JP2011099890A - Light scanning device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light scanning device and an image forming device that can display an image having uniform resolution in a whole screen in close projection. <P>SOLUTION: The light scanning device includes: a light source 3 outputting a laser beam; a first light deflecting unit which scans the laser beam along a first direction by reflecting the laser beam with a first reflecting unit being adapted to be rotatable about a first axis; a second light deflecting unit which scans the laser beam deflected by the first light deflecting unit along a second direction by reflecting the laser beam with a second light reflecting unit being adapted to be rotatable about a second axis; a driving controlling unit 7 controlling a rotational angle variation of the second light reflecting unit 1b per unit time so that an interval between scanning lines in the second direction is constant when the scanning lines along the first direction line up with the second direction; and a driving unit 2b rotationally driving the second light reflecting unit in accordance with the rotational angle determined by the driving controlling unit 7 utilizing the expansion and contraction of a piezoelectric element 31. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical scanning device and an image forming apparatus.

  In an optical deflector intended to be applied to a display, a printer, or the like using laser light, further high-speed scanning is required. However, there is a limit to improving the performance of polygon mirrors and galvanometer mirrors currently used. As an optical deflector that replaces these, a mirror device manufactured by processing a silicon substrate by MEMS (Micro Electro Mechanical System) is expected. Since the MEMS mirror can be driven at a higher resonance frequency, an image with higher resolution can be formed. A projector that performs projection from a short distance (proximity projection) using such a MEMS mirror is convenient for use in a meeting with a small number of people.

In Patent Document 1, the passage time of a reciprocatingly scanned light beam is measured at a specific position on a scanning line, and the time of reciprocating scanning of the deflector with respect to the driving signal of the deflector is determined from the measured two reciprocating passage time values. An optical deflecting device is described that prevents variation in an image by calculating delay time data corresponding to the target delay and further calculating timing data corresponding to the modulation start time or end time of the light beam within one scanning period. ing.
Further, Patent Document 2 describes a projection display device that is easy to use when a small number of people meet in a small place.

JP 2003-131151 A JP 2003-280091 A

  However, in the case of proximity projection, the distance between the scanning lines in the vertical direction increases as the distance from the mirror increases, so that the resolution of the image is not uniform over the entire screen, and the conventional apparatus described in Patent Documents 1 and 2 Then, this point could not be solved.

  Therefore, an object of the present invention is to provide an optical scanning device and an image forming apparatus that can make the resolution constant over the entire projection surface when performing proximity projection.

  The optical scanning device according to the present invention includes a light source that emits a laser beam, and a first light reflecting unit that rotates the laser beam about a first axis to scan along a first direction. And a second light deflecting unit that reflects the laser beam deflected by the first light deflecting unit by a second light reflecting unit that rotates about a second axis and scans the laser beam along the second direction. And the rotation angle change amount per unit time of the second light reflecting portion is controlled so that the line interval in the second direction when the scanning trajectory lines along the first direction are arranged in the second direction is constant. A drive control unit; and a drive unit that drives the second light reflecting unit to rotate using the expansion and contraction of the piezoelectric element according to the rotation angle determined by the drive control unit.

  According to the present invention, the amount of change in the deflection angle per unit time of the second light deflection unit is controlled so that the interval between the scanning lines in the second direction is constant, so that the resolution is constant over the entire projection surface. Can be.

  In addition, since the piezoelectric element can be step-driven in units of several nanometers, it becomes easy to control a fine deflection angle.

Further, the drive unit includes a transmission unit fixed to the second light reflection unit with a spacer interposed therebetween, and the piezoelectric element has one end in an expansion / contraction direction in contact with the transmission unit, and the transmission unit It is preferable that the second light reflecting portion rotate about the second axis by transmitting a driving force generated by expansion and contraction of the piezoelectric element to the light reflecting portion.
Thereby, since the displacement of the piezoelectric element is directly transmitted to the light reflecting portion, it is not necessary to consider damping or the like.

An image forming apparatus according to the present invention includes the above optical scanning device.
According to the present invention, the amount of change in the deflection angle per unit time of the second light deflection unit is controlled so that the interval between the scanning lines in the second direction is constant. The resolution can be made constant over the entire projection surface.

