WO1993015588A1

WO1993015588A1 - Positioning mechanism

Info

Publication number: WO1993015588A1
Application number: PCT/GB1993/000172
Authority: WO
Inventors: Martin Kavanagh
Original assignee: Rank Brimar Limited
Priority date: 1992-01-28
Filing date: 1993-01-27
Publication date: 1993-08-05
Also published as: AU3364393A; GB9201810D0

Abstract

A mechanism for adjusting the position of optical components (e.g. spatial light modulators in a video display system) comprising a first plate (21) carrying a shaft (25) about which second and third plates (29, 31) are loosely mounted. The plates (29, 31) act on the shaft (25) through a silicone rubber O-ring (37). Tightening one of the bolts (45a, b, c) acts to move a portion of the plates (29, 31) together, compressing a portion of the O-ring (37), which then displaces the plates (29, 31) radially outwardly from the shaft (25). The displacement from the shaft (25), for a given adjustment of each of the bolts (45a, b, c) becomes progressively less with greater compression of the ring (37) so that an initial 'coarse' adjustment of the plate position may be followed by a subsequent 'fine' adjustment. This increases the ease of positioning to high accuracies.

Description

POSITIONING MECHANISM This present invention relates to a positioning mechanism. The invention has particular, but not exclusive, relevance to a positioning mechanism for use in a display system in which a plurality of separate light generating or modulating elements provide beams which are combined into a single display.

One example of such a display system is disclosed in the applicant's earlier International Applications W091/15842 and 091/15843. Another is described in US 4680579. In these projection systems, a colour projected image is generated from separate electrical colour component signals by providing at least one illumination source (a lamp), and separate spatial light modulator devices in the path of the or each light source, directing the light on to a common projection screen. The spatial light modulators are each controlled by a respective colour component signal. Separate different colour beams may be provided, one to illuminate each light modulator device.

Spatial light modulator devices include so called "active matrix" devices, such as those disclosed in the above references, in which an array of light modulating elements, or "light valves", each of which is controllable by a control signal, is arranged to controllably reflect or transmit light in accordance with the control signal. A liquid crystal array is one example of an active matrix device (as disclosed in EPO 402137); another example is the deformable mirror device (DMD) array described in, for example, US 4615595 or in I.E.E. Trans. Electron Devices, Ed-30, 539 (1983), "128 x 128 deformable mirror device", by L.J. Hornbeck. An example of a spatial light modulator device which is not an active matrix device is the "Eidophor" system, in which an oil film, is illuminated by a light beam and, simultaneously, scanned by an electron beam controlled by a video signal, which acts to control the reflective state of the oil film.

With such a projection system, the light modulator device is generally much smaller than the projection screen to which light from the modulator device is directed. For example, in the case of an active array device, the spacing between individual pixel elements of the array may be on the order of micrometers. Therefore, where multiple array devices are provided, they must be mutually aligned to within a fraction of the pixel resolution if the sub images modulated by each array are to be aligned to form a correct image. Assembling the components to exactly the correct alignment would be very difficult, however.

Furthermore, in the case of DMD devices, the active arrays are mounted on a heat sink, which makes both manual adjustment of the positions of the array, or the mounting of suitable mechanical adjustment means effective to adjust the positions of the arrays difficult.

Accordingly, the invention provides, in one aspect, a plurality of spatial light modulator devices mounted so as to be capable, when illuminated, of directing light on to a common surface to provide a composite projected image, and adjustment means for adjusting the relative positions of at least some of the array devices so as to permit the components of the projected image directed from said array devices to be mutually aligned.

The invention also provides in a different aspect, an adjustment means arranged such that movement of a first part of the adjustment means in a first direction causes movement of a second part of the adjustment means in a second direction transverse to the first direction.

The inventors have discovered that a mechanism which has a "coarse" initial positioning mode and a "fine" further positioning mode is considerably quicker and easier to use; accordingly, a preferred embodiment of the invention provides such a mechanism. The inventors have invented a mechanism, which provides "coarse" and "fine" modes by providing first and second portions and resilient means exhibiting non linear elasticity acting between the portions under the control of adjustment means; the non linear elasticity is such that initial motion of the adjustment means causes a relatively large change of position between the portions, but subsequent movement of the adjusting means produces less effect. This position adjusting mechanism may also be used for other applications, and therefore provides a further aspect of the invention.

