JP2657824B2 - Laser beam control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Technical Field) In the present invention, since a laser beam divergence angle of a laser diode (LD) serving as a laser beam light source differs for each LD, when the LD is incorporated in an apparatus and used, The present invention relates to a laser beam control system capable of obtaining the same light amount (beam intensity, beam shape) for any LD.

(Prior art) As a laser beam light source used in a laser printer, etc., the divergence angle of the laser beam differs for each LD as described above. The light amount was adjusted in the section to optimize the image quality.

FIG. 5 is a structural sectional view showing an example of a laser printer embodying the present invention, and FIG. 6 shows a laser unit in the writing optical unit of FIG.

An outline of the configuration and operation of this laser printer is as shown in FIG. 5, on the peripheral surface of the photosensitive drum 1, in the order of its rotation indicated by an arrow, a charger 2, a developing unit 3, a transfer charger 4, a cleaning A unit 5 is provided, and a writing optical unit 7 is provided so that a writing light beam enters the photosensitive drum 1 and is exposed at a position 6 between the charger 2 and the developing unit 3.

In this device, the charger 2 and the optical writing position 6 are arranged below the photosensitive drum 1, and the writing optical unit 7 is provided below the photosensitive drum 1, the developing unit 3 and the cleaning unit 5. The transfer charger 4 is arranged above the photosensitive drum 1. A paper feed cassette 8 for feeding a transfer sheet to a transfer section between the transfer charger 4 and the photosensitive drum 1 is provided further below the writing optical unit 7, and the transfer sheet is in contact with a feed roller 9 and a friction contacting the feed roller 9. The double feed is separated by the pad 10 and fed one sheet at a time. A large U-turn is made at the side of the developing unit 3, and a pair of registration rollers 11 and 12 provided above the developing unit 3 are provided.
As a result, the paper is fed to the transfer unit at a proper timing so that the image and the image formed on the photosensitive drum 1 are aligned.
A fixing unit 13 is provided on the transfer paper path after the transfer, and a paper discharge tray 14 is provided on the discharge side.

As shown in FIGS. 5 and 6, the writing optical unit 7 reflects light (shown by a dashed-dotted line) that blinks in response to the image information signal emitted from the laser unit 15, The light enters a pyramidal mirror 18 as a mirror integrally attached to the axis of a deflector 17 driven by a scanner motor, and repeatedly deflects a fixed angle range. The deflected light is corrected by the fθ lens 19 so as to form a linear image at the light writing position 6 on the photosensitive drum 1, and enters the photosensitive drum 1 via the second mirror 20 and the toroidal lens 21. The main scanning is performed by the deflection of light, the sub-scanning is performed by the rotation of the photosensitive drum 1, an image corresponding to the image information signal is written, and an electrostatic latent image is formed. The components of the writing optical unit 7 are mounted directly on the base cover 22 of the device.

The electrostatic latent image formed on the photosensitive drum 1 forms a toner image developed by the developing unit 3 and is transferred to the transfer paper fed by the pair of registration rollers 11 and 12 by the action of the transfer charger 4. You. After the transfer, the transfer paper separated from the photosensitive drum 1 is fixed by the fixing unit 13,
The paper is discharged to the paper discharge tray 14.

On the other hand, the toner remaining on the photosensitive drum 1 after the transfer is cleaned by the cleaning unit 5 to prepare for the next image formation.

In the laser printer having the above configuration, a beam shaping slit is provided on an optical path before the imaging lens in order to form a beam with a required spot diameter required for image formation on a surface to be scanned (for example, a photoconductor). The beam after passing through the slit is made incident on the reflecting surface of the deflector (biramidal mirror) at an angle to the normal direction, and the reflected light is made incident on the imaging lens as an incident beam. Light beam scanning devices are known.

For example, as shown in the optical component arrangement of the laser unit of FIG. 6 and the writing optical unit of FIGS. 7 and 8,
In FIG. 6, a beam diverged from a semiconductor laser 23 (LD) as a light source is collimated by a collimator lens 24 and then shaped by a slit 25 to form a semiconductor laser unit 15.
Is emitted.

Then, this beam is deflected by a first mirror 16 to a deflector 17.
The light is incident along a substantially rotating axis of the pyramidal mirror 18 on the reflecting surface as if the cylinder constituting the reflecting surface was cut obliquely.

When the pyramidal mirror 18 rotates in such a state,
Along with this, the light is deflected and proceeds to the fθ lens 19 shown in FIGS. 5, 7 and 8, the optical axis is bent by the reflecting portion 26 of the second mirror 20, passes through the toroidal lens 21, and passes through the photosensitive member. An image is formed on the outer peripheral surface of the drum 1.

