WO2003056692A1

WO2003056692A1 - Mini-kraftformer

Info

Publication number: WO2003056692A1
Application number: PCT/IB2002/005586
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: AU2002353397A1; NO20016399D0

Abstract

Method and device for transforming kinetic energy in a fluid stream to mechanical energy in at least one elastic, mechanical element (1, 2). The fluid stream is fed through a channel system (5) comprising said at least one mechanical element (1, 2) implemented in a MEMS structure. The fluid stream creates an oscillation that acts on said at least one mechanical element (1, 2). The fluid stream oscillation sets said at least one mechanical element (1,2) in a bending motion, for instance oscillation, such that said at least one mechanical element (1, 2) thus acquires energy from the fluid stream. The mechanical element (1, 2) is arranged to interact with a system that converts mechanical energy to electrical energy, heat or other forms of energy.

Description

MINI-KRAFTFORMER

Technical Area

The invention concerns a micromechanical unit for mechanical actuation and transformation of pneumatic/hydraulic to mechanical energy in a unit that further also can be arranged to transform the mechanical energy to electrical energy. More specifically the invention concerns a unit for mechanical actuation and transformation of pneumatic/hydraulic to mechanical energy.

State of the art. Micro-electromechanical units/systems (MEMS) are different from other traditional electromechanical systems in their method of production and the materials used among others. These units are produced mainly through processes for the production of semiconductor circuits/chips. Typically the units are produced of silicon or glass. Typical processes applied are photo lithography, etching (for example DRJE - Deep Reactive Ion etching), doping, epitaxial growth and deposition of (metallic) materials (sputtering).

These processes make possible the production of small units with very small geometrical details (< 1 μm). The production methods are especially suitable for high volume production. The costs related to design and production of mesh are relatively high. For a high volume the component price can become very low as for integrated circuits. A common problem for micro-electromechanical units is tribology, i.e. frictional forces and wear between two gliding surfaces. The coefficient of friction can be very high (approximately 1000 times higher than for steel) so that any direct contact between movable elements becomes very unfavourable when the relative velocity is high. This results in major limitations for the functionality of the units and the problem is given much consideration in research.

In the publication "An electrostatic induction micromotor supported on gas- lubricated bearings" by L.G.Frechette et al, pp 290-293, Proc. MEMS 2001. 14^th IEEE International Conference of Micro-electromechanical Systems, New York, USA, 2001, describes a rotating electrical machine with a pneumatic bearing. The rotating element (a rotor disk) is kept suspended from the stationary element by control of the pressure on both sides of the rotor disk. In this manner a direct contact between the two gliding surfaces is avoided. The problem with this design is that the unit requires a pneumatic control system in order to keep the rotating plate in the correct position, especially in cases where the unit vibrates. The publication "Vibration-to-Electrical Energy Conversion" by S.Meininger 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 that needs no bearing in the traditional sense of the word. The movable element is arranged suspended between two beams that are stretched/bent with the movement of the swinging matter. The energy conversion takes place when using variable capacitors where stationary and movable elements are designed as chambers that overlap in a so called comb structure. The unit described in the publication has an effect of 8 μW. The effect is fundamentally restricted by two factors, the force between the stationary and movable elements and the frequency (velocity) of the movable element(s). In the present unit the force is restricted by a low capacitance due to the capasitor's small area even though the comb has many teeth. MEMS units are typically planar structures and it is therefore desired that the force should act in an air gap that is parallel to the substrate. This is not the case in the present unit.

