JP2000249962A - Light deflection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the noise of electromagnetic force generated at the time of rotating a motor in a very high speed polygon motor. SOLUTION: In this light deflection device equipped with a polygon motor which is provided with a magnet coil 4 and a Hall elements 51 mounted on a printed circuit board 3 on a fixed base board, and where a permanent magnet for generating torque is stuck to be opposed to the coil 4 on a mirror unit supporting a polygon mirror and rotating at high speed, and which is constituted of the coil 4, the elements 51 and the permanent magnet; the elements 51 is mounted at an electric angle between 5 deg. to 30 deg. on an upstream side with respect to the rotation of the mirror unit from the center position of the coil 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light deflecting device having a polygon mirror used for, for example, a laser printer, a bar code reader, a laser copying machine, and the like.

[0002]

2. Description of the Related Art In an image recording apparatus such as a laser printer, a laser beam enters a polygon mirror (rotating polygon mirror) which rotates at a high speed of a light deflecting device based on information read as writing means of the image, and is reflected. The image is recorded by scanning the light and projecting it on the photoreceptor surface. FIG. 10 is a perspective view showing an embodiment of a beam scanning optical device using a polygon mirror optical deflection device.

In the figure, reference numeral 80 denotes a semiconductor laser; 81, a collimator lens of a beam shaping optical system; 82, a first cylindrical lens; 83, a polygon mirror;
84B denotes an fθ lens, 85 denotes a second cylindrical lens, 86 denotes a third mirror, 87 denotes a cover glass, and 88 denotes a photosensitive drum. In addition, 89 is an index mirror for detecting timing, 89S is an index sensor for an index for detecting synchronization, and 83M is a rotation drive unit of the polygon mirror 83 of the optical deflection device.

The beam light emitted from the semiconductor laser 80 is converted into parallel light by a collimator lens 81, passes through a first cylindrical lens 82 of a first imaging optical system, and is incident on a mirror surface of a polygon mirror 83 rotating at a high speed at a constant speed. I do. The reflected light passes through the second imaging optical system including the fθ lenses 84A and 84B and the second cylindrical lens 85, and passes through a third mirror 86 and a cover glass 87 onto a predetermined spot on the peripheral surface of the photosensitive drum 88. A (main) scan is performed on the diameter. The main scanning direction is finely adjusted by an adjustment mechanism (not shown), and synchronization detection for each line is performed by irradiating a beam before scanning to the index sensor 89S via the index mirror 89.

In order to obtain a good latent image on the photosensitive drum 88 with such a beam scanning optical device, a polygon mirror that rotates at a high speed is formed as a polygon mirror that forms a highly accurate regular polygon. On the other hand, it is required to rotate without inclination and without displacement in the axial direction.

In the case of high-speed rotation, the polygon mirror rotates at high speed using an air bearing. That is, a polygon mirror is attached to the rotating mirror unit, and the mirror unit rotates at a high speed between the outer cylinder bearing and the fixed inner cylinder bearing.

[0007]

In such a light deflecting device, a fixed base plate is provided with a magnet coil and a Hall element mounted on a printed circuit board, and a mirror unit which supports a polygon mirror and rotates at high speed is provided with a magnet coil. A permanent magnet for torque generation is fixed oppositely,
The Hall element provided at the center position of the magnet coil recognizes the magnetized pattern from the rotating permanent magnet and outputs a position signal and a speed signal, and the magnet of the polygon motor composed of the magnet coil and the permanent magnet High-speed rotation is performed by controlling the energization of the coil.

According to the study by the present inventors, in the polygon motor having such a configuration, when the current flowing through the magnet coil suddenly flows in the case of ultra-high speed rotation, the electromagnetic force noise during the driving rotation of the polygon motor is increased. I discovered that. A first object of the present invention is to provide an optical deflecting device that reduces electromagnetic noise caused by a rapid current flow to a magnet coil and reduces noise when a polygon motor is driven and rotated.

In the light deflecting device, the polygon mirror of the regular polygon mirror is rotated at high speed as described above, and scanning is performed by the surface of the polygon mirror. At this time, a mirror surface phase indicating which of the polygon mirrors is operating as a reflecting surface for scanning is detected. As means for detecting the mirror surface phase, means as shown in FIG. 9 has conventionally been used.