Other aspects and preferred features of the invention are as defined in the accompanying claims, or will be apparent from the following description. A number of embodiments of the invention will now be illustrated, by way of example only, with reference to the accompanying drawings in which:

Figure 1 illustrates schematically the elements of an active matrix device optical projection display system;

Figure 2 shows schematically the elements of a colour active matrix device optical projection display system; Figure 3 illustrates a position adjusting mechanism according to an embodiment of the invention, mounted on part of an active matrix device optical projection display system;

Figure 4 is a to scale semi-sectional side elevation through a position adjusting mechanism according to an embodiment of the invention of similar form to that shown in Figure 3;

Figure 5 is a corresponding right hand end elevation of the mechanism of Figure 4; Figure 6 shows the mechanism of Figure 4 adjusted to produce a change in position; and

Figure 7 shows schematically how a pair of position adjusting mechanisms in accordance with an embodiment of the invention which may be used to adjust the position of a matrix device within an active matrix device optical projection display system.

Referring firstly to Figure 1, a projection system comprises a reflective screen (for example a cinema screen) 1 and a projector indicated generally as 3, positioned and aligned relative to the screen 1 so as to generate a focused image on the screen 1.

The projector 3 comprises a lamp 5, typically rated at several kilowatts for a cinema application, which is arranged to generate a light beam directed onto a planar active matrix display device 7 comprising, for example, a DMD array of 576 x 768 individual deformable mirror devices . Each mirror device of the matrix display device 7 is individually connected so as to be addressable by an addressing circuit 9 which is arranged to receive a video signal in any convenient format (for example, a serial raster scanned interlaced field format), the orientation of each individual mirror device thus being controlled in accordance with the corresponding pixel signal value within the video signal. The arrangement may, for example, correspond to that described in the applicant's copending International Application No. PCT/GB92/00002.

The modulated reflected beam from those deformable mirror devices within the matrix display device which have been selectively activated by the address circuit 9 is directed to a projector lens system 11 which, in a conventional manner, focuses, magnifies and directs the beam onto the screen 1 as shown schematically in Figure 1.

Turning now also to Figure 2, in a three colour system, three separate active matrix display devices 7a,7b,7c are provided, each device being driven by one of three separate colour video signals from the address circuit 9, with separate illumination arrangements 5a,5b,5c producing beams of the different colours. The arrangement may be as disclosed in US4680579, for example, but is more preferably as disclosed in the applicant's copending International Application No. PCT/GB92/00132. The light reflected from the three matrix devices 7a,7b,7c is combined and directed to the lens system 11. The light sources 5a,5b,5c may be separate coloured lamps, or alternatively may be three coloured beams derived from a single lamp by beam splitters and filters (not shown) . In use in an auditorium, the projector 3 is positioned at a distance from the screen 1 on a line passing through the centre of the screen 1 . The viewing space or auditorium thus lies between the projector 3 and the screen 1.

One type of display device comprises a plurality of row enable lines and a plurality of column enable lines. The address circuit 9 comprises an input port receiving a digital video signal in an input format (for example, a conventional line scanned interlaced field format), a scan convertor circuit for converting the input video signal format into one suitable for the matrix display device 7, and a circuit arranged to activate selectively corresponding pixel mirrors of the display device 7 in accordance with a signal from the scan convertor circuit. In a colour system of the type shown in Figure 2, the scan convertor circuit may be arranged to receive a composite colour video signal, and generate therefrom three separate colour component video signals which are then supplied to three separate addressing circuits, one for each display device 7a,7b,7c .

Each of the active matrix display devices 7 contains, for a cinema application, in the order of 1100 x 2035 deformable mirrors; using integrated circuit techniques, the spacing between pixel mirrors can be reduced to 17 microns, so that the overall linear dimension of the matrix display device is in the order of 20 millimetres. Conveniently, each matrix display device 7 may be fabricated on a circuit board which includes the address circuit 9. For this scale of integration, the weight of each circuit board including the addressing circuit 9 is on the order of 200-300g. For accurate image alignment, the three arrays 7a,7b,7c need to be aligned to a resolution better than one pixel spacing, and very preferably to better than 1/4 pixel spacing, which in the above example requires a positional accuracy of better than 4 microns .

Figure 3 is a schematic diagram of a practical implementation of a matrix device and the components of the address circuit 3 , indicated generally as 13 mounted on a circuit board 15. Generally some form of heat sink 17 will be proviced on the board 15, the particular example shown being as described in the applicant's copending U.K. Patent Application No. 9212674.7 to which reference should be made for further details. The matrix device is carried on the underneath surface of the heat sink 17, and thus is not visible in Figure 3.

It will be appreciated from inspection of Figure 3, that the provision of a heat sink 17 makes positional adjustment of the matrix display device mounted on the board 15 extremely difficult. Thus, in accordance with an embodiment of the present invention there is provided on the board 15, two positional adjustment mechanisms 19a,19b so as to permit positional adjustment of the matrix display device 7 to a sub pixel level of accuracy, the form of the mechanisms 19a,19b being described in some detail hereaf er.

