Abstract:
A micromachined pump apparatus  1  includes a substrate  2  having upper and lower surfaces and a plurality of lengthwise arranged apertures  2 A- 2 E, each of which has an upper surface opening and a lower surface opening. A plurality of diaphragms  6 A- 6 E close the upper surface openings of the apertures  2 A- 2 E, respectively. A guide plate  3  is fixedly mounted on the upper surface of the substrate  2  and defines a passage  3   a  through which an object fluid is moved by cooperating with the diaphragms on the upper surface of the substrate  2 . A base plate  4  is fixedly mounted at its upper surface on the lower surface of the substrate  2 , thereby enclosing an operating fluid in each of the apertures  2 A- 2 E. An electrically operated heater device  5  is provided on the upper surface of the base plate  4  for heating the fluids in the apertures  2 A- 2 E, respectively, in such a manner that whenever the fluids are heated the resultant expansion of the respective operating fluid expands the diaphragms, respectively, toward the passage. The expansions of the diaphragms  6 A- 6 E are made in sequence, thereby forcing the object fluid to move through the passage  3   a.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to a micromachined pump apparatus having a diaphragm adjacent an internal closed space for the closure thereof which operates in such a manner that whenever the volume of the internal closed space is increased, the diaphragm is deformed or expanded toward a passage, thereby forcing an object fluid to move in the passage. 
     Miniature pumps, hereinafter referred to as micropumps, can be constructed using fabrication techniques adapted from those applied to integrated circuits. Such fabrication techniques are often referred to as micromachining. 
     Micromachined pumps or micropumps are disclosed for example in Japanese Patent Laid-open Print No. Hei. 10(1998)-159811 and Japanese Patent Laid-open Print No. Hei. 7(1995)-139471. 
     In the former, the increase of pressure in the closed space which causes the expansion of the diaphragm is made in such a manner that a light beam is applied to a light/heat converting substance accommodated in the closed space and the resultant heat generation causes the operating fluid in the closed space to expand. However, the light application requires an optical fiber which is not very efficient in transmitting light and an optical transmission mechanism per se is expensive. 
     In the latter, the diaphragm is expanded by supplying air into the closed space. However, a large pressure loss occurs between a pressure source and the micropump, thereby requiring a relatively large scaled pressure source for effective expansion of the diaphragm. 
     Accordingly, a need exists for a micromachined pump apparatus without the foregoing drawbacks. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed to satisfy the need noted above and thus has for a primary object the provision of a micromachined pump apparatus which comprises a substrate having upper and lower surfaces, the substrate having a plurality of lengthwise arranged apertures each of which has an upper surface opening and a lower surface opening, a plurality of diaphragms closing the upper surface openings of the apertures, respectively, a guide plate fixedly mounted on the upper surface of the substrate and defining a passage through which an object fluid is moved by cooperating with the diaphragms on the upper surface of the substrate, a base plate fixedly mounted at its upper surface on the lower surface of the substrate and enclosing an operating fluid in each of the apertures, and an electrically operated heater device provided on the upper surface of the base plate, the heater device heating the fluids in the apertures, respectively, in such a manner that whenever the operating fluids are heated the resultant expansion of the respective operating fluid expands the diaphragms, respectively, toward the passage, the expansions of the diaphragms being made in sequence, thereby forcing the object fluid to move though the passage. 
