SOLID STATE BLOWER

Abstract: A pumping device for gases or liquids having a housing and a substantially planar resilient impeller mounted to the housing to be free to move perpendicular to the impeller plane. Apparatus for driving the impeller and acting at least one point in the impeller is provided which acts to propagate a travelling flexure wave along the impeller in the plane of the impeller to pump gas or liquid. In the preferred embodiment of the invention, the impeller is an elongated blade (18) and is driven by a piezoelectric bending element (28) movable back and forth by a controlled alternating voltage power supply (39). The blade or diaphragm may be contained in a channel or duct, so that the undulating motion of the blade against the walls of the duct act as a valving means.

Description: Description Solid State Blower Technical Field The invention relates to pumping devices for air or liquids and specifically to a blower utilizing an undulating blade. Background Art Electronic equipment is customarily cooled using rotary fans or blowers, which circulate air through the entire housing to maintain a constant operating tempera¬ ture. Steady state temperature maintenance of the electronic components is important not only to prevent overheating, but also to assure reliable operation. Most electronic equipment now contains only solid state electronic components, such as miniaturized transistors and integrated circuits, and no longer utilizes vacuum tubes and other generally large heat producing components. The amount of cooling required to maintain stable operating temperatures has therefore been substantially reduced. Also, the cooling require¬ ments have been localized, since only several very small components, typically mounted on printed circuit boards, actually require cooling. Thus, cooling of the entire cabinet is not required. Nevertheless, even though wasteful, electronic equipment has continued to be cooled in this manner, since neither rotary fans nor other cooling devices have successfully been miniaturized, and rotary fans, which have been substantially improved OMPI over the years, continue to offer the most reliable and efficient method of cooling. Comparatively, however, when used in solid state electronic equipment, rotary fans or blowers stand out as the largest, noisiest, and most short-lived part of the assembly, the only moving component, and the component which most severely limits environmental tolerance specifications. Another form of blower, using the principle of a vibrating blade, has been proposed in the past. Austrian Patent No. 167,983 to Anderle and U.S. Patent No. 4,063,826 to Riepe are typical of such designs. In the Riepe patent a flexible blade is driven magnetically to deflect from side to side. The blade bends back and forth about a node point. The flapping end of the blade to the outside of the node point is disposed in a pumping duct to pump liquid through the duct. In the Anderle patent, a flexible blade is fixedly mounted at the inlet end of a blower duct and driven magnetically from side to side. Theoretically, due to the few moving parts, blowers of these types are susceptible of miniaturization; as a practical matter, however, they are generally so inefficient that they are better suited for producing heat than for generating cooling air movement, with the result that none has found any significant commercial acceptance. Disclosure of Invention The present invention is a revolutionary solid state blower of the -undulating blade type which is extremely efficient, inexpensive to manufacture, and designed for a long service life. More specifically, the present invention is a pumping device which may be used to pump gases or liquids having a housing and an elongated impeller or blade mounted to the housing and free to move laterally. A piezo¬ electric bending element, or so-called "bilaminate", is mounted at one end on the housing, and on its other end supports the blade ' to apply a sinusoidal driving force to the blade for propagating a traveling flexure wave along the blade, preferable in a quadrature rela¬ tion, thereby to pump the gas or liquid. As thus mounted, the entire length of the blade is free to move laterally as it is driven back and forth by the piezo- electric element. The blade may be contained in a pumping duct or channel in the housing so that the blade motion itself provides inlet and outlet valving. The piezo-electric bilaminate is a strip consisting of two layers of piezo-electric ceramic, polarized in opposite directions, which on their facing sides are separated by a conducting layer and which on their outside faces are surrounded by conducting layers. The two outside conducting layers are connected as electrodes to a controlled alternating current supply. Since the piezo-electric layers have opposite polarity, voltage applied across the bilaminate strip induces bending of the element. Accordingly, alternating voltage across the piezo-electric element will drive the blade back and forth at the point of attachment. When driven at one point, the blade material, resiliency, taper, and width are preferably selected to tune the impeller to the oscillating frequency of the drive arrangement to result in stable and efficient operation. Alternatively, the blade may be driven at two or more points, in which case these considerations become less critical, and high efficiency can be attained at other than resonant frequency. The blower operates without any substantial mechanical friction to permit high operating speed, a consequently high throughput relative to size, a virtually unlimited service life, and may be miniatur- ized