EP3341929A1

EP3341929A1 - Display systems

Info

Publication number: EP3341929A1
Application number: EP16724097.7A
Authority: EP
Inventors: Guy Margetson; Michael Andrew Beadman; Ben James Crundwell; Willem Paul Beeker
Original assignee: Speed Of Light Holdings Ltd
Current assignee: Lightz Ltd
Priority date: 2015-05-11
Filing date: 2016-05-11
Publication date: 2018-07-04
Anticipated expiration: 2036-05-11
Also published as: ES2959209T3; EP3341929B1; EP3341929C0; WO2016181134A1; GB201507979D0

Abstract

We describe a method of displaying information on the wheel of a vehicle, the method comprising: mounting first and second strips of light emitting elements on the wheel such that they lie substantially along first and second radii of the wheel; wherein said light emitting elements are arranged along each said strip and define radial lines of pixels; and wherein radial positions of the light emitting elements of said first strip are interleaved in a radial direction with respect to positions of the light emitting elements of said second strip; and driving said first and second strips of light emitting elements to display an image, wherein said image is represented by radial lines of pixels at successive angular positions; and wherein said driving comprises: driving said first strip of light emitting elements with a first subset of pixels of a first radial line of said image at a first said angular position in the image when said first strip of light emitting elements is at a reference angular position; driving said second strip of light emitting elements with a second subset of pixels of said first radial line of said image at said first angular position in the image when said second strip is at or adjacent said reference angular position, wherein said first and second subsets of pixels comprise interleaved pixels of said first radial line of said image.

Description

Display systems

FIELD OF THE INVENTION

This invention relates to methods and apparatus for electronically displaying information on the wheel of a vehicle.

BACKGROUND TO THE INVENTION

Background prior art relating to visual display systems can be found in W098/59333 and WO97/25703.

It is generally desirable to provide a displayed image which is bright and has good resolution.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is therefore provided a method of displaying information on the wheel of a vehicle, the method comprising: mounting first and second strips of light emitting elements on the wheel such that they lie substantially along first and second radii of the wheel; wherein said light emitting elements are arranged along each said strip and define radial lines of pixels; and wherein radial positions of the light emitting elements of said first strip are interleaved in a radial direction with respect to positions of the light emitting elements of said second strip; and driving said first and second strips of light emitting elements to display an image, wherein said image is represented by radial lines of pixels at successive angular positions; and wherein said driving comprises: driving said first strip of light emitting elements with a first subset of pixels of a first radial line of said image at a first said angular position in the image when said first strip of light emitting elements is at a reference angular position; driving said second strip of light emitting elements with a second subset of pixels of said first radial line of said image at said first angular position in the image when said second strip is at or adjacent said reference angular position, wherein said first and second subsets of pixels comprise interleaved pixels of said first radial line of said image. In embodiments of the method a display somewhat akin to an interlaced television display is created, by defining interlaced display lines (more properly "rings") using interleaved light emitting elements on two (or more) strips of light emitting elements. Thus the subsets of displayed pixels are interleaved correspondingly with the light emitting elements of said first and second strips of light emitting elements.

In some preferred embodiments two strips are employed with two-times interleaving, but in principle three or more strips could be employed with three or more times interleaving. In broad terms the n strips are driven with Mn of the display pixels when at the reference position - which may be, for example, top dead centre (TDC) of the system when mounted on the wheel. In embodiments the number of rows may be adapted to the vehicle, more particularly to a usual speed of the vehicle. For example for a relatively slow moving vehicle such as a city taxi it can be advantageous for three, four, five or more strips of light emitting elements to be employed, to reduce flicker where the wheel speed is not sufficient to provide persistence of vision.

In principle the strips of light emitting elements need not lie along radii of the wheel - for example two strips may be positioned, one to either side of a radius. However if the strips do not lie along radii this tends to smear the resulting display. In preferred embodiments the light emitting elements are arranged substantially regularly along each strip. Potentially, however, a greater number density of elements may be employed at larger radii to compensate for effectively decreasing brightness with increasing radius. In some preferred embodiments the light emitting elements comprise colour light emitting elements - for example each element may comprise three differently coloured LEDs (light emitting diodes), optionally with a shared diffuser. Preferably high brightness LEDs are employed, for example greater than l OOOmcd.

It is preferable, though not essential, for the displayed image to be substantially non- rotating. The image itself may be static or animated. In preferred embodiments, therefore, a rotational position of the wheel is sensed and the strips of light emitting elements are driven synchronously with rotation of the wheel such that they appear to display a substantially non-rotating image. The skilled person will appreciate that many different techniques may be employed for sensing rotation of the wheel including, for example, an accelerometer or - in preferred embodiments - a magnetic sensor, such as a Hall effect sensor, sensing a magnet behind the wheel.

As previously mentioned, in embodiments each strip of light emitting elements is driven with appropriate image data when that strip is at or passing a reference angular position, such as top dead centre of the wheel. The appropriate image data is readily determined if the image is represented in polar co-ordinates (where rows and columns of a Cartesian image translate to "rings" and "radii" in a polar co-ordinate system).