     In accordance with the present invention having the foregoing structure, unlike the conventional devices, the expansion of the enclosed fluid which causes the expansion of the diaphragm is made electrically, which simplifies the structure for the fluid inflation. In addition, the amount of heat on which the degree of expansion of the diaphragm depends can be easily controlled by adjusting the current. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be more apparent and more readily appreciated from the following detailed description of preferred exemplary embodiments of the present invention, taken in connection with the accompanying drawings, in which; 
     FIG. 1 is an exploded perspective view of a micromachined pump apparatus in accordance with a first embodiment of the present invention; 
     FIG. 2 is a lengthwise cross-sectional view of the micromachined pump apparatus shown in FIG. 1; 
     FIG. 3 is a view showing how heaters are positioned in the micromachined pump apparatus shown in FIG. 1; 
     FIG. 4 is a cross-sectional view taken along line A—A in FIG. 3; 
     FIG. 5 is an enlarged view of a portion shown in FIG. 2; 
     FIG. 6 is an enlarged view showing another mode of the portion shown in FIG. 2; 
     FIG. 7 shows an electric circuit for a heater device employed in the micromachined pump apparatus shown in FIG. 1; and 
     FIG. 8 shows another mode of the heater device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention will be described hereinafter in detail with reference to the accompanying drawings. 
     With reference to FIGS. 1-6, there is illustrated a miniature pump apparatus  1 . The miniature pump apparatus  1  is constructed by using fabrication techniques adapted from those applied to integrated circuits. As well known, such fabrication techniques are often referred to as micromachining. 
     The miniature pump apparatus  1 , which is used to force a very small amount of object fluid whose viscosity is relatively low, includes a substrate  2  which is formed with five equi-spaced pass-through apertures  2 A,  2 B,  2 C,  2 D, and  2 E, five diaphragms  6 A,  6 B,  6 C,  6 D, and  6 E closing upper openings of the respective apertures  2 A,  2 B,  2 C,  2 D, and  2 E, a guide plate  3  secured to the upper surface of the substrate  2  is formed with a concave passage  3   a  in the lower surface thereof through which a fluid passes, and a base plate  4  closing the apertures  2 A,  2 B,  2 C,  2 D, and  2 E from the bottom and provided with five heaters  5 A,  5 B,  5 C,  5 D, and  5 E for heating the fluids in the respective apertures  2 A,  2 B,  2 C,  2 D, and  2 E. An operating fluid is provided in each of the apertures  2 A,  2 B,  2 C,  2 D, and  2 E, before the base plate  4  is coupled to the bottom of the substrate  2 . 
     The substrate  2  is formed of single crystal Silicon and has a thickness of 250 μm. Each of the apertures is formed into a trapezoid structure by means of anisotropy etching in such a manner that a top side is smaller than a bottom side in area. The top sides of the respective apertures  2 A,  2 B,  2 C,  2 D, and  2 E are closed in fluid-tight manner by the diaphragms  6 A,  6 B,  6 C,  6 D, and  6 E, respectively. Thus, each of the apertures  2 A,  2 B,  2 C,  2 D, and  2 E becomes a closed space. 
     Each of the diaphragms  6 A,  6 B,  6 C,  6 D, and  6 E is made in such a manner that one side of an original diaphragm material is formed thereon with an oxidized thin film while the original diaphragm material is kept at a high temperature, and thereafter the other side is provided with a metal thin film while the original diaphragm material is kept at a room temperature so as to establish a difference of thermal expansion rate across the original diaphragm material. Thus, each of the diaphragms  6 A,  6 B,  6 C,  6 D, and  6 E is bent into a curvature. 
     The guide plate  3  is formed of glass for easy positioning thereof during assembly. The guide plate  3  is provided at its opposite ends with a first port  3   b  and a second port  3   c  which are in fluid communication with opposite ends of a concave portion  3   a , respectively. The lateral width of the concave portion  3   a  is identical with that of each of the diaphragms  6 A,  6 B,  6 C,  6 D, and  6 E. The guide plate  3  has a thickness of 250 μm. The concave portion  3   a  has a depth of 15 μm. The guide plate  3  is fixedly mounted by means of a bonding agent on the upper side of the substrate  2  in such a manner that the diaphragms  6 A,  6 B,  6 C,  6 D, and  6 E are aligned with the concave portion  3   a.    
     Similar to the guide plate  3 , the base plate  4  is formed of glass for easy positioning thereof when assembled. The base plate  4  is identical with both the substrate  2  and the guide plate  3  in length but is wider than the substrate  2  and the guide plate  3 . The base plate  4  has a thickness of 250 μm. 
