GB2498179A

GB2498179A - Projection display system

Info

Publication number: GB2498179A
Application number: GB201122404A
Authority: GB
Inventors: Samuel James Cox; Jan Jozef Lewandowski; Andrew Graham Walton
Original assignee: PRP OPTOELECTRONICS Ltd
Current assignee: PRP OPTOELECTRONICS Ltd
Priority date: 2011-12-23
Filing date: 2011-12-23
Publication date: 2013-07-10
Also published as: GB201122404D0; WO2013093510A2; WO2013093510A3

Abstract

A projection display system comprising an array of LEDs 10 in at least first and second rows 10a,10b, the LEDs in each row being spaced from each other. The LEDs in the second row 10b are offset in a direction parallel to the length of the row relative to the LEDs in the first row 10a. A micro-electro-mechanical system (MEMs) scanning mirror 11 is mounted for movement about an axis with a movement means for moving the MEMs mirror about the axis. The array of LEDs are positioned so that light emitted therefrom is directed towards the MEMs mirror and reflected therefrom to form a display 12 comprising one or more lines, each line comprising a plurality of pixels. The movement means is arranged so that light from said first row of LEDs and light from the second row of LEDs is used to form each line of the display so the spacing between pixels along each line of the display is reduced compared to the spacing of the LEDS in the rows of the array. The display system can be used in a head up display or helmet mounted display or in a digital printing system.

Description

A PROJECTION DISPLAY SYSTEM

FIELD OF THE INVENTION

This invention relates to a projection display system, eg for use in a micro-display or for use in a head up display or head mounted imaging system. The invention also relates to a head up display and head mounted display incorporating such a system.

BACKGROUND ART

Various image projection systems are known which use light emitting diodes (LEDs) as the light source. Some of these systems use a 2D array of LED emitters integrated on a single chip. The individual LED emitters in such an array are separated from each other by electrically isorating boundaries. The LED emitters are thus typically separated by a distance similar to the width of each emitter (eg 5-8 microns) and this limits the display resolution achievable with such arrays. Large area LED arrays are also relatively expensive as the production yield falls as the size of the array increases.

In another arrangement, wavefront correcting micro-mirrors are used to improve the resolution (with one micro-mirror per LED). Such arrangements are however very complex and are difficult to align and assemble (again increasing the cost).

In a further arrangement, single light emitters are used and these are scanned by ** MEMS micro-mirrors to produce an X-Y matrix for the display. However, in order to provide the required intensity, the single light source is usually a laser diode. The * use of these raises eye safety issues. They also tend to suffer from laser speckle.

The present invention seeks to provide a projection display system which overcomes or reduces such problems and is relatively simple and inexpensive to manufacture.

The invention also seeks to provide a projection display system with improved resolution.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a projection display system comprising an array of light emitting diodes comprising at least first and second rows of diodes, the diodes in each row being spaced from each other, the diodes in the second row being offset in a direction parallel to the length of the row relative to the diodes in the first row, a reflector mounted for movement about an axis, and movement means for moving said reflector about said axis, the array of light emitting diodes being positioned such that light emitted therefrom is directed towards the reflector and reflected therefrom to form a display comprising one or more lines, each line comprising a plurality of pixels, the movement means being arranged such that light from said first row of diodes and light from said second row of diodes is used to form each line of the display so the spacing between pixels along each line of the display is reduced compared to the spacing of the diodes in the rows of the array.

It should be noted that the term spacing' as used herein refers to the distance between pixels relative to their size rather than the absolute size of the spacing (which wilt vary according to the magnification of the image compared to the size of the array of light emitting diodes).

The term display' as used herein includes an image formed by scanning light over one or more lines, eg in the form of a raster scan, and other arrangements in which light is directed onto an object in one or more lines as if an image was being formed thereon.

***. : According to another aspect of the invention, there is provided a head up display * (HUD) comprising a projection display system as detailed above.

: According to a further aspect of the invention there is provided a helmet mounted display (HMD) comprising a projection display system as detailed above.