In embodiments of the system the first and second strips of light emitting elements are separated by an included angle. Then each radial line of the image may be considered as comprising first and second interleaved subsets of pixels of the image (or more subsets with greater interleaving). Thus in embodiments the second strip of light emitting elements is driven with a first subset of pixels of a second radial line of the image when the first strip of light emitting elements is at or adjacent the reference angular position. The second radial line of the image is angularly displaced (in polar co-ordinates) from the first radial line of the image by the included angle between the strips of light emitting elements. Preferably (beforehand) the first strip of light emitting elements is driven with the second subset of pixels of the second radial line of the image when the first strip of light emitting elements is at or adjacent a position defined by the reference angular position offset by the included angle. The skilled person will appreciate that this approach may be extended to three or more strips of light emitting elements.

In some embodiments of the technique the first and second strips of light emitting elements are driven simultaneously, in particular when the first strip of light emitting elements is at the angular reference position. In other approaches the driving is staggered or offset so that the first and second strips of light emitting elements have a reduced overlap, or no overlap (in time), to smooth the current consumption and in particular to reduce the peak current consumption. This is potentially advantageous where high current, high brightness LEDs are employed. As the skilled person will appreciate, embodiments of the technique effectively multiply the resolution of the display by a factor of n, where n is the number of interlaced rings of pixels, and also facilitate achieving a brighter display. In embodiments the image represented by the display may have a number of radial pixels (akin to pixels in columns of the display) defined by the total number of pixels in the strips of light emitting elements. For example the image may have a resolution of 160 radial pixels if two strips of 80 pixels are employed. However in embodiments additional strips of light emitting elements may be employed to effectively duplicate the information already displayed, for example for increased brightness or reduced flicker at low speeds. Thus, for example, a third and/or fourth strip of light emitting elements could be employed to display other "columns" of the image at different angular positions, but with pixels at the same radial positions as, say, the first and second strips. The number of "columns" (the resolution in a row or "ring") may be defined by how fast the light emitting elements "flash" or change their data as the device rotates; this number may be relatively high, for example greater than 1000 pixels, such as 1080 or 1920 pixels (equivalent to high definition television).

The image is effectively divided into two (or more) interlaced frames. In some embodiments a controller or driver(s) of the system may automatically generate the interleaved data for driving these strips of light emitting elements. In other embodiments two separate image frames may be provided to the system, each at Mn resolution. In this latter case the two images are preferably angularly displaced from one another by the included angle between the strips of light emitting elements (expressed in terms of a pixel count). This simplifies the simultaneous or staggered driving of the two strips of light emitting elements.

As used herein, references to 'pixels' are to pixels of a single colour display, or to pixels comprising two, three or more colour sub-pixels of a multicolour display. The skilled person will appreciate that there are many applications of the systems we describe. One application is to provide a display on two or more wheels of a racing vehicle such as a racing car for displaying information, advertising and the like. Counter-intuitively the two front (or two rear) wheels of a car or other vehicle rotate in opposite senses - that is one rotates clockwise whilst the other rotates anticlockwise. Where it is desirable to display an image with the correct (mirror reflection) handedness - for example where it includes text - one approach is to provide left handed and right handed versions of the system for mounting on corresponding wheels. In other embodiments, however, the system may automatically detect a sense of rotation of the wheel to determine how the image is displayed, that is whether 'columns' (radii) of the image are read out clockwise or counter clockwise. The skilled person will appreciate that many techniques may be employed to detect a sense of rotation of a wheel including, for example, the previously mentioned accelerometer or magnetic sensor.

As the strips of light emitting elements rotate it will be appreciated that those at the end of a radius travel further than those towards the middle of the wheel. This creates an effective brightness variation dependent upon a radial distance from the hub of the wheel, the brightness varying (reducing) with the square of the radial distance. Whilst it is not essential, it is preferable to improve the appearance of the display by compensating for this brightness variation in whole or in part. This can be done by, for example, changing digital values provided to drivers for the light emitting elements.

In embodiments of the system it can be preferable to provide two modes of operation for controlling the brightness of a light emitting element. At low light outputs (for example at some level less than 50% full output) it can be preferable to employ pulse width modulation. This is because LED response can be non-linear at low drive levels and PWM can achieve accurate dark (low output) levels, with good linearity and high contrast. However at higher light outputs (for example some light output greater than 50% of full output) using PWM can result in the appearance of radial stripes on the display. This is because at high brightness there is a proportion of time where the LED is on as a strip sweeps around its path, and a further proportion of time where the LED is off. Since these periods can align the result can be dark radial stripes. It can therefore be preferable to control the brightness of a light emitting element at relatively higher brightness by controlling a drive current or voltage of the light emitting element rather than by employing PWM control.

