FIELD OF THE INVENTION This invention relates to systems, methods and computer program code for levelling a rotating platform much as a roulette wheel.

BACKGROUND TO THE INVENTION A roulette wheel is a well-known apparatus used in a casino for generating a random number for the purposes of gaming.

An example roulette wheel 100 is shown in Figure 1 which comprises an inner rotating part (the rotor) 3 which contains a number (typically 37 or 38) of numbered depressions (called pockets) 15 separated by frets 13 into which a ball can rest. Each pocket 15 is associated with a respective number indicated on a number ring 1 1. Surrounding the rotor is the static housing (the bowl) 10 which contains a bearing which supports the rotor 3 (also referred to herein as a wheelhead). The bowl has a circular banked track (the ball track) 12 surrounding the rotor around which the ball is pushed at the start of the game. The wheel has a turret 9 mounted on a cone 5 but normally the rotor is spun by a finger in one of the pockets, and at the start of a game a ball is tossed onto the ball track 12. The ball remains in the ball track until its speed reduces so that centrifugal force cannot prevent it moving down the banked track and coming to rest in a pocket. The number associated with the pocket containing the ball is the game result.

It is desirable for casino operators that game results be uniformly distributed (meaning that all results are equally probable) and that for practical purposes the result be unpredictable (meaning that the result is independent of previous results and difficult to predict by observation of the position and speed of the rotor and ball, or difficult to influence by dealer skill at setting up the rotor and ball at precise speeds).

Uniform result distribution and unpredictability depend on the symmetry, cleanliness and condition of the bowl, the ball track, the rotor and the pockets. Damage or misalignment of the parts can cause either a non-uniformity or predictability of the result, or both.

A perfectly constructed, maintained and operated roulette wheel will always produce a uniform distribution of random numbers, however the result may still be predictable.

It is well known that if the ball track of a roulette wheel is not level (meaning that it is not in a plane perpendicular to the local gravitational field) even by a tenth of a degree then the game result is easily predictable with basic instrumentation or a simple hidden device which a gambler may input data to manually. This is due to the fact that the tilt of the ball track causes both the ball speed and the track bank angle (relative to local gravity) to vary around the circumference. The ball is more likely to leave the ball track at the high side of the track, where it is moving slowest and where the bank angle is steepest, that is, where the steeper bank angle is most likely to overcome the reduced centrifugal force on the slow ball. The prediction task is reduced to predicting the rotor position at that time, and the integer number of rotations of the ball remaining.

Known methods of measuring the level of a roulette wheel include using a spirit level placed across the rim of the bowl, or on a tripod that sits in the ball track or in the pockets of the rotor, allowing measurement of the level of the components which a normal spirit level cannot reach. Some roulette wheels have an electronic inclinometer (also known as a tilt sensor, which is just a low-range accelerometer) installed in the bowl of the wheel. Levelling a Roulette Wheel typically involves adjusting its three feet which can be screwed in or out of the wheel.

The drawback of the current practices is that they are inaccurate, cumbersome, or time consuming for a casino operator.

In particular, spirit levels are not sensitive or easy to read for the small angles being measured. Electronic tilt sensors may be very sensitive but have problems with output drift, and they need to be calibrated to remove the inherent bias and the inevitable variation in orientation with which they are fitted to the bowl, so that they read zero when the bowl is level. Furthermore both spirit levels and electronic tilt sensors suffer from the accuracy of construction of the support which they are fixed to, and also the accuracy of the part of the wheel they are placed on. A system for levelling a roulette wheel is described in US2007/0026925. This uses an inclination detector to automatically correct the levelling of the bowl in which the roulette wheel rotor rotates. This is, however, relatively inaccurate and requires a specially modified roulette wheel. There therefore exists a need for improvement.

SUMMARY OF THEINVENTION According to a first aspect of the invention there is therefore provided roulette wheel system comprising: a bowl; a roulette wheelhead mounted for rotation within said bowl, said bowl having a balltrack around said wheelhead; an accelerometer on said roulette wheelhead to provide an accelerometer signal; and a signal processor coupled to said accelerometer and to memory storing code to determine a tilt of said roulette wheelhead, wherein said code is configured to: identify an oscillating component of gravitational acceleration seen by said accelerometer as the wheelhead rotates, when the wheelhead is rotating about an axis of rotation tilted off a vertical axis, to determine one or both of a degree of tilt and a direction of tilt of said roulette wheelhead or of said balltrack.

In broad terms the inventor has recognised that the ability of the wheelhead of a roulette wheel to rotate provides a mechanism by which a very accurate determination of the tilt of the wheelhead axis of rotation away from the vertical may be made. This is done by detecting a time-varying component of the Earth's gravitational field, which is only present when the axis of the rotating wheel is not exactly aligned with the direction of the local gravitational field (local vertical). Thus identification of a varying gravitational field component with a period equal to the period of rotation of the wheelhead enables a very small signal to be detected in the presence of background noise or other sources of error. In this way very small deviations from the vertical can be determined and/or a relatively insensitive or noisy measurement of the gravitational field direction may be employed. In preferred embodiments the time variation of the gravitational field (vector) is measured using an accelerometer (since the effect of gravity is equivalent to an acceleration). In some preferred embodiments the accuracy and noise-immunity of the measurement may be improved by detecting the (oscillating component of the) signal over a greater length of time. One method is to store the acceleration signal from an integral number of periods of rotation of the wheelhead and then, for example, use Fourier Series to calculate the signal component at the rotation frequency (period), in effect applying a very narrow band pass filter to the signal. Because the wheelhead slows down, albeit gradually for a good quality wheel (of order 3% per revolution), the accuracy of this multi-period approach can be improved by measuring the instantaneous orientation or period of rotation of the wheelhead and from these measurements constructing a timebase for the integration. The skilled person will appreciate that the rotation period or orientation may be measured in many ways, for example magnetically by sensing a magnet on the bowl, or using a magnetic sensor on the wheelhead to sense the direction of magnetic north. Other techniques such as optical techniques may also be employed.