FIG. 9 (a) shows an example of such a case, in which a mirror surface phase detecting mark is provided on a mirror unit which rotates together with a polygon mirror which is a rotating body, and a photosensor substrate is provided separately from a driving coil substrate. The mark is detected by a photo sensor provided on the photo sensor substrate to detect the mirror surface phase. In the detection of the mirror surface phase by such means, it is necessary to separately provide a photosensor substrate facing the rotating mirror unit, and the size of the light deflecting device has been increased.

FIG. 9B shows another example, in which a mirror for detecting a mirror surface phase is provided on a mirror unit which rotates together with a polygon mirror, and a magnetic sensor (Hall element) is provided at a position facing the magnet. To detect the mirror surface phase. In the detection of the mirror surface phase by such means,
By additionally providing a magnet for the mirror unit that rotates at high speed, the balance fluctuates, and the rotation loses stability.

A second object of the present invention is to provide an optical deflecting device in which the size of the device can be reduced, the balance can be stabilized, and high-speed rotation can be performed.

[0013]

Means for Solving the Problems A first object of the present invention is to provide a magnet coil, a detecting means for detecting a magnetization pattern of a permanent magnet disposed in the magnet coil, a permanent magnet and a polygon mirror. In the optical deflector that has a rotating mirror unit and that controls the rotation of the mirror unit based on a signal detected by the detecting unit, the installation position of the detecting unit is
An optical deflecting device (first invention), wherein the optical deflecting device is disposed in a circuit board of the magnet coil and shifted from the center position of the magnet coil upstream in the rotation direction by an electrical angle of 5 ° to 30 °. ).

A second object of the present invention comprises a driving magnet coil provided on a coil substrate, and a mirror unit which rotates with a driving permanent magnet facing the magnet coil and a polygon mirror. In the light deflecting device, a detection mark having a different light reflectance is provided on a part of the permanent magnet, and light detection means for detecting the detection mark and detecting a mirror surface phase is provided inside the magnet coil. This is achieved by the optical deflection device (second invention) described above.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention comprises the first invention and the second invention, and an embodiment of an optical deflecting device common to both inventions will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of the light deflecting device. The light deflecting device 1 of this embodiment is incorporated in, for example, the beam scanning optical device of FIG.
6 is deflected by the rotation of 6 and is fixed to the apparatus side by the base plate 2.

The flange 15 is made of aluminum or iron, and is provided with a disk portion 15a at the end of the cylindrical portion 15b.
One end surface 16a of the polygon mirror 16 is brought into contact with the mirror-mounted reference surface 15a1 of the disk portion 15a, and the mirror holding plate 6
Are integrally rotatably assembled via an elastic member 20. The cylindrical portion 15b of the flange 15 is joined to the outer cylindrical bearing 12b by means such as shrink-fitting and integrated to form the mirror unit 100.

The mirror unit 100 is interposed between the upper and lower lower thrust bearings 10, the upper thrust bearing 11, and the inner cylinder bearing 12a, is inserted into the shaft portion 2a of the base plate 2, and is screwed through the plate 13. 14 is attached by screwing to the shaft 2a.

A fixed yoke 50 is provided on the base plate 2, and a printed board 3 on which a magnet coil 4 is mounted is provided. A permanent magnet 5 for generating torque is arranged facing the magnet coil 4, and the permanent magnet 5 is formed by a concave portion 6 a formed in a disk-shaped mirror holding plate 6.
Are provided via an adhesive, and a polygon motor is constituted by the above arrangement.

The rotary shaft 12 is composed of an inner cylinder bearing 12a and an outer cylinder bearing 12b. The outer cylinder bearing 12b is rotatable with respect to the inner cylinder bearing 12a, and a flange 15 is provided on the outer cylinder bearing 12b. They are joined by the cylindrical portion 15b. In this embodiment, the bearing structure is a dynamic pressure bearing structure including a lower thrust bearing 10, an upper thrust bearing 11, an inner cylinder bearing 12a, and an outer cylinder bearing 12b, and the dynamic pressure generating groove is formed on the lower thrust bearing surface. And at least one of the outer peripheral surface of the inner cylindrical bearing 12a.

The cylindrical portion 15b of the flange 15 is
By joining the outer cylindrical bearing 12b to the outer cylindrical bearing 12b, the joining strength is improved. Further, by setting the outer periphery of the cylindrical portion 12b as a reference for mounting the rotation center axis of the polygon mirror 16, the axial center accuracy of the polygon mirror 16 is improved. Have been.

