JPH1016291A - 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

Abstract

(57) Abstract: A recording head is adjusted to such an extent that a good quality halftone image can be realized without providing a correction circuit in a light emitting element driving circuit. SOLUTION: While making all light-emitting elements of a light-emitting element array 2 of a recording head 1 emit light, an image-capturing element array 42 is used to determine a light amount distribution in an array direction (Y direction) at or near an image plane of a lens array 4 of all light-emitting elements. , And the light quantity distribution is subjected to spatial frequency decomposition by the fast Fourier transform circuit 48, and the spatial frequency distribution is displayed on the display device 50. The display device 50 also displays the allowable value distribution for the spatial frequency component. The lens array 4 is orthogonal to the light emitting element array 2 in both the lens optical axis direction (Z direction) and the array direction (Y direction) such that the low frequency side spatial frequency component decreases and the high frequency side spatial frequency component increases. By moving the lens array 4 in the direction (X direction), the position of the lens array 4 in the X direction with respect to the light emitting element array 2 is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art
A light emitting element array formed by arranging a plurality of light emitting elements capable of controlling light emission by combining an LED or a light source with a liquid crystal shutter is combined with an array of refractive index distribution type lenses [SLA] such as Selfoc (registered trademark of Nippon Sheet Glass). An LED printer or a liquid crystal printer that forms an image (latent image) by forming light from the light emitting element on a photoreceptor of an electrophotographic apparatus and transfers the latent image to recording paper to form an image. It has been known.

[0003] These conventional devices are suitable for forming an image having no halftone, for example, an image composed of characters. However, in order to form an image having a halftone such as a photographic image, the above-mentioned lens array is used. There is a drawback that the resulting periodic image unevenness is conspicuous.

In order to correct the image unevenness, after the heads are manufactured, the image unevenness is measured for each head, so that the image unevenness does not occur in the driving circuit of the light emitting element (ie, the image unevenness is canceled. (2) The drive signal for adjusting the light emission amount was corrected.

However, in order to correct the image unevenness of each head in this manner, it is necessary to provide a correction circuit in the drive circuit, which causes a problem that the product cost is significantly increased. On the other hand, if this correction is not performed, the quality of the halftone image will be significantly reduced, and the application of the printer will be limited.

It is an object of the present invention to adjust a recording head to such an extent that a good quality halftone image can be realized without providing a correction circuit in a light emitting element driving circuit.

[0007]

According to the present invention, in order to achieve the above object, an image of light from a light emitting element array is formed on a recording medium by using a lens array arranged in parallel with the light emitting element array. The method of adjusting the position of the lens array with respect to the light emitting element array of the recording head that performs recording on the recording medium by using the lens array of all the light emitting elements while causing all the light emitting elements of the light emitting element array to emit light The light amount distribution in the array direction at or near the image plane is measured, and the light amount distribution is spatially frequency-resolved, and the spatial frequency component on the low frequency side of the light amount distribution decreases and the spatial frequency component on the high frequency side increases. Moving the lens array with respect to the light emitting element array in a specific direction orthogonal to both the lens optical axis direction and the array direction so that Adjusting the position of a specific direction of the lens array with respect to the light-emitting element array, and wherein the method of adjusting the recording head, it is provided.

In one embodiment of the present invention, the lens array is moved relative 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. Is moved in such a direction that, for a spatial frequency component whose distribution value exceeds an allowable value, the distribution value decreases.

According to the present invention, there is provided a recording head characterized by the above-described method, and an image forming apparatus including the recording head.

Further, according to the present invention, the above object is achieved by forming an image of light from a light emitting element array on a recording medium by using a lens array arranged in parallel with the light emitting element array. An apparatus used for adjusting a position of the lens array with respect to the light emitting element array of a recording head that performs recording on a medium, wherein the light from the light emitting element array is provided at or near an image forming plane by the lens array. A one-dimensional imaging element array arranged in parallel with the light emitting element array, a conversion unit for spatial frequency decomposition of a light amount distribution obtained by the imaging element array,
A display unit for displaying a spatial frequency distribution obtained by the conversion unit; and a device for adjusting a recording head.

In one embodiment of the present invention, the display means can also display an allowable value distribution for a spatial frequency component.

