WO2007017521A1

WO2007017521A1 - Apparatus and method of projection control

Info

Publication number: WO2007017521A1
Application number: PCT/EP2006/065191
Authority: WO
Inventors: David John White
Original assignee: Thales Holdings Uk Plc
Priority date: 2005-08-10
Filing date: 2006-08-09
Publication date: 2007-02-15
Also published as: GB0516441D0; GB2429075A

Abstract

A control apparatus for a display projector (7) for projecting light onto a surface (6) for display, the control apparatus including a monitoring means (2-5) having a light sensor means and being arranged to monitor light generated by the display projector (7) for projection at the surface and to generate a control signal according to whether or not display light generated by the display projector is detected by the light sensor means, and control means (20) for controlling an operation of the display projector means according to the control signal thereby to control the projection of light.

Description

Apparatus and Method of Projection Control

The present invention relates to apparatus and methods for controlling the projection of light onto a display screen. In particular, though not exclusively, the present invention relates to laser light display projectors and their control.

Light projection systems, such as laser projector display systems, typically include a light projector device arranged to project light on to a display surface for the purposes of generating a visual display. Often, the projector device is simply aligned with, or "aimed at", a chosen display surface prior to operation/projection by the projector device with, perhaps, manual adjustments in orientation being made to suitably position the projected image upon the display surface. Generally speaking, once any such manual adjustments have been made, the projection system is left unchanged until/unless it is subsequently deemed that further manual adjustments in orientation are required.

Such manual adjustments may be necessary due to changes in the position of the display screen and/or the position of the projector device. Furthermore, changes in the internal mechanisms of the projection device (e.g. the light projection mechanisms) may also result in changes in the position or location of projected light upon a display surface even though neither the display surface nor the body of the projection device has moved.

The resulting requirement for manual adjustment of the orientation of the projection device is time consuming, inconvenient and often rather inaccurate. Indeed, where complicated projection images are formed by a projection device, it may be apparent to the user that adjustment of projector orientation is required, but the user may not be able to determine the manner of that adjustment. This is particularly the case in respect of the projection display devices typically employed in vehicle simulator machines, such as aircraft simulator machines.

In aircraft simulator machines, for example, a simulated cockpit view is typically generated using complex light projection apparatus. In order to generated visually acceptable/believable cockpit views, a great amount of detail is required in a created image and this typically requires a correspondingly great amount of accuracy in the position and timing of the projected light forming the image . Misalignments of projected image light may not only- produce distorted and unacceptable simulated cockpit views, but may also be physically hazardous should that misalignment result in projected light missing the projection screen entirely and therefore potentially impinging either directly or via a reflective surface upon an eye of any person in the environs of the simulator machine (e.g. the pilot) .

Existing display projection systems do not provide an effective means of controlling the projection of light at a display surface in a manner which would address the above problems. The present invention aims to address these deficiencies in the prior art.

At its most general, the present invention proposes monitoring projector display light at e.g. the projector or at a display surface or any point between them, and controlling a display projector according to the results of that monitoring. For example, one may monitor for the presence or absence of projector display light at places where projector display light either should or should not be found. For example, one may monitor parts of the projector for desired/undesired projector display light, or part of the display surface where projected light either should or should not be found, in either case the projector being adjusted either to adjust the direction of projector light, or the position of projected light on the surface, or to shut down the projector, in order to rectify any condition found to be undesirable. Measurements of a change of location of projector display light may be made by this monitoring, as may measurements of properties of the projector display light itself (e.g. intensity, spatial intensity profile) and the projector device adjusted according to these measurements in order to adjust the measured properties.

Most preferably, the invention may provide an automatic monitoring system which functions while the projector being controlled is in normal operation; i.e. while the projector is projecting in normal use. Thus, one need not switch the projector off-line to implement any of the control adjustments possible according to the present invention.

In a first of its aspects, the present invention may provide a control apparatus for a display projector for projecting light onto a surface for display, the control apparatus including a monitoring means having a light sensor means and being arranged to monitor the display light generated by the display projector for projection at the surface and to generate a control signal according to whether or not display light generated by (e.g. from) the display projector is detected by the light sensor means, and control means for controlling an operation of the display projector according to the control signal thereby to control the projection of light.

For example, the monitoring means may be arranged adjacent or internal to the display projector to monitor a location at or adjacent the projector light generator or light output aperture/area for the presence, absence or location of projector display light.

The light sensor means of the monitoring means may be arranged to be attached to the display projector (e.g. connected, mounted etc) to sense light generated by the display sensor. For example, the light sensor means may be arranged to be located within the body of the display projector to sense within the projector display light generated by it. For example, the monitoring means may include a beam splitter placed in the path of display light generated by the display projector for the purposes of directing a portion of that light towards one or more light sensors of the monitoring apparatus for the purposes of monitoring that display light. Additionally or alternatively, one or more light sensor means of the monitoring means may be placed internally within the display projector at locations upon which the display projector is arranged to project light. In this way, projected light generated by the display projector may be monitored internally of the display projector apparatus.

For example, the monitoring means may be arranged to monitor a location on the display surface, for the presence, absence or location of projected display light.

Preferably, the monitoring means is arranged to generate the control signal according to whether or not the sensor means detects light from or generated by the display projector by direct receipt.

