System and method for high resolution volume display using a planar array

An image display apparatus comprises a main display and an auxiliary display. The main display is used to produce a volumetric image such as graphical image, and the auxiliary display is used to generate two dimensional image such as text image. The auxiliary display is located adjacent the the main display and being able to move relative to the main display along a path extending in a direction substantially circumferential to the main display.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to a system and method for a high resolution, fully
 addressable volumetric display using a planar array.
 2. Brief Description of the Prior Act
 It has been known in the prior art to modulate or scan a beam, such as a
 laser beam, and then to project the scanned beam onto a screen. Examples
 of such systems are set forth in the Brief Description of the Prior Art in
 Garcia, Jr. et al. U.S. Pat. No. 5,042,909 and as well as in that patent.
 The prior art listed hereinbelow is incorporated herein by reference.
 Such autostereoscopic volumetric display systems and methods have been
 described in the prior art and include a vertical planar screen rotated
 about a vertical axis, a first mirror located away from the vertical axis
 facing and below the screen which is also rotated with the screen about
 the same vertical axis and a second mirror located on the same rotational
 vertical axis, rotated with the screen and the first mirror and tilted so
 that an image projected parallel to the vertical axis is reflected from
 the second mirror to the first mirror and from the first mirror to the
 screen. The disclosures in the patents to Solomon (U.S. Pat. No.
 4,983,031), Garcia (U.S. Pat. No. 5,042,909) and Botchko (U.S. Pat. No.
 5,148,310) are exemplary of such prior art. Methods of generating such
 images using one or more scanned serial light sources are also described
 in the prior art as exemplified by the disclosures in the above mentioned
 Garcia and Botchko patents. Transformations are further described which
 translate a serial light beam input into flat images which are
 subsequently projected onto various display surfaces, this being
 exemplified in the disclosures of each of the above-mentioned patents.
 Image sources described in the prior art comprise serial light sources
 where a light beam is cut into slices and projected onto the display. This
 limits the ability of the prior art to generate an image with resolution
 sufficiently high to be useful or to place a sufficient number of points
 of light simultaneously onto the display screen. The term "simultaneously"
 is defined herein as--appearing to the viewer to be simultaneous--even
 though the points of light are not initially generated simultaneously in
 time. Defects inherent in the prior art as described hereinabove include
 distortion, focus and image rotation errors.
 The prior art also describes gas ion laser image sources which cannot
 generate full color images. Generating any color other than red, green or
 blue requires illuminating the same physical location simultaneously with
 more than one laser (in the case of a multicolor system including colors
 other than the primary colors). For example, a yellow point requires both
 a red and a green laser. To accomplish this, first, multiple lasers must
 be very precisely aligned to generate a single point. Voltage controlled
 oscillators or scanners suffer from both non-linearities of positioning
 and electrical drift. This, in essence, prevents the perfect alignment of
 multiple image sources which is necessary to generate nonprimary colors.
 Second, using two or more points of laser light to generate one viewable
 spot significantly reduces the number of points of light available to form
 an image, further reducing the resolution of the display.
 One well known problem with volumetric displays is selection of the viewing
 perspective from which to display text and other two-dimensional symbology
 or icons. Although the volumetric image may be both viewable and useful
 from all aspect angles, it is impossible to pre-select the position of the
 viewer. Furthermore, doing so would obviate the usefulness of a volumetric
 display which can be viewed from all sides. This problem is not addressed
 by the prior art.
 SUMMARY OF THE INVENTION
 In accordance with the present invention, the aforementioned problems
 inherent in the prior art as well as other problems are overcome or
 minimized. There is provided a three-dimensional, full color, fully
 addressable high resolution display system. The system generates
 three-dimensional images by projecting light beams onto a rotating
 surface. The size of the spinning surface defines the projectable volume.
 Points are plotted in a pre-defined two-dimensional space (x-y, z-r or
 other coordinate system). The flat images are projected against the
 spinning display surface using mirrors and lenses. When the light beams
 strike the display surface, the surface diffuses the beam to form a point.
 By timing the light beams as the rotating surface sweeps through the
 display volume, the light patterns allow viewers to perceive a
 three-dimensional image.
 A planar light array is controlled to place multiple beams of light
 simultaneously onto the display surface, enabling high resolution images
 to be generated. Unlike gas-ion laser systems described in the prior art,
 the system can generate full color images. In the preferred embodiment,
 three planar arrays are used, with a white illumination source and filters
 or dichroic beam splitters to separate the incoming light into red, green
 and blue components. In a second embodiment, three planar arrays are used,
 each with a separate illumination source. The illumination sources or
 lamps are red, green and blue, respectively. In a third embodiment, a
 tri-colored wheel (red, green, blue) is used with a white illumination
 source and image generation is timed to generate full color images.
