JP3450601B2 - Method of adjusting recording head for recording by imaging light emission of light emitting element array by lens array and apparatus used for implementing this method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording head adjusting technique for an image forming apparatus, and more particularly, a method of adjusting a recording head for recording by forming light emission of a light emitting element array by a lens array. And the apparatus used to carry out the method. The recording head adjusted by the present invention can be applied to, for example, a color printer or a color copying machine.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
A light emitting element array formed by arranging a plurality of light emitting elements capable of controlling light emission, which is a combination of LEDs and a light source and a liquid crystal shutter, is combined with an array [SLA] of gradient index lenses such as SELFOC (registered trademark of Nippon Sheet Glass Co., Ltd.) An LED printer or a liquid crystal printer which is used to form an image (latent image) by forming light from the light emitting element on a photoconductor of an electrophotographic apparatus and transferring the latent image to a recording sheet to form an image. It has been known.

These conventional apparatuses are suitable for forming an image having no halftone, for example, an image composed of characters, but for forming an image having a halftone such as a photographic image, the above-mentioned lens array is used. There is a drawback that the periodical image unevenness caused by it is easily noticeable.

In order to correct the image unevenness, after the head is manufactured, the image unevenness is measured for each head so that the image unevenness does not occur in the drive circuit of the light emitting element (that is, the image unevenness is canceled). (1) The drive signal was adjusted to adjust the light emission amount.

However, in order to correct the image unevenness of each head in this way, it is necessary to provide a correction circuit in addition to the drive circuit, which causes a problem of significantly increasing the product cost. On the other hand, if this correction is not performed, the quality of the halftone image is significantly deteriorated, and the use of the printer is limited.

Therefore, an object of the present invention is to adjust the recording head to such an extent that a good-quality halftone image can be realized without providing a light emitting element drive circuit with a correction circuit.

[0007]

According to the present invention, in order to achieve the above object, light of a light emitting element array is imaged on a recording medium by using a lens array arranged in parallel with the light emitting element array. a method of adjusting the position of the lens array with respect to the light emitting element array of the recording head for recording to the recording medium by said Renzua
Ray is made up of multiple gradient index lenses whose optical axes are
Be parallel and in two rows in a direction orthogonal to the direction of the optical axis
Are arranged close to each other so that
Make sure that the gradient index lenses do not shift by half a pitch.
Shall be and, the light intensity distribution over the array direction of the image plane or in the vicinity thereof by the lens array of該全light emitting element while emit all the light emitting elements of the light emitting element array to measure the spatial frequency light amount distribution The lens array is disassembled so that the spatial frequency component on the low frequency side of the light quantity distribution decreases and the spatial frequency component on the high frequency side increases, and the lens array is orthogonal to both the lens optical axis direction and the array direction with respect to the light emitting element array. And a position in the specific direction of the lens array with respect to the light emitting element array is adjusted by moving the recording head in a specific direction.

In one aspect of the present invention, the lens array is arranged in the specific direction with respect to the light emitting element array so that the low frequency side spatial frequency component of the light quantity distribution decreases and the high frequency side spatial frequency component increases. The direction in which the distribution value is moved is a direction in which the distribution value of the spatial frequency component decreases if the distribution value exceeds the allowable value.

[0009]

According to the present invention, the adjustment is performed by the above method.
Recording head characterized by being aligned and the recording
An image forming apparatus comprising a head,
Provided.

