GB2228315A - Colour recognition system for table ball games - Google Patents

Abstract

A colour recognition system for a coin-operated snooker game has a ball tunnel containing three coloured light emitting diodes (1) arranged at the Brewster angle relative to a photocell (4) which is shielded so as to pick up primarily reflected and polarised light from the ball surface. Three broad spectral channels of light are used for colour sensing. These spectral channels are simply generated without filters or spectral analysis devices (e.g. prisms) by using appropriate light-emitting diodes; conveniently red, yellow and blue. A single broadband photocell is used to detect all channels, flashed on and read out in a predetermined sequence which in practice (and including determinations of dark currents) takes about 15 mS. A microprocessor based controller enables the colour detector to "learn" and distinguish the colours of different sets of snooker ball. <IMAGE>

Description

"COLOUR RECOGNITION SYSTEM FOR TABLE BALL GAMES" This invention relates to a colour recognition system for use in a table used for playing ball games such as snooker and pool. It has particular though not sole application to coin operated tables.

The invention relates to improvements to our invention entitled "Improvements in or relating to tables" the subject of UK patent GB 2,158,360B published on 23 April 1987 (previously application No.

8506922) the contents of which are incorporated herein by way of reference. In that earlier patent we described a snooker table in which a colour detector utilising a white light source was mounted beneath the snooker table so that a ball falling down a pocket would land on a ball rung and pass through a tunnel containing the colour detector. The original colour detector was based on an invention described and claimed in New Zealand patent No. 202895 entitled "Improvements in or relating to colour indication" patented by the University of Auckland. That system however is expensive to construct, and has not proved to be entirely reliable in detecting the colour of balls used in snooker, billiards, pool and other ball games, as the balls vary in colour from batch to batch and from manufacturer to manufacturer.

It is an object of this invention to provide an improved colour recognition system for table ball games.

In one aspect the invention provides a colour recognition system for table ball games including a plurality of light emitting diodes of at least two different colours mounted within a housing through which balls may pass, a photoreceptor mounted within the housing and adapted to receive light reflected from the surface of a ball within said housing, and means for providing a colour recognition signal based on information received from said photoreceptor.

Preferably there are at least three diodes encompassing the visible light spectrum, each of which is mounted on either side of a centrally placed photoreceptor such as a photocell, and preferably each is so aligned that light will pass from one of the light emitting diodes and be reflected from the ball surface at the "Brewster angle" so that the reflected light reaching the photocell is polarised.

Preferably the light emitting diodes are controlled by a microprocessor, and are switched on in turn as a ball is detected within the housing. In the preferred embodiments the diodes are switched on when a moving ball is detected entering a ball tunnel and the measurements are made as the ball moves through the tunnel. Thus the microprocessor "knows" which colour causes the photocurrent at a given time.

This has the advantage that the colour recognition system can be of low cost, and in its preferred form, can be "trained" to discriminate between balls of different colours even though the colours may vary from batch to batch or manufacturer to manufacturer.

These and other aspects of the invention, which should be considered in all its novel aspects, will become apparent from the following description, which is given by way of example1 with reference to the accompanying drawings, in which: Figure 1: illustrates a vertical cross-section through the colour detection portion of a ball tunnel (similar to item 8 of Figure 1 of our earlier patent GB 2,158,360B).

Figure 2: is a top plan view of the colour detection head of Figure 1 showing the relative placement of the diodes and photocell.

Two working examples of the invention will now be described with reference to Examples I and II. The Examples differ in the colour of diodes selected but in most other aspects are of similar design.

The invention will be described with reference to a coin operated snooker table, although it will be appreciated that it can be applied to similar table ball games.

Snooker Table Controller The colour detector is part of a novel controller which includes means to supervise a coin-operated snooker game by measuring the colours of the balls as they are potted and immediately returning to the players any balls that are not yet expected - e.g. any coloured balls (as distinct from reds) during the early phase of the game and later just the coloured balls not arriving in the correct order.

In more detail; the device incorporates means to establish the current state of the game, means to determine the colour of the ball rolling through its sensing gate, and means to check that colour against the single colour expected at that stage of the game. Should the ball be not recognised as a version of the expected colour, then the ball is rejected, e.g. a solenoid pushes the ball onto an alternative track thus returning it to play.

