JP2007226108A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce variation in oscillation angle even when ambient temperature varies and to reduce variance of oscillation angle due to the variance of resonance frequency. <P>SOLUTION: First fixed electrodes 51 and 52 are connected to second fixed electrodes 53 and 54 via an insulation layer 48. The frequency of a driving signal is compared with the resonance frequency which is decided by the inertia of a mirror 44 and the torsion spring constant of a beam 45. The driving signal is applied on the first fixed electrodes 51 and 52 when the driving frequency is larger than the resonance frequency and the mirror is oscillated by the electrostatic force acting on a movable electrode 46 and the first fixed electrodes, and the driving signal is applied on the second fixed electrodes 53 and 54 when the driving frequency is smaller than the resonance frequency and the mirror is oscillated by the electrostatic force acting on the movable electrode 46 and the second fixed electrodes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning device having a micro optical system to which micromachining technology is applied, for example, an optical scanning device used in a writing system such as a digital copying machine and a laser printer, or a reading device such as a barcode reader. The present invention relates to a technology suitable for

  In a conventional oscillating mirror, a mirror substrate supported by two beams provided on the same straight line is twisted by electrostatic attraction between an electrode provided at a position facing the mirror substrate. A reciprocating vibration is used as a rotating shaft (see Non-Patent Document 1, for example). This optical scanning device formed by micromachining technology has a simple structure and can be formed in a batch in a semiconductor process compared to a conventional optical scanning device using a polygon mirror rotation using a motor. It is easy and low in production cost, and since it is a single anti-slope, there are no variations in accuracy due to multiple surfaces, and further, since it is reciprocating scanning, it can be expected to be effective in speeding up.

  As such an electrostatically driven vibrating mirror, the beam is made into an S-shape to reduce the rigidity so that a large deflection angle can be obtained with a small driving force (for example, see Patent Document 1). A mirror substrate, a substrate thinner than the frame substrate (for example, refer to Patent Document 2), a fixed electrode disposed at a position that does not overlap the vibration direction of the mirror part (for example, refer to Patent Document 3, Non-Patent Document 2), or In some cases, the drive voltage is lowered without changing the deflection angle of the mirror by installing the counter electrode so as to be inclined from the center position of the deflection of the mirror (for example, see Non-Patent Document 3).

IBM J.M. Res. Develop Vol. 24 (1980) The 13th Annual International Workshop on MEMS2000 (2000) p. 473-478 The 13th Annual International Workshop on MEMS2000 (2000) p. 645-650 Japanese Patent No. 2924200 Japanese Patent Laid-Open No. 7-92409 Japanese Patent No. 30111144 JP-A-9-197334

  A conventional problem will be described with reference to FIG. The optical deflection element shown in FIG. 17A has a problem that when the environmental temperature changes, the resonance frequency of the optical deflection element changes, and therefore the deflection angle of the optical deflection element decreases.

  17 (a) and 17 (b), a mirror substrate (movable part) 44 supported by two beams provided on the same straight line as a rotation axis, a movable electrode 46 provided on the mirror substrate 44, and a movable Light deflection that has a fixed electrode 20 provided opposite to the electrode 46, and causes the mirror substrate 44 to reciprocately vibrate with the two beams 45 being twisted and rotated by the electrostatic attraction between the movable electrode 46 and the fixed electrode 20. In the element, the resonance frequency is approximately given by the following equation.

f = (1 / 2π) v (Kθ / I) (1)
Where Kθ = torsion spring constant,
Kθ = β · t · c ^ 3 · E / L (1 + v)
t; spring thickness, L; length, c; width v; Poisson's ratio I = Miller moment of inertia
When the temperature coefficient of Si is Δht, the Young's modulus at the temperature T is given by the following equation.

Young's modulus E = E0 (1-Δht * T) (2)
However, E0 = 1.9e + 12 (dyne / cm2),
Δht = 75e−6 / ° c
From equation (2), it can be seen that the Young's modulus E decreases as the temperature T increases. Thereby, in (1), if the temperature T becomes large, it turns out that a resonant frequency becomes small.

