GB2371365A

GB2371365A - Identification and location sensor

Info

Publication number: GB2371365A
Application number: GB0101201A
Authority: GB
Inventors: Richard Geoffrey Woodham; Matthew Emmanuel Milto Storkey; James Mark Carson England
Original assignee: Sentec Ltd
Current assignee: Sentec Ltd
Priority date: 2001-01-17
Filing date: 2001-01-17
Publication date: 2002-07-24
Also published as: GB0101201D0

Abstract

Method and apparatus for identifying and locating items, in particular playing pieces for board games, comprises a board consisting of multiple locations each of which comprise insulated conductive tracks (5, 6, 7) in which one track (5) is excited with an alternating electric signal and the other tracks (6, 7) are connected to sensing circuits. The pieces have flat insulating bases with conductive patterns thereon which overlay the conductive tracks when placed at a location, and resistive elements (8) whose values determine the identity of the piece. The location of a piece is determined by the sequential excitation of the transmitting tracks over multiple locations and sensing of magnitudes of received signals, whilst piece identification is achieved by measuring the magnitude and phase of the received complex impedance signal which is unique to each piece. Single frequency excitation is disclosed although a range of frequencies may be used, and capacitive, inductive or resonant elements may also be used with the resistive elements.

Description

Identification and Location Sensor.

Field of the Invention This invention relates to the field of identification and sensing, particularly but not exclusively for use in identifying and locating playing pieces in games applications.

Background Determination of the identity and location of objects generally requires energy to be coupled into the object by some means (or some source of energy to be provided in the object), and energy (containing information) to be coupled from the object to some form of detector. The forms of energy coupling do not have to be the same, and can potentially be selected from a wide range of different sources. A few of the existing technologies are described below.

Inductive methods There are a number of patented systems making use of inductive coupling to coils.

GB2103943 (1983) describes a system in which multiple pieces are coded using resonant circuits, each tuned to a different frequency. An array of coils in the game board allows interrogation of each piece independently.

A number of patents build on this fundamental piece of work, often by merely improving the interrogation electronics, e. g. US 5188368. US 5129654 uses row-column multiplexing to determine position, rather than individual coils at each location. US5082286 uses variable inductive coupling between rows and columns, e. g. using ferrous material. US 3760404 uses a resonant frequency method. US 5853327 uses interpolation to determine position.

No patents were found that detailed measuring any secondary characteristics of the resonator, such as the Q, and using this to distinguish between pieces.

Patents assigned to Absolute Sensors Ltd (Synaptics UK) such as W09858237 cover a number of alternative sensing arrangements, including different resonator types, multiple resonators, second harmonic detection etc. Additionally, there are a large number of co

ordinate input device patents relating to multiplexed arrangements of coils interrogating resonators.

DC Magnetic Methods There are a number of examples in the art describing reed switches operated by permanent magnets to determine location at different cells on a playing board.

Capacitive Methods There are a number of patents relating to multiplexed arrays of electrodes used for capacitive fingerprint recognition. These are generally in the form of integrated circuits.

Electromagnetic (RF) Methods RFID chips have been used for identification of, for example, casino chips (US5, 941,769) during game play.

Summary of the Invention This invention describes a method for determining the identity and location of multiple items from a set on a flat surface. The method makes use of AC impedance measurement techniques, either capacitively and/or inductively coupled to the piece. Identity is coded, in part, by combinations of any of the real (resistive) part of this impedance and the number and/or locations of the conductors involved in the coupling. The system required to implement the sensing method comprises a sensing board, a number of items (pieces) that are placed on the board, and signal processing/electronics connected to the board. In a typical implementation, the pieces are to be placed only at pre-defined positions on the boards, for example, constrained by pegs, grids, indentations etc.

Brief Description of the Drawings Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which : Figure 1 illustrates an example of the pattern of conductive material for one predefined position on a board.

Figure 2 illustrates an example of a playing piece for use with the board pattern shown Figure 1.

Figure 3 illustrates the system diagram for a 2 by 2 array of pre-defined positions on a board.

