WO2003056691A1

WO2003056691A1 - Mini-kraftformer

Info

Publication number: WO2003056691A1
Application number: PCT/IB2002/005575
Authority: WO
Inventors: Arne Nysveen; Knut Asskildt
Original assignee: Abb Research Ltd.
Priority date: 2001-12-27
Filing date: 2002-12-20
Publication date: 2003-07-10
Also published as: AU2002354285A1; WO2003056691A9; NO20016398D0

Abstract

A micro-electromechanical energy transformer comprising a stationary element (6) with a planar surface and a movable element (1) with a planar surface (1) arranged in such a manner that an air gap arises between the two plane surfaces (1). A first electrode system (4) belonging to the stationary element (1) and co-operating means (3) belonging to the movable element (1) create an electrical field in the air gap. The movable element (1) is integrated in an elastic mechanical element (1,2) such that the movement takes place through bending, for instance oscillation, of the elastic mechanical element (1,2).

Description

Technical Area

The invention concerns a micro-electromechanical system (ME] mechanical actuation and transformation of pneumatic/hydraulic, mechanical ai energy.

State of the art.

Micro-electromechanical units/systems (MEMS) are different fr< traditional electromechanical systems among others in their method of producti materials used. These units are produced mainly by processes for production of semiconductor circuits/chips. Typically, the units are produced of silicon or gla processes applied are photo lithography, etching (for example DRIE - Deep Re etching), doping, epitaxial growth and deposition of (metallic) materials (sputte

These processes make possible the production of small units wit geometrical details (< 1 μm). The production methods are especially suitable fc production; the costs related to design and production of mesh are relatively hi^ volume the component price can become very low, just as for integrated circuit

A common problem for micro-electromechanical units is tribolo frictional forces and wear between two gliding surfaces. The coefficient of frict very high (approximately 1000 times higher than for steel) such that the direct < between movable elements becomes very unfavourable when the relative speed results in major limitations for the functionality of the units and the problem is consideration in the research community.

The publication "An electrostatic induction micromotor support lubricated bearings" by L.G.Frechette et al, pp 290-293, Proc. MEMS 2001. 14 International Conference of Micro Electro Mechanical Systems, New York, US describes a rotating electrical machine with a pneumatic bearing. The rotating e shaped rotor) is kept suspended from the stationary element by control of the pi sides of the rotor plate. In this manner a direct contact between the two gliding avoided. The problem with this design is that the unit requires a pneumatic con order to keep the rotating plate in the correct position, especially in cases when vibrates. The publication "Vibration-to-Electrical Energy Conversion" by J et al, pp 48-53, Proc. of ISLPE99, San Diego , USA, 1999, describes a micro- electromechanical unit for conversion of mechanical energy to electrical energy bearing in the traditional sense of the word. The movable element is suspended 1 beams that are stretched/bent with the movement of the swinging matter. The en conversion takes place when using a variable capacitance in which the stationar elements are designed as chambers that overlap (comb). The unit described in th has an effect of 8 μW. The effect is fundamentally restricted by two factors, the between the stationary and movable elements and the frequency (speed) of the n element(s). In this unit the force is restricted by a low capacitance due to a smal though the comb has many teeth. MEMS units are typically planar structures an therefore desired that the force should act in an air gap that is parallel to the subi not the case in the present unit.

In US patent no. 4,943,750 "Electrostatic micromotor" by Howe selection of embodiments are shown where the energy interaction between the s and movable unit takes place in a air gap that is parallel to the substrate. Both re translatory movement is described. The mounting of the movable unit can be pri and/or electromagnetic (levitation). The patent describes several principles for c mechanical and electrical effects. The methods can be divided into two main gi Electrical and mechanical. In traditional electrical machines it is only the magm are used. In the case of micro-machines transformation of effect based on elect: sometimes preferred. Both electrical and magnetic induction is described in the output of the unit can be substantially enlarged since the area where the transfoi power takes place can be large. Further the number of revolutions of the rotatin comprises the rotor can be high. In "An electrostatic induction micromotor supj lubricated bearings" by L.G.Frechette et al, pp 290-293, Proc. MEMS 2001. ref a comparable structure is used in a unit with 900,000 rpm and a performance of are not published any results that show that these units have a long longevity. It that this may be due to problems with the mounting. US patent no. 5,043,043 "Method for fabricating side drive elect micromotor" by Howe et al. describes another embodiment where the power in place in an air gap radially to the rotational axis of the rotor (as in the traditiom machines). For this motor the area of power interaction will be smaller and dep thickness of the rotating plate.

Micromachines can further be produced by taking advantage of effect to create ultrasonic waves. However can these only be used as motors ai generators. The article "Smart motors in Germany" by W. Seeman , pp 472-48! of SPIE, vol 3321, 1998 describes such a motor.

