Coherent light generators – Particular component circuitry
Reexamination Certificate
1999-04-09
2002-04-09
Font, Frank G. (Department: 2877)
Coherent light generators
Particular component circuitry
C372S038020, C372S038070, C372S029015, C372S029011, C372S029010, C372S024000, C372S026000, C347S246000, C347S236000
Reexamination Certificate
active
06370175
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a laser beam luminous energy correction method for correcting the variation caused by a scanning optical system of the luminous energy of a laser beam incident on a scanned surface via the scanning optical system, a laser driving apparatus adopting the laser beam luminous energy correction method, a laser beam scanner for scanning the predetermined scanned surface by a laser beam emitted from a semiconductor laser driven by the laser driving apparatus and incident via the scanning optical system and an image recording device for recording an image using such a laser beam scanner.
Heretofore, for a method of correcting the variation caused by a laser beam scanning optical system of the luminous energy of a laser beam on a scanned surface (the surface of a photoconductor) and the unevenness in density of an image output according to laser xerography, there are first earlier technology (disclosed in the Unexamined Japanese Patent Publication Application No. Sho 53-87747) in which an ND filter for correcting luminous energy distribution is arranged on the optical path of a laser beam, second earlier technology (disclosed in the Examined Japanese Patent Publication Application No. Hei 2-51188) in which correction current based upon a function showing luminous energy distribution is superposed on driving current and makes electric correction, third earlier technology (disclosed in the Unexamined Japanese Patent Publication Application No. Hei 1-182819) in which the gain of a D/A converter is controlled based upon a reference value for controlling luminous energy, fourth earlier technology (disclosed in the Examined Japanese Patent Publication Application No. Hei 5-15339) in which the output of a D/A converter is regulated manually in place of controlling the gain of the D/A converter, fifth earlier technology (disclosed in the Unexamined Japanese Patent Publication Application No. Hei 1-302367) in which the maximum luminous energy and the minimum luminous energy are respectively regulated to the maximum driving current and the minimum driving current and the difference is linearly corrected and others.
However, there is a problem in the first earlier technology using the above ND filter that as the cost of the ND filter itself is high and in addition, the distribution of luminous energy varies according to the design of an optical system, the ND filter is required to be remodeled every time. There are also various problems in an electric correction method heretofore proposed as explained below.
FIG. 37
is a circuit diagram showing the above second earlier technology. An added value is acquired by adding a function value generated in a function signal generator
331
and according to a scanned position and a reference value from a reference signal circuit
332
by an adder
333
so as to use the added value for the reference value of current for driving a laser.
There is a problem that as in this method, a function value is added to the reference value using the adder
333
, a function is required to be reset every time the characteristics of a laser vary because of the environmental change of temperature, humidity and others, aging change and others and this method cannot correspond to the change of the characteristics of the laser.
In the above circuit, current flowing to a laser
334
is detected and led to a comparator
335
, however, there is a problem related to not current flowing in the laser
334
but the luminous energy of a laser beam emitted from the laser
334
and the variation caused by the change of the characteristics of the laser
334
of the luminous energy of a laser beam for current flowing in the laser
334
cannot be corrected.
FIG. 38
is a circuit diagram showing the above third earlier technology. Reference voltage Vref acquired by a reference voltage generator
341
and a voltage value showing the emission luminous energy of a laser
343
and detected by an optical detector
342
are compared by a comparator
344
, a count value showing laser emission luminous energy according to the reference voltage Vref is acquired in an updown counter
348
by transmitting the result of the comparison to the updown counter
348
, the count value is converted to an analog signal by a D/A converter
346
and transmitted to a computing element
347
. In the meantime, a digital value according to a signal showing a scanned position acquired by an image scanning clock generator
349
is output from a digital value setting circuit
353
, the digital value is converted to an analog signal by a D/A converter
350
and input to the computing element
347
. The computing element
347
applies predetermined operation to two analog signals respectively transmitted from the two D/A converters
346
and
350
and transmits the result of the operation to a semiconductor laser driving circuit
351
. Gain control based upon reference voltage Vref is applied to the D/A converter
350
by a gain control section
352
. That is, a correction coefficient every scanned position is generated in the digital value setting circuit
348
and the correction coefficient is multiplied by a coefficient varying according to reference voltage Vref in automatic luminous energy control so as to suppress the a variation of luminous energy on a scanned surface.
However, in the above Examined Japanese Patent Publication Application No. Hei 2-51188, it is not described that any current component of current supplied to a semiconductor laser is to be corrected and there is a problem that a method of controlling the gain of the D/A converter
350
by the gain control section
352
is required to be changed every time the characteristic of a laser varies and the third earlier technology cannot correspond to the change of the characteristic of a laser as in the earlier technology described referring to FIG.
37
.
In the above fourth earlier technology, an amplifier for controlling the output of the D/A converter
350
manually in provided in place of the gain control section
352
shown in FIG.
38
and as manual control is executed in this case, manual control is naturally executed every time the characteristic of a laser varies.
Further, in the Examined Japanese Patent Publication Application No. Hei 4-750702, the technique of controlling the emission luminous energy of a laser beam by controlling bias current is disclosed, however, the above technique also has a problem that is cannot correspond to the change of the characteristic of a laser.
As the above fifth earlier technology respectively relates the maximum luminous energy and the minimum luminous energy to the maximum driving current and the minimum driving current and linearly corrects the difference, the problems in the second and third earlier technologies are solved. However, if the fifth earlier technology is applied to laser xerography, the maximum luminous energy and the minimum luminous energy are required to be regulated due to ambient temperature and humidity or the deterioration of a photoconductor, however, reference voltage for the maximum and minimum luminous energy is fixed and it is not considered that if the maximum and minimum luminous energy is not controlled holding proportional relationship between the maximum luminous energy and the minimum luminous energy, laser beam luminous energy is not corrected right. The fifth earlier technology adopts a method that relationship between a correction value acquired by a correction coefficient circuit and the actual variation of laser beam luminous energy is defined by controlling luminous energy based upon two reference values Vp and Vb. As a result, though automatic luminous energy control is required only once if on-off control is executed by fixed luminous energy as in prior pulse length modulation, the above control is required to be executed twice in the case of the fifth earlier technology. In laser xerography, as automatic luminous energy control is required twice and effective time in which modulation by a picture signal is
Higashi Koichi
Ikeda Chikaho
Font Frank G.
Fuji 'Xerox Co., Ltd.
Rodriguez Armando
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