Detailed Description First embodiment-capacitive sensing Sensing Board The board consists of patterns of conductive material sandwiched between a flat insulating substrate and a thin insulating cover layer at marked positions where, on placement of a suitable playing piece, the piece's location and identity may be determined. At each marked position on the board at least two conductive tracks pass under the area that would be covered by the playing piece. Figure 1 illustrates an example with 3 conductive tracks (marked 1,2 and 3). One track (marked 1) is excited with an alternating electrical signal (either voltage or current) and the other tracks (marked 2 and 3) are connected to (either voltage or current) sensing circuits. The transmitting tracks may be used to excite multiple locations. Similarly, the sensing circuits may sense signals from multiple locations. Each location has a unique combination of transmitter track and sensing track. All of the tracks are covered by a thin insulating layer (marked 4).

Playing pieces The playing pieces consist of insulating material with a flat bottom surface, on which there are at least two conductive patterns. The patterns on the playing piece are arranged such that when the piece is placed on a suitable location on the board, one conductive track on the piece lies in close proximity to the transmitter track on the board, and the other tracks on the piece lie in dose proximity to the sensing tracks on the board. Figure 2 illustrates an example of a playing piece designed to operate with the board layout of Figure 1. The conductive patterns on the piece (marked 5,6 and 7) are connected in the piece by resistive elements (marked 8), whose resistive values are used to determine the identity of the piece.

Determination of the locations of the playing pieces The position of playing pieces at the specified locations on the board can be determined by sequential excitation of the transmitting tracks with an appropriate electrical signal and sensing the magnitude of the received signal on the sensing tracks. The geometry of the tracks on the board and on the playing pieces is arranged such that when the board location is unoccupied the sensed signal is of a low magnitude; and when the location is occupied the sensed signal is of large magnitude. This is illustrated, by example, in Fig. 3 where four pre-defined locations for a 2-channel coding system are arranged in a 2-by-2 array (marked 9). The signal to the board is supplied from an oscillator (marked 10) and is diverted, in the first instance, to the top row of positions by the electronic switch (marked 11). Selection of the signals for the left column is by electronic switches (marked 12 and 13) for amplification and processing by electronic circuits (marked 14 and 15). Thus a piece placed on the top left-hand position can be detected and identified. By successive combinations of switches and ! or multiple instances of detection circuitry, all the positions on the board can be sensed for the placement of a piece, and if so, the identity of that piece.

Determination of the identity of the playing pieces The identities of the playing pieces are coded in the values of the resistive elements in the pieces. The electrical coupling between the tracks and the piece being measured is capacitive. The sensing circuits are designed to be sensitive to both the magnitude and phase of the received signal. These sensing circuits are designed assuming that the whole electrical circuit comprising of board and the playing piece, is equivalent to a reactive component in series with a resistive component. The sensing circuits are also designed to cope with the case that the reactive part may vary (depending on how exactly the piece is placed on the board), but that the resistive part will remain constant. These circuits will calculate the resistance of the piece, and, based on a pre-defined coding scheme, will assign a code element for that resistance value. For designs with more than one sensing track per board location, the code for the piece will consist of a plurality of measured resistance values. By this method the number of recognisable codes is increased greatly.

Further Embodiments The embodiment described above uses complex impedance at a single frequency to identify a playing piece at a particular position on a board. Identity information is stored by the

resistive part of this impedance. This approach can be generalised by measuring the complex impedance of the transmitter/receiver network over a range of frequencies.

Identification information can be stored by means of a more complex network of components on the piece, such as an LCR network, or resonant components, such as a ceramic resonator. If the topology of the circuit is known, then the frequency-dependent complex impedance data can be used to determine the best-fit values of the components in the network, and hence data about the identity of the object.

The capacitive sensing method described above may be adapted to use inductive coupling, either to couple energy to the piece from the board, or energy from the piece to the board, or both. In this case, a resonant element may be used advantageously in the piece, for example, an LC resonator, a ceramic resonator, a quartz crystal or a magnetostrictive resonator.

