JPH0147070B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to an optical reading device, and particularly to an optical reading device that detects a state in which the amount of light from a light source fluctuates over time.
The light amount is always controlled to be kept within a certain range, and fluctuations within the range are controlled by controlling the gain of an amplifier that amplifies the image signal, thereby obtaining a high-quality image signal from the original. The present invention relates to a light amount control method for a reading device.

(b) Conventional technology and problems Generally, in optical reading devices such as copying machines and facsimile machines, a light source illuminates a document, and the reflected light is imaged on a parallel light-receiving element, such as a CCD, and converted into an electrical signal. . This electrical signal is then converted into a binary or multivalued signal and sent out as a digital image signal. In this case, to always obtain a good quality image signal,
It is necessary to control fluctuations in the white level of the image signal due to differences in the reflectance of the base due to differences in originals, variations in sensitivity between parallel light-receiving elements such as CCDs, and changes over time in the amount of light from the light source. For this reason, the image output signal from a photoelectric conversion element such as a CCD is used to obtain, for example, a white level using a so-called white level follower circuit, and the image output signal is binarized based on this white level. However, when the light intensity of the light source decreases significantly, the image signal output from the light receiving element such as a CCD becomes small and it becomes impossible to obtain a high quality image signal using only this white level follower circuit. For this reason, it is important to correct large changes in light intensity due to aging of the light source, etc., in stages by the light source drive circuit, to always read stable and high-quality image signals, and to extend the life of the light source. Hope
58-114879.

However, the proposal made in the patent application No. 58-114879 corrects for large changes in the light intensity of the light source in stages, and then uses a white level follower circuit to compensate for differences in the reflectance of the background of the document, differences in sensitivity between light receiving elements, and correction of the light source. Since it only corrects minute changes such as fluctuations in the amount of light, it is not possible to correct intermediate changes between a large change in the amount of light and a slight change in the amount of light of the light source. However, the amount of light fluctuates as time passes after the light source is turned on, which may exceed the correction ability of the white level follower circuit, resulting in the disadvantage that stable and high-quality image signals cannot always be read.

(c) Object of the Invention In order to eliminate the above-mentioned drawbacks, the object of the present invention is to provide a threshold value for detecting the light intensity level of a light source, detect a state in which an original reading operation is not performed, and set the threshold value except during the reading operation. An object of the present invention is to provide a light amount control method for an optical reading device, which corrects the input level of a white level follower circuit and, when the correction is insufficient, performs stepwise correction of the light source.

(d) Structure of the Invention The structure of the present invention includes a photoelectric conversion section that converts an image of a document illuminated by a light source into an electrical signal, and a photoelectric conversion section that converts the image of the document outputted from the photoelectric conversion section into white level data for each pixel. A white level follower circuit that respectively corrects the white level based on the signal, a light amount sensor that detects the light amount of the light source, and a light amount control section that controls the light source drive circuit in stages based on the light amount signal from the light amount sensor. In an optical reading device having
providing a first threshold, a second threshold, and a third threshold for classifying the light amount signal level from the light amount sensor;
A relationship of a first threshold < a second threshold < a third threshold is given to the threshold, and the light amount signal level is set to the first threshold and the third threshold at a predetermined time interval, excluding the period of the document reading operation state. When the light amount signal level is between the second threshold value and the third threshold value, the amplification degree of the photoelectric conversion section is increased, and when the light amount signal level is between the second threshold value and the third threshold value, the amplification degree of the photoelectric conversion section is decreased. , the light amount signal level is the first
When the light amount signal level is lower than a third threshold, the driving circuit for the light source is controlled to be driven one step more strongly, and when the light amount signal level is higher than a third threshold, the driving circuit for the light source is controlled to be driven one step weaker. It is something.

(e) Embodiment of the Invention FIG. 1 is a block diagram of a circuit showing an embodiment of the invention. A light source 2, such as a fluorescent lamp, is driven by a drive circuit 14 and turned on. The reflected light from the document 1 irradiated by the light source 2 is reflected by the mirror 3 and enters the lens 4 . A lens 4 forms an image of the original onto a photoelectric converter 5 such as a CCD. An image corresponding to one scanning line of the original is input by the photoelectric converter 5 to the amplifier 6 as a serial signal, and after being amplified, the image is input to the white level follower circuit 8 via the DC reproduction circuit 7. On the other hand, the original 1 is mechanically moved in the direction indicated by the arrow, and plane scanning is performed.

The white level follower circuit 8 is a well-known circuit that maintains a constant white level signal corresponding to each pixel of a serial image signal, and operates as an automatic gain adjustment circuit for each pixel signal. This white level follower circuit 8 corrects minute changes such as differences in reflectance due to different documents, differences in sensitivity between light receiving elements, and fluctuations in the amount of light from the light source. The output signal of the white level follower circuit 8 is converted into a digital signal by an A/D converter 9 and sent out as a digital image output signal.

