JPS6349724A - Optical scanner - Google Patents

Abstract

PURPOSE:To form dots at equal intervals without any optical correction by providing a photoelectric converting device which has many conversion parts at equal intervals in a photosensitive body, and driving a light source with large power with an image signal in synchronism with conversion part outputs. CONSTITUTION:The photoelectric converting device 5 constituted by arraying photoelectric conversion parts 5a... as many as dots formed on a scanning line 3 at equal intervals is provided in the photosensitive drum 1 on the side of a transparent base 11. The light source 2 is driven by a control circuit 8 normally with small power, so output pulses which are proportional to 1/tantheta are generated by the photoelectric converting device 5 by the rotation of a rotary polygon mirror 4. Then when the control circuit 8 receives an image data signal 9, the light source 2 is driven with the large power in synchronism with output pulses of the photoelectric converting device. Consequently, beam spots scanned on a scanning line are formed at equal intervals without any special correcting device.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical scanning device used in an optical printer or the like.

(Prior Art) A known optical scanning device includes a light source such as a laser that generates a light beam, and a deflector that causes the light beam to scan along a scanning line of a photoreceptor.

As the deflector, a rotating polygon mirror that rotates at a constant speed, a galvanometer mirror that rotates in a sine vibration mode with a constant amplitude, or the like is used. FIG. 4 shows an example in which a rotating polygon mirror a is used as a deflector. The light beam L1 from the light source is reflected by the rotating polygon mirror a and is irradiated onto the scanning surface of the photoreceptor as a beam spot. This beam spot moves on the scanning surface in the range from the scanning start point x1 to the scanning end point x2 as the rotating polygon mirror a rotates. Assuming that the distance from the reflective surface of the rotating polygon mirror a to the scanning surface is 1, the position X of the beam spot on the scanning surface when the deflected beam L2 is deflected at an angle θ with respect to the scanning center line is 1. -tanθ. In other words, the position of the beam spot is not proportional to the angle θ but proportional to tan θ, and as the resulting dots approach the scanning start point X1 or the scanning end point x2, the dot spacing becomes wider than at the center. .

If a galvano mirror is used as a deflector, on the other hand, the dot spacing will be wider at the center of the scanning line than at both sides.

For this reason, in the past, an optical correction device such as an fθ lens or an arcs1nθ lens was provided between the deflector a and the scanning surface in order to move the beam spot at a constant speed on the scanning surface. Furthermore, in laser printers, when obtaining modulated light, the beam spot has been moved at a constant speed on the scanning surface by changing the period of the clock pulse. However, an optical correction device is usually composed of a plurality of lens groups, and the position of each lens is i;
The 1121 adjustment is very complicated and requires a lot of time and effort, and the lens itself requires high precision and is expensive, increasing manufacturing costs. In addition, when changing the period of the clock pulse, the circuit configuration becomes complicated, and since the interval between the beam spots in the scanning direction has a certain value T<M, a huge amount of memory capacity is required to reduce the error. °ru

Therefore, in order to solve the above problem, the applicant of the present application previously proposed in Japanese Patent Application No. 128497/1982 a first light source that generates modulated light corresponding to an image signal, and a second light source that generates continuous light. , modulated light along the scanning line on the photoreceptor,
The photoelectric conversion device also includes a deflector that scans the continuous light along the scanning line on the photoelectric conversion device, and the photoelectric conversion device has a large number of photoelectric conversion sections arranged at equal intervals along the scanning line. It has been proposed that the driving of the first light source is controlled via the output.

(Problems to be Solved by the Invention) However, the invention previously proposed by the applicant requires two light sources, leading to an increase in cost.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to enable a beam spot to be uniformly scanned along a scanning line on a photoreceptor by a single light source without using an optical correction device;
The aim is to be able to provide it at a low price.

(Means for Solving the Problems) A feature of the present invention is that a photoconductor consisting of a transparent support, a transparent electrode, and a photoconductive layer is used, and light from a light source is transmitted from the photoconductive layer side to the photoconductor using an optical system. scan along the scanning line.

A photoelectric conversion device is arranged on the transparent support side of the photoreceptor, and this photoelectric conversion device is provided with a large number of photoelectric conversion parts arranged at equal intervals parallel to the scanning line, and receives the light transmitted through the photoreceptor. It is something. The control circuit normally drives the light source continuously with low power, and when an image data signal is received, the light source is driven with high power in synchronization with the output of the photoelectric conversion device.

(Function) During normal times, the control circuit continuously drives the light source with low power to scan the light along the scanning line on the photoreceptor through the optical system. This light does not form a beam spot on the photoreceptor, but is transmitted through the photoreceptor and received by the photoelectric conversion device. When the optical system is a rotating polygon mirror, the photoelectric conversion device generates output pulses at a period proportional to 1/tanθ. Therefore, when the control circuit receives the image data signal, it drives the light source with high power in synchronization with the output pulse of the photoelectric conversion device. As a result, beam spots, or dots, scanned along the scanning line on the photoreceptor by the high power light from the light source are formed at equal intervals on the photoreceptor.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

As shown in FIG. 1.2, a photoreceptor (photoreceptor drum) 1 consists of a transparent support 11, a transparent electrode 12, and a photoconductive layer 13. Δ is an optical system, which is composed of a light source 2 and a polarizer 4 that scans the light L3 emitted from the light source 2 along the scanning line 3 of the photoreceptor 1. In this example, a semiconductor laser oscillator is used as the light source 2. Further, as the polarizer 4, a rotating polygon mirror that rotates at a constant speed is used, but a galvanometer mirror or other appropriate polarizer may also be used.