The capacitive sensing arrangement above results in the observation of a residual capacitance in the absence of a piece. In a further embodiment, a balanced transmitter/receiver network can be adopted to avoid the observed residual capacitance.

For example, each single sensing conductor, 2 and 3, can be replaced with a differential pair of sensing conductors, symmetrically disposed about the driven element, 1. In the absence of a piece, there is virtually no residual coupling to the sensing conductors. The conductors on the piece are arranged such that, when placed in the correct position, the driven element is coupled only to one of the two sensing conductors, via a resistive or other element. The other sensing conductor in the pair may be coupled to a ground conductor on the board for best results. The piece may therefore couple in-phase or out-of-phase signals to the differential sensing elements, depending on the layout of tracks on the playing piece, adding to identification information stored on the piece.

Claims

Claims 1. A method and apparatus for identifying and locating items comprising the steps of - generating a first AC electric or magnetic field from an arrangement of a first set of conductors on a first substantially flat substrate - coupling said first field to a second set of conductors arranged on a second flat substrate placed in close proximity to said first substrate, said second substrate also containing one or more resistive elements connected to the second conductors, whose resistance represents identification data - generating a second AC electric or magnetic field from said second set of conductors - coupling said second field into a third set of conductors on said first substrate - measuring any of current or voltage in any of said first or third sets of conductors - determining which conductors from said first and third sets of conductors are significantly coupled together by the conductors and resistors on said second substrate - determining a value for the impedance of resistive element by combinations of the measurements; and hence

- determining the position and identity of the second substrate.
2. A method according to any of the preceding claims wherein there are multiple sets of first conductors.
3. A method according to any of the preceding claims wherein there are multiple sets of second conductors and associated resistive components.
4. A method according to any of the preceding claims wherein there are multiple sets of third conductors.
5. A method according to any of the preceding claims wherein identification information is stored by the presence of coupling between specific conductors in said first and third sets of conductors, by specific arrangement of said second conductors.
6. A method according to any of the preceding claims wherein location determined by the

presence of coupling between specific conductors in said first and third sets of conductors.
7. A method according to any of the preceding claims, wherein said fields are electric.
8. A method according to any of the preceding claims wherein information is coded by the value of one or more resistors.
9. A method according to any of the preceding claims, wherein the value of the resistors is substantially zero.
10. A method according to any of the preceding claims, wherein said first and third sets of conductors are substantially orthogonal.
11. A method according to any of the preceding claims, wherein said first conductors are excited using time and/or frequency multiplexing.
12. A method according to any of the preceding claims, wherein currents and/or voltages on said first and/or third conductors are analysed at more than one frequency.
13. A method for remote determination of identity, wherein energy is coupled to/from the remote object using electric and/or magnetic fields, and identification information is stored by the values of a network of components in said object, said components including, without restriction : resistors, capacitors, inductors, resonators.
14. A method according to claim 13, where the components are resistors.
15. A method and apparatus for identifying and locating items comprising the steps of - generating a first AC electric or magnetic field from an arrangement of a first set of conductors on a first substantially flat substrate - coupling said first field to a second set of conductors arranged on a second flat substrate placed in dose proximity to said first substrate, said second substrate also containing one or more resistive, capacitive, inductive or resonant elements connected to the second conductors and/or to each other in a network, whose values represents identification data - generating a second AC electric or magnetic field from said second set of conductors - coupling said second field into a third set of conductors on said first substrate - measuring any of current or voltage in any of said first or third sets of conductors - determining which conductors from said first and third sets of conductors are significantly coupled together by the conductors and resistors on said second substrate - determining a value for the impedance of the network or components connected to said second conductors by combinations of the measurements; and hence - determining the position and identity of the second substrate by a combination of the physical position and/or layout of the significantly coupled conductors on said first substrate and/or the values of the components on said second substrate
16. A method of distinguishing between a pre-defined set of objects by a loosely-coupled measurement of the resistive loss.