Thus, it is preferable that the light being monitored is light received directly from or generated by the display projector without having undergone any intermediate reflections or scatterings, or the like, such that properties of the light can be monitored directly. The light may be monitored directly at the display surface, or may simply be monitored at locations adjacent or in association with the surface (e.g. in front, to one side etc) . Most preferably, the light sensor means is arranged in association with the display projector such that light generated by the display projector is directly projectable into the sensor means for sensing thereby. The monitoring means maybe arranged internally of the body of the projector apparatus in this arrangement, instead of (or in addition to) an arrangement at or adjacent the display surface.

The monitoring means is arranged preferably to generate a control signal indicating when no detection of light from or generated by the projector means has occurred at the light sensor means when the monitoring means had expected light detection to occur.

In this way, the monitoring means may indicate when projected display light has unexpectedly shifted its location/position upon the display surface and/or shifted the direction in which it propagates from or through the projector. For example, when light is projected by the scanning of a light beam across the display surface (e.g. raster scanning, calligraphic light point scanning) , one would expect a correctly operating display projector to project light at a predetermined location upon the display surface at a predetermined time when generating successive image frames or the like. The absence of detected light at a predetermined location on the display surface, when it is expected to be there at a predetermined time, is therefore indicative of an error in the display projector. Similarly, a correctly operating display projector may be arranged to cause display light generated by it to propagate through or from the projector (having been generated internally) in a predetermined direction at a predetermined time, illuminating a predetermined location at that time. Absence of such illumination indicates error. The predetermined location is preferably within the body or structure of the projector.

The control apparatus may be arranged to receive projection signals indicating when, in use, the monitoring means can expect light to be detected by the light sensor means .

For example, the control apparatus may receive the control signals used to control operations (e.g. light deflection) of the display projector itself, or it may be pre-programmed with timings indicative of when light can be expected to be received by the light sensor means thereof.

The monitoring means may be arranged to detect a change in the location of light generated by the projector, e.g. projected light at the surface or within the projector, and to generate a control signal indicating detection of such a change and/or a measure of that change. Thus, the monitoring means may be arranged to detect not only the existence of e.g. a drift in projected light position at for example a display surface, but may also be arranged to measure the magnitude and/or direction of that drift.

In any of the above arrangements, it may be the case that, even when operating properly, the display projector should project light directly at certain parts of a display surface only within or during certain predetermined time intervals. This may arise simply because of the nature of the displayed image, or may arise due to the nature of the method of projection (e.g. a scanning method of projection) . The monitoring means is preferably arranged to take account of this and to effectively monitor the presence of light at predetermined locations (e.g. at the surface or within the projector body) only within or during predetermined time intervals.

The monitoring means may be arranged to monitor detection by the light sensor means of light from or generated by the projector during successive predetermined time intervals, and to generate the control signal according to whether or not light from or generated by the projector is detected during such a time interval.

The monitoring means may be arranged to monitor display projector light at several different locations about the display surface or adjacent or within the body of the projector, and this monitoring may be done concurrently or successively. That is to say, the monitoring means may be arranged to monitor for the presence of light simultaneously at a number of separate light sensors, or may be arranged to monitor for the presence of light at different locations at different times or during different time intervals.

The control apparatus may preferably include a plurality of said light sensor means each one of which is arranged to be located at a respective one of a plurality of separate locations about e.g. the surface or the projector body in use. The monitoring means may be arranged to receive detection signals from each of the plurality of light sensors and to determine from the plurality of detection signal whether or not images formed by the display projector have changed location upon the display surface. Thus, the monitoring means may be arranged to calculate image drift (e.g. an image frame) using the detections signals received by a plurality of light sensors collectively.

The monitoring means is preferably arranged to monitor whether or not said light is detected during one of a plurality of temporally separate time intervals, at each one of the plurality of light sensors and to generate said control signal accordingly.

In this way, each of the separate light sensors may be assigned its own monitoring time interval during which a control signal is generated by the monitoring means according to the light detected by it (or not detected as the case may be) during that interval. This also permits versatility in being able to account for variations in the projected image itself, as well as variations or differing techniques in the manner of projection. This arrangement is particularly well suited to scanning projector arrangements in which one necessarily expects to receive projected light at a plurality of different locations during a plurality of different time intervals. The monitoring means may therefore monitor the accuracy with which the projector scans light across the display surface . The (or a) light sensor means may include a light sensing area and the monitoring means is preferably arranged to identify which parts of the sensing area are in receipt of said light and which parts of the light sensing area simultaneously are not in receipt of said light, thereby to determine the position of received light on the sensing area.

For example, the sensing area may be formed from an array of light sensitive elements such as a CCD sensor array, or a CMOS light sensor. Other means for providing a light sensor area, such as would be readily apparent to the skilled person, are possible of course. In providing a light sensing area upon which the location of impinging light may be determined (e.g. the position of a light beam such as a laser beam) the monitoring means may be arranged to determine changes, over time, of the determined position of the impinging projected light upon the sensing area. In this way, the drift in position of projected light (e.g. a light beam) may be determined. Consequently, the display projector may be controlled according to the determined change in position so as to rectify or reverse that change.