and still produce a significant flow of air to cool miniature components. In its miniaturized form, the device may be mounted directly on printed circuit boards, alongside the individual components which require cooling, and due to its high efficiency will provide sufficient cooling air. The blower preferably is constructed with a pair of counter-oscillating blades in parallel pumping channels so that it is dynamically balanced and vibration free. Pumping efficiency of the device may be improved by providing venturi intake ports along the output half of the duct to increase the air flow through the ducts. Brief Description of the Drawings For a better understanding of the invention, reference may be had to the following detailed descrip- tion of the preferred embodiments, taken in conjunction with the accompanying drawings, in which: Fig. 1 is a pictorial view of a solid state blower having a pair of blades driven by piezo¬ electric elements according to the invention; Fig. 2 is a longitudinal-sectional view of a piezo-electric bilaminate driving element for use with the blower of Fig. 1; Figs. 3a, 3b, 3c, 3d, 3e and 3f are schematic representations of first the blade at rest and then the pumping motion of the blade, phased in quadrature, at various points of the oscillation cycle; and Fig. 4 is a pictorial view of a modified form of the solid state blower shown in Fig. 1. OΛΪP A JF Best Mode For Carrying Out the Invention Referring to Fig. 1, a solid state blower according to the present invention has a housing 10, outer walls 12 and an inner divider 14 forming a pair of air channels 16 between the bottom 17a and top 17b (lifted* out of the way for clarity). A pair of resilient blades 18 are mounted in the channels 16 for driving air through the device. The blades 18 are generally tapered from their inlet ends 24 toward the outlet ends 22 and have whip portions 20 at their outlet ends 22 to improve the air throughput pumping capacity. The whip portions 20 are preferably made of Mylar. A piezo-electric bilaminate 28 is attached at one end 40, for example by a plastic holder and screws 41, to each of the housing walls 12 and at the other end 42, by cementing or any other suitable means to a point on each blade 18 to support the blade in the channel 10 in a manner such that upon lateral movement of the bilaminates the blades 18 are free to undergo simul- taneous lateral deflection. " This mounting arrange¬ ment permits free lateral movement of the blade 18 along the entire length with corresponding lateral movement of the end 42 of the piezo-electric element 28. A piezo-electric element suitable for use in the present invention is marketed by Gulton Industries, Inc., Piezo Products Division, Metuchen, N.J., under the name "Piezo Ceramic Bender Element", No. G1195. Each bi¬ laminate strip 28 (Fig. 2) has two layers of piezo- electric ceramic 29 separated by a layer of conducting material 30, e.g. brass. The outside layers 32, 34 are silver, and connected to the leads 36, 38 of a controlled alternating current supply 39. The two ceramic layers 29 are polarized in opposite directions, so that voltage across the bilaminate induces a bending motion in the strip. Since the bilaminate strip 28 is fixed on the housing at 41, controlled alternating voltage, therefore, causes the free end 42 of the piezo-electric element 28 to move back and forth at the voltage frequency. The bending movement of the bilaminates 28, in turn, drives the blades 18 back and forth at the point of attachment 42 at a controlled rate. Although not illustrated in Fig. 1, the connections from the piezo-electric elements 28 to the power supply 39 are conveniently made at the end 40, beneath the holder 41. When driven back and forth, the blade 18 represents a beam subjected to combined bending and shearing loads varying so rapidly that inertial effects dominate to propagate a traveling flexure wave along the impeller or blade from the inlet end of the duct toward the outlet end of the duct. Typically a voltage oscillating in the range of 60-400 hz is applied. The most efficient pumping action results when the driving force is applied in quadrature, that is, to produce a 90 degree ( β ) phase lag in the oscillation cycle between two points along the blade, for example near the inlet end of the duct and near the outlet end, as illustrated schematically in Figs. 3a-3f. The driving force (F) is applied at a single point, and with a selected frequency range ' depending, e.g., upon the blade material, taper, and resiliency and thus the blade resonant frequency, such that the blade undergoes both lateral displacement and bending at the point of applied force. The driving force F on the blade produces the successive blade shapes shown in Figs. 3a-3f and directions of air motion (A) indicated by arrows, as described below. iU 0 Referring to Fig. 3a, with the blade 18 at rest, an initial lateral force F is applied (by the piezo¬ electric element) to the blade at point 42. Thereafter, the rear portion of the blade 18 moves toward the duct wall 16a, with the forward end of the blade lagging (Fig. 3b) due to inertia. Lateral movement of the blade 18 at 42 not only pushes air in the duct toward the outlet end, but draws air in from the inlet end. When the rear portion (at 42) of the blade 18 reaches the duct wall 16a (Fig. 3b) , the force F applied by the bilaminate is reversed (Fig. 3c) to move the rear portion of the blade toward the other wall 16b (Fig. 3d) . The forward end of the blade, however, continues to lag behind by 90° of the oscillation cycle. When the driven point 14 of the blade reaches the other wall 16b, the force F is again