Further, according to the present invention, in order to achieve the above object, the light from the light emitting element array is focused on a recording medium by using a lens array arranged in parallel with the light emitting element array. An apparatus used for adjusting a position of the lens array with respect to the light emitting element array of a recording head that performs recording on a medium, wherein the light from the light emitting element array is provided at or near an image forming plane by the lens array. A one-dimensional imaging element array arranged in parallel with the light emitting element array, a conversion unit for spatial frequency decomposition of a light amount distribution obtained by the imaging element array,
A driving means capable of moving the lens array in both directions with respect to the light emitting element array in a specific direction orthogonal to both the lens optical axis direction and the array direction, and a spatial frequency distribution obtained by the conversion means exceeding an allowable value. When there is a frequency component having a distribution value, the driving unit moves the lens array in the specific direction until the distribution value of the frequency component is equal to or smaller than the allowable value of the frequency component. Control means for instructing
An apparatus for adjusting a recording head is provided.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

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

In FIG. 1, reference numeral 1 denotes a recording head;
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 configured 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 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 close to each other so as to be almost two rows in the direction. Incidentally, 24 is a protection member.

FIG. 3 is a schematic structural view of an electrophotographic image forming apparatus using the recording head 1. A photosensitive drum 32 is disposed below the recording head 1 having the above-described configuration. The photosensitive drum 32 is rotated in the direction of the arrow around the center of rotation in the Y direction. Light emission of each light emitting element of the light emitting element array 2 of the recording head 1 is controlled so as to be at 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. Reference numeral 34 denotes a developing device, where toner is supplied to the photosensitive drum 32 to develop a toner image. Numeral 36 denotes a conveying means for conveying a recording sheet as a recording medium. The recording sheet is placed on the upper surface thereof and is conveyed in the direction of the arrow. Photosensitive drum 3
2 is transferred to a recording sheet. The recording sheet carrying the transferred toner image is further conveyed, and is thermally fixed by a fixing device (not shown), thereby completing the image formation on the recording sheet. In the case of forming a color image, the above-described processes up to the development are separately performed on a plurality of primary color images, and the plurality of primary color images are sequentially superimposed and transferred onto a recording sheet conveyed by the conveying unit 36. After that, the fixing process is executed.

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. For example, the lens array 4 is configured to be 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 is variable until the adjustment is completed. This can be achieved by:

In FIG. 1, reference numeral 42 denotes a one-dimensional image sensor array, for example, a CCD. The image sensor array 42 is arranged so that the light emitted from the light emitting element array is directed in the Y direction at or near the image forming plane where the light is formed by the lens array 4. Note that it is desirable to use an image sensor array 42 having a sufficiently high resolution.

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

FIGS. 4A to 4C show the display device 50.
FIG. 6 is a diagram showing an example of a spatial frequency component distribution displayed in FIG.
The display device displays a curve A indicating a distribution of allowable values for each predetermined spatial frequency component. This allowable value distribution curve A is determined as follows.

The periodic image unevenness caused by the lens array 4 changes due to the fluctuation of crosstalk in the transmission of the amount of light between the lenses constituting 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, thereby changing the periodicity (spatial frequency characteristic) of the periodic unevenness of the image.

The degree of influence of the periodic unevenness on image evaluation differs depending on the spatial frequency component of the unevenness. That is, the criterion for determining the acceptability of an image 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 for the acceptability is determined by the human visual characteristics. It becomes severe when the sensitivity is high, and becomes gentle when the sensitivity is low. The absolute value of the tolerance value due to the spatial frequency of the unevenness varies depending on the viewing angle and the observation distance at the time of image observation, but generally,
The higher the spatial frequency, the smaller the unevenness becomes, which is less visible, and the lower the spatial frequency, the easier the unevenness is, the smaller the unevenness. However, if the spatial frequency becomes excessively small, the spatial frequency can be regarded as being substantially uniform within the viewing angle range, and the tolerance value of the spatial frequency for unevenness also increases. Thus, the distribution allowance value of the spatial frequency component becomes a curve as indicated by A in FIG. Note that the absolute value of the distribution tolerance value of the spatial frequency component is
It can be determined appropriately according to the desired recording head specifications.

The output from the fast Fourier transform circuit 48
The signal of the spatial frequency (f) component distribution shown in FIG.
And L and H. Part L is a space
Frequency f_L And the portion H has a spatial frequency f_H To
Has a peak. Of the lenses constituting the lens array 4
Assuming that the diameter is d (for example, about 1 mm), the spatial frequency f_LIs
1 / d, and the spatial frequency f_H Is 2 /
This is a frequency corresponding to d. Thus, the spatial frequency distribution
Is the part of the fundamental frequency corresponding to 1 / d and the fundamental frequency
And a frequency portion that is an integral multiple of
This spatial frequency f _L The frequency part more than 3 times
Ignore it.

