GB2069783A - Position detecting apparatus - Google Patents

Abstract

Position sensing apparatus, e.g. for detecting the angular position of a fruit machine reel, has magnets 50-54 and Hall devices 16-20 arranged in pairs and fixed. A coding disc 14 rotates with the reel 10 and has code elements 21 which pass between the various magnet and Hall device pairs. The elements 21 are either metal slugs 55 in a dielectric disc or apertures 56 in a metal disc and shunt magnetic field to effect coded switching of the Hall devices. <IMAGE>

Description

SPECIFICATION Position detecting apparatus The present invention is concerned with position detecting apparatus particularly for detecting the position of a first member which is movable relative to a second member. The invention is applicable, though not exclusively, to angular position detecting. There are various apparatus for angular position sensing, e.g. shaft encoders. Many different kinds of machine include movable, especially rotatable, parts and members whose, e.g. angular, positions must be sensed or detected either continuously or at various times. The present invention is particularly, though not exclusively, applicable to detecting the angular positions of rotatable members in amusement and gaming machines of the so-called fruit machine or slot machine type.

Gaming machines of this type are well-known and typically have at least one and usually three or four rotatable reels which ere set in motion at the beginning of each playing cycle of the machine. The reels are marked around their peripheries with a number of indicia and they are arranged to stop rotating after random intervals so that a random selection of the indicia are visible behind a window of the gaming machine. The stop positions of the reels, as indicated by the visible indicia, may represent a winning combination in which case the gaming machine operates automatically to pay out the win or notify the player of the win, or in some cases to permit the player to select one or more further functions or operations of the machine.Any gaming or amusement machine of this general kind with rotatable reels whose stop positions determine winning combinations will be described hereinafter as a gaming or amusement machine of the fruit machine type.

In such machines it can be seen that it is important to be able to detect the stop positions of the various reels of the machine so that the machine can determine whether the indicia appearing behind the window of the machine represent a winning combination. Various methods of detecting the stop positions of the reels of machines of the fruit machine type have been proposed and operated. For example, it is known to employ photoelectric detectors. In such arrangements it is usual to provide a plurality of detectors and one or more light sources which are fixed in the machine. A disc is provided rotatable with the reel with the disc being coded with holes arranged to align with the photo detectors so that a unique combination of detectors is exposed to light from the light source or sources at each of the stop positions of the reel which are at equal angular spacings.

A summary of various techniques for detecting the stop position of rotatable reels in machines of the fruit machine type is given in the specification of British patent 1268104. Various magnetic techniques are also mentioned in this specification including the use of magnets and reed switches with the magnets located on the rotating reel in a coded pattern. The specification also suggests detecting variations in the induction of a circuit and the use of hall-effect devices. However, no detailed arrangements are disclosed.

In accordance with the present invention, apparatus for detecting the position of a first member which is movable relative to a second member comprises a plurality of magnetic field responsive sensing devices fixed relative to the second member, a corresponding plurality of magnets fixed relative to the second member at locations spaced from respective said magnetic field responsive sensing devices whereby each sensing device can respond to the magnetic field from a respective one of the magnets, and position coding means movable with said first member to pass between the sensing devices and their respective magnets, the position coding means having spacially varying magnetic permeability in the direction of movement relative to the sensing devices and magnets whereby the sensing devices are responsive to the resultant variations in the magnetic fields from their respective magnets to provide an indication of the relative position of the first member.

Conveniently, the position coding means has a first magnetic permeability with code elements of a second magnetic permeability distributed therein so that each element passes between at least one of the sensing device and magnet pairs on movement of the first member. Conveniently, the sensing devices are each responsive to provide a first output indication in the absence of a said code element between the device and the associated magnet and a second output indication in response to the presence of a said code elementtherebetween, the code elements being distributed in the coding means so that a unique combination of the sensing devices provides said second indication for each of a predetermined number of relative positions of the first member.

