JP3833781B2 - Exposure control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exposure control apparatus, and more particularly to an exposure control apparatus that controls exposure by a light emitting element such as an LED chip or an LD (laser diode).
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image recording apparatus such as a printer that exposes a photosensitive material based on image data and transfers and outputs an image recorded on the photosensitive material by this exposure to plain paper or the like emits light for exposure. A plurality of LED chips as light emitting elements are provided, and exposure by these LED chips is controlled by an exposure control device.
[0003]
In such a conventional exposure control apparatus, when the image data is a digital signal, a digital / analog converter (hereinafter referred to as a D / A converter) for converting the image data into an analog signal is equal to the number of channels ( LED chip number).
[0004]
However, the DA converter has a high cost per channel, and when the DA converter is provided for the number of channels, there is a problem that the cost of the exposure control apparatus becomes high.
[0005]
In order to solve such problems, conventionally, as shown in FIG. 14, an analog switch 34 is connected to the output end of a DA converter 32 that converts a digital signal for one channel into an analog signal._n(N is 1 to N, the same applies hereinafter), capacitor 36_nAnd buffer amplifier 38_nAre connected in parallel for the number of channels (N channels in FIG. 14), and a digital signal corresponding to each channel is divided and input to the input end of the DA converter 32 for each channel. A timing generation circuit 46 generates a sampling signal at a timing synchronized with the timing, and each analog switch 34 for each channel by the sampling signal._nThe analog signal for each channel output from the DA converter 32 is converted into a capacitor 36 by controlling on / off switching of the capacitor 36._nEach buffer amplifier 38 of the analog signal for each sampled and held channel._nOutput signals (1ch to Nch) from the channel 1 were used as analog signals for each channel.
[0006]
[Problems to be solved by the invention]
However, in the above conventional technique, in order to make the DA converter for one channel into multiple channels, the sample and hold circuits for the number of channels are connected in parallel to the output terminal of the DA converter. There is a problem in that an offset voltage different for each channel is generated in the output due to an amplifier or the like. When such a multi-channel DA converter is used as a drive circuit for emitting LED chips for the number of channels, even if it is not desired to emit LED chips, light is emitted due to the influence of the offset voltage. Become.
[0007]
The present invention has been made to solve the above problems, and an object of the present invention is to provide an exposure control apparatus that can prevent erroneous light emission of a light emitting element due to an offset voltage.
[0008]
[Means for Solving the Problems]
  In order to achieve the above object, an exposure control apparatus according to claim 1 comprises:A digital / analog converter for converting a digital signal of one channel into an analog signal; input means for dividing and inputting a digital signal of a plurality of channels into the digital / analog converter for each channel; and an output terminal of the digital / analog converter Each analog signal connected in parallel and output from the digital / analog converterGenerates a drive signal for causing the light emitting element to emit light based onpluralA drive circuit;Based on the amount of light when the light emitting element is caused to emit light by the predetermined drive signal generated by each of the plurality of drive circuits, and the predetermined drive signal,SaidpluralDriving circuitEach ofOffset detecting means for detecting the offset voltage ofPredeterminedVoltageOutput of the digital / analog converterAn adder circuit to add toThe digital signal for each channel input to the digital / analog converter is converted so that the offset voltage of each of the plurality of drive circuits detected by the offset detection unit is canceled by applying the predetermined voltage. Conversion means toIt has.
[0009]
  According to the exposure control apparatus of claim 1., DepartureGenerate a drive signal for causing the optical element to emit lightpluralDriving circuitEach ofIs detected by the offset detection means. Here, the offset voltage is a voltage that is a difference between the target voltage and the actual voltage.
[0010]
  In addition, a digital signal of a plurality of channels is divided for each channel by an input unit and input to a digital / analog converter that converts a digital signal of one channel into an analog signal. Therefore, the analog signal output from the digital / analog converter is divided for each channel.
  afterwards,A plurality of drive circuits each connected in parallel to the output terminal of the digital / analog converter generates a drive signal for causing the light emitting element to emit light based on the analog signal for each channel output from the digital / analog converter. .
In this way, the exposure control apparatus according to claim 1 supports multiple channels by generating a drive signal based on an analog signal output for each channel from one digital / analog converter and causing the light emitting elements to emit light. An exposure control apparatus using the digital / analog converter is realized.
Further, in the exposure control apparatus according to claim 1, a predetermined voltage is applied to the output of the digital / analog converter by the adding circuit, and the offset voltage of each of the plurality of drive circuits is canceled by applying the predetermined voltage. The digital signal for each channel input to the digital / analog converter is converted by the conversion means.
  Therefore,Multi-channelDriving circuitEach ofThe offset voltage is canceled.
[0011]
  Thus, according to the exposure control apparatus of the first aspect, the offset detection meanspluralDriving circuitEach ofOffset voltage is detected and based on the detected offset voltagepluralDriving circuitEach ofBecause the offset voltage ofIt can prevent the occurrence of offset voltage in the output of multiple channels.Driving circuitEach ofIt is possible to prevent erroneous light emission of the light emitting element due to the offset voltage.
[0012]
By the way, when there is no offset voltage in the drive circuit, the light emitting element emits light with a predetermined light amount corresponding to the magnitude of the drive signal by a predetermined drive signal. However, when the drive circuit has an offset voltage, the light amount is increased or decreased compared to the predetermined light amount by the amount of light corresponding to the offset voltage.
[0013]
  Take advantage of this,in frontThe offset detection meanspluralDriving circuitEach ofBased on the amount of light when the light emitting element is caused to emit light by the predetermined drive signal generated by the above and the predetermined drive signal,Each of a plurality of drive circuitsDetect offset voltage.
[0014]
In general, an exposure control apparatus is provided with a sensor (photodiode, phototransistor, etc.) for detecting the amount of light emitted from a light emitting element in order to adjust the amount of exposure. An offset detecting means can be configured.
[0015]
  Thus, the claim1According to the exposure control device described inTheSince the facet detection means can be configured using a light quantity sensor that is generally provided in the exposure control apparatus, the exposure control apparatus can be configured at low cost.
[0016]
  Claims2As in the exposure control apparatus according to claim 1,1Preferably, the predetermined drive signal in the exposure control apparatus described in (1) is a drive signal that does not cause the light emitting element to emit light when it is assumed that an offset voltage of the drive circuit does not occur.
[0017]
  Thus, the claim1Assuming that the offset voltage of the drive circuit is not generated for the predetermined drive signal in the exposure control apparatus described in 1., the light quantity of the light emitting element at this time is directly proportional to the offset voltage. Therefore, the offset voltage can be detected more easily than in the case where the predetermined drive signal is not used in this way.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In the present embodiment, a case will be described in which the exposure control apparatus of the present invention is applied to an image recording apparatus that records an image on a photosensitive material by controlling light emission of an LED chip based on image data.