The cylindrical portion 15b of the flange 15 is
Is preferably shrink fit to the outer cylinder bearing 12b,
Bonding by other press-fitting means may be used. Such joining eliminates the tilt angle when the polygon mirror 16 is attached, and can more reliably achieve the accuracy with respect to the axis.

In the fabrication, after the flange 15 and the outer cylinder bearing 12b are joined, a mirror mounting reference surface 15a for attaching the polygon mirror 16 to the disk portion 15a.
1 and a polygon mirror 16 is inserted into the cylindrical portion 15b of the flange 15 so that one end face 1 of the polygon mirror 16 is cut.
6a is brought into contact with the reference surface 15a1.

An elastic member 20 such as a leaf spring is interposed between the other end surface 16b of the polygon mirror 16 and the mirror holding plate 6, and the end surface of the cylindrical portion 15b of the flange 15 and the mirror holding plate 6 are fastened with screws or the like. Fastened and fixed by the member 21,
The pressing force of the polygon mirror 16 by the elastic member 20 is stabilized, and the polygon mirror 16 is fixed without being distorted.

With respect to the light deflecting device having the configuration described above,
The polygon motor will be described in more detail.

FIG. 2A is a plan view showing an arrangement relationship of the magnet coil 4 provided on the printed circuit board 3. FIG.
(B) is a plan view of the permanent magnet 5 fixed to the mirror pressing plate 6 rotating at high speed. In this embodiment, as shown in FIG. 2A, six sets of magnet coils 4 are equally arranged on the same circle, and the magnet coils 4a1 and 4a2 are located opposite to each other.
2. The magnet coils 4c1 and 4c2 are located facing each other. Also, the magnet coils 4a1, 4b
The Hall elements 51 for detecting the magnetized state of the permanent magnet passing directly above are provided in the elements 1 and 4c1, and information on the rotational speed and position of the mirror unit is obtained based on the detection signals from the three Hall elements. That is, this Hall element has a function as a speed sensor and a position sensor means. A permanent magnet 5 having four poles to eight poles on the same circle is provided opposite the magnet coil 4 as shown in FIG.

FIG. 3 shows a basic circuit for driving a polygon motor. The magnet coils (4a1, 4a2), (4b1, 4b2) facing each other in FIG.
(4c1, 4c2) are connected to the series, respectively, and the three connected wires are connected to one point, and the other terminal is connected to the U,
V and W are connected respectively. The three Hall elements 51 detect a change in the magnetic field from the N and S poles of the permanent magnet 5 located opposite to each other, and output an analog signal. The analog output signals from the three Hall elements 51 are converted into digital signals at 51a and output as H or L signals. And the other input to the gate driver as a position signal, and the control unit controls the switching transistors Tr1, Tr2, Tr3, Tr4, T4 of the driver based on the position signal.
ON / OFF operation of r5 and Tr6 is performed. For example, when Tr3 is turned ON and Tr5 is turned ON, the terminal (U-
V), that is, the magnet coils 4a1, 4a2,
Power is supplied to 4b1 and 4b2.

In the present embodiment, the magnet unit 4 is composed of six sets of magnet coils 4 and four pole pairs of permanent magnets 5, and the energization is switched 24 times during one rotation of the mirror unit 100, that is, 1 /.
Switching of energization is performed six times during four rotations. For example, during one rotation, (U-V), (U-W), (V-W),
The switching of energization of (VU), (WU), and (WV) is repeated four times. The switching of the energization is performed by switching transistors Tr1, Tr2, Tr3.
ON / OFF and switching transistors Tr4, T
This is performed by a combination of ON / OFF of r5 and Tr6 and switching thereof. The rotation control of the polygon mirror performing the ultra-high-speed rotation with the above basic circuit is performed based on the detection of the magnetic field fluctuation by the Hall element 51.

(Embodiment 1 First Invention) In the optical deflecting device of the present invention, the mounting position of the Hall element 51 disposed inside the magnet coils 4a1, 4b1, 4c1 is located upstream of the center position of the magnet coil in the rotational direction. 5 as electrical angle
The electromagnetic noise generated during high-speed rotation can be reduced by displacing them at an angle of 30 ° to 30 °. Hereinafter, the present invention will be described in detail.

