Background to the Invention Mobile telephones are operated by a re-chargeable battery which needs to be re- charged when it has run out of available electricity. This is normally done by means of a re-charger which is plugged into the mains electricity supply and provides a low current at the required voltage to recharge the battery. This is inconvenient and cumbersome and it would be advantageous if the battery could be re-charged on a continuous basis whether or not the mobile telephone was in use.

Mobile telephones and like battery-powered electrical devices are normally carried by people in their everyday lives and we have now devised a generator which will gener- ate an electric current which can re-charge a battery and which is powered by the move- ment of, for example, a person carrying the generator.

Summary of the Invention According to the invention there is provided an electricity generating device, com- prising a curved surface, a magnet adapted to roll on the curved surface in response to movement of the surface, and at least one coil arranged adjacent to the surface such that rolling of the magnet thereon induces an electrical charge in the coil.

It will be understood that, while the magnet will typically be caused to roll, and thereby generate electricity in the coil or coils, by movement of the curved surface, other external influences could also cause the magnet to roll, for example a changing external magnetic field.

The curved surface may be a toroidal tube or a portion thereof, with a spherical magnet rolling in the tube. Alternatively, the curved surface may be a cylindrical surface or a portion thereof, the magnet being spherical or cylindrical or including a cylindrical bearing surface. In another embodiment, the curved surface is an ellipsoid or a portion thereof, the magnet again being spherical. In the latter embodiment, guide means may be

provided for constraining the magnet or magnets to roll in contact with the curved sur- face, irrespective of the orientation of the generator. For example, the generator may comprise a hollow sphere containing a number of spherical magnets held in dimples or recesses in a core within the hollow sphere in such a manner as to roll freely across the internal surface of the hollow sphere while maintaining their relative positions. Coils wrapped around the sphere have a voltage induced in them as the magnets roll around the sphere.

Preferably, the curved surface is formed of a low magnetic permeability material, for example copper or aluminium or a plastics material. The or each coil may be formed around a body containing the curved surface. The coils are conveniently windings of wire, but they could be formed in other ways, for example as printed circuit elements.

In a preferred embodiment, the generator comprises a toroidal tube made of a non electrically conductive material and a magnet located inside the tube and free to move within the tube, there being at least one wire coil wound around the tube so that, when the magnet moves within the tube, the magnet will pass through the wire coil and gener- ate an electric current therein.

The toroidal tube can have a circular, oval or elliptical or other similar shape and can have a substantially circular cross section or the cross section can be elliptical or oval or other convenient shape. Such shapes are sometimes referred to as doughnut shaped.

While a complete circular, oval or elliptical path may be provided, it may be sufficient to use only a segment of the path, for example a U-shape in elevation, the generator being arranged so as to be oriented in use with the arms of the U-shape generally upwards, so that the magnet tends to roll towards the centre of the U-shape. Where the tube is not a continuous path, springs or magnets may be provided at each end thereof to store the kinetic energy of the moving magnet as it reaches the limit of its movement, and then re- lease the stored energy to accelerate the magnet again towards the other end of the tube.

This is effective in avoiding loss of energy, especially when the device is shaken vigorously.

The wire coil is preferably wound around the tube so that it covers a section of the tube, preferably there are a plurality of coils of wire spaced around the tube so that wherever the magnet is moving within the tube it will pass through a coil.

The magnet is preferably substantially spherical so that it will roll freely within the tube. In one embodiment of the invention the cross section of the tube is substantially cir- cular and the magnetic is also substantially spherical and there is a sufficient clearance be- tween the walls of the tube and the magnet so that the magnet rolls easily within the tube but the gap between the magnet as it moves and the coils is minimised to reduce electro- magnetic losses.

The magnet can be made of any ferromagnetic metal and the strongly ferromag- netic alloys which are capable of retaining a very strong magnetic field are preferred.

There can be more than one magnet in the generator and the tube can be divided into sections so that each magnet will roll in a separate section. Or a series of magnets all free to roll all the way around the toroid like a bearing race, the magnets would have to be separated by non-metallic or magnetic material. It might be possible to separate the mag- nets by arranging the poles of the magnets so as to repel the adjacent magnets to achieve spacing.

As the magnet will move backwards and forwards through the coils, the direction of electric current will vary, so a rectifier is preferably incorporated within the generator so that direct current is taken from the generator. A power management circuit may also be employed to ensure that a substantially constant output voltage is produced from the varying DC output from the rectifier. Such a circuit might incorporate a switched mode power supply or DC/DC converter.