  FIG. 17C shows the actual measurement result of the relationship between temperature and resonance frequency. In the figure, it can be seen that the resonance frequency changes according to the temperature change.

  Therefore, as shown in FIGS. 18A and 18B, in order to suppress such a variation in the resonance frequency, an electric resistance element 6 is provided in the elastic deformation portion 13 and the electric resistance element 6 is energized to thereby generate electricity. A method has been proposed in which the resistance element 6 generates heat and the temperature of the elastic deformation portion 13 changes, thereby changing the spring constant of the elastic deformation portion 13 and changing the resonance frequency of vibration (see, for example, Patent Document 4). reference).

By providing the electric resistance element 6 in the elastic deformation portion 13, it is also possible to suppress the fluctuation of the resonance frequency due to the fluctuation of the environmental temperature. However, the process for providing the electric resistance element 6 in the elastic deformation portion 13 is complicated, which causes an increase in cost. Further, the temperature control circuit 30 for the electric resistance element 6 is required, which also causes an increase in cost.
There is also a problem of variation in deflection angle due to variation in resonance frequency. As described above, the resonance frequency is approximately given by equation (1). The moment of inertia I varies due to variations in the mirror shape. Further, the spring constant Kθ varies due to variations in the shape of the torsion beam. Thereby, the dispersion | variation in a resonant frequency generate | occur | produces from (1) Formula.

  Consideration will be given to problems when the optical scanning device having such resonance frequency variation characteristics is used in an optical writing device such as a laser printer.

  The writing device of the laser printer shown in FIG. 16A is composed of a plurality of optical scanning devices and is arranged in the main scanning direction. Writing is performed with respect to the writing width by a plurality of optical scanning devices. FIG. 19A shows the result of measuring the variation in the resonance frequency of this optical scanning device. Further, FIG. 19B shows the measurement result of the shake angular frequency characteristic of the optical scanning device. In such a laser printer, the optical writing device is driven by a drive signal Fd having the same frequency. FIG. 19C shows the shake angular frequency characteristics of each optical scanning device at the drive signal Fd. In FIG. 19C, the deflection angle of each scanning device is given by the intersection of the drive signal and each frequency characteristic, and the variation of the deflection angle is given in the range shown in FIG. 19C.

The present invention has been made in view of the above problems,
An object of the present invention is to provide an optical deflector structure in which the fluctuation of the swing angle is small even when the environmental temperature changes without performing temperature control by an electric resistance element or the like as in the conventional example, and the variation in resonance frequency. It is an object of the present invention to provide an optical scanning device and an image forming apparatus in which variation in the deflection angle due to the above is small.

  The present invention provides a movable electrode provided on both end faces of a mirror, a first fixed electrode provided opposite to the movable electrode, and a second fixed provided overlapping the same plane in the swing direction of the first fixed electrode. The first fixed electrode and the mirror are arranged in a straight line, and reciprocally vibrate using a beam provided on the same side of the mirror as a torsional rotation axis to deflect and scan the beam from the light source. In the optical scanning device, one of the electrostatic force acting between the movable electrode at both ends of the mirror and the first fixed electrode and the electrostatic force acting between the movable electrode at both ends of the mirror and the second fixed electrode. The most important feature is to vibrate the mirror.

  According to the present invention (claim 1), the frequency characteristic of the deflection angle becomes broader than the frequency characteristic of the conventional configuration, and the variation of the deflection angle is reduced.

  According to the present invention (Claim 2), since the region where the deflection angle change is large with respect to the frequency change can be excluded, the optical scanning device operates stably.

  According to the present invention (Claim 3), a large frequency band satisfying the rated deflection angle θm can be obtained.

  According to the present invention (Claim 4), the working angle of the electrostatic force acting between the second fixed electrode and the mirror electrode can be widened, whereby the band of the deflection angular frequency characteristic can be widened.