Purpose of the Invention

One purpose of the invention is describing a technical solution tl several of the above described limitations to the present state of the art.

Another purpose of the invention is providing an arrangement fo the mechanical energy in a moving, elastic element to electrical energy, which j used to provide electrical energy to further electrical circuits.

It is also a purpose of the invention to provide an arrangement wl elastic mechanical element which can be set in motion is included in a generate produce electrical effect.

It is a further purpose of the invention to provide an arrangement elastic mechanical element can be set in motion through the supply of electrical order to produce a fluid stream. It is still a further purpose of the invention to provide an arranger an elastic mechanical element can be set in motion or translocation through the i electrical energy in order to form an actuator arrangement.

More especially the invention is aimed at providing different emt achieving the above mentioned purposes without applying mechanical elements immanent tribology problems.

The purpose of the invention is achieved according to the inventi< micro-electromechanical energy transformer that comprises a stationary element surface and a movable element with a planar surface that are arranged in such a ; there is an air gap between the two planar surfaces and where a first system of el belonging to the stationary element and co-operating means belonging to the mo can form an electrical field in the said air gap. The energy transformer is charact movable element being integrated in an elastic, mechanical element such that thϊ takes place through bending, for instance oscillation, of the elastic, mechanical e In one embodiment the energy transformer is adapted for use as a generator whe mechanical energy is converted to electrical energy in that it comprises an electr conjunction with the first electrode system wherein electrical effect is generated induced electrical current through the movement of the movable element, for ex resulting from an oscillating fluid stream, and wherein the electrical circuit trans energy to an electrical cargo.

In a further embodiment the energy transformer is adapted for us< actuator wherein electrical energy is converted to mechanical energy through th< an electrical driver circuit in conjunction with an electrical energy source in ordi the first electrode system with electrical energy in the form of electrical current resulting electrical forces between the stationary and the movable elements sets element in motion.

Further advantageous embodiments of the invention will appear 1 dependent claims and the description. Below are described the embodiments of the invention through e: examples are illustrated through the following enclosed figures:

Fig. 1 depicts an example of a planar rotor plate at the end of an elastic element in the form of a bendable beam.

Fig. 2 depicts a cross section seen from the front and perpendicular to tl movement of a beam.

Fig. 3 shows a typical structure seen from the side in a cut through a sv

Fig. 4 shows the swinging beam in the energy transformer seen from ab

Fig. 5 depicts how electrostatic forces act between the rotor electrodes ; electrodes. Fig. 6 shows a schematic view of an unfolded cross section of the surfa stator and rotor (planar rotor plate) against the air gap where the > placed.

Fig. 7 depicts the rotor electrode system arranged on the upside of the s beam. Fig. 8 a shows a cross sectional view of the air gap with the electrode sys stator and with a permanently polarised material (electret) in the of an electrode system as on figure 7. Fig. 8b shows a cross sectional view of the air gap with the electrode sys stator and with a space charged material in the rotor instead of an system as on figure 7.

Fig. 9 - shows the electrical coupling when the unit is used an generator. Fig. 10 shows a cross sectional view of the air gap with the electrode sys stator and with conductive material on the rotor surface (inductio

Detailed description.

In the following it is described firstly how the micro-electromecl transformer is designed and how it can be used as an electrical generator. Figure preferred embodiment of a movable element (1) with a planar sheet executed as plate 1. The plate 1 is set in motion back and forth along a curve, typically appn arch of a circle, when the mechanical element 2 is bent. In figure 1 the elastic n element 1,2 is in principle formed as a beam 2. The beam 2 is set in a swinging alternating pneumatic pressure on both sides of the beam, for instance through e a fluid stream directed against the longitudinal direction of beam 2. The beam 2 planar rotor plate are typically produced from a larger silicon chip. The beam 2 have no contact with other elements, except for the beam being suspended from chip at one end 22 as shown on figure 1. The beam can be mounted in such a manner that the movable en< against the flow direction of a fluid stream or it can be mounted such that the m turned towards the flow direction. The structure of figure 1 can be implemented technology (Micro-electromechanical system) among others.

On figure 2 it is shown how the movable element, the plate 2, ha with the stationary element, in this case the stator structure 4,6 or the underlyin; The electrodes 4 are placed on the backside of the stator plate 6 and on the tops plate 1. The beam 1 is driven to the right on the figure by a higher pneumatic pi first chamber 20 on the left hand side of the beam 2, than pressure P₂ in a secon on the right hand side of the beam 2. The pneumatic energy, represented by air pressure, is converted firstly to mechanical kinetic energy as the air (the gas) is beam in motion. This kinetic energy can be converted to electrical energy by th electrodes 3,4 on the plate 1 and on the upper edge of the cavernous space, i.e. < underside of an upper glass plate 6 that represents the stator 6 in the constructic Figure 3 shows a cross sectional view through the MEMS structn preferred embodiment of the power transformer in the longitudinal direction of

Beam 2 is etched from a substrate 5 that is bound to an underlying substrate 7. 1 is closed for example with a glass plate 6, whereon also the stator electrode syst mounted. In this manner the movable element 1 becomes an integral element of mechanical element 1,2.