The generating device of the invention could be, for example, a hand-portable de- vice for use in providing electrical power for portable devices such as mobile telephones.

However, the invention is not limited to this scale of device. It would be possible to con- struct a larger-scale device, for example for extracting energy from wave motion in a floating or semi-submerged construction, or a smaller-scale device, for example for pro- viding power for a medical device implanted in or otherwise associated with a human or animal body.

In use as a hand-portable device, the generator can be carried by a person who has a mobile telephone or other portable electric device, e. g. in a pocket, handbag or other convenient location, or even incorporated into clothing. As the person moves

around during their normal activities the generator is shaken or moves around with the person and this causes the magnet to roll around in the tube and to generate an electric current. This current is then fed through a rectifier to a battery and so charges the bat- tery. The battery can be in the portable electric device or it can be a spare battery. Alter- naively, the generator may directly power the device where continuous operation is not required, or it may charge a capacitor which in turn powers the device.

We have found that with such a generator electricity at four volts and 8 milliamps can be generated by walking carrying the generator and fast shaking e. g. by running or shaking by hand can generate 12 volts at 51 milliamps. This current is adequate to charge an electric battery of the type used in mobile telephones, for example. It will be appreci- ated, however, that the invention is not limited to these levels of power output and volt- age.

It is a feature of such a device in accordance with the invention that it is portable and compact and so is easily carried and will operate during all the time it is being carried so that, although the power generated is relatively small, it is adequate to trickle charge a battery.

While specific embodiments of the invention are described herein generally as de- vices to be carried by a person and to generate electricity as a result of the normal move- ments of that person, it will be understood that the invention is not limited to such use.

For example, the generator may be used in any environment where movement of the device occurs, for example in a motor vehicle, for powering accessories without the need for a wired connection to the vehicle's electrical system. The generator of the invention could be used, for example, to power a communication device attachable to a vehicle's window, perhaps in turn connecting to other equipment, such as a cellular telephone, within the vehicle by short-range radio. An example of a suitable short-range radio sys- tem is that identified under the trade mark Bluetooth.

The generator can also be incorporated in a mobile telephone or other device so that no connections or wires are needed and the battery is charged continuously whilst the device is being carried around.

In addition to mobile telephones a hand-portable generator according to one em- bodiment of the invention can be used to provide electrical power for other portable elec- tric devices, examples being PDA's, GPS systems, displays, lap top computers, calculators, and portable audio reproduction devices, such as minidisc players, and other portable ra- dio devices, including communications devices.

While physical movement of the generator will typically be required to generate electricity, there are certain locations at which the generation of sudden transient mag- netic fields will cause the magnet or magnets within the generator to move, and the resid- ual kinetic energy in the magnets is sufficient to induce a short-term electrical charge in the coil or coils. For example, a device mounted adjacent to a cathode ray tube incorpo- rating automatic degaussing coils will be activated briefly as the cathode ray tube is first switched on. The resultant small electrical charge could, for example, be used to power a device which releases treating molecules into the air, for example a fragrance or an anti- bacterial substance. The device may operate by vibrating a surface carrying the sub- stance, for example in gel form, as described and claimed in our co-pending application GB0209673.3.

It will be appreciated that the uses of the generator are not limited to powering mobile telephones or other devices mentioned herein. The generator may be configured as an integral part of the device it is powering, or as a separate unit connectable to the device by a plug-in lead or by direct plug-in connection between the generator and the device.

Brief Description of the Drawings In the drawings, which illustrate exemplary embodiments of the generator of the invention: Figure 1 is a plan view of a generator according to one embodiment of the inven- tion; Figure 2 shows a cross section on line AA in Figure 1; Figure 3 is a cross-sectional view through a generator according to a second em- bodiment of the invention;

Figure 4 is a cross-sectional elevation through a generator according to a third embodiment; Figure 5 is a cross-sectional elevation through a generator according to a fourth embodiment; and Figure 6 is a circuit diagram showing a typical electrical circuit for a generator ac- cording to the invention.