  According to the present invention (Claim 5), since the mirror substrate is sealed under reduced pressure in the space between the base substrate and the cover glass, the viscosity resistance coefficient is reduced and the deflection angle can be increased.

  According to the present invention (Claim 6), the deflection angle of the mirror can be increased.

  According to the present invention (Claim 7), since the first fixed electrode and the second fixed electrode have a comb shape, the facing area between the electrodes can be increased. As a result, the electrostatic force proportional to the facing area is increased, and the vibration amplitude can be increased.

  According to the present invention (Claim 8), since the number of parts is very small as compared with the conventional polygon scanner, a reduction in cost can be expected.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1:
FIG. 1 shows the configuration of Embodiment 1 of the present invention. FIG. 1B is a cross-sectional view of FIG. In FIG. 1A, 42 is a first substrate and 43 is a second substrate. The first substrate 42 is provided with torsion springs 45 and 45 ′ on both side surfaces of the movable portion 44 by etching. In addition, movable electrodes 46 and 46 ′ are provided on both end faces of the movable portion 44, and first fixed electrodes 51 and 52 are formed facing the movable electrodes 46 and 46 ′. The first substrate 42 is divided into a movable part 44 having a mirror surface, a first fixed electrode 51, and a first fixed electrode 52 by a separation groove 49.

  The second substrate 43 is bonded to the first substrate 42 via the insulating layer 48 to form a swing space 59 of the movable portion 44. The second substrate 43 is divided into two second fixed electrodes 53 and 54 by the separation groove 49.

  In this embodiment, a voltage is applied between the first fixed electrode and the movable electrode, and an electrostatic force acting between the two electrodes is used as the driving force, and a voltage is applied between the second fixed electrode and the movable electrode. In some cases, the driving force is an electrostatic force acting between the two electrodes.

  The operation of the optical scanning device will be described by taking a one-degree-of-freedom vibration system as a mechanical model of the optical scanning device.

  The analysis is performed using a model having a one-degree-of-freedom vibration system in which the spring has nonlinearity (duffing equation).

In FIG.
・ Torsion spring / electrostatic torque is modeled by a spring with linear spring constant k and nonlinear spring constant β,
・ Model the inertia of the mirror with the mass (I),
・ Air viscosity is modeled in a dashpot (c),
・ When external force is modeled as a sine wave with amplitude q and angular velocity ω0,
I · X ″ + c · X ′ + (k · X + β · X ^ 3) = q · cos ωt (3)
(X is displacement, X ′ is the first derivative, X ″ is the second derivative, and X ^ 3 is the third derivative).

Vibration characteristics are analyzed using a model in which a sinusoidal external force acts on this one-degree-of-freedom vibration system.
(A) When a voltage is applied between the first fixed electrode and the movable electrode, and the electrostatic force acting between the two electrodes is used as the driving force:
FIG. 3A shows torque acting between the first fixed electrodes 51 and 52 and the movable electrode 46. The return spring force in the equation (3) is given by the sum of the torsion spring force and the electrostatic torque Trq.

  FIG. 3B shows the result of obtaining the electrostatic force between the first fixed electrode and the movable electrode shown in FIG. The calculation was obtained by the finite element method. A force obtained by adding the electrostatic torque and the torsion spring force acts as a return force of the mirror.

  FIG. 3C shows a force obtained by adding the electrostatic torque and the torsion spring force, and a return force (k · X + βX ^ 3). This return force is symmetric with respect to the origin, and is convex upward at a deflection angle θ> 0 and convex downward at a deflection angle θ <0. Therefore, it can be approximated by a cubic polynomial (k · X + βX ^ 3, where β <0).

  FIG. 5B shows the result of obtaining the frequency response characteristic in the steady state from the equation (3).

  In FIG. 5B, the shaded area indicates a range where there is no steady-state solution of equation (3). Due to the existence range of this solution, a jump decrease and a hysteresis decrease that are characteristic of the nonlinear vibration system occur. Since a steady solution cannot exist in the shaded area, the frequency response changes discontinuously as the drive frequency increases and decreases. When the drive frequency is increased, a jump of A '-> B' occurs. Further, when the drive frequency is decreased, a jump of C ′-> D ′ occurs.