In one preferred implementation, the processing comprises a Fourier transform of the signal from the accelerometer. If the rotation period is known, the Fourier transform may be performed at a single frequency corresponding to the period of rotation of the wheelhead. This extracts a single component at the period of rotation, which is the desired oscillating component of gravitational acceleration. In principle other time- frequency transforms or signal modelling and parameter fitting may also be employed to facilitate extraction of the target oscillating signal component.

A potential source of systematic error in a Fourier transform (or related approach) as described above is that the oscillating component of gravitational acceleration is not the only time-varying acceleration felt by the accelerometer - whilst the wheelhead is rotating there is also an inwards centripetal acceleration, which is gradually decaying. Thus a Fourier transform may be biased by the Fourier representation of this monotonic component.

One approach to addressing this error is to align an accelerometer axis to the tangential direction to the rotation; this axis will not "see" the decaying centripetal acceleration, but will still see the desired oscillating component. However this would involve an alignment procedure which is cumbersome for a user and potentially introduces inaccuracies. This may therefore be appropriate for an embodiment in which the system is installed in a wheel during manufacture.

Another approach to addressing this error is to employ a 2-axis accelerometer to measure acceleration in two orthogonal axes in a plane perpendicular to the axis of rotation. From such a measurement the signal could then be decomposed into radial and tangential (centripetal and oscillatory) components, using a mathematical rotation. In practice the radial direction is most accurately determined by determining the direction of decay of the centripetal acceleration over several periods (or in the long- term if the accelerometer is in a constant position on the wheelhead). The centripetal acceleration is a relatively large signal component in the radial direction which decays in the radial direction.

Another approach is to model the centripetal acceleration and use parameter-fitting to isolate it from the oscillatory components. However, the inventor has recognised that with a small but ingenious modification to the Fourier mathematics the centripetal component of acceleration can be automatically removed.

With an angle of tilt of the rotational axis of the wheelhead to the vertical of Φ, the amplitude of the oscillatory component of the gravitational acceleration (in a plane perpendicular to this axis (is g.s/ ^' ηΦ). In principle one could obtain a value of Φ directly from a measured component of acceleration along the tilted axis (this is g.cosO), but this has a reduced sensitivity and, because it is an absolute measurement, it can be affected by an offset in the signal from the accelerometer.

The phase of the oscillating component of gravitational acceleration identifies the direction in which the axis is tilted - the oscillating component has a maximum when the accelerometer axis producing that signal points parallel to the tilt direction of the wheelhead as the wheelhead rotates. If the phase can be measured with respect to a (constant) reference direction external to the wheelhead, the direction of tilt of the axis may be reported in absolute terms.

A 2-axis accelerometer measures acceleration components in orthogonal x and y directions in a plane perpendicular to the axis of rotation (which is in the z- direction). The skilled person will appreciate that the accelerometer does not have to be aligned in any particular orientation to measure these components. In the general case that the x- and y- directions are not aligned to the radial and tangential directions, each of the x- and y- components of the sensed acceleration will have both an oscillating component (due to the wheelhead tilt) superimposed on a larger, decaying centripetal acceleration component (due to the accelerometer not being located on the axis of rotation).

As the skilled person will appreciate, Fourier (and related) time-frequency analysis represents a particular frequency component as a sum of a sine and a cosine wave of certain amplitudes. As the skilled person will know, a cosine function has "even symmetry" about the time t = 0, whereas a sine function has "odd symmetry" about this point. The decaying centripetal acceleration signal has largely odd symmetry, therefore the cosine component of the oscillatory signal (which is superimposed on the centripetal acceleration) is immune to the centripetal acceleration. This is because the cosine component of the straight line centripetal acceleration is zero due to conflicting symmetry.

The inventor has recognised that rather than employ sine and cosine Fourier components, because the accelerometer x- and y- directions are orthogonal the sine component of the acceleration along one axis may be replaced (substituted) by the cosine component of the acceleration along the orthogonal axis.

Thus the Fourier sum, rather than identifying sine and cosine components of a single signal, instead identifies cosine components of accelerometer signals from each of two orthogonal axes from the accelerometer. The two integrations (as implemented in software, sums) automatically substantially remove the centripetal acceleration from the determined result. In embodiments the result of such a process may comprise x- and y- components of a vector in a plane orthogonal to the axis of rotation, the vector length defining the angle of tilt (the length being equal to g.s/ ^' ηΦ), and the vector direction defining the direction of tilt.

The skilled person will appreciate that an embodiment of the above described procedure may be employed to calculate the angle and direction of tilt as a measurement in absolute terms, for example an angle of tilt in degrees or radians and/or a direction of tilt (in degrees or radians) with respect to a reference direction. This may therefore be used to provide a form of spirit level or inclinometer based upon a rotating platform, whether or not a roulette wheel. Thus in one aspect the invention provides a spirit level or inclinometer comprising a support mounting a rotatable platform comprising or upon which may be placed an accelerometer, and including signal processing for performing an embodiment of the above described method.