[0019]
[First Embodiment]
(Overall configuration "Appearance")
1 to 3 show an image recording apparatus 100 according to the first embodiment.
[0020]
The image recording apparatus 100 reads image data recorded on a CD-ROM 102 or an FD (floppy disk) 104 (see FIG. 3), exposes an image based on the image data onto the photosensitive material 106, and the photosensitive material 106. Is an apparatus for transferring and outputting the image recorded on the plain paper (image receiving paper 108).
[0021]
The upper part of the front surface (left side in FIG. 3) of the box-shaped casing 110 is an inclined surface, and an operation display unit 112 is provided.
[0022]
As shown in FIG. 2, the operation display unit 112 is classified into a monitor unit 114 located on the right side and an input unit 116 located on the left side. The monitor unit 114 is configured to project the read image.
[0023]
The input unit 116 includes a plurality of operation keys 118 and an input data confirmation display unit 120. Data necessary for image recording, such as the number of recordings, size setting, color balance adjustment, and negative / positive selection. Can be entered.
[0024]
A deck unit 122 is disposed below the operation display unit 112. The deck unit 122 includes a CD-ROM deck unit 124 positioned on the right side of FIG. 2 and an FD deck unit 126 positioned on the left side.
[0025]
The CD-ROM deck unit 124 can open and close the tray 130 by pressing an open / close button 128. By placing the CD-ROM 102 on the tray 130, the CD-ROM 102 can be loaded into the apparatus.
[0026]
On the other hand, the FD deck unit 126 is provided with an FD insertion throttle 132, and by inserting the FD 104, the drive system inside the apparatus operates to draw in the FD 104. Note that when the FD 104 is taken out, the FD 104 can be pulled out by pressing the operation button 134.
[0027]
The CD-ROM deck unit 124 and the FD deck unit 126 are provided with access lamps 136 and 138, respectively, and these access lamps 136 and 138 are lit while being accessed in the apparatus.
[0028]
A discharge tray 140 is disposed further below the deck portion 122. The discharge tray 140 is normally accommodated in the apparatus, and can be pulled out by placing a finger on the grip portion 142 (see FIG. 1).
[0029]
On the discharge tray 140, the image receiving paper 108 on which the image is recorded is discharged.
[0030]
The image receiving paper 108 is previously stored in a layer on the tray 144, and the tray 144 is loaded into a tray loading port 146 provided on the upper surface of the casing 110. The image receiving paper 108 is taken out one by one from the tray 144 loaded in the tray loading port 146, transferred to the image, and then guided to the discharge tray 140.
[0031]
Two circular cover members 148 and 150 are attached to the right side surface of the casing 110 (the front side in FIG. 1). The cover members 148 and 150 can be individually attached and detached. As shown in FIG. 3, the roll photosensitive material 106 is wound around the inside of the apparatus along the axial direction of the cover members 148 and 150. A reel 152 and a take-up reel 154 are provided, and these reels can be taken out or loaded with the cover members 148 and 150 removed.
[0032]
(Image receiving paper transport system)
As shown in FIG. 3, the tray 144 loaded in the tray loading port 146 is configured such that the upper surface of the front end of the tray 144 faces the meniscal roller 156.
[0033]
The half-moon roller 156 has a part of the circumferential surface cut away in a plane parallel to the axis. Normally, the cutout 158 is opposed to the uppermost image receiving paper 108 in the tray 144 at a predetermined interval. ing. Here, when the half-moon roller 156 rotates, the uppermost image-receiving paper 108 and the peripheral surface of the half-moon roller 156 come into contact with each other, and the half-moon roller 156 rotates once to slightly pull out the image-receiving paper 108. The pulled-out image receiving paper 108 is sandwiched between the first roller pair 160 and is completely pulled out from the tray 144 by the driving force of the first roller pair 160.
[0034]
A second roller pair 162, a guide plate 164, and a third roller pair 166 are sequentially arranged on the downstream side of the first roller pair 160, and the image receiving paper 108 is sandwiched between the first roller pair 160. After that, it is sandwiched between the second roller pair 162, guided by the guide plate 164, and sandwiched by the third roller pair 166.
[0035]
In the third roller pair 166, the photosensitive material 106 is also superimposed. That is, the third roller pair 166 is also used as a conveyance path for the photosensitive material 106.
[0036]
(Photosensitive material transport system)
The photosensitive material 106 is loaded into the apparatus in a long form wound in layers on a supply reel 152. The supply reel 152 can be loaded at a predetermined position by removing the cover member 150 (on the rear side of the apparatus) and inserting it in the axial direction.
[0037]
In a state where the photosensitive material 106 is loaded at a predetermined position, the outermost layer is pulled out and loaded along a predetermined conveyance path as an initial setting. In the loading procedure, the outermost layer is pulled out from the supply reel 152 and is sandwiched between the fourth roller pair 168 in the vicinity of the loading position of the supply reel 152, and the third roller pair is interposed via the reservoir 170 and the guide plate 172. After being pinched by 166, it is wound around the heat roller 174 and wound around the take-up reel 154. In this case, a leader tape having a length necessary for loading may be provided at the front end portion of the photosensitive material 106 wound around the supply reel 152.
[0038]
An exposure unit 176 is provided between the fourth roller pair 168 and the reservoir unit 170 in the conveyance path of the photosensitive material 106. A water application unit 178 is provided between the reservoir unit 170 and the guide plate 172. Although details of the exposure unit 176 and the water application unit 178 will be described later, as a process, after the image is exposed on the photosensitive material 106 by the exposure unit 176, the third is performed in a state where water is applied to the emulsion surface (exposure surface). The pair of rollers 166 is overlapped with the image receiving paper 108.
[0039]
(Heat roller)
The heat roller 174 is a heat development transfer portion of the apparatus, and includes a cylindrical roller main body 180 and a heater 182 provided along the axis inside the roller main body 180. By the operation, the surface of the roller main body 180 is heated and has a function of applying heat to the members (the photosensitive material 106 and the image receiving paper 108) wound around the roller main body 180. By this heating, heat development transfer processing is performed, and the image recorded on the photosensitive material 106 is transferred to the image receiving paper 108.
[0040]
A peeling roller 184 and a peeling claw 186 are provided in the vicinity of the lower left of the heat roller 174. The image receiving paper 108 wound about 1/3 around the heat roller 174 is peeled off from the photosensitive material 106, and the image is received in the direction of the discharge tray 140. The paper 108 is guided.