In US patent no. 4,943,750 "Electrostatic micromotor" by Howe et al a great selection of embodiments are shown where the force interaction between the stationary unit and movable unit takes place in an air gap that is parallel to the substrate. Both rotational and translatory movement is described. The mounting of the movable unit can be pneumatic and/or electromagnetic (levitation). The patent describes several principles for conversion of mechanical and electrical effect. The methods can be divided into two main groups: Electrical and mechanical. In traditional electrical machines only the magnetic forces are used. In the case of micromachines transformation of effect based on electrical forces is sometimes preferred. Both electrical and magnetic induction is described in the patent. The output from the unit can be substantially enlarged since the area where the transformations of force takes place can be large. Further the number of revolutions of the rotating plate that comprises the rotor can be high. In "An electrostatic induction micromotor supported on gas- lubricated bearings" by L.G.Frechette et al, pp 290-293, Proc. MEMS 2001. referred to above a comparable structure is used for a unit with 900,000 rpm and a performance of 3W. There are not published any results describing that these units have a long longevity. It is presumed that this may be the result of problems with the mounting. There are several known methods for taking out effect from a system with streaming and/or pressurised fluid to another system. In a majority of situations it is desirable to conduct the conversion with the highest possible efficiency. One example is a hydroelectric power station where a turbine converts effect in streaming water to mechanical effect on the turbine' s axle. An electrical generator further converts the mechanical effect to electric effect. The technique used to obtain maximum total efficiency has as is well known been developed over a long period of time. Units referred to in the patents discussed above belong to this category. In other applications a high efficiency is not the most important aspect, as in several of the embodiments envisaged for the present invention. An example of this is a factory that uses pneumatic actuators for mechanical work operations, possibly heavy operations, such as closing/opening/regulating valves, for example large high pressure valves, lifting/manipulating objects, for example heavy objects, operation of pneumatic tools and so forth. The fluid will normally be air, optionally filtered, from a compressor which air is distributed in the factory localities through plastic or steel piping. A certain leaking of air is acceptable in such systems. As an example a commonly used unit, a so called IP (electrical current (I) to pneumatic pressure (P)) regulator has a rate of leakage of approximately 0.2 kg/min. This corresponds to a pneumatic effect of approximately 6.5 watt at a compressor pressure of 1.4 barg (1.4 bar above atmospheric pressure) which is a commonly used pressure standard for such applications. It is therefore acceptable to "use" more watt of the pneumatic effect without it being considered a major drawback for the application. An efficiency in the order 1% for conversion of pneumatic energy to mechanical energy would be acceptable.

Purpose of the invention

It is one purpose of the invention to describe a technical solution that solves several of the above described problems of the prior art. Especially the invention seeks to provide a unit that convents the effect of a fluid stream to mechanical effect through a mechanical bending movement, for example an oscillating movement, based on a geometry that is adapted the properties necessary for the envisaged micro-electromechanical construction used as a micro-electromechanical generator/motor with no bearing.

The invention also seeks to provide a unit that transforms the effect of a fluid stream to mechanical effect in a movement and with a geometry that can be produced using mainly processes commonly employed in the production of MEMS components. It is also a purpose of the present invention to provide a unit that transforms the effect of a fluid stream to mechanical effect in a movement and with a geometry that at the same time has long longevity by avoiding movements that cause friction and avoiding use of a bearing between movable elements. It is a further purpose of the invention to provide a new and improved method and arrangement for transforming pneumatic or hydraulic effect to mechanical effect.

It is a further purpose of the invention to provide a new and improved method and arrangement for transforming pneumatic or hydraulic effect to mechanical effect with a robust, simple and low cost construction having a long longevity.

According to the invention these purposes are achieved especially with the features mentioned in the independent claims. Further advantageous embodiments will appear from the dependent claims and the accompanying description. In the following the embodiments of the present invention shall be described through examples. The examples are illustrated by the enclosed figures:

Fig. 1 depicts a planar rotor plate the end of a bendable beam.

Fig- 2 cross sectional front view and perpendicular to the beam's direction of movement.

Fig. 3 depicts the structure seen from the side in a cut through the swinging beam. F Fiigg.. 4 4 shows the swinging energy transformer seen from above.

Fig. 5A-C depict how the fluid stream can oscillate between two channels.

Fig. 6 shows an alternative way of achieving pneumatic feedback in channels in order to achieve an oscillating current.

Fig. 7 shows a further principle that can be employed to achieve an oscillating current.

Detailed description.

Figure 1-3 describes a MEMS structure for converting kinetic energy in a fluid stream to mechanical energy in an elastic mechanical element 1,2. There can be more than one elastic mechanical element 1,2. The fluid stream is conducted through a system of channels 5 where the mechanical element(s) 1,2 are arranged. The fluid stream produces an oscillation that acts on one or more mechanical elements 1,2 such that they take on a bending movement, for example oscillation and in such a manner that they take up energy from the fluid stream. One or more mechanical elements are typically directed and arranged to interact with a system that converts mechanical energy to electrical energy, heat or other forms of energy.

