JP2529318B2 - Document reader - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading device used in a digital copying machine, an electronic file, etc., and more particularly to detecting an abnormality of a light source that illuminates the document.

2. Description of the Related Art In such a document reading apparatus, it is known that shading distortion occurs due to a decrease in the light amount in the peripheral portion of the light source, a decrease in the light amount in the peripheral portion of the lens of the imaging optical system, and the like. Conventionally, in order to electrically correct this shading distortion, the method of taking the product of the reciprocal of the white reference plane read signal and the read signal, and the white reference plane read signal are A / D
A method of digitally converting a read signal as a reference voltage of the converter is already known.

However, even with such a method, when the light amount difference between the central portion and the peripheral portion of the light source becomes large due to deterioration of the light source, the correction accuracy may be deteriorated or may not be corrected. For this reason, it is necessary to detect the deterioration of the light source and notify the time to replace the light source.

Due to such a need, for example, a technique as disclosed in JP-A-59-25474 has been proposed. This technique is configured to detect and notify deterioration of the fluorescent lamp by comparing the white signal level of the image sensor before a document is inserted and reading is started with a preset level.

Problems to be Solved by the Invention However, according to the above-mentioned conventional configuration, the deterioration of the light source is judged only by the light amount decrease due to the deterioration of the light source. Even if the driving voltage is lowered and the light amount is totally lowered, it is determined that the light source is deteriorated.

Means for Solving the Problems In order to solve the above problems, the present invention provides a light source for illuminating a document, a photoelectric conversion element for photoelectrically converting reflected light or transmitted light of the document, and an output of the photoelectric conversion element. An amplifier for amplifying the signal, sample-hold means for sampling and holding the output of the amplifier, maximum-value detecting means and minimum-value detecting means for detecting the maximum and minimum values of the output of the sample-hold means when reading the white reference plane. A subtractor for taking a difference between the output of the maximum value detection means and the output of the minimum value detection means, a first comparator for comparing the output of the subtractor with a first reference level, and the maximum value detection A second comparator for comparing the output of the means with a second reference level, or the output of the minimum value detection means with a third reference level, and a first light source that is turned on in response to the output of the first comparator. Display means, The second display means is turned on according to the outputs of the first and second comparators.

With the above-described structure, the present invention displays the decrease in the light amount due to the deterioration of the light source when the difference between the maximum value and the minimum value of the image signal when the white reference document is read is larger than the predetermined level. The deterioration of the light source is notified by means of a means, and the difference between the maximum value and the minimum value of the image signal when the white reference document is read for the decrease in the light amount due to other than the light source deterioration is smaller than a predetermined level and the white reference document is read. The second display means notifies when the maximum value of the image signal at that time is lower than a predetermined level.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. In FIG. 1, 1 is a light source for illuminating a document, 2 is an image sensor for photoelectrically converting reflected light (document image) of the document, 3 is an amplifier for amplifying the output of the image sensor with a predetermined gain, and 4 is an output of the amplifier. Sample and hold means for sampling and holding every 1 bit of the image sensor, 5 is a light source deterioration detecting means for detecting deterioration of the light source, 6 is a shading correction means, and 7 is
Is a switch for selecting the light source deterioration detection means 5 and the shading correction means 9 according to the control signal S. The light source deterioration detecting means 5 is a maximum value detecting means 51 for detecting the maximum value of the image signal when the white reference plate is read, a minimum value detecting means 52 for detecting the minimum value, the maximum value detecting means 51 and the minimum value. Subtractor 53 for detecting the difference between the outputs of detecting means 52, and first reference level generating means for generating the output of subtractor 53 and a predetermined voltage
A first comparator 55 for comparing the output of 54, and a second comparator 57 for comparing the output of the maximum value detecting means 51 with the output of the second reference level generating means 56 for generating a predetermined voltage. , A light source warning lamp for controlling the light source deterioration display means 59-1 for notifying the deterioration of the light source by the output of the first comparator 55 and for controlling the light quantity reduction display means 59-2 by the outputs of the first and second comparators. The lighting means 58 is used.

FIG. 2 is a diagram showing the light amount distribution in the main scanning direction of the light source, the solid line shows the light amount distribution when the light source is normal, and the broken line shows the light amount distribution when the light source deteriorates.