Preferably, said sensing devices are Hall-effect devices. With Hall-effect devices power supply means are necessary for energising the devices and the power supply means may include gating means arranged to remove the energising voltage from the devices before their output indications are to be read to determine the relative position of the member, and reapplying the energising voltage when the output indications are to be read. This gating arrangement overcomes the problem arising from the inherent hysteresis of the switching effect of typical Hall-effect devices. In some devices it might be necessary actually to reverse the magnetic field in order to ensure the device switches back to its high level state.However, in the absence of an energising voltage, the device automatically reverts to the high output state so that on reapplying the energising voltage the Hall device will immediately adopt a state dependent on whether the magnetic field at the moment of application of the voltage is above or below the threshold level at which the device normally switches from high output to low output The coding means is preferably formed as a sheet extending transversely between the sensing device and magnet pairs of a material of high relative magnetic permeability and the code elements then comprise apertures through the sheet.Then, preferably, the apparatus includes a magnetic shunt means arranged to provide a path of relatively high magnetic permeability between the magnets and the coding means to shuntthe magnetic field of any of the magnets in the absence of an aperture between the respective magnet and its associated sensing device, whereby the sensing device is responsive to a relatively increased magnetic field to indicate the presence of a code element. Alternatively, said second magnetic permeability of the code elements may be greater than said first magnetic permeability, whereby the presence of a said code element bet- ween any of the sensing device and magnet pairs enhances the magnetic field at the sensing device.

The code elements may be ferro-magnetic.

In one arrangement, the sensing device and magnet pairs are spaced apart one pair from another transversely of the direction of relative movement of the first member, and the position coding means has a respective track, including at least one of said code elements, for each said pair.

instead, the sensing device and magnet pairs may be spaced one pair behind another in the direction of relative movement of the first member and each code element may then pass between each of said pair successively on movement of said first element.

In a preferred arrangement, said sensing device and magnet pairs are positioned with the sensing device and magnet of each pair on opposite sides of a common plane containing the direction of relative movement of the first member and the coding means is formed as a sheet in or tangential to said common plane.

The first member may be rotatable relative to the second member and the apparatus is then suitable for detecting the relative angular position of the first member. In this case, the above mentioned common plane may be perpendicularto the axis of rotation of the first member.

The present invention further envisages a gaming or amusement machine of the fruit machine type as hereinbefore defined which includes apparatus for detecting the angular position of a rotatable member as described above and which is adapted for detect ing the stop positions of the or at least one of the rotatable reels of the machine.

Examples of the present invention will now be described in greater detail with reference to the accompanying drawings in which: FIGURE 1 is a view along the axis of rotation of part of a reel assembly from a gaming or amuse ment machine of the fruit machine type, including position sensing apparatus embodying the present invention; FIGURE 2 is a sectional view along line X-X of FIGURE 1 illustrating one embodiment of the inven tion; FIGURE 3 is a view corresponding to FIGURE 2 but illustrating a different embodiment of the invention; FIGURES 4 and 5 illustrate graphically the range of response characteristics of Hall-effect devices which can be used in the apparatus illustrated in FIGURES 2 or 3.

FIGURE 6 illustrates a simple method of energising Hall-effect devices in the apparatus of FIGURES 1,2 or3 using devices having characteristics as illustrated in FIGURE 4; FIGURE 7 is a diagram of a circuit for energising Hall-effect devices enabling devices having a full range of characteristics to be employed; FIGURE 8 illustrates a circuit for energising simul- taneousiy all the Hall-effect devices used in the position sensing apparatus of FIGURES 2 or 3;; FIGURE 9 is a timing diagram illustrating the sequential scanning of the position sensing devices of each of four reels in a gaming machine and FIGURE 10 is a simplified block diagram illustrate ing the connection of the position sensing apparatus illustrated in FIGURE 1 into a micrncomputersystem for controlling the operation of the gaming machine.

