REFLEX OFF-AXIS COLLIMATING DISPLAY
This invention adapts an off axis collimator to enable it to merge real world and synthetic data. This system can be used to provide a head up display for automobiles.
Automobile design provides copious quantities of data for to the driver. Multifunction displays are used to manage this information. In addition, the introduction of automated enforcement systems places additional demands on driver attention. The driver though is poorly served in the presentation of information requiring visual attention to be directed away from the roadway being negotiated.
Head up displays have been proposed that adapt aviation systems or use invehicle projection systems that are expensive and limiting. Many of these displays are not collimated.
This invention provides a simple low cost display that can be integrated into a dashboard or glareshield and includes a reversionary mode for use in difficult ambient lighting conditions. It provides a collimated image of the displayed information close to the line of sight so that the minimal re-direction of attention enables ready access to such information. The system largely replaces the existing process of data acquisition, viz. move eyes away from roadway, search for appropriate instrument, refocus eyes, assimilate information, return gaze to the roadway, refocus eyes, update situation.
Off-axis collimators that use spherical image sources and tilted spherical mirrors are commonly used to provide large held of view display devices especially for flight and ground vehicle simulations. In these systems a spherical projection screen is located close to the focal surface of a spherical mirror. Such systems are well described in prior art. A number of systems have been described in which the spherical screen is replaced with a planar surface and which have an accompanying optical correction system either through the use of aspheric mirrors or other transmission/reflection components. In addition there are a class of display systems that utilise a spherical mirror / planar source combination to provide magnifying viewers that are not collimators.
In this invention a plane image source is located close to the focal surface of an inclined spherical mirror. This arrangement will produce acceptable levels of collimation providing only a small fields of view of around 5 are required. Two characteristics affecting the collimation are the radius of curvature of the mirror and the linear extent of the image source. Both of these characteristics govern the approximation of the plane of the image to that of a sphere. Variations from the ideal spherical surface can therefore be kept small and consequently, vergence errors can
be kept acceptable.
There are significant benefits in utilising a plane image source as miniature high resolution micro-displays can be simply employed.
According to the present invention there is provided a visual display apparatus, for presenting simultaneously within a user's line of sight a real image and a virtual image of synthetic data, comprising: - a display means from which said synthetic data originates and - a collimator which collimates light from said display device to create said virtual image within said user's line of sight of said real image wherein said display device is positioned substantially at the focal surface of said collimator.
A plane light emitting data display is located before a concave spherical mirror. The relative positions of the display surface and mirror section is such that light reflected towards an observer is essentially collimated such that the display surface appears to be located some distance away (Fig 1). A mirror is located directly between the observer and the spherical mirror and inclined to the reflected light so that it is directed out of the line of sight. Located at the exit aperture is an image combining element that is inclined so that a proportion of the light emerging is directed towards the observer (Fig 2). Data formed on the display surface will appear as a ghost image located some distance in front of the vehicle. If the mirror is moved so that it doesn't intercept the light reflected from the spherical mirror then the image is directly accessible to the observer (Fig 3).
By adjusting the corresponding inclination of the plane mirror and beamsplitter the image location can be made to appear substantially coincidental for both modes of operation.
In an alternative configuration (Fig 4) a plane mirror replaces the image combining element but inclined so as to direct light into the system. An image combining element is located within the body of the system and inclined so as to direct light incident from the plane mirror above towards the observer. Light emitted from the source is reflected by the spherical mirror and is transmitted through the image combining element towards the observer.
Such a device could be used to overlay real world scenes with synthetic data that is spatially significant.
The size and quality requirements of the optical components would enable them to be produced at a low cost and the system could be largely produced as a sealed unit.
Such components may be located within a dashboard assembly. Once assembled there would be no need to adjust the system for optical alignment. Some pitch and yaw adjustment of the entire unit may be necessary to facilitate normal variations in users' viewing position.
It is envisaged that an automatic gain control would be added to the system so that the displayed image brightness would track ambient light levels in addition to offsets or user preferences.