The skilled person will appreciate that in embodiments the image data may be delivered in an appropriate form (preferably in polar coordinates), to a display device for attaching to the wheel of a vehicle. In embodiments, however, the system may include software, for example to run on a general purpose computer system, for generating data for the image. Image data for the system may be generated by mapping Cartesian input image data into polar co-ordinate image data. In embodiments the input image pixels (in Cartesian co-ordinates) are smaller, that is have a smaller area, than display pixels displayed by the strips of light emitting elements on the rotating wheel. Thus one preferred mapping procedure comprises tiling a region of the image with display pixels as displayed by the rotating strips of light emitting elements (that is the interlaced display pixels). Then a value for each display pixel is obtained from the one or more Cartesian image pixels it partially or wholly covers. In embodiments a brightness or colour value for a display pixel may be selected based upon an average of the Cartesian image pixels it covers, preferably a weighted average dependent upon a proportion of a Cartesian image pixel covered.

In a related aspect the invention provides a device for displaying information on the wheel of a vehicle, the device comprising: a mount for attaching to the wheel of vehicle, the mount comprising: first and second strips of light emitting elements disposed such that when the device is attached to the wheel said first and second strips lie along respective first and second radii of the wheel for defining radial lines of pixels; and wherein radial positions of the light emitting elements of said first strip are interleaved in a radial direction with respect to positions of the light emitting elements of said second strip.

In principle data for driving the strips of light emitting elements may be transmitted on- the-fly to the device via a wired or wireless link, but in preferred embodiments data for displaying an image using the strips of light emitting elements is stored in local memory. Preferably when the device includes a controller to control illumination of the light emitting elements of the first and second strips in accordance with the stored image data. In preferred embodiments the image data is stored in polar co-ordinates so as to simplify this process. In some preferred embodiments, as previously described, the device includes a sensor to sense a rotational position of the wheel so that the light emitting elements can be driven synchronously with rotation at the wheel, so as to display a substantially non-rotating image. Preferably the sensor also detects whether the wheel is rotating clockwise or anticlockwise, and controls the image display accordingly so that the image is displayed with the same mirror reflection handedness whichever direction the wheel is rotating. In preferred embodiments the device includes drivers for the light emitting elements. As previously described, in preferred embodiments the drivers are able to operate in two modes, a first, PWM mode in which brightness of a light emitting element is controlled primarily by a pulse with modulation, and a second current/voltage control mode in which brightness of a light emitting element is controlled primarily by the level of a current and/or voltage drive to the element. Preferred embodiments also provide radial-distance-based brightness compensation as previously described. Thus the controller, or a driver, a combination of the two, may drive elements at a greater radial distance more brightly than those closer to a centre of the wheel.

Some embodiments of the device may be battery powered - such an approach is suitable, for example, for motor sport applications. Other embodiments of the device are able to harvest power for driving the light emitting elements from rotation of the wheels. Thus the device may include a generator (or at least the rotor part of a generator), preferably in combination with an electrical power store such as a rechargeable battery. In embodiments the generator may comprise a set of one or more magnets mounted to a part of the vehicle which is stationary with respect to the wheel, for example a region behind the wheel. The magnets may be permanent or electromagnets. This provides a stator for the generator. A second set of one or more coils may then be mounted on the device to generate power from rotation of the wheel.

In embodiments, particularly embodiments designed for use at low speed such as driving around town or the like, the mount for the device may comprise a one-way freewheel clutch such as a sprag clutch. This allows the device to continue to rotate when the wheel stops rotating, for example at traffic lights. In this way an image can be displayed by the rotating device whilst a vehicle is substantially stationary, which is potentially a particularly advantageous type of display for advertising and the like. Where such an approach is employed the device may even include a motor to rotate the device when the wheel is stationary. Such a motor may be powered by energy previously harvested from rotation of the wheel whilst the vehicle was in motion.

The skilled person will appreciate that these techniques are not limited to use in the context of an interleaved high resolution, high brightness image display of the type described above. In addition these techniques may be employed only when the vehicle is substantially stationary rather than also when a vehicle is moving.

Thus in a further related aspect the invention provides a method of displaying information on the wheel of a vehicle, the method comprising: mounting at least one strip of light emitting elements on a support configured for attaching to a wheel; attaching the support to the wheel said that the support is able to rotate with the wheel and is able to continue rotating when the wheel ceases to rotate; and driving said at least one strip of light emitting elements whilst the support is rotating and the wheel is not rotating, synchronously with the rotation of the support, such that the light emitting elements appear to display a substantially non-rotating image whilst the support is rotating when the vehicle is stationary.

In some preferred embodiments the device may be mounted on or used as a substitute for a hub cap of the wheel. The skilled person will appreciate that features and aspects of the previously described system may be incorporated into this further aspect of the invention.

The invention also provides a device for displaying information on the wheel of a vehicle, the device comprising: a mount for attaching to the wheel of vehicle, the mount comprising a one-way freewheel clutch to allow the device to rotate when said wheel is stationary; and bearing at least one strip of light emitting elements.

The invention still further provides a display system comprising: a device for attaching to a wheel of a vehicle; the device comprising at least one strip of light emitting diode (LED) pixels which, when the device is attached to said wheel extend in a radial direction; and wherein the device is configured such that, when said vehicle is in motion, the device displays an image formed by said strip of LED pixels lighting in synchronism with rotation of the wheel; and such that, when said vehicle is stationary, the device rotates to display said image in synchronism with rotation of the device, using said strip of LED pixels.