Referring to FIGURE 1,there is illustrated a reel 10 which is mounted for rotation about an axis 11. The reel 10 forms part of a gaming or amusement machine of the fruit machine kind as hereinbefore defined and in atypical complete machine there may be three or four such reels which are commonly arranged on a common axis. In operation of the machine, the reels are set in motion, rotating in the direction of arrows 12, when a player initiates a play cycle of the machine. After predetermined lengths of time, the reels are stopped, usually one reel afterthe other.The reels normally have a predetermined number of indicia, e.g. pictures of fruit or other devices, arranged equally spaced about the outer periphery 13 of the reel, and the reels are normally indexed so as to be stopped at a randomly selected one of the stop positions corresponding to one of the indicia being aligned behind a viewing window of the gaming machine.

As explained previously, it is important for operation of the gaming machine to determine the positions at which the various reels of the machine have stopped and for this purpose apparatus is provided for sensing the stop positions of the various reels. In FIGURE 1, the apparatus for one of the reels is illustrated and comprises a coded disc 14 mounted for rotation with the reel 10 about the axis 11. Mounted fixed adjacent the disc 14 is a printed circuit board 15 on which are mounted inter alia, five hall-effect devices 16 to 20.

The Hall-effect devices 16 to 20 are mounted on the circuit board 15 so as to be radially aligned relative to the axis 11. Printed circuit board 15 with the Hall effect devices is fixed to the chassis of the assembly containing the rotatable reel 10. The coded disc 14 contains a plurality of code elements 21 arranged in five concentric annular tracks 22 to 26. The radial spacing of the tracks 22 to 26 is the same as the spacing between adjacent Hall-effect devices 16 to 20 and the Hall-effect devices are located on the printed circuit board 15 to one side, behind in FIG URE 1, the disc 14 so that, as seen in FIGURE 1, the elements 21 of each track pass immediately in front (in FIGURE 1 ) of a respective one of the Hall-effect devices.

FIGURE 2 is a cross-sectional view taken along line X-X of FIGURE 1. A horseshoe bracket of a ferromagnetic material is fixed to the printed circuit board by one arm 28 which is provided with apertures for the Hall-effect devices 16 to 20. The other arm 29 of the bracket 27 extends radially on the opposite side of the disc 14 from the Hall-effect devices. Magnets 50 to 54 are mounted on the arm 29 of the bracket 27 between the bracket and the disc 24. The magnets 50 to 54 are aligned with respective Hall-effect devices on the opposite side of the disc 14 so that each Halleffect device is predominantly in the influence of the magnetic field from a respective one of the magnets.

Normally, the magnets are arranged with corresponding poles adjacent the arm 29 of the bracket 27 and opposite poles nearest the respective Hall-effect devices.

In the example of FIGURE 2, the coded disc 14 is formed of a dielectric material having a low relative permeability. The code elements 21 are then formed as inserts 55 in the disc 14 of a material having a high relative permeability, typically of a ferro-magnetic material.

It will be appreciated that the presence of a ferromagnetic insert 55 immediately between an adjacent pair of Hall-effect devices and magnets has the effect of enhancing the magnetic field strength at the Halleffect device. The spacing between the Hall-effect devices and the magnets must, of course, be sufficient to accommodate the width of the disc 14 with insert 55. However, this spacing, the size of the inserts 55 and also the field strength of the magnets is carefully selected to ensure that the hall-effect device will adopt its high field (low voltage output) state only when there is an insert 55 immediately between the device and its respective magnet. In the absence of an insert, the field strength at the Halleffect device is too low to switch the device.

It will be appreciated that for a fruit machine, there are a predetermined number of equally spaced possible angular stopping positions corresponding to the number of indicia marked about the periphery 13 of the reel 10. The code elements 21 are arranged on the coded disc 14 so that at each of the predetermined stopping positions, a predetermined unique combination of elements, from respective tracks 22 to 26, are located between respective magnets and Hall device pairs. It is important to ensure that a Hall device adopts its high field state only when there is an insert 55 correctly located between the device and its associated magnet. Clearly, the angular selectivity of the switching of the Hall-effect devices must be less than the angular spacing between adjacent stop positions of the reel, so as to ensure unambiguous reading of the actual stop positions.Furthermore, it is importnatto ensurethatthe inserts 55 in one track do not cause switching of a Hall device associated with a different track.

