GB2543733A

GB2543733A - Energy conversion apparatus

Info

Publication number: GB2543733A
Application number: GB1513723.5A
Authority: GB
Inventors: Bilchrist Murray Brian
Original assignee: Tern Tech Ltd
Current assignee: Tern Tech Ltd
Priority date: 2015-08-03
Filing date: 2015-08-03
Publication date: 2017-05-03
Anticipated expiration: 2035-08-03
Also published as: GB2543733B; GB201513723D0

Abstract

An energy conversion apparatus employs a rolling or oscillating magnet for deriving small amounts of electrical current from ambient movement or vibration. The apparatus comprises a first magnetic or magnetised element, such as a ball 3, provided with at least one magnetic pole pair and a finite longitudinal pathway, such as a magnetically transparent cylinder 1, along which the magnetic element 3 experiences pendular or rolling movement. A conductive coil 4 is adjacent at least a portion of the pathway, and a current is induced in the coil 4 by movement of the first element 3. A second magnetic or magnetised element 5a, 5b is fixable in position relative to the pathway, and imposes a net magnetic attraction force on the first element 3. The second magnetic or magnetised element may be a fixed element such as coiled or annular wire 5b or a protrusion (7, figure 2) or it may be an adjustable element such as screw 5a facilitating a variable magnetic flux density B.

Description

ENERGY CONVERSION APPARATUS

The present invention relates to an energy conversion apparatus and particularly, but not exclusively, to an energy converter employing a rolling or oscillating magnet for deriving small amounts of electrical current from ambient movement or vibration.

The concept of "energy harvesting” or "energy scavenging” whereby small amounts of power are harnessed for low-energy electronics is known and numerous applications for micro-generator technology are emerging. An obvious advantage of a fully autonomous power source is the convenience and environmental benefits associated with avoiding the need for period replacement and disposal of batteries. The technology is also suited to applications where the use of batteries or an external power supply is impracticable, e.g. because the apparatus being powered is vulnerable to damage, is susceptible to water ingress, or is inaccessible for maintenance. Applications include wearable technology, industrial machinery and transportation.

Known energy converters employ a magnetic or magnetised ball caused to roll - by ambient movement - along a channel or track surrounded by a conductive coil. The resulting time varying magnetic field generates power by virtue of Faraday’s Law of Induction which can be stored for later use, or used concurrently to power a device. Such known devices are simple, inexpensive to manufacture, and are small in size. For example, UK Patent Publication No. GB2463129A (Marson) discloses a wave power generator for use in buoyant element floating in water. In this device a magnetic element moves relative to an electrical conductor due to the influence of gravity.

However, the efficiency of known energy converters can be highly sensitive to changes in orientation of their ball tracks or channels. In particular, the simplest type of energy converters employing a substantially straight, finite ball track will cease producing power when inclined in such a way that its magnetic ball comes to rest against an end wall of its track by virtue of external gravitational or other forces. This problem may be overcome by providing a track in the form of a partial or complete toroid; however, this necessitates a much longer - and hence more complex and expensive - conductive coil arrangement to ensure that power is generated continuously at all circumferential positions of the magnetic ball. Further challenges surround ensuring that the magnetic poles of a magnetic ball remain optimally aligned relative to its rotational axis, irrespective of the inclination of the ball track.

It is an aim of the present invention to provide an alternative or improved energy converter, and/or one which overcomes, or at least ameliorates, one or more of the aforementioned disadvantages associated with known devices.

According to a first aspect of the present invention, there is provided an energy converter apparatus comprising: (i) a first magnetic or magnetised element provided with at least one magnetic pole pair; (ii) a finite longitudinal pathway along which the first magnetic or magnetised element may experience pendular, or a combination of rotational and translational, movement; (iii) a conductive coil adjacent at least a portion of the pathway; and (iv) a second magnetic or magnetised element which is fixable in position relative to the pathway; wherein the second magnetic or magnetised element imposes a net magnetic attraction force on the first magnetic or magnetised element.