Conveniently in some embodiments a motor and generator function of the device are combined. Thus the device may be provided with a set of rotor coils to interact with a corresponding set of stator coils to generate power when the vehicle is rotating, and to drive the device to rotate when the vehicle is stationary. Optionally, when the device is being driven the stator coils may generate a magnetic field to drive the rotor coils of the device to rotate the device. Thus in embodiments the device may include part of an axial flux or pancake motor, another part of which is attached to a stationary part of the vehicle, for example to a bearing mount of the wheel.

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 in which:

Figures 1 a to 1 e show, respectively, front and side views of a display device according to an embodiment of the invention, first and second enlarged views of light emitting elements of the device, and a schematic illustration of the device attached to the wheel of the vehicle:

Figure 2 shows a block diagram of the device at Figure 1 ;

Figures 3a and 3b show a schematic representation of image data for display using the device of Figure 1 , and a flow diagram for display of the image data;

Figures 4a and 4b show, respectively, a flow diagram of a pixel display procedure and a schematic illustration of pulse width modulated displayed pixels;

Figure 5 illustrates a method for converting Cartesian image data to polar co-ordinate image data for use in embodiments of the invention; and Figure 6 shows a schematic view of a cross-section through a vehicle wheel assembly including a display device configured for rotation when the vehicle wheel is stationary. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to Figures 1a and 1 b, these show front and side views respectively of an embodiment of a display device 100 for displaying information on the wheel of a vehicle, according to embodiments of the invention. In the illustrated example the device is fabricated on a printed circuit board 102, provided with a number of mounting holes for attaching to the wheel of a vehicle. The skilled person will appreciate, however, that there are many ways of attaching the device of Figure 1 to a wheel. Depending upon the application a housing for the device may, but need not be provided. For simplicity details of the electronic components are not shown in Figures 1 a and 1 b, but are described later with reference to Figure 2.

The device comprises first and second strips 110, 1 12 of light emitting elements, in preferred embodiments relatively large, high-brightness light emitting diodes (LEDs), for example 3 mm, 2500mcd LEDs. In one embodiment each strip has around 80-100 LEDs, but it will be appreciated that this number may be varied. Similarly, although two strips are shown more may optionally be employed.

As shown in the enlargement of Figure 1 c the LEDs 1 14 of the first strip are offset radially with respect to the locations of the LEDs 1 16 of the second strip. In the illustrated example the offset is half a pixel (as there are two strips) so that the centres of the LEDs are interleaved. Figure 1d shows an enlargement of a single LED which may, in embodiments, comprise red, green and blue (R, G, B) LEDs under a common diffuser 118.

Figure 1e shows the device mounted on the wheel 150 of a vehicle. As can be seen, preferably the device does not extend quite to the central hub 152 because this introduces difficulties in mapping an image onto the rotating wheel. As can be seen in the cross-section of Figure 1 b, in embodiments a magnetic (Hall) sensor 122 is mounted on a projection 120 extending behind the device into the wheel assembly. This interacts with a magnet mounted on the wheel assembly, for example at a top dead centre (TDC) position (Figure 1 e). In this way the device can be synchronised with the rotation speed and position of the wheel. Figure 2 shows a block diagram of electronics for the device of Figure 1 , to control the device to provide an interlaced display synchronous with rotation of the wheel. Thus in embodiments the device is controlled by a controller 200, which may comprise dedicated hardware such as a gate array, or a microcontroller, or a combination of the two. The controller is coupled to a set of drivers 202, 204, one for each strip of LEDs 1 10, 112. In embodiments one driver is provided for each RGB colour. The controller is coupled to image memory 206 which stores one or more images for display, preferably in polar co-ordinates and with a resolution adapted to the number of rows (rings) and columns (radii) implemented by the device.

The total number of rows (rings) is defined by the total number of LEDs in strips 110, 1 12; the number of 'columns' is effectively defined by the number of 'flashes' which the LEDs make in one rotation of the wheel. It will be appreciated that it is relatively straightforward to change this latter parameter; in an example embodiment the device may have 1500 'columns'. In some preferred embodiments the controller 200 reads the image data and drives LED strips 110, 112 in an interleaved manner, as described later. Alternatively, however, image memory 206 may effectively store a pair of separate images, each at half resolution, for interleaved display. Preferably but not essentially the device includes RF communications 208 such as a Bluetooth™ or WiMax™ RF link. This may be used to download images for display to the device, optionally to command the device for example on/off and, potentially, to capture data from the device, for example relating to vehicle wheel rotation. The device includes a sensing and timing (clock) module 210. In some preferred embodiments this provides one pulse per revolution, indicating when the device is at top dead centre (TDC) of the wheel.