Figure 4 illustrates how the beam 2 is attached at its one end and shown when the planar rotor 1 is moving along a curvature on the underside of , is designed as a circular sector. The beam 2 is as mentioned preferable producer. (DRJE) from a larger Si-disk. This achieves a very good mechanical strength fo attachment of beam 2 to the remainder of the silicon piece. The planar rotor plai along a curvature, approximately a circular curvature when beam 2 is bending.

The stiffness of beam 2, its mass distribution as well as the powe pneumatic system determines the swing frequency. As an approximation of the may be presumed that the speed of the planar rotor plate will be sinus variable \ motion between the stationary and movable element takes place tangentially to The longitude of the air gap does therefore not change as a function of the air g; common problem with traditional capacitance actuators.

The movable element is as mentioned mounted on a bendable be assures that the movable element does not come into contact with the stationary beam therefore defines a specific motion area for the movable element. The stif beam can be adapted to the application.

As opposed to a traditional electrical machine the power betweer and rotor 1 is electrical power arising from electrical charge and not magnetic p electrical current as its source. In order to achieve an energy transformation the power must work against (generator) or with (motor) the rotor direction of mov 5 illustrates how this can be accomplished. The charge along the air gap to both rotor is varied between a given positive and negative value in such a manner th; charge in stator and rotor is zero. When the positions of the charges in stator an dislocated as shown on the figure, this results in a net axial power to the left on

The forces between the movable element and the stationary elern transmitted in an air gap parallel to the substrate whereby an active surface typi lxl mm. Specific power density is limited; this means that the area where the p transmission takes place should be as large as possible. In a preferred embodim< power interaction is applied between movable and stationary element. If the po tangential direction between stator 4 and planar rotor plate 1 is constant the turn will also vary as a sinus function with time. The speed variation with time is noi importance for the function of the unit as generator.

It is possible to produce a charge distribution that moves along tr arranging an electrode pattern as shown on figure 6. The electrodes in stator 4 a three phases all of which are to connected to their own AC voltage source 8, corresponding electrode pair on rotor in this case is connected to DC voltage so voltage sources connected to the stator 8 are alternating voltage sources that

displacement phase of 120 degrees. Thus the charge distribution will move alon as a wave. The speed is determined by the frequency of the voltage and the dist; the electrodes. In US Patent no 4,943,750 "Electrostatic micromotor" by Howe detailed description is given of how a moving electrostatic field may be arrange the power not to change its direction and not to have a too large variation it is m the velocity of the rotor and the electrical field from stator are the same. This is with the working principle of a common magnetic synchronous machine

Figure 7 illustrates the direct voltage electrode pattern 3 on the r "synchronous machine" that is based on electrical forces can also be produced \ electrode pattern on the rotor as shown on figure 7. An electrical field distributi stationary can as an alternative be mounted by using electret in rotor or through space charges in rotor as shown in figure 8. The electret is a material that has a polarisation. This results also in a "synchronous generator". One advantage wit] is that is no need for an electrode pattern on the oscillating beam as shown on fi disadvantage with this solution is that it is vulnerable to pollution in the form ol permanent charge of the rotor will attract dust. This also applies to the DC-exci figure 6, but in this case the polarity of the rotor electrodes can be altered after , Any dust that has collected on the rotor electrodes will then be set free.

The shown beam design according to the invention gives an imp the prior art as it makes it possible to have an electrode system on the movable the rotor, without the need for gliding contacts ("combs"). The electrode patten rotor plate can be contacted by means of the swinging beam. This is not possib] where there is a rotating plate needing gliding contacts ("combs"). When the unit operates as a generator it is normally not connects external voltage source as shown on figure 6. It is not necessary as only the rote placed in a voltage field in order for the unit to work. One example is the emboc on figure 9. The stator in this instance is connected to a rectifier that is further c< cargo. The advantage with such a system is that the need for a control system is passive rectifier can operate without control and regulation. In order for the syst is possible to use a capacitor that applies a voltage on the rotor. When the unit is necessary maintenance voltage for the rotor can be collected from the stator. Tl analogous with a traditional synchronous machine with static magnetising suppl stator clamps.