However the skilled person will also appreciate that in embodiments of the above described methods, in particular when used for levelling a roulette wheel, there is no need to explicitly calculate a value for either the tilt angle or tilt direction. Instead in embodiments a procedure is employed which uses feedback so that an adjustment may be made to one or more supports of the wheel to bring the wheelhead, more especially the balltrack of the bowl, into an accurately horizontal orientation. It will be appreciated that for such a process an absolute measurement of tilt angle/direction is not needed, merely some indication as to whether or not an adjustment made the alignment better or worse. Nonetheless some indication of the degree to which the wheelhead is misaligned may be helpful.

In one embodiment the accelerometer of a mobile phone or other similar portable computing device is employed and for such an embodiment the say, mobile phone may simply be placed on the roulette wheel and the wheelhead rotated. Alternatively the accelerometer may be attached to or built into the wheelhead. In a mobile phone- based approach or similar the signal processing described above may be performed locally, on the phone, or remotely, for example by another computer such as a nearby laptop in (wireless) communication with the device.

Where a mobile phone is employed conveniently the phone may also be employed to measure a period of rotation of the wheel and/or to determine a direction of tilt with respect to a reference direction. This may be performed using an internal magnetic field sensor (magnetometer) where present, for example using magnetic north as a reference direction or using a locally defined "north" defined by a magnet on the roulette wheel. In another approach a camera of the mobile phone may be employed for a similar purpose (capturing images to determine rotation of the phone, for example images of ceiling tiles or the like). Conveniently in such an approach the device may display the tilt angle and/or direction, for example as a vector on a display screen of a device. In embodiments the display may be automatically rotated in synchrony with rotation of the wheel to compensate for rotation of the wheel so that the direction (of the vector) on the display appears substantially unchanging - that is in embodiments, a mobile phone may display an arrow which, even as the wheel rotates, points in the direction of tilt, and which may have a length which indicates the angle of tilt. Text which so rotates on the display is also easy to read by the operator.

Additionally or alternatively to a display as described above the system may automatically control one or more levelling devices such as controllable jacks under the wheel. In one embodiment a wheel may be mounted on three supports, one of a fixed height and two comprising controllable jacks which may, for example, have a Bluetooth™ or other wireless connection to the computing device. Where such an arrangement is employed to automatically level the wheelhead it can be useful to establish an approximate calibration between the tilt angle and drive signal to a levelling device. This can be achieved using a calibration procedure which, in embodiments, applies a known drive to a levelling device or jack and measures a change in tilt, for example by measuring a change in Φ in radians. Such a procedure may also perform a transform to convert from a tilt angle/direction representation to a representation in terms of levelling device (jack) values, which may thus take account of the jack positioning at, say, 120° apart.

In a mobile phone-based system the mobile phone may have one or more gyroscope (angular velocity) sensors in which case such a sensor may be employed to identify the axis of rotation and/or rotation rate. Once the axis of rotation has been defined (defining the z- direction), the directions of orthogonal x- and y- axis may be arbitrarily defined (that is, in embodiments, there is no need to define the x- and y- directions in a plane of the wheel to lie in any particular direction). These axes are used to resolve the 3-axis accelerometer data typical of a mobile phone into the two axes of interest for this process, by application of a rotation matrix. Such an approach for finding the plane of rotation is convenient but not essential. For example without a gyroscope, the plane of rotation (in the accelerometer frame of reference) can be obtained from the plane of the locus of the mobile phone's magnetometer output during rotation, or from the directions of centripetal or angular acceleration or from the trend or decay of the centripetal acceleration vector, preferably over a plurality of revolutions of the wheelhead. As previously noted, a reference direction/orientation for the wheelhead is useful and may be obtained magnetically but this is also not essential. For example without knowing the direction of tilt the wheelhead may nonetheless be levelled by a Monte Carlo process, that is by making random adjustments and then determining whether or not the determined tilt is better or worse. Although this sounds cumbersome, in practice such an approach may be implemented relatively quickly and efficiently with a processor and automatically controlled jacks. It is convenient to employ a 2-axis or three-axis accelerometer, in particular with a sensor to sense a reference direction such as north, as this facilitates use of the mathematical approach described above, and also permits the device containing the sensors to be placed on the wheelhead in any orientation. However a single axis accelerometer may also be employed since this will also see an oscillatory component of the gravitational acceleration when the wheel is out of alignment. The skilled person will appreciate that with a single axis accelerometer it is preferable either to align the accelerometer axis in some known direction, for example parallel to a radial or tangential direction, and/or to place the accelerometer on the rotation axis to suppress or eliminate centripetal acceleration, and/or to employ a sensor such as a magnetometer to determine a reference direction/orientation for the wheelhead, to facilitate separation of the tilt signal from the centripetal acceleration signal (if the aforementioned Monte Carlo method is not to be employed).

The skilled person will recognise that although some preferred processing techniques have been described others may alternatively be employed. For example one way to separate the centripetal acceleration from the oscillating component of acceleration is to employ a low pass filter (tuned to block frequencies equivalent to the rotation period or higher) to separate out the centripetal acceleration, and once this has been obtained it can be subtracted from the signal to obtain the oscillatory component. The skilled person will appreciate that numerous variations are possible.