 Because all of the elements of the array of the first and second
 embodiment can be used simultaneously to place light onto the display
 surface, generating full color displays does not reduce the points of
 light available for the images.
 Volume display system practice is refined and extended by defining a system
 which corrects defects inherent in the prior art, including distortion,
 focus and image rotation errors by defining a modular, optical system
 which allows the effective interface of various image sources, including
 non-scanned planar arrays, to display devices of various configurations
 and by defining a configuration in which the first rotating mirror may be
 replaced by a fixed toroidal mirror, further simplifying the mechanical
 complexity. An auxiliary display can be provided to augment the
 three-dimensional images with text. This auxiliary display may be
 positioned anywhere around the circumference of the volumetric display.
 An image is projected along an optical axis which is parallel to the
 rotation axis. For mechanical practicality, it is desirable to minimize
 the size of the first rotating mirror to reduce the moment of inertia that
 must rotate and to minimize the diameter of the optics below the second
 mirror so that a shaft may be formed which can be supported by
 through-mounted bearings of minimum size. In order to satisfy these
 constraints, a pupil must be formed by the optics at or near the second
 mirror. For mechanical convenience, the optics within the shaft will
 rotate with the mirrors and screen, but are not required to do so. Due to
 the configuration of the rotation axis with respect to the projected
 image, the image will appear to rotate about the center of the screen. A
 planar image source of fixed pixel arrangement will not generally be used
 efficiently in this case, because the array must be oversized to allow for
 the image rotation. In this situation, optical means for derotation of the
 various configurations such that they contain an odd number of
 reflections, is rotated about the optical axis in such a way as to
 counteract the image rotation induced by the rotation of the original
 mirrors and screen. Alternatively, image sources which do not necessarily
 include a fixed pixel pattern may correct for image rotation optically as
 above or electronically or in software.
 For aesthetic reasons, the first mirror is placed below the rotating screen
 in order to avoid entering the line-of-sight of the viewer. As a result,
 the screen is effectively tilted with respect to the original axis. This
 results in two defects. First, the image cannot be in focus throughout the
 full screen area and second, a non-symmetric distortion commonly known as
 keystone distortion afflicts the image. For the focus error, two solutions
 are provided. First, the cone angle of the light converging to each image
 point may be reduced to minimize the effect of the defocus. This solution
 is limited by the optical invariant and results in reduced illumination at
 the screen, but is practical for scanned laser systems, at least. The
 second solution results from the application of the Schelmpflug effect,
 tilting the image source in such a way as to compensate for the apparent
 tilt of the screen. The second error may be solved electronically, for
 example, by warping the raster of a CRT used as an image source or in
 software, by calculating the warping of the object to compensate for the
 optical keystone.
 The optical system is intimately associated with a particular mechanical
 configuration in order to satisfy the mechanical constraints described
 above, yet must be sufficiently flexible to allow for various potential
 image sources. By providing for a modular interface at the end of the
 rotating mechanical shaft, various optical configurations can be easily
 implemented. The optical system associated with the rotating display is
 designed to accept light of a specified nature. In general, the interface
 will occur in a collimated space, with a real pupil. A maximum aperture
 diameter and field angle are specified at the interface pupil. For a given
 screen format, these values then define the focal length and f/ number of
 the display optics. Hence, various display formats can be designed, all
 with the same interface parameters. Similarly, on the source side of the
 interface, optical systems are designed for various types of light
 sources, including CRT, scanned lasers, emitting arrays, such as laser
 diode arrays, or reflective arrays, such as digital micromirror device
 arrays. Each system is designed to have the same parameters at the
 interface and therefore can be used with any display system designed with
 the same parameters. Since not all sources will require correction of
 image rotation and/or keystone distortion and/or image plane tilt, these
 corrections are not provided on the display side. Such correction must be
 added, as necessary, on the source side of the interface.
 A further refinement of the display eliminates the first rotating mirror,
 reducing the moment of inertia of the mechanical system. A fixed toroidal
 or conical mirror, symmetric about the axis of rotation, can be used to
 provide the same function as the rotating mirror. Because of the geometry
 of the toroidal mirror, severe constraints are placed on the optical
 system. In particular, the mirror located on the axis of rotation and the
 optics adjacent thereto will be much larger due to the pupil being more
 distant from the fixed mirror than it would have been from the rotating
 mirror which was replaced. Of course, this method of use of the fixed
 toroidal or conical mirror to replace the first rotating mirror can be
 designed with the modular interface as well, allowing conversion to this
 method when optical and mechanical tradeoffs are justified.