[0041]
On the other hand, the photosensitive material 106 is wound around the heat roller 174 by about ½, and is turned 180 ° to be guided to a position where the take-up reel 154 is loaded.
[0042]
(Water application part)
As shown in FIG. 3, the water application unit 178 has a function of applying water as an image forming solvent to the photosensitive material 106 or the image receiving paper 108, bringing the two overlapping surfaces into close contact, and performing heat development. The coating piece 188 is long along the width direction of the photosensitive material 106 and a tank 190 for storing water.
[0043]
The application piece 188 is a highly absorbent member such as felt or sponge and has an appropriate hardness so that the photosensitive material 106 contacts with a predetermined pressure during conveyance. An appropriate amount of water in the tank 190 is always transferred to the application piece 188 by utilizing a capillary phenomenon. When the photosensitive material 106 and the application piece 188 come into contact with each other, the application piece 188 makes a photosensitive action. In this configuration, water is applied to the surface (emulsion surface) of the material 106.
[0044]
Further, since the application piece 188 is in contact with the photosensitive material 106 with an appropriate pressure, water is applied uniformly.
[0045]
The water in the tank 190 is replenished by removing the entire water application unit 178. However, water may always be supplied from outside the apparatus by providing piping.
[0046]
In the first embodiment, water is used as the image forming solvent. However, this water is not limited to pure water, and includes water in a widely used sense. Further, it may be a mixed solvent of water and a low boiling point solvent such as methanol, DMF, acetone, diisoptyl ketone or the like. Further, it may be a solution containing an image formation accelerator, an antifoggant, a development stopper, a hydrophilic thermal solvent, and the like.
[0047]
(Exposure part)
FIG. 4 shows an exposure unit 176 according to the first embodiment.
[0048]
The exposure unit 176 is connected to the controller 202 with the light source unit 200 provided above the conveyance path of the photosensitive material 106 as a main component. Image data is stored in the controller 202 (image data read from the CD-ROM 102 or the FD 104), and the light source unit 204 for full color image formation in the light source unit 200 is turned on according to the image data. It has become. Note that the configuration of the portion for turning on the full-color image forming light source unit 204 in the controller 202 particularly related to the present invention, that is, the portion corresponding to the exposure control apparatus of the present invention and the surrounding configuration will be described later.
[0049]
The light source unit 200 can be moved in the width direction (main scanning direction) of the photosensitive material 106 by driving a main scanning unit 206, which will be described later, and the main light source unit 200 is stopped when the photosensitive material 106 is moved stepwise through the exposure unit 176. Scanning is performed.
[0050]
The light source unit 200 of the exposure unit 176 is covered with a box-type exposure casing 214, and a full-color image forming light source unit 204 is disposed on the upper end surface of the exposure casing 214. The light emitting surface is directed to the opening portion side of the exposure casing 214. On the light emitting surface side of the light source portion 204 for full color image formation, an aperture 216 provided with a rectangular aperture for each emission color is disposed, and R (red), G (green), and B (blue) are provided. The light spreading from the R-LED chip 208R, the G-LED chip 208G, and the B-LED chip 208B (11 for each color, see FIG. 5) as light emitting elements that emit light of each color is limited.
[0051]
A lens 212 is disposed at the center of the exposure casing 214 on the downstream side of the aperture 216, and has a function of condensing the light from the full-color image forming light source unit 204 and forming an image in the vicinity of the photosensitive material 106. Yes. In addition, the resolution of the imaged light is about 300 to 400 dpi. Further, although the lens 212 is shown alone in the drawing, a single lens system may be configured by combining a plurality of lenses.
[0052]
Here, the lens 212 is composed of a plurality of lenses and an aperture, and when the lens 212 has a characteristic that the magnification does not change even if the height of the image plane changes to some extent, It is possible to absorb minute errors due to scanning movement and the attachment state of the LED chip 208.
[0053]
The focus is always adjusted by an autofocus mechanism (not shown).
[0054]
The light source unit 200 is supported by a pair of parallel guide shafts 218 that constitute a part of the main scanning unit 206. The guide shaft 218 is disposed along the width direction of the photosensitive material 106 (the direction of the arrow W in FIG. 4), and the full-color image forming light source unit 204 is guided by the guide shaft 218 to be photosensitive material 106. It is possible to move in the width direction.
[0055]
A part of an endless timing belt 220 is fixed to the exposure casing 214 of the full-color image forming light source unit 204. Both ends of the timing belt 220 are wound around sprockets 222 located near both ends of the guide shaft 218, respectively. The rotating shaft of one sprocket 222 is connected to the rotating shaft of the stepping motor 226 via the transmission 224, and the full-color image forming light source unit 204 is moved along the guide shaft 218 by the reciprocating rotation of the stepping motor 226. It is reciprocated.
[0056]
The driving of the stepping motor 226 is controlled by the controller 202 and is synchronized with the step movement of the photosensitive material 106. That is, in a state where the photosensitive material 106 has moved and stopped by one step, the stepping motor 226 starts to rotate, and the full-color image forming light source unit 204 moves on the photosensitive material 106 along the width direction of the photosensitive material 106. After confirming the predetermined pulse, the full-color image forming light source unit 204 returns to the original position by rotating the stepping motor 226 in the reverse direction. The next movement of the photosensitive material 106 is started simultaneously with the returning operation of the full-color image forming light source unit 204.
[0057]
A photodiode 228 is disposed on the light output side of the light source unit 200, on the surface facing the photosensitive material 106 and in the vicinity of the main scanning start position, and is an analog whose size is proportional to the amount of light from the light source unit 204 for full color image formation. A signal is output. The photodiode 228 is connected to the light amount correction unit 230, and the analog signal is input to the light amount correction unit 230.
[0058]
The light amount correction unit 230 has a function of comparing the detected light amounts from the LED chips 208 of the respective colors, adjusting the light amount and the color balance, and outputting a correction value to the controller 202. Based on this correction value, the image data sent to the full-color image forming light source unit 204 is corrected, and each LED chip 208 is lit with an appropriate amount of light.
[0059]
As shown in FIG. 5, the full-color image forming light source unit 204 includes a B-LED chip 208 </ b> B, a G-LED chip 208 </ b> G, and an R-LED chip 208 </ b> R. Along the width direction (main scanning direction) 106, they are attached according to the same arrangement rule. That is, eleven B-LED chips 208B are arranged in two rows and zigzag at the right end in a plan view of the substrate 210, and eleven R-LED chips 208R are arranged in two rows at the left end. Arranged in a zigzag pattern, 11 G-LED chips 208G are arranged in a zigzag pattern in the middle, and a total of 6 LED chips are arranged in the center.