A system/method as described above may be employed to level one or both of a wheelhead and a ball track of a roulette wheel. In the latter case the ball track may be levelled by levelling the wheelhead and then using a mechanical jig, measuring device, or similar to establish a relationship between a surface of the ball track and the levelled wheelhead and/or its axis of rotation. Potentially, however, the ball track may be levelled directly with respect to the rotational axis of the wheelhead by means of a similar jig. Thus the invention also provides a mechanical arm or jig to measure relative alignment of the ball track and wheelhead, wherein the arm or jig comprises a micrometer, strain gauge or other measuring device which enables a measurement of a degree of bending of the arm or jig up or down relative to the rotor, to identify that the balltrack is parallel to the rotor.

In a related aspect the invention provides a method of levelling a roulette wheelhead, the method comprising: mounting an accelerometer on said roulette wheelhead to provide an accelerometer signal; identifying an oscillating component of gravitational acceleration seen by said accelerometer as the wheelhead rotates, when the wheelhead is rotating about an axis of rotation tilted off a vertical axis, to determine one or both of degree of tilt and a direction of tilt of said roulette wheelhead or of a ball track of said roulette wheelhead; and levelling said roulette wheelhead using said determined degree and/or direction of tilt. The invention further provides processor control code to implement the above- described systems and methods, for example on a general purpose computer system or on a digital signal processor (DSP). The code is provided on a non-transitory physical data carrier such as a disk, CD- or DVD-ROM, programmed memory such as non-volatile memory (eg Flash) or read-only memory (Firmware). Code (and/or data) to implement embodiments of the invention may comprise source, object or executable code in a conventional programming language (interpreted or compiled) such as C, or assembly code, or code for a hardware description language. As the skilled person will appreciate such code and/or data may be distributed between a plurality of coupled components in communication with one another.

The invention further provides a signal processor to implement one or more of the techniques described above, for example for a roulette wheel system as described above. Such a signal processor may operate under the control of stored program code, or may comprise dedicated hardware implemented in electronic circuitry, or may comprise a combination of some dedicated hardware modules and some system(s) under program control.

In a further aspect the invention provides a wheelhead for a roulette wheel system as described above, in particular comprising an accelerometer mounted on or within the wheelhead and further comprising one or both of a wired or wireless connection to the accelerometer to provide sensed acceleration data from the accelerometer. This may be provided in combination with a signal processor, in particular configured to implement signal processing as described above. In embodiments such a wheelhead may further comprise a power supply, in particular a wireless power supply such as an inductive loop power supply, to allow the wheelhead to derive power from a wireless power source.

In a related aspect the invention provides a method of levelling a rotating platform, the method comprising: providing an accelerometer on the platform such that as the platform rotates the accelerometer experiences: i) a downwards gravitational force due to gravity; and ii) a centripetal acceleration due to angular velocity and the radius of the accelerometer mounting; wherein, when an axis of said rotating platform is not parallel to local gravity, an output representing acceleration of said accelerometer has an oscillating gravitational component due to a changing direction of said gravitational force in the frame of reference of said accelerometer during rotation of said platform; processing a signal from said accelerometer to determine one or both of an amplitude and a phase of said oscillatory gravitational component of said acceleration; and using said amplitude or phase of said oscillatory gravitational component of said acceleration to level said rotating platform or a ball track or fiducial surface of said rotating platform.

The skilled person will appreciate that features of the above described roulette wheel system may also be employed in embodiments of this method. In a further related aspect a system and/or method as described above is employed to determine or measure a degree of tilt, or how level a surface is with respect to a vertical direction defined by gravity. In such an approach a value dependent upon the degree and/or direction of tilt (amplitude and/or phase of signal) may be output as a data signal and/or displayed, preferably but not essentially after calibration. Thus a system/method as described above may be employed to measure the degree to which the alignment of a surface departs from a horizontal alignment by providing a mount or support which sits upon the surface and defines an axis of rotation for a rotating platform, the tilt of the surface then being measured by the tilt of the defined axis. In embodiments of the above described methods/systems one technique for determining a degree of deviation of the axis of rotation from a vertical direction orthogonal to the horizontal direction is to determine the dimension (radius or diameter) of a circle defined by a locus of the end point of a vector of the oscillatory gravitational component of the acceleration sensed by the accelerometer (for example, as depicted later).

As previously described, a direction of inclination of the axis from the vertical may be determined from a phase of the oscillatory gravitational component of acceleration with respect to a reference orientation, which may be defined by a reference direction of the platform. For example the tilt direction may be defined with respect to a reference direction; more particularly it may be defined by a phase angle of rotation of the platform from the reference direction.

As previously, in embodiments the method further comprises sensing the rotation of the platform and integrating orthogonal signals (from a 2-axis or 3-axis accelerometer responsive to acceleration in two orthogonal directions in a plane perpendicular to the axis of rotation) over a whole number of periods of the rotation to determine the amplitude and the phase. The integrating may comprise integrating the product of each of the orthogonal signals and a cosine function of time with a period matching a sensed period of the rotation. In embodiments the method determines orthogonal components of a projection of the gravitational acceleration vector (measured by the accelerometer) onto a plane perpendicular to the axis of rotation in a stationary, real- space frame of reference, to determine a tilt angle of the axis with respect to the vertical direction and a tilt direction with respect to the reference direction.