Alternatively or additionally, the monitoring means may be arranged to receive multiple simultaneous detection signals from various of the sensing elements within the light sensing area, and to determine a measure of the spatial distribution of light (e.g. intensity profile) of the received projected light at the light sensing area. This is particularly useful in controlling a laser projector device of a light, such as a calligraphic light point projector as used in vehicle simulator displays (e.g. aircraft simulator displays). Monitored variations in the intensity profile of a calligraphic light point, for example, may be used to control or adjust the calligraphic light point projector device to either maintain or to deliberately adjust the intensity and/or intensity profile of the projected light point.

The monitoring means may include a light metering means arranged to measure the intensity of the projected light received by a light sensor means .

The monitoring means is preferably arranged to determine the spatial distribution of the intensity of projected light received by an aforesaid light sensor means .

The above provision may also be provided by a plurality of the aforesaid light sensor means suitably arranged. The light sensing area may be defined by a plurality of said light sensor means forming an array in which each light sensor means is arranged to generate a detection signal in response to receipt of said light thereby. The monitoring means is preferably arranged to identify which of the sensor means of an array are in receipt of said light and which of the sensor elements of the array simultaneously are not in receipt of said light, thereby to determine the position of received light on the array.

Control apparatus may include a plurality of the light sensor means forming an array, each light sensor means being arranged to generate a detection signal indicating the intensity of said light received thereby, the monitoring means being arranged to generate from the detection signals a control signal from which the spatial distribution of the intensity of projected light received by the array of light sensor means is derivable.

The response of the control means to control signals generated by the monitoring means may be to adjust the deflection apparatus of the display projector thereby to adjust the position upon the display screen of projected light, or maybe to adjust the intensity or intensity profile of projected light at certain places on the display surface, or may simply be to shut down the projector in the event of a fail-safe situation in which it is considered dangerous to continue projection.

The control means may be arranged to shut down the projector means in response to a control signal indicating that: no light was detected by a light sensor when light was expected to be detected thereby; or, an unsafe condition exists. The control signal may indicate how the projector means should be adjusted to change the location of projected light at the display surface. The control signal may indicate how the projector means should be adjusted to adjust the light intensity and/or the spatial intensity profile of projected light at the display surface. Preferably, the control means is responsive to the control signal to control the projector means so as to implement an adjustment indicated by the control signal.

For example, the control means is preferably in communication with the display projector and is arranged to control any one or more of the following projection functions of the display projector: light beam deflection control (in the case of a deflected-beam light projector) ; projected light intensity; projected light intensity profile (particularly in the case of a deflected beam projector); projector power. In this way, the control means may control any one or more of the aforementioned projection features of the display projector (separately or concurrently) in response to control signals from the monitoring means.

The light may be projected as a light beam and the projector means is arranged to scan the light beam across the surface when projecting light to produce the display.

The control apparatus may include the display projector.

In a second of its aspects, the present invention may provide a method of controlling a display projector for projecting light onto a surface for display, the method including monitoring (e.g. the location of) the light generated for projection by the display projector at the surface by generating a control signal according to whether or not display light from or generated by the display projector is detected thereat, and controlling an operation of the display projector according to the control signal to control the projection of light.

The control signal may be generated according to whether or not light is detected (e.g. at the surface or otherwise) by direct receipt from the display projector or from the light source of the display projector. A control signal may be generated indicating when no detection of light from the projector means has occurred when detection of that light was expected.

The method may include monitoring the projected light to detect a change in the location of projected light (e.g. projected at the surface or within the body of the projector) , and generating the control signal to indicate detection of such a change and/or a measure of that change .

The method may include monitoring detection of light from or generated by the projector during successive predetermined time intervals, and generating the control signal according to whether or not light from or generated by the projector is detected during such a time interval .

The method preferably includes monitoring detection of light at a plurality of separate locations in use. For example the locations may be locations within the body of the projector, between projector and display surface, and/or at or about the display surface. The method may include monitoring whether or not said light is detected during one of a plurality of temporally separate time intervals at a respective one of each of the plurality of locations and to generate said control signal accordingly.

The method may include providing a light sensing area and monitoring the detection of light over a light sensing area and identifying which parts of the sensing area are in receipt of said light and which parts of the sensing area simultaneously are not in receipt of said light, thereby to determine the position of received light on the sensing area.

The method may also include measuring the intensity of detected projected light and/or may include determining the spatial distribution of the intensity of detected projected light.

Preferably, the method includes providing a plurality of light sensors forming an array defining a sensing area in which each light sensor is arranged to generate a detection signal in response to receipt of said light thereby, the method including identifying which of the sensors of an array are in receipt of said light and which of the sensors of the array simultaneously are not in receipt of said light, thereby to permit determination of the position of received light on the array.

The method may include generating a detection signal indicating the intensity of said detected light, and determining from the detection signals the spatial distribution of the intensity of said detected light.

The control signal may be arranged to cause the projector means to shut down if: no light is detected during said monitoring when light is expected to be detected; or, an unsafe condition exists.

The control signal may be arranged to indicate how the projector means should be adjusted to change the location of projected light (e.g. at said surface) .

The control signal may be arranged to indicate how the projector means should be adjusted to adjust the light intensity and/or the spatial intensity profile of projected light at said surface.