More especially figure 1 illustrates a beam 2 with a plate 1 that is placed in a fluid stream. The beam 2 is attached at its one end and freely bendable at its other end near the plate 1. When the fluid stream in a fluid based channel system 5, as shown in figure 2 is set in oscillating movement, the beam 2 is set in a corresponding oscillating bending movement..

The plate 1, that can be attached on the upper side of and outmost on the beam as shown in figure 1, is set in motion back and forth along a curvature when the beam is bent. The beam can be mounted in such a manner that the oscillating end is turned either towards the fluid stream of against the fluid stream. The structure shown in figure 1 is implementable in MEMS technology (Micro-ElectroMechanical Structure) among others. A production alternative for the structure can be based on a three-layered structure where a silicon chip is arranged between two glass chips. The beam 2 and the plate 1 are then produced in the silicon chip and thereby they acquire the advantageous properties from such silicon microstructures in relation to fatigue failure among others, which would represent a real failure mode in "macroscopic" units, hi this manner it is achieved a movable structure 1,2 that is set in motion by a fluid stream and a mounting of this structure that avoids tribology problems and is nearly without any mechanisms for fatigue failure.

The plate 1 has a typical function of a rotor plate where the structure 1,2 is arranged to interact with a system that converts mechanical energy, that is energy from a swinging motion of the swinging beam 2 and the plate 1, to electrical energy, heat or other forms of effect. In order to perform as a rotor plate there is arranged on the plate 1 in one embodiment of the invention a structure comprising a first system of electrodes 3. These first electrodes are arranged in a specific distance from a stationary system that comprises a second system of electrodes 4. The first and second system of electrodes 3,4 form an electrical machine that can generate electrical effect when the beam 2 is set in swinging motion for example by an oscillating fluid stream.

According to one embodiment of the invention the structure 1,2 through the motion of the beam is arranged to interact or co-operate with another stationary structure such that effect is generated by the beam movement in the fluid stream is retarded and thereby takes out effect from the fluid stream. Arrangements for such interaction or co-operation comprise typical combinations of electrical coils and magnetic materials that together form electromagnetic machines.

As an example there can be arranged on the beam 2 a structure that either comprises a permanent magnet or an electrical coil. This structure can be placed in a distance from respectively a (stationary) electrical coil or a permanent magnet, such that coil and magnet together form a magnetic machine that generates electrical effect. Alternatively different arrangements of electrodes and/or charge distributors, for instance in space charge zones or areas, form electrostatic machines.

The beam and plate can be designed in such a manner that they get a swing and a frequency that is adapted to what is needed in connection with a rotor function in an electrical generator or motor. This can be achieved in several different ways through setting the fluid stream in an oscillating motion and beam/rotor plate following this movement. It is for instance possible to dimension beam and fluid channels such that the self resonant frequency of beam/rotor plate becomes (approximately) the same as the oscillation frequency in the fluid. In this way there is created a swing that is great enough for use in an electrical unit.

Figure 2 illustrates a typical cross section of a fluid containing channel 5 where the beam is driven to the right on the figure by a higher pneumatic pressure Pi in a first chamber 20 on the left hand side of the beam 2, than the pressure P₂ in the second chamber 21 on the right hand side of the beam 2. The pneumatic energy represented by air (gas) under pressure is thereby converted to mechanical kinetic energy as the air (gas) sets the beam 2 in motion. Figure 2 further illustrates how the beam 2 and the plate 1 is a part of a silicon chip 8 that is placed between a first glass chip 6 and a second glass chip 7 and form a three layered structure. The glass chips are attached to the silicon chip by anodical bindings 9 on the boundary surfaces. It should be mentioned that there can be used structures where major parts of the fluid stream passes by the swinging beam 2 without transferring any effect to its motion. This means that it is allowable with structures that have a relatively large leakage rate and thereby avoid clogging elements that often will have a tribologous nature, which is undesired in this connection. This is a direct result of the fact that a low degree of efficiency can be allowed.