[0060]
The substrate 210 is provided with predetermined wiring by an etching process or the like, but is covered with metal so as not to short-circuit between the wirings, and has a heat dissipation function. For this reason, the heat_generation | fever by lighting of the LED chip 208 can be suppressed, and the fluctuation | variation of emitted light amount can be suppressed. The outer dimension (xx) of the LED chip 208 is about 360 * 360 [mu] m.
[0061]
By the way, as shown in FIG. 5, the pitch between columns (the pitch in the main scanning direction) P of the same color of the LED chips 208 to be mounted on the substrate 210 is 600 μm, and the row pitch (the pitch in the sub scanning direction) L of each column. Is preferably 520 μm, the step size D is 260 μm, and the gap size G between the colors is preferably the same between RG and GB. The hatched portion of the LED chip 208 shown in FIG. 5 is a region that actually emits light, and the boundaries of the light emitting regions between adjacent rows in the staggered LEDs of the same light emitting color are matched.
[0062]
With the full-color image forming light source unit 204 having the above-described structure, 11 main scanning lines can be recorded on the photosensitive material 106 by one main scanning for each color. Note that there is an even number 10 between the main scanning line pitches.
[0063]
Here, in the first embodiment, as shown in FIG. 6, the step movement of the photosensitive material 106 indicates that the current first main scanning line recorded on the photosensitive material 106 is the sixth and seventh previous times. It is controlled to repeat the sub-scanning driving and stopping at a pitch (5.5 line pitch) at the intermediate position of the main scanning line. In FIG. 6, the thin solid line is 11 main scanning lines formed by the previous main scanning, the chain line is 11 main scanning lines formed by the current main scanning, and the thick solid line is the next time. 11 main scanning lines formed by main scanning.
[0064]
In this way, by setting the odd number of LED chips 208, the number of main scan lines is even (that is, 10 intervals), and half the main scan lines are further formed to form main scan lines. It has increased by a factor of two. As described above, since the odd number of LED chips 208 is provided for each emission color, the spacing between the LED chips 208 is an even number, and the scanning lines are formed for each half of the main scanning lines, the same sub-scanning pitch can be set. it can. In addition, the first to fifth main scanning lines at the time of the first main scanning drive are not written for control purposes.
[0065]
Next, referring to FIG. 7, the configuration of the portion for turning on the full-color image forming light source section 204 in the controller 202 particularly related to the present invention, that is, the configuration corresponding to the exposure control apparatus of the present invention and the surrounding configuration. This will be described in detail.
[0066]
The controller 202 includes an image memory 10 that temporarily stores input image data, and an output end of the image memory 10 stores in advance a conversion table for converting the input image data according to a predetermined rule for each channel. The LUT 12 is connected to the input end of a DA converter 32 that converts a digital signal for one channel into an analog signal. It is connected.
[0067]
Note that the conversion table stored for each channel in the LUT 12 is, for example, as shown in FIG. 9A, 2-digit hexadecimal input data ('00' to 'FF') is output as 3-digit hexadecimal output data. ('000' to 'FFF'). In this conversion, as shown in FIG. 9B, the input / output characteristics of the DA converter 32 are adjusted so that the output voltage from the DA converter 32 is proportional to the input data of the DA converter 32, that is, the output data of the LUT 12. Accordingly, for example, as shown in FIG. 9A, the output data range X1 of the LUT 12 near the minimum value and the maximum value of the LUT 12 is larger than the output data range X2 of the input data near the center value. To be. In the following description, it is assumed that a table that performs the conversion shown in FIG. 9A is stored in advance as a conversion table corresponding to each channel in the LUT 12.
[0068]
The output terminal of the DA converter 32 generates a predetermined voltage and adds a plurality of (through the addition points from the offset adder circuit 14 as an adder circuit to be added to the output of the DA converter 32 (in the first embodiment, the LED chip 208). Branching to 33) corresponding to the number of analog switches 34_nEach analog switch 34 is connected to one end of a switch unit (n is 1 to N, N = 33 in the first embodiment, the same applies hereinafter)._nThe other end of the switch portion is a capacitor 36._nAnd one end of the buffer amplifier 38_nIs connected to the non-inverting input terminal. Capacitor 36_nThe other end of is grounded.
[0069]
On the other hand, the buffer amplifier 38_nThe output terminal is the buffer amplifier 38_nInverting input terminal and analog switch 40_nIs connected to one end of the switch portion of the analog switch 40_nThe other end of the switch part is a capacitor 42._nOne end, and buffer amplifier 44_nIs connected to the non-inverting input terminal. Further, the capacitor 42_nThe other end of is grounded.
[0070]
On the other hand, the buffer amplifier 44_nOutput terminal of the buffer amplifier 44_nAnd the switching transistor 46_nConnected to the base of the transistor 46, and further to the transistor 46_nAre connected to the cathodes of eleven LED chips 208R, 208G, and 208B, respectively, in the full-color image forming light source unit 204, and the anodes of the LED chips 208R, 208G, and 208B each have a resistance 48._nA predetermined voltage is applied via. The transistor 46_nThe emitter of is grounded.
[0071]
In addition, the analog switch 34_nEach switch switching input terminal is connected to the output terminal of the sampling signal 46A corresponding to each channel of the timing generation circuit 46, and the analog switch 40 is connected._nEach switch switching input terminal is connected to the same output terminal of the sampling signal 46B of the timing generation circuit 46.
[0072]
Thus, the analog switch 34_n, Capacitor 36_nAnd buffer amplifier 38_nAs a result, the first-stage sample and hold circuit is connected to the analog switch 40._n, Capacitor 42_nAnd buffer amplifier 44_nThus, each of the second-stage sample and hold circuits is configured. Accordingly, the buffer amplifier 38 provided in the sample hold circuit at each stage._n44_nEtc., the output terminal of the second stage sample and hold circuit of each channel, that is, the buffer amplifier 44_nDifferent offset voltages are generated at the output terminals. In order to set this offset voltage to 0 V (cancel), in the first embodiment, the offset addition circuit 14 adds a predetermined voltage to the output of the DA converter 32 and rewrites the conversion table for each channel of the LUT 12. However, details of this will be described later. The two-stage sample and hold circuit corresponds to the driving circuit of the present invention.
[0073]
The controller 202 includes a CPU 16 that is connected to the light amount correction unit 230 and the image memory 10 and corrects image data stored in the image memory 10 based on correction values input from the light amount correction unit 230.