The method preferably includes controlling the projector according to the control signal to implement the adjustment indicated in the control signal. The light may be projected as a light beam scanned across the surface to produce the display.

In a third aspect, the invention may provide a projection display apparatus including the control apparatus according to the invention in its first aspect and further including the display surface.

In a fourth aspect, the present invention may provide a vehicle simulator including a control apparatus according to the invention in its first aspect or including a projection display apparatus according to the third aspect of the invention.

In a fifth aspect, the present invention may provide an aircraft simulator according to the invention in its fourth aspect.

In any preceding aspect, the control apparatus may preferably be arranged to monitor projected light in which the projected light is a laser beam.

There now follow non-limiting examples of the present invention with reference to the accompanying drawings in which: Figure 1 schematically illustrates a display projector apparatus including a projector, a display screen and a projector control apparatus;

Figure 2 schematically illustrates an example of a raster-type scan path of a point of projected laser light upon the display screen of figure 1 as determined by the projector;

Figure 3 schematically illustrates example of a calligraphic-type scan path of a point of projected laser light upon the display screen of figure 1 as determined by the projector;

Figure 4 schematically illustrates an example of a light sensor of the control apparatus comprising a sensing area including an array of sensing elements; Figure 5 schematically illustrates an example of detection of a shift in the location of projected light upon the display screen, and the re-calibration of the projector by the control apparatus according to the measure and nature of the detected shift; Figure 6 schematically illustrates an example of the control apparatus in which light sensors are arranged internally of a projector unit.

Figure 1 illustrates a display projector apparatus including a laser projector unit (7), a display screen

(6) upon which the laser projector is arranged to project a beam of laser light (8) to form, instantaneously, a point of projected laser light (14) visible upon the display screen in use, and a projector control apparatus.

Arranged in association with the display screen and the laser projector unit is a projector control apparatus including a group of four light sensors (2, 3, 4, 5) each arranged to be able to receive (and detect) laser light directly from the projector unit (7) and to generate detection signals in response thereto in use, a monitoring unit (1) arranged to receive light detection signals from any one or more of the four light sensors and to generate a control signal according to those signals for use in controlling the projector unit. Each one of the four light sensors is connected to the monitoring unit by a respective one of a group of four detection signal conduits (9, 10, 11, 12) The projector control apparatus also includes a control unit (20) operably connected to both the projector unit (7) and the monitoring unit (1), in the latter case via a control signal conduit (13) . The control unit (20) is responsive to control signals from the monitoring unit to control functions and operations of the projector unit (7) to control the manner in which the projector unit projects the beam of laser light (8) . Each of the four light sensors (2, 3, 4, 5) comprises an array of light sensing elements defining a light sensing area or surface. Each light sensor may comprise, for example, a CCD sensor array, a MOS-type sensor array or any other suitable light sensor apparatus .

Each of the four sensors (2-5) may be mounted upon the display screen (6), or in front of it. Alternatively, the light sensors may be positioned adjacent the display screen, for example to one side of the screen at its periphery. Of course, some or all of the light sensors may be arranged off-screen in this way. In other embodiments, sensors may be internal to the projector unit itself.

In this way, the plurality of light sensors may be arranged in any required configuration or pattern in order to monitor whatever region/area of projection required by the user. Most preferably, the or each light sensor is arranged in association with the display screen so as to be outside the field of view of viewers of the light projected by the projection system. In such an arrangement, the projector unit (7) may be controlled to deflect the laser beam (8) to impinge upon a predetermined light sensor at or during a predetermined time interval . In this way, it is to be understood that any embodiment of the present invention may be arranged such that the control apparatus may monitor light projected at the display screen (6) by the projector unit indirectly by monitoring the detection of light projected off-screen at a light sensor. That is to say, abnormalities in the off-screen projected light indirectly infer an abnormality in on-screen projected light.

The monitoring unit (1) may be any suitable circuitry such as would be readily apparent to the skilled person, or may be a processing unit suitably programmed to respond to detection signals and to generate appropriate control signals in response thereto for transmission to the control unit (20) . The monitoring unit (1) may be a computer such as a PC or the like.

The projector arrangement of figure 1 may be, for example, an image projector machine for use in a vehicle (e.g. aircraft) simulator for projecting a simulated image for view by one or more observers from the cockpit of any position at the simulator machine.

The image projector unit (7) is arranged to generate, for example, a background image representing landscape or terrain. The projector unit may be arranged to generate a light-point image representing points of light or brightness at various locations within a projected background landscape/terrain image. The light-point image projection process is known as "calligraphic" projection in the art.

The term "calligraphic" is a historical term which refers to the manner in which light-points are typically generated in a projected image. Whereas raster-scan image generation processes involve the orderly and repetitious side to side scanning of an image-forming beam (such as a laser beam) across an image forming surface, a "calligraphic" light point is generated by specifically directing (in any direction) the image- forming beam towards specific predetermined points on the image display surface in other than a regular linear scanning procedure. Thus, by a "calligraphic" process, a light point may be "drawn" directly on to an image display surface by the appropriate direct manipulation of the image-forming beam. Conversely, raster-scanning images are effectively indirectly built-up over successive raster-scan lines.