* ** Preferred and optional features of the invention wilt be apparent from the following * . . description and from the subsidiary claims of the specification. *eseS * 0

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, merely by way of example, with reference to the accompanying drawings in which; Figure 1 is a schematic diagram showing a perspective view of a first embodiment of a display system according to the invention using a single LED array; Figure 2a is a schematic diagram of a square LED emitter array used in Fig 1; Figure 2b is a schematic diagram illustrating an illumination pattern produced by scanning of the square LED emitter array shown in Fig 2a; Figure 2c is a schematic diagram of a square LED emitter array having three rows of LED emitters; Figure 3a is a schematic diagram of a diamond-shaped LED emitter array that may be used in place of the array shown in Fig 2a; Figure 3b is a schematic diagram illustrating an illumination pattern produced by scanning of the diamond-shaped LED emitter array shown in Fig 3a; Figure 4 is a schematic side view of a first embodiment of a monochrome projection display assembly comprising a display system as illustrated in Fig 1; Figure 5 is a perspective view of a monochrome projection display assembly such as that shown in Fig 4; Figure 6 is a schematic side view of a colour projection display assembly similar to that shown in Fig 4 including red, blue and green LED arrays; ** Figure 7 is a perspective view of a colour projection display assembly such as that shown in Fig 6; Figure 8 is a perspective view of the colour projection display assembly of Fig 7 also showing an illumination pattern produced thereby; : *. Figure 9 is a schematic side view of a second embodiment of colour projection

S

display assembly; Figure 10 is a schematic side view of a second embodiment of a monochrome projection display assembly comprising a display system as illustrated in Fig 1; Figure 11 is a schematic side view of a third embodiment of a monochrome projection display assembly comprising a display system as illustrated in Fig 1; Figure 12 is a perspective view of a third embodiment of a colour projection display assembly; Figure 13 is a schematic perspective view of a colour projection display assembly such as that of Fig 7 within a micro projection display system; Fig 14a is a schematic diagram illustrating use of a projection display system according to an embodiment of the invention in a head up display on a vehicle windscreen; Fig 14b is a schematic diagram illustrating use of a projection display system according to an embodiment of the invention in a head mounted display on a reticule or helmet visor; Fig iSa is a schematic side view of a fourth embodiment of a colour projection display assembly; Fig lSb is a diagram showing the functional relationship between scan angle and time for the embodiment shown in Figure 15a; Fig 16 is a schematic side view of a fifth embodiment of a colour projection display asseni bly; Fig 17 is a schematic side view illustrating use of a scanning projection assembly according to an embodiment of the invention in a digital printing system; and ""I * Fig 18 is a schematic side view illustrating use of a scanning projection assembly *. : according to another embodiment of the invention used in a digital printing system. * * S. * * 0 **eS$ * S

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 shows a rectangular LED array 10 comprising first and second linear rows of LED emitters formed in a single monolithic chip. Each LED emitter in the array is individually addressable.

Figure 2a shows a plan view of the LED array 10 with the LED emitters in each row being spaced from each other by a distance D1 (between adjacent edges of the LEDs), the diodes in the second row being offset from those in the first row in a direction parallel to the length of the rows. Preferably, the distance D1 corresponds to the width of the diodes and the offset is also by a distance D so that the LED array comprises a two row chequer board pattern of LEDs (as shown in Figures 1 and 2). The first and second row are spaced from each other by a distance D2 (Di and D2 may be substantially the same, as shown in the Figures).

As shown in Fig 1, light from the LED array 10 is directed towards a rectangular oscillating or rotating reflector 11, such as a micro-electro-mechanical system (MEMS) mirror. Movement means (not shown) are provided so the reflector 11 is arranged to oscillate or rotate about an axis A parallel to the length of the reflector 11 and parallel to the length of the LED array 10. Oscillation means (not shown) in the form of electrostatic or magnetic devices (as commonly used in the art for MEMS scanning mirror devices) may be provided to oscillate the reflector 11, eq by resonant vibration, controlled by an electronic control system (not shown), eg providing a square wave or sinusoidal wave pulsed voltage which to controls the scanning movement of the reflector by maintaining the resonant vibration of the mirror. In another arrangement, the motion of the reflector may be controlled by a different periodic oscillating waveform, for example a linear saw tooth voltage waveform. o*.