Referring now also to Figure 4, each positional adjustment mechanism 19a,19b comprises a first portion mounted to a reference position (for example, fixed relative to the projector 3) with reference to which the other spatial modulator array devices are mounted, and a second portion to which the array 7 to be adjusted is mounted. The first portion comprises a plate 21 securable to the chassis of the projector 3. A threaded bore 23 within the plate 21 receives a correspondingly threaded shaft 25 which is locked axially in position relative to the plate 21 by a nut portion 27 solid with the shaft 25. The second portion of the mechanism comprises a pair of parallel plates 29,31 which include a pair of aligned bores 33,35 within which the shaft 25 is a loose fit. In the particular embodiment illustrated in Figure 3, it will be seen that the plate 29 is formed integrally with the heat sink 17 which is in turn mounted on the circuit board 15. The shaft 25 is shown in an extended form to that illustrated in Figure 4 in the embodiment of Figure 3, passing through an aperture in the board 15 to the plate 21 which is secured to the chassis (not shown) of the projector 3.

The shaft 25 may be unscrewed from the plate 21, when required in order to permit servicing of the matrix display device 7 (not seen in Figure 4) mounted on the mechanism 19.

Received between the two plates 29,31, and surrounding shaft 25, is a resiliently deformable ring 37, which in this embodiment is an "0" ring of the type widely used as washers, made of silicone rubber having a Shore hardness of approximately 60. The ring 37 is seated within a confor al recess 39 within the plate 29.

Referring now also to Figure 5, three aligned bores 41a,b,c and 43a,b,c in the two plates 29,31 are provided; the bores 43a,b,c in the plate 31 receive respective bolts 45a,b,c which also pass through corresponding threaded bores 41a,b,c in the plate 29. The bores 43a,b,c in the plate 31 are recessed, so as to permit the plate 31 to be somewhat angularly inclined relative to the plate 29. It will be appreciated that whilst in this particular example three sets of bores 41a,b,c, 43a,b,c and corresponding bolts 45a,b,c are provided,in practice any number of bores may be chosen.

Interspersed between the. bores 43a,b,c in the plate 31 in this embodiment are three further bores 47a,b,c, it being appreciated that any number of further bores 47 may be provided.

At the end of the shaft 25 which is not received in the plate 21, a threaded axial bore 49 is provided into which an inner threaded bolt 51 is received. The head 53 of the bolt 51 bears against the plate 31 via an internal toothed vibration proof washer 55, and holds the plates 29, 31 and 0 ring 37 together when first assembled.

The plates 21, 29, 31 and the shaft 25 may be made of, for example, mild steel. Preferably, they are made of a material selected to exhibit a low thermal expansion coefficient, since within the projector 3, the lamp 5 will generate considerable heat and the temperature of the components may vary considerably during a display operation; high dimensional stability is therefore desirable to avoid misalignment on heating.

In Figure 5, the diameter of the plate 31 is, for example, 20 millimetres in this embodiment; since Figures 4 and 5 are to scale, the remaining dimensions will readily be derivable therefrom.

The use of the mechanism 19 shown in Figures 4 and 5 will now be described in more detail . The parts shown in Figures 4 and 5 are assembled as shown. The position of the plates 29 which as can be seen in Figure 3 is integral with the heat sink upon which the matrix display device 7 is mounted is then adjusted relative to that of the plate 21 and shaft 25 by successively tightening the bolts 45a,b,c. Turning now also to Figure 6, if, for example, the bolt 45a is tightened, the part of resilient ring 37 in the region of the bolt 45a is compressed parallel to the shaft 25. Accordingly, this part of the ring 37 will expand in the direction normal to the shaft 25 by an amount dependent upon the ring's Poisson's ratio, the geometry of the recess 39, and the space between the plates 29,31. Rubber has a Poisson's ratio of nearly 0.5, and is thus virtually incompressible. The portion of the ring 37 adjacent the bolt 45a will therefore bear back against the shaft 25 to a greater extent than the corresponding portion of the ring 37 on the opposite side of the shaft, and will likewise bear against the portion of the recess 39 adjacent the bolt 45a. Thus displacement of the plates 29,31 outwardly from the shaft 25 at the position of the bolt 45a will take place as indicated in Figure 6. The uppermost plate 31 will be caused to tilt slightly from the horizontal. The recessed form of the bores 43a,b,c in the plate 31 enables this tilting of the plate 31 to be accommodated by the mechanism 19 despite the lower plate 29 remaining horizontal in view of its attachment to the heat sink 17 as described in relation to Figure 3.

