Patent Publication Number: US-6214294-B1

Title: Stirring device and automatic analyzer incorporating the stirring device

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a stirring device for use in inspection of samples in chemical and biochemical fields, which is designed to mix reagents, reaction liquids or the like and to stir the resultant mixture. 
     Stirrers, each having piezoelectric elements, are superior to rotary-type stirrers in terms of stirring efficiency. They therefore help to enhance the operating performance of automatic analyzers. 
     A conventional stirrer having piezoelectric elements will be described, with reference to FIGS. 2A,  2 B and  2 C. FIG. 2A is a front view, FIG. 2B is a rear view, and FIG. 2C is a side view. 
     This stirrer has a so-called “bimorph” structure. That is, it comprises a metal shim  201  and two piezoelectric ceramic elements  202  are attached to both surfaces of the shim  201 . The metal shim  201  and the elements  202  constitute an actuator. 
     When an AC voltage is applied to the piezoelectric ceramic elements  202 , the elements  202  are repeatedly expand and contract. The metal shim  201  is thereby vibrated. One end of the shim  201  is held in place by a screw  203 . The other end of the shim  201  extends with the same material having a narrow portion, thus forming a blade  204 . The blade  204  is inserted into a reaction cell and immersed in the liquid contained in the reaction cell. By the metal shim  201  is vibrated, the blade  204  is vibrated, so the liquid in the reaction cell is stirred. The weight of the screw  205  controls the vibration amplitude of the blade  204 . 
     A cover  206  conceals all but the blade  204 . Cover  206  protect the vibration of the piezoelectric ceramic element. 
     In recent years it has been demanded that automatic analyzers be made smaller and that two or more automatic analyzers be used in combination. To make an automatic analyzer, the reaction tubes in the reaction tank of the analyzer are arranged at a shorter distance. 
     An automatic analyzer may have two stirrers that are arranged side by side when they stir the liquid in two adjacent reaction tubes at the same time. To stir the liquid in the two adjacent reaction tubes, the stirrers need to be spaced for the same distance as the reaction tubes are spaced apart. If the stirrers are arranged very close to each other, their covers  206  may interfere with each other. 
     Therefore, reducing the distance between adjacent blades  204  has its limit, so the distance between the adjacent reaction cells is limited. Consequently, the automatic analyzer cannot be made as small as is demanded. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a stirring device which can be manufactured with high efficiency and which can help to miniaturize automatic analyzers. 
     According to the invention, there is provided a stirring device comprising: an actuator having a vibration element; a cover covering the actuator; a blade designed to be vibrated by the actuator; and connecting means connecting the blade to the actuator like the central axis of vibration amplitude of the blade is situated substantially along the side of the cover. 
     The blade is secured to the spacer, and the spacer is fastened to the actuator. Thus, if two stirring devices of the invention are simultaneously used to stir the liquids contained in two reaction cells, the distance between the blades of the stirrers can be shortened by the thickness of the spacer. This makes it possible to reduce the distance between the adjacent reaction cells arranged in the reaction tank of an automatic analyzer. Therefore, the stirring device according to this invention serves to miniaturize the automatic analyzer. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments give below, serve to explain the principles of the invention. 
     FIG. 1A is a front view of a stirrer according to the present invention; 
     FIG. 1B is a side view of the stirrer according to the invention; 
     FIG. 1C is a bottom view of the stirrer according to the invention; 
     FIG. 2A is a front view of a conventional stirrer; 
     FIG. 2B is a side view of the conventional stirrer; 
     FIG. 2C is a rear view of the conventional stirrer; 
     FIG. 3 is a graph showing how the vibration amplitude of the blade changes as the frequency of the AC power supplied to the piezoelectric ceramic elements is changed, while the voltage of the AC power remains at 20V; 
     FIG. 4 is a graph depicting how the vibration amplitude of the blade changes as the frequency of the AC power supplied to the piezoelectric ceramic elements is changed, while the voltage of the AC power remains at 25V; 
     FIG. 5 is a table showing the amplitudes at which the blade of the stirrer vibrated at various frequencies, when different voltages were applied to the piezoelectric ceramic elements; 
     FIG. 6 is a graph illustrating the relation between the time for the conventional stirrer is operated and the stirring degree, which the conventional stirrer achieves; 
     FIG. 7 is a graph showing the relation between the time for the stirrer of this invention is operated and the stirring degree which the stirrer of the invention achieves; 
     FIG. 8 is a plan view of an automatic analyzer in which the stirrer of the invention is stirring the liquid in two adjacent reaction cells; 
     FIG. 9 is a diagram showing two conventional stirrer arranged side by side, above two adjacent reaction cells; and 
     FIG. 10 is a diagram showing two stirrer of the present invention, arranged side by side above two adjacent reaction cells. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the present invention will be described, with reference to the accompanying drawings. 
