with prior art systems requires the optical axis of a photodetector  78  be held exactly coincident with that of a light source  71 . More specifically, the center of an axis of laser light  72  emitted from a light source  71  is required to be coincident with a center of a light receiving device of the photodetector  78 . Commonly, the foregoing axis become misaligned due to the thermal deformation of the light source  71 , the thermal deformation of the optical bench, thermal deformations in the cell  75 , condenser lens  76 , or photodetector  78 . 
     In an effort to correct the foregoing misalignment issues, conventional particle size distribution measuring systems having utilized optical stages  83 , commonly referred to as X-Y stages, to maintain the optical axis. As shown in FIG. 7, the X-Y stage moves a photodetector  78  in parallel, and corrects the foregoing misalignment of the optical axis. To correct a misalignment, the operator is required to manually actuate the direct acting actuator  85 , to correct misalignment along the X axis, or the direct acting actuator  84 , to correct a misalignment along the Y axis. Generally, the direct acting actuators  84  and  85 , respectively, having included piezoelectric devices or a stepping motor. 
     The above-referenced optical axis adjustment work is required to be performed for every measurement and takes several minutes for each adjustment. As such, it has been required for an operator to expend considerable time and effort for each measurement. In addition, inaccurate measurements could occur should there be a time lag between the optical axis adjustment work and the measuring operation due to a plurality of factors, such as, for example, vibrations, changes in temperature, or other environmental conditions. 
     The present invention has been made in view of the foregoing matters, and an object of the present invention is to provide a light scattering particle size distribution measuring apparatus which does not require a burdensome optical axis adjustment of operator for every measurement, thereby maintaining a state most suitable for measuring. 
     SUMMARY OF THE INVENTION 
     To achieve the above object, the present invention discloses a light scattering particle size distribution measuring apparatus which irradiates a sample with light from a light source, detects the resulting scattered light from the sample by a photodetector, and measures the size distribution of particles in the sample on the basis of a scattered light intensity pattern obtained. More specifically, the present invention comprises an automatic adjustment mechanism which aligns and maintains a central position of the foregoing photodetector with a central position of the foregoing light source is provided. 
     In another embodiment, a light scattering particle size distribution measuring apparatus is provided comprising an optical axis adjustment mechanism capable of automatically adjusting the central positions of the light source and the photodetector in a state most suitable for measuring. The system monitors the quantity of light antecedent to irradiating a sample and quantity of light on a photodetector after irradiating a sample, and adjusts the position of a light source, the photodetector, or an optical device positioned between the light source and the photodetector. 
     In yet another embodiment, the present invention discloses a light scattering particle size distribution measuring apparatus capable of holding the control data antecedent to the decrease of the quantity of light when the quantity of light on a photodetector is significantly lowered compared with the quantity of light antecedent to irradiating a sample by monitoring the quantity of light antecedent to irradiating a sample and the quantity of light on a photodetector. In addition, the present embodiment is capable of retrieving the optimal positions of various optical components in a range, thereby automatically controlling the quantity of light on a photodetector. 
     In the light scattering particle size distribution measuring apparatus having the constitution described above, an automatic adjustment mechanism aligns the central position of the photodetector with the central position of the light source. The optical axis adjustment, which, conventionally was required to be manually performed by the operator, or through a control software stored on the personal computer, before measuring the particle size, becomes unnecessary. It is, therefore, possible to reduce the time required for each measurement, such as preparatory work before measuring. In addition, the present system is capable of always measuring in optimal conditions, thereby consistently achieving a particle size distribution measurement having a high degree of measuring precision. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing a first embodiment of the present invention. 
     FIG. 2 is a view showing a second embodiment of the present invention. 
     FIG. 3 is a view showing a third embodiment of the present invention. 
     FIG. 4 is a view showing a fourth embodiment of the present invention. 
     FIG. 5 is a view showing a fifth embodiment of the present invention. 
     FIG. 6 is a view showing a sixth embodiment of the present invention. 
     FIG. 7 is a view to illustrate a prior art system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a first embodiment of the present invention. As shown in FIG. 1, the particle size measuring system comprises a light source  1  capable of emitting laser light  2 . The quantity of light emitted from this light source  1  is controlled and monitored by a CPU  15  described herein. The laser light  2  is modulated by a light shutter  3 , which comprises a shutter member  4  and a shutter driving member  5 . Thereafter, a beam expander  6  expands laser light  2  emitted from the light source  1 . The laser light  2  continues through a flow-through cell  7  containing a material sample  8 , and is focused with a condenser lens  9  onto a photodetector  10 . In an alternate embodiment, the condenser lends  9  may be between the beam expander  6  and the cell  7 , thereby condensing the laser light  2  incident upon the sample  8 . The photodetector detects  10  comprises a light receiving device  11  having a plurality of arc-shaped receiving devices  12  located an appropriate distance from the center of the optical axis. The foregoing light receiving devices  11  and  12  comprise and may include a plurality of light receiving device known in the art, including, for example, photodiodes. The light receiving devices  11  and  12  may be positioned at a predetermined position on a base member  13 . A multiplexer  14  captures the signal from the photodetector  10 . The CPU  15  processes the signal from the multiplexer  14  and determines the particle size distribution by performing arithmetic computations on the basis of a scatter light intensity pattern. Thereafter, a personal computer  16  may be used for controlling arithmetic computations, controlling the measuring apparatus, and performing image processing functions. A display unit  17 , in communication with the personal computer  16 , may be used to display the computational results. 