reversed (Fig. 3e) to move the blade back, again the forward end of the blade reaching the duct wall 16b 90° later in the oscillation cycle (Fig. 3f) . The motion of the blade " continues to draw in air into the blower and expel air once in the duct. Optimum pumping efficiency results when the blade resonance frequency is at or near the driving frequency of the piezo-electric bilaminate assembly 28, since this maintains a quadrature relation between the leading (rear) and lagging (forward end) portions of the blade 18, and provides inlet and outlet valving as illustrated in Figs. 3b-3f. The blade may be operated either in a free medium or in a duct, e.g. 16. In the latter embodiment, the duct 16 has a width such that the ends 24, 22 of the blades 18 contact, or almost contact, the duct walls, during the back and forth lateral movement, the down¬ stream contact lagging the upstream point of contact by 90° of the oscillation cycle. Thus, the two contact points will have a quadrature relation with respect to each other so that the blade tips perform the functions of intake and outlet valves. See Figs. 3b-3f. Air throughput is also improved if venturi air louvers 56 are provided in the duct walls in the output half of the blower. In the Fig. 1 embodiment, the blower contains two counter-oscillating blades 18 to operate 180° out of phase with each other. The complementary back and forth motion of the two blades 18 provides dynamic balancing and prevents vibration of the device. As an example of the efficient operation of the present invention, a miniaurized form of blower con¬ structed in accordance with Fig. 1, having an overall length of about 1.75 inches, a width of 0.75 inches and a height of 0.5 inches, and operated at a frequency of 60 hz by the piezo-electric bilamibates, produces a sufficient throughput of air and a sufficient output pressure to be capable of blowing out a Zippo wind- proof lighter. Thus the device is very efficient, and in tests, operation has been very stable, with efficiency so high that rises in temperature of the bilaminates have been virtually undetectable. A modified embodiment of the solid state blower illustrated in Fig. 1 is shown in Fig. 4, where in place of the side mounted piezo-electric element 28, a pair of end-mounted bilaminate piezo-electric elements 128 drive respective ones of a pair of flat resiliant blades 118. The free ends of the blades are terminated in whip portions 122, preferably made of Mylar. The blower assembly includes a housing 110, side walls 112 and a bottom plate 117a. A top cover may be added if desired, similar to cover 17b shown in Fig. 1. In this embodiment, the blades 118 are not disposed in separate pumping ducts, yet efficient pumping action is achieved without the enhanced valving action produced by the ducts due to the quadrature travelling wave induced in the blades 118. The piezo-electric bilaminates 128 are mounted at one end 140 to a cross member 141 bridging the walls 112 of the housing 110. The member 141 is provided with a pair of vertical slots 142, each of which is sized to snugly receive the end of the bilaminate 128 and a pair of electrically conductive contact leaves 144, one on either side of the bilaminate. Conductors, not shown, are connected to the leaves for coupling to the alternat¬ ing voltage supply. The free ends of the bilaminates 128 are attached to coupler weights 150, which in turn support the resilient blades 118. The weights 150 have vertical slots along their narrow edges for snugly engaging the bilaminates and blades, respectively. As shown in Fig. " 4, the blades preferably are substantially wider than the bilaminates, to maximize air flow. In this mounting arrangement, as in the Fig. 1 embodiment, the blade 118 is not fixed at any point relative to the housing and is free to move laterally (i.e., perpendicular to the flat surface of the blade 118) back and forth along its entire length when driven by the free end of the piezo-electric element 128. As in the case of the blade in Fig. 1, when alter¬ nating voltage is applied across the bilaminates 128, a cyclical back and forth movement occurs in the free ends of the bilaminates 128 which in turn drives the weights 150 and the ends of the blade 118 fixed to the weights 150 back and forth in the housing. Since the entire length of the blade 118 is free to move back and forth relative to the housing, a traveling flexure wave is propagated when the blade is driven at an appropriate frequency, i.e. to produce quadrature similar to that illustrated in Figs. 3a-3f, from the inlet end 124 toward the outlet end 122. Since, however, the propa- gated wave travels along the blade from one end 125 to the other 122, the blower works very efficiently in pumping fluids, especially air, without the need for blade valving action. To effect dynamic balancing of the system, the two bilaminates are driven to opposing phase relationship, as in the Fig. 1 embodiment. Although for dynamic balancing purposes, it is preferable to employ a pair of counter-oscillating blades, the embodiments of both Figs. 1 and 4 can provide effective air movement with a single oscillat- ing blade. Variations and modifications of the disclosed embodiments, without departing from the inventive principles disclosed herein, will be apparent to those • skilled in the art. For example, the blade may be driven at two or more points along its length, in which case the resonant frequency and driving frequency become less of a factor in determining efficiency. All such modifications and variations are intended to be within the scope of the invention as defined in the following claims . " fUK O.V.

