JP2001138568A - Method for correcting quantity of light of optical printer head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for correcting the quantity of light of an optical printer head which can correctly express a gray level even when the gray level of photographic images or the like is required. SOLUTION: According to the method, an optical printer head having a lens array 4 arranged on many light-emitting elements 2 is used and the quantity of light is corrected by adjusting the size of power to be impressed to each of the light-emitting elements 2. At least, two light-emitting elements 2 are let to emit light simultaneously and the intensity of light passing the lens array 4 is measured at an image form position. An MTF value is obtained from a peak value IMAX corresponding to each light-emitting element 2 and bottom values IMIN (>0) proximate to both sides of the peak value or to one side of the peak value in an intensity distribution obtained by the measurement. The size of power to be impressed to each light-emitting element 2 is adjusted in accordance with a difference of the MTF value and an average value of all MTF values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light amount correcting method for an optical printer head used as an exposure means for an electrophotographic printer, a facsimile, a copying machine or the like.

[0002]

2. Description of the Related Art Conventionally, optical printer heads such as LED array heads have been used as exposure means for electrophotographic printers and the like.

In such an LED array head, a plurality of LED array chips in which, for example, 128 light emitting diode elements are linearly arranged are arranged in a line on a circuit board, and a rod is mounted on these LED array chips. The LED array chip has a structure in which erecting equal-magnification lenses such as a lens array are arranged, and selectively emits light-emitting diode elements of the LED array chip individually based on image data. By irradiating and forming an image on an external photoreceptor via a photoconductor, a predetermined latent image is formed on the photoreceptor, thereby functioning as an exposure unit.

Incidentally, the latent image formed on the photoreceptor is thereafter
A toner image is formed through a development process, and a predetermined image is recorded on the recording paper by transferring and fixing the toner image on the recording paper.

[0005]

However, in the above-mentioned conventional LED array head, since the light-emitting characteristics and the lens characteristics of the light-emitting diode elements usually vary, a constant power is supplied to the light-emitting diode elements. When the light is applied to emit light, the intensity of light applied to the photoreceptor via the lens array becomes non-uniform in accordance with the above-mentioned variation, and there is a defect that image density unevenness is formed. .

Therefore, in order to solve the above-mentioned drawback, the spot diameter of the light applied to the photoreceptor is measured in advance for each light emitting diode element, and the power applied to the light emitting diode element is individually adjusted so as to be constant. By adjusting to LED
Correction of the light quantity of the array head has been studied.

By the way, the light emitted from the light emitting diode element partially spreads toward the periphery before reaching the photoreceptor, so that the intensity distribution has a peak value I _MAX in the central region as shown in FIG. The surrounding area of such light (the area corresponding to the foot of the mountain distribution)
Overlaps with a neighboring peak to form a valley having a bottom value I _MIN between neighboring peaks.

However, in the light amount correction simply adjusting the spot diameter as in the above-described correction method, the peak value I
_{If the} values of _MAX and I _MIN cannot be uniformly adjusted to the magnitudes of _MAX and the bottom value I _MIN , and if these values I _MAX and I _MIN vary greatly for each light emitting diode element, it becomes difficult to finely adjust the contrast of the image. When a gradation expression such as a photographic image is required, the gradation cannot be accurately expressed, and the image becomes unclear.

[0009]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks, and a method for correcting the amount of light of an optical printer head according to the present invention uses a lens array on a plurality of linearly arranged light-emitting elements. Using an optical printer head consisting of
When forming a latent image by irradiating the light emitted from the light emitting element on the photoreceptor through the lens array to form a latent image, light for correcting the light amount by adjusting the amount of power applied to each light emitting element A method of correcting the amount of light of a printer head, comprising: simultaneously emitting at least two light-emitting elements, transmitting the light through the lens array, and measuring the intensity of the transmitted light at the image forming position. From the intensity distribution obtained by this measurement, the MT expressed by the following equation is obtained from the peak value I _MAX corresponding to each light emitting element and the bottom value I _MIN (> 0) adjacent to both sides or one side thereof.
An F value is obtained, and the light amount is corrected by adjusting the magnitude of electric power applied to each light emitting element according to a difference between each MTF value and an average value of all MTF values. is there.

[0010]

(Equation 1)

Further, in the light amount correcting method for an optical printer head according to the present invention, the MTF value is obtained by using an average value of two bottom values I _MIN adjacent to both sides of the peak value I _MAX. is there.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a perspective view showing an embodiment in which an optical printer head for which light amount is corrected according to the present invention is applied to an LED array head. FIG. 2 is a side view of the LED array head of FIG. An LED array chip having light emitting elements, 3 is a driver IC, and 4 is a rod lens array as a lens array.