In a further related aspect the invention provides a system for levelling a rotating platform, the system comprising: an accelerometer located on or in the platform such that as the platform rotates the accelerometer experiences: i) a downwards gravitational force due to gravity; and ii) a centripetal acceleration; wherein, when an axis of said rotating platform is misaligned with a direction defined by gravity, an acceleration of said accelerometer has an oscillating gravitational component due to a changing direction of said gravitational force experienced by said accelerometer during rotation of said platform; and a signal processor to: process a signal from said accelerometer to determine one or both of an amplitude and a phase of said oscillatory gravitational component of said acceleration; and display and/or output data representing said amplitude or phase of said oscillatory gravitational component of said acceleration for levelling said rotating platform or a ball track or fiducial surface of said rotating platform. In a further related aspect the invention provides a mobile computing device comprising: an accelerometer to provide an accelerometer signal; a memory storing code to determine a tilt of a rotating platform on which the mobile computing device is positioned; and a processor coupled to said accelerometer and to said memory, wherein said code is configured upon execution on said signal processor to: receive the accelerometer signal; and identify an oscillating component of gravitational acceleration seen by the accelerometer as the rotating platform rotates, when the rotating platform is rotating about an axis of rotation tilted off a vertical axis, to determine one or both of a degree of tilt and a direction of tilt of the rotating platform.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be further described by way of example only, with reference to the accompanying Figures, wherein like numerals refer to like parts throughout, and in which:

Figure 1 is a schematic illustration of a roulette wheel;

Figure 2 is a schematic block diagram of a roulette wheel system;

Figure 3a illustrates a top view of an accelerometer positioned on a rotating roulette wheelhead; Figure 3b is an example waveform illustrating inwards centripetal acceleration experienced by the accelerometer, and a further example waveform illustrating the degree of rotation of the accelerometer from a reference position; Figure 4a illustrates the gravitational field and centripetal acceleration experienced by the accelerometer in the frame of reference of the roulette wheelhead when the roulette wheelhead is level;

Figure 4b illustrates the gravitational field and centripetal acceleration experienced by the accelerometer in the frame of reference of the roulette wheelhead when the roulette wheelhead is tilted;

Figure 4c illustrates the gravitational field and centripetal acceleration experienced by the accelerometer in the frame of reference of the accelerometer when the roulette wheelhead is tilted;

Figures 5a and 5b illustrate how the gravitational field vector and centripetal acceleration in the frame of reference of the accelerometer change as the roulette wheelhead rotates;

Figure 6a illustrates a top view of an accelerometer positioned on a rotating roulette wheelhead;

Figure 6b illustrates waveforms of measured acceleration in two orthogonal axes in a plane perpendicular to the axis of rotation of the roulette wheelhead;

Figure 7a is flow chart for a process performed by code when executed on a signal processor of the roulette wheel system; Figures 7b illustrates example magnetometer signals; and

Figure 7c is flow chart for a process performed by code when executed on a signal processor of the roulette wheel system. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments will now be described by way of example only. Reference is first made to Figure 2 which illustrates a system 200 for determining one or both of a degree of tilt and a direction of tilt of a rotating platform which may be used to level the rotating platform. Embodiments are described in the context of a roulette wheel system whereby the system determines one or both of a degree of tilt and a direction of tilt of a roulette wheelhead 3 (otherwise referred to herein as a rotor) or of a balltrack 12 of the wheel. However as will be described in more detail embodiments of the present disclosure may be applied in other contexts.

As shown in Figure 2, the system 200 comprises a signal processor 202 (e.g. a microcontroller) which is coupled to an accelerometer 204. The term "accelerometer" is used herein to refer to any sensor capable of measuring the acceleration (or equivalently, gravitational field) it experiences. As will be appreciated by persons skilled in the art, there are many implementations, such as spring or magnetically-stabilised masses, or microscopic semiconductor devices. Accelerometers may be marketed as tilt-sensors, inclinometers or electronic spirit-levels, but these terms typically refer to the number of dimensions, range and sensitivity of measurement of the accelerometer; these terms are synonymous for the purposes of this disclosure.

The accelerometer 204 may be coupled to the signal processor 202 by way of a wired connection (for example if the accelerometer 204 and the signal processor 202 are co- located in the same device such as a mobile phone). Alternatively the accelerometer 204 may be coupled to the signal processor 202 by way of a wireless connection e.g. a Wi-Fi, Zigbee, Bluetooth or other short-range radio frequency (RF) wireless access technology connection (for example if the accelerometer 204 and the signal processor 202 are not co-located in the same device).

The accelerometer 204 provides an accelerometer signal to the signal processor 202. The accelerometer 204 provides single axis measurements (e.g. the accelerometer is a 1-axis accelerometer) or multi axis measurements (e.g. the accelerometer may be a 2- axis or 3-axis accelerometer). The signal processor 202 may also be coupled (by way of a wired or wireless connection as described above) to a magnetometer 206 and/or a gyroscope 208.

The magnetometer 206 provides single axis measurements (e.g. the magnetometer is a 1-axis magnetometer) or multi axis measurements (e.g. the magnetometer may be a 2-axis or 3-axis magnetometer).

As shown in Figure 2, the signal processor 202 is coupled to memory 212 storing code (software) 216 for execution by the signal processor 202. The code 216 is configured so as when fetched from the memory 212 and executed on the processor 202 to perform operations in line with embodiments discussed below.