It will be appreciated that, by virtue of the above arrangement, the first magnetic or magnetised element will tend to move to an equilibrium position on the pathway which lies closest to the second magnetic or magnetised element. Furthermore, if the energy converter apparatus is subject to external forces - e.g. forced vibrations - at least a component of which are applied in the longitudinal direction of the pathway then the first magnetic or magnetised element will oscillate about the equilibrium position.

Optionally, the net magnetic attraction force imposed by the second magnetic or magnetised element on the first magnetic or magnetised element is adjustable.

Optionally, the first magnetic or magnetised element is spherical or spheroidal and suitable for combined rotational and translational movement along the pathway; and is provided with at least one diametrically opposed magnetic pole pair.

It will be appreciated that one or more diametrically opposed magnetic pole pairs may be provided around the circumference of the first magnetic or magnetised element. The higher the number of magnetic pole pairs, the higher will be the number of magnetic field fluctuations per rotation.

Optionally, the pathway is a part-circular arc and the first magnetic or magnetised element forms part of a pendulum suitable for pendular movement along the pathway.

The pendulum may comprise a rigid rod and a bar magnet located at a distal thereof which oscillates about the aforementioned equilibrium position in a similar manner to a spherical or spheroidal element.

Optionally, the conductive coil surrounds at least a portion of the pathway.

When the energy converter apparatus is subject to external forces - e.g. forced vibrations - the magnetic field within the conductive coil is caused to fluctuate and generate a voltage by virtue of Faraday’s Law of Induction.

The first and/or second magnetic or magnetised element may comprise a particle composite comprising a permanent-magnet powder embedded in a plastic binder.

Optionally, the second magnetic or magnetised element extends through, or proximate to, the conductive coil.

Optionally, the distance between the second magnetic or magnetised element and the pathway is variable.

It will be appreciated that varying the separation between the second magnetic or magnetised element and the pathway will alter the flux density B at the aforementioned equilibrium position. This in turn will alter net magnetic attraction force experienced by the first magnetic or magnetised element.

Optionally, the second magnetic or magnetised element may be provided in the form of a ferrous pin or screw capable of being slid or rotated toward and away from the pathway.

It will be appreciated that a plurality of ferrous pins or screws may be distributed along the length of the pathway to thereby provoke accelerated translational and rotational movement of the first magnetic or magnetised element and thereby generate higher rates of magnetic flux and voltage generation.

Optionally, the longitudinal axis of the pin or screw extends perpendicularly with respect to the longitudinal direction of the pathway.

Optionally, a magnetically opaque housing encloses the pathway.

Optionally, the second magnetic or magnetised element may be integrated within, or attached to, a wall or walls of the housing.

It will be appreciated that integration of the second magnetic or magnetised element with the housing will simplify manufacturing of the energy converter.

Optionally, the second magnetic or magnetised element may comprise one or more helical coils and/or annular rings arranged proximate or around the pathway.

When the energy converter is subject to external applied forces - e.g. forced periodic vibrations - in the longitudinal direction of the pathway, a variation in the net magnetic attraction force causes a corresponding variation in the frequency of oscillation of the first magnetic or magnetised element about its equilibrium position. It will be appreciated that the ability to adjust or tune the oscillation frequency is valuable in terms of optimising the performance of an energy converter dependent upon the nature of the vibrations it experiences. For example, whilst under the influence of the restoring force of the first magnetic or magnetised element, the resonant oscillation frequency of the first magnetic or magnetised element can be matched to the externally applied periodic vibration to maximise the energy conversion efficiency of the energy converter.

According to a second aspect of the present invention, there is provided a method of providing autonomous power generation by coupling an energy converter apparatus according to the first aspect to an external article subject to periodic or chaotic vibrational forces.

Optionally, the method comprises the step of adjusting the net magnetic attraction force experienced by the first magnetic or magnetised element such that the frequency of oscillation of the first magnetic or magnetised element about an equilibrium position is matched to the periodic frequency of the external apparatus.

Optionally, the external article may comprises industrial machinery, transport machinery or a person or animal.

