3-D HOLOGRAPHIC ELECTROMECHANICAL METER

Abstract: A 3-D holographic meter having a first fixed hologram (19) for creating a meter dial face virtual image, a second rotatable hologram (21) for creating a rotating pointer on the dial face, a shaft (23) for rotating the rotatable hologram in response to a variation in a measured parameter and an illumination source (27) for the fixed and rotatable holograms.

Description: 3-D HOLOGRAPHIC ELECTROMECHANICAL METER BACKGROUND OF THE INVENTION 1. Field of the Invention The subject invention relates to displays and, more particularly, to a holographic display which creates a virtual image representing a meter. 2. Description of Related Art Conventional electromechanical dial instruments provide a method for an observer to assimilate infor¬ mation rapidly without reading a number by glancing at the coarse position of an indicator needle. Persons whose eyes cannot accommodate to near distances have difficulty reading such instruments. In addition, the time required to assimilate information from such instruments, while relatively rapid, still involves an outside-distant to inside-instrument viewing accommodation delay. At least one prior art automobile instrument display has mounted a tachometer outside the front fender of an automobile at some distance from the driver. While this system provided a distant image, it was subject to criticism as being too small, too expensive and subject to obstruction by rain or snow. SUMMARY OF THE INVENTION According to the invention, an electromechanical meter is made to appear as a virtual image at a distance without additional collimating optics by physically moving a first hologram in relation to a second so that the first hologram generates a fixed reference background and the second hologram generates a moving positional indicator on the fixed reference background. The movable hologram is preferably moved by a shaft or by other mechanical elements associated with conventional transducers, for example, as used in automotive instruments. The invention permits modification of current automotive instruments at moderate cost so that they can be read by farsighted individuals. BRIEF DESCRIPTION OF THE DRAWINGS The just summarized invention will now be described in detail in conjunction with the drawings of which: FIG. 1 is a pictorial illustration of a meter configuration according to the preferred embodiment; FIG. 2 is a schematic diagram of a meter according to a first preferred embodiment; FIG. 3 is a schematic design of a meter according to a second preferred embodiment utilizing a converter hologram; FIG. 4 is a schematic diagram illustrating distortion of a holographically generated pointer by off—axis illumination; FIG. 5. is a schematic diagram illustrating a wavefront converter hologram; FIG. 6 is a schematic perspective diagram illustrating the construction of a wavefront converter hologram; FIG. 7 is a schematic diagram illustrating use of a master hologram; and. FIG. 8 is a schematic diagram of the hologram of FIG. 6 perpendicular to the optical axis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT _0 The following description is provided to enable any person skilled in the optical and automotive fields to make and use the invention, and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain _5 readily apparent to those skilled in the art since the general principles of the present invention have been defined herein specifically to provide a relatively economical and easily manufactured holographic electromechanical meter. 0 FIG. 1 discloses a hologram arrangement for creating a virtual image 12 of an electromechanical meter, including a rotating pointer 11 on a dial face 13. The virtual meter image 12 is created by a dial face hologram 15 and a rotating pointer hologram 17. 5 FIG. 2 illustrates the preferred embodiment of a holographic meter 14 in an automobile. A first fixed holographic disc 19 creates the image of the meter face 13. The meter face 13 may include indicia of a parameter of vehicle operation, for example, vehicle speed or fuel Q consumption. A second rotating holographic disc 21 provides the rotating pointer 11. The shaft 23 normally used for the mechanical pointer of, for example, an automobile speedometer or tachometer, extends through an opening 24 in the fixed disc 19 and is fixedly attached to the rotating disc 21. The shaft 23 is driven by a suitable transducer 26, as conventionally used in automobiles, in order to pivot or rotate the disc 21. Various other rotating mechanisms are possible including stepping motors and suitable gearing mechanisms. The holographic discs 19, 21 are illuminated by a suitable illuminator source 27 attached to the steering column 29 of the automobile. A virtual image 12 of a pointer 11 on a dial face 13 is thereby created on the side of the discs 19, 21 opposite the viewer 30. Holographic procedures for forming holograms such as holograms 19, 21 can be found in known reference works, such as "Optical Holography" by Collier et al., Academic Press, New York, N.Y. (1971). If desired, the holographic image can be developed to be particularly sensitive to only a predetermined bandwith of the illumination source. As is well known in the holographic field, the hologram can be made to operate over a broader wavelength band giving increased brightness for a broadband source, but trading off increased coloration provides a lower photo—optic see-through capability. FIG. 3 discloses an improved embodiment wherein a holographic converter disc 35 is inserted between the off-axis illumination source 27 and the rotating holographic disc 21. The converter disk 35 is designed to provide a radially symmetrical illumination wavefront to the holographic discs 19, 21 to create a more accurate virtual image 12. The utility of such an off-axis source will now be discussed in conjunction with FIG. 4. As shown in FIG. 4, when the illumination comes from an illumination source 27 located off the optical axis 37, such as at "A", the pointer image 11 can change with rotation. If the pointer 11 is rotated 180 degrees, 5 for example, the effect would be the same as moving the illumination source to "A*". The effect on the image could be a movement of the pointer 11 from a point touching the axis 37, as at "B", to a position spaced away from the axis 37, as at "C". At position "C", the O pointer 11 no longer properly aligns with a fixed holographic dial face 13. Also, the pointer image would be very dim because it is now generated by a light source that is not at the reference beam angle. The pointer image movement might be small enough to tolerate in an j ς "in-plane" hologram, but would become more severe for the deep holograms needed to provide far-sighted eye compen¬ sation. The apparent solution to the problem is to illuminate the hologram with an on-axis source, as at points "D" or "E". o However, placing the illumination source on-axis at points "D" or "E", creates other problems. For a reflection hologram, the source blocks the view of the hologram. For a transmission hologram, the undiffracted light shines directly back into the eyes of the viewer. 