* In another arrangement, the reflector may be rotated continuously about an axis of a shaft of a rniniaturised galvanometric motor (rather than oscillatory rotation in opposite directions as described above). In this case, the reflector may be multi-faceted, eg having a hexagonal or octagonal cross-section (perpendicular to the axis of rotation), so a series of reflective surfaces are used to reflect the light as the reflector is rotated about the axis.

Figure 1 also shows a display 12 formed by light reflected from the oscillating reflector 11. The reflector is arranged to scan through an angle sufficient to scan the light reflected therefrom from the top to the bottom of the image 12 to be formed.

Thus, as shown in Fig 1, light from LED emitter ba in the first row of the LED array is scanned up and down the band or column 12a of the image formed. Similarly, light from LED lOb in the second row of the LED array is scanned up and down the band or column 12b of the image formed. The same applies to light from each of the other LED emitters in the array 10. Each of the LED emitters is operated in pulsed mode by the electronic control system referred to above and the timing of each pulse is arranged so that the LED is on (ie emitting light) as the reflected light therefrom passes though each tine (or row) of the image to be formed (the lines extending across the width of the image and thus being perpendicular to the columns shown in Figs 1 and 2). Thus, if the image to be formed is made up of 500 lines, each LED is switched on 500 times as the reflected light therefrom is scanned from the top to the bottom of the image 12.

Pixels of the image are thus, in effect, formed at the intersection of the lines and columns in the arrangement shown in Fig 1, all of the pixels in a given column being iltuminated by a single LED emitter of the LED array 10.

If scanning of the reflector 11 is controlled by a sinusoidal signal so its speed of rotation varies as it is moved, the timing and/or length of pulses from each LED emitter are controlled to ensure that the LED is on as the reflected light therefrom passes through the respective lines of the image. Preferably, the arrangement is such that the LED pulse timings compensate for the non linear scanning across visible parts of the image, so that the intensity of the illumination pulses of the LEDs across the scanned display can be substantially uniform.

The LED emitters and the oscillation or rotation means are operated so that tight from the first row and light from the second row of the LED array 10 is combined in each line of the display 12. Thus, in the arrangement shown, the pixels of each line of the display are alternately formed from light from the first and second rows of the * , LED array 10. As indicated above, this is achieved by operating the LED array in pulsed mode and synchronising the pulsed period to the scan frequency of the oscillation or rotation of the reflector such that light from two rows of the LED array is combined to form a single line of the display with minimal flicker.

By this means, the resolution of the display 12 is increased relative to the LED array 10. The inter-pixel separation (relative to the size of the pixels) of the display 12 (along the lines of the image) is a fraction of that (D1) of the LED emitters in the LED array 10 (and may be zero). The resolution in the direction perpendicular to the lines (ie in the scanning direction) is determined by the illumination pulses of the LEDs, and particularly the rise and fall times of the LEDs as they are turned on and off. LED emitters with rise times of "tOns are readily available and this is sufficient to provide a spacing (relative the size of the pixels) between lines of the image less than the spacing (D2) between rows of the LED array 10. It will be appreciated that the absolute size of the spacing between pixels may be larger if the display is magnified relative to the size of the LED array.

The resolution can be further improved in the scanning direction by using additional grey scale variation, ie controlling the rise and fall times of the output of each LED emitter -the limits to resolution achievable being determined by the rise and fall times of the LED turn-on and turn-off characteristics.

In the optimal case, the resolution of the display (in both directions) is limited only by the size of the LED emitters themselves. Preferably, these have a width of 10 microns or less. In the example shown, as the spacing between LED emitters in the LED array corresponds to the width of the LED emitters, adjacent pixels in the display abut one another along the length of each row of the display. The spacing between lines of the display is determined by the movement of the reflector and the timing of the pulses emitted by the LEDs and, in a preferred arrangement, the spacing is zero so pixels in adjacent rows also abut each other.

* It will be appreciated that other arrangements are possible; the pixels in each row of the display need not abut each other but their spacing should be less than the spacing (D1) of the LEDs in each row of the LED array so as to improve the resolution of the display. * 0* * 0

*** * It is also possible to arrange the system such that adjacent pixels in each line of the * display overlap each other to some extent. This would result in over-scanned sections with higher brightness but this may be preferable to the possibility of gaps being visible between pixels. This would also only be desirable if the resulting brightness variations would not be visible within the perception of the response of the observer's eye.