In the following a description is given for how the unit works as motor/generator. The micro-electromechanical unit is a linear motor where the i element ("rotor") is mounted on a bendable beam that defines its area of moveπ Somewhat simplified it can be said that the unit is a linear motor/generator whei element is a plate with a power efficiency tangential to the surface of the plate. ' supported on a bendable beam which defines the area of movement for the plate then supplied with electrical power from an external source and converts this pc mechanical movement. The stator circuit is supplied by an external voltage gene control both the amplitude and the frequency of the applied voltage. When the r designed with DC-excitated electrodes as on figure 6 or electret or with space c] figure 8 this is a "synchronous motor drive". This requires a position sensor du for knowledge of the mechanical position of rotor in order to operate the voltac. Thus it requires a larger control and regulation system. As one example piezore elements can be integrated on the beam 2 or on the plate 1, for example parallel electrodes 13 shown on figure 7 . By measuring the electrical resistance in these piezoresistive elements using one of several well-known techniques in the art, t beam 2 can be calculated in a calculator unit and further be used in the control i system for operating the beam movement.

In a preferred embodiment the motor is executed as an electroqu (EQS) motor, see figure 10. This is analogous to a magnetic induction motor. I based on electrical induction the surface of the rotor is doped such that the trans current and the conductive current are of the same order. This means that the pe the conductivity g and the frequency ω must be adapted to each other. The mor when the induced charge on the rotor surface is relocated in its position compar charge distribution on stator as the rotor moves asynchronous with the electrica on the stator electrodes. An example of such a motor with a rotating rotor is giv publication "Electroquasistatic induction micromotors" by S.F.Bart and J.L.Lar IEEE Micro-electromechanical Systems, New York, USA, 1989. In this case it necessary to know the exact position of the rotor. Deviation in speed between tl the voltage wave erected by stator will change the retardation and thus the prop unit. However is the requirement for accuracy and complexity reduced in the o] control system when the unit is operated in a swinging modus as compared wit] embodiment of a synchronous motor.

Typical applications for the invention are power generators whei set in motion by a fluid or air current. The energy of the moving fluid is then ce electrical energy. The converse transformation of energy is also possible, i.e. v invention is used as a pump motor to set the fluid in streaming motion in a pipe The invention may further be used as an actuator for instance for actuation of power and position of the moving element can be driven by the electrical drive great precision in all areas of movement. Thus this makes possible the use of t] actuator for dosimeters and micro-manipulators. An especially good control wi is achievable when a position sensor is included in the arrangement.

Claims

Patent claims:

1. A micro-electromechanical energy transformer comprising a stat (6) with a planar surface and a movable element (1) with a planar surface arranj manner that an air gap arises between the two plane surfaces (1), a first electrode system (4) belonging to the stationary element (1) and co-oper∑ belonging to the movable element (1) in order to create an electrical field in the charcterized in that the movable element (1) is integrated in an elastic mechanic (1,2) such that the movement takes place through bending, for instance oscilla elastic mechanical element (1,2).

2. An energy transformer according to claim 1, wherein the first ele (4) is a multiphased alternating voltage system.

3. An energy transformer according to claim 1, wherein the electric from the stationary element (6) and the electrical system mounted on the moval are moving synchronously.

4. An energy transformer according to claim 1, wherein said co-op (3) at the movable element (1) comprises a second electrode system (3).

5. An energy transformer according to claim 4, wherein the second system is a direct voltage system that erects an electric field in the air gap that : compared to the movable element.

6. An energy transformer according to claim 1, wherein said co-op (3) at the movable element (1) comprises areas with space charge dopings (10)

7. An energy transformer according to claim 1, wherein said co-op (3) at the movable element (1) comprises an electret material (11).

8. An energy transformer according to claim 1, wherein said co-opi

(3) at the movable element (1) comprises a conductive or semi-conductive surf. movable element (1).

9. An energy transformer according to claim 1, wherein the elastic element (1,2) is principally designed as a beam fastened at one end.

10. An energy transformer according to claim 1, wherein the moveπ the two planar elements (1,6) are mainly transitory with an approximately consi of the air gap between the two planar elements.

11. An energy transformer according to claim 1 , wherein the movab is moving approximately along a curve.

12. An energy transformer according to claim 4, wherein it comprise arranged along the bendable beam at least to its fastened end.

13. An energy transformer according to claim 1-7 and 9-12 adapted generator where mechanic energy is converted to electrical energy, further com electrical circuit (14) attached to the first electrode system (4) where electrical e generated in the form of induced electrical current by movement of the movab] for example caused by an oscillating fluid stream, and where the electrical circi transfers electrical energy to the electrical cargo (16).

14. An energy transformer according to any claim 1-12 adapted for i or as actuator wherein electrical energy is converted to mechanic energy, furthe an electrical drive circuit (15) attached to an electrical energy source in order tc electrical energy to the first electrode system (4) as electrical current such that t electric forces between the stationary element (6) and the movable element (1) movable element ( 1 ) in motion.