     The miniature pump apparatus  1  is provided with a heater device  5  which includes five heating elements  5 A,  5 B,  5 C,  5 D, and  5 E which are deposited on the upper surface of the base plate  4  so as to be aligned with the lower sides of the respective apertures  2 A,  2 B,  2 C,  2 D, and  2 E. The heating elements  5 A,  5 B,  5 C,  5 D, and  5 E are formed of NiCrSi and have a resistive value ranging from 20 to 100 Ohms. The heater device  5  also includes six terminal elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e , and  5   f  which serve for connecting between a current supply source or a power source  7  (cf. FIG. 7) and each of the heating elements  5 A,  5 B,  5 C,  5 D, and  5 E. The terminal elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e , and  5   f  are formed of Au having a resistive value ranging from 1 to 5 Ohms which is smaller than the resistive value of each heating element. In light of the fact that Au is difficult to adhere directly to glass, six Cr plates are deposited on the base plate  4  and the Au terminal elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e , and  5   f  are deposited on the Cr plates, respectively, thereby forming the Au terminal elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e , and  5   f  on the glass base plate  4 . The deposition or sputtering of NiCrSi is made for alignment with the lower sides of the respective apertures  2 A,  2 B,  2 C,  2 D, and  2 E for forming the heating elements  5 A,  5 B,  5 C,  5 D, and  5 E. 
     As best shown in FIG. 3, each of the heating elements  5 A,  5 B,  5 C,  5 D, and  5 E is divided in to three spaced parallel parts. The parallel-three-part-structured heating element  5 A is layered on a distal end of the terminal element  5   a  and a distal end of the terminal element  5   b , the parallel-three-part-structured heating element  5 B is layered on another distal end of the terminal element  5   a  and a distal end of the terminal element  5   d , the parallel-three-part-structured heating element  5 C is layered on a distal end of the terminal element  5   c  and another distal end of the terminal element  5   d , the parallel-three-part-structured heating element  5 D is layered on another distal end of the terminal element  5   c  and a distal end of the terminal element  5   f , and the parallel-three-part-structured heating element  5 E is layered on a distal end of the terminal element  5   e  and another distal end of the terminal element  5   f.    
     As best shown in FIG. 4, the thickness of the heating element  5 A becomes minimum at positions  5 A 1  when layered on upper two edge portions of the terminal element  5   a , while the thickness of the heating element  5 A also becomes minimum at positions  5 A 1  when layered on two upper edge portions of the terminal element  5   b . Such a structure is found in each of other heating elements  5 B,  5 C,  5 D, and  5 E. When a current is applied to the heating element  5 A, the resulting amount of heat generation becomes maximum at the portions  5 A 1 . This establishes a quick evaporation of the fluid which is of a low boiling point, thereby shortening the time period duration which the current is supplied to each of the heating elements. Thus, the returning motion of each diaphragm from its expanded position to its original position can be made as quick as possible, which lessens the amount of heat involved in the concave portion  3   a , and provides a quick responsiveness for the miniature pump apparatus  1 . It is to be noted three parts of each of the heating elements  5 A,  5 B,  5 C,  5 D, and  5 E can be arranged in a curved manner instead of the illustrated straight lined manner. 
     As illustrated in FIG. 7, the current supply source  7  includes a 5-volt battery  7 A which is in association with a set of the switches  7   a ,  7   b ,  7   c ,  7   d ,  7   e ,  7   f ,  7   g ,  7   h ,  7   i , and  7   j  and depending on conditions thereof current supply to each of the heating elements  5 A,  5 B,  5 C,  5 D, and  5 E is made as will be detailed later. The switches  7   a ,  7   b ,  7   c ,  7   d ,  7   e ,  7   f ,  7   g ,  7   h ,  7   i , and  7   j  are under the control of a controller  8  which is a CPU or micro-processor. Depending on a desired flow-rate of the fluid and/or a temperature thereof, the controller  8  operates to close one or more switches. 