The optical fiber 27 shown in FIG. 7 disposed between the fθ lens 19 and the second mirror 20 is guided to a photo sensor 28, which is for taking out synchronous light for determining a writing position. is there.

In such an optical system, the slit 25 related to beam shaping before the deflector 17 in FIG.
15 and fixed to an immovable member, and such a configuration causes the following problem.

(Problems to be Solved by the Invention) The above-described elliptical incident beam _LN shaped by the slit 25 of the laser unit 15 is reflected by the first mirror 16 and is reflected by the pyramidal mirror 18 in FIGS. 9 and 10. And the reflected beam L _O.

That is, as shown in FIG. 9, the pyramidal mirror 18 is rotated by the deflector 17 and reflected by the inclined reflecting surface 18A.
After reflection, the diameter a of _LN becomes an elliptical beam having a diameter a having a major axis in the x-axis direction in which the diameter of the reflected beam L _O is the main scanning direction.
However, since the incident angle is inclined with respect to the normal direction, when the pyramidal mirror 18 rotates 90 °, the diameter of the reflected beam L _O becomes longer in the y-axis direction, which is the sub-scanning direction orthogonal to the main scanning direction, as shown in FIG. It becomes an elliptical beam having a diameter a and having an axis.

Of course, in the elliptical beam, the diameter in the short axis direction orthogonal to the long axis direction is also deformed in the coordinate axis direction. As a result, the deflection beam rotates on the photosensitive member 1 while the pyramidal mirror 18 rotates 90 °. Just after the 90 ° rotation, the positions of the major axis and the minor axis are reversed in the main scanning direction and the sub-scanning direction.

In the imaging optical system such as the fθ lens 19 and the toroidal lens 21, the imaging diameter is usually determined by the diameter of the beam incident on the lens, and the diameter of the incident beam incident on the lens depends on the main scanning direction, Since the diameter varies in the sub-scanning direction, if the diameter of the deflecting beam changes as described above, the final spot diameter on the surface of the photoreceptor varies and the image quality deteriorates.

That is, in a beam scanning device that irradiates an elliptical beam at a finite angle with respect to the normal direction of the reflection surface of the pyramidal mirror 18 rotated by the deflector, and deflects the beam,
In particular, in the case of an optical arrangement in which the incident angle and the reflection angle form about 45 °, the elliptical beam deflected by the rotation of the deflector,
Scanning is performed while rotating, and the spot diameter of the condensed beam on the surface to be scanned by the imaging lens changes in the main scanning direction and the sub-scanning direction. Such a change in the light amount (change in the beam power) at the optical writing position 6 is called shading, which has a problem of adversely affecting the image quality.

An object of the present invention is to prevent image quality from being degraded due to such a situation.

(Structure and Function) In order to achieve the above object, the present invention integrates a laser diode (LD) as a laser beam light source and a driving circuit board thereof, and outputs a signal corresponding to a selection class regarding the laser beam divergence angle of the LD. The integrated drive circuit board outputs the light to the light amount control unit.

The shape of the beam emitted from the LD is an elliptical beam as shown in FIG. 4 (a), and this light quantity distribution is shown in FIG. When measured in the horizontal direction (θ in the x direction) and in the vertical direction (θ⊥ in the y direction), the widths of the half point of the maximum intensity of the beam light amount (full width at half maximum) are θ (horizontal direction) and θ⊥, respectively. (Vertical direction)
It is known that θ and θ⊥ vary greatly from one LD to another. FIG. 3C shows a peak intensity of 1/2.
Shows the light output at the point of.

FIG. 3 shows the divergence angles θ and θ of the LD in addition to the pyramidal optical system.
Shading amount including the variation of ば ら つ き (vertical axis)
With respect to the deflection angle (horizontal axis, beam deflection angle at the time of optical writing). (1) to (7) in FIG.
Is 8 ゜, 9 ゜… 14 ゜ (7 types), θ⊥ is 20 ゜, 24
゜… 38 ゜ (six types) are shading amounts, all of which largely swing in the positive and negative directions based on 100%,
It can be seen that the image quality is adversely affected and cannot be used as it is.

In the present invention, classification is performed according to the combination of θ and θ⊥, and in the example of FIG. 3, from a maximum of 42 types of 7 types of θ and 6 types of θ⊥, light amount control is performed so as to electrically correct each variation. Is performed.

(Embodiment) FIG. 1 shows an LD drive circuit for implementing the method of the present invention. For example, the LD drive circuit is provided in an LD drive circuit board 29 integrated with the laser unit 15 shown in FIG.
Compatibility is provided in units, and the light amount of the LD can be adjusted as described later.