Lens array 4 for light emitting element array 2
If the relative position adjustment in the X direction is not sufficiently performed, the portion L exceeds the allowable value distribution curve A and the portion H exceeds the allowable value distribution curve, as shown in FIG. Do not exceed A. In this case, since it is understood from the display on the display device 50 that adjustment is required, the lens array 4 is moved in the X direction by a suitable distance in the first direction, and then the display device 5 is again moved.
Looking at the display of 0, if 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 on 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 portion H
Gradually increases, and through the state of FIG.
Finally, as shown in FIG.
A state is realized in which none of the peaks of H exceed the allowable value distribution curve A. When this state is realized, the adjustment is completed. 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 equal to or higher than the fundamental frequency, the allowable value distribution curve A substantially monotonically increases 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, after taking into account the accuracy of the lens array 4 and the like, FIG.
The allowable value distribution curve A is set so that the state of (c) can be realized.

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

In this embodiment, the fast Fourier transform circuit 48
Is input to the control device 52. The control device 52 is provided with a memory 54. Lens array 4
Has been released from the holding member 16 and is held by the X-direction movable holder 56. Reference numeral 58 denotes a driver for driving the X-direction movable holder 56 to move in the X-direction. The holding member 16 is held by means (not shown).

FIG. 6 is a flowchart 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, in the same manner as in the first embodiment,
The spatial frequency component distribution is measured by the image sensor array 42, analog amplifier 44, A / D converter 46, and fast Fourier transform circuit 48 [S1].

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

If 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 compared for the frequency of the measured value larger than the allowable value. Compare [S3]. At the start of operation, this stored value is stored in memory 5 for all frequencies.
4 is stored as a sufficiently large value in dummy.

In S3, when it is determined 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 a value measured only for the frequency of the measured value larger than the allowable value, and the other values are deleted [S4]. After 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.

In S3, if it is determined that the measured distribution value is larger than the stored value [N], the X-direction movable holder 56 is moved to the driver 58 by an appropriate distance in the direction opposite to the previous direction in the X direction. And the direction of this movement is stored in the memory 54 [S6]. After S5 and 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 low device cost. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a first embodiment of a method for adjusting a recording head of an LED printer 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 illustrating an example of a spatial frequency component distribution displayed on a display device.

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording head 2 Light emitting element array 4 Refractive index distribution type lens array 12 Light emitting element array substrate 14 Fixing member 16 Holding member 22 Refractive index distribution type lens 24 Protective member 32 Photosensitive drum 34 Developing device 36 Recording paper conveying means 42 Imaging element array 44 Analog amplifier 46 A / D converter 48 Fast Fourier transform circuit 50 Display device 52 Controller 54 Memory 56 X-direction movable holder 58 X-direction movable holder driver A Allowable value distribution curve L, H Part of spatial frequency component distribution

Claims (7)

[Claims] 1. A recording head for performing recording on a recording medium by forming 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, while emitting light from all the light emitting elements of the light emitting element array, measure the light amount distribution in the array direction at or near the image plane of the lens array of all the light emitting elements, The light amount distribution is spatially frequency-decomposed, and the lens array is moved in the lens optical axis direction with respect to the light emitting element array so that the spatial frequency component on the low frequency side of the light amount distribution decreases and the spatial frequency component on the high frequency side increases. The lens array is moved in a specific direction orthogonal to both of the array directions, and the position of the lens array in the specific direction with respect to the light emitting element array is moved. To adjust,
A method for adjusting a recording head. 2. A direction in which the lens array is moved in the specific direction with respect to the light emitting element array such that a spatial frequency component on a low frequency side of the light quantity distribution decreases and a spatial frequency component on a high frequency side increases. 2. The printhead adjusting method according to claim 1, wherein the distribution value of the spatial frequency component whose distribution value exceeds an allowable value is in a decreasing direction. 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 recording head for recording on a recording medium by focusing 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. An apparatus used to adjust the position of the lens array, wherein a one-dimensional image sensor 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 by the lens array. A recording unit comprising: a conversion unit for spatial frequency decomposition of a light amount distribution obtained by the imaging element array; and a display unit for displaying a spatial frequency distribution obtained by the conversion unit. Equipment for adjustment. 6. The apparatus according to claim 5, wherein said display means can also display an allowable value distribution for a spatial frequency component. 7. A recording head for recording on a recording medium by forming 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, the recording head corresponding to the light emitting element array. An apparatus used to adjust the position of the lens array, wherein a one-dimensional image sensor 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 by the lens array. Conversion means for spatial frequency decomposition of the light quantity distribution obtained by the imaging element array; and both directions of the lens array 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. A frequency component having a distribution value exceeding a permissible value in the spatial frequency distribution obtained by the driving means and the conversion means which can be moved to If there is, control means for instructing the driving means to move the lens array in the specific direction until the distribution value for the frequency component is equal to or smaller than the allowable value for the frequency component. And characterized by having
A device for adjusting the recording head.