The amount of light from the light source 2 is detected by a light amount sensor 10 and converted into an electrical signal. This electrical signal is amplified by an amplifier 11 and converted into a digital signal by an A/D converter 12. This digital signal enters the system control circuit 13 and is compared with a predetermined threshold value at predetermined time intervals.
This threshold value is assigned three levels as shown in FIG. Threshold A is greater than Threshold B, and Threshold B is greater than Threshold C.
bigger. Here, the digital signal has a threshold value A
and B, the system control circuit 13 reduces the amplification of the amplifier 6 by a predetermined level. If the digital signal is between thresholds B and C, the system control circuit 13 increases the amplification of the amplifier 6 by a predetermined level. If the digital signal is lower than the threshold value C, the drive circuit 14 is driven to drive the light source 2 at a drive level one step higher. If the digital signal is higher than the threshold value A, the drive circuit 14 is driven to drive the light source 2 at a drive level one level lower. If the drive level of the drive circuit 14 is at the maximum and the drive level cannot be increased any further, the light source deterioration indicator 15 is turned on to issue an alarm.

When the document 1 is inserted and the transport mechanism moves between the light source 2 and a light amount sensor 10 that detects the amount of light from the light source 2, a large variation in the amount of light is detected. When this fluctuation is detected, the system control circuit 13 determines that the document 1 is being read, and does not perform the gain adjustment of the amplifier 6 and the drive level change control of the drive circuit 14 described above.

FIG. 3 is a diagram illustrating an example of the operation of the system control circuit 13. After turning on the power, preheat the light source 2 for at least 2 seconds and turn on the light source 2 with 70% of the rated current. When the document 1 is inserted and the document detector detects the document 1, it is determined that the document has started to be conveyed, and a check is performed when 160 ms has elapsed. If it is necessary to change the drive level of the drive circuit 14 at the time of checking, change it within 2ms. In this case, the current is 50% of the rating of light source 2. Then, check again after 70ms. If the drive level needs to be changed at this point, do so within 2ms. In this case, the current is 30% of the rating of light source 2. Then check after 70ms. This completes the drive level change for the normal light source. As the light source 2 deteriorates, the number of drive level changes decreases, and finally, when the amount of light is insufficient even when driven at 70% current, the light source deterioration indicator 15 is turned on. If no original is inserted and no original is detected by the light sensor for more than 3 minutes, the light turns off.

(f) Effect of the invention As explained above, the present invention provides a threshold value for the detection level of the light amount sensor, and based on this threshold value,
For deterioration of the light source or large changes in light intensity at low temperatures, correction is performed stepwise by changing the drive current of the light source, and for minute changes in light intensity within the threshold, the amplification degree of the output amplifier of the photoelectric converter is changed. Since the white level follower circuit is configured to compensate for a wide range of light intensity changes, it is possible to always obtain a stable and high-quality image signal, and the auto-drive of the light source is prevented. This has the effect of increasing lifespan.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a circuit showing an embodiment of the present invention, FIG. 2 is a diagram explaining a threshold value of an embodiment of the present invention, and FIG. 3 is a diagram explaining an example of the operation of the system control circuit. . 1 is the original, 2 is the light source, 3 is the mirror, 4 is the lens, 5
1 is a photoelectric converter, 6 and 11 are amplifiers, 7 is a DC regeneration circuit, 8 is a white level follower circuit, 9 and 12 are A/D converters, 10 is a light amount sensor, 13 is a system control circuit, 14 is a drive circuit, 15 is a light source deterioration indicator.

Claims (1)

[Claims] 1. A photoelectric conversion unit that converts the image of the original illuminated by a light source into an electrical signal, an amplifier that amplifies the output of the photoelectric conversion unit, and white level data for each pixel of the image of the original output from the amplifier. a white level follower circuit that corrects the white level based on the signal; a light amount sensor that detects the amount of light from the light source;
an optical reading device having a light amount control section that controls a light source drive circuit stepwise based on a light amount signal from the light amount sensor; A threshold value and a third threshold value are provided, and the relationship of the first threshold value < the second threshold value < the third threshold value is provided to the threshold value, and the above-mentioned data is read at predetermined time intervals except for the period of the document reading operation state. When the light amount signal level is between a first threshold value and a second threshold value, the amplification degree of the amplifier is increased; when the light amount signal level is between the second threshold value and a third threshold value, the amplification degree of the amplifier is increased. When the light amount signal level is lower than a first threshold value, the driving circuit of the light source is controlled to be driven one step more strongly, and when the light amount signal level is higher than a third threshold value, the light source driving circuit is controlled to be driven one step more strongly. 1. A light amount control method for an optical reading device, comprising controlling a light source drive circuit to drive the light source one step weaker.