JPS6253984B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric conversion device that irradiates a document with light from a light source, guides the reflected light to a photoelectric conversion element, and converts the reflected light into an electrical signal with a strength corresponding to the density of pixels of the document. It is something.

For example, in a discharge-destructive copying paper plate making machine, an electric discharge is applied to the base paper using a discharge needle in response to the above-mentioned photoelectric conversion output signal, and an image identical to the original is formed on the base paper by mechanical scanning. ing. In this case, if the intensity of reflected light from the document changes due to deterioration of the light source lamp, temperature change, etc., this will immediately affect the intensity of the discharge against the base paper, and the plate-making quality will change.

The present invention uses fluctuations in reflected light from a document to
The object of the present invention is to provide a light amount correction device that can prevent fluctuations in electrical signals proportional to pixels of a document and eliminate changes in the quality of images reproduced by copying paper plate making machines, etc. as described above.

The invention will now be described with reference to the illustrated embodiments.

In FIG. 1, reference numerals 1 and 2 denote a document and a base paper, respectively, which are wound on the same drum, and are rotated together with the drum (main scanning) by an induction motor M1. 3 is an optical system, which includes lens lamps 4 and 4' as a light source for illuminating a part of the document;
It has a light-receiving lens 5 and a slit 6 for guiding only the reflected light from a minute portion corresponding to a pixel in the irradiated portion to a photoelectric conversion element, and a photomultiplier tube 7 as a photoelectric conversion element. This optical system 3 includes a solenoid as well as a discharge needle 12 for the base paper 2.
It is connected to the synchronous motor M2 by the SOL and is moved in the axial direction of the drum (sub-scanning).

Generally, in this type of plate-making machine, the density of the plate-made image depends on the discharge pulse width (duty) when the discharge is carried out in a continuous discharge or at the same repetition period. Therefore, in this embodiment, a pulse width modulation method is adopted as a means for producing a gradation adjustment corresponding to the original document, and a discharge flow control method is adopted as a means for correcting plate-making density accompanying linear density switching. An electrical signal proportional to the density of the original obtained from the photomultiplier tube is passed through an amplifier 8, modulated by a pulse width modulation circuit 9, and then sent to a current limiting circuit 10. The discharge of the discharge needle 12 against the base paper 2 is performed by the output of the discharge output circuit 11, and the output current of this output circuit 11, that is, the discharge current is limited by the above-mentioned current limiting circuit 10. Therefore, the discharge current always becomes the limit value of the current limit circuit 10.
The limit value of this circuit 10 is configured to be changeable by a base paper transmission density switching switch 13 and a linear density switching switch 13'.

Due to the presence of the current limiting circuit 10, the discharge current to the base paper becomes constant, so that plate making with an appropriate transmission density that is neither too dark nor too light is possible.

On the other hand, the electric signal SO obtained from the photomultiplier tube 7 through the amplifier 8 is input to the photocurrent control circuit 15. The photoelectric control circuit 15, for example, as shown in FIG. 17 is designed such that when the input peak voltage (the photoelectric conversion output of the part of the document 1 with the highest reflectance) is smaller than the reference voltage E, the output voltage increases. The time constant CR of this peak voltage holding circuit is set to be sufficiently long so that the operation does not become unstable depending on the content of the document, and is approximately 10 seconds in the embodiment.
The comparison output from the photocurrent control circuit 15 is input to the control terminal of the stabilized power supply 14 for the light source of the optical system and the photomultiplier tube, and the brightness of the light source and the photoelectron The sensitivity of the multiplier tube is controlled. For example, due to deterioration of the lamp, the amount of light irradiated on the document decreases, the output voltage of the amplifier 8 decreases, and the terminal voltage of the capacitor C decreases to the resistor R.
If the decrease is due to discharge due to the comparator 17
As a result, the output voltage of the power supply 14 is increased. Then, the control circuit 15
will supply power to the lamps 4, 4' and the electron multiplier tube 7.

In FIG. 1, 20 is a pulse generator consisting of a slit disk 21 and a photointerrupter 22 attached to a drum shaft, and 23 is an erasing circuit. 2
4 is an oscillation circuit that generates a rectangular wave S1 for the pulse width modulation circuit 9, and this circuit also generates a triangular wave S2 for the gradation correction circuit 25. Tone correction can be performed as necessary using a switch SW.

In the above embodiment, the photoelectric conversion output signal is applied to the current limiting circuit 10 through the modulation circuit, but it is directly applied to the current limiting circuit 10 without passing through the modulation circuit, thereby changing the discharge current value limited by the circuit 10. You can also do so.

According to the present invention, the photocurrent control circuit 15 allows
Since the power supply voltages of the lamp and photomultiplier tube are controlled so that the peak value of the amplifier 8 (i.e., the whitest part of the original) is always constant, fluctuations in the amount of light reflected from the original are suppressed, and a constant plate-making quality is achieved. can be obtained. In this case, as long as either one or both of the light source and the photoelectric conversion element is a combination of elements whose light amount or conversion rate depends on the power supply voltage, the present invention is applicable to all of them, even if the combination of this embodiment is not used. obtain. Further, in the embodiment, an optical system of a so-called flood light irradiation method is shown, but it is clear that a light spot irradiation method may be used.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a copying paper plate making machine according to the present invention, and FIG. 2 is a configuration diagram of its photocurrent control circuit. 1... Original, 2... Base paper, 3... Optical system, 4, 4'...
Lamp (light source), 7... Photomultiplier tube (photoelectric conversion element), 8... Amplifier, 10... Current limiting circuit, 11...
Discharge output circuit, 12...Discharge needle.

Claims (1)

[Claims] 1. In photoelectric conversion, which illuminates a document with light from a light source and guides the reflected light to a photoelectric conversion element to convert it into an electrical signal proportional to the density of pixels on the document, a photoelectric conversion element whose photoelectric conversion rate depends on the power supply voltage. using
A photocurrent control circuit is provided that compares the photoelectric conversion peak value of the most reflective part of the document with a reference voltage, and this photocurrent control circuit adjusts the power supply voltage of the light source and the power supply voltage of the photoelectric conversion element, or the power supply voltage of the photoelectric conversion element. A light amount correction device characterized in that the power supply voltage is controlled so that the photoelectric conversion peak value is always constant.