In the example of FIGURE 2, the horsehoe bracket 27 provides a return path shuntforthe magnetic field of the magnets 50 to 54.

FIGURE 3 shows a different arrangement but parts of the apparatus in FIGURE 3 which are the same as those in FIGURE 2 are given the same references. In FIGURE 3 the coded disc 14 is itself formed of a ferro-magnetic material. In this arrangement, the code elements 21 are formed as apertures 56 through the disc 14. Then, in the absence of an aperture 56 correctly located between a Hall-effect device and its associated magnet, the magnetic field from the magnet is shunted and diffused in the coded disc 14.

On the other hand, the diffusing effect of the disc 14 is much less in the presence of an aperture 56.

Again, the arrangement is made such that each Hall-effect device adopts its high field state only when there is an aperture 56 correctly positioned between the device and its associated magnet.

The spacing between the outer peripheral edge 57 of the disc 14 and the adjacent part of the horseshoe bracket 27 may conveniently be kept relatively small to improve the magnetic shunting effect of the disc 14.

FIGURES 4 and 5 illustrate graphically the variation in the switching characteristics of Hall-effect devices.

Hall-effect devices have three terminals and a predetermined energising voltage is applied across two of the terminals. The third, output, terminal then adopts a voltage dependent on the magnetic flux density to which the device is exposed. The output voltage on the third terminal is normally high until the flux density reaches a threshold level at which the output voltage switches suddenly to a relatively low level. However, there is considerable hysteresis in the operation of the device so that the device only switches back again to the high output level when the flux density is reduced to a second threshold level considerably below the first threshold level.

Thus, the operation of a typical device as illustrated in FIGURE 4 with the arrows indicating the direction of switching between the high output voltage level VOH and the low output voltage level VOL. Variation between devices produced even on the same production run can cause the switching threshold, for the device to return to the high output voltage state, to be shifted to the left of they-axis, as shown in FIGURES, and corresponding to the need to reverse the direction of magnetic flux in order to switch the device back to the high output voltage state. Clearly, a device having the characteristic of FIGURE 5 could not be made to work if constantly energised in the position sensing apparatus of the present invention using fixed magnets since it would not be possible to reverse the flux.However, selected devices all having characteristics as illustrated in FIGURE 4 could be used in a simple circuit as shown in FIGURE 6 in which all five of the Hall-effect devices 30 are connected in parallel between a supply rail at an energising voltage Vcc and a O volts rail. If some of the devices 30 are exposed to flux above the upper threshold level (the right-hand vertical line in FIG URE 4) as illustrated in FIGURE 6 by the sign "+" and others of the devices are exposed to substantially no flux or flux which is less than the lowerthreshold voltage (the left-hand vertical line in FIGURE 4) as illustrated by the sign "0" in FIGURE 5 then the outputs of the devices will be low or high as shown in the figure. These output levels can be read in the usual way to generate a binary number representative of the stop position of the reel.

FIGURE 7 illustrates a simple circuit which enables Hall devices having characteristics ranging from those illustrated in FIGURE 4 to those of FIGURE 5 to be used in the described apparatus. In the circuit of FIGURE 7, a gating transistor 31 has its emitter collector circuit connected in series with the Hall-effect device 32 so as to control the application of energising voltage to the device. A control pulse can then be supplied to the base of transistor 31 via a resistor 33 to switch off the transistor 31, de-energising the Hall device 32. It is a characteristic of Hall-effect devices that they automatically adopt the high output voltage state when first energised unless the magnetic flux is above the upperthreshold level.Therefore, if the Hall-effect device 32 is de-energised until it is desired to determine the position of the reel, on energising the device when the reel position is to be measured the Hall device immediately adopts the state corresponding to the magnetic flux density at that time. Thus, as shown in FIGURE 7, a negativegoing pulse is applied to the base of transistor 31 to switch the transistor on whenever it is desired to read the position of the reels. The output from the Hall-effect device 32 adopts a state dependent on the magnetic flux level at the moment when it is first energised.