[0074]
The CPU 16 is further connected to the stepping motor 226, the timing generation circuit 46, and the LUT 12. The CPU 16 controls the step movement of the full-color image forming light source unit 204 and records one pixel in the main scanning direction with respect to the timing generation circuit 46. The output of the pixel clock signal 16A (see FIG. 8) indicating one cycle when performing the above, the rewriting of the conversion table of each channel of the LUT 12, etc. are performed.
[0075]
The timing generation circuit 46 is further connected to the image memory 10 and inputs image data stored in the image memory 10 to the DA converter 32 via the LUT 12 based on the pixel clock signal 16A input from the CPU 16. .
[0076]
Further, as described above, the output terminal of the photodiode 228 that outputs an analog signal having a magnitude proportional to the amount of light of the LED chips 208R, 208G, and 208B in the full-color image forming light source unit 204 performs analog / digital conversion. An analog / digital converter (hereinafter referred to as an AD converter) 50 is connected to the CPU 16. Based on the output signal of the photodiode 228 converted to a digital signal by the AD converter 50, the CPU 16 converts each image channel by a combination of conversion of image data by the conversion table of the LUT 12 and addition of a predetermined voltage by the offset addition circuit 14. The contents of the conversion table corresponding to each channel of the LUT 12 are rewritten so as to cancel the offset voltage of the two-stage sample hold circuit. The photodiode 228 and the AD converter 50 correspond to the offset detection means of the present invention.
[0077]
The analog switch 34_n, 40_nFor example, an FET switch or a reed relay can be applied.
[0078]
(Reservoir part)
As described above, the reservoir unit 170 is disposed between the exposure unit 176 and the water application unit 178, and includes two pairs of sandwiching rollers 192 and 194 and one dancer roller 196. The photosensitive material 106 is stretched over two pairs of sandwiching rollers 192 and 194, and a substantially U-shaped slack is provided in the photosensitive material 106 between them. In response to this slack, the dancer roller 196 is moved up and down to hold the photosensitive material 106 in the slack portion.
[0079]
In the exposure unit 176, the photosensitive material 106 moves stepwise, but in the water application unit 178, it is necessary to transport the photosensitive material 106 at a constant speed for uniform application of water. For this reason, a conveyance speed difference of the photosensitive material 106 occurs between the exposure unit 176 and the water application unit 178. In order to absorb this speed difference, the dancer roller 196 is moved up and down to adjust the slack amount of the photosensitive material 106 so that the photosensitive material 106 can be moved stepwise and at a constant speed simultaneously.
[0080]
The operation of the first embodiment will be described below. In the first embodiment, the offset addition circuit 14 adds a predetermined voltage to the output of the DA converter 32 and cancels the offset voltage of the two-stage sample hold circuit of each channel. The conversion table corresponding to each channel of the LUT 12 is rewritten in advance for each apparatus, and details thereof will be described later.
[0081]
First, the overall flow for image recording will be described.
The tray 144 is loaded in the tray loading port 146, the supply reel 152 with the photosensitive material 106 wound up and the take-up reel 154 in the empty state are loaded at predetermined positions, respectively, and the loading is completed. When the print start key of the display unit 112 is operated, the controller 202 reads image data from the CD-ROM 102 or the FD 104 and stores it in the image memory 10.
[0082]
When image data is stored by the controller 202, the supply reel 152 is driven to start conveying the photosensitive material 106.
[0083]
When the photosensitive material 106 reaches a predetermined position of the exposure unit 176, the photosensitive material 106 is temporarily stopped, and image data is output from the controller 202 to the full-color image forming light source unit 204. This image data is output every 11 lines, and the full-color image forming light source unit 204 is guided by the guide shaft 218 by the driving of the stepping motor 226 and moves along the width direction of the photosensitive material 106 (main scanning).
[0084]
Before starting the output of this image data, the light amount of each color from the light source unit 204 for full color image detection is detected by the photodiode 228, and the light amount correction unit 230 sets a correction value for adjusting the light amount, the color balance, and the like. The data is supplied to the CPU 16 of the controller 202 and the image data is corrected. This correction is performed for each image.
[0085]
As shown in FIG. 6, when one main scanning is completed, the photosensitive material 106 is stopped by moving one step (5.5 line pitch), and the second main scanning is performed. By repeating this, an image for one frame is recorded on the photosensitive material 106. That is, the main scanning line is formed at a pitch that is half the arrangement pitch of the LED chips 208, and the resolution is improved. In this case, the upper five lines at the time of the first main scanning drive on one screen and the lower five lines at the time of the last main scanning driving may be unexposed (the LED chip 208 is turned off).
[0086]
The photosensitive material 106 that has been recorded is wound around the dancer roller 196 by driving only the pair of nip rollers 192 on the upstream side of the reservoir unit 170 (the pair of nip rollers 194 on the downstream side is stopped). It is held in a slack state and does not reach the water application part 178.
[0087]
When the photosensitive material 106 having a length of one image is accumulated in the reservoir unit 170, the pair of nipping rollers 194 on the downstream side of the reservoir unit 170 starts to be driven. As a result, the photosensitive material (image recorded) 106 is conveyed to the water application unit 178. In the water application unit 178, the photosensitive material 106 is conveyed at a constant speed, and water is uniformly applied by the application piece 188.
[0088]
The application piece 188 is constantly supplied with water from the tank 190 and presses the photosensitive material 106 with a predetermined pressure, so that an appropriate amount of water is applied to the photosensitive material 106.
[0089]
The photosensitive material 106 coated with water is guided by the guide plate 172 and conveyed to the third roller pair 166.
[0090]
On the other hand, when the half moon roller 156 rotates once, the peripheral surface of the half moon roller 156 comes into contact with the leading edge of the image receiving paper 108, and the uppermost image receiving paper 108 is pulled out, and the first receiving roller 108 160. By the driving of the first roller pair 160, the image receiving paper 108 is pulled out from the tray 144 and waits for the arrival of the photosensitive material 106 while being sandwiched between the second roller pair 162.
[0091]
In synchronism with the passage of the photosensitive material 106 through the guide plate 172, the driving of the first roller pair 160 and the second roller pair 162 is started, and the image receiving paper 108 is guided by the guide plate 164 and the third roller pair 160 is driven. It is conveyed to the roller pair 166.
[0092]
In the third roller pair 166, the photosensitive material 106 and the image receiving paper 108 are nipped in an overlapped state and sent to the heat roller 174. At this time, the two are brought into close contact with water applied to the photosensitive material 106.
[0093]
The photosensitive material 106 and the image receiving paper 108 in a superposed state are wound around a heat roller 174, receive heat from the heater 182, and are subjected to heat development transfer processing. That is, the image recorded on the photosensitive material 106 is transferred to the image receiving paper 108 and visualized.