In embodiments the device is powered by a (rechargeable) battery 212. Depending upon the display brightness a battery life of around an hour may be obtained, which is sufficient for motorsport use. In other embodiments the device includes a power supply unit 214 coupled to a power recovery system 216, to harvest power from rotation of the wheel. In a simple embodiment this may be achieved by providing a coil on the device which, in conjunction with a magnet on a stationary part of the wheel assembly, acts as a generator. Referring to Figure 3a this shows columns of a displayed image 'unwrapped' - that is showing angular positions Θ0, Θ1 , Θ2 and so forth at which the strips of LEDs are driven. For any particular rotational speed of the wheel the angles Θ may be labelled with equivalent column display times. Referring back to Figure 1a the angle between the strips of LEDs 1 10, 1 12 is identified as Φ, where Φ measures the angle between the strips of LEDs in terms of the number of columns of the displayed image.

Figure 3b shows a flow diagram of a procedure for driving the strips of LEDs. Thus at the step S300 the procedure (or controller 200) reads the data for strip /, and at step S302 drives a first strip of LEDs 1 10 with the data for every other row (ring) in this column of the image. At the same time the procedure also reads data for strip /^' + Φ from the image memory (step S304), and drives the second strip of LEDs 1 12 with data for every other row (ring) in this column. The data driven in step S306 is interleaved with the data driven in step S302 - that is if, say, one strip of LEDs is driven with even pixels of the image, the other is driven with odd pixels of the image. Since, in embodiments, the LEDs in the two strips are displaced by half a pixel with respect to one another this effectively creates an interlaced display with double the resolution achievable with a single strip of LEDs.

After driving the two strips of LEDs the procedure waits for one angular pixel (S308), that is for the wheel to rotate sufficiently for the strips of LEDs to line up with the next respective columns of data to be displayed. The procedure then loops. It will be appreciated that, as described above, Φ is an integer. More particularly Φ represents the number of 'columns' of the image through which the device must rotate in order for the position originally occupied by strip 1 10 to be occupied by strip 1 12 (or vice versa). The order of reading the columns of data for display may depend upon the sense of rotation of the wheel which, optionally, may be determined by a sensor. For example, referring to Figure 3a, if the successive angles Θ label successive times then moving to the right moves anticlockwise through the displayed image for a clockwise rotating wheel. The wheels on opposite sides of a car rotate, respectively, clockwise and anticlockwise and the direction of rotation may be sensed by employing a pair of magnetic (Hall) sensors in the arrangement of Figurel b.

As described with reference to Figure 3b the two strips of LEDS are illuminated at the same time, but in an alternative approach the illumination of these strips of LEDs may be offset (for example displaced by half an angular pixel relative to one another) to smooth the current consumption.

Referring next to Figure 4a, this shows an example of a procedure implemented by controller 200 of Figure 2 to convert colour image data from image memory 206 to data for display on the strips of LEDs 1 10, 1 12. In preferred embodiments RGB colour values are used but it will be appreciated that other colour space representations may be employed. Thus at step S402 the controller reads target RGB pixel value data and, at step S404, performs a brightness correction for radial position of the target LED pixel. This may comprise, for example, scaling by the square of the radial position of the pixel (distance to the centre of the wheel). Preferably the procedure also performs a gamma correction (S406) to improve the appearance of the displayed image. The controller then outputs, for example, 24 bits of data per pixel, 8 bits for each (corrected) colour; this provides a large dynamic range, which is helpful.

The corrected colour data is provided to drivers 202, 204 which drive the relevant LED pixel with either PWM control or current control (or potentially both). Figure 4b illustrates a portion of a displayed image in which the LEDs are controlled using pulse width modulation: the LEDs are on 402 for some proportion of the total angular extent of a pixel and off 404 for the remaining proportion of the angular extent. As illustrated in Figure 4b this can result in radial stripes, but these are not easy to see when region 402 is of low brightness. Thus preferably pulse width modulation is used for low LED brightness levels because this can provide good linearity (current drive tends to be non-linear at low levels). Preferably, however, current drive control is employed at high brightness levels to avoid the appearance of dark stripes from regions 404.

Referring now to Figure 5, this shows how an image 500 with square or rectangular pixels 502, defined in Cartesian co-ordinates, may be converted to pixel data for an image 550, which is substantially circular and defined by rotating strips of LEDs. We will describe one technique for such mapping but the skilled person will appreciate that others may also be employed. Thus region 550 is tiled by pixels 552 of a shape provided by rotation of the device 100. In this example procedure it is assumed that pixels 552 are essentially non- overlapping, and that these tile the image 550 at a resolution of the interleaved display. That is although the interleaved rows (rings) of the display will in practice overlap (Figure 1 c), a non-overlapping assumption is made when converting to image data for display.

As shown in Figure 5 the pixels are defined by the angular positions of the 'columns' of the display at angles Θ0, Θ1 and so forth (for clarity only two such angles are illustrated).