     FIGS. 1A,  1 B and  1 C are schematic front, side and bottom views of a stirrer according to the invention. In FIGS. 1A,  1 B and  1 C, the broken lines indicate the components that cannot be seen from outside. 
     As shown in  1 A,  1 B and  1 C, the stirrer comprises a metal shim  101  and the piezoelectric ceramic element  102 . The piezoelectric element  102  may be attached to only one surface of the shim  201 . In this case, stirrer has a unimorph structure. Alternatively, two piezoelectric ceramic elements  102  may be attached to both surfaces of the shim  201 . If so, the stirrer has a bimorph structure. The metal shim  101  and the piezoelectric ceramic element or element  102  constitute an actuator. 
     When an AC voltage is applied from a power supply (not shown) to the piezoelectric ceramic elements  102 , the elements  102  are repeatedly expand and contract. The metal shim  101  is thereby vibrated. One end of the shim  101  is firmly held in place by a screw  105  so that it may not vibrate by itself or may not be displaced. A blade  103 , provided for stirring the liquid in a reaction cell, is connected to the other end of the shim  201  through a spacer  104 . The blade  103 , the spacer  104  and the shim  210  are fixed by a screw  106 . The spacer  104  has a thickness of 10 mm and bellow. The vibration of the metal shim  101  is transmitted to the blade  103 . The distal end of the blade  103  is thereby vibrated to stir the liquid in the reaction cell. 
     The blade  103  is made of the same material as the metal shim  101 . The surfaces of the blade  103  are covered with a protective coating, so that the blade  103  may not be affected by various kind of liquids in the reaction cell. 
     The spacer  104  needs to be hard and heavy enough to enable the blade  103  to vibrate at its distal end at such amplitude as to stir thoroughly the liquid in the reaction cell. More specifically, it must be hard not to absorb the vibration of the metal shim  101 . The amplitude at which the distal end of the blade  103  vibrates depends on the voltage and frequency of the AC power driving the piezoelectric ceramic elements  102  and the weights of the spacer  104  and screw  106 . The spacer  104  has a thickness a which is greater than the thickness b defined by screws  105  that fasten the metal shim  101 . 
     The inventors hereof conducted experiments to determine the values at which the voltage and frequency of the AC power for driving the elements  102  and the weights of the spacer  104  and screw  106  should be set in order to vibrate the blade  103  at secondary mode. The results were as is shown in FIGS. 3 and 4. Here, vibration of Nth mode means that N fixed points exist on the blade  103  which is vibrating. Since the blade  103  vibrates in the secondary mode, there is one fixed point other than the point where the screw  106  fastens the blade  103  to the shim  102 . (For details, see Jpn. Pat. Appln. KOKAI Publication No. 4-363665, for example.) 
     The spacer  104  and the screw  106  used in the experiments had a total weight of 0.8 g. 
     FIG. 3 shows how the vibration amplitude of the blade  103  changes as the frequency of the AC power supplied to the piezoelectric ceramic elements  102  is changed from 0 Hz to 200 Hz, while the voltage of the AC power remains at 20V. The frequency is plotted on the abscissa, while the voltage converted from the vibration amplitude of the distal end of the blade  103  is plotted on the ordinate. The larger the amplitude, the higher the voltage which is generated. 
     As seen from FIG. 3, the vibration amplitude at the distal end of the blade  103  reached a peak when the frequency of the AC power was about 66.0 Hz, and reached another peak when the frequency of the AC power was about 127.0 Hz. The voltage at the second peak was about half the voltage at the first peak, or at the frequency of about 66.0 Hz. Namely, the blade  103  vibrated in the primary mode at the frequency of about 66.0 Hz and in the secondary mode at the frequency of about 127.0 Hz. 
     FIG. 4 shows how the voltage converted from the vibration amplitude of the blade  103  changes as the frequency of the AC power supplied to the piezoelectric ceramic elements  102  is changed from 0 Hz to 200 Hz, while the voltage of the AC power remains at 25V. As can be understood from FIG. 4, the distal end of the blade  103  vibrated in the primary mode when the frequency of the AC power was about 66.0 Hz as in the case where the voltage of the AC power remained at 20V, and in the secondary mode when the frequency of the AC power was about 126.5 Hz. 