FIG. 5B shows a response curve when the frequency obtained from the above result is lowered, and a so-called soft spring effect (a phenomenon in which the resonance point C ′ becomes lower as the drive frequency becomes lower) appears. Recognize.
(B) When a voltage is applied between the second fixed electrode and the movable electrode, and the electrostatic force acting between the two electrodes is used as the driving force:
FIG. 4A shows torque acting between the second fixed electrodes 53 and 54 and the movable electrode 46. The return spring force in the equation (3) is given by the sum of the torsion spring force and the electrostatic torque.

  FIG. 4B shows the result of obtaining the electrostatic force between the second fixed electrode and the movable electrode shown in FIG. The calculation was obtained by the finite element method. A force obtained by adding the electrostatic torque and the torsion spring force acts as a return spring force of the mirror.

  FIG. 4C shows the return force and the force obtained by adding the electrostatic torque and the torsion spring force. This return force is symmetric with respect to the origin, and is convex downward at a deflection angle θ> 0 and convex upward at a deflection angle θ <0. Therefore, it can be approximated by a cubic polynomial (k · X + βX ^ 3, where β> 0). This is completely opposite to the case of (A) above.

  FIG. 5A shows the result of obtaining the frequency response characteristic in the steady state from the equation (3).

  In FIG. 5A, the shaded area indicates a range where the steady state solution of Equation (3) exists. Due to the existence range of this solution, a jump decrease and a hysteresis decrease that are characteristic of the nonlinear vibration system occur. Since a steady solution cannot exist in the shaded area, the frequency response changes discontinuously as the drive frequency increases and decreases. When the drive frequency is increased, a jump of A-> B occurs. Further, when the drive frequency is decreased, a jump of C-> D occurs.

  FIG. 5A shows a response curve when the frequency obtained from the above results is increased, and it can be seen that a hard spring effect (a phenomenon in which the resonance point A increases as the drive frequency increases) appears.

  FIG. 5C is a graph showing the angular frequency response in both cases based on the analysis results in the cases (A) and (B) described above. Both response curves (A) and (B) have a peak value at the resonance frequency determined by the inertia of the mirror and the torsion spring constant of the torsion beam. As shown in FIG. 5C, it can be seen that the deflection angular frequency characteristic is broader than the frequency characteristic of the conventional configuration. FIG. 6 shows variation in deflection angle when a plurality of optical scanning devices of the present invention are used simultaneously. A deflection angle with respect to a single drive signal frequency (Fd) is obtained from a deflection angle response characteristic of each optical scanning device. The intersection of the frequency Fd and the deflection angle response characteristic of each scanning device gives the deflection angle at the frequency (Fd). Thus, when the fluctuation of the deflection angle is obtained, it can be seen that the fluctuation of the deflection angle is reduced as compared with the conventional example as shown in FIG.

The deflection angle required for the optical deflection element is θm. FIG. 7 is a diagram in which the deflection angle θm is added to the deflection angular frequency characteristic. In FIG. 7, when a band greater than the deflection angle θ is obtained by the following method, f1 to f2 and f3 to f4 are obtained.
(1) In the vicinity of the resonance frequency, the change of the deflection angle with respect to the frequency change is remarkable, and since it is a very narrow band as a frequency band, it can be excluded from practical use.
(2) The deflection angle is proportional to the electrostatic force, and the electrostatic force is proportional to the applied voltage. In a region where the deflection angle is larger than the deflection angle θm, the applied voltage can be lowered to make the adjustment angle coincide with the deflection angle θm. Therefore, the region excluding the vicinity of the resonance frequency is set as the drive region.

(First driving method)
In FIG. 1B, a drive circuit 60 and a comparison circuit 61 are added to the optical scanning device 55. The movable portion 44 is connected to GND, and the first fixed electrodes 51 and 52 and the second fixed electrodes 53 and 54 are connected to the drive circuit 60, respectively.