The LED array head shown in FIG. 1 has a plurality of LED array chips 2 and driver ICs 3 mounted on an upper surface of a circuit board 1 and an erecting equal-magnification lens on a light emitting surface of the LED array chip 2. It has a structure in which a certain rod lens array 4 is arranged and these are housed inside a housing (not shown).

The circuit board 1 has a rectangular base made of an electrically insulating material such as glass and a number of circuit wirings adhered and formed in a predetermined pattern on a rectangular base.
It functions as a supporting base material for supporting the D array chip 2, the driver IC 3, and the like.

A plurality of LED array chips 3 mounted on the circuit board 1 are arranged in a row along the longitudinal direction of the circuit board 1, and each of the LED array chips 3 has a 600 d
128 light emitting diode elements arranged linearly at a dot density of pi and electrode terminals of the elements are provided.

As the light emitting diode element of the LED array chip 2, a GaAlAs-based or GaAsP-based light-emitting diode element or the like is used, and the electrode terminals of the chip 2 are connected to a corresponding circuit on the circuit board 1 by a conventionally known wire bonding or the like. It is electrically connected to the wiring. The LED array chip 2 emits light at a predetermined luminance when power is applied to the light emitting diode element via circuit wiring on the circuit board 1.

On the other hand, the driver IC 3 mounted on the circuit board 1 is for individually controlling light emission of the above-mentioned light emitting diode elements based on image data. A shift register and a latch for light amount correction data are provided in addition to the shift register and the latch for controlling the power supply to the light emitting diode element based on two types of data stored in the two latches.

In this embodiment, when performing light quantity correction,
A plurality of constant current power supplies having different current values are prepared, and one or more of these constant current power supplies are selected based on the light quantity correction data stored in the latch, and corresponding light emission is performed. The connection to the diode element adjusts the power applied to the light emitting diode element.

The driver IC 3 is electrically connected to the corresponding circuit wiring on the circuit board 1 by a conventionally known wire bonding or the like, similarly to the LED array chip 2 described above.

The rod lens array 4 on the LED array chip 2 is for irradiating the light emitted from the light emitting diode element on the external photosensitive member P to form an image.
The rod lens array 4 is composed of a large number of rod-shaped lenses arranged linearly or a large number of rod-shaped lenses arranged in two rows in a staggered manner, and is held and fixed in a holder by an adhesive.

The above-mentioned LED array head selectively emits light-emitting diode elements of the LED array chip 2 individually based on image data, and emits the emitted light via the rod lens array 4 to an external photosensitive member P. By forming a predetermined latent image on the photoreceptor P, it functions as an exposure unit.

Next, a method for correcting the light quantity of the LED array head will be described.

The light quantity correction data will be described in the following (1) to (1).
It is created by the process of (3).

(1) First, the luminous outputs of all the light emitting diode elements are measured, and from this measurement result, first light quantity correction data for making the luminous outputs of all the light emitting diode elements uniform is created.

The measurement of the light emission output is performed by the rod lens array 4.
Is performed before mounting the LED array chip 2
The light emitted from the light emitting diode element is directly observed with a CCD camera. Then, based on the intensity distribution obtained by performing image processing on the CCD image, a predetermined power value required to fill the difference between the light emission output of each light emitting diode element and their average value (reference value) is obtained. Then, first light amount correction data corresponding to the power value is created.

For example, the adjustment of the applied power should be 1% in 3% steps.
In the case of performing in six stages, light amount correction data of 4 bits per dot is required.

(2) Next, the rod lens array 4 is
Attach on the light emitting surface of array chip 2 and then LE
The light emitting diode elements of the D array chip 2 are made to emit light with substantially the same luminance every other light using the above-mentioned first light amount correction data, and the intensity of the light transmitted through the rod lens array 4 is measured at the image forming position.

This light quantity measurement is performed in the MTF as shown in FIG.
(Modulation Transfer Function) This is performed by a measuring device.

The MTF measuring device includes a rod lens array 4
CCD moving on the top parallel to the array of light emitting diode elements
A camera is provided, and an intensity distribution is obtained by performing image processing on a CCD image read by the CCD camera.

This intensity distribution is shown in FIG. 4 because a part of the light emitted from the light emitting diode element spreads toward the periphery.
The peak distribution _IMAX has a peak in the central region as shown in FIG. 2. The peripheral region of such light (the region corresponding to the foot of the mountain distribution) overlaps with the neighboring one,
A valley with a bottom value I _MIN is formed between the peaks.

In the light quantity measurement described above, the light emitting diode elements of the LED array chip 2 were caused to emit light every other one because the finest gradation expression other than all black (solid printing)
This is because the light emission is performed by the above-described light emitting diode elements arranged alternately, and in this case, it is important to perform light quantity correction in consideration of the influence of light emission of two light emitting diode elements adjacent to each other.

(3) Next, second light quantity correction data is created from the above-mentioned intensity distribution.