As shown in the figure, the semiconductor laser 23 includes a laser diode (LD) 23 and a monitor photodiode 30.
The 23 output beams 31 are monitored by a monitor photodiode 30. The light amount of this LD is adjusted to be constant by the variable resistor 35 under certain conditions (such as fixing the deflection angle to be constant). Amplifier 32
Amplifies the input signal LDDIN of the LD drive current and supplies it to LD23. Inverter driver 33 outputs video signal ▲
▼ turns ON / OFF the current supplied to LD23 to write. Amplifier 34 the reference voltage V _S monitor from the connection point between the monitor photodiode 30 through the variable resistor 35 from the current (LD
23 Output beam 31 detects signal current proportional to
The comparator 38 compares the reference signal constituted by 36 and 37 with a reference signal, and outputs a coincidence signal COMS.

Although the laser unit 15 mentioned that LD driving circuit board 29 are integrated, a signal corresponding to the classification of Shiedingu amount due to variations in divergence angle of each LD in the substrate, for example, ID ₁ ~ID ₃ Is provided. This is for example prepared jumpers J ₁ through J _3, or to connect a jumper wire of each of terminals 39 and 40, 41, 43 and 44 as shown by a dotted line shown in the illustrated example and do not 2 ³ = The combination of 8 kinds, the class of the laser unit 15 is resistance 45-47
And outputs it to the outside as an electric signal (combination of ID ₁ ~ID ₃₎ through. For example, θ = 10 ° and θ⊥ = 20 °, θ = 11 ° and θ⊥ = 24 °, θ = 12 ° and θ⊥ = 24 °, θ = 13 ° and θ
Connect or not connect the jumper wire to the LD sorting group with ⊥ = 28 ゜ and θ = 14 ゜ and θ⊥ = 28ID and ID
_{1 to} ID ₃ = H level is output, and LDDIN is controlled by the light amount control unit of the main body to correct this shading.

FIG. 2 shows the ID signal and the coincidence signal of the comparator 38.
FIG. 3 shows a block diagram of an example of a circuit for performing light quantity control by COMS.

In the figure, reference numeral 48 denotes a host machine which sends write data ▼ to a write frequency control unit 49, and the control unit outputs a video signal ▼ to the impeller driver 33. Reference numeral 50 denotes a light amount control unit, which is controlled by a write position control unit 51 and a write frequency control unit 49 which periodically operate with an optical synchronization signal, and which amplifies an input signal LDDIN of an optimum LD drive current by the ID signal and the coincidence signal COMS. Output to 32.

In this way, it is possible to equivalently eliminate shading and improve image quality.

(Effects of the Invention) As described above, the present invention provides a laser unit having compatibility even when the divergence angle of a laser beam from a laser diode varies from laser diode to laser diode and the shading amount is largely varied. The ID signal corresponding to the LD is transmitted from the laser diode drive circuit board to the light amount control unit to adjust the light amount, equivalently eliminating shading, and improving image quality.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an LD drive circuit for implementing the method of the present invention, FIG. 2 is a block diagram of a control section for a video signal and an LD drive current, and FIG. FIG. 4 is a graph showing the radiation characteristic of LD, FIG. 5 is a cross-sectional view showing the configuration of a laser printer embodying the present invention, and FIG. FIGS. 7 and 8 are diagrams showing the arrangement of the optical system of the light beam scanning device, FIG. 9 is a diagram showing the deflection mode of the pyramidal mirror at an arbitrary rotational position, and FIGS.
The figure shows the deflection mode when rotated by 90 ° from the rotation position in FIG. 1 ... Photoconductor drum, 15 ... Laser unit, 16 ...
1st mirror, 17 ... deflector, 18 ... pyramidal mirror,
18A: inclined reflecting surface, 19: fθ lens, 20: second mirror, 21: toroidal lens, 23: semiconductor laser, 24: collimator lens, 25: slit, 26 ...
Reflector, 27 ... optical fiber, 28 ... photo sensor,
29… LD drive circuit board, 30… Monitor photodiode, 31… Output beam, 32,34… Amplifier, 33… Inverter driver, 35… Variable resistance, 36,37,45-47 ……
Resistance, 38 Comparator, 39 to 44 Jumper wire terminal, 48 Host machine, 49 Writing frequency control unit, 50
... Light quantity control unit, 51... Write position control unit.

Claims (1)

(57) [Claims] 1. A laser diode (LD) serving as a light source of a laser beam and a driving circuit board thereof are integrated, and a signal corresponding to a selection class relating to a laser beam divergence angle of the LD is transmitted from the integrated driving circuit board. A laser beam control system characterized by outputting to a control unit.