JPH1013670A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the reduction of power consumption by always suppressing the amount of currents to be supplied to a light source to an irreducible minimum. SOLUTION: An input voltage level discrimination circuit 7 discriminates the level of white reference signal generated by photoelectrically transducing reflected light from a transmission white roller 1f through a line sensor 3. A current control circuit 8 controls the amount of currents to be supplied to a light source 2 so that the signal level discriminated by this input voltage level discrimination circuit 7 can become a prescribed level which can be amplified by the maximum value within the gain variation range of a gain control circuit 5 or a prescribed gain a little lower than this maximum value so as to be almost matching the upper limit of digital conversion range of an A/D converter 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for converting an image formed on an original by photoelectrically converting reflected light from the original when illuminated by a light source such as an LED array with an image sensor such as a CCD line sensor. The present invention relates to an image reading device that performs reading.

[0002]

2. Description of the Related Art Generally, an image reading apparatus of this type converts an analog electric signal output from an image sensor into an A / D signal.
Image data is generated by digitization by a converter.

[0003] Light sources such as LED arrays sometimes emit different amounts of light even when driven with a constant current, due to variations in characteristics among products. Even with a single LED array, the amount of light emission is not constant even when driven with a constant current due to the influence of the surrounding environment (temperature and humidity) and the influence of aging.

Further, the sensitivity of image sensors such as CCD line sensors is not constant due to variations in characteristics of each product, the influence of the surrounding environment (temperature and humidity), and the influence of aging.

Therefore, the level of an electric signal generated when a certain document is read is not constant,
The density of the image indicated by the generated image data, that is, the reading density may vary.

Therefore, conventionally, a gain adjustment circuit capable of changing the gain has been used, and the input level to the A / D converter has been set to a specified maximum level which is set to be substantially maximum within the input specifications of the A / D converter. To keep it constant. That is, in the gain adjustment circuit, an electric signal generated by photoelectrically converting the reflected light from the predetermined white reference plane by the image sensor is used as a white reference signal, and the level of the white reference signal can be set to a specified maximum level. Is determined as follows. Then, the gain adjustment circuit amplifies or attenuates the electric signal generated by photoelectrically converting the reflected light from the original by the image sensor with the determined gain, and then inputs the amplified signal to the A / D converter.

FIG. 4 is a diagram schematically showing the operation of adjusting the input level to the A / D converter as described above.
(A) shows that the level Vs of the white reference signal is the specified maximum level Vma.
4 (b) shows the case where the level Vs of the white reference signal is larger than the specified maximum level Vmax.

[0008]

When the input level to the A / D converter is adjusted by amplification or attenuation as described above, the level of the electric signal generated by the image sensor is high and the signal is attenuated. This means that the amount of reflected light, and hence the amount of light emitted from the light source, is excessively large. Therefore, in this state, the power is wasted by consuming excessive current to the light source.

The present invention has been made in view of such circumstances, and has as its object to always reduce the amount of current supplied to a light source to a necessary minimum, thereby reducing power consumption. It is another object of the present invention to provide an image reading apparatus that can perform the above-described operations.

[0010]

In order to achieve the above object, the present invention provides a method for transmitting a document when a document is present at a predetermined reading position, and for transmitting a document when the document is not present at the reading position. A light source such as an LED array for irradiating a white reference surface such as a surface of a white roller with light, and a level corresponding to the amount of the reflected light by photoelectrically converting reflected light from the document or the white reference surface. For example, an image sensor such as a line sensor that generates an electric signal having the gain can be changed within a predetermined variable range, and the reflected light from the white reference plane is photoelectrically converted by the image sensor and generated. For example, a gain adjustment circuit that amplifies the electric signal with a gain determined so that the electric signal can be amplified so that the level of the electric signal substantially matches the upper limit of the predetermined digital conversion range. A digital conversion means such as an A / D converter for generating image data by taking in the digital conversion range an electric signal amplified by the amplification means and digitizing the same, and the image sensor A detecting unit such as an input voltage level determining circuit for detecting the level of an electric signal generated by photoelectrically converting the reflected light from the white reference surface, and a controlling unit such as a current control circuit. For example, as a preparatory operation before starting document reading, the level detected by the detecting means may be a maximum value of the gain variable range or a predetermined gain slightly lower than the maximum value. The amount of current supplied to the light source is controlled so as to be a predetermined level that can be amplified so as to substantially match the upper limit.

By taking such means, the level of an electric signal generated by photoelectrically converting the light reflected from the white reference surface by the image sensor is detected by the detecting means. The detected signal level can be amplified by the maximum value of the variable gain range of the amplifying means or a predetermined gain slightly lower than the maximum value so as to substantially match the upper limit of the digital conversion range of the digitizing means. The amount of current supplied to the light source is controlled so as to reach a predetermined level. That is, the light emission amount of the light source is minimized so that a minimum signal level can be obtained within a range that can be amplified by the amplifying means to a level suitable for input to the digitizing means,
Power consumption is kept to a minimum.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a main configuration of an image reading apparatus according to this embodiment. As shown in FIG. 1, the image reading apparatus according to the present embodiment includes a document transport mechanism 1, an LED array 2, a line sensor 3, a sample and hold circuit 4, a gain adjustment circuit 5, an A / D converter 6, an input voltage level determination circuit. 7 and a current control circuit 8.