Exceptional-state processing: 1. Balls potted in the correct order but as a result of a foul shot are able to be recalled on the press of a button.

2. The game can be re-started halfway through simply by inserting more money. An on-site learning facility is provided. With the optional aid of an external test board, the device can learn the particular colours of the sets of balls actually available. This also compensates for minor between-instrument and time-related variations in sensitivity, and the machine tests each new colour against all different colours already stored in order to detect possible conflicts. It is no longer necessary for the manufacturer to have all possible sets to hand, and the mask-programmable version of the microprocessor can be used in production to reduce the component count.

The device includes novel design in both software and electronic hardware elements to achieve the desired function.

Ball Tunnel.

The ball tunnel is preferably a short length of tubing or ducting through which the ball may pass along a central tract, and from which incident light may be excluded from the portion housing the colour detection system.

The colour detection system is fitted across the top of the ball tunnel as shown in Figure 1, in which a portion of the ball is illustrated. The colour detection head is preferably formed from a block of material, most conveniently by injection moulding a plastics material, although prototypes have been machined from a solid block of plastic.

Colour Detector - Example I.

In the prototype, shown in Figures 1 and 2, apertures 3 have been machined at precise angles to house high intensity light emitting diodes (LEDs), and one such LED is shown by reference numeral 1, ready for insertion in its aperture 3, whilst the corresponding LED on the right of the diagram is shown mounted within its aperture. Note that the aperture on the right is positioned at a slightly different angle with respect to the top of the ball than aperture 3 on the left of the block. A photocell 4, preferably a single broadband photocell capable of detecting three broad spectral channels of light (supplied by three LEDs) is positioned in the centre of the block as shown in Figure 1.

Preferably the photocell 4 is covered with a layer of polarising material, preferably a sheet of "Polaroid" material.

As shown in Figure 2, it is preferred that the apertures 3 are in the form of slots, so that two LEDs may be provided in one of the apertures 3, with their light paths inclined with respect to one another as shown by the dotted lines in Figure 2. This enables two LEDs to be positioned in each aperture in such a way that light emitted from one of them will be reflected from the top of the ball at the required Brewster angle. By setting the alignment of the apertures 3 at the Brewster angle, light reflected from the top of the ball will be polarised, and the sheet of Polaroid material can be used to exclude specular reflections from the shiny ball surface, and avoid most reflections from scratches. It being appreciated that snooker balls are of a high gloss appearance, and specular reflections from this glossy surface interferes with accurate colour detection.

In this example the LEDs include a red LED, a green LED, and an infra-red LED.

We have found that the red and green LEDs are sufficient to distinguish between most ball types, but that in the case of blue balls, some of them are difficult to distinguish from black balls. We have found that blue snooker balls reflect infra-red brightly, and thus the infra-red LED can be used to distinguish between all types of blue balls and black balls.

It will be appreciated that the number and type of LEDs will depend upon the number and type of balls used in a particular ball game. [A blue diode as described in Example II will also perform the function of distinguishing between blue and black balls.] Hardware and Software elements for colour determination will now be described in more detail.

Hardware elements. Colour determination.

Three broad spectral channels of light are used for colour sensing. These spectral channels are simply generated without filters or spectral analysis devices (e.g. prisms) by using appropriate LEDs; conveniently red, green, and infra-red high-intensity diodes in the case of Example I and red, yellow and blue diodes in Example II. A single broadband photocell is used to detect all channels, flashed on and read out in a predetermined sequence which in practice (and including determinations of dark currents) takes about 15 mS.

The advantages of this approach are: Lamps: Diodes are cheap and in good supply, have long lives (almost indefinitely long in this application) and are easy to drive in a pulsed mode. They have a very fast response.

Spectral purity is a function of the semiconductor crystals used and is independent of time and (within safe operating limits) current. A particular advantage is that no infra-red radiation emerges from the red and green diodes. Had an incandescent lamp with dye filters been used, near infra-red light which is almost always transmitted well would emerge.

Silicon photosensors have a high sensitivity to that unwanted "colour", thus the true colour signal will be obscured.

The physical design of the colour-sensing head is such that the red and green photodiodes are aimed at one spot - the top of the ball - with light reflected into the sensor at the Brewster angle. A sheet of "Polaroid" plastic in front of the detector is oriented to exclude specular reflections from the shiny ball surface, and avoid most reflections from scratches. The infra-red diode light does not meet the Brewster angle criterion but near infra-red light is not affected by "Polaroid" in any case.