It will thus readily be seen that the position of the plates 29,31 relative to the shaft 25 and plate 21 can be adjusted by adjusting the bolts 45a,b,c. If all three bolts 45a,b,c exert the same compression on the ring 37, the plates 29,31 will be aligned symmetrically coaxially around the shaft 25. If, however, one of the bolts 45a,b,c exerts a greater pressure on the ring 37 than the other bolts 45a,b,c , the plates 29,31 will be displaced radially towards that bolt relative to the shaft 25.

Referring now again to Figure 3, it will be seen that even when mounted in an optical projection display system, the bolts 45a,b,c are readily adjustable by means of a screwdriver, indicated as 46. Thus accurate positioning of the matrix display device 7 mounted in the display system is achievable by means of a mechanism in accordance with the invention, even though the devices 7 themselves are not readily accessible.

When a resilient ring 37 of rubber or a similar high polymer is provided, it is found that the displacement of the plates 29,31 becomes progressively smaller for a given rotation of a bolt 45, as the displacement distance or total force on the ring is increased. This is thought chiefly to be due to the non linear elasticity of rubbers, although the geometry of the recess 39 and the shape of the ring 37 are also of significance. This progressive decrease in displacement, relative to the adjustment of the bolt 45, is advantageous in precise alignment of the matrix 7 as it permits an initial, "coarse", adjustment to be followed by progressively finer adjustments. For example, the plates 29,31 may be swiftly displaced in a first direction by tightening a first bolt 45a, to effect a relatively coarse adjustment. When it is desired to move the plates 29,31 back in the opposite direction, instead of loosening the bolt 45a, the bolts 45b and/or 45c are tightened. Since the overall compression on the ring 37 has been increased, the same amount of rotation of the bolts 45b, 45c will produce less movement than the rotation of the bolt 45a did, so that the adjustment becomes progressively more sensitive. By continuing to tighten the bolts, progressively finer adjustments are effected on the position of the matrix display device 7.

Once the plates 29,31 are at the desired displacement from the plate 21, they may if required be permanently locked in position. Conveniently, this is achieved by injecting epoxy resin through the holes 47a,b,c in the plate 31 .

This arrangement still permits the mechanism to be relatively simply disassembled, as the ring 37 prevents the epoxy resin from reaching the shaft 25. To disassemble the mechanism, the bolt 51 is removed by slackening the head 53. The plates 29,31 are retained on the shaft 25 only by the resilience of the ring 37, and can thus be removed from the shaft 25 if force is exerted. The ring 37 is a consumable, and after removal of the bolts 45a,b,c the two plates 29,31 can relatively simply be separated. The above described construction is inexpensive to make, whilst exhibiting good accuracy.

Referring now to Figure 7, in one preferred embodiment which is also illustrated in Figure 3 , a pair of position adjusting mechanisms 19a,19b which may be of the type disclosed above, support in parallel, the heat sink 17 which is shown schematically in Figure 7 as a support plate 51 on which a matrix display device 7 is mounted. In this arrangement, the support plate 51 and matrix display device 7 may be translated in the X and Y directions by adjusting the position adjusting mechanisms 17a and 17b, as described above. However, the matrix display device 7 may also be rotated by applying different positional adjustments to the positional adjusters 19a and 19b. Preferably, the position adjusting mechanisms 19a and 19b are provided on opposite sides of the matrix display device 7. In this arrangement, the matrix display device 7 may be rotated without moving its spatial position, by complementary adjustments of the two position adjusting mechanisms 19a,19b (i.e. by adjusting the two mechanisms 19a,19b in opposite directions). Conveniently, they are equally spaced about the matrix display device 7.

It will be appreciated that many modifications to the embodiment of the invention shown herebefore by way of example may be made.

For example, other types of 0 ring could be employed, although silicone rubber is advantageous for its high deformability. Alternatively, instead of employing a rubber resilient ring, a putty or similar curable or settable viscoelastic polymer compound could be employed, which exhibits sufficient non linear elasticity to be compressed during adjustment, but sets shortly after adjustment is complete. This avoids the need for a separate epoxy injection in order to "set" the position of the mechanism 19.

Equally, it is not necessary to provide an 0 ring as the resilient member 37; rings having other cross sections could equally be employed, or separate independent rubber pieces distributed around the shaft 25 (or any combination of these) could be used. Equally, one or other of the plates 29, 31 could be replaced with separate segments for applying pressure to the resilient member; this assists in decoupling the action of the bolts, and is useful in arrangement where the bolts are not symmetrically positioned.