[0094]
The heat development transfer is completed in a state of being wound about 1/3 around the heat roller 174, and the image receiving paper 108 is peeled off from the photosensitive material 106 by the peeling roller 184 and the peeling claw 186 and wound around the peeling roller 184. Is discharged onto the discharge tray 140.
[0095]
On the other hand, the photosensitive material 106 is wound about 1/2 on the heat roller 174, moves in the tangential direction, and is taken up on the take-up reel 154.
[0096]
Next, the operation of the part that emits the LED chip 208 of the full-color image forming light source unit 204, that is, the part corresponding to the exposure control apparatus of the present invention will be described with reference to the circuit diagram of FIG. 7 and the time chart of FIG. To do.
[0097]
First, the operation of adding a predetermined voltage to the output of the DA converter 32 by the offset adding circuit 14 is started.
[0098]
Next, when the pixel clock signal 16A input from the CPU 16 goes to a high level (see FIG. 8), the timing generation circuit 46 has each period obtained by equally dividing one period of the pixel clock signal 16A into two by time division. The analog switch 34 corresponding to each channel in each section in which the period SH1 in SH1 and SH2 is further divided into N (divided into the number of channels)._nAre generated in order of channels, and a sampling signal 46A is generated, and each analog switch 34 of the sampling signal 46A is generated._nStart applying to. At the same time, the timing generation circuit 46 performs the analog switch 40 during the period SH1._nOf the timing signal 46B generated to turn off the analog switch 40_nStart applying to. The analog switch 34 used in the first embodiment is used._n, 40_nIs turned on when the signal applied to the switch switching input terminal is at a low level.
Each analog switch 34 of the sampling signal 46A_nTo the switch switching input terminal and each analog switch 40 of the sampling signal 46B._nIs applied to the switch switching input terminal, the timing generation circuit 46 is provided in the image data for N channels from the image memory 10 to the DA converter 32 via the LUT 12, that is, in the full-color image forming light source unit 204. Input of image data for causing the N LED chips 208 to emit light is started. At this time, the image data of each channel is input within the period when the sampling signal 46A corresponding to each channel is at a low level, as shown in FIG._nThe capacitors 36 that fall within the period when the signal is on and correspond to each channel_nThe image data of each channel is divided and inputted for each channel so as to cover a period during which the sample data can be sampled and held. At this time, the image data for N channels input to the DA converter 32 is converted by the conversion table stored for each channel in the LUT 12.
[0099]
Each analog switch 34 of the sampling signal 46A described above._nAre applied to the switch switching input terminal, and image data is input to the DA converter 32, whereby each analog switch 34 is switched._nCapacitor 36 connected to_nThe voltage corresponding to the image data of each channel is sampled, and each capacitor 36 is sampled._nEach buffer amplifier 38 connected to_n, That is, the output voltage of the first-stage sample and hold circuit starts rising substantially simultaneously with the input of the image data of each channel to the DA converter 32 as shown in FIG. When the application of the low level of the signal 46A is finished, the output voltages corresponding to the image data of all the channels are held.
[0100]
Thereafter, the timing generation circuit 46 outputs the sampling signal 46B to the analog switch 40 in the period SH2._nIs turned on, that is, at a low level.
[0101]
Thus, the analog switch 40_nSampling signal 46B for turning on each analog switch 40_nAre simultaneously applied to all switch switching input terminals of the buffer amplifier 44._nThe output at the output end of the first sample hold circuit at the second stage is started simultaneously. Therefore, the buffer amplifier 44_nTransistor 46 connected to each output terminal of_nSince the signal corresponding to the image data is simultaneously applied to the base of the transistor 46, the transistor 46_nThrough the switching operation, a drive current corresponding to the image data flows through each LED chip 208 at the same time, and the LED chip 208 is lit during the period SH2.
[0102]
As a result of the above operation, the exposure of the photosensitive material 106 for 11 lines of the first pixel in the main scanning direction by each LED chip 208 is performed.
[0103]
Thereafter, similarly to the above, exposure corresponding to the image data of the second and subsequent pixels in the main scanning direction is performed.
[0104]
Next, addition of a predetermined voltage to the output of the DA converter 32 by the offset addition circuit 14 performed to cancel the offset voltage of the two-stage sample hold circuit of each channel, and a conversion table corresponding to each channel of the LUT 12 The rewriting will be described in detail. First, the addition of a predetermined voltage to the output of the DA converter 32 by the offset addition circuit 14 will be described.
[0105]
In the first embodiment, the value of the predetermined voltage added to the output of the DA converter 32 by the offset adding circuit 14 is obtained as an offset voltage of the two-stage sample and hold circuit in the controller 202 obtained in advance. The voltage is larger than the maximum voltage that can be generated. The addition of the predetermined voltage by the offset addition circuit 14 is performed by applying a voltage larger than the maximum voltage in reverse polarity and in series to the output of the DA converter 32, for example. As a result, the output voltages of the two-stage sample-and-hold circuits are all reversed in polarity.
[0106]
Next, rewriting of the conversion table corresponding to each channel in the LUT 12 will be described.
[0107]
First, each offset voltage of the two-stage sample and hold circuit corresponding to each channel is detected by the following procedure, for example.
[0108]
First, all analog switches 34_n, 40_nIs turned on and ‘0’ is input to the DA converter 32 in a state where the offset addition circuit 14 does not add a predetermined voltage to the output of the DA converter 32. Next, the light quantity of each of the eleven LED chips 208R, 208G, and 208B in this state is detected by the photodiode 228. Since the photodiode 228 outputs an analog signal having a magnitude proportional to the detected light amount of each LED chip to the AD converter 50, the two stages of each channel are determined from the magnitude of the signal digitized by the AD converter 50. The offset voltage of each of the sample and hold circuits can be specified.
[0109]
That is, in the state where the offset addition circuit 14 does not add the predetermined voltage to the output of the DA converter 32 and “0” is input to the DA converter 32 as described above, The voltage value applied to is 0V, and each sample and hold circuit has a transistor 46._nSince the LED chip connected via the LED emits light with a light amount corresponding only to the magnitude of the offset voltage by each sample-and-hold circuit, the photodiode 228 detects the light amount so that the AD converter 50 can detect the light amount. The CPU 16 can know the offset voltage of each sample and hold circuit according to the magnitude of the signal output to the CPU 16 via the.