 Other potential improvements include dual off-axis optical systems which
 project on both sides of the screen simultaneously, thereby effectively
 doubling the available scene detail. Constraining the image to either the
 left or right half of the screen increases resolution while still allowing
 the whole volume to be addressed (at the expense of more potential
 scheduler conflicts).
 A "Head-Up Display" is placed on a track which runs around the
 circumference of the volumetric display. The display is movable along the
 track to a position convenient to the viewer, eliminating the need to
 predefine the position of the viewer. Two-dimensional icons and/or text
 are projected onto the Head-Up Display. The projection system for the
 Head-Up Display moves on a carriage with the Head-Up Display screen. The
 Head-Up Display provides transparency through which the volumetric display
 may be viewed if the viewer so desires. The Head Up Display further
 increases the resolution of the volumetric display by removing the
 requirement for the volumetric display to display text. All points of
 light on the volumetric display can thus be used for volumetric images.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring first to FIG. 1, there is shown a display system in accordance
 with the present invention. The system comprises a work station 1 which is
 a standard commercial computer whereat software including image data base
 functions and manual data entries can be performed to control a three
 dimensional display system or advanced volume visual display (AVVD) 3
 interconnected by a voxel bus 25. The work station 1 includes a standard
 keyboard and monitor 5 as well as host graphics accelerator hardware, such
 as, for example, an Analogic Corp. Model MSP 6C30 which performs
 conversions and table look-ups very rapidly necessary to generate the
 display list or dlist (all of the information required to recreate a three
 dimensional image for a complete rotation of the disk or screen), data
 storage and data processing equipment 7 to store application program
 interface (API) software, correction software, host system software and
 host graphics. The data processing equipment includes all of the software
 required to program the display and some of the software to convert the
 program into the electronic signals that drive the device. The three
 dimensional display system 3 includes an image projector 9 with projector
 electronics 11 for projecting a two dimensional image, the image projector
 being. embodied by any of the prior art two dimensional image projectors
 or being a matrix of digital micromirror devices (DMDs), also known as
 deformable mirror devices (DMDs), such as , for example, described in U.S.
 Pat. No. 5,061,049 of Larry J. Hornbeck, projector optics 13 for
 projecting and derotating the two dimensional image as will be explained
 hereinbelow, a motor 15 and mechanical assembly 16 for driving the screen
 17, synchronization electronics 19 for synchronizing the two dimensional
 image projected by the image projector with the speed of the motor and a
 containment dome 21 within which the display is disposed. It should be
 understood that though specific forms of DMDs are discussed herein, types
 of such devices which can be operated digitally or non-digitally and which
 provide various gradations of reflected light in addition to only on or
 off can be used and are contemplated for use in conjunction with the
 invention. The screen 17 can be a flat vertical screen, as shown, a helix,
 a double helix and other surface configurations. An optional Head-Up
 Display 23 (not shown in FIG. 1) for auxiliary text, symbology or icons
 can be provided on the display system and either be stationary or
 translate around the circumference of the external dome 21. The interface
 between the work station 1 and the three dimensional display hardware 3 is
 the voxel bus 25.
 The host system software comprises the host system operating system,
 networking capabilities, windowing system and tools such as libraries and
 compilers. The application program interface (API) software is the
 software that provides a programmer access to the advanced volume
 visualization display (AVVD) and provides an object oriented approach to
 programming applications. The API includes the SIGMA classes and the AVVD
 library which is a more traditional function oriented set of routines and
 support libraries. The correction software provides corrections to display
 lists that are the result of electrical mechanical and optical noise or
 nonlinearities. The work station high speed bus is one of the main buses
 of the host system and represents the interface between the main
 CPU/memory and the host graphics accelerator. Some examples are VME,
 S-bus, Future Bus, SCSI and M-Bus. The host graphics accelerator is the
 hardware that provides fast computations for scheduling and image
 transformations as well as a high speed image output rate to the AVVD. The
 scheduling and image transformations could also be performed in software
 and part of the main CPU, rather than with graphics accelerator hardware.
 The voxel bus is the link between the host computer and the AVVD. The
 image projector is the system that generates synchronized RGB images in
 two dimensions that are displayed on the rotating screen. The projector
 electronics receives data from the voxel bus and drives the projector's
 light valves and or modulators. The projector optics provides focusing and
 optical derotation prior to light entering the rotating mechanical system.
 The synchronization electronics takes information from the mechanical
 assembly regarding the screen position and uses it to control the rotation
 speed and the image update rate of the image projector. The screen is a
 flat surface either rectangular or semicircular supported vertically and
 covered with a diffusive coating. As the screen rotates, light is
 projected and diffused, resulting in three dimensional images. The
 external dome is mainly for safety reasons as well as reducing air
 turbulence. The motor drives the mechanical assembly and rotates the
 screen. The mechanical assembly is composed of the rotating screen, the
 motor, the vertical optics shaft (to be described hereinbelow) and
 positional sensing electronics to indicate the rotational position of the
 screen.