For each radial (polar) pixel a determination is made of which Cartesian pixels this intersects, resulting in a set of Cartesian pixels. Thus, for example, polar pixel 552a intersects Cartesian pixels 502a-h. Then a brightness, or in preferred embodiments a colour, is selected for the polar pixel based on data from the Cartesian pixels it intersects. This may be done by, for example, taking an average, more preferably a weighted average of the values of the set of Cartesian pixels it intersects. Thus, referring to the previous example, pixel 552a barely intersects pixels 502e, f, g, h, and these therefore receive a low weighting. In embodiments the procedure steps through each of the polar pixels, determining the value for each pixel in this way to generate image data for storage in memory 206 and display. For a colour image the three colour channels (RGB) may be treated essentially independently.

Preferably the procedure described with reference to Figure 5 is performed off-line and the image data for display is loaded into image memory 206 in polar co-ordinate form, adapted to the number of rows (rings) and columns (radii) of the interlaced, rotating LED display. In principle, however, this conversion or mapping may be performed by controller 200. Multiple such images may be stored in memory 206 and selected, for example, by the RF link 208. Figure 6 shows a version of a wheel-mounted display device 600 which rotates with the vehicle wheel but which continues rotating when the wheel ceases to rotate and which, in embodiments, may be driven to rotate under these conditions. Figure 6 shows the device 600 mounted on a wheel assembly 650, shown in simplified cross-section.

Thus the wheel assembly comprises an axle 652 mounted in a wheel bearing 654, and supporting a plate 656 mounting a wheel 658 with a tyre 660. The device 600 is mounted on a rotating part 662 of the wheel (which may comprise a hub cap) via a one-way freewheel clutch 664, in embodiments a sprag clutch. As illustrated in cross- section, embodiments of device 600 may be generally circular rather than of the generally longitudinal type illustrated in Figure 1.

The sprag clutch 664 drives the device 600 to rotate with the wheel, but when the wheel slows or ceases rotating the device 600 is able to continue to rotate substantially freely. Device 600 preferably includes a sensor, such as a magnetic sensor, to identify a reference angular position of the device relative to wheel 658, and bears one or more strips of LEDs to display an image, preferably a substantially non-rotating image, as the device rotates. For simplicity in Figure 6 the one or more strips of LEDs are not shown. The (magnetic) sensor may be of the type previously described or may be integrated with the motor/generator described below.

In embodiments of the arrangement of Figure 6 it is preferable to employ two or more strips of LEDs to provide increased brightness and resolution, but this is not essential. Nonetheless in some preferred embodiments of the arrangement of Figure 6 the device may be applied to slow moving vehicles, for example in city traffic. In such applications it can be useful to have more than two strips of LEDs, to help give the appearance of a substantially non-flickering display even when the device is rotating relatively slowly. It will further be appreciated that the use of two or more strips of LEDs in such an arrangement does not necessarily require that the data displayed on the strips is interlaced: Referring again to Figure 3 it will be appreciated that multiple strips may be illuminated simultaneously using the procedure described with reference to Figure 3, by driving each strip of LEDs with all the data for a 'column' of the display rather than by driving with interlaced data. In the context of Figure 3 the procedure of Figure 3b then reads the data for strip /+Φ, strip /+2Φ, strip /+3Φ, and so forth, and drives each strip of LEDs with data for all the pixels of the relevant image column (radius). In still other embodiments a hybrid approach may be employed in which multiple strips of LEDs are used, but in which only some are interlaced.

Referring again to Figure 6, embodiments of device 600 may include a set of one or more coils 602 to interact with a set of one or more magnets 604 on a portion of the wheel assembly which is stationary relative to the rotating wheel. Magnets 604 may be permanent magnetic or electromagnets. In this way coils 602 may form part of the rotor of a generator to generate power for device 600, coils 604 comprising the stator of the generator. Power from coils 602 may be temporarily stored on device 600, for example in a battery or supercapacitor. When the wheel slows or stops coils 602 may be driven so that device 600 then becomes the rotor of a motor, the stator of which is defined by magnets 604. In this way an image may be displayed or maintained when the vehicle is stationary. Irrespective of the above described implementation details, potentially in a display system of this general type an image may be selectively displayed only when the vehicle is below a threshold speed or substantially stationary, for example for safety reasons. In a variant of the above described implementation, when the vehicle is slow or stopped device 600 may be driven to rotate by driving coils 604 to act on coils (magnets) 602, for example driving coils 604 with a rotating magnetic field to drive rotational device 600.

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 lying within the spirit and scope of the claims appended hereto.

Claims

CLAIMS:

1. A method of displaying information on the wheel of a vehicle, the method comprising:

mounting first and second strips of light emitting elements on the wheel such that they lie substantially along first and second radii of the wheel;

wherein said light emitting elements are arranged along each said strip and define radial lines of pixels; and

wherein radial positions of the light emitting elements of said first strip are interleaved in a radial direction with respect to positions of the light emitting elements of said second strip; and

driving said first and second strips of light emitting elements to display an image, wherein said image is represented by radial lines of pixels at successive angular positions; and

wherein said driving comprises:

driving said first strip of light emitting elements with a first subset of pixels of a first radial line of said image at a first said angular position in the image when said first strip of light emitting elements is at a reference angular position;

driving said second strip of light emitting elements with a second subset of pixels of said first radial line of said image at said first angular position in the image when said second strip is at or adjacent said reference angular position, wherein said first and second subsets of pixels comprise interleaved pixels of said first radial line of said image.