Figure 3 is a longitudinal cross-section along the direction of the fluid stream in the channel containing fluid on figure 2. The beam 2 is etched out of a silicon substrate/chip 8 which is (anodically) bound 9 to a lower substrate 7 (layer 1), preferably produced from glass. The structure is closed up through a top substrate 6, preferably also produced from glass and being bonded (anodically) 9 to the (silicon) substrate 8. The stator electrode system 4 is mounted on the upper substrate 6.

The beam 2 is attached at its one end 22 and can bend as shown on figure 4. The planar rotor plate 1 moves along a curvature when the beam 2 is bending. The stiffness of beam 2, its mass distribution as well as the power from the pneumatic system will determine the swing frequency. As an approximation of the first order one can assume that the velocity of the planar rotor plate 1 will be sinus variably with time. If the force in tangential direction between stator 4 and planar rotor plate 1 is constant the used effect will vary as a sinus function with time. The velocity variation with time is not significant for the unit's function as generator.

A disadvantage of the structure shown on figures 1 to 4 is that it is asymmetrical. The rotor plate 1 does not get a fully planar movement. This can be a disadvantage especially when it is used in the electrical generator because the air gap possibly must be enlarged to avoid that the rotor plate "hits the roof by torsion near the maximum swings. When the air gap is enlarged the outtake of electrical effect will be reduced. In many cases this is undesirable. However can such an undesired torsion effect be counteracted in several ways: 1. Increase the stiffness of beam 2 in the relevant direction. 2. Reduce the mass of rotor plate 1 through reduction of its thickness.

3. Arrange a ribbed structure on the underside of plate 1.

4. Arrange counterweights to plate 1 on the underside of beam 2 in order to make beam/rotor plate more symmetrical.

These measures will normally work on the self resonant frequency and the swing. The fluid channels 5 can in addition be designed in such a manner near beam's

2 maximum swing that the pressure between the underside of rotor plate 1 and the outer side of beam 2 and the walls of channels 5 increases and counteracts the torsion of beam 2 and rotor plate 1. Thereby it is achieved a hydraulic/pneumatic alleviation in the outer positions of the beam 1. Several different embodiments of channels system 5 where the fluid stream is set in oscillation can be envisaged. The beam 2 is set in a swinging motion by an alternating pneumatic or hydraulic pressure on each side of the beam, for instance as shown on figures 5- 7.

Figures 5 A, 5B, 5C show a preferred embodiment of the channel structure 5 where an admission channel 10 with two branching channels 11 and two feedback channels 12 can set the fluid stream in oscillation between the two branching channels 11 and as such also between the feedback channels 12, as depicted in figures 5B and 5C. All these channels 10, 11, 12 can be implemented in the substrate 7 (layer 1), preferably by glass, and be connected to cavities and channels in the silicon substrate (layer 2) such that silicon beam(s) 2 with its/their rotor plate(s) 1 is set in motion by the oscillating fluid stream. One or more beam(s)/rotor element(s) 1,2 can be arranged in each branching channel 11. Each branching channel 11 may further be envisaged to branch off further and to be equipped with beam/rotor elements 1,2. This can be one way of increasing the net efficiency factor where it is desirable.

Figure 6 shows a variation of the feed back principle of figure 5 where the feed back channels are designed to have open ear like structures 13, where the feedback stream mainly will follow the outer edges of the ears 13 and return to the admission stream and thus set this in oscillating motion from one side of the channel to the other side or optionally from the first branching channel to the second (not shown on the figure, but designed as shown on figure 5). Such ear shaped feedback elements 13 can be advantageous when there is a polluted fluid stream that easily can block narrow channels as on figure 5 and can further be easier to produce. Figure 7 depicts another principle where vortex shedding produces the oscillating stream that it is desired to utilize in order to set the beam/plate 1,2 in motion. The vortex shedding is created by placing a vortex producing structure 14 in the fluid stream. Beam/plate 1,2 is not shown on figure 7, but will typically be placed in the vortex shedding shown on figure 7. The vortex shedding can be defined by Strouhals' number, S given as f = S* U/D where U is the fluid velocity against a body 14 with a diameter D. Vortex having a frequency f will be formed on the backside of body 14. S has a typical value of 0.2 and typical numbers for MEMS structures, for instance D = 1 mm, U = lOOm/s, results in f = 20 kHz, which can be a suitable frequency for the beam/rotor system 1,2, for example the self frequency, and for conversion of mechanical energy to electrical effect. Typical applications for the invention are power generators where the beam 2 is set in swinging motion by a fluid or gas stream. The energy in the streaming medium is first converted to mechanical energy and thereafter to electrical energy.