  An optical deflection element drive signal 62 corresponding to an image signal from an image signal generation device (not shown) is first input to the comparison circuit 61. The comparison circuit 61 compares the drive signal frequency 62 with the resonance frequency determined by the inertia of the mirror movable part and the torsion spring shown in FIG. When the drive signal frequency 62 is higher than the resonance frequency, the comparison circuit 61 selects the first fixed electrodes 51 and 52, and the drive circuit 60 generates a voltage between the movable electrode 46 of the movable part and the first fixed electrodes 51 and 52. Apply.

  When the drive signal frequency 62 is lower than the resonance frequency, the comparison circuit 61 selects the second fixed electrodes 53 and 54, and the drive circuit 60 generates a voltage between the movable electrode 46 of the movable part and the second fixed electrodes 53 and 54. Apply.

  As described above, it is determined whether to apply the drive signal to the first fixed electrode or to apply the drive signal to the second fixed electrode based on the result of comparing the drive signal of the optical scanning device and the resonance frequency. Therefore, as shown in FIG. 7, a large frequency band satisfying the rated deflection angle θm can be obtained.

  As shown in FIG. 8, the thickness of the second fixed electrodes 53 and 54 is made larger than the thickness of the first fixed electrodes 51 and 52. Typically, the thickness of the second fixed electrodes 53 and 54 is set to about twice that of the first fixed electrodes 51 and 52.

  FIG. 9B shows the result of obtaining the electrostatic force acting between the two electrodes by applying a voltage between the second fixed electrodes 53 and 54 and the movable electrode 46 having such a configuration. It can be seen that by increasing the thickness of the electrode, the angle θ0 ′ at which the electrostatic force almost does not act is wider than the angle θ0 when the electrode is not thickened. FIG. 9A shows the torque acting between the second fixed electrode and the movable electrode, and FIG. 9C shows the return force. FIG. 10 shows the obtained frequency characteristic of the deflection angle in the steady state. As a result, it can be seen that the operating range of the electrostatic torque is increased, and the bandwidth of the deflection angle is increased.

  FIG. 11 shows a diagram for assembling the optical scanning device. (B) is sectional drawing of the assembled state. In FIG. 11A, 31 is a cover substrate made of a transparent member such as glass, 42 is a first substrate having a twist rotating shaft 45 and a movable portion 44, and 35 is a through hole for electrically connecting to the first substrate 42. This is a base substrate for sealing with the electrode. The first substrate 42 is divided by a separation groove 49 into a movable portion 44 having a movable electrode 46 and a mirror 33 and a fixed portion 58 having fixed electrodes 51 and 52. The base substrate 35 is provided with through electrodes 36 connected to the fixed electrodes 51 to 54 and the movable electrode 46, respectively. In FIG. 11B, the through electrode 36 is in contact with and electrically connected to the fixing portion 47. Similarly, the movable part contacts the through electrode 36 and is electrically connected.

(Second driving method)
The deflection angle θres near the resonance point of the optical scanning device of the present invention is given by the following equation (4).
θres = (Trq / I) * K (f0, C) (4)
However, K (f0, C) is a function of the resonance frequency f0 and the viscous resistance C, and is inversely proportional to f0 and C.

Kθ: Torsion spring constant Trq: Electrostatic torque between electrodes I: Mirror inertia moment C: Viscous resistance coefficient K (f0, c) is inversely proportional to the viscous resistance coefficient c when the resonance frequency f0 = const.

  As shown in FIG. 12, the viscous resistance is approximately proportional to the pressure. When the pressure is lowered, the viscous drag coefficient can be reduced. Therefore, K (f0, c) increases and the deflection angle θres increases.

  The drive circuit 60 generates a drive pulse having a frequency twice that of the drive signal 62 for the first fixed electrodes 51 and 52. The drive circuit 60 generates drive pulses having the same frequency as the drive signal 62 for the second fixed electrodes 53 and 54. With these drive pulses, the movable portion 44 starts to vibrate due to the electrostatic force generated between the first and second fixed electrodes and the mirror movable electrode 46. At the start of vibration, vibration is started at the natural frequency, and when it reaches a steady state, it vibrates at the same frequency as that of the drive signal 62.