Further, according to the present invention, in order to achieve the above object, the light of the light emitting element array is imaged on a recording medium by using a lens array arranged in parallel with the light emitting element array. in the device used to adjust the position of the lens array with respect to the light emitting element array of the recording head for recording to medium, said Ren
This array has a plurality of gradient index lenses whose optical axes are mutually
2 rows parallel to each other and perpendicular to the direction of the optical axis
So that they are close to each other and arranged,
Make sure that the gradient index lenses in the rows are offset by a half pitch
And a one-dimensional imaging element array arranged in parallel with the light emitting element array on or near an image forming plane of the light from the light emitting element array formed by the lens array,
A conversion means for spatial frequency decomposition of the light quantity distribution obtained by the image pickup element array, and the lens array is moved in both directions with respect to the light emitting element array with respect to a specific direction orthogonal to both the lens optical axis direction and the array direction. If there is a frequency component having a distribution value exceeding the allowable value in the spatial frequency distribution obtained by the converting means and the converting means, the distribution value related to the frequency component is equal to the allowable value in the frequency component. Control means for instructing the drive means to move the lens array with respect to the specific direction until it becomes smaller than or equal to or smaller than that, or a device for adjusting a recording head. It

[0012]

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing a first embodiment of an adjusting method for an LED printer recording head according to the present invention, together with a configuration of an apparatus used for carrying out the adjusting method.

In FIG. 1, reference numeral 1 denotes a recording head, and 2
Is a light emitting element array, and 4 is a gradient index lens array. The light emitting element array 2 is formed on the lower surface side of the substrate 12, and is formed by arranging a large number of light emitting elements in one row in the Y direction. The light emitting element array substrate 12 is attached to the fixing member 14. A holding member 16 is attached to the fixing member 14, and the lens array 4 is held by the holding member 16.

FIG. 2 is a schematic explanatory view of the lens array 4. The lens array 4 includes a large number of gradient index lenses 22.
Are arranged parallel to each other so that the optical axis is in the Z direction, and Y
They are arranged in close contact with each other so as to form almost two rows in the direction. Incidentally, 24 is a protective member.

FIG. 3 is a schematic configuration diagram of an electrophotographic image forming apparatus using the recording head 1. The photosensitive drum 32 is arranged below the recording head 1 having the above structure. The photosensitive drum 32 is rotated in the direction of the arrow around the center of rotation in the Y direction. The light emission of each light emitting element of the light emitting element array 2 of the recording head 1 is controlled so as to have a desired timing based on an input signal corresponding to an image to be recorded. The light emitted from each light emitting element is imaged on the surface of the photosensitive drum 32 by the lens array 4, whereby a latent image is formed on the surface of the photosensitive drum 32. A developing device 34 supplies toner to the photosensitive drum 32 to develop a toner image. A conveying unit 36 conveys a recording sheet, which is a recording medium, and the recording sheet is placed on the upper surface and conveyed in the direction of the arrow. Photosensitive drum 3
The toner image formed on No. 2 is transferred to the recording paper. The recording paper carrying the transferred toner image is further conveyed and heat-fixed by a fixing device (not shown), whereby image formation on the recording paper is completed. In the case of forming a color image, the above-described process up to development is separately performed for a plurality of primary color images, and the plurality of primary color images are sequentially superposed and transferred onto the recording sheet conveyed by the conveying unit 36. After that, the fixing process is performed.

In FIG. 1, the position of the lens array 4 in the X direction with respect to the light emitting element array 2 is variable. This is, for example, configured such that the lens array 4 is movable in the X direction relative to the holding member 16, and is supported by a jig (not shown) so that the position in the X direction can be changed until the adjustment is completed. It can be realized.

In FIG. 1, reference numeral 42 is a one-dimensional image pickup device array such as a CCD. The image pickup element array 42 is arranged such that the light emitted from the light emitting element array is oriented in the Y direction on or near an image forming surface on which the lens array 4 forms an image. As the image pickup element array 42, it is desirable to use one having a sufficiently high resolution.

From the image pickup element array 42, an analog output signal indicating the image formation state of the light emission of the light emitting element by the lens array 4 is obtained. This corresponds to the light amount distribution on the image sensor array 42. An output signal of the image pickup element array 42 is appropriately amplified by an analog amplifier 44, and if necessary, unevenness of characteristics of the image pickup element array 42 itself is corrected by a correction circuit (not shown), and then A / D converter 46 is used. / D conversion. Then, the light amount distribution digital signal output from the A / D converter 46 is input to a fast Fourier transform circuit (FFT) 48, where it is decomposed into spatial frequency components, and the resulting spatial frequency component distribution is displayed. It is displayed on the device 50 such as a CRT.