Detailed Description of the Illustrated Embodiment Referring to Figures 1 and 2, a toroidal tube 1 made of a non-electrically conduc- tive plastics material has a spherical permanent magnet 2 made of strongly ferromagnetic material mounted within it so the magnet can roll in the tube. Wound around the outside of the tube are six coils of wire 3 each of which consists of 2000 turns of wire. The ends of each coil of wire are connected to rectifier 4. The output from the rectifier is fed out at 5. There is an outer protective covering 6. The tube 1 as shown in Figure 1 can be circu- lar or elliptical, oval etc. and the cross-section of tube 1 as shown in Figure 2 can be circu- lar, elliptical, oval etc. and In use a person carries the generator on him or her and, as they move about, the magnet 2 will roll around inside the tube 1 and so pass through one or more of coils 3.

This movement will generate an electric current in the wire which is rectified by a rectifier unit 4, described hereinafter in more detail with reference to Figure 6, and led off via an output lead 5. The output can then be fed to a battery in a mobile telephone where the battery is charged. Such a generator generated electricity at about four volts and 8 milli- amps by walking carrying the generator and fast shaking e. g. by running or shaking by hand can generate 12 volts at 51 milliamps. This current is adequate to charge an electric battery of the type used in mobile telephones, for example.

The generator shown in Figure 3 comprises a hollow spherical body 30 around which are wound a plurality of coils 31 (it will be understood that the number and con- figuration of the coils may vary from what is illustrated) connected to a rectifier unit (not shown), for example of the type described with reference to Figure 6. contained within the hollow sphere 30 is a free core 32 having a number of dimples or recesses 33 in the surface thereof, the core having a diameter sufficiently smaller than the internal diameter

of the hollow sphere 30 to permit a respective spherical magnet 34 to be located in each of the dimples 33 and to roll freely over the internal surface of the hollow sphere 30. It may be desirable to position the dimples 33 on the surface of the core 32 in such a man- ner that the arrangement is dynamically imbalance relative to the centre of the core 32 and the sphere 33, so that the magnets are more readily induced to move relative to the coils as the generator is moved, in use.

In the generator shown in Figure 4, the curved surface 40 is an ellipsoid, provided by a generally bowl-shaped container 41 having a cover 42, which may, if desired, be at least partially concave to constrain the spherical magnet 43 contained within the genera- tor to roll across the curved surface in response to movement of the generator without lifting off the surface to any significant extent. Coils 44 are provided around the container 41 arranged such that rolling movement of the magnet 43 on the curved surface 40 in- duces a voltage into each adjacent coil, the outputs from the coils being rectified and regu- lated, for example by a rectifier unit of the type described with reference to Figure 6.

Figure 5 shows another alternative to the configuration of the generator shown in Figures 1 and 2, in which, in place of the complete toroidal tube, the generator has a por- tion thereof. In the embodiment illustrated, the generator has a semi-circular segment, but it will be appreciated that a greater or smaller segment could be employed, and that, while the cross-section of the tube itself will need to be circular to accommodate a spheri- cal magnet, the path of the tube need not be a segment of a circle, but may be elliptical or such other non-linear shape as to cause the magnet to move readily in response to movement of the generator in use. As in the embodiment of Figures 1 and 2, the device has a cover or casing 6 in which the segment of the toroidal tube 1 is mounted, with coils 3 wound around the tube and connected to a rectifier unit 4 provided with an output lead 5. The magnet 2 rolls within the tube, which needs to be maintained with the centre of the tube generally lowermost in use, to ensure that the magnet remains free to roll, thereby inducing a voltage in the coils. It will be appreciated that the number of coils may be greater or fewer, extending over more or less of the tube.

The rectifier unit of the generator illustrated in the Figures may incorporate an electrical circuit generally as shown in Figure 6. The coils 60 into which the moving mag-

nets induce a voltage, of which only one is shown in the figure for clarity, are connected to a rectifier 61. As illustrated, this comprises a full wave diode rectifier bridge, but it will be appreciated that other configurations of rectifier may also be employed. A capacitor 62 is connected across the output of the bridge, and a DC/DC converter 63 receives the varying DC output resulting from the random interaction of the rolling magnet with the coil or coils and outputs a predetermined constant DC voltage when the input is within the specified input voltage range of the converter, for example from 1.25V to 15V. This output voltage is applied to a storage battery 64 within the unit, which in turn is con- nected to a second DC/DC converter 65 whose function is to control the discharge rate from the storage battery 64, allowing it to discharge fully. The second converter 65 also allows control of the voltage at the supply terminals 66 of the output lead to ensure that it is at the desired value for any of a range of different electronic or electrical devices which might be connected to it, operating individually at different voltages and drawing different currents.