JPH02174366A - Image reading device - Google Patents

Abstract

PURPOSE:To correct a difference in storage time depending on a different synchronizing signal and to attain stable picture read by revising the gain of an amplifier amplifying an electric signal from a CCD image sensor based on a difference of the period of the internal and external synchronizing signal. CONSTITUTION:Since the input luminous quantity of the CCD 12 depends on the product between the storage time and the input luminous intensity, the storage time when an internal horizontal synchronizing signal is in use is a multiple of T'/T in comparison with that when an external synchronizing signal is in use, where T is the period of the internal horizontal synchronizing signal and T' is the period of the external horizontal synchronizing signal. Then an amplifier control circuit 206 receiving the information of two periods T,T1 controls a variable amplifier 203 to multiply the output of the CCD 12 with T/T' with the output when the internal synchronizing signal is used. Thus, an analog signal entering an A/D converter 204 is kept constant independently of the period difference of the two synchronizing signals. Thus, the stable original read is attained.

Description

[Detailed description of the invention] Field of use in Ea industry] The present invention relates to an image reading device.

[Conventional technology]

FIG. 4 shows the photoelectric conversion characteristics of the CCD image sensor. The human power device is a product of the human power light intensity and the accumulation time, and it is best to set the human power light amount to around 1/2 of the saturation exposure amount.

Conventionally, in image reading devices, the period of the horizontal (main scanning direction) synchronization signal is used for the accumulation time of the CCD image sensor, and the amount of human light is determined by the period of the synchronization signal and the input light intensity of the illumination system. . Light applied to the CCD image sensor is converted into an analog electrical signal and output, and is amplified by an amplifier or the like to perform analog/digital conversion.

[Problems to be Solved by the Invention] However, in the conventional example described above, when the device is operated in response to an external synchronization signal, the storage time fluctuates due to the period difference between the external synchronization signal and the internal synchronization signal, and the original The disadvantage is that the read density becomes inaccurate.

An object of the present invention is to provide an image reading device that solves the above problems.

[Means for Solving the Problems] The present invention includes a photoelectric conversion device that converts reflected light from a document illuminated by a light source into an electrical signal, and a variable device that amplifies the electrical signal from the photoelectric conversion device with a changeable gain. It comprises an amplifier and means for controlling the gain of the variable amplifier based on the period difference between an internal horizontal synchronizing signal and an external horizontal synchronizing signal for driving the photoelectric conversion means.

[Function] According to the present invention, for example, by changing the gain of the amplifier that amplifies the electrical signal from the CCD image sensor based on the period difference between the internal and external synchronization signals, the difference in accumulation time due to different synchronization signals can be reduced. can be corrected.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the internal configuration of a document image reading device according to an embodiment of the present invention. Reference numeral 1 denotes a main body of a document image reading apparatus, which illuminates a document on a platen glass 17 with a document illumination unit 15, and forms a document image on a CCD 12 with a lens 14.

FIG. 2 is a block diagram showing the circuit configuration.

The operation of the document reading device Δ will be explained using FIGS. 1 and 2. This document reading device (hereinafter referred to as the scanner) is connected to external devices (digital printer, personal computer, etc.), and communication of control signals with these external devices and image output to the external devices are performed using the interface. This is done via circuit 211.

The original is placed 1 on the original 141 on the platen glass 17 and on the loading section 18.
, so that the right end in FIG. 1 is the leading edge of the document.

Further, the original illumination unit 15 of the optical system has its initial position at the right end in FIG. 1, and its position is confirmed by an optical position sensor (not shown). Further, with the document placed on the platen glass, instructions for each ladder mode are input from an external device. For example, if you set the pixel density to 400d
pi, 300dpi.

260 dpi, whether the image signal should be a binary code or a multi-value signal, etc. CP who received this
The U 210 outputs a control signal in advance to set the pixel density and image signal. Next, when a document reading start command is input from an external device, the CPU 210
First, a signal is output to the lamp voltage control circuit 205 to turn on the lamp. At this point, do not immediately start scanning for document reading, but wait approximately 300 to 500 seconds until the light intensity of the lamp stabilizes.
Wait for 0m5ec. During this time, the interface circuit 21
Although an image signal is manually input to the CPU 210, it is not output to an external device due to a control signal from the CPU 210. Thereafter, the original illumination unit 15 starts scanning in the direction of arrow IA in FIG. The distance from the initial position of the original illumination unit 15 to the leading edge position of the original on the platen glass 17 is approximately 2 to 3 m+.
During this time, the scanning speed of the optical system by the motor is controlled to be stable. When the document illumination unit 15 reaches the document leading edge position, the CPU 210 outputs a control signal to enable image signal output to the interface circuit 211, and the read image signals are sent one after another to an external device. The scanning length of the optical system is uniquely determined by the number of pulses that the CPU 210 drives the motor;
When the U210 outputs the required number of pulses to the motor, it determines that reading the original is complete, turns off the lamp, disables image signal output, and reverses the motor, and outputs an original reading end signal to an external device. CP Ll 2
10, the original illumination unit 15
moves in the direction of arrow IB in FIG. 1 and stops when the optical position sensor detects that the initial position has been reached.