FIGS. 4A to 4C show the display device 50.
It is a figure which shows the example of a spatial frequency component distribution displayed on.
On this display device, a curve A showing a distribution of allowable values for each predetermined spatial frequency component is displayed. This allowable value distribution curve A is determined as follows.

The periodic image unevenness caused by the lens array 4 changes due to a change in crosstalk in the transmission of the amount of light between the lenses forming the lens array 4. Therefore,
By changing the relative positional relationship of the lens array 4 with respect to the light emitting element array 2 in the X direction, it is possible to change the crosstalk and change the periodicity (spatial frequency characteristic) of the periodic unevenness of the image.

The degree of influence of the periodic unevenness on the image evaluation depends on the spatial frequency component of the unevenness. That is, the criterion of image quality judgment is related to the human visual characteristics, and even if the physical characteristic values are the same, the tolerance of the physical characteristic value used as the criterion of the quality judgment is the human visual characteristics. When the sensitivity is high, it becomes severe, and when it is low, it becomes gradual. The tolerance value due to the spatial frequency of the unevenness varies in absolute value depending on the viewing angle and the observation distance at the time of image observation, but in general,
The higher the spatial frequency, the less likely the unevenness is to be visually recognized, and the larger the spatial frequency, the more easily the unevenness is visually recognized. However, when the spatial frequency becomes excessively small, it can be gradually regarded as substantially uniform within the viewing angle range, and therefore, the tolerance value of the unevenness due to the spatial frequency becomes large. Thus, the distribution tolerance value of the spatial frequency component becomes a curve as indicated by A in FIG. The absolute value of the distribution tolerance value of the spatial frequency component is
It can be appropriately determined according to desired printhead specifications.

Output from the fast Fourier transform circuit 48
The signal of the component distribution of the spatial frequency (f) shown in FIG.
Two parts designated L and H. Part L is space
Frequency f_L Has a peak at, and the part H has a spatial frequency f_H To
Has a peak. Of the lenses that make up the lens array 4
Spatial frequency f with diameter d (for example, about 1 mm)_LIs
Frequency corresponding to 1 / d, spatial frequency f_H Is 2 /
It is a frequency corresponding to d. Thus, the spatial frequency distribution
Is a portion of the fundamental frequency corresponding to 1 / d and the fundamental frequency
, Which is an integral multiple of
This spatial frequency f _L The part of the frequency more than 3 times is small
Ignore with.

Lens array 4 for light emitting element array 2
When the relative position in the X direction is not sufficiently adjusted, as shown in FIG. 4A, the part L exceeds the allowable value distribution curve A and the part H exceeds the allowable value distribution curve. Do not exceed A. In this case, since it can be seen from the display of the display device 50 that adjustment is necessary, the lens array 4 is moved in the first direction in the X direction by an appropriate distance, and then the display device 5 is again displayed.
When the display of 0 is seen and the peak value of the portion L is lower than the previous time, the movement of the lens array 4 in the first direction is continued. Further, looking at the display of the display device 50 again, if the peak value of the portion L is higher than the previous time, the lens array 4 is moved in the second direction opposite to the first direction.
As a result, the peak value of the portion L gradually decreases and the peak value of the portion H
The peak value of gradually increases, and after going through the state of FIG.
Finally, as shown in FIG. 4 (c), two parts L,
A state in which none of the H peaks exceeds the allowable value distribution curve A is realized. When this state is realized, the adjustment is completed, and in order to fix the positional relationship at that time, the holding member 16 and the lens array 4 are joined by an appropriate means such as an adhesive.