[0110]
When the offset voltage of each of the two-stage sample and hold circuits is detected, the predetermined voltage applied to the output of the DA converter 32 by the offset adding circuit 14 and the two-stage sample and hold circuit of each channel detected as described above The offset addition circuit 14 applies the predetermined voltage to the output of the DA converter 32 based on the offset voltage of each of the channels, thereby canceling the offset voltages of the two-stage sample hold circuits of each channel. As described above, the CPU 16 rewrites the contents of the conversion table of each channel stored in the LUT 12.
[0111]
For example, the predetermined voltage applied to the output of the DA converter 32 by the offset addition circuit 14 is −50 mV, and the offset voltage of each sample hold circuit of each channel is 50 mV, 30 mV,. In this case, −50 mV is always added to the output of the DA converter 32 from the offset addition circuit 14, and thereby the offset voltage (50 mV) of the first channel is canceled, so that it corresponds to the first channel of the LUT 12. There is no need to change the contents of the conversion table. Therefore, the conversion table corresponding to the first channel is not rewritten in the state shown in FIG.
[0112]
As a result, the output voltage of the second-stage sample and hold circuit of the first channel is proportional to the size of the input data to the DA converter 32 as shown in FIG. When the voltage is 0 V and the input data is the maximum value (hexadecimal number 'FFF' in the first embodiment), the output voltage is the maximum voltage V_maxThus, no offset voltage is generated. The drive current of the LED chip 208 at this time is proportional to the output voltage of the second-stage sample hold circuit of the first channel, that is, the input voltage of the LED chip 208, as shown in FIG. 9C. The input voltage increases to the maximum voltage V_max, The drive current of the LED chip 208 is the maximum drive current I which is the maximum allowable current of the LED chip 208._maxTo be.
[0113]
On the other hand, the offset voltage of the second channel is 30 mV, and by adding -50 mV to the output of the DA converter 32 by the offset addition circuit 14, an offset voltage of -20 mV is generated at the output of the second-stage sample hold circuit. Therefore, in order to cancel this offset voltage, as shown in FIG. 11A, the conversion table corresponding to the second channel in the LUT 12 is set so that the minimum value of the output voltage of the DA converter 32 is 20 mV. rewrite.
[0114]
By this rewriting, as shown in FIG. 11B, the output voltage of the second-stage sample-and-hold circuit of the second channel is totally compared with the case where the conversion table shown in FIG. 9B is not rewritten. When the input data of the DA converter 32 is the maximum value (hexadecimal number 'FFF' in the first embodiment), the maximum voltage V_max20 mV lower. Therefore, the maximum voltage applied to the LED chip 208 is the maximum voltage V as shown in FIG._maxAnd the maximum drive current of the LED chip 208 is the maximum drive current I when the conversion table is not rewritten._maxAlthough slightly smaller, as shown in FIG. 12A, the maximum output power of the LED chip 208 is set to the maximum drive current I._maxSmaller current I_DminIs input, the density of the image recorded on the photosensitive material 106 is the minimum density D._minOutput power W (maximum density in the case of positive photosensitive material, maximum density in case of negative photosensitive material)_DminThus (see FIG. 12B), even if the maximum drive current of the LED chip 208 slightly decreases, the image quality does not decrease.
[0115]
As a result, the offset voltage 30 mV of the sample and hold circuit of the second channel is canceled as a result of the conversion of the image data by the conversion table corresponding to the second channel of the rewritten LUT 12 and the addition of −50 mV by the offset addition circuit 14. It will be.
[0116]
Similarly, the conversion table corresponding to channels 3 to N in the LUT 12 is rewritten so that the offset voltage of the sample hold circuit of each channel can be canceled as a result.
[0117]
As described in detail above, the exposure control apparatus according to the first embodiment detects the offset voltage of each of the two-stage sample and hold circuits, and based on each detected offset voltage, the offset addition circuit 14, the image data for each channel input to the LUT 12 is converted so that the offset voltage of each sample hold circuit of each channel is canceled by applying a predetermined voltage to the output of the DA converter 32. As described above, since the conversion table corresponding to each channel in the LUT 12 is rewritten, it is possible to prevent the output offset voltage of each channel from being generated, and to prevent erroneous light emission of the light emitting element due to the offset voltage.
[0118]
Further, the exposure control apparatus according to the first embodiment uses the photodiode 228 provided in advance in the image recording apparatus 100 as means for detecting the offset voltage of each of the sample and hold circuits. The exposure control apparatus can be configured at a low cost.
[0119]
In the first embodiment, the case where the offset addition circuit 14 adds a predetermined voltage to the output of the DA converter 32 has been described. However, the present invention is not limited to this, and each channel sample An addition may be made to the outputs of the hold circuits.
[0120]
In the first embodiment, the predetermined voltage applied by the offset adding circuit 14 is larger than the maximum voltage that can be generated as the offset voltage of the two-stage sample-and-hold circuit in the controller 202 that has been obtained empirically in advance. However, the present invention is not limited to this, and for example, the predetermined voltage may be set to 0V. In this case, the offset voltage is canceled only by converting the image data using the conversion table of the LUT 12.
[0121]
Furthermore, in the first embodiment, the case where the predetermined voltage added by the offset addition circuit 14 for each device is set in advance and the conversion table of each channel in the LUT 12 is rewritten has been described. The present invention is not limited, and may be performed each time image recording is performed, for example.
[0122]
[Second Embodiment]
Next, a second embodiment of the present invention will be described.
[0123]
Since the configuration other than the portion that turns on the full-color image forming light source unit 204 in the controller 202 of the image recording apparatus according to the second embodiment and the overall flow for image recording are the same as those in the first embodiment, A description will be omitted, and the configuration of the portion that turns on the full-color image forming light source unit 204 in the controller 202 of the second embodiment will be described with reference to FIG. 13 that are the same as those in the first embodiment shown in FIG. 7 are assigned the same reference numerals, and descriptions thereof are omitted.
[0124]
The configuration of the portion that turns on the full-color image forming light source unit 204 in the controller 202 of the second embodiment is an LUT 12A in which the LUT 12 stores digital data to be input to the DA converter 33 in a storage area other than the conversion table. There is no offset adding circuit 14, a DA converter 33 is added as an adding circuit for generating a voltage for canceling the offset voltage of each channel, and a timing generation circuit 46 is also connected to the LUT 12A. This is different from the configuration of the first embodiment. The input end of the DA converter 33 is connected to the output end of the LUT 12A, and the output end of the DA converter 33 is connected to the addition point for the output of the DA converter 32.
[0125]
In the LUT 12A of the second embodiment, in addition to the conversion table for performing conversion as shown in FIG. 9A, the offset voltage of each sample hold circuit of each channel is added to the output of the DA converter 32. Is stored in advance for each channel, and image data corresponding to each channel is inputted to the DA converter 32. By inputting cancel data corresponding to the channel in synchronization with the timing from the LUT 12A to the DA converter 33, a voltage is generated by the DA converter 33 and applied to the output from the DA converter 32, whereby the sample hold of each channel. Each offset of the circuit To cancel the door voltage. Therefore, in the second embodiment, the conversion table in the LUT 12 does not need to be prepared for each channel, and the basic one as shown in FIG. You only have to.
[0126]
Here, the cancel data may be digital data that can cause the DA converter 33 to generate substantially the same voltage as the offset voltage of each of the two-stage sample and hold circuits of each channel, and is generated by the cancel data. The applied voltage may be applied to the output of the DA converter 32 in reverse polarity and in series.
[0127]
At this time, the offset voltages of the two-stage sample-and-hold circuits of each channel are all analog switches 34, for example, substantially the same as in the first embodiment._n, 40_nCan be detected by detecting the amount of light of each of the LED chips 208R, 208G, and 208B with the photodiode 228.
[0128]
In the second embodiment, the image data corresponding to each channel is input to the DA converter 32, and the cancel data corresponding to the channel synchronized with the input timing is input from the LUT 12A to the DA converter 33. The timing generation circuit 46 performs this operation.
[0129]
As described above in detail, in the exposure control apparatus according to the second embodiment, the voltage at which each offset voltage of the sample hold circuit of each channel is canceled by being added to the output of the DA converter 32 is the DA converter 33. And is added to the output of the DA converter 32, so that it is possible to prevent the occurrence of an offset voltage of the output of each channel, and to prevent erroneous light emission of the light emitting element due to the offset voltage. In addition to the same effect, since it is not necessary to store the conversion table for each channel, the storage capacity of the LUT 12A can be reduced as compared with the first embodiment.
[0130]
In the second embodiment, the case where the DA converter 33 adds the predetermined voltage to the output of the DA converter 32 has been described. However, the present invention is not limited to this, and the sample hold of each channel is performed. It is good also as a form added with respect to each output of a circuit.
[0131]
In the second embodiment, the case where the cancel data is stored in the empty area of the LUT 12A has been described. However, the present invention is not limited to this, and a storage unit other than the LUT 12A is newly provided. It is good also as a form memorize | stored in a memory | storage means.
[0132]
In each of the above embodiments, the light amount of each LED chip 208 when 0 V is applied to each of the two-stage sample and hold circuits is detected by the photodiode 228 and output in proportion to the light amount from the photodiode 228. Although the case where the offset voltage of each of the two-stage sample and hold circuits is detected based on the magnitude of the signal to be processed has been described, the present invention is not limited to this, and for example, each transistor 46_nIt is also possible to branch the connecting line between each of the collectors and the cathode of the LED chip 208, detect the voltage at this branching point, and use the detected voltage as the offset voltage.
[0133]
Further, in each of the above embodiments, the case where the photodiode 228 is used as means for detecting the light amount of the LED chip 228 has been described. However, the present invention is not limited to this, and for example, a photoelectric conversion element such as a phototransistor Thus, the light quantity of the LED chip 228 may be detected.
[0134]
【The invention's effect】
  According to the exposure control apparatus of claim 1, the offset detection meanspluralDriving circuitEach ofOffset voltage is detected and based on the detected offset voltagepluralDriving circuitEach ofBecause the offset voltage ofIt can prevent the occurrence of offset voltage in the output of multiple channels.Driving circuitEach ofThus, it is possible to prevent erroneous light emission of the light emitting element due to the offset voltage.
[0135]
  AlsoTheSince the facet detection means can generally be configured using a light quantity sensor provided in the exposure control apparatus, an effect that the exposure control apparatus can be configured at low cost is obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view of an image recording apparatus according to an embodiment.
FIG. 2 is a front view of the image recording apparatus according to the present embodiment.
FIG. 3 is a side sectional view showing an internal configuration of the image recording apparatus according to the present embodiment.
FIG. 4 is a front view showing a schematic configuration of an exposure unit.
FIG. 5 is a plan view showing an arrangement state of LED chips in a light source unit.
FIG. 6 is a plan view of a photosensitive material showing a state of a main scanning line and a sub-scanning pitch.
FIG. 7 is a circuit diagram showing a circuit configuration of a part for turning on a light source unit in the controller according to the first embodiment.
FIG. 8 is a time chart for explaining the operation of the controller 202;
9A is a graph showing an example of the relationship between input data and output data in the conversion table of the lookup table, and FIG. 9B shows the relationship between the input data of the DA converter and the output voltage of each channel. (C) is a graph which shows the relationship between the voltage input into an LED chip, and LED drive current.
FIG. 10 is a graph showing an example of an offset voltage of a sample hold circuit of each channel.
11A is a graph showing the relationship between input data and output data in the rewritten conversion table, and FIG. 11B shows the relationship between the input data of the DA converter and the output voltage of each channel at that time. It is a graph and (C) is a graph which shows the relationship between the voltage input into the LED chip at that time, and LED drive current.
12A is a graph showing the relationship between LED drive current and LED output power, and FIG. 12B is a graph showing the relationship between LED output power and the density of an image recorded on a photosensitive material.
FIG. 13 is a circuit diagram showing a circuit configuration of a part for turning on a light source unit in a controller according to a second embodiment.
FIG. 14 is a circuit diagram showing a circuit configuration of a conventional multi-channel DA converter.
[Explanation of symbols]
14 Offset addition circuit (addition circuit)
33 DA converter (adder circuit)
50 AD converter (offset detection means)
228 photodiode (offset detection means)

Claims (2)

A digital / analog converter for converting a digital signal of one channel into an analog signal;
Input means for dividing and inputting a digital signal of a plurality of channels into the digital / analog converter for each channel;
A plurality of drive circuits connected in parallel to the output terminals of the digital / analog converter and generating drive signals for causing the light emitting elements to emit light based on the analog signals for each channel output from the digital / analog converter When,
Based on the light amount when the light emitting element is caused to emit light by the predetermined drive signal generated by each of the plurality of drive circuits and the predetermined drive signal, the offset voltage of each of the plurality of drive circuits is calculated. Offset detecting means for detecting;
An adding circuit for applying a predetermined voltage to the output of the digital / analog converter ;
The digital signal for each channel input to the digital / analog converter is converted so that the offset voltage of each of the plurality of drive circuits detected by the offset detection unit is canceled by applying the predetermined voltage. Conversion means to
An exposure control apparatus comprising: The exposure control apparatus according to claim 1, wherein the predetermined drive signal is a drive signal that does not cause the light emitting element to emit light when it is assumed that an offset voltage of the drive circuit does not occur .

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