JP2006343397A - Image projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniform the lightness of a projected image in an image projector which projects an image on a screen by raster-scanning laser beams by using an MEMS (Micro Electro Mechanical System) resonance mirror. <P>SOLUTION: The raster on the screen 14 is made uniform in lightness by adjusting the light emission intensity of the laser light corresponding to the variation in the raster scanning speed in horizontal direction when a horizontal scan is performed by an resonance scan and a vertical scan is performed by a static scan by using the MEMS resonance mirror 15 and a laser scan is performed by outputting respective pixel image data of three primary colors R, G and B by indicating the address in a frame memory 17. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image projection apparatus that raster scans laser light using a MEMS (Micro Electro Mechanical System) resonant mirror and projects an image on a screen.

  Conventionally, for example, a projector (image projection apparatus) is used to project an image stored in a personal computer onto a screen.

  As an image projection method in this image projection apparatus, an optical image is generated by transmitting strong light from one side of a transmissive liquid crystal panel on which an image to be projected is displayed, and this optical image is passed through an optical lens. There is a transmitted light system that magnifies and projects the image onto a screen.

  On the other hand, there is a laser beam scanning method in which a screen is projected by irradiating a laser beam of three RGB colors constituting pixels of an image to be projected onto a screen (see, for example, Patent Document 1).

  In the case of such a laser beam scanning image projection apparatus, it is necessary to use a micromechanical mirror, a galvanometer mirror, or the like in order to scan the laser beam. Patent Document 1 describes that a mirror having a so-called gimbal structure may be used.

A MEMS resonant mirror is commercially available as a gimbal structure mirror (for example, see Non-Patent Document 1).
JP 2003-021800 A Nippon Signal Co., Ltd., “ECO SCAN” [online], product information, [searched on May 25, 2005], Internet <URL: http://www.signal.co.jp/vbc/mems/index.html >

  In the conventional device for raster scanning of laser beams, a mechanical mirror is required. However, when a resonant mirror for MEMS application as shown in Non-Patent Document 1 is used, resonant operation is performed in a horizontal scan for scanning at high speed. Is used.

  However, since the scanning speed accompanying the scanning operation changes in a sine curve during this resonance operation, the scanning speed of the left and right cut-back portions changes slower than the central portion of the horizontal scanning. For this reason, there has been a problem that the center portion of the projected image displayed on the screen becomes dark and the left and right edge portions become bright.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an image projection apparatus in which the brightness of a projected image is uniform even when a laser beam is raster scanned using a MEMS resonant mirror. To do.

  The image projection apparatus according to claim 1, wherein a laser beam is raster-scanned using a MEMS resonant mirror and an image is projected onto a screen, and the laser beam is emitted in response to a change in a horizontal raster scan speed. A control means for adjusting the strength is provided.

  The image projection apparatus according to claim 2 is characterized in that in the image projection apparatus according to claim 1, the output of the projection image is prohibited during a fixed period at both right and left ends of the raster scan in the horizontal direction.

  According to the image projecting device of the first aspect, since the emission intensity of the laser light is adjusted in response to the change in the raster scan speed in the horizontal direction, the bright spots of the image projected on the screen have uniform brightness. To be able to.

  According to the image projecting device according to claim 2, in the image projecting device according to claim 1, since the output of the projected image is prohibited during a certain period at both right and left ends of the horizontal raster scan, the vertical scan Further, it becomes possible to project an image without distortion by blanking the image output at both the left and right end portions where the horizontal scanning speed fluctuates significantly during the unstable period of the mirror turning operation accompanied with the.

  Therefore, according to the present invention, it is possible to provide an image projection apparatus in which the brightness of a projected image is uniform even when a laser beam is raster scanned using a MEMS resonant mirror.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of an image projection system using an image projection apparatus that raster-scans a laser beam with a MEMS resonant mirror according to an embodiment of the present invention and projects an image on a screen.

  This image projection apparatus includes an image projection control circuit 10 and a red laser beam, a green laser beam, and a blue laser beam corresponding to the R, G, and B3 primary color image signals output from the image projection control circuit 10, respectively. The laser beams from the red laser light source 12R, the green laser light source 12G, the blue laser light source 12B, and the laser light sources 12R, 12G, and 12B including the optical lens system L for emitting and outputting light are focused on the RGB laser beam LRGB having a single pixel density. A trichromatic prism 13 and a RGB laser beam LRGB having a one-pixel density converged and output by the trichromatic prism 13 in the direction of the screen 14 and a raster scan with respect to the projection surface 14a of the screen 14 The MEMS resonant mirror 15 for this is provided as a main component.