FIG. 4 shows the state of the voltage at the U, V, and W terminals in the basic circuit for driving the motor shown in FIG. 3, and the current iu flowing through the U terminal when focusing attention on the U terminal.
FIG. 4A shows magnet coils 4a1, 4a2; 4b.
1, 4b2; the state of the back electromotive force excited by the permanent magnet 5 passing over 4c1, 4c2. FIG.
(B) shows a Hall element 5 at the center of the magnet coil.
1, the switching transistor is activated based on the output from the Hall element 51 and the voltage U,
The state of the drive voltage at the V and W terminals is shown. FIG. 4C shows a current waveform of the current iu flowing through the terminal U under the voltage conditions shown in FIGS. When observing this current waveform, a sudden large current flows at the falling portion of the current. According to the study of the present inventors, it has been found that this rapid current flow is greatly related to electromagnetic force noise, and that noise is reduced at the same time by reducing the portion of this rapid current flow. The present invention reduces the portion of the rapid current flow at the time of the fall of the current to reduce noise, and will be described with reference to the explanatory diagram of FIG.

FIG. 5A shows a current waveform portion of the current iu surrounded by a dotted line in FIG. 4C.

When the Hall element 51 is located at the center of the magnet coil and there is no deviation of the driving voltage with respect to the back electromotive voltage, it indicates that a sharp current flows when the driving current falls. . Looking at this current waveform, the current cannot flow rapidly due to the L component of the coil in the rising portion, and the shoulder has a rounded waveform, but in the falling portion, the voltage compensated by the drive side. The difference flows through the coil at a stretch and shows a high and sharp waveform. This waveform portion is a cause of noise, and the flow of this current which affects noise is determined by the voltage difference between the drive voltage and the back electromotive voltage.

FIG. 5B shows a state in which the operation of the driving voltage is hastened by shifting the Hall element 51 from the center position of the magnet coil to the upstream side of the rotation. By advancing the operation of the drive voltage, the rise of the drive current is slightly earlier, and the rounded portion of the shoulder is shaped to be smaller. 5 (a), the sharp part is also lowered, and a gentle current flows, so that the electromagnetic noise is also reduced. According to the study of the present inventors, the installation position of the Hall element 51 is changed to the magnet coil 4a1 shown in FIG.
By arranging the electric angle between 5 ° and 30 ° as an electrical angle on the upstream side in the rotation direction from the center positions of 4b1 and 4c1 and speeding up the operation of the drive voltage, the electromagnetic force noise was significantly reduced. FIG. 6 shows a mounting state of the Hall element 51 in the magnet coils 4a1 (4b1, 4c1).

Here, the electrical angle is one electrical cycle (360
°), and in the three-phase drive polygon motor described in the present embodiment having six sets of magnet coils and eight magnetic poles, the mirror unit has one cycle in four cycles.
Since it rotates, there is a relationship of (mechanical angle) = (electric angle) / 4. In the case of a three-phase drive polygon motor having nine magnet coils and 12 magnetic poles, the mirror unit makes one rotation in six cycles.
= (Electrical angle) / 6.

FIG. 7 is a graph showing the relationship between the detection position of the Hall element 51 and noise. Under a predetermined environment, the Hall element 51 is connected to the magnet coils 4a1, 4b1, 4c1.
The relationship between the electrical angle and the noise shifted from the respective center positions to the upstream side in the rotation direction is shown as an electrical angle of 5 ° to
It is appropriate to shift by 30 °. When the electric angle for shifting the installation position of the Hall element 51 to the upstream side in the rotation direction is less than 5 °, the reduction of the electromagnetic noise is hardly recognized. When the installation position of the Hall element 51 exceeds 30 ° on the upstream side in the rotation direction, an increase in noise is also recognized, but at the same time, the electric efficiency decreases, so that a large amount of current flows through the magnet coil. And the rotation of the polygon motor becomes unstable, which is not preferable.

(Second Embodiment / Second Invention) In the light deflecting device of the present invention, a detection mark 61 having a light reflectance different from that of the magnet surface is provided on a part of the driving permanent magnet 5, and this detection mark is provided. A photo sensor 70 is provided inside the magnet coil 4 to detect the mirror surface phase as light detecting means for detecting the mirror surface phase by detecting 61. The photo sensor substrate is compared with the prior art. 9 (a), and the rotation balance is stabilized by removing the magnet for detecting the mirror surface phase attached to the mirror unit (see FIG. 9 (a)). b)
reference).

An embodiment of the present invention will be described. As shown in FIG. 2B, a detection mark 61 for detection is provided on the surface of the permanent magnet 5 by marking with a black body spray having a different light reflectance from the surroundings. The detection mark 61 may be formed by coating, pasting or the like other than spraying.