     It is known that the blade  103  can stir a reaction liquid to render the same homogeneous within a shorter time when it vibrates in the secondary mode than when it vibrates in the primary mode, as is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 4-363665. 
     The inventors applied AC powers of 20V and 25V, each at various frequencies (i.e., 120 Hz, 115 Hz, 110 Hz and 105 Hz), vibrating the piezoelectric ceramic elements  102  to vibrate the blade  103  in the primary mode. And they measured the amplitudes at which the distal end of the blade  103  vibrated in the primary mode. The results were as is shown in FIG.  5 . 
     Reaction cells have a width of about 4 to 5 mm. The amplitude at which the distal end of the blade  103  vibrates must therefore be 3 mm or less. FIG. 5 shows that the distal end of the blade  103  vibrated in secondary mode at an amplitude of 3 mm or less when the piezoelectric ceramic elements  102  were supplied with AC power of a frequency ranging from 105 Hz to 120 Hz and a voltage of 20V or 25V, furthermore the spacer  104  and the screw  105  had a total weight of 0.8 g. 
     Further, the inventors operated the conventional stirrer shown in FIGS. 2A to  2 C, wherein the screw  205  has a weight of 0.8 g, by supplying AC power having a voltage of 25V and a frequency of 120 Hz to the piezoelectric ceramic elements  202 , thereby stirring the liquids in a reaction cell. And they measured the time required to stir the liquid in each reaction cell thoroughly. The results are shown in FIG.  6 . 
     More specifically, saline solution was poured into the reaction cell and dye liquid (Evans blue) was then poured thereinto, thus forming two layers of liquids as is illustrated in the left part of FIG.  6 . Then, chromaticity was measured at five levels A to E in the reaction cell, at different times as the saline solution and the dye liquid were stirred by the conventional stirrer. The chromaticities thus measured plotted, obtaining the graph shown in the right part of FIG.  6 . In this graph, the chromaticity is plotted on the ordinate, and the stirring time on the abscissa. The greater the value of the ordinate, the higher the transparency of the liquids. 
     As seen from FIG. 6, the chomaticities at levels A to E, which differed before the stirring of the saline solution and dye liquid, approached an average value as the stirring proceeded. When the chromaticities changed to the average value, the saline solution and the dye liquid were mixed completely. As can be understood from FIG. 6, it took about 0.6 to 0.7 seconds until the chromaticities measured at levels A to E changed to the average value, in the case of the conventional stirrer. 
     The inventors operated the stirrer according to the invention (FIGS.  1 A- 1 C), wherein the spacer  104  and the screw  106  have a total weight of 0.8 g, by supplying the same AC power AC power to the piezoelectric ceramic elements  102  as was supplied to the elements  202  of the conventional stirrer (FIGS.  2 A- 2 C). More precisely, saline solution was poured into the reaction cell and dye liquid (Evans blue) was then poured thereinto, thus forming two layers of liquids as is illustrated in the left part of FIG.  7 . Then, chromaticity was measured at five levels A to E in the reaction cell, at different times as the saline solution and the dye liquid were stirred by the stirrer of the present invention. The chromaticities thus measured plotted, obtaining the graph shown in the right part of FIG.  7 . 
     As is evident from FIG. 7, it took about 0.8 to 0.9 seconds until the chromaticities measured at levels A to E changed to the average value, in the case of the stirrer according to the present invention. The time required to stir the saline solution and dye liquid completely is almost the same as the time the conventional stirrer required to stir the solution and liquid thoroughly. This means that stirring efficiency is much the same the stirrer of the invention as the conventional stirrer. 
     An automatic analyzer incorporating stirrers according to the invention will be described, with reference to FIG.  8 . The automatic analyzer comprises a reaction tank, a plurality of reaction cells arranged side by side in the reaction tank, and a plurality of stirring units, and a plurality of drive units. Each stirring unit has one stirrer of the type shown in FIGS. 1A-1C. Each drive unit is designed to drive one stirrer vertically so that the blade of the stirrer may move into and out of the liquid contained in a reaction cell. 
     FIG. 8 is a plan view of the automatic analyzer. As shown in FIG. 8, the automatic analyzer comprises two drive units (not shown), two stirring units  801  and  802 , two shafts  803  and  804 , and two reaction cells  805  and  806 . The reaction cells  805  and  806  are arranged side by side, each containing liquid. The stirring units  801  and  802  can be turned on the shafts  803  and  804 , respectively, and can stir the liquids in the reaction cells  805  and  806  at the same time. 