Figure 2c shows another form of LED array having three rows of emitters in which the third row is offset by a distance (D3) which is half of the offset distance (D1) between the first and second rows of emitters, This results in light from emitters in the third row overlapping with light from emitters in the first and second rows of the LED array in the non-scanned direction (along the lines of the display) and with appropriate pulsing of the emitters the eye then perceives a pixel size smaller than the size of the emitters. This has the advantage of providing a display having a pixel size in the non-scanned direction (ie along the lines of the display) which is half that of the emitter elements themselves. The emitter size does not therefore necessarily determine the pixel size in the non-scanned direction of the display.

Other arrangements can be used having a plurality of rows of LED emitters such that the relative pixel size (along the lines of the display) is less than half of the size of the emitters themselves in the non-scanning direction.

Figure 3 shows another embodiment of the invention where the elements of the emitting array 20 have a diamond shape, eg so their sides lie at 45 degrees to the length of the row but spaced from each other by a distance (D1) (between corners of adjacent LED emitters along the length of the row). As before, light from the two rows of the LED array is reflected from a mirror and scanned across the image 22 to be formed so the spacing between pixels in each line of the image 22 is less than that between the LED5 in each row of the LED array 20. As before, the spacing may be reduced to an extent that adjacent pixels overlap. This would again result in areas of increased brightness but as the overlap between adjacent pixels would be points rather than lines, this may be more acceptable as it reduces the artefacts within the scanned image.

The spacing D2 between the first and second rows of the diamond shaped emitters may be zero (as shown in Fig 3a). -9-.

In a further embodiment (not shown) of the invention, the LED emitters may be hexagonal in shape. The LEDs may also have other shapes.

The MENIS micro-mirror 11 in the embodiment of Figure 1 may, for example, comprise a rectangular silicon-based MEMS device which is electrostatically or magnetically actuated. The mirror shape may alternatively be ellipsoidal, or the mirror may have some other shape which is able to reflect light from all the LEDs in the LED array.

The MEMs mirror 11 is preferably as large as possible so it can reflect light from large linear LED arrays. For example, an array of 1024 emitters could be defined by two rows of 512 stepped emitters. For state of the art emitter sizes of around lOum, the full array width would be around 1.024cm. A suitable MEMS mirror for reflecting light from such an array which is projected onto the mirror as a collimated beam preferably has a width of at least 1.1cm.

The light emitted by the LEDs is preferably collimated as it is directed towards the NIEMS mirror. It may also be imaged such that a demagnified image of the array is incident upon the reflector (in which case the reflector may be smaller than the LED array). Preferably, the reflector is of a size such that light from all LEDs in the array is incident upon the reflector.

In a preferred arrangement, the MEMS mirror 11 would be designed to enable scanning between 100Hz and 10kHz. Preferably, the scan frequency would be in the range 500Hz-2kHz. It is desirable for the scan frequency to be as low as possible to simplify the high speed electronics that drive the LED array.

The lowest possible operating frequency for MEMS mirror and rotating micro-motor structures is commonly higher than 100Hz. For reflector structures with dimensions required for the present invention, stable resonant frequencies typically lie between 1kHz and 20kHz. This is due to the requirement for stable and reliable operation and the subsequent need to minimise coupling of energy into other vibrational modes.

For cases where the resonant frequencies are far higher than the response of the * * eye, there is the advantage of a high modulation bandwidth of the display signal resulting in a high dynamic range as each pixel will be written to many times within the response time of the eye.

Preferably, the mirror scan angle wourd be in the range 5-30 degrees. Figure 4 shows a side view of an LED array 30 as described in Figures 1 and 2 in a projection display system. This Figure shows the LED array 30 mounted on a sub-mount 33. In all following embodiments it will be understood that the LED arrays are mounted on such a sub-mount, Preferably, the LED emitter array 30 has its elements collimated by a lens array 34. The collimated light from the LED lens array 34 is reflected in a prism 35 towards a NIEMS mirror 31 so that the MEMS mirror 31 can project the scanned display image 32 in a plane parallel to that of the LED emitting array 30.