It is a block diagram which shows the structure of the optical scanning device by this embodiment. It is a top view which shows the structure of the horizontal scanning light deflector by this embodiment. It is sectional drawing in the II-II line of FIG. It is a top view which shows the structure of the vertical scanning light deflector by this embodiment. It is sectional drawing in the II-II line of FIG. It is a perspective view which shows the projector provided with the optical scanning device of this embodiment, and a projection surface. It is the figure which looked at the projector and the projection surface S from the side. (A) is a diagram showing a method for controlling the vertical deflection angle of the optical scanning device according to the comparative example, and (B) is a diagram showing a method for controlling the vertical deflection angle of the optical scanning device according to the present embodiment. .

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the case where the first direction is the horizontal direction and the second direction is the vertical direction will be described as an example.
FIG. 1 is a block diagram showing a configuration of an optical scanning device 10 according to the present embodiment. As shown in the figure, an optical scanning device 10 includes an optical deflector (light deflector) 1, a drive unit 2, a light source 3, a dichroic mirror 4, a laser drive unit 5, an image information storage unit 6, a drive control unit 7, and a mirror. A position detection unit 40 is provided.

  The optical deflector 1 scans the laser beam transmitted from the dichroic mirror 4 in the vertical direction and the horizontal scanning mirror 1a that is a first light reflecting unit that scans the laser beam in the horizontal direction and the laser beam reflected by the horizontal scanning mirror 1a in the vertical direction. And a vertical scanning mirror 1b which is a two-light reflecting portion. The driving unit 2 includes a horizontal scanning mirror driving unit 2a that drives the horizontal scanning mirror 1a and a vertical scanning mirror driving unit 2b that drives the vertical scanning mirror 1b. FIG. 2 is a plan view showing the configuration of the horizontal scanning mirror 1a and the horizontal scanning mirror driving unit 2a. 3 is a cross-sectional view taken along the line II-II in FIG.

  The horizontal scanning mirror 1 a includes a movable plate 11 having a reflective film 21 formed on the surface side, a support frame 12, and a pair of elastic support portions 13 that support the movable plate 11 in a torsionally rotatable manner with respect to the support frame 12. The movable plate 11, the support frame 12, and the elastic support portion 13 are integrally formed, for example, by etching a silicon substrate.

  Further, the horizontal scanning mirror driving unit 2 a in the present embodiment includes a permanent magnet 22, a coil 23, and an alternating current signal generation circuit 24. The permanent magnet 22 is bonded to the side of the movable plate 11 opposite to the reflective film 21. The permanent magnet 22 is magnetized in a direction orthogonal to the axis A that is the rotation center axis of the movable plate 11 when the movable plate 11 is viewed in plan. That is, the permanent magnet 22 has a pair of magnetic poles that are opposed to each other via the axis A and have different polarities. The support frame 12 is joined to the holder 20, and a coil 23 for driving the movable plate 11 is disposed on the holder 20.

  A current (alternating current) that periodically changes is supplied to the coil 23 by the alternating current signal generation circuit 24. As a result, the coil 23 alternately generates a magnetic field directed upward (movable plate 11 side) and a magnetic field directed downward. As a result, the movable plate 11 moves around the A axis while twisting and deforming the elastic support portion 13 such that one of the pair of magnetic poles of the permanent magnet 22 approaches the coil 23 and the other magnetic pole is separated. It can be rotated. At this time, the frequency of the current generated by the alternating current signal generation circuit is set so as to substantially match the torsional resonance frequency of the vibration system formed by the movable plate 11, the elastic support portion 13, and the permanent magnet 22.