Optionally, the external article is a wheel.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic cross-section of an energy conversion apparatus;

Fig. 2 is a schematic cross-section of an alternatively configured energy conversion apparatus; and

Fig. 3 is a graph showing the relationship between natural frequency and magnetic force ( FJ;

Fig. 4 is a schematic end view of an enclosed non-cylindrical pathway for the first magnetic or magnetised element; and

Fig. 5 is a schematic illustration of two modes of operation of the energy conversion apparatus when connected to an external rotating entity.

Fig. 1 shows an energy converter comprising a longitudinal pathway in the form of a magnetically transparent cylinder 1 the ends of which are closed off by end caps 2. It will be appreciated that other cross-sectional shapes are possible, one of which is discussed below. A magnetised spherical ball 3 is held captive within the cylinder 1 and is free to rotate along its length between the two end caps 2. The ball 3 is provided with at least one diametrically opposed magnetic pole pair. A conductive coil 4 - typically of copper -surrounds the cylinder 1. Rotation of the ball 3 causes the magnetic field associated with the, or each, magnetic pole pair to alternate in direction. A total of n cycles of magnetic field reversal per rotation of the ball 3 in the axial direction of the conductive coil 4 occurs (where n = the number of magnetic pole pairs). The material characteristics of the end caps 2 and the ball 3 are such that there is a high coefficient of restitution (e), i.e. the energy loss as a consequence of the ball 3 impacting an end cap 2 is minimal.

In the embodiment of Fig. 1, an adjustable ferromagnetic element 5a is located externally with respect to the cylinder 1 and extends radially with respect to its longitudinal axis. The ferromagnetic element 5a may be provided in the form of an elongate pin or screw which extends through (as illustrated in Fig. 1) or proximate the conductive coil 4. The ferromagnetic element 5a is moveable in the radial direction so as to increase or decrease the distance between it and the longitudinal axis of the cylinder 1. When in a fully inserted position, the magnetic flux density B provided by the ferromagnetic element 5a at the longitudinal axis of the cylinder 1 is maximised. Conversely, when in a fully retracted position, the magnetic flux density B provided by the ferromagnetic element 5a at the longitudinal axis of the cylinder 1 is minimised. The magnetic flux density B may be varied between those two extremes via intermediate positional adjustment of the ferromagnetic element 5a and fixed in a desired position relative to the cylinder 1.

It will be appreciated that the magnetic attraction force imposed by the ferromagnetic element 5a is greater than the corresponding magnetic attraction force imposed by the ball 3. Consequently, a continuous net magnetic attraction force is applied to the ball 3 by the ferromagnetic element 5a.

An alternative to the adjustable pin or screw 5a is also illustrated in Fig. 1 in the form of a non-adjustable coiled wire 5b. The wire 5b is shown as being coiled around the exterior of the conductive coil 4, but it could equally be located within the body of the conductive coil 4, or interposed between it and the external surface of the cylinder 3. It will be appreciated that the wire 5b may instead be provided in the form of one or more annular rings.

In the further alternative embodiment of Fig. 2 there is disclosed an arrangement similar to that of Fig. 1 enclosed within a magnetically opaque housing 6. However, the arrangement of Fig. 2 differs from that of Fig. 1 in that the second magnetic or magnetised elements are provided as fixed non-adjustable protrusions 7 forming an integral part of the upper and lower walls of the housing 6. The upper and lower walls may be removable and replaceable with the possibility that protrusions 7 of differing magnetic strengths may be employed depending upon operational requirements. In all other respects, the arrangement of Fig. 2 operates in a like manner to that of Fig. 1. By integrating the second magnetic or magnetised element with an interior surface of the housing 6 the manufacturing of the energy converter may be simplified and less prone to damage or misalignment of a pin, screw, ring or coil.