The operation of the embodiment thus configured will be described. First, the white reference plate is read before actually reading the original. The image signal photoelectrically converted by the image sensor 2 is amplified by the amplifier 3 with a predetermined gain. The image signal amplified to a predetermined level is sampled and held by the sample and hold means 4 for each bit of the image sensor 2. The output of the sample hold means 4 becomes an output proportional to the light amount distribution. At this time, the switch 7 selects the light source deterioration detecting means 5 by the control signal S. Maximum value detection means 51
The minimum value detecting means 52 detects the maximum value Vmax and the minimum value Vmin of the image signal when the white reference plate is read. If the light source is normal, the difference between Vmax and Vmin will be V1 as shown in Fig. 2. However, when the light source deteriorates, the decrease in light amount due to the deterioration of the light source is often found in the peripheral portion of the light source in the main scanning direction. Because
The difference is V2 (> V1). Therefore, if the voltage of the first reference level generating means for generating the first predetermined voltage is set to V3 (where V1 <V3 <V2), deterioration of the light source is detected by the first comparator 55. Here, the output of the first comparator 55 becomes "1" when the output of the subtractor 53 is larger than V3, that is, when the difference between the maximum value and the minimum value is larger than a predetermined level, otherwise it becomes "0". To decide. The output of the maximum value detecting means 51 is compared with a predetermined level generated by the second reference level generating means 56 by the second comparator 57. If the light source is normal, the light amount distribution is as shown by the solid line in FIG. 3, but if the drive voltage of the light source is lowered, for example, it will be as shown by the broken line in FIG. Therefore, the maximum value Vmax of the image signal when the white reference plate is read is detected by the maximum value detection means 51, and the output of this maximum value detection means 51 and the second reference voltage generation means
The second predetermined voltage V4 generated at 56 is compared by the second comparator 57, and if the output of the maximum value detecting means 51 is lower than the second predetermined voltage, the second comparator 57 indicates "1". Decide to output "," and output "0" otherwise. Then the first comparator 5
The outputs of 5 and the second comparator 57 are input to the light source warning lamp lighting means 58. The light source warning lamp lighting means 58 lights the light source deterioration display means (for example, a light emitting diode) 59-1 when the output of the first comparator 55 is "1" as shown in FIG. When the output of the first comparator 55 is "0" and the output of the second comparator 57 is "1", the light quantity reduction display means (for example, light emitting diode) 59-2 is turned on. In this way, the abnormality of the light source is detected and the operator is notified.

Although the maximum value of the image signal at the time of reading the white reference plate is compared with the second predetermined reference voltage in the embodiment, there is no problem even if the minimum value is compared with the third predetermined reference voltage.

EFFECTS OF THE INVENTION As described above, according to the present invention, the deterioration of the light source can be correctly known, and further, the decrease of the light amount due to other than the deterioration of the light source can be known, which is very effective in practice.

[Brief description of drawings]

FIG. 1 is a block diagram of a document reading apparatus according to an embodiment of the present invention, FIG. 2 is a view showing a light amount distribution in a main scanning direction of a light source, and FIG. 3 is a light amount distribution when a light source drive voltage is normal and when it is abnormal. FIG. 4 is a corresponding diagram showing the operation of each part. 1 ... Light source, 2 ... Image sensor, 3 ... Amplifier, 4 ... Sample and hold means, 5 ... Light source deterioration detection means, 6 ... Shading correction means, 7 ... Switch.

Front page continuation (72) Inventor Shuji Yasuoka 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP 62-135065 (JP, A) JP 62-2772 (JP) , A) Actually open 62-64063 (JP, U) Actually open 59-3662 (JP, U)

Claims (1)

(57) [Claims] 1. A light source for illuminating an original, a photoelectric conversion element for photoelectrically converting reflected light or transmitted light of the original, an amplifier for amplifying the output of the photoelectric conversion element, and a sample hold for sampling and holding the output of the amplifier. Means, a maximum value detecting means and a minimum value detecting means for detecting the maximum value and the minimum value of the output of the sample holding means at the time of reading the white reference surface, and the output of the maximum value detecting means and the output of the minimum value detecting means. , A first comparator for comparing the output of the subtractor with a first reference level, the output of the maximum value detecting means and a second reference level, or the minimum value detecting means Second comparator for comparing the output of the first comparator with the third reference level, first display means lit according to the output of the first comparator, and outputs of the first and second comparators Second table that lights according to Document reading and means.