JPH01282516A - Optical unit for laser printer - Google Patents

Abstract

PURPOSE:To prevent deterioration and to compact the titled optical unit compact by uniting a semiconductor laser element, a semiconductor laser element driving circuit, a period signal detecting element, and a period signal detecting circuit on a substrate integrally, and fitting them to the plane part of an optical unit case. CONSTITUTION:The plane part 112a is provided on the wall part 112 of the optical unit case 101 and the substrate 104 is fitted outside it. This substrate 104 is fitted with a semiconductor laser element 201 for light emission and a photodiode 203 for synchronizing signal detection. Then a constant voltage power circuit is provided on the substrate 104, so even if an unnecessary surge enters the substrate 104 from a power source line, it is cut off by the constant voltage element 301 without fitting any LC filter like before. The semiconductor laser element never deteriorates.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical unit for forming a latent image on a photoreceptor by driving a light emitting element such as a laser according to an image signal.

(Prior Art) In a laser printer that is commonly used as a printer, an optical scanning system including a semiconductor laser, a polygon mirror, etc. is usually installed as a unit. In this type of optical unit, a semiconductor laser element emits a laser beam in response to an image signal from an external image reader, etc., and a polygon mirror deflects the laser beam to a photoreceptor installed outside the optical unit. Expose the drum. The electrostatic latent image formed on the photoreceptor drum is printed by electrophotography.

As shown in FIG. 5, the optical unit (print head) 2 is installed, for example, in the upper part of the laser printer main body l. FIG. 6 shows an example of a conventional optical unit. Place the print head case 1 on the print head base li.
2, a semiconductor laser drive circuit board 13, and a polygon mirror drive board 14 are attached. The print head case 12 includes two protrusions 12a and +2b.

A substrate I5 for mounting a semiconductor laser element is fixed to the outside of the convex portion 12a. A laser beam emitted from a semiconductor laser element (not shown) is corrected into parallel light by a collimator lens 16 attached to an aperture provided in a convex portion 12a, and further focused by a cylindrical lens 17 onto one deflection point of a polygon mirror 18. be illuminated.

The focused laser beam is deflected according to the rotation of the polygon mirror 18, passes through the f-theta lens 19 for optical path correction, is reflected diagonally downward by the mirror 20, and passes through the opening of the optical unit case I2 to the outside. go out to On the other hand, the synchronization signal generation board 22 that generates the synchronization signal for the start of deflection (scanning) by the polygon mirror I8 is
It is attached to the convex portion 12b of the optical unibody h12. At the start of deflection, the laser beam reflected from the polygon mirror 18 is reflected by the mirror 21 and detected by a photodiode (not shown) on the substrate 22.

(Problem to be Solved by the Invention) In the optical unit of a conventional laser printer, generally, the semiconductor laser element, semiconductor laser drive circuit board, synchronization signal detection element, and synchronization signal detection circuit board are the most important components in the mechanical configuration. Each is placed in an easy-to-place position. The optical path length from the polygon mirror to the photoconductor needs to be approximately the same as the optical path length from the polygon mirror to the optical sensor for synchronization detection, but conventional optical units are large and each circuit is mounted on one board. Optically, it was impossible to integrate them.

Alternatively, one end of the tip fiber is installed at the same amount signal detection position, the other end is led directly to the printer control board, and the control board is provided with a synchronization signal detection circuit.

In this case too, each circuit is arranged 4 on a separate board.

However, with recent downsizing of printing systems and improvements in lens performance, it has become possible to make optical units more compact.

Constructing each circuit integrally on a board and attaching it to the optical unit has the advantage of lowering the cost of parts and improving reliability, and also facilitates miniaturization of the optical unit.

An object of the invention is to provide a compact optical unit.

(Means for Solving the Problems) An optical unit for a laser printer according to the present invention is provided with a weir plate attached to a part of the side wall of an optical unit case that houses a scanning optical system for scanning a photoreceptor with a light beam. A flat part for emitting a light beam is formed on the flat part.
A light emitting element faces the first opening, and a synchronizing signal detecting element faces the second opening. are installed respectively, and inside the optical unit case,
The present invention is characterized in that, prior to the start of scanning, an optical system for detecting a synchronization signal is arranged to guide the light beam emitted by the light emitting element to the second aperture.

(Function) A semiconductor laser element, a semiconductor laser element drive circuit, a synchronization signal detection element, and a synchronization signal detection circuit are integrated into a substrate and attached to the flat surface of the optical unit case. The positions of the semiconductor laser element and the synchronous signal detection element on the substrate are determined by the configuration of the optical system within the optical unit case.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view of an optical unit 100 according to an embodiment of the present invention. Inside the optical unit case lO1, a polygon mirror 102, a cylindrical lens 103, f-e
A lens 106, mirrors 108, 109 and 110 (not shown) are arranged.

The optical unit case 101 consists of a planar bottom plate part 111 and a surrounding wall part 112. The upper part of the wall part 112 is sealed by a planar lid part (not shown). The wall portion 112 includes a mounting bracket portion +13. for attaching the optical unit case 101 to the printer body. l 13. ...is provided.

