JPS6330828B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is configured such that a light source is intermittently turned on to illuminate a subject, and an image of the subject is photoelectrically converted using a solid-state image sensor that scans in synchronization with the light source. The present invention relates to a photoelectric conversion device.

As a conventional device of this type, there is a document reading device shown in FIG. In the figure, 1 is a document, 2 is a roller for conveying the document 1, 3 is a fluorescent lamp for illuminating the scanning surface of the document 1, 4 is a lens for forming an image of the light reflected from the document 1, and 5 is a roller for conveying the document 1. 6 is a one-dimensional solid-state image sensor that photoelectrically converts the image formed on one side of the original through the lens 4; 6 is a lighting power source that lights the fluorescent lamp 3; and 7 is a scanning device for the one-dimensional solid-state image sensor 5. This is a control circuit that controls lighting of the lighting power source 6.

Next, the operation will be explained. The document image on one side of the original is focused by the lens 4 onto the light-receiving surface of the one-dimensional solid-state image sensor 5, and photoelectrically converted. The document 1 is conveyed by the rollers 2, and even if it is necessary to vary the conveyance speed of the document 1, this reading device can synchronize the reading speed with the conveyance speed of the document 1 at a variable speed. Can be done. For example, when reading a document using a facsimile device, the scanned image signal is band-compressed and transmitted, so the transmission time per scanning line varies depending on the amount of information on one page of the document. Variable speed original reading is required. In order to perform such variable speed reading, when the document 1 passes through each reading scanning position, the fluorescent lamp ₃ is turned on for a certain period t1 to illuminate the document 1, and at the same time the one-dimensional solid-state image sensor 5 scans the document 1. I do.

FIG. 2 shows the respective timings for conveyance of the original 1, lighting of the fluorescent lamp 3, scanning of the one-dimensional solid-state image sensor 5, and signal output of the one-dimensional solid-state image sensor 5 in the case of variable speed reading. This shows the relationship between Here, the scanning period t ₂ of the one-dimensional solid-state image sensor 5,
and the lighting period t ₁ of the fluorescent lamp 3 are both for the original 1
is selected to be equal to or smaller than the minimum value of the time T ₁ , T ₂ , T _{3 .} . . for conveying per scanning line.

Next, the reason for lighting the fluorescent lamp 3 intermittently will be explained. As is well known, the photoelectric conversion operation of a one-dimensional solid-state image sensor operates in an accumulation mode, and the output level of a photoelectric conversion signal is proportional to the exposure amount, that is, the accumulation time, and the brightness of illumination light. Therefore, if the fluorescent lamp 3 is turned on all the time, the photoelectric conversion signal level will not be constant depending on the conveyance speed of the document 1. Therefore, if we decide to illuminate the fluorescent lamp 3 for a certain period _t1 , the effective accumulation time will be equal to the period _t1 during which the fluorescent lamp is lit, and the exposure amount will be equal to the time T1 during which the original ₁ is transported. , T ₂ , T ₃
It remains constant regardless of...

Note that the signal output from the one-dimensional solid-state image sensor 5 is delayed by one scanning time as shown in FIG. 2d. That is, the photoelectric conversion signal accumulated during the original transport period Tn is output during the original transport period Tn+1.

Since the document reading device shown in FIG. 1 uses the scanning method described above, variable speed reading is possible. However _, the conventional _one -dimensional solid-state image sensing device scanning method shown _in FIG. That is, the times T ₁ , T ₂ , T ₃ for conveying the original 1
When the period of time becomes as long as several hundred ms, the dark current output of the one-dimensional solid-state image sensor 5 becomes extremely large, and the signal output component due to the slight disturbance light that exists during the period when the fluorescent lamp 3 is turned off cannot be ignored. For this reason, the reading scan shown in FIG. 2 has the disadvantage that it cannot substantially accommodate a wide range of reading speeds from low speed to high speed.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional method, and by controlling the scanning of a solid-state image sensor according to the light source state at the end of scanning, it can be used in cases where the document reading speed is slow. The aim is to provide a photoelectric conversion device that can handle even

An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a diagram showing the relationship between the timings of conveyance of the original 1, lighting of the fluorescent lamp 3, scanning of the one-dimensional solid-state image sensor 5, and signal output of the one-dimensional solid-state image sensor 5. The scanning of the one-dimensional solid-state image sensor 5 shown in FIG. The scanning of the image sensor 5 is performed by turning on the fluorescent lamp 3 at the time when one arbitrary scanning is completed.
The control circuit 7 is configured to determine the start time of the next scan depending on whether or not the light is in the lighting period. That is, if the time when one scan ends is in the off period of the fluorescent lamp 3, the next scan is started immediately without providing a blanking time, and conversely, the time when one scan is completed is when the fluorescent lamp 3 is turned off. If the lamp 3 is in the lighting period, a blanking period is set until the lighting period of the fluorescent lamp 3 ends, and the next scan is started from the time when the lighting period of the fluorescent lamp 3 ends. The reason for doing this is to ensure that the lighting period of the fluorescent lamp 3 always exists within one storage time of the one-dimensional solid-state image sensor 5, and does not extend over two storage times. At this time, the lighting period t ₁ of the fluorescent lamp 3 and the scanning period t ₂ of the one-dimensional solid-state image sensor 5 are as in the case of FIG.
In both cases, the time T ₁ for transporting the original 1 per scanning line,
It is chosen to be equal to or smaller than the minimum value of T ₂ , T ₃ . Therefore, the storage time of the one-dimensional solid-state image sensor 5 takes a value between t ₂ and t ₂ +t ₁ regardless of the time for conveying the original 1, and does not become as long as in the conventional case. Therefore, unlike the conventional method, the influence of the dark current component of the one-dimensional solid-state image sensor 5 and the disturbance light that exists during the period when the fluorescent lamp 3 is turned off can be almost ignored, and even if the time for conveying the original 1 becomes somewhat longer, the image quality can be improved. Can be photoelectrically converted.

In the above embodiment, the original 1 is driven by the roller 2 and photoelectrically converted by the one-dimensional solid-state image sensor 5. However, a two-dimensional solid-state image sensor is used as the photoelectric converter, and fluorescent light is Exactly the same effect can be obtained when a discharge lamp such as a lamp is lit intermittently at a variable period to illuminate the entire surface of a document or other object, and the entire surface of the document or other object is photoelectrically converted at once.

As described above, according to the present invention, by controlling the next scan start time depending on whether the arbitrary scan end time of the solid-state image sensor is in the lighting period or the off period of the light source, the solid-state image sensor This eliminates the effects of dark current and ambient light, making it possible to read at a wide range of variable speeds, from high speeds to low speeds, including when stopped.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a document reading device according to the present invention, FIG. 2 is a timing diagram showing the relationship between operation timings in a conventional document reading device, and FIG.
The figure is a timing diagram showing the relationship between the operation timings of the document reading device in one embodiment of the present invention. In the figure, 1... original, 2... roller, 3...
... Fluorescent lamp, 4... Lens, 5... One-dimensional solid-state image sensor, 6... Lighting power source, 7... Control circuit.
In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a photoelectric conversion device composed of a light source that intermittently illuminates a subject at a variable period, a lens that forms an image of the subject, and a solid-state image sensor placed on this image-forming plane, any photoelectric conversion of the solid-state image sensor is performed. The present invention is characterized in that when the end time of the scan is within the period when the light source is turned off, the next scan is started, and when it is during the period when the light source is on, the next scan is started after the end of the period when the light source is on. photoelectric conversion device.