Figure 5 shows a perspective view of this embodiment. Preferably, the prism 35 would make use of total internal reflection to redirect the light to the mirror 31 with minimum optical loss. In another embodiment, a fixed reflector could be used in place of the prism 35.

In a further arrangement (not shown), the LED array 30 could be imaged onto the MEMS reflector 31 using bulk imaging optics.

The embodiments described in relation to Figures 1 to 5 are for a monochrome display. A full colour display may be provided by using three primary colour LED arrays (red, green and blue), a spectral beam combiner and a single MEMS reflector arranged so as to produce a single multi-colour display 42. Arrangements for achieving this are shown in Figs 6, 7 and 8.

Fig 6 shows a side view of an LED array and MEMS mirror assembly with conibined primary colour displays. The arrangement provides red, green and blue LED arrays, collimating lens arrays 44, 54, 64 and three dichroic filters 45, 55, 65 optimised so that the relative transmission and reflection ratios result in the recombinatiori of all ". : three arrays onto the scanning MEMS reflector 41. Figure 7 shows a perspective view * of this embodiment and Figure 8 shows the projected display relative to the S.,...

* 5 perspective view of this embodiment. In another arrangement (not shown), the collimating lens array may be replaced by bulk imaging optics.

As in the embodiments described above, light from the two rows of each of the LED * .. arrays 40, SD, 60 is scanned by the MEMS reflector 41 to form each line of the display such that the spacing of the pixels in each line of the display is less than the * spacing of the LEDs in each row of the LED arrays 40, 50, 60.

The red, green and blue LED arrays in the embodiment of Figures 6-8 need to be accurately aligned to result in superposed arrays of red, green and blue light on the N1EMS mirror 41. This can be achieved, by for instance, using state of the art pick and place soldering systems or by using techniques employing solder bump alignment.

Figure 9 shows another full colour embodiment of the invention in which alignment issues relative to the arrangement of Figure 6, are simplified. The arrangement of Figure 9 provides three blue-emitting LED arrays 70 defined on the same chip with each array consisting of two rows of LED emitters as described in the first embodiment. The present arrangement provides a collimating lens array 74 to collimate the light from the arrays 70 and a phosphor screen 76 to convert the blue light to white light. The arrangement also provides colour filters 77 to define the three primary colours and three suitably chosen dichroic filters 75 which, as in the previous embodiment, act to combine the arrays 70 onto the mirror 71.

White or other multi-wavelength emitters may be used in place of the blue-emitting LEDs and other forms of wavelength selection means may be used to select the desired wavelengths from the light emitted therefrom.

In another arrangement (not shown), bulk imaging optics can be used instead of a collimating lens array 74.

Figure 10 shows a side view of a projection display system with a different geometry.

This provides an LED array 80, collimating lens array 84 and N1EMS scanning reflector 81 where the projected display is perpendicular to the plane of the LED array 80.

Figure 11 shows an alternative geometry in which an LED array 90 is provided on a sub-mount with a prism 95 located above the LED array 90 to reflect light through degrees towards a MEM5 mirror 91 which reflects the light through a further 90 degrees to form a display behind the LED sub-mount.

Figure 12 is a perspective view of another embodiment of a full colour projection system having three LED arrays 100 formed as in previous embodiments consisting of two rows of offset emitters, and having collimating optics and a prism 105 (as in Fig 11), two polarising beamsplitters 106 and a MEMS reflector 101. Light from the three LED arrays 100 is combined by the beamsplitters 106 and directed to the mirror 101 as a two-row array of coloured light sources. This embodiment can be used to combine red, green and blue arrays as an alternative to using dichroic filters as used in Figures 6-9. Alternatively, this embodiment can be used to combine the light from three single colour, monochrome arrays to result in a higher brightness display.

The examples given above combine light from one or more two-row arrays of LEDs but it would also be possible to combine light from more rows, eg three or four rows, in order to increase the brightness of the displays. In this case, there would be higher brightness areas in regions where light from separate emitters is overlapping.

It will be appreciated that LED arrays with only a small number of rows have the advantage of being much smaller than the arrays used in the prior art (in which the number of rows corresponds to the number of lines of pixels making up the display).