If the next document reading start command is not received from the external device during this optical system return period, the optical system stops at the initial position and the operation ends.

Next, the main operations of this embodiment will be explained using the block diagram shown in FIG.

The analog image signal output from the CCD 12 is amplified by a set magnification by the variable amplifier 203. The amplified analog signal is input to the A/D converter 204. The A/D converter 204 converts the analog signal into a 6-bit digital signal. This digital image signal can be used in the two modes mentioned above, namely the binary mode,
It can be output to an external device in any of the multi-value modes.

Which of these two modes is to be output is determined by a command from an external device, and the CPU 210 outputs a control signal to the first selector 209. In the binary mode, the 6-bit image signal is changed to 1-bit by the binary circuit 208 according to the slice level output from the CP 0210, and is input to the interface circuit 211 via the selector 209. In the multi-value mode, a signal from the A/D converter 204 is input to the interface circuit 211 via the selector 209.

When there is no horizontal (main scanning direction) synchronization signal from an external device, the CPU 210 sends a control signal to the second selector 212 and outputs an internally generated horizontal synchronization signal. The CPU 210 controls a motor drive signal for moving the lighting unit using the horizontal synchronization signal, and the storage time of light entering the CCD 12 is determined by the movement time of the lighting unit.

When a horizontal synchronization signal is input from an external device, the CPU 21
0 sends a control signal to the second selector 212 to output an external horizontal synchronization signal, and the CPU 210 outputs a pulse synchronized with the horizontal synchronization signal as a motor drive signal.

The amount of manual light on the CCD 12 is determined by the product of the accumulation time (in this embodiment, the same period as the horizontal synchronizing signal) and the human power light intensity.For example, as shown in FIG. If the period of the external horizontal synchronization signal is To, the storage time will be T'/T times that when using the internal horizontal synchronization signal.

Therefore, the amplification control circuit 206, which manually inputs the information of the two periods T and T', controls the variable amplifier 203 to
By multiplying the output of 12 by T/T' when using the internal synchronization signal, the analog signal input to the A/D converter 204 can be kept constant regardless of the period difference between the two synchronization signals.

In the above embodiments, a variable amplifier is used to
Although the analog output of the image sensor is amplified, as shown in FIG. The comparison voltage is
T'/T of the voltage value set to the internal synchronization signal at period 1
Even if the setting is changed to double, the same effect as in the above embodiment can be obtained.

[Effects of the Invention] As described above, according to the present invention, even if the same density is read with different synchronization signals, the same digital value can be obtained for both, and image reading can be performed stably.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the internal configuration of an image reading device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the circuit configuration, FIG. 3 is a diagram showing internal and external synchronization signals, and FIG. A diagram showing the photoelectric conversion characteristics of the COD image sensor. FIG. 5 is a block diagram of another embodiment. DESCRIPTION OF SYMBOLS 1... Image reading device, 11... Control unit, 12... COD. 13... CCD driver, 14... Lens, 15... Original illumination unit, 16... Reflective mirror 17... Platen glass, 18... Original placing section, 19... Platen cover. ...Lamp, ...Variable amplifier, ...A/D converter, ...Lamp voltage control circuit, ...Amplifier control circuit, ...Synchronization signal generation circuit, ...Binarization circuit, ... ...Selector 11 ...CPU. ...Interface circuit, ...Selector I! , ...comparison voltage control circuit, ...amplifier. Group

Claims (1)

[Scope of Claims] 1) Photoelectric conversion means for converting reflected light from a document illuminated by a light source into an electrical signal; and a variable amplifier for amplifying the electrical signal from the photoelectric conversion means with a changeable gain; An image reading device comprising: means for controlling the gain of the variable amplifier based on a period difference between an internal horizontal synchronizing signal for driving a photoelectric conversion means and an external horizontal synchronizing signal. 2) photoelectric conversion means for converting reflected light from a document illuminated by a light source into an electrical signal; analog/digital conversion means for converting the electrical signal from the photoelectric conversion means from analog to digital using a changeable comparison voltage; The analog/
An image reading device comprising means for controlling a comparison voltage of a digital conversion means.