     At opposite ends of the substrate  2 , there are provided slits  2   a  and  2   a , respectively, by means of anisotropy etching. The slits  2   a  are used as an inlet and outlet, respectively. The fluid supplied to one slit  2   a  by way of a conduit connected thereto is moved through  3   b ,  3   a , and  3   c  by the pumping action of the apparatus  1  as will be detailed later and forced out from the other slit  2   a  to another conduit connected thereto. 
     As explained above, on the upper surface of the base plate  4  there are deposited the heating elements  5 A,  5 B,  5 C,  5 D, and  5 E. Thus, when the substrate  2  is mounted on the upper surface of the base plate  4 , gaps (not indicated) are defined therebetween. However, such gaps are filled with a bonding agent used for coupling the base plate  4  and the substrate  2  subject to the thickness of the bonding agent layer being larger than the thickness of each of the heating elements  5 A,  5 B,  5 C,  5 D, and SE. Upon completion of the coupling of the base plate  4  and the substrate  2 , in each of the apertures  2 A,  2 B,  2 C,  2 D, and  2 E, an inner fluid is enclosed in fluid-tight manner. 
     The apparatus  1  having the foregoing structure operates as follows. While all the switches are opened if the controller  8  detects a flow rate and the temperature of the fluid, the controller  8  closes the switches  7   a  and  7   d , thereby applying a current to the heating element  5 A and the resultant heat evaporates the fluid having a low boiling point which is enclosed in the aperture  2 A. Thus, the diaphragm  6 A is brought into an operative or convex condition (FIG. 6) from an assembled or concave condition (FIG.  5 ). Then, closing the switch  7   h  concurrently with opening the switch  7   d  brings both concave conditions of the diaphragms  6 A and  6 B. Subsequently, establishing simultaneous closing of the switches  7   e  and  7   j  and opening the switches  7   a  and  7   h  brings current supplies to both the heating elements  5 B and  5 C, whereby the diagram  6 A is returned to the original condition shown in FIG.  5  and simultaneously the diaphragms  6 B and  6 C are brought into convex conditions, respectively. Thus, similar switching operations can control the convex condition of the diaphragms in sequence in such a manner that two adjacent diaphragms are convex simultaneously which forces the fluid in the passage  3   a  from the inlet port to the outlet port. 
     It is to be noted that other than the foregoing diaphragm convex mode, other modes can be employed. For example, the diaphragms can be brought into convex condition in turn one by one. In the foregoing structure, despite the use of five heating elements the number of terminals is merely six, thereby simplifying the wiring. Thus, this apparatus  1  can be miniaturized. 
     As shown in FIG. 8, another heater device  25  is illustrated. In this heater device  25 , a heating element  25 A is formed between terminal elements  25   a  and  25   f  in such a manner that the heating element  25 A is formed into a bottlenecked shape for enabling easy heat generation at the heating element  25 A. Current supply through the terminal element  25   a , the heating element  25 A, and the terminal element  25   f  brings immediate heat generation at the heating element  25 A due to the fact the current passing area is much smaller than that of each of the terminal elements  25   a  and  25   f.    
     Heating elements  25 B,  25 C,  25 D, and  25 E, which are between terminal elements  25   b  and  25   g , between terminal elements  25   c  and  25   h , between the elements  25   d  and  25   i , and between the elements  25   e  and  25   j  are designed on the basis of the foregoing concept. 
     Such heat generation at the heating elements  25 A,  25 B,  25 C,  25 D, and  25 E allows each diaphragm to return from its expanded position to its original position as quickly as possible, which lessens the amount of heat involved in the concave portion  3   a , and provides for a quick responsiveness of the miniature pump apparatus  1 . 
     The invention has thus been shown and described with reference to specific embodiments. However, it should be understood that the invention is in no way limited to the details of the illustrated structures but changes and modifications may be made without departing from the scope of the appended claims.