The document transport mechanism 1 includes a kick roller 1a,
It comprises a self-supplying rubber plate unit 1b, a self-supplying roller 1c, a transmission driving roller 1d, a pinch roller 1e, a transmission white roller 1f, a transmission driving roller 1g, and a pinch roller 1h. The original transport mechanism 1 is configured such that the kick roller 1a, the self-supply roller 1c, the transmission driving roller 1d, and the transmission driving roller 1g receive the torque of a motor (not shown) via a transmission mechanism (not shown) and rotate. The document D is conveyed from right to left in the figure.

The LED array 2 irradiates the document D transported by the document transport mechanism 1 with light below the transmission white roller 1f.

The line sensor 3 is formed by integrating a large number of photoelectric conversion elements (not shown) in a one-dimensional array, and a direction in which the arrangement direction of the photoelectric conversion elements intersects the conveying direction of the document D (depth in the figure). Direction). The line sensor 3 detects the document D emitted from the LED array 2
Alternatively, the light reflected by the transmission white roller 1f is photoelectrically converted by each of the photoelectric conversion elements, and charges obtained by the photoelectric conversion elements are sequentially output, whereby 1 is obtained.
Generates and outputs electrical signals for scanning lines. Then, the electric signal output from the line sensor 3 is given to the sample and hold circuit 4.

The sample and hold circuit 4 captures an electric signal output from the line sensor 3 at a predetermined sampling cycle and holds the signal until the next capture timing.

The gain adjustment circuit 5 can change the gain, and amplifies or attenuates the signal output from the sample-and-hold circuit 4 at an arbitrary gain and outputs the amplified signal. The gain adjustment circuit 5 uses the output signal of the sample and hold circuit 4 when the line sensor 3 outputs an electric signal generated by photoelectrically converting the light reflected by the transmission white roller 1f as a white reference signal. Set the level of the white reference signal to A / D
The gain is determined so that a specified maximum level slightly smaller than the maximum value of the digitizable range of the converter 6 can be obtained.

The A / D converter 6 includes a gain adjustment circuit 5
The image data is generated by digitizing the signal output from the.

The input voltage level determination circuit 7 receives the output signal of the sample and hold circuit 4, determines the level of the signal, and notifies the current control circuit 8.

The current control circuit 8 supplies a current to the LED array 2 to cause the LED array 2 to emit light. Further, the current control circuit 8 has a function of changing the amount of current supplied to the LED array 2 so that the signal level notified from the input voltage level determination circuit 7 falls within a predetermined range.

Next, the operation of the image reading apparatus configured as described above will be described focusing on the processing procedure by the current control circuit 8. First, when it becomes necessary to read the document D, for example, a control unit (not shown) of a facsimile apparatus to which the image reading apparatus is applied instructs the current control circuit 8 to start lighting.

In the standby state, the current control circuit 8 waits for an instruction to start lighting as shown in FIG. 2 (step ST1). When an instruction to start lighting is given as described above, the current control circuit 8
The current supply to the D array 2 is started (step ST
2). Thereby, the LED array 2 emits light.

At this time, the conveyance of the document D by the document conveyance mechanism 1 has not been started, and the document D does not exist between the transmission white roller 1f and the line sensor 3. Therefore, the light emitted from the LED array 2 is reflected by the transmission white roller 1f and enters the line sensor 3, and the line sensor 3 photoelectrically converts the reflection light from the transmission white roller 1f to a white reference signal. Will be output.

[0025] Therefore the current control circuit 8, the signal level determination result by the input voltage level detector 7 takes as a signal level Vs of the white reference signal (step ST3), also the signal level Vs is above a predetermined upper limit value V _H Big or
Alternatively, it is determined whether it is smaller than a predetermined lower limit value _VL (steps ST4 and ST5).

Here, the lower limit value _VL is set to a level at which a specified maximum level Vmax is obtained by amplification by the gain adjustment circuit 5 in a state where the gain is set to the maximum value.
_H is set by adding a slight margin α to the lower limit value _VL . That is, the lower limit _VL and the upper limit _VH
Is set in a relationship as shown in FIG. 3 with respect to a digitizable range of the A / D converter 6 and a specified maximum level Vmax slightly smaller than the maximum value of the digitizable range.

When the signal level Vs of the white reference signal is higher than the upper limit value V _H , the current control circuit 8
The amount of current supplied to the array 2 is reduced by a predetermined amount (step ST
6) After that, the processing after step ST3 is repeated.
When the signal level Vs of the white reference signal is smaller than the lower limit value _VL , the current control circuit 8 increases the amount of current supplied to the LED array 2 by a predetermined amount (step ST7), and then performs the processing after step ST3. repeat.