In use, the energy converter apparatus of the present invention is attached to an external article which is subject to periodic or chaotic vibrational forces, e.g. an industrial machine, transportation machine, or even a person or animal. The transfer of energy to the energy converter will cause relative movement between the cylinder 1 and the ball 3, i.e. its equilibrium state will be disturbed such that the ball 3 is caused to roll along the cylinder 1 away from the central magnetic axis of the ferromagnetic element 5a. However, the presence of a net magnetic attraction force means that movement of the ball 3 is restrained and there is a tendency for the ball 3 to be restored it to its equilibrium position nearest the ferromagnetic element 5a coincident with its central magnetic axis. The extent to which the ball 3 rolls away from its equilibrium position will be a function of its mass, the strength of the magnetic field, and the magnitude of the external vibration.

If at least a component of the external vibrational forces are applied in the direction of the longitudinal axis of the cylinder 1 then the ball 3 will oscillate about its equilibrium position causing the magnetic field within the conductive coil 4 to fluctuate, thus generating a voltage. Oscillation of the ball 3 will occur for as long as the net magnetic attraction force of the ferromagnetic element 5a towards the equilibrium position is greater than the oppositely directed force of the ball 3 in the direction of an end cap 2. When in this oscillation mode the motion of the ball 3 is analogous to a pendulum or a spring mass system whereby the force tending to restore it to its equilibrium position is proportional to the displacement of the ball along the cylinder away from the equilibrium position. The ball’s inertia is a function of its mass and the surface characteristics of its rolling contact with the cylinder 1.

Reducing the net magnetic attraction force will reduce the range within which oscillation of the ball 3 occurs in the cylinder 1 for a given applied external vibrational force. In the embodiments of Fig. 1 and 2, this is achieved by retracting the ferromagnetic element 5a away from the cylinder 1 or selecting a wire 5b or protrusion 7 having reduced magnetic field strength. The magnetic field strength generally diminishes exponentially with increasing distance from a magnet's centre.

If a spherical body of radius R and Mass M oscillates about a mean position, under the influence of magnetic force Fs, it can be shown that its natural frequency £ is determined by the formula:

The functionality of the energy converter of the present invention can be understood by applying this formula, whereby the first magnetic or magnetised element 3 is a spherical Neodymium /Iron magnet with the following characteristics:

Radius (R) = 5 mm

Magnetic attraction force ( Ft) to a steel surface = 14N

Magnetic Flux density = 6300 Gauss Weight (M) = 0.04 Newton = 0.00408kg

The relationship between natural frequency (/J and magnetic force ( Fs) is shown in the graph of Fig. 3

For example, a ball 3 brought into close proximity of a magnet having the above characteristics, will result in a natural frequency (/a) of 111Hz. This is typical of a vibration frequency encountered on high speed industrial machinery. Reducing the attractive force to 3N, e.g. by moving an adjustable ferromagnetic element 5a away from the ball 3, has the consequence of reducing the natural frequency to 50Hz, this frequency being more typical of electric motors and generators used extensively in industrial applications. Reducing the attractive force even further such that it is substantially equal to the weight of the ball 3 (in earth’s gravity) produced a natural frequency of 3.5Hz. This is typical of vibration experienced in railway vehicles and is also a useful natural frequency for wearable devices.

When an applied external excitation is such that the force of the ball 3 moving in the direction of an end cap 2 is sufficient to overcome the diminishing magnetic attraction force of the ferromagnetic element 5a, the ball 3 will cease operating within the oscillation mode and translate and roll away from the equilibrium position towards an end cap 2, and perhaps even rebound from the end cap 2 surface. When in this alternative nonoscillation mode, the motion of the ball 3 is analogous to a pendulum except that the force tending to restore it to its equilibrium position is non-linearly related to the displacement of the ball along the cylinder away from the equilibrium position.

