Projection apparatus

• US 20040218155A1
• Filed: 04/05/2004
• Published: 11/04/2004
• Est. Priority Date: 10/05/2001
• Status: Active Grant

• Current Assignee: Fraunhofer-Gesellschaft
• Original Assignee: Fraunhofer-Gesellschaft ZUR Forderung Der Angewandten Forschung EV
• Inventors: Wolter, Alexander, Schenk, Harald, Schwarzenberg, Markus
• Granted Patent: US 6,843,568 B2
• Time in Patent Office: Days
• US Class Current: 353/98
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G02B 26/105 with one or more pivoting mirrors or galvano-mirrors G02B26/101 takes precedence
• CPC Class Codes: G02B 27/18 for optical projection, e.g. combination of mirror and condenser and objective photographic, cine and overhead projectors G03B21/00; photographic projection printing G03B27/32; photolithographic projectors G03F7/20; projection television H04N5/74; colour projection television H04N9/31
• CPC Class Codes: H04N 5/7416 involving the use of a spatial light modulator, e.g. a light valve, controlled by a video signal

Abstract

The present invention is based on the finding that the previous column and row representation in the scanning image projection has to be given up, in order to enable that the ratio between row and column frequency or vertical and horizontal deflection frequency is not critical and may be decreased. An inventive projection apparatus for projecting an image on an image field includes a deflection means for deflecting a light beam about a first deflection axis at a first deflection frequency and about a second deflection axis at a second deflection frequency different from the first, in order to move the light beam across the image field, as well as a modulation means for modulating an intensity of the light beam depending on the image to be projected. The first and second deflection frequencies differ by less than an order of magnitude.

Claims

1. Projection apparatus for projecting an image on an image field, comprising:

a deflection means for deflecting a light beam about a first deflection axis and about a second deflection axis in order to move the light beam across the image field; and

a modulation means for modulating an intensity of the light beam depending on the image to be projected, wherein the first and second deflection frequencies differ by less than an order of magnitude,

characterized in that

the deflection means is formed such that the light beam is deflected about the first deflection axis at a first deflection frequency f₁ and about the second deflection axis at a second deflection frequency f₂, wherein the deflection means comprises means adjusting the frequency ratio to f₁;

f₂=n;

m, with m and n being unequal integers, so that the light beam describes a Lissajous figure on the image field and repeatedly passes through it with a repetition frequency f_r of f_r=f₁/n=f₂/m.

2. Projection apparatus of claim 1, wherein the deflection means has a first resonance frequency with reference to the deflection about the first deflection axis and a second resonance frequency with reference to the deflection about the second deflection axis, and wherein the first deflection frequency lies in the vicinity of the first resonance frequency and the second deflection frequency in the vicinity of the second resonance frequency.

3. Projection apparatus of claim 1, wherein the first and second deflection frequencies are greater than 500 Hz and n and m are greater than 10.

4. Projection apparatus of claim 1, wherein the difference between n and m is 1.

5. Projection apparatus of claim 1, wherein the image to be projected is defined by pixels arranged as an array in columns and rows, wherein each pixel is associated with an image area on the image field and wherein the deflection means deflects the light beam such that the light beam crosses through image areas of different rows on the image field before it has reached all image areas of a complete row.

6. Projection apparatus of claim 5, wherein the modulation means is adapted to modulate the intensity of the light beam depending on in which of the image areas a momentary projection place of the light beam in the image field is and according to the pixel associated with the image field in which the momentary projection place of the light beam is.

7. Projection apparatus of claim 1, wherein the deflection means comprises:

a means for fading out the light source as soon as the light beam is deflected in a margin area of the image field by the deflection means.

8. Projection apparatus of claim 1, wherein the modulation means performs the modulation of the intensity of the light beam based on a momentary projection place of the light beam on the image field and image data defining the image.

9. Projection apparatus of claim 8, wherein the modulation means comprises:

a means for determining the momentary projection place based on either a momentary first and second deflection angle of the light beam or based on a time signal using a predetermined connection between the first and second momentary deflection angles of the light beam and the time.

10. Projection apparatus of claim 1, wherein the deflection means comprises:

a synchronization means for sending the time signal to the modulation means for the synchronization of the modulation means with the deflection means, wherein the time signal indicates reversal points in the deflections of the light beam by the deflection means.

11. Projection apparatus of claim 1, wherein the deflection means is arranged to send information about the first and second momentary deflection angles to the modulation means.

12. Projection apparatus of claim 1, wherein the modulation means is arranged to feed a reference voltage to the deflection means, which has a progress in time corresponding to a target progress in time of at least a first or a second momentary deflection angle of the light beam.

13. Projection apparatus of claim 1, wherein the deflection means is arranged to send a trigger signal to the modulation means.

14. Projection apparatus of claim 1, further comprising:

a rendition means for changing an order of pixel values in an input data stream defining the image and for feeding a control signal to the modulation means, which corresponds to the input data stream in changed order.

15. Projection apparatus of claim 1, further comprising:

a rendition means for interpolating the image at positions corresponding to image points of the image field, in order to obtain interpolation values, wherein the modulation means is adapted to perform the modulation on the image points based on the interpolation values.

16. Projection apparatus of claim 1, wherein the deflection means includes either one biaxially suspended movable mirror or two uniaxially suspended movable mirrors.

17. Projection apparatus of claim 1, which further comprises a light source for creating the light beam.

18. Projection apparatus of claim 1, wherein the projection apparatus is a miniaturized projection apparatus in which the deflection means comprises one biaxially suspended or two uniaxially suspended mirrors that are micromechanically manufactured.

19. Method for projecting an image on an image field comprising:

deflecting a light beam about a first deflection axis and about a second deflection axis, in order to move the light beam across the image field; and

modulating an intensity of the light beam depending on the image to be projected, wherein the first and second deflection frequencies differ by less than an order of magnitude,

characterized in that

the step of deflecting is performed such that the light beam is deflected about the first deflection axis at a first deflection frequency f₁ and about the second deflection axis at a second deflection frequency f₂, for which f₁;

f₂=n;

m applies for unequal integers n and m, so that the light beam describes a Lissajous figure on the image field and repeatedly passes through it with a repetition frequency f_r of f_r=f₁/n=f₂/m.