  The operation will be described with reference to FIGS. A case will be described in which vibration is applied by electrostatic force generated between the movable electrode 46 and the first fixed electrode 51, 52 (FIG. 13A). The electrostatic force generated between the movable electrode 46 and the first fixed electrode acts as a force in a direction that pulls the movable portion 44 back to the vibration center 63. Therefore, it can be applied at a timing when the movable portion 44 rotates toward the center. Since the vibration of the movable part is in a state of moving toward the center, the vibration is accelerated in accordance with the rotation direction of the movable part. Therefore, as shown in FIG. 14, excitation can be performed with a drive signal having a frequency twice as high as the drive frequency.

  Next, a description will be given of a case where vibration is applied by an electrostatic force generated between the movable electrode 46 and the second fixed electrode (FIG. 13B). The electrostatic force generated between the movable electrode 46 and the second fixed electrode uses a force in a direction in which the movable electrode 44 is pulled back to the vibration center. In the case of the second fixed electrodes 53 and 54, the electrode arrangement is asymmetric with respect to the vibration center. When applying at the timing when the movable part moves toward the center, one excitation can be performed for one cycle of vibration of the movable part. Thereby, the deflection angle of the mirror 33 can be increased.

Example 2:
FIG. 15 shows the configuration of the second embodiment of the present invention. In FIG. 15, 42 is a first substrate and 43 is a second substrate. The first substrate 42 is provided with torsion springs 45 and 45 ′ on both side surfaces of the movable portion 44 by etching. Further, movable electrodes 46 and 46 ′ are provided on both end faces of the movable portion 44, and the first fixed electrodes (A) and (B) are formed facing the movable electrodes 46 and 46 ′. The movable electrodes 46 and 46 'are formed in a comb shape. The first substrate 42 is divided into a movable part 44 having a mirror, a first fixed electrode (A) 51, and a first fixed electrode (B) 52 by a separation groove 49. Similarly, the first fixed electrodes (A) and (B) are formed in a comb shape. The second substrate 43 is bonded to the first substrate 42 via the insulating layer 48 to form a swing space 59 of the movable portion 44. The second substrate 43 is divided into two second fixed electrodes (A) and (B) by the separation groove 49. The second fixed electrodes (A) and (B) are formed in a comb-tooth shape, and the first and second fixed electrodes and the movable electrode are opposed to each other in a nested state with a narrow gap.

  A movable electrode provided on both end faces of the movable part, a first fixed electrode provided opposite to the movable electrode, and a second fixed electrode provided overlapping the first fixed electrode in the swinging direction, Since each has a comb-teeth shape, the facing area between the electrodes can be increased, and the electrostatic force is proportional to the facing area, so that the vibration amplitude can be increased.

Example 3:
FIG. 16 shows the configuration of Embodiment 3 of the present invention. FIG. 16A shows an optical writing means provided with the optical scanning device of the present invention, and FIG. 16B shows an image forming apparatus provided with the optical scanning device of the present invention. In FIG. 16, the optical writing device comprising the optical scanning device of the present invention has a plurality of optical scanning devices 40 arranged in the main scanning direction. Writing is performed with respect to the writing width by a plurality of optical scanning devices 40. A semiconductor laser 85 emits light based on an image signal from an image signal generator (not shown). The laser beam 86 enters the optical scanning device 40, and the reflected laser beam deflected by the mirror of the optical scanning device forms an electrostatic latent image on the photoconductor 87. The electrostatic latent image formed on the photosensitive member by the developing and fixing unit 88 generates a toner image on the recording paper fed by the recording medium conveying unit 89.

  The optical writing means comprising the optical scanning device of the present invention has a plurality of optical scanning devices arranged in the main scanning direction. In a laser printer, a commonly used optical scanning device is a polygon scanner. Since the optical writing means comprising the optical scanning device of the present invention has a very small number of parts compared to a polygon scanner, a reduction in cost can be expected.