In the case of a commonly used lens array,
At frequencies above the fundamental frequency, the allowable value distribution curve A increases almost monotonically as the spatial frequency increases. Therefore, by decreasing the spatial frequency component on the low frequency side and increasing the spatial frequency component on the high frequency side, it is possible to prevent the allowable value distribution curve A from being exceeded for all frequencies. That is, in consideration of the accuracy of the lens array 4 and the like, as shown in FIG.
The allowable value distribution curve A is set so that the state of (c) can be realized.

FIG. 5 is a schematic view showing the second embodiment of the adjusting method of the LED printer recording head according to the present invention together with the configuration of the apparatus used for carrying out the adjusting method. In this figure, members having the same functions as those in FIGS. 1 to 4 are designated by the same reference numerals.

In the present embodiment, the fast Fourier transform circuit 48
The output from is input to the controller 52. A memory 54 is attached to the control device 52. Lens array 4
Has been released from the restraint with respect to the holding member 16 and is held by the X-direction movable holder 56. Reference numeral 58 is a driver for driving movement of the X-direction movable holder 56 in the X-direction. The holding member 16 is held by means (not shown).

FIG. 6 is a flow chart for explaining the operation of the control device 52. This embodiment will be described with reference to FIGS. 5 and 6 and also FIG.

First, similarly to the first embodiment,
The spatial frequency component distribution is measured by the image sensor array 42, the analog amplifier 44, the A / D converter 46, and the fast Fourier transform circuit 48 [S1].

This measured value is compared with the allowable value stored in advance in the memory 54 for each frequency [S2]. S
In FIG. 2, when the measured values are equal to or smaller than the allowable value for all frequencies in the measurement range [N], the state of FIG. End the operation (of course, with the completion of adjustment,
At this time, the work of fixing the positional relationship between the lens array 4 and the holding member 16 is performed, for example, bonding with an adhesive).
In S2, when there is a frequency with a measured value larger than the allowable value [Y], it is determined that the X-direction position adjustment is necessary because of the states of FIGS. 4 (a) and 4 (b).

When it is determined in S2 that the X-direction position adjustment is necessary, the measured distribution value and the frequency distribution value (stored value) stored in the memory 54 are set for the frequency of the measured value larger than the allowable value. Compare [S3]. At the start of operation, the memory 5 is used as the stored value for all frequencies.
A sufficiently large value is dummy stored in 4.

If it is determined in S3 that the measured distribution value is equal to or smaller than the stored value [Y],
The stored value of the frequency distribution stored in the memory 54 is updated to the value measured only for the frequency of the measured value larger than the allowable value, and the other values are deleted [S4]. After the end of S4, the driver 58 is instructed to move the X-direction movable holder 56 in the X direction in the same direction as the previous time by an appropriate distance, and the direction of this movement is stored in the memory 54 [S5]. At the start of the operation, one of the two directions is dummy stored as the direction of the previous movement.

When it is determined in S3 that the measured distribution value is larger than the stored value [N], the X-direction movable holding tool 56 is moved with respect to the driver 58 by an appropriate distance in the direction opposite to the previous direction in the X-direction. Then, the direction of this movement is stored in the memory 54 [S6]. After the end of S5 and the end of S6, the process returns to S1.

[0035]

As described above, according to the present invention,
It is possible to adjust the recording head to such an extent that a good-quality halftone image can be realized without providing a correction circuit in the light emitting element drive circuit, and a high quality image can be realized at a low device cost. .

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of an adjusting method for an LED printer recording head according to the present invention, together with a configuration of an apparatus used for implementing the adjusting method.

FIG. 2 is a schematic explanatory diagram of a lens array.

FIG. 3 is a schematic configuration diagram of an electrophotographic image forming apparatus using a recording head.

FIG. 4 is a diagram showing an example of a spatial frequency component distribution displayed on a display device.