  A personal computer 11 is connected as an image information source to the image projection control circuit 10. The image to be projected is not limited to image data stored and managed by the personal computer 11 and may be any image information output from various images and video equipment such as a digital camera.

  The image projection control circuit 10 (see FIG. 2) has a system interface 16 for inputting an image information signal output from the personal computer 11, and image data for one screen based on the image information signal input by the system interface 16. Frame memory 17 composed of a semiconductor memory for storing image data, image information signals input by the system interface 16 and image data for one screen stored in the frame memory 17, R, G, B3 primary color image signals SigR, SigG and SigB are output to the red laser light source 12R, green laser light source 12G, and blue laser light source 12B for each pixel, and along with this, a vertical scan control signal SigY and a horizontal scan control signal SigX (raster) for the MEMS resonant mirror 15 are output. Scan control signal) Because of the mirror / laser controller 18 is provided.

  FIG. 2 is a block diagram showing an internal configuration of the image projection control circuit 10 in the image projection apparatus.

  FIG. 3 is a diagram for explaining a step conversion circuit for performing interlaced scanning by the vertical scan control signal SigY provided in the mirror / laser controller 18 of the image projection control circuit 10.

  As shown in Non-Patent Document 1, the MEMS resonant mirror 15 has a gimbal-like mirror formed by processing a silicon wafer having a permanent magnet arranged around it, and a current is supplied to an electric wire wired in the mirror. The mirror is rotated in the X direction and the Y direction by controlling the current waveform by electromagnetically operating it, and the MEMS resonant mirror 15 is generally commercialized.

  The MEMS resonant mirror 15 has a specific frequency depending on a combination of the size and weight of the mirror, the elasticity of the stem, and the like, and by controlling the current waveform in accordance with the natural frequency and swinging it, It has the feature that it can be driven at high speed and with low power consumption. On the other hand, there is a drive method called static drive that stabilizes at a certain angle by flowing a constant current regardless of the natural frequency and changes the magnitude of the current stepwise to make a transition to a different angle. In some cases, the transition operation is performed at a frequency much lower than the natural frequency, that is, slowly.

  In this image projection apparatus, by applying positive and negative rectangular waveforms alternately as drive signals in the X direction, a high-speed swing motion in the horizontal direction is performed, and in the Y direction, a drive signal with a changed current value is applied in the vertical direction. Make the direction static drive.

  FIG. 4 is a diagram showing a state of the horizontal swing operation of the MEMS resonant mirror 15 in the image projection system as a graph.

  5 and 6 are diagrams for explaining the swinging operation of the MEMS resonant mirror 15 in the vertical direction.

  FIG. 7 is an enlarged waveform view showing the state until the mirror is step-responseed and stabilized as the MEMS resonant mirror 15 swings vertically.

  When displaying an image by raster scanning a light spot with high luminance, the frame frequency is said to be 60 Hz or more. Here, in this image projection apparatus, when the number of scanning lines is 600 and the frame frequency is 60 Hz, the line frequency is 36 KHz.

  However, the mirror swinging operation is ideally performed in accordance with a sawtooth waveform as shown in FIG. 5, for example, similarly to the beam scan waveform in the television signal, but as described above, the MEMS resonant mirror 15 is operated. Therefore, it is impossible to perform a swinging step operation corresponding to such a sawtooth waveform by static driving of about 1 mm square and to perform the swinging operation at a frequency of 36 KHz.

  Therefore, in the image projection apparatus of the present embodiment, the resonance mirror 15 is designed to swing at a resonance frequency of 9 KHz, which is a quarter of 36 KHz, and operates so as to draw two lines in one round trip. Let In this case, if the frame frequency is 60 Hz, the number of lines becomes 300. Therefore, the frame frequency is set to 30 Hz. Instead, one frame is divided into two fields, and lines are drawn every other line at the field frequency of 60 Hz. Thus, the odd lines are drawn in the first field, the even lines are drawn in the second field, and a total of 600 lines are drawn. This method is similar to a technical method called interlaced scanning in a television or the like.