 The image projector is an electro-optical system that combines images
 generated from three independent subsystems. Each of the independent
 subsystems (RGB) is capable of generating parallel randomly addressed
 points of light. This array of individually addressable light sources is
 updated in rapid succession to generate a sequence of frames that, when
 projected onto the rotating screen, produces three dimensional images.
 Each element of the array is also capable of modulating to produce various
 levels of shading.
 Several embodiments of image projectors are shown in FIGS. 2a to 2e. All of
 these embodiments use passive subsystems which are illustrated using
 external light sources. Active subsystems would only have outgoing light
 with no external light source.
 Referring first to FIG. 2a, there is shown an image projector having a
 light source 31, which can be either a white light source or independent
 red, green and blue (RGB) sources (coherent or incoherent). The light
 passes to a first dichroic beam splitter 33 which passes two of the three
 colors from the light source and reflects the third color onto a digital
 micromirror device (DMD) 35 which, depending upon. the voltage on the
 control electrode 37 thereof, controls the deflection of the DMD anywhere
 from zero or no deflection of the light to deflection of all of the light
 impinging thereon back along the light path travelled by the other two
 colors. This same action takes place at the second and third dichroic beam
 splitters 33' and 33" except that each of these beam splitters is
 responsive to a different one of the three colors generated by the light
 source 31. The result is that some combination of red, green and blue
 light (the amount of transmitted light of one or two of the colors can be
 zero) is ultimately reflected onto the output path 39 to provide the
 desired color programmed into the DMDs 37, 37' and 37".
 Referring to FIG. 2b, the system operates as above described except that
 the initial light from the light source 31 is broken into the red, green
 and blue light components by the prism 41 and lens 43. The light
 components are individually directed thereby to DMDs 35, 35' and 35" and
 reflected therefrom onto dichroic beam splitters 33, 33' and 33", all of
 which direct the individual colors along the same output light path 39 to
 provide the desired color.
 Referring now to FIG. 2c, the light source 31 directs light as in FIG. 2a
 except that the reflected light from each DMDs 35, 35' and 35" is
 reflected to dichroic beam splitters 33, 33' and 33" which reflect and
 pass light as shown so that the three light paths coincide and provide the
 output light path 39 of the desired color.
 Referring now to FIG. 2d, the light source 31 directs light to dichroic
 beam splitters 49 and 49' which reflect one color to a first DMD 35 which
 can reflect some or all of such light back to dichroic beam splitter 49
 and then onto output light path 39. The remainder of the light from the
 light source 31 travels to mirror 491, part of which is reflected to DMD
 35' and then back to mirror 49' and then to light path 39 and the
 remainder of the light passes through mirror 49' to DMD 35", this light
 being reflected back through mirror 49' to the output light path 39.
 Referring now to FIG. 2e, the light source 31 provides light through a
 prism 41 and lens 43 as in FIG. 2b which breaks up the light into three
 separate paths, each path of a single one of the colors red, green and
 blue. The light paths strike a convex mirror 51 which reflects each light
 path to an individual DMD 35, 35' or 35". The light is reflected from the
 DMDs in accordance with the signals on the control electrodes 37, 37' or
 37" thereof via dichroic beam splitters 33, 33' and 33" onto the output
 light path 39 to provide the desired output color.
 All of the mirrors referred to above with reference to FIGS. 2a to 2e which
 both transmit light of predetermined frequencies therethrough and reflect
 light of predetermined frequencies are preferably dichroic beam splitters.
 The DMDs reflect back anywhere from none to substantially all of the light
 impinging thereon, this being dependent upon the signal of the control
 electrode 37, 37' or 37" thereof.
 The projector optics 13, which is shown in detail in FIG. 3, provides the
 proper focusing and optical derotation for the images emanating from the
 image projector 9. The projector optics as set forth in FIG. 3 also
 includes the common optics disclosed in FIGS. 4a to 4d.