Hardware elements. Electronics.

The control of the game is managed with a relatively small number of integrated circuits. A recently available 8-bit microprocessor of the "Intel" 8051 family, the "Philips" 83C552, includes eight channels of 10bit A- > D conversion functions. Eight solenoids are driven by parallel Darlington drivers from decoded external-memory data bytes. One quad op-amp (type LM324) controls three channels of diode; aided by transistors in the standard constant-current configuration, the other amplifier is wired as a conventional integrator to collect photocurrents.

This photo-integrator configuration has the following advantages... All the available current (in this case; from a photovoltaic diode) emanating during the flash of light is converted into data, The circuit has a fast response, Random noise is integrated out, On termination of the flash the integrator output is immediately stable so no external sample-and-hold circuit is required.

Sensitivity is adjusted by varying the integrating capacitor, and for fine adjustments in the field or for green vs red sensitivity by varying the settings of two potentiometers which are read from at the start of each game.

The microprocessor can reset the integrator by means a field-effect transistor across the integrating capacitor.

Means (a 10-turn preset potentiometer) exists to compensate for large amounts of drift due to many sources; residual drift is subtracted by measuring "dummy flashes" of duration equal to the genuine flashes.

Several components of the 'Philips' I2C serial digital information transfer family of integrated circuits are used during testing and especially for storage of ball brightness data.

An electrically programmable read-only memory (EEPRO - Philips type PCF8572) can store 256 bytes of data for at least 10 years and with up to 10,000 revisions. In practice, we can store data for 8 sets of 8 colours of balls, using 4 bytes per ball (code, IR, red and green values for Example I) tor different codes for Example II] in one chip. However remembering the data for that many sets is a disadvantage as it takes 1/4 sec to read a full E ROM. This delay, compared with the arrival times of a possible series of balls, is likely to be excessive.

A jumper-selected learn mode averages the values from four passes of a given ball (used in strict sequence) and stores each value. A review mode can display them conveniently on the display module which is a 'Philips' I2C evaluation board. It carries 2 sets of 4 x 7-segment displays, an EEPROM socket, and a beeper having a variety of tones. It is preferable to load the EEPROM while installed on this board, and transfer it to the controller's own board afterwards, because the evaluation board/display board shows messages to keep the ball-learning process in step.

The controller circuit board is located on top of the tunnel for convenience; the tunnel top thus bears all the "high-technoloy" material including the ball position-sensing light beam and the colour photosensor, all of which can be replaced as a single unit for simpler field servicing.

Colour Detector Example II.

The ball tunnel is unaltered; and the printed-circuit board carries only a few minor modifications. The colour-sensing head was redesigned to expose the bodies of the three LEDs to the interior of the tunnel and' this resulted in a greater light-detection efficiency. A KTY81 (Philips) temperature sensor is mounted within the colour-sensing head in order to monitor actual temperature. An improved diagnostics test-board has been designed as an optional plug-in device; using a standard 40 x 2 character liquid-crystal display, with an I2C standard four-wire interface to the microprocessor. Appropriate display subroutines to make use of this board have been added to all programmes.

Three broad spectral bands of light are again used; as emitted by red LEDs, (dominant wavelength 650 nm), yellow LEDS (dominant wavelength 590 nm), and blue LEDs which have a comparatively broad spectral distribution through green and blue wavelengths. Yellow light was found to be better than light from green diodes to distinguish between the dyes currently in use for snooker ball colours The same type as in the first example of a broad-band silicon photocell - a Siemens BPW21 device operated in the photovoltaic mode - is mounted behind a sheet of polarising filter Blue LEDs are expensive and very much less bright than the high-intensity red and yellow diodes with which they are used. This system energises the single blue diode for 20 milliseconds (mS) in order that the integration time used equals a full cycle of the UK and NZ mains supply voltage, so that interference from that source tends to cancel itself out. Different times shall be used for countries having other AC mains supply frequencies. The red and yellow channels are energised for just a few mS each and the consequent photocurrents are substantially unaffected by stray electrostatic fields. The exact durations which depend on component efficiency and sensing head dimensions are defined at setting-up time, and are stored in the EEPROL memory for later use.