Figure 2 schematically illustrates the process of raster- scan image formation on a display surface (6) using a deflected laser beam. Each frame of a raster-scan image is begun by deflecting the laser beam to one corner of the image display screen (6) . The laser beam is subsequently deflected to scan horizontally across the display screen towards an adjacent corner thereof thereby forming a single image scan line (14a) joining the initial corner with a subsequent corner of the screen. The laser beam is subsequently swept back diagonally (direction 14b) from the terminal end of the first raster-scan line (14a) to be in a subsequent horizontal and parallel scan line (14c) to be formed by horizontal laser beam deflection across the display screen (6) . This process is repeated an additional predetermined number of times resulting in subsequent diagonal deflections (14d, 14f) with intermediate horizontal and parallel laser beam deflections which generate subsequent scan lines (14e, 14g) . At the terminal end of the ultimate horizontal scan line of a given image frame, the laser beam is diagonally deflected from the terminal end of the final horizontal scan line to the beginning of the first horizontal scan line of a subsequent image frame (deflection 14h) . It is to be understood that during each diagonal deflection in-between successive horizontal scan lines, the laser beam is most preferably prevented from impinging upon the display surface (6) by suitable blocking means within the projector unit. Thus, it will be readily appreciated that, when generating a projected image by the raster-scanning of a laser beam, one can expect the laser beam to be deflected in predetermined directions (e.g. to impinge upon predetermined parts of a display surface, or light sensor) at a pre-determined time, or at least during a predetermined time interval. This results from the regular and periodic nature of beam deflection inherent in raster-scanning.

Figure 3 schematically illustrates the process of calligraphic light-point image formation on the display surface (6) . Here, a laser beam is caused to jump from one predetermined location upon the display surface (14i) to a plurality of subsequent predetermined locations (14j-14v) upon that surface, and is controlled to dwell or pause for a predetermined period of time at each location in order to generate at the display surface a light point of predetermined size and/or brightness. Only at the predetermined locations (14i-14v) is the laser beam permitted to settle or dwell, and at times intermediate the settle/dwell times, during which the laser beam is being deflected from one predetermined location to another, the laser beam is either prevented from impinging upon the display surface or is deflected with such rapidity as to be invisible to the human eye.

Once more, the method of calligraphic light point projection also results in an expectation of predetermined laser beam deflections at predetermined times, or during predetermined time intervals (e.g. the dwell/settle time intervals) . Both raster-scanning and calligraphic light point projection techniques share this predictability inherently. Of course, the present invention may be employed in other regulated protection methodologies and is not limited solely to raster- scanning or calligraphic light point projection techniques .

Referring to figure 2 and figure 3, a given one of the four light sensors (2-5) is located upon the display surface adjacent a respective one of the four corners of the display surface. This arrangement is purely for illustrative purposes, and it is to be understood that any suitable positioning of the light sensors may be employed whether internal to the projector unit, upon, in front or to the side of the display surface.

Thus, in one mode of operation, the monitoring unit (1) is arranged to generate a control signal according to whether or not any one of the four sensor means (2-5) detects light during a corresponding respective time interval when the monitoring unit expects light to be detected by the given light sensor. In particular, the monitoring means is arranged to generate a control signal indicating that no detection of light by a given light sensor has occurred during a predetermined time interval when the monitor expected the given light sensor to detect light directly from the projector unit.

Control signals generated by the monitoring unit are then transmitted along signal conduit (13) to the control unit (20) which is responsive to those signals so as to control an operating characteristic of the projector unit (7) thereby to adjust/alter or reverse the projection error which resulted in the generation of the control signal .

Referring to Figures 2 and 3, a first light sensor (2) is positioned upon the display surface (6) so as to directly receive laser light projected by the projector unit during the beginning of the first raster-scan line (14a) of a given frame of a raster-scan projected image. The monitoring unit (1) is arranged to expect such detection at the predetermined interval of time during which the projector unit (7) is supposed or intended to begin the first scan line of each image frame. The absence of such detection during this predetermined/allotted time interval results in the aforementioned control signal being generated. Conversely, the absence of a detection signal from the light sensor (2) during periods of time other than the allotted time interval will not result in the generation of a control signal by the monitoring unit (D •

Similarly, a second light sensor (3) is located at a region of the display surface (6) at which the light projector is supposed to terminate the first projection line (14a) of each raster-scan image frame. Once more, this end of the first scan line can be expected to be generated during certain predetermined time intervals, and the monitoring unit is arranged to monitor this light sensor during those predetermined time intervals and to generate the aforementioned control signal when no light detection occurs .

Second and third separate light sensors (4, 5) are respectively arranged at the locations upon the display surface (6) at which the projector unit is supposed to generate the beginning and end, respectively, of the terminal raster-scan line of a given frame of an image. Of course, the monitoring means is also arranged to monitor light detection signals generated by these latter two light sensors during those respective predetermined time intervals when one would expect the projected laser beam to impinge upon one of those light sensors . Once more, absence of such a detection signal results in generation of the aforementioned control signal by the monitoring unit.