FIG. 5 is a schematic view showing a second embodiment of an adjusting method for an LED printer recording head according to the present invention, together with a configuration of an apparatus used for implementing the adjusting method.

FIG. 6 is a flowchart for explaining the operation of the control device.

[Explanation of symbols]

1 recording head 2 Light emitting element array 4 Gradient Index Lens Array 12 Light emitting element array substrate 14 Fixed member 16 Holding member 22 Gradient Index Lens 24 Protective member 32 photosensitive drum 34 Developer 36 recording sheet conveying means 42 Image sensor array 44 analog amplifier 46 A / D converter 48 Fast Fourier Transform Circuit 50 display 52 Control device 54 memory 56 X direction movable holder 58 X direction movable holder driver A allowable value distribution curve L, H spatial frequency component distribution part

Continuation of the front page (56) References JP-A-6-155806 (JP, A) JP-A-3-119862 (JP, A) JP-A-6-246968 (JP, A) JP-A-9-66628 (JP , A) JP-A 2-111571 (JP, A) JP-A 10-811 (JP, A) JP-A 63-33876 (JP, A) JP-A 56-67870 (JP, A) JP-A 62-111268 (JP, A) JP 62-147471 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/44 B41J 2/445 B41J 2/45 B41J 2 / 455

Claims (5)

(57) [Claims] 1. A recording head for recording on a recording medium by forming an image of the light of the light emitting element array on a recording medium by using a lens array arranged in parallel with the light emitting element array. In the method of adjusting the position of the lens array, the lens array includes a plurality of gradient index lenses on an optical axis.
One in which the two are parallel to each other and orthogonal to the direction of the optical axis
Arrange them in close proximity to each other so that there are two rows,
And the gradient index lenses in each row are displaced by a half pitch
The light amount distribution in the array direction is measured at or near the image plane of the lens array of all the light emitting devices while causing all the light emitting devices of the light emitting device array to emit light. Is spatially decomposed, and the lens array is arranged in the lens optical axis direction and the array direction with respect to the light emitting element array so that the low frequency side spatial frequency component of the light quantity distribution decreases and the high frequency side spatial frequency component increases. By moving in a specific direction orthogonal to both, to adjust the position of the lens array in the specific direction with respect to the light emitting element array,
A method for adjusting a recording head, which is characterized in that 2. The direction in which the lens array is moved with respect to the light emitting element array in the specific direction so that the spatial frequency component on the low frequency side of the light quantity distribution decreases and the spatial frequency component on the high frequency side increases. 2. The recording head adjusting method according to claim 1, wherein the distribution value of the spatial frequency component is decreased when the distribution value exceeds an allowable value. 3. A recording head adjusted by the method according to claim 1 . 4. An image forming apparatus comprising the recording head according to claim 3 . 5. A light-emitting element array of a recording head for performing recording on the recording medium by forming an image of the light of the light-emitting element array on the recording medium using a lens array arranged in parallel with the light-emitting element array. In the apparatus used to adjust the position of the lens array, the lens array includes a plurality of gradient index lenses on the optical axis.
One in which the two are parallel to each other and orthogonal to the direction of the optical axis
Arrange them in close proximity to each other so that there are two rows,
And the gradient index lenses in each row are displaced by a half pitch
And a one-dimensional image sensor array arranged in parallel with the light emitting element array on or near the image plane of the light from the light emitting element array formed by the lens array. A conversion means for spatial frequency resolution of the light quantity distribution, and a drive means capable of moving the lens array with respect to the light emitting element array in both directions with respect to a specific direction orthogonal to both the lens optical axis direction and the array direction, When there is a frequency component having a distribution value exceeding the allowable value in the spatial frequency distribution obtained by the converting means, the distribution value related to the frequency component is equal to or smaller than the allowable value in the frequency component. Control means for instructing the drive means to move the lens array with respect to the specific direction. Characterized Rukoto, apparatus for recording head adjustment.