Image input device

Details Image input device Image input device

2002-07-15

2003-12-30

Nguyen, Hoang V. (Department: 2879)

Electric lamp and discharge devices: systems

With radiant energy sensitive control means

C315S307000, C315S360000

Reexamination Certificate

active

06670769

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image input device and particularly to an image input device in which an image sensor output is not affected by fluctuations in frequency when a rare gas discharge lamp is turned on.
2. Description of the Related Art
Conventionally, various apparatuses using an image input device, particularly a color image input device have been produced, for example, a color copying machine, which uses a combination of a color image input device and a laser beam printer (LBP), and a film scanner. Generally, these apparatuses are required to process a large amount of image data at high speed.
In the image input device, a photoelectric converting unit, which sheds light on an object and converts light reflected at the object into an electrical signal, includes a light source for shedding light on the object, an optical system for focusing the reflected light from the object, and image sensors for receiving the light focused and converting it into an electrical signal.
The image input device uses one-dimensional image sensors and two-dimensional image sensors according to the shape of the object, speed, and resolution, and also uses various transferring mechanisms for transferring the object. In the color image input device, the optical system uses color filters for color separation.
In order to process images at high speed, the image sensors constituting the image input device must be operated at high speed. An output I(&lgr;) of each image sensor varies with the illuminance of light shed on an object, namely, an output L(&lgr;) of a light source, the reflectance K of an object, the brightness (transmittance) U of a lens, the accumulating time T of each image sensor, the sensitivity S(&lgr;) of a wavelength of each image sensor, and the transmittance F(&lgr;) of each color separation filter. Strictly speaking, the reflectance K of an object varies with the wavelength of light. However, this fact does not affect the spirit of the present invention, so the reflectance K of an object and the brightness U of a lens are set to respective constant values independently of the wavelength of light. For the purpose of simplification, the description hereinbelow will be made on the assumption that the reflectance K of an object and the brightness U of a lens are each set to 1 and that the amount P(&lgr;) of light incident on each image sensor is proportional to the output L(&lgr;) of a light source.
For example, a xenon lamp, which is one kind of rare gas discharge lamp and affects the incident light amount P(&lgr;), is used in the color image input device because it generates an output L(&lgr;) which has rumination characteristics similar to the wavelength characteristics of natural daylight, and which has high luminance. The spectral sensitivity of a CCD line sensor, which is generally used as a color image sensor and which affects the sensitivity S(&lgr;) of an image sensor, is low for short-wavelength light. As to the characteristics of optical glass filters, which are generally used as color separation filters affecting the transmittance F(&lgr;), generally speaking, a blue-base optical glass filter has a high transmittance and gentle characteristics, and gets mixed therein light having a wavelength other than the blue-base wavelength, a green-base optical glass filter has a low transmittance, and a red-base optical glass filter gets light of an infrared range mixed therein.
The output I(&lgr;) of each image sensor is deteriorated due to the influence of the wavelength characteristics of the constituent members. Particularly for the blue-base light, the output is low in the sensor sensitivity, the filter transmittance and the light output, and the output of the image sensor influenced thereby is reduced compared with the red-base sensor and is most strongly affected by fluctuations in the amount of light from the lamp.
The above mentioned parameters are determined in consideration of the characteristics of the constituent members so that respective outputs of the image sensors for generating colors are as equal to one another as possible. Among the parameters, the S(&lgr;) and the F(&lgr;) do not vary once determined, while the P(&lgr;) to be inputted and the T fluctuate by a turn-on circuit in such a manner that the P(&lgr;) varies with fluctuation in a lamp-driving voltage and the T varies to a driving frequency of the image sensor.
In order to solve the above-mentioned problem that the image sensor output varies with fluctuation in a lamp-driving voltage, an invention was disclosed in Japanese Patent Laid-open No. Sho 59-53865. The invention includes image sensors having optical filters corresponding to respective wavelengths of three colors of red, blue and green, and scans one same image three times corresponding to the three color sensors. Since the sensitivities of the image sensors differ for the wavelength of a light source, the voltage of the light source is varied for each image sensor in the three-time scanning operation to control the outputs of the image sensors at a predetermined value.
FIG. 4
shows a conventional circuit using a xenon lamp as a light source. The circuit has a turn-on circuit
6
and a converting circuit
10
, as described below. The turn-on circuit
6
includes an oscillator
1
a,
a frequency divider
2
a
, a waveform converting unit
3
a
, a lamp turn-on circuit
4
and a xenon lamp
5
. In order to obtain a high power, the xenon lamp
5
is generally driven by an AC pulse voltage. The converting circuit
10
, which receives light reflected at an object and converts it into an electrical signal, includes an oscillator
1
b
, a system control unit
7
having a microprocessor to control the whole image input device, and image sensors
8
B,
8
G and
8
R. When the converting circuit
10
is combined with a laser device
9
, the system control unit
7
is connected to the laser device
9
.
The turn-on circuit
6
operates as follows. A clock having a frequency f
1
is supplied from the oscillator
1
a
to the frequency divider
2
a
. The clock with the frequency f
1
is frequency-divided by the frequency divider
2
a
and then supplied to the waveform converting unit
3
a
. The waveform converting unit
3
a
, which includes a triangular wave generator and a pulse width modulator (they are not shown), generates a conventionally-known two-phase rectangular wave and supplies it to the lamp turn-on circuit
4
. The lamp turn-on circuit
4
generates a predetermined voltage with a predetermined frequency. The xenon lamp
5
is turned on at the predetermined frequency by the applied voltage.
The converting circuit
10
operates as follows. A clock CP having a frequency f
2
is supplied from the oscillator
1
b
independent of the oscillator
1
a
to the system control unit
7
. Then, a microprocessor (not shown) starts a predetermined operation. The system control unit
7
outputs from a terminal CPI a clock ICP to drive each image sensor and from a terminal I
1
a reset signal R to read an electrical signal stored in each image sensor, and supplies the clock ICP and the reset signal R respectively to a clock terminal C and a reset terminal RE of each of the image sensors
8
B,
8
G and
8
R, and each image sensor performs conventionally-known operation.
That is, each of the image sensors
8
B,
8
G and
8
R has a buffer memory (not shown) for one line therein and transfers the electrical signals stored by the previous scanning to the buffer memory for one line on the basis of the signal R. Synchronizing with the scanning for next one line, each image sensor outputs the contents of the buffer memory for the one line from respective terminals IO. Signals
8
BS,
8
GS and
8
RS of the image sensors
8
B,
8
G and
8
R outputted from the respective terminals
10
are supplied respectively to terminals IB, IG and IR of the system control unit
7
, and stored in buffer memories (not shown) located in the system control unit
7
.
The signals of the image sensors stored in the buffer memorie

Affiliated with

Also associated with

Rating

Image input device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Image input device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image input device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3149944