  That is, in the MEMS resonant mirror 15 in the image projection apparatus of this embodiment, in order to perform the interlaced scanning, as shown in FIG. In this case, steps 2, 4, 6, 8, 10, and 12 are scanned, and steps 11, 9, 7, 5, 3, and 1 are scanned in the downstream direction. In FIG. 6, the number of steps is 6 for each of the upstream and downstream, for a total of 12. However, when the number of scanning lines is 600, the number of steps may be 300.

  The vertical swing operation is the same as that for a television or the like, and is performed in accordance with the sawtooth waveform as shown in FIG. 5, but the saw-like staircase waveform shown in FIG. Then, the amount of angle variation when switching from the top level to the bottom level is large, and it takes a long time for the mirror to respond to the step response and stabilize, so when returning from the top level, A method of stepping in the reverse direction as it is without returning to the above is adopted.

  In the state of the horizontal swing operation of the MEMS resonant mirror 15 shown in FIG. 4, the vertical axis t is time, and the horizontal axis x is the swing angle. That is, the graph depicting the sine curve represents the movement of the bright spot on the screen 14 with respect to time t. Here, since the vertical scanning of the mirror performs a step operation on the actual screen 14, the lines from point a to point b and point c to point d in FIG. 4 are horizontal straight lines on the screen. Will be displayed. On the other hand, since the mirror is step-responsive in the vertical direction from the point b to the point c and from the point d to the point e, it cannot be a straight line. Therefore, the projection of images at both ends of the horizontal scan where such a vertical scan is involved is prohibited.

  That is, the waveform of the swing motion of the MEMS resonant mirror 15 shown in FIG. 6 corresponds to the signal current applied to the mirror as it is, but the actual movement of the mirror is the moment of inertia of the mirror. Because of this, it takes time from the start of the response operation to stabilization, and as shown in FIG. 7, there is an unstable operation period tm at the beginning of each step response operation.

  In FIG. 7, the temporal positions of points a, b, c, d, and e correspond to the positions (a to e) corresponding to the horizontal swing operation of the MEMS resonant mirror 15 shown in FIG. Point).

  In this way, a period in which the horizontal resonance scan is not displayed on both the left and right sides (no RGB laser emission) is provided, and the transient response of the vertical step operation is stabilized during that period. On the other hand, the possibility of causing distortion can be completely eliminated, and high-definition image projection can be performed.

  The lateral movement of the bright spot on the screen 14 performed by the raster scanning operation of the MEMS resonant mirror 15 is the movement of the point moving at a constant angular velocity on the locus of the circle as shown by the circle at the top of FIG. It is easy to understand if you replace it with.

  The magnitude of the swing angle in the horizontal direction X can be expressed by a value on the x-axis. That is, it can be expressed by the swing angle x0 = cos θt. Further, the speed of horizontal scanning (horizontal scanning) can be expressed by the size on the vertical axis. That is, it can be expressed by the swing speed y0 = sin θt. As a result, it can be seen that the scanning speed in the central portion of the horizontal line is high and decreases as it goes to both ends.

  Therefore, in the image projection system of the present embodiment, the laser light source is set so that the bright spots on the screen 14 scanned in the horizontal direction by the laser light output from the laser light sources 12R, 12G, and 12B have uniform brightness. The light emission drive control of 12R, 12G, and 12B is performed.

  The operation of each functional block in the image projection control circuit 10 shown in FIGS. 2 and 3 will be described.

  In the image projection control circuit 10, first, the frame counter 20 performs a counting operation according to the reference signal generated by the clock generator 19 in the mirror / laser controller 18. In the count data by the frame counter 20, the value of the lower digit is the rotation angle θt of FIG. 4 and represents the position in the X axis (horizontal) direction in the raster scan, and the value of the upper digit is the Y axis (vertical) in the raster scan. ) Express the position of the direction.

  The lower digit value obtained from the frame counter 20 is calculated by the cos θ calculator 23 and then given as address information in the X direction of the frame memory 17 via the address multiplexer 22, and the upper digit value is supplied to the step conversion circuit. After being converted at 21, it is given as address information in the Y direction of the frame memory 17 via the address multiplexer 22, and indicates the storage position of the frame memory 17 in pixel units.