It was found desirable to monitor the ambient temperature in the vicinity of the LEDs and to compensate the perceived photocurrents within the software in order to minimise temperature induced variations in brightness - mainly owing to LED temperature coefficients and also to photosensor temperature coefficients.

Several circuit components were altered from the hardware of Example I to: (a) Provide an I;C interface connection, (b) Provide more current to the blue LED (c) Provide energising current to the temperature sensor (d) Use a larger integrating capacitor, to minimise effects of junction capacitance, capacitative coupling from switching impulses, and to make the input stage less sensitive to noise.

Software elements.

An interrupt subroutine is entered when inserted coins are detected by a separate mechanism. This commences supervision of the whole game. The other interrupt subroutine is a timer which starts whenever a ball other than red is accepted; it sets up a 20 second period during which time the recovery of inadvertently potted foul balls is allowed. If the player presses the button while the adjacent light is on, the most recent coloured ball (including black (with white) at the end of the game) can be recovered for replay.

The program first considers the current state of the game in order to evaluate the ball colour currently expected, and loads all available colour sets for that ball colour from the EEPROM into a microprocessor memory cache.

When a ball rolls into the sensing light beam, its colour is evaluated and the corrected set of data for all available LED channels is checked against all sets in the cache. If no match is found the ball is returned; otherwise it is kept. At this stage of development the "colour" is simply used as three separate brightness values.

Tolerances for the colours read are provided for, since the algorithm must allow for least-significant-bit digitizing scatter, balls with scratches, dirt and chalk, and natural fading; a particular problem with the red balls. If tolerances are too wide, balls of other colours will be assumed to be of the currently expected colour.

Once the expected ball has been kept - which is carried out by a solenoid-driven deflector not being triggered at the moment when the ball leaves the sensing light beam - the program updates the game status, collects a new set of colour data and waits for the next ball. The deflector pushes all non-expected balls along a track towards a receptacle from which the player can retrieve them. If the FOUL button is pushed within the allowed period, the latest ball is immediately returned by means of a solenoid and the game status is set back one step. The game terminates once the black ball has been potted and the 20 second foul period is over. The processor then waits for the coin signal, which is set up to cause an interrupt within the program so that the players can cancel a game in progress and make a fresh start simply by inserting the appropriate coins.

This system allows the controller to be re-trained by teaching it ball colours in the event that the ball colours with which it is to be used in future varies from the preset colour memory stored in the controller.

Although the combination of red, yellow, and blue LEDs was the best found so far at differentiating balls from the various manufactured sets available, substitution of a green diode for the yellow diode was almost as suitable and is a closer match to the theoretical ideal of red, green, and blue primary colours. In fact the light from a green diode includes a substantial amount of yellow light. The principle of the system also allows for the use of more than three separate colours of illumination.

Finally, various alterations or modifications may be made to the foregoing without departing from the scope of this invention, as set forth in the following claims.

Claims (8)

1. A colour recognition system for table ball games including a plurality of light emitting diodes of at least two different colours mounted within a housing through which balls may pass, a photoreceptor mounted within the housing and adapted to receive light reflected from the surface of a ball within said housing, and means for providing a colour recognition signal based on information received from said photoreceptor.

2. A colour recognition system for table ball games as claimed in claim 1, wherein the photoreceptor and each said light emitting diode are mounted relative to one another at a required Brewster angle for the light from said respective diode.

3. A colour recognition system for table ball games as claimed in claim 1 or claim 2, wherein the light emitting diodes are controlled by a microprocessor, and in use are switched on in turn when a ball is detected within the housing.

4. A colour recognition system for table ball games as claimed in any preceding claim, wherein the diodes include red, yellow and blue light-emitting diodes.

5. A colour recognition system for table ball games as claimed in any one of claims 1 to 3, wherein the diodes include red, green and blue light-emitting diodes.

6. A colour recognition system for table ball games as claimed in any one of claims 1 to 3, wherein the diodes include red, green and infra-red light-emitting diodes.

7. A colour recognition system for table ball games substantially as described in Example I or Example II herein.

8. Apparatus for use in the colour recognition system for table ball games claimed in any one of the preceding claims substantially as described in the Description with reference to and as shown in the accompanying diagrammatic Drawings.