Inside the optical unit case 101, a polygon mirror 10
The reflected light from 2 passes through f-theta lens +06 to mirror 1.
09, the polygon mirror 102, f-θ
Lens +06 and mirror I09 are arranged in a row. The mirror 109 is rectangular and has a polygonal shape.
The laser beam, which is deflected in the elongated direction with the rotation of 02, is reflected diagonally downward. This reflected light passes through a slit 114 provided in the bottom plate portion Ill of the optical unit case 101 and exits to the outside. The wall portion 112 of the optical unit case 101 accommodates these optical components 102, 106, 109.
It has a shape that can accommodate.

Further, on the side of the optical path from the polygon mirror 102 to the mirror 109, a semiconductor laser element (not shown) 201,
Collimator lens +05, lens +03
, an optical path for a laser beam consisting of a polygon mirror 102 is provided, and the laser beam emitted from the semiconductor laser element 201 is focused on the deflection surface of the polygon mirror 102 to be used for a person q(.

Therefore, the wall portion 112 of the optical unit case 101 is
As shown in the upper right side of FIG. 1, it includes a flat part 112a,
A substrate 104 is attached to the outside thereof. This board! 04, a semiconductor laser element (not shown) 20+ for emitting light and a photodiode (light receiving element) 203 for detecting a synchronizing signal are attached, as will be explained later. Therefore, all opto-electronic components 201, 203 necessary for laser beam exposure are mounted on the same substrate 104.

Parts 201 and 203 on the board and optical unit case +0
In order to form an optical system with the optical components inside the optical unit case 1, the beam exit side of the semiconductor laser element 20+ and the beam incidence side of the photodiode 203 are formed through holes 115 and 11 opened in the flat part 112a of the optical unit case 101, respectively.
Optical unit case through 6! 01, and a collimator lens 105 is attached to the aperture +15.

For synchronization signal detection, a mirror 108 is provided near the end of the mirror 109 on the scanning start side, and a mirror +0
The mirror 110 reflects the reflected light of 8 to the hole +16.
(not shown) is provided near the end of the scan end of the mirror 109.

FIG. 2 shows the operation of the optical system in the optical unit 100. The laser beam emitted from the semiconductor laser element 20+ in accordance with the drive signal passes through the collimator lens 105.
The light passes through the lindrical lens lO3 and enters one surface of the polygon mirror 102. The beam reflected by this passes through the r-〇 lens +06 and becomes a mirror! 09, exits the optical unit +00 through the slit +14, enters the photoreceptor drum 202, and enters the photoreceptor drum 202.
to expose. As the polygon mirror 102 rotates, the emission direction of the beam reflected from one surface of the polygon mirror changes as shown in the figure and scans the photoreceptor drum 202 in the axial direction. In order to synchronize this axial scanning, at the start of scanning, the laser beam is reflected by mirrors 108 and 110, passes through aperture 116, and enters photodiode 203. Note that when arranging the optical system, the polygon mirror 10
The mirror 108°+10 and the photodiode 203 are arranged so that the optical path length from the polygon mirror 102 to the photosensitive drum 203 is approximately equal to the optical path length from the polygon mirror 102 to the photosensitive drum 202. Conventionally, a semiconductor laser element 20
It may be impossible to arrange a synchronization signal detection element near 1. However, in recent years printing systems (photoreceptor drum 202
Due to the miniaturization and improvement of lens performance (e.g.), it has become possible to arrange the semiconductor laser element 201 and the synchronization signal detection photodiode 203 in close proximity on the same substrate while keeping both optical path lengths equal.

FIG. 3 is a diagram of the circuit configured on the substrate 104. This circuit is characterized by comprising a semiconductor laser driving circuit and a synchronization signal detection circuit similar to the conventional circuit, and also includes a power supply circuit. Moreover, FIG. 4 shows a perspective view of the board 104 to which each circuit component is attached.

The circuit on the upper left side of FIG. 3 is a power supply circuit that supplies a constant voltage of +5V to the elements on the substrate. Connector (4th
For example, a voltage of +12■ is supplied through the DC-1 (see figure) 400, and the voltage is stabilized by a constant-voltage power supply element (for example, a 3-terminal regulator (7805) (voltage specification 5±0.2V) 301.DC-1 ) A constant voltage power supply element such as a converter may be used.

Fixed? 1tl) Terminal A to which +5V voltage is supplied by E'ffl source element 301 is connected to each terminal A° in the figure, and to G
The ND terminal B is connected to each terminal 13° in the figure, but these connecting lines are omitted in FIG. 3 to avoid cluttering the drawing.

Since a constant voltage power supply circuit is provided on the board +04, there is no need to install an LC filter like in the past, and the power supply line (+
Even if an unnecessary color surge enters the substrate IO.1 from 12V), it is blocked by the constant voltage element 301. Therefore, the semiconductor laser element 201 will not deteriorate. Also, the laser light output is kept constant.