A photoelectric conversion device 5 is disposed inside the photosensitive drum 1, that is, on the transparent support 11 side. The photoelectric conversion device 5 includes a large number of photoelectric conversion units 5a and 5a arranged at equal intervals in parallel to the scanning vA3.
As shown in an enlarged view in FIG. 2, it is equipped with an insulating substrate 51, a full-surface electrode 52 formed on its upper surface, and a thin film layer of photoconductive material formed on its upper surface. 5
3 and a transparent electrode 54 formed on its upper surface, and this transparent electrode 54 includes a large number of comb-shaped electrode elements 54a.
have. The number of electrode elements 54a, that is, the number of photoelectric conversion parts 5a, corresponds to the number of dots to be formed on the scanning line 3 of the photoreceptor, and the pitch thereof is determined by the distance from the optical system A of the photoelectric conversion device 5.

A bias voltage VB is supplied to the transparent electrode 54, and the entire surface electrode 52 is connected to the comparator 6.

A reference voltage source 7 is connected to the comparator 6 for providing a reference level thereto. When the light is scanned over the photoelectric conversion device 5, the light beam hits the comb-shaped electrode elements 54 of the transparent electrode 54.
When irradiated with a, the electrical resistance of the photoconductive thin film layer 53 between the electrode element 54a and the entire surface electrode 52 decreases, and a bias voltage VB is supplied to the comparator 6;
generates a level 1 pulse. Since the speed of the light beam moving on the photoelectric conversion device 5 is proportional to tanθ (θ is shown in FIG. 4), the period of the pulse train generated by the photoelectric conversion device 5, that is, the comparator 6, is 1/tanθ. Proportional. The comparator 6 is connected to a control circuit 8, and the output of the comparator 6 and the image data signal 9 are connected to each other via the control circuit 8.
The light rfj2 is controlled by the ND signal. That is, in normal times, the control circuit 8 drives the light source 2 continuously with low power, but when it receives the image data signal 9, it drives the light source 2 in synchronization with the output of the photoelectric conversion device 5, that is, at 1/tanθ. The light source 2 is driven with high power at a proportional period.

Since the photoreceptor 1 has a three-layer structure as described above,
When the photoconductive layer 13 on the surface of the photoconductor 1 is exposed to the light L3, the photoconductive layer 13 exhibits electrical conductivity corresponding to the amount of exposure, so that the charge on the surface of the photoconductor 1 is reduced by the amount of light L3. It leaks to the transparent electrode through the conductive layer 13, and the surface potential at the exposed area decreases. In this way, an electrostatic latent image is formed on the surface of the photoreceptor due to the contrast of the surface potential, but as can be seen from the light attenuation characteristic line R of the photoreceptor 1 shown in FIG. 3, the amount of exposure is small. In this case, since the electrical conductivity of the photoconductive layer is also low, the surface potential at the exposed area is not sufficiently lowered, and therefore a predetermined electrostatic latent image cannot be formed.

Therefore, as mentioned above, the light source 2 is operated at low power during normal times,
When driving with high power when forming image data, an electrostatic latent image is formed on the photoreceptor 1 because the amount of exposure is large when driving with high power, but when driving with low power, the exposure amount is large. Since the amount is small, no electrostatic contrast is formed on the photoreceptor 1. Therefore, when the light source is driven with low power in normal times, the light transmitted through the photoreceptor 1 is received by the photoelectric conversion device 5 and only contributes to generating output pulses from the photoelectric conversion device 5.

(Effects of the Invention) According to the above-described optical scanning device according to the present invention, in order to form dots at equal intervals, an optical correction device consisting of various lenses that are expensive and require position adjustment is provided, and light modulation is required. There is no need to provide a special circuit for changing the period of the light or to provide two light sources. Therefore, the configuration of the optical system is simpler than before, and can be manufactured at low cost.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view showing an embodiment of an optical scanning device according to the present invention, FIG. 2 is a circuit diagram showing the cross-sectional structure of the photoreceptor and photoelectric conversion device in FIG. 1, and FIG. 4 is a graph showing a light attenuation characteristic line of a photoreceptor, and FIG. 4 shows a conventional example, and is an explanatory diagram showing the deflection of a light beam when a rotating polygon mirror is used as a deflector. DESCRIPTION OF SYMBOLS 1... Photoreceptor, 11... Transparent support, 12...
Transparent electrode, 13... Photoconductive layer, 2... Light source,
3... Scanning line, 5... Photoelectric conversion device, 5a... Photoelectric conversion unit, 8... Control circuit, 9... Image data signal, L3... Light. Δ...Optical system Fig. 2 Fig. 3 Fig. 4

Claims (1)

[Scope of Claims] A photoreceptor comprising a transparent support, a transparent electrode, and a photoconductive layer; an optical system that scans light from a light source along a scanning line of the photoreceptor from the photoconductive layer side; a photoelectric conversion device disposed on the transparent support side of the photoreceptor, having a large number of photoelectric conversion units arranged at equal intervals parallel to the scanning line, and receiving the light transmitted through the photoreceptor; An optical scanning device comprising: a control circuit that continuously drives a light source with low power, and drives the light source with high power in synchronization with the output of the photoelectric conversion device when receiving an image data signal.