A light attenuating device may be located between the image combining device and the outside world or a mirror may replace the image combining device to improve brightness ratios.
The various features and advantages of the present invention may be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawings wherein like reference numerals designate like structural elements and in which; Figure 1 depicts a side elevation ray tracing of a basic off-axis collimator.
Figure 2 depicts a ray tracing of the invention in normal operating configuration.
Figure 3 is the same as figure 2 but with the invention configured in the reversionary mode.
Figure 4 depicts a ray tracing of an alternative configuration of the invention.
Referring now to the drawings in Figure 1; item 1 comprises a light emitting source that is substantially having a plane geometry such that the light emanating from the source does or appears to originate from a 2D planar surface. This device need not necessarily be self luminous but may constitute a light valve in that it is a light modulating device such as a liquid crystal display (LCD) or such i.e. moving mirror display (MMD) , grating light valve (GLV) etc. Item 2 comprises of a reflecting concave spherical mirror possessing horizontal and vertical dimensions appropriate for the required display field of view and disposed in accordance with the principles of the invention such that item 1 is located close to the focal surface of item 2. Item 2 shall in plan view be arranged symmetrically with respect to item 1 such that item 1 shall lie directly between the centre of curvature of item 2 and the pole or centre of the mirror. In the vertical plane and as illustrated in Figure 1 item 2 is inclined such that light reflected from its surface is substantially not impeded by item 1 and corresponds to off axis collimator practice.
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In operation light reflected from item 2 and leaving the system will be substantially collimated over a small field of view. Item 1 may be orientated so that keystone geometry errors are optimised with respect to collimation. In the intended application of information display geometric distortion of the image is not considered to be a significant factor. With raster displays forming item 1 objectionable distortion can be addressed through pre-distorting the source image through available techniques, i.e. pixel mapping, that may be incorporated into the display processor function.
Referring now to Figure 2; items 1 and 2 remain as described before but now items 3 and 4 are included. Item 3 comprises a plane or flat mirror that is substantially disposed so that light reflected from item 2 is directed towards the corresponding element item 4. Item 3 together with its supporting structure shall obstruct item 2 from view. Item 3 shall be mounted so that it may be moved out of the light path of item 2 and this will be described in further detail in the following paragraph. Item 4 is a combining element that will be preferentially served by a plane beamsplitter that possesses the properties of both transmitting and reflecting relative proportions of incident light. Thus a proportion of the light reflected from item 3 shall be subsequently reflected by item 4 towards the observer who will then observe the image displayed on item 1 superimposed on the outside scene directly in line with item 4.
Figure 3 now illustrates substantially the same invention as depicted in figure 2. In this illustration item 3 has been moved out of the path of light reflected from item 2 so that this light proceeds unimpeded towards the observer. This provides a reversionary mode of operation for instances when ambient light conditions become unfavourable for viewing via the combiner.
Referring now to figure 4 which depicts an alternative configuration of the invention and in which item 1 the plane image source and item 2 the concave spherical mirror retain substantially the same relationship as depicted in figure 1 such that light reflected from item 2 is incident upon item 4 a combining element and a proportion of this incident light is transmitted towards the observer. In this embodiment item 4 would take the form of a beamsplitter. Item 4 is disposed such that light entering the invention from item 3 shall be proportionally reflected by item 4 towards the observer.
Item 3 is a plane mirror and is disposed such that light from the outside world and originating in the direction in which the observer is viewing is merged with reflections from item 2 such that the data displayed on item 1 shall substantially correspond.
In this embodiment the invention as described in Figure 4 would be mounted on movable orthogonal axes with attached rotational encoders such that the orientation of the invention is identified and can be input into a data processing unit. Alternative orientation devices are available that may also be applicable.
In figures 2 & 3 the reflex system comprising item 3 together with item 4 are disposed in the vertical plane. These can, however, be orientated in other planes, for instance the horizontal, in order to accommodate packaging requirements.