Referring to figure 3, this same arrangement of the four light sensors (2-5) upon the display surface (6) is also suitable for the monitoring of the projection of calligraphic light points upon the display surface. When the projector unit (7) operates as a calligraphic light point projector, it will, when operating properly, direct a laser beam at predetermined points upon the display surface during predetermined pause/dwell time intervals. Each of the four light sensors of the projection control apparatus is located at a respective one of four separate light-point projection locations, and the monitoring unit (1) is arranged to monitor detection signals generated by a given one of these four light sensors during a respective predetermined time interval associated with that light sensor. The absence of such a detection signal causes the monitoring unit to generate the aforementioned control signal. In this way, the monitoring means is arranged to monitor whether or not light is detected during one of a plurality of temporarily separate time intervals at a respective one of each of the plurality of light sensors, and to generate the control signal accordingly.

The control signal may be such as to force the control unit to prevent subsequent projection of light by the projector unit. This may provide a fail-safe mechanism, particularly useful in laser light projectors, which may prevent the projector unit from continued projection in directions which are unsafe. For example, the laser beam deflection apparatus within the projection unit, or the display surface itself, may have altered in position, function or orientation over time with a result that laser light is caused to miss the display surface (and/or a sensor unit) with the possibly hazardous consequences to equipment or persons upon which the misdirected laser beam ultimately impinges .

Additionally or alternatively, the control signal may be arranged to cause the control unit to adjust operational properties of the projector unit without preventing subsequent projection. These adjustments may include adjustment in the direction of projection, in the intensity of projected light, and in the spatial distribution of intensity (i.e. cross sectional) of the projected light beam. The latter control mechanism is particularly useful when controlling a calligraphic light point projector.

Figure 4 schematically illustrates an example of any one, or each of the light sensor units (2-5) employed in the control apparatus. The light sensor comprises a plurality of separate light sensing elements arrayed in a regular array of rows (A-E) and columns (1-5) thereby forming a light sensing surface. This array may be provided by a CCD light sensor array, or by any other suitable light sensor or imaging device (CMOS devices or the like) . Each one of the array of 25 sensing elements (element IA to element 5E) is arranged to generate an individual light sensing signal separately of whether or not any of the other sensing elements also generates such a signal. The monitoring unit (1) is arranged to detect which of the 25 sensing elements has generated a detection signal, and which has not. It is also arranged to detect the strength of each such signal, and to generate a measure of the intensity of light received by a given sensing element according to the strength (or other measure) of the signal so received. This has two consequences . A first consequence, resulting from the ability to measure the intensity of light received at each sensing element, is the ability of the monitoring unit to determine the spatial distribution of projected light intensity across the laser beam impinging upon the sensor unit (sensor unit 2 in this case) in question. As discussed above, the monitoring unit may generate control signals according to these measures, which control signals are arranged to control the projector unit so as to control that cross-sectional light intensity.

A second consequence is schematically illustrated in figures 4 and 5. If, during a first predetermined detection time interval, a given light sensor (2) detects the projected light beam as impinging upon a given sensing element of the sensor surface, for example light point 14w at sensor element 2D, but subsequently detects the light point (e.g. light point 14x) as impinging upon a different sensor element of the array, element 4C for example, then the interpretation made by the monitoring unit (1) is that the projected image has a shifted/drifted in position upon the display surface. By- using the coordinates within the array of the sensor element which initially detected the light point (14w) and the coordinates within the array of the sensor element which subsequently detected that light point (14x) the monitoring unit is arranged to detect both the direction and magnitude of the drift/shift in the position of the projected image upon the display surface in the region of the sensor unit (2) in question at least. Control signals are then generated by the monitoring unit according to the magnitude and direction of the shift in order to adjust operating characteristics of the projector unit so as to rectify or reverse the error therein which resulted in the shift/drift.

Most preferably a plurality of the light sensors of the control apparatus are provided in the form of the array discussed above with reference to figure 4. For example, each of the four light sensors (2-5) of the embodiment of the invention illustrated in figure 1 may comprise a light sensing area formed by a light sensor array of the type describe with reference to figure 4. In such an arrangement the monitoring unit is arranged to determine the magnitude and direction of any shift occurring in predicted light positions upon the respective sensing area which occur during a common image frame. In this way, the monitoring unit may be operable to calculate not only a drift in position of a given image frame but also a drift or change in orientation of that frame. For example, referring to figure 5, consider a first image frame projected upon display surface (6) and resulting in a display W thereupon. Within this frame, a selected light point (e.g. the beginning of a raster-scan line, or a calligraphic light point) associated with the beginning of the frame of display W impinges upon a first sensor (2) at location 140W thereupon. Subsequently, a predetermined light point of the same frame (e.g. the terminal end of the first raster-scan line of the frame, or a selected calligraphic light point) impinges upon a subsequent sensor (3) at location 141W. Subsequent selected light points of this frame impinge upon the remaining two sensors (4, 5) at distinct separate locations (143W, 142W respectively) , and may correspond with opposite ends of the last raster-scan line of the frame, or may correspond with the last few calligraphic light points of the frame.

In subsequent frames, each one of the four light sensors (2-5) detects the projected light beam as impinging upon the respective sensor element array of the sensor at a different location (e.g. locations 140X-143X, for sensors 2-5 respectively) . As a result, the monitoring unit calculates both the magnitude and direction of the change in the detected position of light upon the sensor array of each of the four light sensors, and from this is arranged to calculate the change in position and/or orientation of the projected image at the display surface (6) causing this collective change in detected position.