A practical circuit for controlling the energising of all five Hall devices simuitaneously is shown in FIG URE8.

The position sensing apparatus described can be used in a gaming machine of the fruit machine type which has a microcomputer system programmed and arranged to control the operations of the machine. Thus, as illustrated in FIGURE 10, a complete gaming machine may have four reels with each reel having its own position sensing apparatus comprising a group 40 of five Hall-effect devices with associated coded discs having magnetic inserts.

Each of the groups 40 of the devices are mounted on a respective printed circuit board 41 corresponding to the board 15 of FIGURE 1. The output indications from the Hall-effect devices on the various boards are fed into a microcomputer 42 under the control of a peripheral interface unit 43. The microcomputer 42 typically includes a microprocessor and random access memory as well as read-only memory containing its instruction programme and data. In order to reduce the number of signal lines required connecting the circuit boards 41 with the peripheral interface unit 43, the peripheral interface controls the circuitry on the boards 41 so that each of the boards is scanned in turn and presents data representing the output indications of its five Hall-effect devices sequentially on a common five-bit bus 44 connected to all four boards 41.The boards 41 are controlled by scanning pulses supplied by the peripheral interface unit 43 on a four-bit control bus 45. FIGURE 9 illustrates the timing sequence of the scanning pulses on the bus 45. One of the lines of the bus 45 is fed to a respective one of the four boards 41 and the scan ning pulses sequentially energise the boards 41 so that for example the board for reel 1 is energised during the pulse starting T,, the board for reel 2 is energised during the pulse of T1 and so forth.

Conveniently, the scanning pulses are used in the boards 41 to gate the transistor supplying energising voltage to the Hall-effect devices so that the five devices on any one board are all energised simultaneously so that signals representing their output indications are suppiied on the data bus 44 and can be read in the peripheral interface 43 for onward transmission to the microcomputer 42. Typically, the peripheral interface unit 43 itself communicates with the microcomputer by sending the five-bit words received from the boards 41 as serial information along a single data line. The timing pulses for serialising the five-bit words are illustrated in the bottom half of FIGURE 9.

In a preferred embodiment of microprocessor controlled machine, the instantaneous angular positions of the reels are substantially continuously monitored by the microprocessor by interrogating the Hall-effect devices repeatedly at a relatively high rate. For example, each bank of Hall-effect devices may be interrogated every 10 mS. At typical rotation speeds of the reels, this provides at least two interrogations of each equivalent stop position as the reels are rotating. This technique enables the microprocessorto check that the reels are rotating when they are supposed to be in accordance with processor control. This has special advantages in preventing certain sorts of improper or illegal interference with normal operation of the machine.

A preferred type of Hall-effect device for use in the described example is the device TL 170 G available from Texas Instruments.

A preferred magnetic insert is a ferrite magnet having pole faces 7.7. mm square and 6 mm in length. The above Hall-effect devices have a max- imum upper switching threshold of 25 milliTesla.

Reed switches may be employed as magnetic field sensitive devices in an alternative embodiment of the machine.

The above described examples of the present invention illustrated in FIGURES 1,2 and 3 of the drawings employs Hall-effect devices which are spaced apart transversely of the direction of move mentofthe coded disc 14, i.e. spaced along a radius of the axis of rotation. However, it is also possible to employ the present invention using the Hall-effect device and magnet pairs positioned at the same radius and spaced apart circumferentially. Then, a single track of code elements is provided on the disc 14 at the radius of the sensing devices and each element passes between each sensing device and magnet pair in turn as the reel rotates.It is possible to position the code elements about the circumference of the disc 14 so that a unique combination of elements aligns between sensing device and magnet pairs at each of the stopping positions of the reel.

Furthermore, the present examples have illustrated the invention as applied to detecting the positions of the rotatable reels of fruit machines. The invention is also applicable to detecting the angular positions of rotating members in any other application and is also not restricted to the detection of angular positions. Modifications of the described examples can be envisaged which enable the relative positions of linearly movable members to be determined.