Claims: Claims 1. A pumping device for gases or liquids comprising a housing, a substantially planar resilient impeller mounted to said housing to be free to move perpendicular to said plane, driving means acting on. said impeller at least at one point for driving said impeller perpendicular to said plane for propagating a traveling flexure wave along said impeller to pump said gas or liquid. 2. A device according to claim 1, wherein said impeller is an elongated blade, and said driving means are adapted for progagating a traveling flexure wave along said impeller longitudinally from one end toward the opposite end. 3. A device according to claim 2, comprising piezo¬ electric driving means coupled between said housing * and a point on said impeller for moving said im¬ peller perpendicular to said plane when voltage is applied across the piezo-electric driving means, ... and controlled alternating voltage power supply means connected to said piezo-electric driving means for moving said driving means back and forth perpendicular to said plane. 4. A device according to claim 1, 2, or 3, wherein said housing has confining walls forming a channel or duct, and said impeller is disposed in said channel or duct. -12- 5. A device according to claim 3, wherein said housing has confining walls forming a channel or duct, said impeller is disposed in said channel or duct, and said driving means are adapted to act on said impeller such that said impeller contacts said duct walls during back and forth movement, the downstream end of the blade contacting the wall approximately 90° of the oscillation cycle after the upstream end of the blade, so that the upstream contact serves to establish intake valving and the downstream contact serves to establish outlet valving. 6. A device according to claim 5, further comprising a second impeller mounted in a second pumping channel or duct in said housing to be free to move perpendicular to said plane and opposed to the other impeller, second driving means acting on said second impeller at least one point for driving said impeller perpendicular to said plane for propagating a traveling flexure wave along said impeller in said plane to pump said gas or liquid, wherein said second driving means is 180° out of phase with the driving means for said other impeller so that said impellers counter-oscillate to achieve dynamic balance and reduce vibration of said device. 7. A device according to claim 6, wherein said duct walls have air or liquid venturi intake ports along the output half of said device to increase the pumping capacity of said device. ■ BU 8. A device according to claim 7, wherein said impeller is essentially stiff from the driving point to said other end, and tapered from said driving point to said other end to oscillate flexibly from the driving point. 9. A device according to claim 1, 2, or 3, wherein said driving means drives said impeller in a quadrature relationship. 10. A device according to claim 3, wherein said piezo- electric driving means comprises an elongated piezo-electric bilaminate having one end connected to said housing and the other end coupled to said impeller. 11. A device according to claim 10, wherein said bi- laminate is coupled to said impeller by a connect¬ ing member, the weight of said member, together with said impeller, producing a system resonant at the frequency of the applied alternating current power. 12. A device according to claim 9 or 10, wherein said bilaminate is co-planar with said impeller. 13. A device according to claim 9, wherein said impeller is disposed within said housing, and said bilaminate is arranged on the outside of said housing parallel to said impeller. 14. A process for pumping fluid using a substantially planar resilient impeller comprising the steps of supporting said impeller to be free to move per¬ pendicular to said plane and to be restrained from movement in said plane, applying a cylical force, perpendicular to said plane, to said impeller at least at one point at a frequency wherein a traveling flexure wave is imparted to said impeller for pumping said fluid. 15. A process as defined in claim 14, wherein said impeller is an elongated blade, and is supported and said force is applied by a piezo-electric bending element producing quadrature motion in the blade. 16. A process as defined in claim 15, wherein said blade is disposed in a pumping duct having walls disposed on either side of said blade, and said blade contacts said duct walls for producing valv¬ ing action. O

Inventors: KOLM E, KOLM H
Applicants: ROTRON INC
Application year: 1980
Main classification: F04B17
IPC codes: F04B17, F04B43, F04D33