When in this alternative non-oscillation mode the ferromagnetic pin 5a performs three functions. Firstly, provided that the influence of its magnetic field extends is sufficient to extend along the full length of the cylinder 1, it provides a continuous attraction force on the ball 3 so as to restore it to the equilibrium position. This tendency to continuously revert to the oscillation mode maximises coupling of the magnetic field with the conductive coil 4 and hence allows the energy converter to function irrespective of the orientation of the cylinder 1, i.e. when it is horizontal, partially inclined, or fully vertical. Secondly, the ferromagnetic element 5a tends to align the magnetic poles of the ball 3 so as to be perpendicular to its axis of rotation, this being the most favourable orientation within the cylinder 1 for maximum power generation. Thirdly, as the ball 3 approaches the ferromagnetic element 5a it is caused to accelerate by virtue of the net magnetic attraction force, thus generating an increased rate of change of magnetic field, and hence maximising voltage output.

As explained above, the position of the ferromagnetic element 5a relative to the equilibrium position of the ball 3 can be adjusted to increase or decrease the magnetic field strength experienced at given points along the pathway within the cylinder 1. For example, the ferromagnetic element 5a may be in the form of a ferrous bolt or screw engagable with a threaded portion on the cylinder 1 to provide a means of adjusting its position. Adjustment of the ferromagnetic element 5a may be performed once during manufacture; manually before or during operation; or automatically on an ongoing basis based on predefined parameters. As an example of the latter, the apparatus may be arranged such that the position of the ferromagnetic element 5a is adjusted in response to changes in frequency and/or amplitude of applied external vibrational forces so as to optimise power generation. In particular, the ferromagnetic element 5a may be adjusted so as to match the oscillation frequency of the ball 3 to applied external vibrational frequency. A plurality of ferromagnetic elements 5a may be distributed along the length of the cylinder 1 to accelerate the translational and rotational movement of the ball 3, with a consequent increase in the rate of change of magnetic flux and power output.

The embodiments of Figs 1 and 2 employ a finite pathway in the form of a cylinder 3 along which the ball 3 may roll. In Fig. 4 an alternative non-cylindrical pathway is shown in schematic form. The pathway of Fig. 4 is hexagonal in shape and dimensioned such that the ball 3 contained therein has two points of contact on its inclined side walls. The larger the separation of the two points of contact, the less will be the rolling diameter of the ball 3. Consequently, the number of rotations of the ball 3 will be increased for a given longitudinal distance travelled. It will be appreciated that the natural frequency (/J of the ball 3 can be changed by adapting the cross-sectional shape and dimensions of the pathway along which it travels. Whilst a fully enclosed hexagonal shape is disclosed in Fig. 4, other enclosed or non-enclosed arrangements are of course not excluded.

Fig. 5 is a schematic representation of the energy converter of Fig. 1, 2 or 4 attached to the wheel of vehicle and exhibiting the aforementioned oscillating and non-oscillating modes at different points during its rotation. When the energy converter is horizontally orientated the ball 3 is constrained by the net magnetic attraction force provided by the ferromagnetic element 5a, 5b or 7, and hence occupies the oscillation mode (Mode 1) whereby it oscillates about its equilibrium position in response to externally applied vibrational forces.

When the energy converter is vertically orientated due to rotation of the wheel, the influence of gravity on the ball 3 overcomes the magnetic attraction force provided by the ferromagnetic element 5a such that the ball is no longer constrained by it. The energy converter therefore switches from its oscillation mode (Mode 1) to its non-oscillation mode (Mode 2) whereby the ball 3 impacts against the lowermost end cap 2. In view of the end cap’s high coefficient of restitution (e) the ball 3 rebounds with minimal energy loss and its kinetic energy is converted into a decaying oscillation as it is recaptured by the magnetic attraction force provided by the ferromagnetic element 5a, i.e. the energy converter switches modes.

Continued rotation of the wheel produces multiple cycles of flux reversal for each passage of the ball along the cylinder 1, and the interaction between the ball 3 and the ferromagnetic elements) 5a can be arranged so as to maximise the occurrence of such flux reversals per unit time.