Rather than applying pressure to the ring parallel to the shaft, and relying upon Poisson's ratio to generate pressure against the shaft, it would equally be possible to provide for the bolts 45a,b,c to act inwardly towards the shaft, to compress the ring 37 directly.

It may be convenient to provide bolts 45 or other compression arrangements distributed along mutually normal axes, so that adjustments in the X and Y directions (for example, two axes in the plane of a DMD array) can be uncoupled. The mechanism need not be capable of disassembly, or cementing, in many applications. Either of the two plates 29, 31 may be used to support an array; the illustrated embodiment moves the matrix display device 7 relative to plate 21 on progressive compression, but where the reverse is desired the matrix display device may be mounted on the plate 21. In use, in a colour projection system employing three modulator matrix display devices, one in respect of each of the three colours green, red and blue, it may be convenient to provide each matrix display device with a position adjustment device of the type shown in Figures 5 and 6. Alternatively, one matrix display device may be mounted fixed to the chassis of the projector 3, or some reference point, and the other two matrix display devices may be provided with adjustment devices and adjusted relative thereto. Preferably, a first matrix display device is provided with a relatively coarse adjustment mechanism and the other two are provided with mechanisms capable of high accuracy, as shown in Figures 5 and 6. Whilst the mechanism of Figures 5 and 6 has been described with reference to positioning a light modulator in a projection display system, it is equally applicable to positioning other optical components where a high degree of accuracy is required, or to positioning other components in general.

Claims

CLAIMS ;

1. A positioning mechanism comprising a first part (21) and a second part (29,31) moveable relative thereto by adjustment means (45a,b,c) characterised in that the adjustment means is arranged such that movement of the adjustment means in a first direction causes displacement of the first part relative to the second part in a second direction transverse to the first direction.

2. A mechanism according to claim 1, in which the relative movement of the second part (29,31) for a predetermined adjustment of the adjusting means progressively decreases, to provide a progressively more accurate adjustment.

3. A mechanism according to claim 2, in which the adjustment means act upon a resilient means (37) exhibiting non-linear elasticity.

4. A mechanism according to claim 3, in which the resilient means comprises a member (37) of a high polymer material.

5. A mechanism according to claim 4, in which the material is a rubber material.

6. A mechanism according to claim 5, in which the rubber material is a silicone rubber.

7. A mechanism according to any of claims 3 to 6, in which the first part comprises a portion (25) around which the second part (29,31) is disposed, and the resilient means (37) comprises a ring separating the portion of the first part and at least a portion of the second part (29,31) .

8. A mechanism according to claim 7, in which the ring is of circular cross section.

9. A mechanism according to claim 8, when dependent on any of claims 3 to 8, in which the adjustment means is effective to cause relative movement of two portions (29,31) of the second part causing elastic deformation of the resilient means (37), so as to effect said relative transverse displacement.

10. A deformable mirror device including at least one deformable mirror array wherein adjustment of the position of the deformable mirror array is produced by a positioning mechanism according to any one of claims 1 to 9.

11. A display system comprising a plurality of separate light generating or reflecting elements (7a,b,c) providing beams for combination into a displayed image, in which at least some of the generating or reflecting elements are provided with position adjustment means (17a,17b)according to any one of claims 1 to 9 so as to align the beams to form an aligned image.

12. A display system according to claim 11, in which the light generating or modulating elements comprise separate spatial light modulator devices.

13. A system according to claim 12, in which the modulator devices comprise active array devices (7a,7b,7c) .

14. A system according to claim 13, in which the active array devices comprise deformable mirror devices (7a,7b,7c).

15. A system according to any one of claims 11 to 14, in which each generator or modulator device generates a respective colour component image.

16. Apparatus according tb any one of claims 11 to 15, in which a first generator or modulator element is mounted so as to be less adjustable than other elements.

17. A system according to claim 16, in which said first portion (21) is fixedly mounted.

18. A system according to claim 16, in which said first element is coarsely adjustable and said other elements are finely adjustable.

19. A system according to any one of claims 11 to 18, including a positioning mechanism according to any one claims 1 to 9, arranged to adjust the position of at least one of said elements (7a,7b,7c).

20. A method of positionally adjusting a first portion (21,25) relative to a second portion (29,31) comprising compressing resilient means (37) acting between said first and second portions, said resilient means (37) having a non linear elasticity such as to progressively resist further displacement.

21. A position adjusting mechanism for a spatial light modulator device which comprises first and second positional translating mechanisms connected to act on the device at different spatial locations, so as to cause a rotation of the device.

22. A mechanism according to claim 21, in which the translation mechanisms are provided at either side of the device so as to permit rotation of the device without translation thereof.