 The projector optics includes a lens relay 81 which receives the output 39
 from the image projector and matches this output to the common optics with
 regard to collimation, field angle and entrance pupil diameter. The
 matched light from the relay lens 81 is passed to a derotation prism 83
 which rotates at one-half the angular velocity of the screen to compensate
 for the rotation of the image on the screen caused by the system design
 and causes the image to stand upright on the screen. The derotation prism
 may be one of several possible configurations, all of which share the
 characteristics of having an odd number of reflections, for example, Dove
 prism, Schmidt prism, Pechan prism, K-mirror. The prism 83 is rotated by a
 derotation drive system 85 which synchronizes the rotation thereof to the
 rotation of the screen 17 directly through, gears or by electronic
 synchronization in standard manner. This can also be accomplished with
 software. The output of the derotation prism is a two dimensional image
 located at the modular interface plane 87 which is, a conceptual line
 separating the projection optics from the common optics and which can be a
 scanned image as in the above described prior art or an instantaneous two
 dimensional image as would be provided when the image projector utilizes
 DMDS. The light at the modular interface plane is now operated upon by the
 common optics which includes a fold mirror 89. which directs the image
 through the lens 91 and the refocus and projection lenses 93 in the hollow
 main shaft 57 and optics sleeve 59 therein of the motor rotor (to be
 explained in detail hereinbelow) to the fold mirror 67. The image is then
 reflected onto a last fold mirror 69 which rotates with the screen 17 and
 projects the image onto the screen as will be explained in detail
 hereinbelow.
 Referring now to FIGS. 4a to 4d, there is shown the mechanical assembly,
 which includes the screen, motor and external dome. The mechanical
 assembly includes, as shown in FIGS. 4a and 4b, support legs 53 to which
 is secured a motor housing 55 having a main shaft 57 therein with an
 optics sleeve 59 within the main shaft. Motor control and synchronization
 signal circuitry 61 extends to the motor housing 55 for controlling the
 motor in standard manner. The motor housing includes a support portion 63
 to which is secured a fold mirror support structure 65. On the support
 structure there is disposed a first mirror 67 above the optics sleeve 59
 which reflects light impinging thereon from the optics sleeve onto the
 last fold mirror 69 which is secured to the support structure 65. Light
 from the mirror 69 is reflected onto the vertical screen 17 which is
 secured to the support structure 65 by a screen support 71. A counter
 weight 73 is disposed on the support structure 65 diametrically opposite
 the mirror 69. The external dome 21 is positioned over and around the
 screen 17 and contains the three dimensional image therewithin.
 The motor 54 comprises the motor housing 55 within which are included
 standard motor stator windings and magnets 75 secured thereto and bearing
 supports 77 as shown in FIG. 4c into which the motor rotor is disposed.
 The motor rotor is shown in FIG. 4d and includes a hollow main shaft 57
 with inner windings 82 disposed about the upper portion of the main shaft
 with support and main bearings 84 which mate with the bearing supports 77
 secured to the housing 55. By providing appropriate control signals to
 the. motor electronics 61 and current to the stator windings 75, as is
 well known, the rotor rotates at selected rotational speed with the
 bearings 83 rotating in the bearing supports 77. As will be explained in
 more detail hereinbelow, a two dimensional light array of an image from
 the image projector 9 and projector optics 13 travels through the optics
 sleeve 59 and the optics therein to the first mirror 67 from which it is
 reflected to the fold mirror 69 and then onto the screen 17. The rotation
 of the screen at a rotational speed synchronized to the projection of the
 light image thereon provides the three dimensional image within the
 external dome 21 in known manner as described in the above noted prior
 art.
 As an alternative embodiment, the motor stator can be eliminated and the
 main shaft 57 can be disposed in bearings or the like and driven by a
 gearing system coupled to the exterior of the shaft to cause the shaft
 rotation. The rotational speed of the gearing system is adjusted in
 standard manner to synchronize the rotation of the screen 17 with the
 formation of the two dimensional images.
 As is apparent, it is necessary that the exact location of the screen 17 in
 its rotational cycle be known in order that the images to be projected
 thereon can be scheduled and synchronized therewith. Accordingly, an
 encoder mechanism (not shown) of standard type is disposed on the rotor or
 elsewhere to provide the exact screen location. Signals indicative thereof
 are then transmitted to the appropriate electronics to provide required
 scheduling and synchronization. This is shown schematically with reference
 to FIG. 5 wherein the disk rotation motor 101 is the motor shown in FIGS.
 4c and 4d and provides a signal to an optical encoder 103 to provide an
 indication of the motor and screen position. The optical encoder 103 then
 provides this position information to a motor controller 105 which, in
 turn, controls the rotational speed of the motor 101. The positional
 signals from the optical encoder 103 are also transmitted to a derotation
 prism slave motor controller 107 which also receives positional signals
 from an optical encoder 109 indicating the position of the derotation
 prism 83. The controller 107 then controls the rotational speed of the
 motor, drive system or the like 85 to cause the prism 83 to rotate in
 synchronism with the screen 17. The circuitry for performing the functions
 of the blocks in FIG. 5 is well known and need not be discussed in detail.