  FIG. 2 shows a drive-type vibrating mirror that uses electromagnetic force between the permanent magnet 22 and the coil 23. However, the present invention may adopt a method using electrostatic attraction or a method using piezoelectric elements. For example, in the case of a system using electrostatic attraction, the permanent magnet 22 is not necessary, and one or a plurality of electrodes facing the movable plate 11 are installed instead of the coil 23. Then, by applying an alternating voltage that periodically changes between the movable plate 11 and the electrode, an electrostatic attractive force is applied between the movable plate 11 and the electrode, and the elastic support portion 13 is twisted and deformed. Then, the movable plate 11 is rotated around the A axis. In this case, the torsional resonance frequency of the vibration system formed by the movable plate 11 and the elastic support portion 13 and the frequency of the AC voltage are set to substantially coincide.

The light source 3 is a light source that emits a laser beam.
The light source 3 includes a red laser light source 3R that emits red laser light, a blue laser light source 3B that emits blue laser light, and a green laser light source 3G that emits green laser light. However, a laser light source of 2 colors or less or 4 colors or more may be used.

  The dichroic mirror 4 includes a dichroic mirror 4R that reflects red laser light from the red laser light source 3R, a dichroic mirror 4B that reflects blue laser light and transmits red laser light, and reflects green laser light and blue laser light and red. And a dichroic mirror 4G that transmits laser light. By these three types of dichroic mirrors 4, the combined light of red laser light, blue laser light, and green laser light is incident on the horizontal scanning mirror 1 a.

  The laser driver 5 controls the intensity and emission time of the laser light emitted from each light source by controlling the amount of current supplied to the red laser light source 3R, the blue laser light source 3B, and the green laser light source 3G.

  The image information storage unit 6 stores information on an image formed on the projection surface by the laser light scanned by the optical scanning device 10.

  The drive control unit 7 displays these images based on the image information supplied from the image information storage unit 6 and the deflection angle information of the horizontal scanning mirror 1a and the vertical scanning mirror 1b supplied from the mirror position detection unit 40. Therefore, the operation of the drive unit 2 is controlled. Further, the drive control unit 7 supplies information on the image to be projected to the laser drive unit 5. In particular, in the present embodiment, the drive control unit 7 controls the deflection angle change amount per unit time of the vertical scanning mirror 1b so that the interval between the scanning lines in the vertical direction is constant. The deflection angle information may be generated by detecting light scanned horizontally and vertically by an optical sensor (not shown).

  FIG. 4 is a plan view showing the configuration of the vertical scanning mirror 1b and the vertical scanning mirror driving unit 2b according to the present embodiment. 5 is a cross-sectional view taken along the line II-II in FIG. In the present embodiment, the vertical scanning mirror drive unit 2b of the optical scanning device 10 drives the vertical scanning mirror 1b to rotate using the expansion and contraction of the piezoelectric element caused by energization.

As shown in FIGS. 4 and 5, the vertical scanning mirror 1 b of the optical scanning device 10 has a movable plate (light reflecting portion) 11 having a reflective film 21 formed on the surface, and the movable plate 11 can be rotated with respect to the support frame 12. A pair of elastic support portions 13 supported on the holder, a holder 25 arranged to support the support frame 12 with the connection layer 44 interposed therebetween, and a transmission member (transmission portion) 32 fixed to the movable plate with the spacer 33 interposed therebetween. .
As shown in FIGS. 4 and 5, the vertical scanning mirror driving unit 2 b includes a pair of piezoelectric elements 31 and an AC voltage generation circuit (not shown) that applies an AC voltage signal to the piezoelectric elements 31.

  The piezoelectric element 31 is disposed so as to expand and contract in a direction perpendicular to the axis A. The piezoelectric element 31 is disposed so that one end in the expansion / contraction direction is bonded and supported by the holder 25 and the other end is bonded or contacted to the transmission member 32. At this time, the piezoelectric element may be arranged in a state where an offset voltage is applied (a state in which elongation occurs).

  The piezoelectric element 31 is not particularly limited, but is preferably one in which a plurality of piezoelectric layers and electrode layers are alternately stacked. Thereby, the amount of displacement of the piezoelectric element 31 can be increased while suppressing the dimension of the piezoelectric element 31 in the expansion / contraction direction and the voltage (drive voltage) applied to the piezoelectric element 31. The piezoelectric element 31 is connected to an AC power source (not shown), and a voltage that changes periodically is applied thereto. Thereby, the piezoelectric element 31 can be expanded and contracted.

