Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1999-11-03
2003-08-26
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207240, C324S207250, C324S207230, C345S163000, C200S00600C
Reexamination Certificate
active
06611139
ABSTRACT:
The present invention relates to a positional device which will provide three electrical signals proportional to the movement of a portion of the device in three dimensional space, i.e. proportional to the three coordinate axes x, y and z defining that position, and particularly although not exclusively to a device for use in conjunction with a computer to enable the movement of a cursor or object in the x-y and z directions as represented on a computer monitor.
Conventional arrangements used with computers to locate the precise position of a cursor on a screen (as in the Xerox Corporation “mouse”) are capable only of providing a signal relating to movement in two dimensions. It is known that existing mouse type positioning devices and also similar two dimensional positioning devices such as touch screens, light pens, etc. are often inaccurate, difficult to use, ergonomically tiring, often restrictive in use and particularly in the case of the mouse, prone to degradation through the accumulation of dust and dirt.
Existing positional devices for computers are known, where a signal relating to position is determined by the interaction of a Hall effect device with a magnetic field. Hall devices are a known method of determining magnetic field strength, they depend on the interaction of a magnetic field on the current carried in a conductive material, typically a thin layer of a semiconductor. We refer to the Hall effect, first discovered by E. H. Hall in 1878 and the technology subsequently refined since then.
The principal features of the Hall effect are that the incidence of a magnetic field (B-field) on a current carrying conductor yields a Hall voltage, proportional to B. This Hall voltage is a maximum when the B-field and conductor surface are orthogonal.
Now, any magnetic field exists in three dimensions and a system of Hall devices located near a point in magnetic space will give Hall voltages which are a unique function of that point in magnetic space. If a system of magnets are used to develop a particular spatial magnetic field configuration and this system is mobile, relative to a system of Hall probes, then the Hall voltages generated in these Hall devices will, after processing, define the position of the magnetic system.
A number of patent applications have utilised this approach, in particular the following:
U.S. Pat. No. 4,459,578 Jul. 10, 1984
U.S. Pat. No. 4,639,667 Jan. 21, 1987
U.S. Pat. No. 4,654,576 Mar. 31, 1987
U.S. Pat. No. 4,825,157 Apr. 25, 1989
A disadvantage with this approach is the looseness, ambiguity and lack of precision of the geometric centre of such a magnetic assembly. Other disadvantages are the smallness of the B-field, the difficulty of flux concentration and that the movement of magnets generates circulating currents in the magnetic material creating additional fields superimposed on the main ones. A practical disadvantage is that such a magnetic sensor is often large and very bulky. The use of large magnets may also necessitate the use of shielding to prevent the magnetic field generated from interfering with magnetically sensitive equipment.
Another existing arrangement is described in WO 93/20535. This arrangement takes the form of a joystick and comprises a body including an end wall in which is secured a resilient arm. The resilient arm has secured to its top a tube and a handle. The tube surrounds the arm and mounts an annular magnet at the level of a pivot point, about which the arm flexes. The outputs of four Hall effect probes are affected by the position of the magnet to give an indication of the position of the arm, in two dimensions. The angular position of a, second, rotary handle is sensed by way of a further magnet which is connected for movement with the handle relative to further Hall effect probes.
Another use of a Hall effect device is disclosed in U.S. Pat. No. 5,004,871 which describes a stylus of a type suitable for use with a computer. The stylus has a pressure sensitive switch which may comprise a magnet and a Hall effect device mounted for movement relative to each other.
There are also a number of existing three dimensional positional devices available, for use in conjunction with computers. These devices use a variety of methods for generating a signal which relates to movement in three dimensions, including the use of gyroscopic systems to determine the movement of a device in space, electro-optical systems and in one device the use of strain gauges to determine the movement of a portion of the device relative to the remainder of the device. Existing three dimensional positional devices are expensive and/or imprecise, awkward and tiring to use, and in some cases physical constraints limit the use of the device.
An object of the present invention is to provide a three dimensional positional device which is convenient, simple and accurate and will, when used as an input device for a computer, enhance the capabilities of existing and future software technology and allow the exploitation of new more powerful computers.
Additional devices are foreseen for use with computer games, medical, computer graphics, virtual reality, robotics, security, teaching and other consumer and industrial applications.
According to a first aspect of the present invention there is provided a three dimensional positioning device comprising three Hall effect devices mounted on movable supports and three associated means for producing a magnetic field mounted on stationary supports adjacent but displaced from the movable supports.
Preferably the three magnetic systems are unconnected and unrelated. The magnetic systems each preferably comprise two magnets arranged in repelling mode polarity and the Hall effect devices are arranged to move between the opposed magnets. In this arrangement the Hall voltage measured will correspond to the position of the device between the two magnets, being a positive maximum when the Hall device is adjacent to one of the magnets and a negative maximum when the device is adjacent to the opposite magnet. The magnets preferably comprise small Nd.B.Fe Rare Earth magnets of high coercivity although they could comprise any other suitable magnetic material. The Hall devices are preferably comprised of conventional commercially available semiconductor Hall chips, although they could be effected by highly sensitive two dimensional electron gas (2DEG) Hall devices.
The three Hall devices and associated magnets are preferably mounted in a body having the appearance of the familiar two dimensional positional device, the mouse, but arranged to furnish three dimensional movement achieved by movement of the cover of the device with respect to its base. Movement of the three Hall devices may be proportional to the components of the movement of the cover of the device with respect to its base in three orthogonal directions. Springs may be employed to return the Hall devices to predetermined positions relative to their associated magnets when no external forces are applied to the device. Preferably the distance between any of the three positional modules (each comprising two opposed magnets and an associated Hall device) is greater than the distance between the opposed magnets of any one of the modules, more preferably the distance between any of the modules is at least twice the distance between the opposed magnets of any one module. The Hall voltages are preferably measured using conventional commercially available electronics and encoded for onward transmission to a computer by wire or by infra red or radio transmission, in which case the power supply for the device is preferably provided by means of a rechargeable battery and means for recharging this battery is provided integrally with the equipment that the positional device is intended for use with. The encoded information relating to the three Hall voltages is preferably processed by means of driver software which serves to move a cursor or object on the computer monitor in response to the signals received from the positional device, for example movement in two dimen
Hall Effect Technologies Limited
Patidar Jay
Salter & Michaelson
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