 Referring now to FIG. 6a, there is shown a circuit to adjust the system
 on-line for nonlinearly varying components caused by, for example,
 optical, thermal and/or electrical drift which can degrade the image
 quality for any scanner or array based system, in this case, volumetric
 displays. This is accomplished by providing a sensor 121 which senses the
 degradation and indicates such degradation to a compensation electronics
 circuit or feedback electronics 123 which recognizes the type of
 degradation and provides a compensating or error signal. This feedback
 circuit 123 is a set of analog to digital converters and timing control
 circuits which, on command from system electronics 125, samples the output
 of sensors 121 and passes the sampled output as a digital feedback signal
 to system electronics 125. Compensation for nonlinearities occurs in
 system electronics 125 via a microprocessor controlled lookup table.
 System electronics 125 determines the contents of these lookup tables by
 using a classical control system approach which is that, at reasonable
 intervals, the microprocessor outputs a known positioning signal to the
 laser 129. The laser beam passes through optical system 131 and
 illuminates fold mirror 133 and the sensor 121. A measurement of exact
 position is made by feedback electronics 123 under control of system
 electronics 125 which compares the exact location versus expected location
 and computes an error. New lookup table values are calculated with
 corrections made to compensate for this error and incorporated into the
 lookup table in system electronics 125. Accordingly, the signals now
 entering the nonlinear components 127 have now been compensated to offset
 the nonlinearity in such components. Accordingly, the signal to the image
 projector 39, for example, a laser 129, adjusts the laser output. The
 image projector output then travels through the optical system 131 as
 described hereinabove and to the fold mirror 133 which corresponds to the
 fold mirror 89, 67 or 69.
 The sensor(s) 121 can be disposed in one of the fold mirrors as shown in
 FIG. 6b. In this case, the sensor(s) are located immediately beneath the
 reflective surface of the mirror to allow light to pass to the sensors. A
 fold mirror associated with sensors will have some translucency so that
 the image impinging upon the mirror can travel to the sensor. The sensors
 are placed in precise locations so the signals fed back therefrom can be
 correlated with the precise location of each sensor in the compensation
 electronics.
 The projector electronics 11 for use in conjunction with DMDS, is shown in
 greater detail in FIG. 7, receives data signals from the graphics
 accelerator of the workstation 1 at a control board 141 via the voxel bus
 25. The received data is placed in a FIFO buffer awaiting transfer to the
 DMD Memory and Timing Board 143. At the appropriate time, as controlled by
 board 143, data is transferred from the FIFO to board 143. The graphics
 accelerator control board 141 is a multipurpose custom circuit board which
 generates timing synchronization signals for DMD memory and timing control
 boards 143, 143' and 143" using the disk position optical pickup 103. The
 exact disk or screen 17 position is received at the disk position optical
 pickup 103 and transferred to the control board 141. The graphics
 accelerator control board 141 also interprets system control signals from
 the host graphics accelerator and changes operational characteristics
 (such as DMD timing and number of DMD mirrors updated and the order of the
 update) for DMD memory and control boards 143, 143' and 143"; signals the
 host graphics accelerator that a volume frame has been displayed; swaps
 memory buffers in the DMDS memory and timing control boards 143, 143' and
 143" using a double buffering technique to refresh the display from one
 memory buffer while downloading data from the host graphics accelerator to
 another memory buffer; and receives data from host graphics accelerator
 and control voxel bus handshaking. The control board 141 also includes a
 microsequencer to coordinate the information received on the bus 25. The
 circuit 141 synchronizes the data received on bus 25 so that it can be fed
 into the DMD memory. The clocks are synchronized by the control board 141
 which uses a pulse train generated by the disk position optical pickup 103
 when the screen 17 rotates. These pulses are converted via a programmable
 phase locked loop on circuit 141 to the number of slices per revolution of
 the screen 17. For each slice, the control board 141 sends a pulse to the
 DMD boards 143, 143' and 143" to begin the timing sequence to display one
 slice. The information (all of the information required to recreate a
 three dimensional image for a complete rotation of the disk or screen) is
 then sent to DMD memory and timing control circuitry 143, 143' and 143" on
 a color by color basis, there being one such circuit for each of red,
 green and blue. DMD memory and timing control circuit boards 143, 143' and
 143" are sent color data simultaneously from the host graphics
 accelerator. Each board has a corresponding color control bit in the data
 which word identifies it as a destination. Auxiliary timing, as required,
 is also provided by these circuits. The outputs of each of the circuits
 143, 143' and 143" are sent to DMD boards 145, 145' and 145" respectively
 to provide the controls on the control electrodes 37 of the DMDs 35 as
 shown in FIGS. 2a to 2e to control the angle of deflection of the DMD and
 thereby control the intensity of the light reflected from the DMD. Some
 timing circuitry is provided in this circuit also.
