JPS61257066A - Image reader - Google Patents

Abstract

PURPOSE:To usually make constant an electric charge storage time and stabilize a picture signal by providing plural line memories alternately performing a reading and writing operations, change-over means of this line memory and an image sensor drive circuit. CONSTITUTION:An analog picture signal outputted from line a image sensor 1 of an electric charge storage type is amplified by an amplifier 2, and converted into a digital picture signal through an A/D converter 3. This picture signal is selectively inputted to the first and the second line memories 4, 5 in a state of the writing by a multiplexer 7 and the data of the memories 4, 5 in a state of the writing is externally transferred by the multiplexer 7. In this case, the change-over of the plexers 6, 7 is performed by a change-over control section 9 according to a signal indicating a completion of the transfer of the picture signal to an external device. By an image sensor drive circuit 8 generating the drive pulse of the sensor 1, the electric charge storage time of the sensor 1 is constantly fixed and a stabilized picture signal can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image reading device that uses a charge accumulation type image sensor to optically read documents such as characters and images stably regardless of changes in sub-scanning speed. It is something.

Conventional technology Generally, when image information read by a charge accumulation type image sensor is transferred to an external device (for example, a printer or a computer that performs image processing), the reading speed of the image sensor is faster than the processing speed of the external device. . Therefore, there are methods such as storing one page's worth of reading image signals from an image sensor in memory and transferring it in accordance with the processing speed of an external device, and methods of varying the reading speed in accordance with the processing speed of an external device. However, in the former case, it has a large amount of memory,
In the latter case, there is a drawback that the charge accumulation time changes due to changes in the reading speed, and the output level of the image signal is unstable.

As a means to solve these problems, the output image signal of the charge accumulation type image sensor is stored in the first and second memories.
With a configuration in which lines are written alternately, and these written image signals are read alternately line by line at a predetermined scanning speed, the charge generated by the image sensor for a certain period of time is stored within the shortest time of the variably set succession time. There is a method that completes the accumulation and the operation of writing one line of image signals indicated by the accumulated charge into the memory (Japanese Patent Laid-Open No. 69-1
05763).

FIG. 3 is a diagram for explaining the operating principle of this conventional example. The sample signal S) f has the shortest period of the scan start signal ST determined in synchronization with the processing speed of the external device and the reading speed from the memory, that is, the shortest period of the reading time of the memory. Drives the image sensor. With this configuration, charge is accumulated for a fixed time determined to be less than or equal to 1/2 of the shortest readout time, and the accumulated image signal is read out over the same period of time.

The time required for this is always within the shortest time of the readout time. The image signal obtained by accumulating the charge for a certain period of time for each line is transferred to the first and second signals as shown in FIG.
The image signals are written into the memory alternately, delayed by one line, and the written image signals are read out according to the processing speed of the external device.

Problems to be Solved by the Invention According to the above-described configuration, since the one-line scan start signal synchronized with the memory read time and the image sensor read start signal are synchronized, the image sensor read start signal is synchronized with the read start signal of the image sensor. A problem arises in that the image sensor drive circuit for generating the signal is more complex than the image sensor drive circuit for generating the read start signal with a constant period.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides at least two line memories that perform read and write operations alternately, and a write system that uses a signal indicating the end of reading from the memory in the read operation state. means for switching between a line memory to be read and a line memory to be read; and an image sensor drive that always drives the image sensor at a constant value by setting the read period of the image sensor to 1/2 or less of the shortest time of the read time of the line memory in the read state. It is equipped with a circuit.

Effect of the Invention According to the present invention, since the charge accumulation time of the charge accumulation type image sensor is always constant due to the above-described configuration, a stable image signal can be obtained.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a timing chart showing the operating principle of the embodiment. In Figure 1,
1 is a charge storage type line image sensor; 2 is an amplifier that amplifies the analog image signal output from the line image sensor 1; and 3 is a MU/D converter that converts the analog image signal amplified by the amplifier 2 into a digital image signal. , 4.5 are line memories that perform read and write operations alternately; e is a first multiplexer that selectively inputs the output of the MU/D converter 3 to the line memories 4 and 6 that are in the write operation state; 7; is the line memory 4 in the read operation state.
, 5 to an external device; 8 is an image sensor drive circuit that generates drive pulses for the line image sensor 1; 9 is a signal indicating the end of image signal transfer to the external device; A switching control circuit 10 controls the switching between 6.degree.

Embodiments of the present invention will be described with reference to FIGS. 1 and 2.

The line image sensor is driven with a read cycle Ti of the charge accumulation type line image sensor set to 1/2 or less of the minimum time required for reading from the line memory. Let the charge accumulation time of the line image sensor be τi, and the charge accumulated in the accumulation time Ti is read out in 1,000 hours. To explain with reference to FIG. 2, for example, if the start pulse of the line image sensor has a period Ti, and the time T2
The image signal D (T2) is accumulated at the next time T and read out at the next time T.
is written into the first line memory which is in the writing state. They are simultaneously accumulated at time T3 and read out at the next time T4 to obtain an image signal D (Ts).

However, since the second memory is reading out the image signal of the previous line according to the processing of the external device, it is written to the first memory in the same way as before. Next, the same applies to the case of the image signal D (T4) accumulated at time T4 and read out at time 5. More in the next hour.

Considering the image signal D (Ts) stored in T and read out at time 6, as soon as it is in the read operation state within the storage time T5, the transfer from line memory 2 to the external device is completed, and the transfer ends. Since a transfer end signal indicating the transfer end signal is sent to the switching control section e, when the writing operation state of the image signal D (T4) is completed to the first line memory, the switching control section 9 generates a switching signal and the multiplexer 6.7
switches the read operation and write operation of the first and second line memories. By switching, the image signal D (Ts)
is written into the second line memory which is in the write operation state, and at the same time, the image signal D (T4) written just before switching is read out from the first line memory which is in the read state according to the processing speed of the external device. . This image signal D(T
4) becomes the effective image signal of the second line. In this way, by sequentially repeating this operation, an image signal for each line is obtained.

In addition, as shown in FIG. 2(d), the sub-transmission signal is
Although the transfer end signal and the start pulse are generated by the drive control circuit 10 in synchronization with the start pulse, the sub-scan feed may be performed by the transfer end signal.

Effects of the Invention As described above, according to the present invention, a stable nine-pixel signal output is always obtained with an extremely simple configuration regardless of variations in the sub-scan feed time, and is extremely effective in practice.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an image reading device according to an embodiment of the present invention, FIG. 2 is an operation timing diagram for explaining the operation of the same device, and FIG. K3 is an operation timing diagram of an image reading device in a conventional example. . 1...Charge accumulation type image sensor, 2...
...Amplifier, 3...Person/D converter, 4.5...
...Line memory, 6,7...Multiplexer, 8...Image sensor drive circuit, 9...
...Multiplexer switching control section, 1o...
・Sub-feed feed drive circuit.

Claims (1)

[Claims] A charge accumulation type image sensor, an optical system for forming an image of a document on the image sensor, means for relatively moving the document and the optical system in a sub-scanning direction, and an amplifier for amplifying the output of the image sensor. an A/D converter that converts the output of the amplifier from analog to digital; at least two line memories that alternately perform read and write operations; and a state in which the output of the A/D converter is ready for write operation. a first switching means for selectively inputting the line memory to the line memory; a second switching means for selecting the line memory that is in a read-operable state; switching control means for controlling the moving means according to the read end signal from the line memory; drive control means for driving the moving means according to the read end signal; and an image sensor drive circuit that drives the image sensor in a constant time or less, and that drives the image sensor in a constant time.