They are much thus easier and hence less expensive to produce and enable the system to be more compact. And as conventional incoherent LEDs are used (as opposed to laser diodes), there are no eye safety issues.

The reflector is only required to oscillate or rotate about one axis so is also relatively simple (compared to reflectors that oscillate about two or more axes) and are thus also more suitable for use in environments prone to shock and vibration.

In each of the embodiments described, at least two linear rows of LEDs are scanned by a reflector oscillating or rotating about a single axis to produce a 2D display and the LEDs in the linear rows are stepped such that the pixel density in the scanned display is higher than that of the light source. S. *

A projection display system such as that described above can be used in a variety of * applications. *

. Figure 13 shows a diagram of a scanned LED array with projection optics. This embodiment comprises a line-scanned LED array 110 (such as that shown in Fig 12), * ** collimating optics 117, imaging optics 118 and a projection screen 119. The : collimating optics is required to collimate the scanned light in one axis only. The S * imaging optFcs sets the required magnification and focal length so that an image can be observed on an external projection screen.

Figure 14a illustrates a further application of the projection display system described in a head up display (FIUD) on a window (such as a vehicle windscreen). This embodiment again uses a scanned LED array 120, collimating opticsl27 and imaging optics 128. The imaging optics may be designed such that the display image is projected onto the window 129, such as a windscreen, without distortion (eg as described in GB2458898). The windscreen or window 129 acts as a reflective optical combiner which combines the projected display with the image of distant objects. In another embodiment, the imaging optics 128 may include multiple optical imaging elements. The image is focussed by the [niaging optics 128 such that the focal point is at a virtual image plane more than 2m from the observer's eye so that the display information can be visible while observing distant objects without any perceived need to refocus eyes. In another embodiment, a spherical mirror can be used to image the display instead of the imaging optics 128.

Another application of the projection display system is shown in Figure lAb for projection in a head-mounted display. This may include a helmet mounted display (HMD) or a near to eye (NTE) display. This arrangement again provides a scanned LED array 130, collimating optics 137 and imaging optics 138. In this case, the display image is projected onto a helmet visor, optical combiner or the lens surface 139 of a pair of glasses. As in the previous example, the light from the display is imaged by the imaging optics 138 so that it is projected to a point further than 2m from the eye so that it will lie within the same focal plane as distant objects.

Figure 14b shows an arrangement for single eye monocular vision in a head mounted display. In other applications, two such arrangements may be used to project a stereoscopic image for both eyes.

Figure iSa shows a further embodiment similar to that shown in Figure 9 which uses two sinusoidally resonating mirrors 140, 141 rather than a single mirror. The two mirrors 140, 141 are arranged to oscillate out of phase with one another about parallel axes as shown in Figure iSa. Preferably, the mirrors are arranged to oscillate exactly 90 degrees out of phase. The graph shown in Figure 15b illustrates the relationship between the mirror scan angre and time for each of the two mirrors and their relative phase displacement. This arrangement has the advantage that the sinusoidal variations in the scan speed of the two mirrors combine such that the scan speed of the light reflected from the second mirror 141 is substantially more linear and so provides a more uniform illumination intensity across the scanned display without requiring a reduction in optical power from the LED array during non-linear portions of the scan (and so providing a higher display brightness).

Figure 16 shows another variation of the embodiment shown in Fig 15 in which both of the resonating reflectors are defined on the same substrate 150 (although they can still oscillate independently). Ught is reflected from a first scanning mirror 150 to a stationary reflector 151 which reflects the light back to a second scanning mirror 152. As in the embodiment described in relation to Fig 15, the two mirrors are arranged to oscillate out of phase with each other. The arrangement shown in Fig 16 has the advantage of being more simple and easier (and hence less costly) to manufacture and to align. As the two mirrors are oscillated out of phase they will, at most times1 be in different angular positions. Fig 16 shows them at a time when they happen to lie parallel to each other.

A further embodiment of the invention which uses sinusoidalty resonating mirrors may use a retarding or diverging optical element to project a more uniform illumination density across the scanned display without requiring a reduction in optical power from the LED array during non-linear portions of the scan and resulting in a higher display brightness.