Thus, the signal level Vs of the white reference signal
Until the value satisfies the relationship [ _VL ≦ Vs ≦ _VH ], the amount of current supplied to the LED array 2 is reduced or increased. When the signal level Vs of the white reference signal is [V _L ≦ V
When a value satisfying the relationship of s ≦ V _H ] is satisfied, the current control circuit 8 fixes the amount of current supplied to the LED array 2 to that value, and waits for an instruction to stop lighting (step ST8).

As described above, after the setting of the amount of current supplied to the LED array 2 is completed, the gain is determined by the gain adjustment circuit 5. When the determination of the gain is completed, the conveyance of the document D by the document conveyance mechanism 1 is started,
The reading operation of the document D is performed as is well known. When the reading operation is completed, for example, a control unit (not shown) of the facsimile apparatus to which the image reading apparatus is applied instructs the current control circuit 8 to stop lighting.

Then, the current control circuit 8 stops supplying current to the LED array 2 (step ST9), and thereafter returns to the standby state.

As described above, according to the present embodiment, the level of the white reference signal is supplied to the LED array 2 so that the level can be amplified to the specified maximum level Vmax in the gain adjustment circuit 5. Set the amount of supply current.
That is, the light emission amount of the LED array 2 is minimized,
The signal level required for digitization is obtained by amplifying with a large gain by the gain adjustment circuit 5.

Thus, when the amount of light emitted from the LED array 2 is large or when the sensitivity of the line sensor 3 is high, the amount of current supplied to the LED array 2 is reduced, so that unnecessary power consumption can be prevented.

In the above embodiment, the amount of current supplied to the LED array 2 is set each time the reading operation is started. Therefore, the surrounding environment at that time, the deterioration of the LED array 2 and the line sensor 3 over time. Considering the degree of
The amount of current supplied to the ED array 2 is always set optimally.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the amount of current supplied to the LED array 2 is set each time a reading operation is started. However, the amount of current supplied to the LED array 2 is set, for example, periodically at a constant cycle. Or at an arbitrary timing such as in response to an instruction from a user or a maintenance person.

In addition, various modifications can be made without departing from the spirit of the present invention.

[0036]

According to the present invention, a light source for irradiating light to a document when a document exists at a predetermined reading position, and a light to a white reference surface when no document exists at the reading position. An image sensor that photoelectrically converts reflected light from the original or the white reference surface to generate an electric signal having a level corresponding to the amount of the reflected light, and changing a gain within a predetermined variable range. And a gain determined so that the level of an electric signal generated by photoelectrically converting reflected light from the white reference plane by the image sensor can be amplified so as to substantially match an upper limit of a predetermined digital conversion range. Amplifying means for amplifying the electric signal; and a data for generating image data by capturing and digitizing the electric signal amplified by the amplifying means within the digital conversion range. Digital conversion means, detection means for detecting the level of an electric signal generated by photoelectrically converting the reflected light from the white reference surface by the image sensor, and control means. As a preparatory operation before the reading is started, the level detected by the detecting means is substantially equal to the upper limit of the digital conversion range by the maximum value of the gain variable range or a predetermined gain slightly lower than the maximum value. Since the amount of current supplied to the light source is controlled so as to be a predetermined level that can be amplified, the amount of current supplied to the light source is always minimized, thereby reducing power consumption. It becomes an image reading device.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main configuration of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure of a current control circuit 8 in FIG. 1;

Shows an example of the relationship between the [3] A / digitizing range of D converter 6 and the specified maximum level Vmax slightly determined smaller than the maximum value of the digitized range and the lower limit value V _L and the upper limit value V _H FIG.

FIG. 4 is a diagram schematically showing a conventional operation of adjusting an input level to an A / D converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Document conveyance mechanism part 2 ... LED array 3 ... Line sensor 4 ... Sample hold circuit 5 ... Gain adjustment circuit 6 ... A / D converter 7 ... Input voltage level judgment circuit 8 ... Current control circuit

Claims (2)

[Claims] A light source for irradiating light to a document when a document is present at a predetermined reading position, and a light source for irradiating a white reference surface when no document is present at the reading position; An image sensor that photoelectrically converts the reflected light from the reference surface to generate an electric signal having a level corresponding to the amount of the reflected light; and a gain that can be changed within a predetermined variable range. The electric signal is amplified with a gain determined so that the level of the electric signal generated by photoelectrically converting the light reflected from the white reference plane substantially matches the upper limit of a predetermined digital conversion range. Amplifying means; and a digital converting means for generating image data by capturing and digitizing the electric signal amplified by the amplifying means within the digital conversion range. Detecting means for detecting the level of an electric signal generated by photoelectrically converting the reflected light from the white reference surface with the image sensor; and detecting the level detected by the detecting means to be the maximum of the variable gain range. Control means for controlling the amount of current supplied to the light source to a predetermined level that can be amplified so as to substantially match the upper limit of the digital conversion range by a value or a predetermined gain slightly lower than the maximum value. An image reading apparatus comprising: 2. The image reading apparatus according to claim 1, wherein the control unit controls the supply current amount varying unit as a preparatory operation before starting the document reading.