Claims

Patent claims:

1. A method for transforming kinetic energy in a fluid stream to mechanical energy in at least one elastic, mechanical element (1,2) where the fluid stream is conducted through a channel system 5 comprising said at least one mechanical element (1,2) implemented in a MEMS structure and where the fluid stream creates an oscillation that acts on said at least one mechanical element (1,2), charcterized in that

1) the fluid stream oscillation sets said at least one mechanical element (1,2) in a bending motion, for instance oscillation, such that said at least one mechanical element (1,2) thus acquires energy from the fluid stream and

2) that said at least one mechanical element (1,2) is set to interact with a system that converts mechanical energy to electrical energy, heat or other forms of energy.

2. A method according to claim 1, where said fluid stream is made to oscillate through feeding back a part of the fluid stream in a feedback system (12, 13) connected to the channel system 5, in such a manner that at least a part of the fluid stream is fed back into the fluid stream.

3. A method according to claim 1, where said fluid stream is made to oscillate through creating a vortex shedding system in the fluid stream by placing a body (14) in the fluid stream.

4. A device for transforming pneumatic or hydraulic energy to mechanical effect comprising a fluid based channel system (5) implemented in a MEMS structure, characterized in that at least one elastic mechanical element (1,2) is arranged to interact with the fluid stream in the channel system (5), means to set the fluid stream in the channel system (5) in oscillating motion and at least said one mechanical element (1,2) is arranged to interact with the fluid stream in such a manner that it is set in a swinging motion, for instance an oscillating motion, by the oscillating fluid stream.

5. A device according to claim 4 wherein the channel system (5) comprises a feedback path (12, 13) arranged to lead at least a part of the fluid stream back and thereby bring the fluid stream in oscillation.

6. A device according to claim 4 wherein the channel system (5) comprises at least one body (14) arranged in the fluid stream and wherein the body (14) is arranged to bring the fluid stream in oscillation through creating a vortex shedding system in at least a part of the fluid stream behind the body in the flow direction.

7. A device according to any claim 4 to 6 wherein said mechanical element (1,2) is arranged to interact with a system that converts mechanical effect to electrical effect, heat or other forms of effect.

8. A device according to claim 7 wherein said mechanical element (1 ,2) comprises a structure (1) with a first system of electrodes or charge distributors (3), the structure is arranged in a distance from a stationary system comprising a second system electrodes (4), said first and second electrodes (3,4) are arranged to form an electrical machine that can generate electrical effect.

9. A device according to claim 7 wherein said mechanical element

(1,2) comprises a structure comprising either a permanent magnet (3) or an electrical coil (3), the structure is arranged in a distance from respectively a (stationary) electrical coil (4) or a permanent magnet (4), in such a manner that the coil and the magnet can create a magnetic machine which can generate electrical power.

10. A device according to claim 7 wherein said mechanical element (1,2) comprises a structure (1) arranged to interact through the element movement with another (stationary) structure (4) in such a manner that effect is generated through the retardation of the element movement in the fluid stream and thereby takes out effect from the fluid stream, and wherein the structure comprises combinations of electrical coils and magnetic materials that together are arranged to form electromagnetic machines.

11. A device according to claim 4 wherein said channel system (5) comprises a first and a second feedback channel (12, 13), each arranged to feed a part of the fluid stream from the fluid containing channel (5,11) to a point of withdrawal (16) and lead the withdrawn stream back through the feedback channels (12, 13) to a feed back point (15) in front of the point of withdrawal (16) in the flow direction, where the feed back points in the first and second feedback channels are substantially in the same position along the channel to create an oscillation in the flow direction of the fluid containing channel.

12. A device according to claim 4 wherein said mechanical element (1,2) wherein said channel system (5) comprises a branching at a point between said feed back point (16) and said point of withdrawal (15) such that oscillation will lead fluid in respectively the first and second branching (12).

13. A device according to any of the preceding claims wherein said elastic mechanical element (1,2) in principle is designed as a beam that is restrained at its one end.