Another application of the projection display is shown in Figure 1) for digital printing systems. This arrangement provides an LED array and imaging optics 160, a moving reflector 161, and a printing medium 162 which is in linear motion relative to the scanned LED array in direction Y. Some digital printing processes require a relatively high light dose to effect printing and by scanning the LED array in synchronization with the motion of the printing medium Y from D to 02, the cumulative exposure time of the printing medium to the illumination of the LED array may be enhanced.

* As the printing medium 162 is moving in synchronisation with the scanned light directed thereto by reflector 161, the display or image formed thereon comprises a single line. The reflector can then rotate back to its original position (with no light being reflected therefrom during the back sweep from D2 to D1) and then used to image another single line (spaced from that formed in the previous sweep from D1 to D2) on the printing medium 162. One or more additional LED arrays and imaging optics and associated reflector (not shown) may be used to image additional lines onto the printing medium 162 whilst the reflector 161 is being swept back from D2 to D1 to ensure that all areas of the printing medium can be exposed to an image as required.

In another arrangement (not shown) of a scanned LED array for digital printing, two or more scanned arrays may be used and arranged in such a way so as to optirnise the cumulative optical energy dose that is applied to the printing medium.

Another embodiment of the invention relating to printing applications is shown in Figure 18. This provides two imaged LED array sources 170, Ui, a stationary reflector 172 and two moving reflectors 173, 174. As in the arrangement shown in Fig 16, for ease of manufacture and alignment, the moving reflectors 173, 174 may be formed in a single substrate. This embodiment also provides a print medium 175 travelling in a linear direction of motion Y, In this arrangement, the LED arrays 170, 171 are driven such that the printed medium is scanned only from D1 to D2 and from D3 to D4. Light from LED array source 170 is reflected by the oscillating reflector 174 to stationary reflector 172, then reflected onto oscillating reflector 173 to scan the light from D3 to D4. Likewise, light from LED array source 171 is reflected by the oscillating reflector 173 to stationary reflector 172, then reflected onto oscillating reflector 174 to scan the light from D1 to D2. The arrangement may be such that the scanned areas of the printed medium 175 are interlaced such that the surface of the printed medium 175 receives a continuous illumination in the direction of motion of the print medium. 4e*S* * 0

As indicated, the projection display system described herein can be used in a wide range of applications including head up displays, head mounted displays, digital printing systems and any other arrangement requiring an optical image or a IJght signal to be imaged or scanned over a given area or object.

0**e** * a It will also be appreciated that the lines of a display need not necessarily be written in sequence from one side of the display to the other, For example, in the case of a display to be viewed by the eye, the lines can be written in any order such that the eye perceives the desired image. In the case of a printed image, or other arrangement in which a given area is to be exposed to light, the lines may be written in any order such that all of the desired area is exposed as required.

The display may be formed on an object or form a virtual image and the object may be stationary relative to the array of LEDs or may be moving relative thereto.

Embodiments of the invention may also use arrays of LEDs emitting at a variety of wavelengths (depending upon the application) including non-visible wavelengths, such as ultra-violet, infrared and microwave (and combinations thereof) as well as visible wavelengths. Where required, additional apparatus may then be provided for converting an image to one capable of being seen by the human eye, eg as used in known night vision apparatus.