In embodiments the accelerometer 204 is positioned on the roulette wheelhead 3 of the roulette wheel 100.

Figure 3a illustrates a top view of the accelerometer 204 positioned on the roulette wheelhead 3 of the roulette wheel 100 such that the accelerometer 204 moves when the roulette wheelhead 3 rotates. For simplicity, the accelerometer 204 is shown as a standalone device however it will be appreciated that the accelerometer 204 may be a component of a computing device (e.g. a mobile phone) that is positioned on the roulette wheelhead 3.

The accelerometer 204 is shown as having a solid black line marker, this is merely used to illustrate the orientation of the accelerometer 204.

When the roulette wheelhead 3 rotates, the accelerometer 204 moves in a circular motion such that the accelerometer 204 experiences i) a downwards gravitational force due to gravity; and ii) an inwards centripetal acceleration, c, wherein c=oo ² r (ω = angular velocity, and r= radius).

The upper waveform shown in Figure 3b illustrates the inwards centripetal acceleration, c, experienced by the accelerometer 204, which is gradually decaying due to the rotating roulette wheelhead 3 slowing down. The lower waveform shown Figure 3b illustrates the degree of rotation (defined by Θ) of the accelerometer 204 from a reference position as the accelerometer 204 moves in a circular motion, whereby θ=2π defines one revolution. As is shown by Fig.3b, the time taken for the accelerometer 204 to travel each revolution (three in total) increases over time as the rotating roulette wheelhead 3 slows down. As the roulette wheelhead 3 rotates the accelerometer 204 measure the sum of 1) the local gravitational field, 2) the centripetal acceleration imposed by the rotation speed of the body and the distance of the accelerometer from the rotation axis, and 3) any acceleration of the body at large or changes of rotational speed (referred to as disturbances).

It will be appreciated that when the roulette wheelhead 3 is not rotating the accelerometer 204 reads only the gravity vector plus disturbances, but as it does not know the orientation at which it is placed on the body, or any errors or offsets in the acceleration reading, it does not determine anything except its own rough orientation with respect to local gravity.

Figure 4a illustrates the scenario whereby the roulette wheelhead 3 is perfectly level. If the roulette wheelhead 3 is rotated at a constant speed in this scenario, and there are no disturbances, the accelerometer 204 on the rotating body will measure a constant vector: the sum of gravity and centripetal acceleration. Although the acceleration vector is changing and describing a circle in space (the centripetal component is radially outwards from the axis through the accelerometer), because the axes of the accelerometer 204 are rotating as well, the vector measured by the accelerometer is constant. Because the roulette wheelhead 3 is level, the accelerometer axes are rotating about a vertical axis and so the gravity vector also does not change in the frame of reference of the accelerometer 204.

If the roulette wheelhead 3 is level, but the rotation speed is changing at a constant rate (for example reducing due to friction), then the accelerometer 204 will measure the (constant) gravity vector, plus a changing centripetal acceleration in the radial direction, plus the rotational acceleration in the tangential direction. However these accelerations will change monotonically and not in an oscillatory way. The gravity vector is still constant in the frame of reference of the accelerometer 204, because the rotation axis is vertical. As shown in Figure 4a, the accelerometer 204 will experience acceleration due to gravity (shown by the gravitational field vector, g) and an inwards centripetal acceleration (shown by the vector, c). At a time t1 , the accelerometer 204 has a position and orientation indicated by the solid line of the accelerometer 204. At a time t2, once the roulette wheelhead 3 has done half a revolution, the accelerometer 204 has a position and orientation indicated by the dashed line of the accelerometer 204.

When the roulette wheelhead 3 has been tilted, with an angle of tilt of the rotational axis of the wheelhead to the vertical of Φ, the roulette wheelhead 3 is not in a plane perpendicular to the local gravitational field.

Figure 4b illustrates the gravitational field vector, g, and the centripetal acceleration vector, c, in the frame of reference of the roulette wheelhead 3 in the scenario whereby the roulette wheelhead 3 has been tilted, with an angle of tilt of the rotational axis of the wheelhead to the vertical of Φ.

In contrast, Figure 4c illustrates the gravitational field vector, g, and the centripetal acceleration vector, c, in the frame of reference of the accelerometer 204 in the scenario whereby the roulette wheelhead 3 has been tilted, with an angle of tilt of the rotational axis of the wheelhead to the vertical of Φ. There is a component of the gravitational field vector, g, on the plane of the roulette wheelhead 3 which is shown in Figure 4c as g', whereby g'=g.sin .

When the roulette wheelhead 3 is not level, then the frame of reference of the accelerometer 204 is rotating about an axis which is not parallel to gravity, therefore the gravity vector will change throughout the rotation. This is illustrated in Figures 5a and 5b.

Figure 5a illustrates a top view of the position and orientation of the accelerometer 204 on the roulette wheelhead 3 at points A, B, C, and D as the roulette wheelhead 3 rotates counter-clockwise during a single revolution. Figure 5a also illustrates the gravitational field vector, g, and the centripetal acceleration vector, c, in the frame of reference of the accelerometer 204 at each of these points. Figure 5b illustrates a top view of how the gravitational field vector, g, experienced by the accelerometer 204 rotates in a clockwise direction as the roulette wheelhead 3 rotates counter-clockwise during a single revolution, the x and y directions are shown in the top view (the z- direction is coming out of the paper). Fig.5b also includes a side view of the roulette wheelhead 3 and accelerometer 204 (not in real space) to illustrate the z-direction more clearly. A vector in the z-direction corresponds to the y component (g.cos ⁽ t>) of the gravitational field vector, g. The vector in the z-direction is independent of the orientation of the wheel (it does not change direction).