The transmission member 32 has a function of rotating the movable plate 11 around the axis A by receiving a driving force of the piezoelectric element 31 and displacing in a direction perpendicular to the axis A.
The transmission member 32 is joined to the movable plate 11 at a position eccentric to the axis A in the thickness direction of the movable plate 11, and is configured to transmit the driving force of the piezoelectric element 31 to the movable plate 11. More specifically, the transmission member 32 contacts or is joined to the piezoelectric element 31 and is joined to the movable plate 11 via the spacer 33 in the vicinity of the elastic support portion 13.
In the vertical scanning mirror 1b of this embodiment, the movable plate 11, the elastic support portion 13, the spacer 33, the transmission member 32, the support frame 12, the connection layer 44, and the holder 25 are between the first silicon layer and the second silicon layer. Alternatively, a substrate having an oxide film layer (so-called SOI substrate) may be removed and formed integrally. Specifically, the movable plate 11, the elastic support portion 13, and the support frame 12 are formed on the first silicon layer, the spacer 33 and the connection layer 44 are formed on the oxide film layer, and the transmission member 32 is formed on the second silicon layer. And a holder 25 are formed.

  In the vertical scanning mirror driving unit 2b, the piezoelectric element 31 is expanded and contracted by energization, so that the transmission member 32 applies a torque around the axis A to the movable plate 11 to rotate the movable plate 11. Since the expansion / contraction direction of the piezoelectric element 31 is a direction perpendicular to the thickness direction of the movable plate 11, the length of the piezoelectric element 31 in the expansion / contraction direction is suppressed while suppressing the size of the optical scanning device 10 in the thickness direction of the movable plate 11. To increase the amount of displacement of the piezoelectric element 31.

  The rotation angle of the movable plate 11 with respect to the amount of displacement of the piezoelectric element 31 roughly corresponds to the distance between the axis A in the thickness direction of the movable plate 11 and the piezoelectric element 31 (power point). It is set as appropriate depending on the mounting position and shape of the element 31. The attachment position of the piezoelectric element 31 can be arbitrarily designed according to the thickness and shape of the transmission member 32. Therefore, the design freedom of the optical scanning device 10 can be improved. Further, since the transmission member 32 is joined to one end (in this embodiment, the lower surface) of the movable plate 11 in the thickness direction of the movable plate 11, the transmission member 32 is effectively attached to the movable plate 11 around the axis A. Torque can be given. Therefore, the movable plate 11 can be smoothly rotated while preventing the axis A that is the rotation center axis of the movable plate 11 from being shaken. Further, when the vertical scanning mirror 1b is integrally formed using the SOI substrate, the positional accuracy of each element is high and the productivity is also high.

  As described above, by driving the movable plate 11 of the vertical scanning mirror 1b using the expansion and contraction of the piezoelectric element 31, the piezoelectric element can be step-driven in units of several nanometers. Is easier to do. Further, since the displacement of the piezoelectric element 31 is directly transmitted to the movable plate 11 via the transmission member 32, it is not necessary to consider damping or the like. That is, in the case of electromagnetic driving or electrostatic driving, the movable plate 11 can move freely, so it is necessary to consider damping or the like. In this embodiment, the piezoelectric element 31 is moved via the transmission member 32. 11, the movable plate 11 can be interlocked with the movement of the piezoelectric element 31. Therefore, in the case of controlling the amount of change in the deflection angle in the vertical direction per unit time as in the optical scanning device 10 according to the present invention, the vertical driving means of the optical deflector 1 is used as the vertical driving means. Thus, it is desirable to use the expansion and contraction of the piezoelectric element.

  Next, the operation of the optical scanning device 10 will be described with reference to FIGS. FIG. 6 is a perspective view showing a projector (image forming apparatus) 90 provided with the optical scanning device 10 of the present embodiment and the projection surface S, and FIG. 7 is a view of the projector 90 and the projection surface S viewed from the side.

  As shown in FIG. 6, the projector 90 has a bottom surface in contact with the projection surface S. In FIG. 6, a region surrounded by a one-dot chain line indicates a drawing region by the projector 90. The scanning direction 1 is the horizontal scanning direction, and the scanning direction 2 is the vertical scanning direction.