As can be seen from the schematic example of figure 5, the light sensors positioned to receive light associated with the beginning of the first and last raster-scan lines of a projected frame will each indicate a drift in projected light position inwardly and downwardly of the display surface. Conversely, the two light sensors positioned to detect projected light associated with the terminal ends of the first and last raster-scan lines of a given frame will detect a shift in projected light position upwardly and outwardly of the centre of the display surface. Consequently, the projected image frame with which each of these shifts is mutually associated will be determined by the monitoring unit to have tilted in an anticlockwise sense in the time interval between successive frames. On the basis of these measurements the monitoring unit is arranged to generate control signals to which the control unit (20) of the control apparatus is responsive so as to control operating characteristics of the projector unit (7) to reverse this anticlockwise image rotation, or to effect other alternative or additional control functions to adjust the light projected by the projector unit. It is to be understood that the arrangement illustrated in Figure 1 is purely exemplary, and that light sensor means of the monitoring means and/or the whole monitoring means itself may be located internally of the projector unit (7) employed according to the invention in any of its aspects .

Figure 6 illustrates this alternative embodiment in which like reference numerals are assigned to like articles as between Figure 1 and Figure 6. In the projector arrangement of Figure 6, each of the four light sensors (2-5) , the monitoring unit (1) to which they are operatively connected, and the control unit (20) operatively connected to (and responsive to) monitoring unit (1) are located within the body of the display projector unit (7) . The functionality and operation of each of these components is unaltered by this alternative location and the reader is referred to the functionality of the arrangement illustrated in Figure 1 in this regard. In the alternative embodiment illustrated in

Figure 6, each of the four light sensors (1-5) is located adjacent the beam outlet aperture (700) of the projector unit (7) in order to be in a position to receive display light generated by the light generator (750) of the projector unit at predetermined times. In alternative arrangements, one or more the light sensors may be arranged in conjunction with a beam splitter located in the optical path of the display beam (8) generated by the light source (750) so as to receive a portion of the display light directed to it via the beam splitter. This enables light sensors to be arranged at virtually any location within the body of the display projector unit (7) . Of course, other optical deflector means, instead of or in addition to optical beam splitters, may be employed in directing portions of display light away from the direction of display projection and towards a light sensor of the monitor.

It is to be understood that modifications and variations of the above embodiments of the present invention, such as would be readily apparent to the skilled person, may be made without departing from the scope of the present invention .

Claims

CLAIMS :

1. A control apparatus for a display projector for projecting light onto a surface for display, the control apparatus including a monitoring means having a light sensor means and being arranged to monitor light generated by the display projector for projection at the surface and to generate a control signal according to whether or not display light generated by the display projector is detected by the light sensor means, and control means for controlling an operation of the display projector means according to the control signal thereby to control the projection of light.

2. A control apparatus according to any preceding claim in which a light sensor means of the monitoring means is arranged to be attached to the display projector to sense light generated by the display projector.

3. A control apparatus according to claim 2 in which the light sensor means is arranged to be located within the display projector to sense display light generated by the display projector within the projector.

4. A control apparatus according to any preceding claim wherein the monitoring means is arranged to generate the control signal according to whether or not the sensor means detects light from or generated by the display projector by direct receipt thereof.

5. A control apparatus according to any preceding claim in which the monitoring means is arranged to generate a control signal indicating when no detection of light from or generated by the projector means has occurred at the light sensor means when the monitoring means had expected light detection to occur.

6. A control apparatus according to any preceding claim and arranged to receive projection signals indicating when, in use, the monitoring means can expect light to be detected by the light sensor means .

7. A control apparatus according to any preceding claim in which the monitoring means is arranged to detect a change in the location of projected light and to generate a control signal indicating detection of such a change and/or a measure of that change.

8. A control apparatus according to any preceding claim wherein the monitoring means is arranged to monitor detection by the light sensor means of light from generated by the projector during successive predetermined time intervals, and to generate the control signal according to whether or not display light of the projector is detected during such a time interval .

9. A control apparatus according to any preceding claim including a plurality of said light sensor means each one of which is arranged to be located at a respective one of a plurality of separate locations in use.

10. A control apparatus according to claim 9 in which the monitoring means is arranged to monitor whether or not said light is detected during one of a plurality of temporally separate time intervals, at a respective one of each of the plurality of light sensor means and to generate said control signal accordingly.

11. A control apparatus according to any preceding claim including a light sensing area wherein the monitoring means is arranged to identify which parts of the light sensing area are in receipt of said light and which parts of the sensing area simultaneously are not in receipt of said light, thereby to determine the position of received light on the sensing area.

12. A control apparatus according to any preceding claim in which the monitoring means includes a light metering means arranged to measure the intensity of the projected light received by a light sensor means .

13. A control apparatus according to any preceding claim in which the monitoring means is arranged to determine the spatial distribution of the intensity of projected light received by an aforesaid light sensor means.

14. A control apparatus according to any preceding claim including a light sensing area defined by a plurality of said light sensor means forming an array in which each light sensor means is arranged to generate a detection signal in response to receipt of said light thereby.