In addition, in manufacturing the printer, the optical unit 100
Supply power from an external jig power supply to the board +04 as a single unit,
Once the optical output of the laser is adjusted to a predetermined value, the optical unit 100 is mounted on the printer body (not shown), and power is supplied from the printer side. The light output is maintained at a predetermined value.

Furthermore, in the market, some factors (such as malfunctions)
When it becomes necessary to replace the optical unit lOO, it is sufficient to simply replace it with one that has already been adjusted and shipped as a single optical unit +00, thereby eliminating the need for readjustment in the market.

In Fig. 3, the central part is a semiconductor laser element 2011.
Light intensity adjustment volume 320 and laser drive IC 30
h'4 constitutes a laser driving circuit and a laser beam m control circuit similar to the conventional circuit. The semiconductor laser element 20+ includes a semiconductor laser chip 310 that emits a laser beam to the outside, as well as a semiconductor laser depth 3!0.
A photodiode 311 is provided for detecting the amount of light of the sub-laser beam generated. Since the relationship between the output and current of the semiconductor laser element 20+ significantly depends on temperature, the photodiode 311 is disposed inside to compensate for the decrease in output due to self-heating and stabilize the output.

The laser output is controlled by two transistors 306 and 307. The cathode terminal of the semiconductor laser chip 310 is connected to the GND terminal B', and the other terminal is
It is connected to the collector terminals of both transistors 306 and 307. On the other hand, the plate terminals of both transnostars 306 and 307 are respectively connected to the power supply terminal A° via a resistor.

The transistor 307 allows a constant current to flow when the image signal d is at a high level. On the other hand, current is always passed through the other transistor 306 regardless of the presence or absence of the image signal d. If the current flowing through the semiconductor laser chip 306 is switched from 0 using only the transistor 307,
This is because the responsiveness of the optical output deteriorates due to the transient characteristics of the previous output. Note that when only the transistor 306 passes current, the setting is such that the level of light emission is low enough to draw an image on the photoreceptor 202.

Furthermore, control to keep the laser light output constant is performed by increasing or decreasing the current flowing through the transistor 306 in accordance with the amount of light received by the photodiode 311. The cathode terminal of the photodiode 311 is connected to a volume 320 for adjusting light m.
Power terminal 5~ through.

It is also connected to the ten input terminal of the operational amplifier 302. On the other hand, the other terminal is connected to GND terminal B°. Then, the detection signal of the photodiode 311 is amplified by the operational amplifier 302 and then sent to the analog switch 30.
3. The signal is applied to the base of the transistor 306 via a sample and hold circuit consisting of a cn circuit 304 and an operational amplifier 305.

Therefore, when the analog switch 303 is closed, the current flowing through the transistor 306 is controlled so that the laser light output is constant. Note that the standard for the amount of current is adjusted by a light amount adjustment volume 320 connected in series to the photodiode 311. Also, analog switch 3
03 uses a sample hold signal outside the image recording area to keep the closed end output constant, opens inside the image recording area to keep the current constant, and records an image in the image recording area, but since the sampling period is short, the optical output is remains constant.

In the synchronization signal detection circuit shown on the lower right side of FIG. 3, the detection signal of the photodiode 203 is input to a comparator 330, and the output voltage of the comparator 330 is outputted as a synchronization signal to the printer control system.

The power supply circuit including the constant voltage power supply element does not necessarily need to be substantially integrated with the semiconductor laser drive circuit and incorporated into the same substrate 104, or by incorporating it into the same substrate, it can be made smaller and at lower cost. . Further, the optical unit case 101 is provided with a back surface portion 112a, and this substrate 1
By substantially integrating 04 into the optical unit case lot, it is helpful to downsize the optical unit.

(Effects of the invention) Since each circuit is actively integrated, it is possible to reduce costs and improve reliability. Furthermore, by substantially integrating the substrate with an optical unit case containing optical components, the optical unit can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the optical unit. FIG. 2 is a perspective view of the optical system. FIG. 3 is a diagram of the circuit configured on the board. FIG. 4 is a perspective view of the substrate. FIG. 5 is a perspective view of a conventional printer. FIG. 6 is a perspective view of a conventional optical unit. 100...Optical unit, +01...Optical unit case, +02...Polygon mirror, 104...Substrate, 11
2a-Plane part, 115.116 Opening, 203・
...Synchronization signal detection element, 201... Cliff conductor laser element (light emitting element). Patent applicant Minolta Camera Co., Ltd. agent Patent attorney Aoyama Ao et al.

Claims (1)

[Claims] (1) A flat part for mounting a board is formed on a part of the side wall of an optical unit case that houses a scanning optical system for scanning a light beam onto a photoconductor, and a flat part for mounting a board is formed on the flat part. A first aperture and a second aperture for detecting a synchronization signal are opened, and the substrate attached to the outer surface of the flat part has a light emitting element facing the first aperture and a light emitting element facing the second aperture. A synchronization signal detection element is installed respectively, and an optical system for detecting a synchronization signal that guides the light beam emitted by the light emitting element to the second aperture is further arranged in the optical unit case prior to the start of scanning. An optical unit for laser printers characterized by: