JP3598699B2 - Method for measuring gradation characteristics of solid-state scanning optical writing device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for measuring a gradation characteristic of a solid-state scanning optical writing device for writing an image (latent image) on a photoconductor using a PLZT optical shutter array, an LED array, or the like.
[0002]
[Prior art and problems]
Conventionally, photographic paper using silver halide photosensitive materialOrPLZT, etc. to form an image (latent image) on a film or photoconductor for electrophotographyUsing a light shutter array or LED arrayThere are provided various optical writing devices for controlling ON / OFF of the optical writing. In this type of solid-state scanning optical writing device, each light source is used to obtain an even image.elementIt is necessary to measure the light amount of the light and to correct the light amount based on the measured value.
[0003]
By the way, the drive pulse width modulation method is effective to reproduce multiple gradations.elementIt is difficult to accurately correct the light amount because of the variation in the gradation characteristics. Variations in gradation characteristics are considered to be caused by distortion and dimensional errors during processing of the PLZT chip.element, For example, if the number of pixels is about 512 pixels, a variation in light amount of about ± 15 to ± 20% occurs. In addition, each optical shutterelementDue to the shape error of eachelementThe voltage (half-wavelength voltage) at which the maximum transmitted light amount of the pixel varies also, and the gradation characteristics when the drive pulse width is modulated are different.elementHas unique characteristics.
[0004]
Conventionally, all the optical shutters under a certain driving condition (only one gradation)elementWas turned on to measure the amount of light to obtain correction data. However, with this, the correction data greatly deviates from the actual gradation characteristics, and accurate light quantity correction cannot be realized.
[0005]
Object, Summary and Effect of the Invention
Therefore, an object of the present invention is to provide a light source for each light without significantly increasing the measured gradation.elementIt is an object of the present invention to provide a method for measuring a gradation characteristic of a solid-state scanning optical writing device, which can detect the gradation characteristic of the solid-state image almost accurately.
[0006]
In order to achieve the above object, the first invention isConsists of PLZTA large number of optical elements arranged in the main scanning direction areBy changing the drive pulse width under a constant voltage,In the gradation characteristic measuring method for a solid-state scanning optical writing device in which on / off control is performed in multiple gradations, the output light amount of each of the optical elements at at least three different gradations (ie, measurement points with different light amount settings) is the same. And the gradation characteristics of each optical element are determined from the measured values.Multiple straight lines or at least quadraticIt was calculated as an approximate expression.
[0007]
FirstIn the invention, the gradation characteristics of each optical element are approximated from the measured values of the output light amounts of the optical elements at a small number of gradations of 3 to 5 points. Therefore, the approximated gradation characteristic has an extremely small error from the actual gradation characteristic, so that accurate light amount correction data can be obtained, and a high-quality image with no unevenness can be formed. In addition, since the gradation characteristic itself of each optical element is simulated, accurate correction data can be obtained even if the drive voltage slightly varies. Furthermore, in the light quantity measurement, since the optical element is driven with a small number of gradations, it is not necessary to add a large-scale and expensive circuit. it can.
[0008]
FirstIn the present invention, the number of gradations for measuring the output light amount is a number corresponding to the approximate expression to be calculated. For example, at least three points are measured for a quadratic expression, and at least four points are measured for a tertiary expression. If the measured gradation is set near the inflection point of the actual gradation characteristic of the optical element, more accurate gradation characteristics can be obtained.
According to a second aspect of the present invention, there is provided a method for measuring a gradation characteristic of a solid-scanning optical writing device for controlling on / off of a plurality of optical elements arranged in a main scanning direction in multiple gradations based on image data. The output light amount of the optical element at three different gradations is measured using a sensor, and the gradation characteristic of each optical element is calculated from the measured value as an approximate expression,Before the light quantity measurement for calculating the gradation characteristics, each optical element is driven at a duty of about 50% to determine a drive voltage at which the maximum light quantity is obtained.To obtain gradation characteristicsTurn on each light elementIt was to so. therefore,Correction data with small errors can be obtained for all optical elements.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a gradation characteristic measuring method for a solid-state scanning optical writing device according to the present invention will be described with reference to the accompanying drawings.
[0010]
(Optical writing head)
FIG. 1 shows an optical writing head 20 for writing a full-color image on photographic paper using a silver halide photosensitive material. The optical writing head 20 generally includes a halogen lamp 21, a heat-insulating filter 22, a color correction filter 23, a diffusion tube 24, an RGB filter 25, an optical fiber array 26, a slit plate 27, an optical shutter module 30, an imaging lens array 35, It is constituted by dustproof glass 36.
[0011]
The light emitted from the halogen lamp 21 is cut off the heat rays by the heat prevention filter 22 and the light quality is adjusted by the color correction filter 23 so as to match the spectral sensitivity characteristics of the photographic paper. The diffusion tube 24 is for improving the light use efficiency and reducing the light amount unevenness. The RGB filter 25 will be described below.Optical shutter module 30, And is rotated in synchronization with the writing by the controller, and changes the passing color for each line.
[0012]
The optical fiber array 26 is composed of a number of optical fibers, and one end 26a is bundled and opposed to the diffusion tube 24 via an RGB filter 25. The other ends 26b are arranged in the main scanning direction indicated by the arrow X, and emit light in a line. The slit end surfaces 27a, 27a of the slit plate 27 are mirror-finished, and guide the light emitted from the optical fiber array 26 to the optical shutter module 30 efficiently. Further, a heater (not shown) for maintaining the PLZT shutter chip at a constant temperature is provided on the slit plate 27, and the temperature is determined based on a detection result of a temperature detecting element (not shown) provided on the module 30. Control is performed.
[0013]
The optical shutter module 30 is made of PLZT on a slit-shaped opening of a ceramic substrate or on a glass substrate.An array is constructed by providing a plurality of optical shutter chips., And a driver IC is provided side by side.Each optical shutter element formed on each optical shutter chipOnly those corresponding to predetermined pixels are driven by the driver IC. A polarizer 33 and an analyzer 34 are provided before and after the module 30. As is well known, PLZT is a translucent ceramic having an electro-optic effect having a large Kerr constant, and light linearly polarized by the polarizer 33 is:Each optical shutter elementThe rotation of the polarization plane is caused by the on / off of the electric field generated by the application of the voltage to the light source, and the light emitted from the analyzer 34 is turned on / off.
[0014]
The light emitted from the analyzer 34 passes through the imaging lens array 35 and the dust-proof glass 36 to form an image on photographic paper, thereby forming a latent image. The printing paper is transported at a constant speed in a direction (sub-scanning direction) orthogonal to the main scanning direction X.
[0015]
In the optical writing head 20, each of the optical shutters is provided due to the configuration of the driver IC and the substrate circuit of the optical shutter module 30.elementThe same drive voltage is applied to the same drive voltage or a plurality of IC units or each IC unit (one IC has a plurality of drive pads). When driving the optical shutter module 30 with such a configuration, as is apparent from the following equation, the optical shutterelementIs dependent on the optical path length if the incident light wavelength and electric field strength are constant.
[0016]
I_o/ I_i= Sin²｛-(Πn³RLE²) / 2λ｝
I_i: Incident light amount
I_o: Light output
n: refractive index
R: Kerr constant
L: Optical path length
E: electric field strength
λ: light wavelength
[0017]
That is, due to the processing error when processing PLZT into chips,elementCauses an optical path length error,elementEvery time, a voltage (half-wavelength voltage) at which the amount of emitted light becomes maximum varies. Changed drive pulse application time (pulse width) under constant voltageShutter element in caseFIG. 2 shows the light output waveform of the first embodiment.Note that changing the application time of the drive pulse corresponds to changing the gradation in pulse width modulation. In FIG. 2, (A), (B), and (C) show respective optical output waveforms in different optical shutter elements. In particular,(A) shows that the drive voltage Vd isIn that elementIf the voltage is lower than the half-wave voltage, (B)The driving voltage Vd is equal to the half-wavelength voltage of the device.If equal, (C) isThe driving voltage Vd is higher than the half-wavelength voltage of the device.If highShow. Figure 3, Each element in FIG.This is a graph of gradation characteristics.Specifically, (A), (B), and (C) in FIG. 3 correspond to the elements used in (A), (B), and (C) in FIG. 2, respectively.
[0018]
As is clear from FIG.element, The optimum drive voltage Vd is different, resulting in a difference in the gradation characteristic curve. According to the experiment, the gradation characteristic is concave when “Vd <half-wavelength voltage”, substantially linear when “Vd = half-wavelength voltage”, and convex when “Vd> half-wavelength voltage”. Conventionally, correction data is obtained by measuring the amount of emitted light at one gradation. For example, when measurement is performed only at one point of the 128th gradation, an approximate expression indicated by a two-dot chain line in FIG. 3 is obtained as correction data. However, in this approximation formula, the band other than the measured gradation greatly deviates from the approximation formula, so that the optimal light amount correction cannot be performed and the image becomes uneven.
[0019]
Therefore, in the present embodiment, as shown in FIGS.elementMeasure the light intensity of each light shutterelementEach time, the measured value was approximated by a plurality of straight lines or at least a quadratic or higher-order curve to obtain a gradation characteristic (correction data) with an extremely small error. FIG. 4 shows an example in which measurement is performed at three points (each gradation of 0, 48, and 240) and approximated by linear division. FIG. 5 shows an example in which measurement is performed at four points (each gradation of 0, 48, 160, and 240) and approximated by linear division. FIG. 6 shows an example of measurement at five points (each gradation of 0, 48, 128, 192, and 240) and approximation by linear division. FIG. 7 shows an example in which measurement is performed at four points (each gradation of 0, 48, 128, and 240) and approximated by linear division. FIG. 8 shows the measurement at three points (each gradation of 0, 128 and 240).SecondaryAn example of approximation with a curve is shown. FIG. 9 shows an example of measurement at four points (each gradation of 0, 48, 160, and 240) and approximation by a cubic curve. FIG. 10 shows an example of measurement at five points (each gradation of 0, 48, 128, 192, and 240) and approximation by a cubic curve. FIG. 11 shows an example of measurement at four points (each gradation of 0, 48, 128, and 240) and approximation by a cubic curve.
[0020]
In each of FIGS. 4 to 11, a curve connecting plots for each gradation is an actual gradation characteristic, and a curve connecting based on each measurement value with a circle is an approximate curve (correction data). 4 to 11, the approximate curves are very close to the actual gradation characteristics. The measured gradation number is a number corresponding to the approximate expression to be calculated. For example, a quadratic expression has three or more points, and a tertiary expression has four or more points. Furthermore, when calculating the approximate expression, the gradationelementIs preferably near the inflection point of the actual gradation characteristic (curve) of FIG. In particular, when the gradation range is 0 to 255, an approximate curve with a small error can be obtained by measuring at four points of 0, 48, 160, and 240. In addition, each optical shutterelementOf these, attention is paid to a chip whose half-wave voltage is average, and the voltage at which the maximum light amount is obtained at the time of the middle gradation (duty is 50%) of the used gradation range is set as the driving voltage. With this, it shows a gradation characteristic relatively close to a straight line.elementIncreases and allelement, The correction error is the smallest. If the approximation by the cubic equation is obtained by the least square method, the error becomes small.
[0021]
(Light quantity measuring device and measuring method)
FIG. 12 shows each optical shutter of the optical writing head 20.element1 shows a measuring device 70 for measuring the light quantity of the light.
[0022]
This measuring device 70 has a measuring unit 71 having a photoelectric conversion sensor 72 and a tool microscope 77 slidably mounted on a guide rod 76. The guide rod 76 is installed in parallel with the main scanning direction (the direction of the arrow X) by the optical shutter module 30.elementReciprocate at a constant speed in the direction of the arrow X while being located directly above the More specifically, as shown in FIG. 21, one guide rod 76a has an external thread formed on the outer peripheral surface thereof, and a nut (not shown) provided on the measuring unit 71 is screwed to the external thread. Therefore, the measurement unit 71 reciprocates with the forward / reverse rotation of the guide rod 76a.
[0023]
A slit plate 73 and a light diffusion plate 74 are provided on the incident side of the sensor 72. The slit plate 73 has a slit 73a having a width of 25 to 400% (preferably 50 to 200%) of the width of one pixel, and is located on the focus plane F of the imaging lens array 35. . The sensor 72 whose spectral sensitivity characteristic is substantially equal to or broader than the spectral sensitivity characteristic of the recording medium is used.
[0024]
The tool microscope 77 is provided integrally with the CCD camera 78. The optical shutterelementIs photographed by a CCD camera 78 via a tool microscope 77 and displayed on a monitor television 79. The operator measures the position of the optical writing head 20 with an optical shutter while watching the image on the monitor television 79.elementFine adjustment (focus and position adjustment) at both ends of. That is, the optical writing head 20 is attached to the sensor 72 by a mounting table (not shown) so that the height, inclination, distance to the sensor 72, and the like can be adjusted.
[0025]
The light quantity measuring device 70 and the optical writing head 20 having the above configuration are controlled by a sequencer, and the reciprocating motion of the measuring unit 71 and the timing of the light quantity measurement are controlled. The optical writing head 20 is driven in a drive mode (drive frequency, lighting duty, blinking data) programmed in advance. The measuring device 70 controls each optical shutter in synchronization with this drive.elementIt is configured to obtain the integral value of the light amount of Usually, the relationship between the driving frequency and the driving speed of the sensor 72 is 1elementIt is set so that sampling and holding are performed several times per time. The output of the sensor 72 is A / D converted, transferred to the control unit, and performs necessary processing.
[0026]
The drive mode of the optical writing head 20 is set according to the drive conditions of the actual machine. The optical writing head 20 has a printing density of 400 dpi (dots per inch),Printer running at 1 kHz, ie, system speed is 63.5 mm / sThe case of mounting on a printer is described as an example.
[0027]
First, the optical shutterelementIs turned on repeatedly, and the sensor 72 iselementFrom the initial position outside the scanning area. Then, one line section (1msec) Is integrated, the integrated value is sampled / held, A / D converted, and taken into the control unit. When the sensor 72 is moved at a speed of 1 mm / s, at 400 dpi (63.5 μm), 1elementSampling / holding is performed for 63.5 times (per pixel). After moving the sensor 72 slightly longer than the main scanning length, the control unit stops capturing data and moves the sensor 72 to the initial position. Next, the even-numbered optical shutterelementWhile the light is turned on, the light amount is measured in the same manner as described above, and data is taken in. With this, all the optical shutterselementIs completed. Of course, even-numbered optical shutterselementMay be performed when the sensor 72 is moved backward, which is more efficient.
[0028]
As an effective measuring method considering the light quantity correction, as described above, each optical shutterelementIs to obtain measurements at four different amounts of light. The lighting duty is set to high, medium, and low, and the optical writing head 20 is operated in a drive mode in which the light is turned off (off). In this case, 1elementThe sampling / hold per hit is about 16 times, and a measurement value at four light levels can be obtained by one scan. Of course, the measurement may be performed by dividing the four levels of light amount into two to four scans. It is not necessary to be limited to the four-step light quantity measurement.
[0029]
1elementThe number of samplings / holds per hit can be increased by lowering the moving speed of the sensor 72 or increasing the driving frequency. Although there is no change in the amount of light due to the drive frequency, it is within a practically acceptable level. Further, if the correlation between the drive frequency and the change in the amount of light is clearly grasped in advance, it is possible to cope by introducing a correction coefficient.
[0030]
In addition, when the optical writing head 20 is compatible with color printing, it is necessary to perform measurement separately for each light source color (R, G, B). Therefore, the above-described measurement process is executed three times in total for each color while switching the RGB filters 25. The control unit uses the optical shutter based on the peak value of the measurement dataelement(Address) and the maximum and minimum values are calculated. From these values, each optical shutterelementAs described above, the amount of light is calculated, the measured light amount at four points is approximated by a cubic curve, and the correction coefficient of each light amount (for example, 0 to 255 steps of multiple gradations) is determined.
[0031]
Next, the principle of light quantity measurement will be described with reference to FIGS.
First, the optical shutterelementThe drive signal A is applied to the odd-numbered. The driving signal A has a frequency and a duty that are the same or close to the driving conditions in the actual machine. Each optical shutterelement, An optical output B is emitted, and the same waveform is output from the sensor 72 moving forward in the main scanning direction X. This output is integrated, sampled / held at the end of the ON period, and A / D converted.
[0032]
In light intensity measurement,elementA slit 73a having substantially the same size as the widthelementSince scanning is performed at a speed at which lighting is performed a plurality of times, the A / D converted output is as shown in FIG. Sensor 72 is an optical shutterelementThe maximum light amount is obtained at the position facing 31 andelementThe light quantity becomes the minimum between 31. Therefore, by detecting the peak of this output light quantity,elementThe location can be identified (addressed).elementThe minimum light amount between 31 varies depending on the MTF of the imaging lens, the slit width, and the like. The minimum light amount position can be identified by performing peak detection in the same manner as the maximum light amount, but it is also possible to use a value at a half point between the maximum light amounts.
[0033]
Next, the optical shutterelement, The drive signal A is applied to the even number, and the light amount is measured in the same manner as described above while moving the sensor 72 backward. By overlaying the measurement results with the odd-numbered measurement results,elementThe output light amount characteristics of the reference numeral 31 are found.
[0034]
In the above light quantity measurement,elementSince the position is calculated from the output light amount, detection of the initial position of the encoder and the sensor 72 is not required. In the present embodiment, the on-time light amount and the off-time light amount are measured simultaneously, and the drive signal is configured to measure the on-period and the off-period alternately.
[0035]
The off-time light quantity (leakage light quantity) also integrates the sensor output during the off-period, and performs A / D conversion by sampling / holding at the end of the off-period, similarly to the on-light quantity.elementThe position can be identified by any peak detection as in the case of the on-state. However, since the output signal is weak, the light amount at the same time as the on-time peak is used as the off-time light amount. Regarding the determination of the minimum light amount at the time of ON, it is preferable to experimentally correct by the following equation.
[0036]
specificelementLight intensity = specificelementMaximum light amount + (wraparound light amount-leakage light amount) x correction coefficient
[0037]
The correction coefficient depends on the lighting pattern and the width of the slit 73a, and is 0.2 to 1.0. In the case of a line / dot screen, a specific lightelementIt is sufficient to perform the correction using only the peak value of .times .. In the case of reproducing one dot (specific line / dot image), the specific lightelementIt is more preferable to correct only the peak value of.
The measurement method has been described with an example in which the light is turned on every odd-numbered and even-numbered numbers. However, various lighting patterns can be considered.
[0038]
Here, the light quantity integration circuit 80 is shown in FIG. 15, and its timing chart is shown in FIG.
The light quantity integration circuit 80 is for measuring the light quantity in four stages, that is, three types of duty, high, medium and low, and off, and is composed of four systems (only two systems are shown in FIG. 15). I have. The optical voltage signal from the sensor 72 is input to each integrator 82 via the polarity inverting amplifier 81, and is further A / D converted via the sample-hold amplifier 84. The optical voltage signal is integrated by the integrator 82 while the analog switches 83 are turned on by the signals AS-1 to AS-4, and is held by the sample and hold amplifier 84 at the falling timing of the signals SH-1 to SH-4. It is converted to a digital signal by a / D converter.
[0039]
According to the integration circuit 80, it is possible to measure quaternary light amounts in one scan. By calculating the approximate expression of the gradation characteristics as described above based on these measured values and creating the light amount correction table, it is possible to perform excellent light amount correction for gradation reproduction.
[0040]
(Configuration and operation of driver IC)
Next, a driver IC for driving the optical writing head 20 when measuring the light amount by the light amount measuring device 70 will be described.
Optical shutterelementThe thinning-out lighting executed at the time of measuring the amount of light can be realized by transferring necessary data from the CPU and driving the optical writing head 20, but its function can be added to the driver IC.
[0041]
FIG. 17 shows a configuration when a driver IC for reproducing a binary image is used. The driver IC 60 uses n ICs connected by a ladder chain. Each IC is configured to drive 64 dots, and includes a shift register 61, a latch circuit 62, a gate circuit 63, and a level shift circuit. 64, and a driver circuit 65.
[0042]
The image data DATA (A) and (B) are transferred to the shift register 61 in synchronization with the shift clock signal S-CLK based on the shift signal R / L, and are latched by the latch circuit 62 with the strobe signal STB. When the gate signal GATE is input to the gate circuit 63, the signal D₁~ D₆₄Is transferred to the driver circuit 65 via the level shift circuit 64. The drive voltage Vd is applied to the driver circuit 65, and the signal D from the level shift circuit 64 is applied.₁~ D₆₄Output HV based on₁~ HV₆₄Is an optical shutterelementIs applied.
[0043]
In the driver IC 60, when the light quantity measurement mode is commanded, the data signal DATA is transferred to the shift register 61 in synchronization with the shift clock signal S-CLK, and is latched by the latch circuit 62 with the strobe signal STB. When the gate signal GATE is driven at a predetermined duty, the optical shutter is driven at a predetermined light amount.elementCan be operated. The thinning-out lighting can be realized by operating the data signal DATA and a signal obtained by dividing the frequency of the shift clock signal S-CLK under an AND condition. If the frequency is divided by 1/2, it becomes 1 on / 1 off. The signal for thinning-out lighting is a repetitive signal. If a gate signal GATE having a plurality of duties is prepared, the light quantity measurement mode can be executed without a printer controller. Optical shutterelementIs divided into an odd-numbered column and an even-numbered column.elementAfter transferring more than a number of DATAs to the shift register 61, latching them with the strobe signal STB, and performing the above-described control, 1 ON / 1 OFF can be realized more easily. In addition, a function of forcibly turning on the gate circuit 63 by providing a TEST input terminal in the gate circuit 63 and transferring a predetermined duty signal to this terminal can easily execute the light quantity measurement mode.
[0044]
More specifically, as shown in FIGS. 18 and 19, the basic clock signal CLK oscillated from the oscillator 66 is converted to an appropriate frequency by the frequency divider 67, and becomes a shift clock signal S-CLK and a counter count signal. The line cycle counter 68 counts the line cycle and generates a strobe signal STB. That is, the one-shot multivibrator is operated by counting up to generate the strobe signal STB, and at the same time, the counter 68 is reset, so that the strobe signal STB is output at a constant cycle. The duty can be changed by making the specified value of the counter 68 selectable. The shift amount counter 69 determines the number of data to be transferred to the shift register 61. In order to generate an output during counting, the shift amount counter 69 is operated under the AND condition with the clock signal CLK to generate the shift clock signal S-CLK.
[0045]
As the data signal DATA, various patterns can be generated from the clock signal CLK. If the data signal DATA is used by dividing the frequency by １ ／, a signal for thinning 1ON / 1OFF can be generated. Other patterns can be generated by a simple logic circuit. Optical shutterelementIs divided into odd columns and even columns, the shift amount counter 69 is not required, and the circuit is further simplified. That is, the shift clock signal S-CLK may be continuously output by setting the data signal DATA to “H” at all times.
[0046]
(Color printer)
FIG. 20 shows a schematic configuration of a color printer for photographic printing. This color printer comprises a photographic paper storage unit 1, an image forming unit 2, and a processing unit 3. The printing paper 4 is accommodated in the accommodation unit 1 in a roll shape. The image forming unit 2 is equipped with the optical writing head 20 shown in FIG. 1 and the measuring unit 71 shown in FIG. 12 (however, the tool microscope 77 and the CCD camera 78 are omitted). Further, the image forming section 2 is provided with a pair of transport rollers 5, 6 and 7 for the photographic paper 4, a cutter 8 and transport guide plates 11 and 12.
[0047]
The photographic paper 4 is introduced into the image forming unit 2 from the pair of transport rollers 5 with the photosensitive surface facing downward, and when the photographic paper 4 is fed by a predetermined length, the rotation of the pair of rollers 5 is stopped and the cutter 8 is operated. It is cut. The cut photographic paper 4 is conveyed by a pair of rollers 6 and 7 at a constant speed. When the photographic paper 4 passes over the optical writing head 20, it is exposed through an opening formed in the guide plate 11 to form an image (latent image). The photographic paper 4 after the exposure is developed and dried in the processing unit 3 and discharged onto the tray 15.
[0048]
The photographic paper 4 is conveyed to the exposure section so that the start of writing by the optical writing head 20 and the start position of image writing on the photographic paper 4 are synchronized, and is conveyed continuously at a predetermined speed during the writing period. However, the transport in the exposure unit may be intermittently performed at a pitch corresponding to the density in the sub-scanning direction, instead of being continuous.
[0049]
If the cutting of the photographic paper 4 is performed during the exposure, it is likely to cause a synchronization shift. In order to eliminate such a problem, a configuration is adopted in which the photographic paper 4 is cut by bending it by an appropriate amount before exposure, or the exposure is started after the transport path is slightly elongated but cut in a straight state. Is preferred. When the photographic paper is in the form of a roll, it is necessary to turn off the light source lamp 21 or to shield the optical writing head 20 from light by a mechanical shutter so as not to be exposed at the time of cutting.
[0050]
As shown in FIG. 21, the measuring unit 71 is installed at a position facing the optical writing head 20 so as to be able to reciprocate in the main scanning direction X with forward and reverse rotation of the driving guide bar 76a. Prior to exposure of the photographic paper 4, the measuring unit 71 controls each optical shutter of the optical writing head 20.elementIs measured as described above. The measurement unit 71 is retracted outside the transport path of the photographic paper 4 so as not to interfere with the photographic paper 4 being conveyed except during the light amount measurement (see a two-dot chain line in FIG. 21).
[0051]
The guide plate 11 is set so that the guide surface 11 'coincides with the focus surface F of the optical writing head 20 (see FIG. 22A), so that the focus shift does not occur even if the thickness of the printing paper is different. Further, the conveying roller pairs 6 and 7 are controlled at a constant speed by a pulse motor (not shown) so as to make the sub-scanning speed constant. The upper guide plate 12 is for preventing the photographic paper from rising, and is configured to be pressed against the photographic paper by its own weight or by a spring or the like.
Although the slit plate 73 provided in the measurement unit 71 is set to the same plane as the focus plane F, as described above, the slit plate 73 is retracted from the photographic paper transport path except when measuring the light amount.
[0052]
At the time of measuring the amount of light, the light emitted from the optical writing head 20 enters the sensor 72 through the openings of the guide plates 11 and 12. The guide plate 11 does not need to be provided with an opening if the whole or the light passage portion is formed of a light-transmitting material such as glass or acrylic. Eliminating the opening improves the photographic paper guide function. The upper guide plate 12 may be configured to be retracted from the guide position when measuring the amount of light without providing an opening.
[0053]
On the other hand, as shown in FIG. 22B, a lens 75 may be interposed between the imaging lens array 35 and the slit plate 73. By arranging the lens 75, the measurement unit 71 can be separated from the focus plane F, and it is not necessary to evacuate the measurement unit 71 during exposure, which contributes to downsizing of the apparatus. In this case, the upper guide plate 12 can be formed of a translucent material.
[0054]
In this color printer, the RGB filter 25 of the optical writing head 20 is rotated to switch the light source color at high speed, and the R, B, and G images are switched for each line by a PLZT optical shutter.elementTurn on / off to write. The printer is usually powered on by a timer, and controls the temperature of the developer. During this warm-up period, the optical shutterelementIs measured and its correction (calibration) is performed. As described above, the calibration is a step of driving the optical writing head 20 under substantially the same conditions as the exposure, and performing light amount correction based on the output light amount, and obtains a good gradation image without unevenness.
[0055]
For full-color machines, first, the odd numberselementOnly the light source is driven at a specified frequency (determined by the pixel density in the sub-scanning direction) and light amount (duty or intensity), and the light source color is switched in synchronization with the driving. At the same time, the measurement unit 71 is moved forward to measure the RGB light amounts and the light amounts at a plurality of gradations. Even when returningelementThe RGB light amount and the light amounts at a plurality of gradations are measured.
[0056]
In order to properly perform light quantity correction, measurement in four steps including the off light quantity (leakage light quantity) is effective, and the light source color switching speed is reduced to one-fourth (１ ／) the number of measurement steps in actual use. The measurement is performed at four light levels per color. That is, 1elementThe amount of light per twelve points (RGB × 4) is measured in one scan. After sampling / holding the integrated value of the light voltage output of the sensor 72 and performing A / D conversion, the control unit calculates an approximate curve of the output light amount characteristic from the four light amount values and performs light amount correction. Light shutter is the light shutter with the smallest measured light quantityelementIs performed on the basis of The light amount correction data is stored in a look-up table memory element (for example, a flash ROM).
[0057]
Note that the light source color switching speed may be substantially the same as in actual use. In this case, the drive frequency is increased and a plurality of light quantity measurements are performed for each color. If the driving frequency is the same as that in actual use, a plurality of light amounts may be measured by a plurality of scans.
[0058]
FIG. 23 shows the configuration of the control unit. The output of the light quantity detection sensor 72 is amplified by an amplifier 91, integrated by an integration circuit 80 (see FIG. 15), input to a CPU 94 via a 4-channel multiplexer 92 and an A / D converter 93, and generates correction data. .
[0059]
On the other hand, image data read by the film scanner 95 is developed on a bit map memory of the image memory 96. The information on the bitmap memory is transferred to the driver IC 40 of the optical shutter module 30 in a state where the input image data is corrected by referring to the look-up table 97 storing the light amount correction data by the CPU 94, and Reproduced at the same density as the original image with the light source color switched at the speed.
[0060]
Next, a control procedure of the light quantity measurement will be described with reference to FIG.
The control routine of the light quantity measurement is executed when the power of the printer is turned on. First, in step S1, the RGB filter 25 is switched to a predetermined color, and in step S2, all the optical shutters are set at a duty of 50%.elementDrive at the same time. Then, in step S3, a plurality of optical shutterselementAre collectively searched for a drive voltage that provides the maximum light amount, and the drive voltage is set. Next, in step S4, four gradations (each gradation of 0, 48, 160, and 240) are repeated to form an optical shutter.elementIs driven, and at the same time, the light amount detection sensor 72 is scanned in step S5 to measure the light amount. Further, in step S6, the optical shutter iselementThe tone data (correction data) is calculated for each and the correction data is stored in the lookup table 97 in step S7. Next, in step S8, it is determined whether or not the measurement of the three colors has been completed. If the measurement has not been completed, the process returns to step S1.
[0061]
By the way, in this embodiment, all the scans in one reciprocation are performed.elementHas been completed. However, it is also possible to separately measure each gradation or each light source color. In this case, although the number of scans increases, this is slightly disadvantageous in terms of time, but has advantages such as simplification of the light amount integration circuit.
[0062]
Light shutter for light intensity measurementelementOutput characteristics. If the linearity is good, practical use is possible even with two-point measurement. Furthermore, if the amount of leaked light is zero, one-point measurement is possible. However, usually the light shutterelementOutput characteristics do not match the ideal linearity,elementIs also possible. As for the light source color, if the output characteristics for each color are the same, correction can be performed by measuring one color. In addition, even if there is a slight difference in characteristics, the correction may be performed by measuring one color of green or white as long as it can be tolerated on the image.
[0063]
Also, PLZTConsists ofOptical shutterelementChanges the spectral transmission characteristics due to the driving voltage. Therefore, it is preferable to set the same drive voltage waveform at the time of light quantity measurement and at the time of actual shooting. One of the means is to measure the amount of light by driving the other colors (red and green) with the same voltage while using the optimum voltage at the time of blue exposure as a driving voltage. Another means is to measure the amount of light by driving with the optimum voltage of each light source color. In the present embodiment, it is necessary to change the drive voltage at a high speed, and the waveform of the drive voltage may be distorted. Therefore, the measurement and the actual photographing are performed using the (same) power supply having the same characteristics. Is preferred.
[0064]
According to the light quantity measuring method described above, as described with reference to FIG.elementIn order to determine the address from the peak value of the output light amount without requiring a special device for determining the address of the device, by counting the number of samplings between the peaks, when used as an inspection device, It is possible to detect abnormalities (pitch errors, poor alignment, etc.) of the optical writing head 20. In addition, when the measurement unit 71 is mounted on an actual device, a movement failure of the measurement unit 71 can be detected. In this case, the operation of the printer is stopped by displaying / warning the abnormality. Furthermore, an optical shutterelementLight amount correction corresponding to the deterioration with time can be performed.
[0065]
Note that the measurement and correction of the light amount can be executed at any time other than when the printer is warmed up.
[0066]
(Configuration and operation of driver IC)
Next, a configuration and a timing chart of the multi-value reproducing driver IC 40 are shown in FIGS. The driver IC 40 uses n ICs consecutively in a ladder chain. Each IC is configured to drive 64 dots, a 6-bit shift register 41, a 6-bit latch circuit 42, and a 6-bit latch circuit 42. , A 6-bit counter 44, a gate circuit 45, and a driver circuit 46.
[0067]
The image data DATA (A) and (B) are transferred to the shift register 41 in synchronization with the shift clock signal S-CLK based on the shift signal R / L, and are latched by the latch circuit 42 with the strobe signal STB. Thereby, the number of gradations of each pixel is set. The clock signal C-CLK is counted by the counter 44, the comparator 43 compares the latched value with the counter value, and the gate circuit 45 stops outputting when the two match. The counter 44 is cleared by the clear signal CL.
[0068]
The drive voltage Vd is applied to the driver circuit 46, and the signal D from the gate circuit 45 is applied.₁~ D₆₄Output HV based on₁~ HV₆₄Is an optical shutterelementWill be applied. That is, each pixel has an optical shutter for a time (pulse width) corresponding to the image data DATA.elementWill be turned on.
[0069]
Even when the light quantity measurement mode is executed by the multi-value reproducing driver IC 40 having the above configuration, basically the same control as that of the above-described binary reproducing driver IC 60 is performed. The predetermined light amount is designated by a data signal DATA (dip switch or the like), transferred to the shift register 41, latched by the strobe signal STB, a duty corresponding to the data signal DATA is generated by the comparator 43 or the like, and is determined by the gate signal GATE. Light shutterelementIs operated at a predetermined light amount. Such a signal for thinning-out lighting is a repetitive signal and can be realized by a relatively simple circuit.
[0070]
Also, optical shutterelementIs divided into an odd-numbered column and an even-numbered column, the thinning-out lighting can be easily realized by setting the DATA of one column to "H", and the control is further simplified. In order to change the light amount, the setting of a dip switch or the like may be changed.
[0071]
(Other embodiments)
According to the present invention,Gradation characteristicsThe measuring method is not limited to the above embodiment, and can be variously changed within the scope of the gist.
In particular,In the second invention,As a solid-scanning element used for optical writing, besides PLZT, an LED (Light Emitting Diode), an LCS (Liquid Crystal Shutter), a DMD (Deformable Mirror Device), an FLD (Fluorescent Device), or the like can be used.
[0072]
Further, the present invention is applicable not only to an image writing apparatus for printing paper using a silver halide photosensitive material, but also to an image writing apparatus for a silver halide film or an electrophotographic photosensitive member or an image projection apparatus on a display. It is possible.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an optical writing head used in a gradation characteristic measuring method according to the present invention.
FIG. 2 is an optical shutter corresponding to a drive pulse width.elementFIG. 3 is a chart showing an optical output waveform of FIG.
FIG. 3Optical shutter element5 is a graph showing the gradation characteristics of FIG.
FIG. 4 is a graph showing an approximate curve obtained by a gradation characteristic measuring method according to the present invention and an actual gradation characteristic curve, an example of three-point measurement, and straight line division.
FIG. 5 is a graph showing an approximate curve obtained by the gradation characteristic measuring method according to the present invention and an actual gradation characteristic curve, an example of four-point measurement, and straight line division.
FIG. 6 is a graph showing an approximate curve obtained by the gradation characteristic measuring method according to the present invention and an actual gradation characteristic curve, and is an example of five-point measurement and linear division.
FIG. 7 is a graph showing an approximate curve obtained by the gradation characteristic measuring method according to the present invention and an actual gradation characteristic curve, and is an example of four-point measurement and linear division.
FIG. 8 is a graph showing an approximate curve obtained by the gradation characteristic measuring method according to the present invention and an actual gradation characteristic curve, three-point measurement,2This is an example of a next approximation curve.
FIG. 9 is a graph showing an approximate curve obtained by the tone characteristic measuring method according to the present invention and an actual tone characteristic curve, a four-point measurement, and a cubic approximate curve.
FIG. 10 is a graph showing an approximate curve obtained by the tone characteristic measuring method according to the present invention and an actual tone characteristic curve, a five-point measurement, and an example of a tertiary approximate curve.
FIG. 11 is a graph showing an approximate curve obtained by the tone characteristic measuring method according to the present invention and an actual tone characteristic curve, a four-point measurement, and a cubic approximate curve.
FIG. 12 is a schematic configuration diagram showing a light quantity measuring device.
FIG. 13 is a waveform chart of an analog signal at the time of light quantity measurement.
FIG. 14 is a waveform diagram of a digital signal at the time of light quantity measurement.
FIG. 15 is a block diagram of an integration circuit used for light quantity measurement.
FIG. 16 is a timing chart showing the operation of the integration circuit.
FIG. 17 is a block diagram showing a binary image reproduction driver IC.
FIG. 18 is a block diagram showing a circuit for generating a signal transferred to the binary image reproduction driver IC.
FIG. 19 is a timing chart showing the operation of the signal generation circuit.
FIG. 20 is a schematic configuration diagram illustrating a color printer including an optical writing head according to the invention.
FIG. 21 is a perspective view showing a light amount measurement unit mounted on the color printer.
FIG. 22 is an explanatory diagram showing a positional relationship between an optical writing head and a light quantity measuring unit.
FIG. 23 is a block diagram showing a control unit of the color printer.
FIG. 24 is a flowchart showing a control procedure of light quantity measurement by the control unit.
FIG. 25 is a block diagram showing a multivalued image reproduction driver IC.
FIG. 26 is a timing chart showing the operation of the multivalued image reproduction driver IC.
[Explanation of symbols]
20 Optical writing head
30 ... Optical shutter module
31 ... Optical shutterelement
40, 60 ... Driver IC
70: Light intensity measuring device
71… Measuring unit
72 Photoelectric conversion sensor

Claims (4)

A solid-scanning optical writing device that controls ON / OFF in multiple gradations by changing a drive pulse width under constant voltage on a large number of optical elements arranged in the main scanning direction composed of PLZT based on image data. In the gradation characteristic measuring method,
The output light quantity of each of the optical elements at at least three different gradations is measured using the same sensor,
Calculating the gradation characteristics of each optical element from the measured values as a plurality of straight lines or an approximate expression of at least second order ,
A gradation characteristic measuring method characterized in that: 2. The gradation characteristic measuring method according to claim 1, wherein the number of gradations for measuring the output light amount is a number corresponding to an approximate expression to be calculated. 3. The gradation characteristic measuring method according to claim 2, wherein the gradation for measuring the output light amount is near the inflection point of the actual gradation characteristic of the optical element. In a gradation characteristic measuring method of a solid-state scanning type optical writing device for controlling a large number of optical elements arranged in the main scanning direction at multiple gradations based on image data,
The output light amount of the optical element at at least three different gradations is measured using a sensor,
Calculate the gradation characteristics of each optical element as an approximate expression from the measured values,
Before measuring the light quantity for calculating the gradation characteristics, each optical element is driven at a duty of about 50% to determine a driving voltage at which the maximum light quantity is obtained. Turn on the element,
A gradation characteristic measuring method characterized in that:

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