2. A method as claimed in claim 1 further comprising sensing a rotational position of said wheel, and wherein said driving comprises driving said strips of light emitting elements synchronously with rotation of the wheel such that they appear to display a substantially non-rotating image.

3. A method as claimed in claim 1 or 2 wherein said first and second radii of said wheel are separated by an included angle, and wherein said driving further comprises driving said second strip of light emitting elements with a first subset of pixels of a second radial line of said image when said first strip of light emitting elements is at or adjacent said reference angular position, and wherein in said representation of said image said second radial line of said image is angularly displaced from said first radial line of said image by said included angle.

4. A method as claimed in claim 2 wherein said first subset of pixels of said second radial line of said image is interleaved with a second subset of pixels of said second radial line of said image, and wherein said driving further comprises driving said first strip of light emitting elements with said second subset of pixels of said second radial line of said image when said first strip of light emitting elements is at or adjacent a position offset from said reference angular position by said included angle.

5. A method as claimed in claim 3 or 4 comprising driving said first and second strips of light emitting elements simultaneously when said first strip of light emitting elements is at said angular reference position.

6. A method as claimed in claim 3 or 4 comprising driving said first and second strips of light emitting elements in a staggered or offset manner such that said second strip of light emitting elements is driven at a different time to said first strip of light emitting elements when said first strip of light emitting elements is at said angular reference position, whereby such that said second strip of light emitting elements is driven whilst said first strip of light emitting elements is adjacent said reference angular position.

7. A method as claimed in any preceding claim further comprising storing image frame data for said image in polar co-ordinates, and wherein a radial dimension of said image frame data comprises data for a number of radial pixels which is an integer multiple of a number of light emitting pixels of a said strip.

8. A method as claimed in any preceding claim further comprising automatically detecting a sense of rotation of said wheel to automatically determine a mirror reflection handedness of said displayed image.

9. A method as claimed in any preceding claim wherein said driving further comprises modifying a brightness of a light emitting element dependent upon a radial distance from a hub of said wheel to compensate for a faster pixel motion with increasing said radial distance.

10. A method as claimed in any preceding claim wherein said driving comprises controlling a brightness of said light emitting elements, and wherein said brightness controlling has two modes of operation, a low output mode of operation and a high output mode of operation, wherein said low output mode of operation comprises controlling light emitting element brightness primarily by modulating an on time of a light emitting element, and wherein said high output mode of operation comprises controlling light emitting element brightness primarily by controlling a drive current or voltage of a light emitting element.

1 1. A method as claimed in any preceding claim further comprising generating data for said image by:

inputting Cartesian image data in Cartesian co-ordinates, said Cartesian image data defining Cartesian image pixels, and

mapping said Cartesian image data to polar image data in polar co-ordinates, wherein said polar co-ordinates define said radial lines of pixels at successive angular positions;

wherein said mapping comprises:

tiling a region of said image with display pixels as displayed by said strips of light emitting elements, and

for each said display pixel determining a value for the display pixel from one or more Cartesian image pixels partially or wholly covered by the display pixel.

12. A device for displaying information on the wheel of a vehicle, the device comprising:

a mount for attaching to the wheel of vehicle, the mount comprising:

first and second strips of light emitting elements disposed such that when the device is attached to the wheel said first and second strips lie along respective first and second radii of the wheel for defining radial lines of pixels; and

wherein radial positions of the light emitting elements of said first strip are interleaved in a radial direction with respect to positions of the light emitting elements of said second strip.

13. A device as claimed in claim 12 further comprising a controller coupled to memory storing image data for displaying an image represented by radial lines of pixels at successive angular positions, wherein said controller is configured to drive said first strip of light emitting elements with a first subset of pixels of a first radial line of said image at a first said angular position when said first strip of light emitting elements is at a reference angular position, and to drive said second strip of light emitting elements with a second subset of pixels of said first radial line of said image at said first angular position when said second strip is at or adjacent said reference angular position, wherein said first and second subsets of pixels comprise interleaved pixels of said first radial line of said image.

14. A device as claimed in claim 13 further comprising a sensor to sense a rotational position of said wheel, and wherein said driving comprises driving said strips of light emitting elements synchronously with rotation of the wheel such that they appear to display a substantially non-rotating image.

15. A device as claimed in claim 14 wherein said sensor is configured to detect a sense of rotation of said wheel, and wherein said controller is configured to determine an order of displaying radial lines of said image data responsive to said detected sense of rotation to define a mirror reflection handedness of said displayed image.

16. A device as claimed in claim 13, 14 or 15 wherein said memory is configured to store image frame data for said image in polar co-ordinates, and wherein a radial dimension of said image frame data comprises data for a number of radial pixels which is an integer multiple of a number of light emitting pixels of a said strip.