     As shown in FIG. 1, a diffraction device  18 , capable of producing diffracted light, is inserted into the optical path of the propagating laser light  2 . The diffraction device  18  comprises a plate member  20 , having a central opening  21  formed therein. Those skilled in the art will appreciate the diffraction device  18  of the present invention may be inserted into the optical path manually, or if desired, independently with an appropriate mechanism. The plate member  20  of the present invention may be manufactured from a plurality of materials, including, for example, light extinction materials and light absorbing materials. In an alternate embodiment, a transparent plate member  20  having light absorption material centrally located thereon, thereby enabling the user to produce spherical particle diffraction. 
     FIG. 1 shows an adjusting mechanism  19  which comprises, for example, an X-Y stage capable of movement in two directions X and Y, orthogonal to each other. As shown, the photodetector  10  is positioned on the X-Y stage  19 . Directional actuators  22  and  23  may be used to drive the X-Y stage  19  in X direction (a direction indicated by an arrow  24 ) and Y direction (a direction indicated by an arrow  25 ), respectively. The directional actuators  22  and  23  may comprise direct-acting actuators such as a piezoelectric device or a stepping motor. As shown in FIG. 1, the directional actuators  22  and  23  are controlled by a signal from a personal computer  16 . In an alternate embodiment, a manually controlled adjustment mechanism  19  is contemplated. 
     Those skilled in the art will appreciate the present invention is greatly different from the prior art systems in that the diffraction device  18 , which is positionable within the propagation path of the laser light  2 , is capable of adjusting the optical axis in the optical path between the light source  1  and the photodetector  10 . In addition, further adjustments to the optical axis may be achieved with the adjusting mechanism  19  coupled to the photodetector  10 . 
     FIG. 2 shows a second embodiment of the present invention in which a mirror  26  in communication with an optical axis adjusting mechanism  27  is provided. The mirror  26  directs the laser light  2  emitted from the light source  1  at a 90 degree angle into the beam expander  6 . As shown, the optical axis adjusting mechanism  27 , which is controlled by the CPU  15 , is capable of moving the mirror  26  in the directions indicated by the arrows  28  and/or  29 . 
     FIG. 3 shows a third embodiment of the present invention in which an optical axis adjusting mechanism  30 , which is controllable by the CPU  15 , is provided. As shown in FIG. 3, the optical axis adjusting mechanism  30  is capable of moving the condenser lens  9  and the optical axis in X direction as indicated by the arrow  31  and/or in Y direction as indicated by the arrow  32 . 
     FIG. 4 shows a fourth embodiment of the present invention in which an optical axis adjusting mechanism  33 , which is in communication with the CPU  15 , is provided. The optical axis adjustment mechanism  33  is capable of moving the beam expander  6  in the X direction as indicated by the arrow  34  and/or in Y direction as indicated by the arrow  35 . 
     FIG. 5 shows a fifth embodiment of the present invention in which an optical axis adjusting mechanism  36 , which is controlled by the CPU  15 , is provided. The optical axis adjusting mechanism  36  is capable of moving the light source  1  in the X direction as indicated by an arrow  37  and/or in the Y direction as indicated by an arrow  38 . 
     FIG. 6 shows a sixth embodiment of the present invention in which cuneal prisms  39  and  40  are positioned between the beam expander  6  and the cell  7  within the propagation path of the laser light  2 . As shown in FIG. 6, the cuneal prisms  39  and  40  are connected to an optical axis adjusting mechanism  41 , which is in communication with the CPU  15 . The optical axis mechanism  41  is capable of moving the cuneal prism  39  in the X direction as indicated by an arrow  42 , capable of moving the cuneal prism  40  in the Y direction as indicated by an arrow  43 . 
     The present invention further discloses a method of using the present invention to determine particle size. In the embodiments described above, the central positions of the light source  1  and the photodetector  10  are automatically adjusted to be in a state most suitable for measuring particle size within a sample  8 . The embodiments described above provide various systems capable of monitoring quantity of light prior to irradiating a sample  8  and quantity of light transmitted through the sample  8  incident on a photodetector  10 . In addition, the various embodiments of the present invention permit the user to easily adjust the position of a light source  1 , a photodetector  10 , or an optical device positioned between the light source  1  and the photodetector  10 . In an alternate embodiment, the present invention may also be constructed such that the CPU  15  is capable of performing a control and monitor function for the system. In addition to monitoring the light intensities as various points in the system, the CPU  15  is capable of performing an error detection process. Exemplary errors include bubble contamination of a sample and system misalignment. In another embodiment, the measuring system disclosed herein may also be capable of determining an optimal control position to make a quantity of light fall in a controllable range on the photodetector  10 . Additionally, the present invention is capable of storing the positions of various components, thereby enabling the system to reconstruct a previous experiment. 
     The present invention eliminates the burdensome manual optical axis adjustment currently required for every measurement in current systems. Furthermore, the present system permits the operator to maintain the system configuration best suited for a particular measurement. Accordingly, the present system enables the operator to perform measurements in an optimal condition while achieving a high degree of measuring precision. 
     To practice the first embodiment of the present invention, a diffraction device  18  is inserted into an optical path with the shutter  3  opened thereby creating an optical axis by using diffracted light produced by the diffraction device  18 . Once the optical axis is created, the diffraction device  18  may be removed from the propagation path. The CPU  15 , which is continuously receiving information relating to the position of the optical axis from the photodetector  10 , controls the optical axis adjusting mechanism  19  based on the foregoing information, thereby ensuring the photodetector  10  is always in a condition best suited to measuring. 
     In the embodiment described above, the optical axis adjusting mechanism  19  is in communication with the photodetector  10  and controlled by the CPU  15 . As shown in FIGS. 2 through 6, the present invention permits the user to control and monitor the optical axis with the CPU  15  by positioning the optical axis actuators in a plurality of locations. Accordingly, the operations for the optical axis adjustment in embodiments shown in FIGS. 2 to  6  are similar to that of the first embodiments shown in foregoing FIG.  1 .