In FIG. 7, θ ₀ , θ ₁ , θ ₂ ... Represent the vertical deflection angles by the vertical scanning mirror 1b, draw the 0th line at the deflection angle θ ₀ , and the _first at the deflection angle θ ₁ . Draw one line.
As shown in the figure, the interval between the scanning lines in the vertical direction is constant, and when the number of scanning lines in the vertical direction is m, n (n is from 0 to m−1) from the side closer to the optical scanning device 10. The deflection angle θ _n when the (integer) th scanning line is drawn can be expressed by the following equation (1).
θ _n = tan ⁻¹ (b + n · d / m−1) · 1 / a−tan ⁻¹ (b + (n−1) · d / m−1) · 1 / a (1)
However, a is the height from the projection surface S to the optical deflector 1, and b is the horizontal distance from the optical deflector 1 to the 0th line.

  FIG. 8A is a diagram illustrating a method of controlling the vertical deflection angle of the optical scanning device according to the comparative example. In the example shown in FIG. 8A, the amount of change in the deflection angle θ per unit time is constant, but when controlled in this way, the interval between the scanning lines in the vertical direction becomes wider as the distance from the optical scanning device increases. . For this reason, the resolution of the image does not become uniform over the entire screen.

  On the other hand, in the present embodiment, since the deflection angle of the vertical scanning mirror 1b is controlled by the drive control unit 7 so that the interval between the vertical scanning lines is constant, as shown in FIG. The amount of change in the deflection angle θ is not constant.

  As described above, according to this embodiment, the deflection angle change amount per unit time of the vertical scanning mirror 1b is controlled so that the interval between the scanning lines in the vertical direction is constant. Can keep the resolution constant.

In addition, the structure of each part of the optical scanning device 10 of the present invention can be replaced with an arbitrary structure that exhibits the same function, and an arbitrary structure can be added.
The optical scanning device 10 according to the present embodiment includes the horizontal scanning mirror 1a and the vertical scanning mirror 1b. The optical scanning device 10 includes one mirror that can rotate around two axes, and the horizontal direction is achieved by one mirror. Alternatively, the scanning may be performed in the vertical direction.

  1 optical deflector, 1a horizontal scanning mirror, 1b vertical scanning mirror, 2 drive unit, 2a horizontal scanning mirror drive unit, 2b vertical scanning mirror drive unit, 3 light source, 3R red laser light source, 3B blue laser light source, 3G green laser light source 4, dichroic mirror, 5 laser drive unit, 6 image information storage unit, 7 drive control unit, 10 optical scanning device, 11 movable plate, 12 support frame, 13 elastic support unit, 20, 25 holder, 21 reflective film, 22 permanent Magnet, 23 coil, 24 AC current signal generation circuit, 31 piezoelectric element, 32 transmission member, 33 spacer, 90 projector.

Claims (3)

A light source that emits a laser beam;
A first light deflecting unit that reflects the laser beam by a first light reflecting unit that rotates about a first axis and scans the laser beam along a first direction;
A second light deflecting unit that reflects the laser beam deflected by the first light deflecting unit by a second light reflecting unit that rotates about a second axis and scans the laser beam along a second direction;
Drive control for controlling the amount of change in the rotation angle per unit time of the second light reflecting portion so that the line spacing in the second direction is constant when the scanning trajectory lines along the first direction are aligned in the second direction. And
An optical scanning device comprising: a drive unit that drives the second light reflecting unit to rotate using the expansion and contraction of the piezoelectric element according to the rotation angle determined by the drive control unit. The drive unit includes a transmission unit fixed to the second light reflection unit with a spacer interposed therebetween,
One end of the piezoelectric element in the expansion / contraction direction is in contact with the transmission unit,
2. The second light reflecting portion rotates about the second axis when the transmitting portion transmits a driving force generated by expansion and contraction of the piezoelectric element to the light reflecting portion. The optical scanning device according to 1.   An image forming apparatus comprising the optical scanning device according to claim 1.

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