17. A device as claimed in any one of claims 12 to 16 further comprising drivers to drive said first and second strips of light emitting elements, wherein said drivers have has two modes of operation, a low output mode of operation and a light output mode of operation, wherein said low output mode of operation comprises controlling light emitting element brightness primarily by modulating an on time of a light emitting element, and wherein said high output mode of operation comprises controlling light emitting element brightness primarily by controlling a drive current or voltage of a light emitting element.

18. A device as claimed in any one of claims 12 to 17 further comprising a power supply to power said light emitting elements, wherein said power supply includes a generator to generate power from rotation of said wheel.

19. A device as claimed in any one of claims 12 to 18 wherein said mount comprises a one-way freewheel clutch to allow the device to rotate when said wheel is stationary.

20. A device as claimed in claim 19 further comprising a motor to rotate the device when said wheel is stationary.

21. A device as claimed in any of claims 12 to 20 mounted on said wheel.

22. A method of displaying information on the wheel of a vehicle, the method comprising:

mounting at least one strip of light emitting elements on a support configured for attaching to a wheel;

attaching the support to the wheel said that the support is able to rotate with the wheel and is able to continue rotating when the wheel ceases to rotate; and

driving said at least one strip of light emitting elements whilst the support is rotating and the wheel is not rotating, synchronously with the rotation of the support, such that the light emitting elements appear to display a substantially non-rotating image whilst the support is rotating when the vehicle is stationary.

23. A method as claimed in claim 22 further comprising driving said at least one strip of light emitting elements whilst both the support and the wheel are rotating, wherein said driving is synchronous with the rotation of the support such that the light emitting elements appear to display a substantially non-rotating image whilst the vehicle is moving.

24. A method as claimed in claim 22 or 23 further comprising driving rotation of said support whilst the vehicle is stationary.

25. A method as claimed in claim 24 wherein said driving comprises capturing and storing energy from rotation of said wheel when the wheel is rotating, said storing comprising storing electrical energy in a storage device mounted to said support, and using said stored energy to drive said rotation of said support whilst the vehicle is stationary.

26. A method as claimed in claim 25 wherein said driving comprises driving coils of a set of stator coils of a stator of a motor, wherein said stator does not rotate with said wheel, and wherein a rotor of said motor is attached to or comprises said support.

27. A method as claimed in any one of claims 22 to 26 comprising attaching the support to the wheel using a one-way freewheel clutch.

28. A method as claimed in any one of claims 22 to 27 further comprising powering said light emitting elements by mounting a set of rotor coils on said rotating support, and providing a magnetic field such that said rotor coils generate electrical power on passage through said magnetic field.

29. A method as claimed in claim 28 comprising generating said magnetic field with a set of stator coils, wherein said set of stator coils comprise coils of a motor including said rotor coils, and using the magnetic field generated by said stator coils to power said light emitting elements when said wheel is rotating and to drive rotation of said rotating support when said wheel is stationary.

30. A device for displaying information on the wheel of a vehicle, the device comprising:

a mount for attaching to the wheel of vehicle, the mount comprising a one-way freewheel clutch to allow the device to rotate when said wheel is stationary; and bearing

at least one strip of light emitting elements.

31. A device as claimed in claim 30 further comprising a sensor to sense a rotational position of said wheel; and

a controller responsive to said sensor to control driving of said at least one strip of light emitting elements whilst the device is rotating when the wheel is stationary, synchronously with rotation of the device, to display a substantially stationary image.

32. A device as claimed in claim 30 or 31 further comprising an electrical power store, a generator to generate power from rotation of said wheel for storing power in said power store whilst said wheel is rotating and a motor, powered by said power store, to rotate the device when said wheel is stationary.

33. A display system comprising:

a device for attaching to a wheel of a vehicle;

the device comprising at least one strip of light emitting diode (LED) pixels which, when the device is attached to said wheel extend in a radial direction; and

wherein the device is configured such that, when said vehicle is in motion, the device displays an image formed by said strip of LED pixels lighting in synchronism with rotation of the wheel; and

such that, when said vehicle is stationary, the device rotates to display said image in synchronism with rotation of the device, using said strip of LED pixels.

34. A display system as claimed in claim 33, wherein the device comprises at least two strips of LED pixels, and wherein pixels in said strips of LED pixels are positioned such that they are radially offset with respect to one another.

35. A display system as claimed in claim 33 or 34, wherein a pixel comprises two or more of a red LED, a blue LED and a green LED.

36. A display system as claimed in any one of claims 33 to 35, further comprising a controller coupled to said strips of LED pixels to control the strips of LED pixels, and coupled to image memory, and configured to display said image in synchronism with relative rotation of the wheel and the device.

37. A display system as claimed in any one of claims 33 to 36, wherein said image is substantially non-rotating.

38. A display system as claimed in any one of claims 33 to 37, wherein the device further comprises a generator to generate energy when the vehicle is in motion for powering the rotation of the device when the vehicle is stationary.

39. A display system as claimed in claim 38, wherein the device further comprises a motor to rotate said device, and a battery, wherein the motor is powered by energy from the generator stored in the battery.