The magnets disclosed in the present specification are preferably permanent magnets but electromag nets may alternatively be employed. Such electromagnets may be selectively energised one after another when making a position reading to avoid the possibility of the field from one magnet influencing the sensing device of a different magnet and device pair.

Claims (16)

1. Apparatus for detecting the position of a first memberwhich is movable relative to a second member, comprising a plurality of magnetic field responsive sensing devices fixed relative to the second member, a corresponding plurality of magnets fixed relative to the second member at locations spaced from respective said magnetic field responsive sensing devices whereby each sensing device can respond to the magnetic field from a respective one of the magnets, and position coding means movable with said first member to pass between the sensing devices and their respective magnets, the position coding means having spacially varying magnetic permeability in the direction of movement relative to the sensing devices and magnets whereby the sensing devices are responsive to the resultant variations in the magnetic fields from their respective magnets to provide an indication of the relative position of the first member.

2. Apparatus as claimed in claim 1 wherein the position coding means has a first magnetic permeability with code elements of a second magnetic permeability distributed therein so that each element passes between at least one of the sensing device and magnet pairs on movement of the first member.

3. Apparatus as claimed in claim 2 wherein the sensing devices are each responsive to provide a first output indication in the absence of a said code element between the device and the associated magnet and a second output indication in response to the presence of a said code element therebetween, the code elements being distributed in the coding means so that a unique combination of the sensing devices provide said second indication for each of a predetermined number of relative positions of the first member.

4. Apparatus as claimed in claim 3 wherein said sensing devices are Hall-effect devices.

5. Apparatus as claimed in claim 4 wherein power supply means are provided for energising the Hall-effect devices, the power supply means including gating means arranged to remove the energising voltage from the devices before their output indications are to be read to determine the relative position of the member, and reapplying the energising voltage when the output indications are to be read.

6. Apparatus as claimed in any of claims 3 to 5 wherein the coding means is formed as a sheet extending transversely between the sensing device and magnet pairs of a material of high relative magnetic permeability and the code elements comprise apertures through the sheet.

7. Apparatus as claimed in claim 6 and including magnetic shunt means arranged to provide a path of relatively high magnetic permeability between the magnets and the coding means to shunt the magnetic field of any of the magnets in the absence of an aperture between the respective magnet and its associated sensing device, whereby the sensing device is responsive to a relatively increased magnetic field to indicate the presence of a code element.

8. Apparatus as claimed in any of claims 3 to 5 wherein said second magnetic permeability of the code elements is greater than said first magnetic permeability, whereby the presence of a said code element between any of the sensing device and magnet pairs enhances the magnetic field at the sensing device.

9. Apparatus as claimed in claim 8 wherein the code elements are ferro-magnetic.

10. Apparatus as claimed in any of claims 2 to 9 wherein the sensing device and magnet pairs are spaced apart one pair from anothertransverselyof the direction of relative movement of the first member, and the position coding means has a respective track, including at least one of said code elements, for each said pair.

11. Apparatus as claimed in any of claims 2 to 9 wherein the sensing device and magnet pairs are spaced one pair behind another in the direction of relative movement of the first member and each code element can pass between each of said pairs successively on movement of said first element.

12. Apparatus as claimed in any preceding claim, wherein said sensing device and magnet pairs are positioned with the sensing device and magnet of each pair on opposite sides of a common plane containing the direction of relative movement of the first member and the coding means is formed as a sheet in or tangential to said common plane.

13. Apparatus as claimed in claim 12 wherein the first member is rotatable relative to the second member and for detecting the relative angular position of the first member.

14. Apparatus as claimed in claim 13 wherein said common plane is perpendicular to the axis of rotation of the first member.

15. Apparatus for detecting the angular position of a rotatable member, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

16. A gaming or amusement machine of the fruit machine type as hereinbefore defined and including apparatus as claimed in any of claims 13 to 15 adapted for detecting the stop positions of the or at least one of the rotatable reels.