In order to create the second light quantity correction data, first, in the intensity distribution of FIG. 4, a peak value I _MAX corresponding to each light emitting diode element and a bottom value I _MIN (> 0) adjacent to both sides or one side thereof. ) And MT represented by the following formula:
Find the F value.

As the bottom value I _MIN , a value close to one of the left and right of the peak value I _MAX may be used. However, when it is necessary to perform light quantity correction with higher accuracy,
Two bottom values I _MIN adjacent to both sides of the peak value I _MAX
The MTF value is determined using the average value of.

[0035]

(Equation 1)

Finally, a predetermined power value required to fill the difference between the MTF value corresponding to each light emitting diode element and the average value of all MTF values is obtained, and this power value is out of the allowable range. The second light amount correction data is created only for the dots.

Here, in order to easily use the second light quantity correction data in combination with the first correction data created earlier, it is preferable that both bits have the same number of bits. When the correction is performed in 16 steps, as in the case of the first light quantity correction data, the second light quantity correction data of 4 bits per dot is prepared.

The light quantity correction data obtained as described above is
The data is stored in a recording medium such as an EEP ROM, read out from the recording medium when the LED array head is used, and input to the driver IC 3. The input light quantity correction data is stored in the latch via the dedicated shift register as described above, and is used for light quantity correction.

At this time, since the correction data used for correcting the light quantity of the light emitting diode element is created in consideration of the magnitude of the bottom value I _MIN existing between the peaks in the intensity distribution, the contrast of the image is reduced. Are uniformed, the gradation can be accurately expressed, and a clear and good image without density unevenness can be formed.

In the present embodiment, the first light amount correction data for equalizing the light emission output of the light emitting diode element and the second light amount correction data for correcting the light transmitted through the lens array 4 are provided.
The light amount correction data of the optical printer head is obtained separately, and then the two data are combined to obtain the final light amount correction data. Therefore, the light amount correction of the optical printer head can be accurately performed.

The present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention.

For example, in the above-described embodiment, every second light emitting diode element is made to emit light when measuring the light emission intensity in the step (2). Alternatively, the light may be emitted.

In the above-described embodiment, first, first light quantity correction data for uniforming the light emission output of the light emitting diode element is created, and then second light quantity correction data for correcting the light transmitted through the lens array 4. In the process of creating correction data and then obtaining the final light quantity correction data by combining the two, the dispersion correction of the light emission characteristics and the correction of the lens characteristics were separately performed. By measuring the light transmitted through the array 4 and generating light amount correction data, it is possible to simultaneously perform the variation correction of the light emission characteristics and the variation correction of the lens characteristics.

Further, in the above-described embodiment, the light amount is corrected by adjusting the magnitude of the current flowing through the light emitting diode element. However, instead of this, the power supply time to the light emitting diode element is adjusted to adjust the light amount. Correction may be performed.

Further, in the above embodiment, a CCD camera is used to measure the light emission intensity. However, other light amount detecting means such as a photodiode may be used instead.

Further, in the above embodiment, the light quantity of the light emitting diode element is measured every other dot. However, it is needless to say that the measurement of all dots may be performed.

[0047]

According to the light amount correcting method of the present invention, the light emitted from the light emitting element is measured through the lens array, and the magnitude of the bottom value I _MIN existing between the peaks in the obtained intensity distribution is taken into consideration. The light intensity correction is performed while making the image uniform, so that the contrast of the image can be made uniform and the gradation can be accurately expressed, thereby forming a clear and good image without density unevenness. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment in which an optical printer head whose light quantity is corrected by the present invention is applied to an LED array head.

FIG. 2 is a side view of the LED array head of FIG.

FIG. 3 is a diagram showing a configuration of an MTF device used for light quantity measurement.

FIG. 4 is a diagram showing an intensity distribution of light transmitted through a lens array when a light emitting diode element of an LED array head emits light.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Circuit board, 2 ... LED array chip, 3
..Driver IC, 4 ... Lens array (rod lens array)

Claims (2)

[Claims] 1. An optical printer head having a lens array arranged on a large number of light emitting elements arranged linearly, and irradiates and couples light emitted from the light emitting elements to a photoreceptor via the lens array. A method of correcting the amount of light by adjusting the amount of power applied to each light emitting element when forming a latent image by forming an image, the method comprising: At the same time, the intensity of the transmitted light is measured at the image forming position, and the peak value corresponding to each light emitting element in the intensity distribution obtained by the measurement. From I _MAX and the bottom value I _MIN (> 0) adjacent to both sides or one side thereof, M represented by the following equation is obtained.
An optical printer for obtaining a TF value and adjusting the amount of power applied to each light emitting element according to a difference between each of the MTF values and an average value of all the MTF values, thereby correcting a light amount. Head light amount correction method. (Equation 1) 2. The method according to claim 1, wherein the MTF value is obtained by using an average value of two bottom values I _MIN adjacent to both sides of the peak value I _MAX. .