It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention. 0* S * * * * .*

*.**** * * 0* * * Se * ** * S. * * S S.. * * *5

Claims

<claim-text>CLAIMS1. A projection display system comprising an array of light emitting diodes comprising at least first and second rows of diodes, the diodes in each row being spaced from each other, the diodes in the second row being offset in a direction parallel to the length of the row relative to the diodes in the first row, a reflector mounted for movement about an axis, and movement means for moving said reflector about said axis, the array of light emitting diodes being positioned such that light emitted therefrom is directed towards the reflector and reflected therefrom to form a display comprising one or more lines, each line comprising a plurality of pixels, the movement means being arranged such that light from said first row of diodes and light from said second row of diodes is used to form each line of the display so the spacing between pixels along each line of the display is reduced compared to the spacing of the diodes in the rows of the array.</claim-text> <claim-text>
2. A display system as claimed in claim 1 comprising control means for operating the diodes in a pulsed mode as the light therefrom is scanned across the display by the reflector.</claim-text> <claim-text>
3. A display system as claimed in claim 2 in which the timing of pulses of light from the diodes determines the spacing between pixels of the display in a direction perpendicular to the lines of the display such that said spacing is reduced compared to the spacing between the first and second rows of diodes in the array.</claim-text> <claim-text>
4. A display system as claimed in claim 1, 2 or 3 in which the reflector is a micro-electro-mechanical system (MEMs) scanning mirror.</claim-text> <claim-text>
5. A display system as claimed in claim 1, 2 or 3 in which the reflector is arranged to be rotated by a rotating motor shaft.</claim-text> <claim-text>* *.
6. A display system as claimed in any preceding claim having two or more arrays of light emitting diodes, each comprising at least first and second a rows of diodes arid optical combining means for combining the light from the two or more arrays prior to or as the light is directed to said reflector.</claim-text> <claim-text>7. A display system as claimed in claim 6 in having three arrays of light emitting diodes arranged to provide light of three different colours so as to provide a multi-colour display.</claim-text> <claim-text>8. A display system as claimed in claim 7 having three arrays of light emitting diodes emitting red, green and blue light respectively.</claim-text> <claim-text>9. A display system as claimed in claim 7 in which the diodes of the respective arrays emit white or multi-wavelength light and wavelength selector means are provided to direct a selected wavelength from each of the arrays to the reflector.</claim-text> <claim-text>10. A display system as claimed in any preceding claim comprising a collimating lens or an array of collimating lenses arranged to collimate light emitted from the array of light emitting diodes.</claim-text> <claim-text>11. A display system as claimed in any preceding claim comprising one or more prisms and/or further reflectors for re-directing the light directed towards said reflector whereby the display forms an image in a plane parallel to the plane of the array of light emitting diodes 12. A display system as claimed in any preceding claim comprising a collimating lens and an imaging lens for projecting light reflected from said reflector onto an image plane.13. A display system as claimed in any preceding claim in which the array of light emitting diodes is formed as an integrated device.* * 14. A display system as claimed in any preceding claim in which the array of light emitting diodes comprise two rows of diodes and at least 500 diodes in each row. * ,. * a an *SS S15. A display system as claimed in any preceding claim in which the spacing between the diodes in each row is substantially similar to the width of each diode.16. A display system as claimed in any preceding claim in which the offset between diodes in the first and second rows is substantially similar to the width of each diode.17. A display system as claimed in any preceding claim in which the array of light emitting diodes includes a third row of diodes, the diodes in the third row being offset in a direction parallel to the length of the row relative to the diodes of the second row by a distance substantially half of the offset between the diodes of the first and second rows.18. A display system as claimed in any preceding claim in which each diode has a width of 10 microns or less.19. A display system as claimed in any preceding claim which has first and second reflectors which are arranged to oscillate sinusoidally about parallel axes out of phase to each another, light emitted from the array of light emitting diodes being reflected by the first reflector and then by the second reflector.20. A display system as claimed in any preceding claim which has first and second reflectors which are arranged to oscillate sinusoidally about parallel axes and a stationary reflector, light emitted from the array of light emitting diodes being reflected by the first reflector towards the stationary reflector, and then reflected by the stationary reflector towards the second reflector * and then reflected by the second reflector, wherein the first and *. reflectors are synchronised to oscillate such that their sinusoidal variation is out of phase.21. A display system substantially as hereinbefore described with reference to and/or as shown in one or more of the accompanying drawings. * ** *-* a. *SS S22. A head up display comprising a projection disptay system as claimed in any preceding claim.23. A head up display as claimed in claim 22 arranged to form a virtual image on a vehicle window.24. A helmet mounted display comprising a projection display system as claimed in any of claims 1 -21.25. A digital printing system comprising a projection display system as claimed in any of claims 1-21.26. A digital printing system as claimed in claim 25 arranged such that movement of the reflector is syrichronised with the relative movement of a printing medium so that the time during which a line of the printing medium is exposed to illumination is increased. * . * * U.S * S *5 * * Ss * *0 * U * p * *5S S * S....</claim-text>