The changing direction of the gravity vector referred to above causes sinusoidal variations in the acceleration measurements made by the accelerometer 204 with a period equal to the rotation period of the roulette wheelhead 3.

Figure 6a illustrates a top view of the accelerometer 204 positioned on the roulette wheelhead 3 that has been tilted, with an angle of tilt of the rotational axis of the wheelhead to the vertical of Φ.

In the case that the x- and y- directions are not aligned to the radial and tangential directions, each of the x- and y- components of the sensed acceleration will have an oscillating component (due to the wheelhead tilt) superimposed on a larger, decaying centripetal acceleration component. This is illustrated in Figure 6b.

As shown in Figure 6b the x- component of the sensed acceleration 602 (a _x ) has an oscillating component ^.είηΦ.οοεζθ+Ψ) 604 superimposed on a decaying centripetal acceleration component 606. The y- component of the sensed acceleration 612 (a _y ) has an oscillating component ^.είηΦ.είηζθ+Ψ) 608 superimposed on a decaying centripetal acceleration component 606. Here θ=ωί, and Ψ corresponds to the angular offset from a reference direction (e.g. magnetic north).

In embodiments, the signal processor 202 executes code 216 to process accelerometer data received from the accelerometer 204 to find the amplitude (g.s/ ^' ηΦ) and phase (Ψ) of the sinusoidal variations which occur at the rotation frequency.

In an example embodiment, a mobile phone or other similar portable computing device comprising the system 200 is placed on the roulette wheelhead 3 of a roulette wheel 100 and the wheel is spun. Reference is now made to Figure 7a, which shows a flow chart 700 of steps performed by the signal processor 202 during rotation of the roulette wheelhead 3.

At step S702, the signal processor 202 receives a gyroscope signal that is output from the gyroscope 208.

At step S704, the signal processor 202 determines the axis of rotation z' (in the z- direction) from the gyroscope signal received at step S702.The (') notation indicates that the axis of rotation, z', is in the frame of reference of the roulette wheelhead 3. At step S706, the signal processor 202 determines, using the determined axis of rotation (ζ'),

the two orthogonal axes (x',y') that are in a plane perpendicular to the determined axis of rotation (ζ'). At step S708, the signal processor 202 receives a magnetometer signal that is output from the magnetometer 206.

At step S710, the signal processor 202 determines, using the magnetometer signal received at step S708, a magnetic north datum time (used to establish the period of rotation of the wheelhead).

Figure 7b illustrates an example y-axis magnetometer signal, My, and an x-axis magnetometer signal, Mx, that is output from magnetometer 206 whilst the mobile phone is rotated. As will be appreciated, by looking at one of these magnetometer signals, a completed revolution is indicated each time the particular magnetometer signal reaches a peak.

Reference is now made to Figure 7c, which shows a flow chart 750 of further steps performed by the signal processor 202 during rotation of the roulette wheelhead 3. At step S752, the signal processor 202 receives accelerometer data that is output from the accelerometer 204. In the example of a 3-axis accelerometer, the signal processor 202 receives accelerometer data a _x , a _y , and a _z (which is measured in the frame of reference of the mobile phone). The signal processor 202 may receive the accelerometer data at a frequency of 60Hz (note that this is merely an example). At step S752, the signal processor 202 stores the accelerometer data that is received at step S751 in memory 212. For example the signal processor 202 may store the accelerometer data in a circular buffer (e.g. a 10 sec circular buffer).

As shown in Figure 7c, received accelerometer data is stored in memory 212 until the signal processor 202 detects that a full period of rotation of the wheelhead has been completed (based on the received magnetometer signal). In response to this detection at step S753 the process750 proceeds to step S754.

At step S754, the signal processor 202 retrieves one period of accelerometer data (a _x , a _y , and a _z ) from memory 212 and processes the retrieved accelerometer data to transform it into accelerometer data in the field of reference of the roulette wheelhead 3, which is defined herein as a , a^ , and a _z . The accelerometer data in the field of reference of the roulette wheelhead 3 is obtained by the signal processor 202 performing the following transformations:

a _X ' = a . x!_

a _y ' = a . y'

a _Z ' = a_. z

where x', y' and z' are unit vectors in the respective directions, and a s an acceleration vector and where:

At step S755 the signal processor 202 identifies cosine components of accelerometer signals from each of the two orthogonal axes from the accelerometer 204. As explained above, the integral over a full period of the cosine component of an oscillatory signal (which is superimposed on the centripetal acceleration) effectively removes the centripetal acceleration. This is because the cosine component of the straight line centripetal acceleration in the sum is zero due to symmetry.

In particular, at step S755 the signal processor 202 determines vector components (FCr _f & FC _y ') of the tilt of the roulette wheelhead 3 by performing the following time- frequency transforms: FC _X . = S ₀ a _x . . cos (^) df

FCy = S ₀ a _y . . cos (^) df

The two integrations (as implemented in software, sums) indicated above automatically substantially remove the centripetal acceleration from the determined result. The result of such a process comprises x- and y- components of a vector in a plane orthogonal to the axis of rotation, the vector length defining the angle of tilt (the length being equal to g.s/ ^' ηΦ), and the vector direction defining the direction of tilt.