A photosensor 70 provided on the printed circuit board 3 and provided inside the magnet coil 4 as shown in FIG. 2A is a photocoupler comprising a light emitting element 71 and a light receiving element 72, and emits light from the light emitting element 71. By permanent magnet 5
The light receiving element 72 receives the reflected light, detects the detection mark 61 based on the difference in the amount of reflected light, and detects the mirror surface phase based on this detection.

FIG. 8A is a circuit diagram of the photo sensor 70. A light emitting diode or the like is used as the light emitting element 71, and the amount of emitted light is adjusted by adjusting the variable resistor 71a. A transistor 71b is provided in the circuit so that the light emitting element 71 is turned on in synchronization with the start of rotation of the polygon motor.

A phototransistor or a photodiode is used as the light receiving element 72, and the detection sensitivity is adjusted by a variable resistor 72a. The reflected light on the surface of the permanent magnet 5 is received, and a signal is output. You. FIG. 8B shows an example of an I / V-converted signal output. The output of the reflected light from the surface of the permanent magnet 5 is 5 V, whereas the output of the detection mark 61 is the reflected light. Is 0 V, and the passage of the detection mark 61 is detected by the voltage difference between the two, whereby the mirror surface phase is detected.

With this configuration, the photo sensor 70 is turned on in synchronization with the rotation start signal of the polygon motor.
In this state, the total power-on time of the photosensor 70 is reduced, and the life of the sensor can be extended. Further, since the light emission amount and the sensitivity of the photo sensor 70 are adjusted by the volume, even if the performance of the photo sensor 70 is deteriorated, the deterioration is corrected, and the problem of poor detection is solved.

[0042]

According to the first aspect of the present invention (claim 1), there is provided an optical deflecting device in which the flow of current to the magnet coil becomes gentle, electromagnetic noise is reduced, and noise during rotation is extremely low. It became a thing.

According to the second invention (claim 2), by marking the rotating permanent magnet and providing the light detecting means for detecting the mirror surface phase inside the magnet coil on the printed circuit board, the size can be reduced and the size can be reduced. An optical deflecting device having a reduced balance fluctuation factor has been provided. In addition, the light emitting element of the photo sensor only at the time of rotation, and the effect of reducing the life degradation due to the use are produced. (Claims 3 and 4)

[Brief description of the drawings]

FIG. 1 is a sectional view of a light deflecting device.

FIG. 2 is a plan view of a magnet coil and a permanent magnet.

FIG. 3 is a basic circuit diagram of motor driving.

FIG. 4 is a state diagram of voltage and current at a terminal portion.

FIG. 5 is an explanatory diagram showing voltage and current waveforms.

FIG. 6 is an explanatory diagram showing a mounting state of a Hall element.

FIG. 7 is a graph showing a relationship between a detection position of a Hall element and noise.

FIG. 8 is an explanatory diagram showing a circuit diagram and outputs of a photosensor.

FIG. 9 is a sectional view showing a conventional mirror surface phase detecting means.

FIG. 10 is a perspective view of a beam scanning optical device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical deflector 2 Base plate 3 Printed circuit board 4 Magnet coil 5 Permanent magnet 6 Mirror holding plate 12 Rotating shaft 15 Flange 16 Polygon mirror 51 Hall element 61 Detection mark 70 Photosensor 71 Light emitting element 72 Light receiving element

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Claims (4)

[Claims] 1. A magnet unit comprising: a magnet coil; a detection unit for detecting a magnetization pattern of a permanent magnet disposed in the magnet coil; and a rotating mirror unit including the permanent magnet and a polygon mirror. An optical deflecting device that controls the rotation of the mirror unit based on a signal detected by the detection unit, wherein the installation position of the detection unit is in a circuit board of the magnet coil, and the center of the magnet coil is An optical deflecting device, wherein the optical deflecting device is disposed at an electrical angle shifted from 5 ° to 30 ° upstream of the position in the rotation direction. 2. An optical deflecting device comprising: a driving magnet coil provided on a coil substrate; and a mirror unit that rotates with a driving permanent magnet and a polygon mirror facing the magnet coil. A light deflector, wherein a detection mark having a different light reflectance is provided on a part of a magnet, and light detection means for detecting the detection mark and detecting a mirror surface phase is provided inside the magnet coil. 3. The light deflecting device according to claim 2, wherein the light detection means starts detection in synchronization with the start of rotation of the mirror unit. 4. The light deflecting device according to claim 2, wherein said light detecting means is capable of adjusting an irradiation light amount and / or a detection sensitivity.