  It is assumed that image data is stored in the frame memory 17 with the range corresponding to between the points a and b and c and d in the sine curve of FIG. As a result, the image data divided into the RGB three primary colors read out from the frame memory 17 in units of pixels and latched is converted into corresponding D / A converters R (D / A), G (D / A), B ( D, A) are converted into analog image signals SigR, SigG, SigB, and laser light emitters (light sources) 12R. The light emission output by 12G and 12B is controlled.

  As described above, the lower digit value (position in the X-axis direction) of the count data by the frame counter 20 is given to the address multiplexer 22 as address information after passing through the cos θ calculator 23. That is, as described above, the swing angle in the resonance drive of the MEMS resonance mirror 15 is given by the above equation [x0 = cos θt], and therefore, the lower digit value (position in the X-axis direction) of the count data from the frame counter 20 is calculated. By substituting it as θt and giving the obtained x0 to the address multiplexer 22 as address information, reading out the image data from the frame memory 17 and its RGB three primary color laser at a position that matches the swing angle in the X-axis (horizontal) direction Light output can be performed.

  Further, as described above, the scanning speed in the X-axis direction by the MEMS resonant mirror 15 changes according to the equation [y0 = sin θt] according to the swing angle θt. Therefore, the image data of the RGB three primary colors output from the frame memory 17 according to the address information given from the address multiplexer 22 to the frame memory 17 are output through the corresponding sin θ calculators 23R, 24G, and 24B. Thus, the X-ray image in the projected image is controlled by controlling the image data so that the emission intensity is higher in the central scanning portion where the scanning speed is higher, and the image data such that the emission intensity is weaker in the scanning portions at both ends where the scanning speed is lower. It is configured so that the apparent brightness in the axial (horizontal) direction is uniform.

  Further, a positive / negative rectangular wave that is controlled so that the horizontal turning operation of the MEMS resonant mirror 15 performs the sine wave movement shown in FIG. 4 from the lower digit value (position in the X-axis direction) of the count data output from the frame counter 20. A signal needs to be generated. Therefore, the count data lower digit value is compared with the image edge position value given from the edge position designation register 25, and if they match, the comparator 26 operates so as to invert the output signal. A horizontal scan control signal SigX having a rectangular waveform is output in accordance with the progression of digits.

  The edge position designation register 25 may be provided with two pieces of position information of the rising edge position and the falling edge position of the image data, or only the rising edge position is given. May be configured to output a 1/2 duty waveform.

  The MEMS resonant mirror 15 is supplied with rectangular wave driving power as the horizontal scan control signal SigX through the amplifier 2 (A2). However, in the resonant frequency region, the mirror performs sinusoidal motion as shown in FIG. Become.

  Next, control in the Y-axis (vertical) direction of the MEMS resonant mirror 15 will be described.

  The value of the upper digit of the count data counted by the frame counter 20 is a value indicating the position in the Y-axis (vertical) direction in the raster scan by the MEMS resonant mirror 15.

  The upper digit value (position in the Y-axis direction) of the count data output from the frame counter 20 is converted into a value that becomes a triangular waveform interlaced scanning signal through the step conversion circuit 21 and then the frame memory via the address multiplexer 22. 17 address information. Further, the value of the upper digit (position in the Y-axis direction) of the count data is converted into analog data through a D / A converter (D / A), and passes through an amplifier 1 (A1) as a vertical scan control signal SigY as a MEMS resonant mirror. 15 is given.

  The step conversion circuit 21 is a circuit that converts the sawtooth waveform into a value that becomes a triangular waveform interlaced scanning signal as described above. As shown in FIG. 3, the EX- is used to invert the lower bit by the value of the most significant bit. An arithmetic circuit combined with OR (exclusive OR circuit) is included. Alternatively, it may be configured as a circuit that assigns the most significant bit to the least significant bit of the output for the value of the upper digit (position in the Y-axis direction) of the count data output from the frame counter 20.

  Therefore, according to the image projection apparatus having the above configuration, the MEMS resonance mirror 15 is used to perform horizontal scanning by resonance scanning and vertical scanning by static scanning, and the count data from the frame counter 20 is set in the address multiplexer 22 to set the frame memory. When the laser scan is performed by designating 17 addresses and outputting each pixel image data of RGB three primary colors, the emission intensity of the laser beam is adjusted in accordance with the change in the raster scan speed in the horizontal direction. The bright spot on the top is evenly lit.