 The Projector Subsystem Control Board 141 shown in FIG. 7a has several main
 functions and contains line receivers and drivers for receiving and
 sending data and control information via the voxel bus 25 from the host
 graphics accelerator. In addition, data received at board 141 is placed in
 a FIFO buffer awaiting transfer to the DMD Memory and Timing Control Board
 143. At the appropriate time, as controlled by board 143, data is
 transferred from the FIFO to board 143. A set of control registers is
 loaded from the graphics accelerator board, these registers controlling
 which of two video random access memory (VRAM) banks on boards 143, 143'
 and 143" receives data and which of these two VRAM banks on boards 143,
 143' and 143" send data to the DMD boards 145, 145' and 145". The control
 registers also control whether the above functions are swapped on a volume
 frame interrupt as well as whether to clear one of the VRAM banks on
 boards 143, 143' and 143" on a volume frame interrupt. The control
 registers also control other functions such as the number of rows and the
 number of vertical slices for boards 143, 143' and 143" to send to the DMD
 boards 145, 145' and 145".
 The disk position optical pickup produces a pulse train which is converted
 via a programmable phase locked loop to slice interrupt pulses and volume
 frame interrupt pulses. For each slice interrupt pulse, the DMD Memory
 boards 143, 143' and 143" initiate a timing sequence in step with boards
 145, 145' and 145" downloading a vertical slice from VRAM boards 143, 143'
 and 143" to the DMD boards 145, 145' and 145" DMD devices.
 The DMD Memory and Timing Control Board shown in FIG. 7b has two principal
 functions, these being holding display data in VRAM band #0 and band #1
 and controlling this VRAM. There are two separate banks of VRAM so that
 one bank can be used to refresh, that is, send a volume frame's data to
 DMD boards 145, 145' and 145", while the other bank can be loaded from the
 graphics accelerator board via the projector subsystem control board 141.
 This avoids memory access conflicts that would occur if boards 145, 145'
 and 145" and board 141 accessed the same VRAM bank.
 Circuitry used for timing generates the appropriate addressing and control
 signals to the VRAM bank to write voxel data at the maximum data rate
 possible, given the limitations of the VRAM memorytiming characteristics
 and to generate control signals to the VRAM bank to read back data clocked
 (timed) in step with the DMD device on the DMD boards 145, 145' and 145".
 Other functions include controlling VRAM refresh, a necessary part of
 dynamic random access memory (DRAM) usage and VRAM bank clear, which
 clears a VRAM bank to all zeros on command from the projector subsystem
 control board 141.
 The DMD boards 145, 145' and 145" shown in FIG. 7c each contain circuitry
 to support the DMD device. They include circuitry to address the DMD
 devices, generating consecutive row and column addresses that direct
 incoming data from the VRAM on boards 143, 143' and 143" to the correct
 micro-mirror row and column. The DMD boards 145, 145' and 145" also
 contain timing circuitry which controls the timing of address and reset
 voltages to the DMD devices as well as power control circuitry which
 protects the DMD devices from damage caused by incorrect input voltages
 and incorrect device control timing.
 Referring now to FIG. 8, there is shown a schematic diagram of the work
 station electronics, the projector electronics 11 and the synchronization
 electronics therefor. The work station electronics includes the host
 system CPU which is the main host computer and is the location of the API
 software. The host CPU communicates via a host bus with the graphics
 accelerator which is, for example, a TMS320C40 based processor that
 voxelizes, schedules, corrects and communicates with the DMD subsystem.
 The graphics accelerator communicates via the voxel bus, which is a direct
 digital transfer with line drivers and receivers, with the Projector
 Subsystem Control Board 141 which buffers in a first infirst out (FIFO)
 buffer, voxel data. The DMD memory system communicates with DMDs on a DMD
 board which contains the DMDs and device voltage control and bitplanes or
 slices loaded into the DMD device from the DMD memory system 143, 143' and
 143". The DMD memory system communicates with a DMD controller which
 receives synchronization signals from the motor controller via the system
 synchronization unit. The system synchronization communicates with the DMD
 controller and motor control and includes circuitry which insures proper
 synchronization among the motor controller, derotation prism and DMD
 subsystem. The derotation prism includes circuitry that controls the
 derotation prism and must be synchronized with the motor control. The
 motor control controls the speed of the main rotation system and receives
 feedback from encoders for system synchronization.
 There are many types of software which can be successfully utilized in
 conjunction with the host system. The host system software dictates the
 platform or type of computer used to drive the AVVD. Unix platforms
 including Sun (SunOS-Solaris), Silicon Graphics (Irix), Hewlett Packard
 and IBM RS-6000 systems can be used. Also, PCs running DOS and Windows as
 well as Apple systems and PCs running some type of Unix or OS/2 can be
 used as the host system.