15. A control apparatus according to claim 14 wherein the monitoring means is arranged to identify which of the light sensor means of an array are in receipt of said light and which of the light sensor means of the array simultaneously are not in receipt of said light, thereby to determine the position of received light on the array.

16. A control apparatus according to any preceding claim including a plurality of said light sensor means forming an array, each light sensor means being arranged to generate a detection signal indicating the intensity of said light received thereby, the monitoring means being arranged to generate from the detection signals a control signal from which the spatial distribution of the intensity of projected light received by the array of light sensor means is derivable.

17. A control apparatus according to any preceding claim in which the control means is arrange to shut down the projector means in response to a control signal indicating that: no light was detected by a light sensor when light was expected to be detected thereby; or, an unsafe condition exists.

18. A control apparatus according to any preceding claim wherein said control signal indicates how the projector means should be adjusted to change the location of projected light at said surface.

19. A control apparatus according to any preceding claim in which the control signal indicates how the projector means should be adjusted to adjust the light intensity and/or the spatial intensity profile of projected light at said surface.

20. A control apparatus according to any of claims 18 and 19 wherein the control means is responsive to the control signal to control the projector means so as to implement an adjustment indicated by the control signal.

21. A control apparatus according to any preceding claim in which the light is projected as a light beam and the projector means is arranged to scan the light beam across the surface when projecting light to produce the display.

22. A control apparatus according to any preceding claim including the display projector.

23. A control apparatus according to claim 22 and claim 2 or 3 in which the display projector includes said light sensor means .

24. A method of controlling a display projector for projecting light onto a surface for display, the method including monitoring the light generated for projection by the display projector at the surface by generating a control signal according to whether or not display light generated by the display projector is detected, and controlling an operation of the display projector means according to the control signal to control the projection of light.

25. A method according to claim 24 including generating the control signal according to whether or not display light generated by the display projector is internally detected within the display projector.

26. A method according to claim 24 or 25 including generating the control signal according to whether or not light from or generated by the display projector is detected by direct receipt thereof.

27. A method according to any of claims 24 to 25 including generating a control signal indicating when no detection of light from or generated by the projector means has occurred when detection of that light was expected.

28. A method according to any of claims 24 to 27 including monitoring the projected light to detect a change in the location of projected light, and generating the control signal to indicate detection of such a change and/or a measure of that change.

29. A method according to any of claims 24 to 28 including monitoring detection of light from or generated by the projector during successive predetermined time intervals, and generating the control signal according to whether or not display light of the projector is detected during such a time interval .

30. A method according to any of claims 24 to 29 including monitoring detection of light at a plurality of separate locations in use.

31. A method according to claim 30 including monitoring whether or not said light is detected during a respective one of a plurality of temporally separate time intervals at a respective one of each of the plurality of locations and to generate said control signal accordingly.

32. A method according to any of claims 24 to 31 including providing a light sensing area, and monitoring the detection of light over a light sensing area and identifying which parts of the sensing area are in receipt of said light and which parts of the light sensing area simultaneously are not in receipt of said light, thereby to determine the position of received light on the sensing area.

33. A method according to any of claims 24 to 32 including measuring the intensity of detected projected light.

34. A method according to any of claims 24 to 33 including determining the spatial distribution of the intensity of detected projected light.

35. A method according to any of Claims 24 to 34 including providing a plurality of light sensors forming an array defining a sensing area in which each light sensor is arranged to generate a detection signal in response to receipt of said light thereby, the method including identifying which of the sensors of an array are in receipt of said light and which of the sensors of the array simultaneously are not in receipt of said light, thereby to permit determination of the position of received light on the array.

36. A method according to any of claims 24 to 35 including generating a detection signal indicating the intensity of said detected light, and determining from the detection signals the spatial distribution of the intensity of said detected light.

37. A method according to any of claims 24 to 36 in which the control signal is arranged to cause the projector means to shut down if: no light is detected during said monitoring when light is expected to be detected; or, an unsafe condition exists .

38. A method according to any of claims 24 to 37 wherein said control signal indicates how the projector means should be adjusted to change the location of projected light at said surface.

39. A method according to any of claims 24 to 38 in which the control signal indicates how the projector means should be adjusted to adjust the light intensity and/or the spatial intensity profile of projected light at said surface.

40. A method according to any of preceding claims 38 to 39 including controlling the projector according to the control signal to implement the adjustment indicated in the control signal.

41. A method according to any of claims 24 to 40 in which the light is projected as a light beam scanned across the surface to produce the display.

42. A projection display apparatus including the control apparatus according to any of claims 1 to 23 further including the display surface.

43. A vehicle simulator including a control apparatus according to any of claims 1 to 23 or including a projection display apparatus according to claim 42.

44. An aircraft simulator according to claim 43.

45. A control apparatus according to any of preceding claims 1 to 23 or 41 to 43 in which the projected light is a laser beam.

46. A method according to any of preceding claims 23 to 41 in which the projected light is a laser beam.

47. A control apparatus substantially as described in any one embodiment hereinbefore with reference to the accompanying drawings.

48. A method substantially as described in any one embodiment hereinbefore with reference to the accompanying drawings .