  In the embodiment, the lower digit value (X-axis direction position) of the count data from the frame counter 20 is converted to θt of the swing angle formula [x0 = cosθt] in the resonance drive of the MEMS resonant mirror 15 through the cosθ calculator 23. And the obtained x0 is given to the address multiplexer 22 as address information to read out the image data from the frame memory 17 at the position corresponding to the swing angle in the X-axis (horizontal) direction and the RGB three primary color laser beams. The image data is written in the address of the frame memory 17 as a result of performing the cos θ calculation in advance in the personal computer 11 of the image information supply source, and the counter is used without using the cos θ calculator 23. The data value is given as it is as the address of the frame memory 17 It is good also as a structure.

  Furthermore, in the above embodiment, the scanning speed in the X-axis direction by the MEMS resonant mirror 15 changes according to the equation [y0 = sin θt] according to the swing angle θt, so each of the RGB three primary colors output from the frame memory 17 By outputting the image data through the sin θ calculators 23R, 24G, and 24B, image data that has a higher emission intensity at a portion with a high scanning speed and an image data that has a lower emission intensity at a portion with a low speed. However, the image data obtained as a result of performing the sin θ calculation in advance in the personal computer 11 serving as the image information supply source may be written in the frame memory 17.

  Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Furthermore, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in each embodiment or some constituent features are combined, the problems described in the column of the problem to be solved by the invention can be solved. When the effects described in the column of the effect of the invention can be obtained, a configuration in which these constituent elements are deleted or combined can be extracted as an invention.

The block diagram which shows the structure of the image projection system using the image projection apparatus which carries out the raster scan of the laser beam by the MEMS resonance mirror which concerns on embodiment of this invention, and projects an image on a screen. FIG. 2 is a block diagram showing an internal configuration of an image projection control circuit 10 in the image projection apparatus. 3 is a diagram for explaining a step conversion circuit for performing interlaced scanning by a vertical scan control signal SigY provided in the mirror / laser controller 18 of the image projection control circuit 10. FIG. The figure which shows the mode of the horizontal swing operation | movement of the MEMS resonant mirror 15 in the said image projection system as a graph. The figure for demonstrating the oscillation operation | movement (the 1) of the perpendicular direction of the MEMS resonant mirror 15. FIG. The figure for demonstrating the oscillation operation | movement (the 2) of the perpendicular direction of the MEMS resonant mirror 15. FIG. The figure which shows a mode that a mirror responds to a step response according to the vertical swing operation | movement of the MEMS resonant mirror 15, and becomes an enlarged waveform.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image projection control circuit 11 ... Personal computer 12R ... Red laser light source 12G ... Green laser light source 12B ... Blue laser light source 13 ... Tricroic plasm 14 ... Screen 15 ... MEMS resonance mirror 16 ... System interface 17 ... Frame memory 18 ... Mirror / Laser controller 19 ... clock generator 20 frame counter 21 ... step conversion circuit 22 ... address multiplexer 23 ... cos θ calculator 24R, 24G, 24B ... sin θ calculator 25 ... edge position designation register 26 ... comparator
SigY ... Vertical scan control signal
SigX ... Horizontal scan control signal
SigR, SigG, SigB ... RGB three primary color image signals

Claims (4)

In an image projection apparatus that raster scans laser light using a MEMS resonant mirror and projects an image on a screen,
An image projection apparatus comprising control means for adjusting the emission intensity of laser light in response to a change in raster scan speed in the horizontal direction.   The image projection apparatus according to claim 1, wherein the output of the projection image is prohibited during a fixed period at both right and left ends of the raster scan in the horizontal direction.   The image projection apparatus according to claim 1, wherein the raster scan performs interlaced scanning in the vertical direction. In an image projection apparatus that raster scans laser light using a MEMS resonant mirror and projects an image on a screen,
An image memory for storing an image to be projected;
A frame counter that counts a value corresponding to one frame of image display as an address value corresponding to the lower digit in the horizontal direction and an address value corresponding to the upper digit in the vertical direction;
Cosine computing means for cosine computing the lower digit of the count value by this frame counter;
Step conversion means for step-converting the upper digits of the count value by the frame counter;
Address means for addressing the image memory in accordance with a cosine calculation output by the cosine calculation means and a step conversion output by the step conversion means;
A sine calculating means for calculating a sine of the lower digit of the count value by the frame counter;
Image data output means for outputting the value of the pixel data addressed by the address means via the sine calculation means;
An image projection apparatus comprising:

Images