The structure of Example 1 of this invention is shown. A model example for performing vibration characteristic analysis is shown. The electrostatic torque and the return force when a voltage is applied between the first fixed electrode and the movable electrode are shown. The electrostatic torque and the return force when a voltage is applied between the second fixed electrode and the movable electrode are shown. The characteristic of the deflection angle with respect to the driving frequency is shown. The fluctuation of the deflection angle when a plurality of optical scanning devices of the present invention are used simultaneously is shown. It is the figure which added deflection angle (theta) m to the deflection angular frequency characteristic. The example which comprised the thickness of the 2nd fixed electrode thicker than the 1st fixed electrode is shown. Characteristics such as electrostatic torque when the thickness of the second fixed electrode is made thicker than that of the first fixed electrode are shown. The frequency characteristic of the deflection angle in the configuration of FIG. 8 is shown. The figure which assembles an optical scanning device is shown. The relationship between viscous resistance and pressure is shown. It is a figure explaining the 2nd drive method. It is a figure explaining the 2nd drive method. The structure of Example 2 of this invention is shown. The structure of Example 3 of this invention is shown. It is a figure explaining 1st prior art. It is a figure explaining the 2nd prior art. It is a figure explaining the problem of a prior art.

Explanation of symbols

42 1st board | substrate 43 2nd board | substrate 44 Movable part 45 Beam 46 Movable electrode 51, 52 1st fixed electrode 53, 54 2nd fixed electrode

Claims (8)

  A movable electrode provided on both end faces of the mirror, a first fixed electrode provided opposite to the movable electrode, and a second fixed electrode provided so as to overlap the first fixed electrode. An electrostatic force acting between the movable electrode and the first fixed electrode in an optical scanning device that reciprocally vibrates the mirror using a beam provided on the same straight line as a rotation axis and deflects and scans the beam from the light source; An optical scanning device characterized in that the mirror is vibrated by one of electrostatic forces acting between the movable electrode and the second fixed electrode.   2. The optical scanning device according to claim 1, wherein the driving frequency of the electrostatic force is set to a frequency that does not have a peak in a resonance frequency band determined by the inertia of the mirror and the torsion spring constant of the beam.   When the drive frequency of the electrostatic force is compared with the resonance frequency determined by the inertia of the mirror and the torsion spring constant of the beam, and the drive frequency is greater than the resonance frequency, a drive signal is applied to the first fixed electrode, 2. The optical scanning device according to claim 1, wherein when the frequency is lower than the resonance frequency, a drive signal is applied to the second fixed electrode.   The optical scanning device according to claim 1, wherein a thickness of the second fixed electrode is made larger than a thickness of the first fixed electrode.   A base substrate and a cover glass are provided, and the mirror substrate is vacuum-sealed by bonding the base substrate, the mirror substrate composed of the mirror and the first and second fixed electrodes, and the cover glass in this order. The optical scanning device according to claim 1.   When the drive signal is applied to the first fixed electrode and the second fixed electrode, the frequency is different. When the drive signal is applied to the first fixed electrode, the frequency is twice that of the drive signal. The optical scanning device according to claim 1, wherein the frequency is the same as that of the drive signal when applied to.   Each shape of the movable electrode, the first fixed electrode provided opposite to the movable electrode, and the second fixed electrode provided so as to overlap the first fixed electrode is a comb-like shape. The optical scanning device according to claim 1.   In an image forming apparatus that forms an image by performing optical writing in an electrophotographic process, an image carrier that is held rotatably and carries a formed image, and a latent image is formed by performing optical writing on the image carrier. A latent image forming unit comprising the optical scanning device according to claim 1 and a latent image formed by the optical scanning device of the latent image forming unit are formed to form a toner image. An image forming apparatus comprising: a developing unit; a transfer unit that transfers a toner image formed by the developing unit to a transfer target; and a fixing unit that fixes the toner image transferred to the transfer target.

Images