     In operation, the drive units (not shown) rotate the shafts  803  and  804 , whereby the stirring units  801  and  802  are turned on the shafts  803  and  804 , respectively. When the stirring units  801  and  802  move to the reaction cells  805  and  805 , the drive units stop rotating the shafts  803  and  804 . The stirring units  801  and  802  are thereby located right above these cells  805  and  806 , respectively. Then, the drive units lower the shafts  803  and  804 . As a result, the blade of the stirring unit  801  is thereby inserted into the reaction cell  805 , and the blade of the stirring unit  802  is inserted into the reaction cell  806 . Next, an AC voltage is applied to the piezoelectric elements of both stirring units  801  and  802 , vibrating the blades of the units  801  and  802 . The stirring units  801  and  802  therefore start stirring the liquids in the reaction cells  805  and  806  at the same time. 
     When the liquids in the reaction cells  805  and  806  are stirred completely (or upon lapse of a preset stirring time), the application of AC voltage to the stirring units  801  and  802  is stopped. Thus, the blade of the units  801  and  802  stop vibrating. Then, the drive units (not shown) lift the shafts  803  and  804  simultaneously, thereby moving the stirring units  801  and  802  upward. The blades of the units  801  and  802  are thereby pulled up from the reaction cells  805  and  806 . Thereafter, the drive units rotate the shafts  803  and  804 , thus returning the stirring units  801  and  802  to their respective initial positions. 
     FIG. 9 shows two identical stirrers of the conventional type (FIGS. 2A-2C) arranged side by side when they stir the liquids in the reaction cells arranged side by side at the same time. The blade  204  of each stirrer extends downward from the lower end of the actuator  901 , passing through the center hole made in the bottom of the cover  206  which is a substantially rectangular box. Once the covers  206  of these stirrers touch each other, the blades  204  can no longer approach each other. The shortest possible distance between the blades  204  is 20 mm. It follow that the distance between the center of the reaction cells needs 20 mm or more. 
     As indicated above, the blade  204  of either conventional stirrer is made integral with the metal shim  101 . Inevitably, the step of bonding the piezoelectric ceramic elements  202  to the metal shim  201  and the step of applying a coating to the surfaces of the blade  204  to protect the blade  204  against various kinds of liquids cannot be performed simultaneously; they must be sequentially conducted in the order mentioned. 
     FIG. 10 shows two identical stirrers according to the invention (FIGS. 2A-2C) arranged side by side when they stir the liquids in the reaction cells arranged side by side at the same time. The blade  103  of each stirrer is secured at the end of the actuator  101  through the spacer  104  by a screw  106 . Therefore, the central axis of vibration amplitude of the blade  103  (i.e., the stirring section) is situated substantially along the side of the cover which covers the actuator  101  having two piezoelectric ceramic elements and which allows the actuator  101  to vibrate freely. 
     Since the blade  103  of each stirrer extends in a plane close and parallel to the side of the cover, two stirrers can be arranged as shown in FIG. 10, with their blades  103  located far closer to each other than is possible with the conventional stirrers arranged as shown in FIG.  9 . Hence, in the automatic analyzer shown in FIG. 8, incorporating two stirrers of this invention, the distance between the reaction cells  805  and  806  can be reduced to about 5.3 mm. This helps to make the reaction tank, and ultimately to miniaturize the automatic analyzer. 
     As FIGS. 1A-1C show, the metal shim  101  and the blade  103  are not formed integral. In other words, the shim  101  and the blade  103  are separate components. Hence, the step of bonding the piezoelectric ceramic elements  102  to the metal shim  101  and the step of applying a protective coating to the surfaces of the blade  103  can be performed at the same time. Hence, the stirrer according to the present invention can be manufactured with high efficiency and at high yield. 
     In the stirrer of this invention, the blade is secured to the spacer, which is fastened to the actuator. If two stirrers of the invention are simultaneously used to stir the liquids contained in two reaction cells, the distance between the blades of the stirrers can be shortened by the thickness of the spacer. This makes it possible to reduce the distance between the adjacent reaction cells arranged in the reaction tank of an automatic analyzer. The stirrer according to the present invention, therefore, serves to miniaturize the automatic analyzer. 
     Additional advantages and modifications will readily occurs to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.