5 Improved operation which avoids distortion and viewer interference employs the fixed converter hologram 35 to modify off-axis illumination to create a radially symmetric wavefront for illuminating the on-axis holograms 19, 21. One embodiment of a converter hologram 0 35 is shown in FIG. 5 where the light from on off-axis source "F" is converted to the rays of a radially symmetric wavefront "G." The off-axis illumination SUBSTITUTE SHEET source "F" is located at an angle Q to the optical axis 37. As will be discussed in more detail, the converter hologram 35 contains a recorded interference pattern, preferably recorded in pie-shaped segments, which creates the radially symmetric wavefront. While the converter hologram 35 shown provides a reflected radially symmetric wavefront, a converter hologram for providing a trans¬ mitted radially symmetric wavefront, such as illustrated in FIG. 3, may be readily constructed according to the technique hereafter described. The construction of the converter hologram 35 is illustrated in FIG. 6. According to FIG. 6, a hologram recording plate 45 is sandwiched by a dual mask 40 providing first and second pie—shaped openings 47, 49. The openings 47, 49 are oppositely disposed and in common alignment. The recording plate 45 is rotated while the dual mask 40 remains stationary such that a series of congruent pie—shaped areas ai , a∑ , ... an are successively exposed to the two construction wavefronts 31, 33. The two wavefronts 31, 33 compromise the wavefront 31 from a reference point source "H", and a radially symmetric wavefront 33 from a source "J". The point source "H" is positioned at an angle ® to the optical axis 37 equal to the angle φ between the off-axis illumination source "F" and the optical axis 37 (FIG. 5). As shown more particularly in FIG. 7, prior to exposing the second pie segment a2 , the point source "g ti ^ s ro tated by an angle Δθ such that the second pie segment a2 receives the rays from the point source "H" at the same angle as it would if the mask were removed from the unrotated recording plate and the point source H held fixed at its original position. The angle ΔΘ is the angle between the respective bisectors 51, 53 of the equal size pie segments ai , az . The pie segment technique is useful in that it is difficult to provide a radially symmetric source "J" over a large area of the recording plate 45. While lines are created at the edges of the adjacent pie segments, these do not impair performance in the applications under consideration. The technique can be used to create a reflection converter hologram such as that shown in FIG. 5 by locating the radially symmetric source "J" on the opposite side of the recording plate from the point source "H" and conducting the same successive exposure procedure. In order to produce converter holograms 35 with low cost and high rate, only a master hologram 45 is exposed by the successive segment method of FIG. 6. The master 45 is then used to produce low cost copies in the same manner as low cost point-of-sale scanner holograms are now manufactured. This technique is illustrated in FIG. 8 where a reference beam J impinges on a hologram master 45 located behind a hologram recording plate 48. In response to the reference beam, the master 45 generates a radially symmetric object beam over the full surface of the recording plate 48. It is possible to generate a radially symmetric wavefront by the use of conventional optical elements in those cases where space allows the use of auxiliary optics to shape the wavefronts. Compared to conventional optics, however, the converter hologram has the advan¬ tages of requiring less space, weight and cost. It will be apparent from the above discussion that numerous adaptations and modifications of the disclosed embodiment may be made without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Claims: CLAIMS What is Claimed is 1. A holographic meter for displaying the value of a measurement unit of a parameter comprising: a fixed hologram means for creating a virtual image reference background in response to incident illumination; a movable hologram means for creating a movable indicator on said reference background in response to incident illumination; means for moving said movable hologram in response to said value; and means for illuminating said fixed hologram means and movable hologram means to provide said incident illumination. 2. The holographic meter of Claim 1 wherein said parameter is a parameter of motor vehicle operation. 3. The hologram meter of Claim 2 wherein said means for moving includes a shaft means attached to said movable hologram means. 4. The holographic meter of Claim 3 wherein said means for illuminating includes an off-axis light source. 5. The holographic meter of Claim 4 wherein said light source is attached to the steering mechanism of a motor vehicle. 6. A holographic meter comprising: a fixed hologram means for creating a virtual image of a dial face having indicia of scale thereon in response to incident illumination; a rotatable hologram means for creating a virtual image of a pointer on said dial face for pointing to a selected one of said indicia in response to incident illumination; means for rotating said rotatable hologram means in proportion to variation of a parameter of operation related to said indicia; and means for illuminating said fixed hologram means and rotable hologram means to provide said incident illumination. 7. The holographic meter of Claim 6 wherein said indicia of scale indicate a parameter of motor vehicle operation. 8. The hologram meter of Claim 7 wherein said means for rotating includes a shaft means attached to said rotatable hologram means. 9. The holographic meter of Claim 8 wherein said means for illuminating includes an off—axis light source. 10. The holographic meter of Claim 9 wherein said light source is attached to the steering mechanism of a motor vehicle.

Inventors: MOSS GAYLORD E, MOSS, GAYLORD, E.
Applicants: HUGHES AIRCRAFT CO, HUGHES AIRCRAFT COMPANY
Application year: 1987
Main classification: G01D7
IPC codes: B60K35, G01D7, G02B5, G03H1, G12B11