Whilst the aforementioned embodiments employ a ball 3 adapted for combined rotational and translational movement along a straight pathway, an equivalent effect may be achieved by arranging a rigid pendulum [not shown) to move in a pendular or revolutionary fashion along an arcuate pathway. The rigid arm of the pendulum may comprise a bar magnet which oscillates about the equilibrium position irrespective of the overall inclination of the apparatus with respect to the horizontal. It will be appreciated that the pendulum may move a conductive coil relative to a fixed magnet to achieve an equivalent effect.

It will be appreciated that the energy converter of the present invention provides a small, reliable and inexpensive means of micro-generation of autonomous power suitable for wireless instrumentation, e.g. to record the health or operating environment of a machine or component thereof in industrial or transport settings. The energy converter operates irrespective of whether the input energy is in the form of chaotic vibration, e.g. as experienced on a railway bogey or a buoy or ship; in the form of periodic vibration, e.g. as typically found in a pump or electric motor; in the form of rotational movement, e.g. as experienced when the device is attached to a wheel as discussed above; or in the form of chaotic non-vibratory motion, e.g. as may arise from the movement of a person or animal carrying or wearing a small energy converter to power a personal electronic device such as a watch.

Although particular embodiments of the invention have been disclosed herein in detail, this has been done by way of example and for the purposes of illustration only. The aforementioned embodiments are not intended to be limiting with respect to the scope of the appended claims. It is contemplated by the inventors that various substitutions, alterations, and modifications may be made to the invention without departing from the spirit and scope of the invention as defined by the claims.

Claims

1. A energy converter apparatus comprising: (i) a first magnetic or magnetised element provided with at least one magnetic pole pair; (ii) a finite longitudinal pathway along which the first magnetic or magnetised element may experience pendular or a combination of rotational and translational movement; (iii) a conductive coil adjacent at least a portion of the pathway; and (iv) a second magnetic or magnetised element which is fixable in position relative to the pathway; wherein the second magnetic or magnetised element imposes a net magnetic attraction force on the first magnetic or magnetised element.

2. An energy converter according to claim 1, wherein the net magnetic attraction force imposed by the second magnetic or magnetised element on the first magnetic or magnetised element is adjustable.

3. An energy converter according to claim 1 or 2, wherein the first magnetic or magnetised element is spherical or spheroidal and suitable for combined rotational and translational movement along the pathway.

4. An energy converter according to claim 1 or 2 in the pathway is a part-circular arc and the first magnetic or magnetised element forms part of a pendulum suitable for pendular movement along the pathway.

5. An energy converter according to any preceding claim, wherein the conductive coil surrounds at least a portion of the pathway.

6. An energy converter according to any preceding claim, wherein the second magnetic or magnetised element extends through, or proximate to, the conductive coil.

7. An energy converter according to any preceding claim, wherein the distance between the second magnetic or magnetised element and the pathway is variable.

8. An energy converter according to any preceding claim, wherein the second magnetic or magnetised element may be provided in the form of a ferrous pin or screw capable of being slid or rotated toward and away from the pathway.

9. An energy converter according to claim 8, wherein the longitudinal axis of the pin or screw extends perpendicularly with respect to the longitudinal direction of the pathway.

10. An energy converter according to any preceding claim, wherein a magnetically opaque housing encloses the pathway.

11. An energy converter according to claim 10, wherein the second magnetic or magnetised element may be integrated within, or attached to, a wall or walls of the housing.

12. An energy converter according to claim 10, wherein the second magnetic or magnetised element may comprise one or more helical coils and/or annular rings arranged proximate or around the pathway.

13. A method of providing autonomous power generation by coupling a micro-generator apparatus according to any of claims 1 to 12 to an external article subject to periodic or chaotic vibrational forces.

14. A method of providing autonomous power generation according to claim 13, wherein the method comprises the step of adjusting the net magnetic attraction force experienced by the first magnetic or magnetised element such that the frequency of oscillation of the first magnetic or magnetised element about an equilibrium position is matched to the periodic frequency of the external apparatus.

15. A method of providing autonomous power generation according to claim 13 or 14, wherein the external article may comprises industrial machinery, transport machinery or a person or animal.

16. A method of providing autonomous power generation according to claim 15, wherein the external article is a wheel.