In order to obtain the angle of tilt and the direction of tilt, at step S756 the signal processor 202 performs further processing. In particular, the signal processor 202 determines Ψ (the offset from a reference direction e.g. magnetic north) by performing the following calculation:

Ψ = arctan2 (FC _x . , FCy.) = tan ^"1

where arctan2 is a software code (e.g. C) arctan function which is well behaved at FC _x .=0.

The signal processor 202 determines Φ (the angle of tilt) by performing the following calculation: g. smO = J(FC _X .) ² + ( FCy) ² and obtaining a value for Φ from the result of the above calculation.

Thus it will be appreciated from the above that by performing steps in accordance with process 700 and 750, the signal processor 202 calculates the angle and direction of tilt as a measurement in absolute terms, for example an angle of tilt in degrees or radians and/or a direction of tilt (in degrees or radians) with respect to a reference direction.

Referring back to Figure 2, as shown in Figure 2 the signal processor 202 may be coupled to one or more interface 210 for communication via a connection to one or more controllable jacks of the roulette wheel 100. The connection may be a wireless connection e.g. a Wi-Fi, Zigbee, Bluetooth or other short-range radio frequency (RF) wireless access technology connection.

In these embodiments, the code 216 executed by the signal processor 202 may comprise jack control code which is configured upon execution by the signal processor 202 to perform a transform to convert the calculated tilt angle/direction to a representation in terms of levelling device (jack) values, which may thus take account of the jack positioning (which may for example be 120° apart). The signal processor 202 may be configured to transmit commands (based on the levelling device values) to the one or more adjustable jacks via the interface 210 to automatically adjust the wheelhead axis of rotation.

Additionally or alternatively, the signal processor 202 may transmit the calculated tilt angle/direction via the one or more interface 210 to a database (not shown in Figure 2) via a wired or wireless connection for storage therein. This enables a casino operator to maintain a historical record of the collected data.

As shown in Figure 2 the signal processor 202 may be coupled to a display 214. In response to calculating the angle and direction of tilt, the signal processor 202 may control the display to indicate one or both of the degree of tilt and thedirection of tilt of the roulette wheelhead 3.

In embodiments where a mobile phone or other similar portable computing device comprises the system 200, it will be appreciated that when the mobile phone (positioned on the roulette wheelhead 3 rotates) the display 214 will also rotate in synchrony with the roulette wheelhead 3. In these embodiments, the signal processor 202 may be configured to compensate for rotation of the wheelhead so that the direction (of the vector) on the display 214 appears substantially unchanging - that is in embodiments, a mobile phone may display an arrow which, even as the wheelhead rotates, points in the direction of tilt, and which may have a length which indicates the angle of tilt.

In embodiments in which the system 200 is used calculate the angle and direction of tilt as a measurement in absolute terms, it will be appreciated that whilst embodiments have been described above with reference to a roulette wheel 100, the system 200 may also be used to provide a form of spirit level or inclinometer based upon a rotating platform, whether or not a roulette wheel. For example, the system 200 may also be used in other contexts (which require accurate measurement of the direction of gravity) for example surveying, construction, and geological gravitometry.

The methods described herein produces accurate results of the angle and direction of tilt regardless of offsets in the accelerometer 204 and does not depend on the accuracy or orientation with which the accelerometer is attached to the rotating body. The methods described herein can produce results of the angle and direction of tilt to almost any desired degree of accuracy simply by processing data from several revolutions of the roulette wheelhead 3.

Whilst embodiment have been described in which a mobile phone or other similar portable computing device comprises the system 200, this is merely an example. For example, a device comprising the accelerometer 204 (and optionally the magnetometer 206 and/or gyroscope 208) may be positioned on, mounted on, or designed into the roulette wheelhead 3, and be arranged to communicate sensor data to a separate computing device comprising the signal processor and memory (storing code 216).

It will be appreciated from the above that whilst only an accelerometer 204 (of 1 or more axes) and the signal processor 202 (executing code 216) are required to detect variations of the accelerometer 204 which are synchronous with the rotation of the roulette wheelhead 3, the efficiency of computation and usefulness of the measurement may be increased by including information from other sources on the orientation and rotation speed of the roulette wheelhead 3. The information could be the known rotation speed or phase of the rotating body from the driving mechanism, the expected frictional deceleration, or it could come from sensors. Examples of sensors which can supplement the methods described herein are a rotary encoder (tachometer), a gyroscope (rotation speed sensor), pulse-per-revolution input, or magnetometer (compass) on the rotating part of the body. Knowing the rotation speed and phase of the body can be used to process the data more efficiently, for example to lock a phase-sensitive detector to the accelerometer, or to only calculate relevant Fourier components, or produce closer initial estimates for Monte-Carlo fitting techniques. Also, knowing the absolute orientation of the body from, for example a magnetometer or optical sensor, allows the direction of the inclination of the body (the phase of the sinusoidal components) to be referenced to the environment outside the rotating body, allowing indication to the user or automatic control systems the direction and amount to adjust to achieve level.

Although the relative orientation of the device containing the accelerometers and the rotating body is not known, the sensors in the device which may be used to find absolute direction, such as a magnetometer, are in a known orientation with respect to the accelerometer axes so the direction of inclination relative to North may be deduced from the phase difference between the accelerometer sinusoidal components and the magnetometer components.

No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art and lying within the spirit and scope of the claims appended hereto.