 The API software comprises (1) the SIGMA classes and (2) the AVVD library.
 The SIGMA classes comprise a set of routines that are similar to SGI gl or
 OpenGL. These functions allow for rendering of images, transformations,
 color manipulations, setting of image attributes (point densities) and
 system communication.
 The correction software is to provide compensation for electrical,
 mechanical and optical nonlinearities or deviations from theoretical
 thresholds. In many cases, known hardware problems can be corrected in
 software at a fraction of the cost of rebuilding or retrofitting existing
 hardware. This correction or compensation is seen in derotation to address
 compensation for image rotation resulting from the rotating screen as well
 as in Keystone correction which results from image plane/screen
 misalignment and lookup tables for remapping of scanned or array address
 values that are not in their theoretical position (possibly due to a
 non-functioning pixel, DMD or the like).
 The system control flow is shown in FIG. 9 which is self-explanatory.
 Referring now to FIG. 10a, there is shown an elevational view of a three
 dimensional display, the work station primary monitor (CRT) and Head-Up
 Display in accordance with the present invention. FIG. 10b is a top view
 of the Head-Up Display assembly as shown in FIG. 10a. The work station
 sends graphics or text information across the work station (SCSI) bus to
 the primary display monitor CRT and simultaneously sends either the same
 or different information through a VME-chassis or other bus communication
 card to the communication bus on the HUD. With some combinations of work
 stations and applications, it will be necessary to use a commercially
 available circuit board (such as the Video Splitter for the Silicon
 Graphics) which enables a programmer to drive two different graphics
 application displays simultaneously from the same work station.
 The user commences operation of the display system by generating
 application data on the work station. Data may be (a) xyz points in ASCII
 or binary format, (b) a file with a known format containing point, line or
 facet data, (c) an ASCII Object File (AOF) that contains data already
 converted to be compatible with the SIGMA software, (d) a routine which
 generates three dimensional lines, points or facets or (e) some previously
 undefined data format. The user may generate his own program which
 manipulates his own special data formats or may use the SIGMA command line
 utilities if data is in formats (a), (b) or (c) supra. These SIGMA (C++)
 classes or the AVVD library which runs on top of the SIGMA classes allow
 the user to specify procedures to be invoked which will manipulate (e.g.,
 scale, rotate, translate, etc.) the images when they are displayed. After
 the desired manipulation is defined, the data is in an array format of (x,
 y, z, color, priority). Then the user invokes the scheduler which converts
 this data into a binary array of commands (display list or dlist) for the
 projector electronics where position in the array is related to the
 rotational timing. This dlist is a temporary data structure for a specific
 display image which has been converted into binary commands for the
 projector electronics.
 In the preferred embodiment, the dlist is passed by the API software from
 the work station CPU or disk drives to the Host graphics accelerator which
 communicates via the voxel bus 25 with the AVVD display subsystem 3. In
 one alternative embodiment only the host system CPU remains on the work
 station, allowing multiple work stations to communicate with the AVVD. In
 another alternative embodiment, the host system CPU/memory, work station
 high speed bus, host graphics accelerator and voxel bus are all embedded
 inside the AVVD or the Host graphics accelerator is physically within the
 AVVD display.
 The dlist commands are received by the projector electronics 11 which
 converts the dlist commands into on/off commands for the image projector 9
 (DMDs) at the times specified by the dlist. The DMDs deflect to either
 reflect of not reflect light, creating a two-dimensional image. The
 two-dimensional image is reflected off the DMDs through the projector
 optics 13, where it is transformed into a stable image by the derotation
 system 85. The projected image is reflected off a first fold mirror 89
 into the main shaft 57 containing refocus and projection lenses 93 which
 create an image of the proper size, focus and alignment. The image is
 reflected off a second fold mirror 67 onto the rotating screen assembly
 17. During this process, the disk rotation motor 101 rotates the screen
 17, synchronized to the speed of the derotation prism motor 111 by the
 derotation prism slave motor controller 107. Disk position information is
 passed by the disk position encoder 103 to the projector electronics to
 synchronize the generation of the two-dimensional image with the
 rotational position of the screen. When the two-dimensional image strikes
 the screen, the screen diffuses the light beams to form discrete points of
 light which, due to the rotational component of the screen, appear to form
 a three-dimensional image suspended in space.
 Though the invention has been described with respect to specific preferred
 embodiments thereof, many variations and modifications will immediately
 become apparent to those skilled in the art. It is therefore the intention
 that the appended claims be interpreted as broadly as possible in view of
 the prior art to include all such variations and modifications.