JP4508890B2 - Image forming apparatus, image forming method, and program - Google Patents

Description

  The present invention relates to an image forming apparatus, an image forming method, and a program, and more particularly to an image forming apparatus that forms a gradation image, an image forming method applied to the image forming apparatus, and a computer that executes the image forming method. Related to the program.

  FIG. 7 is a plan view showing a configuration of a conventional image forming apparatus, and FIG. 8 is a side view of the apparatus. The image forming apparatus is an electrophotographic image forming apparatus that performs image exposure with laser light, and an image forming apparatus that outputs a gradation image corresponding to multi-value image data.

  7 and 8, reference numeral 15 denotes a rotating polygon mirror, and 16 denotes a laser scanner motor that drives the rotating polygon mirror 15 to rotate. The rotary polygon mirror 15 in the present embodiment includes six reflecting surfaces. Reference numeral 17 denotes a laser diode which is a recording light source. The laser diode 17 is turned on or off in accordance with an image signal by a laser driver (not shown), and the laser light thus optically modulated is irradiated from the laser diode 17 toward the rotary polygon mirror 15 through the collimator lens 20. The rotating polygon mirror 15 is rotated in the direction of the arrow, and the laser light output from the laser diode 17 is reflected as a deflected beam that continuously changes the emission angle on its reflecting surface as the rotating polygon mirror 15 rotates. . The reflected light is subjected to correction of distortion by the f-θ lens 21, irradiated to the photosensitive drum 10 through the reflecting mirror 18, and scanned on the photosensitive drum 10 in the main scanning direction. At this time, an image for one line is formed in the main scanning direction of the photosensitive drum 10 by the reflection of the beam light through one surface of the rotary polygon mirror 15.

  The photosensitive drum 10 is charged in advance by a charger 11 and sequentially exposed by scanning with a laser beam to form an electrostatic latent image. The photosensitive drum 10 is rotated in the direction of the arrow, and the formed electrostatic latent image is developed by the developing device 12, and the developed visible image is transferred to a transfer paper (not shown) by the transfer charger 13. Is done. The transfer paper on which the visible image has been transferred is conveyed to the fixing device 14 and is discharged out of the apparatus after fixing.

  A BD sensor 19 is disposed in the vicinity of the scanning start position in the main scanning direction on the side of the photosensitive drum 10. The laser beam reflected by each reflecting surface of the rotary polygon mirror 15 is detected by the BD sensor 19 prior to scanning the line. This detection signal is input to a timing controller (not shown) as a scanning start reference signal in the main scanning direction, and the writing start position of each line in the main scanning direction is synchronized with this signal as a reference.

  In an image forming apparatus that forms an image with gradation on a transfer sheet, a laser diode used for image exposure is driven by a PWM signal that is pulse width modulated (PWM) according to multi-value image data. Is called.

  FIG. 9 is a current-light output characteristic of the laser diode 17 showing the relationship between the current supplied to the laser diode 17 shown in FIGS. 7 and 8 and the intensity of light output from the laser diode 17 by the current supply. FIG.

  The laser diode 17 emits LED in the low current region with the threshold value Ith as a boundary, and emits laser in the high current region.

  This characteristic varies depending on the environmental temperature. Therefore, in the conventional image forming apparatus, when the photosensitive drum 10 is scanned by raster scanning to form a latent image, the laser beam output intensity is stabilized against fluctuations in environmental temperature. That is, the laser beam output intensity is detected in the vicinity of the laser by the optical output detection circuit immediately before the horizontal scanning of the image exposure, and this detection signal is fed back to the laser drive circuit so that the laser beam output intensity is always equal to the set value It is controlled to become. This control is performed by an auto power control (APC) circuit.

  In the APC circuit, the drive current Io when the light output intensity of the laser diode becomes a predetermined value Po is detected immediately before the horizontal scanning of the image exposure, and when the image exposure to the photosensitive drum 10 is performed, the laser diode 17 is connected to the drive current Io. Constant current driving is performed at Io, thereby enabling stable exposure at light output intensity Po.

  In the meantime, since the image data is data indicating that exposure is not required during scanning on the photosensitive drum 10, the light output intensity from the laser diode 17 may be set to 0. Even in such a case, the laser diode 17 is driven. There is a control method called bias APC in which the drive current is not zero. That is, in the middle of scanning on the photosensitive drum 10, when the image data is data indicating that exposure is necessary, the drive current amount for driving the laser diode 17 is Io, and when the image data is data indicating that exposure is not required. The drive current (bias current) amount for driving the laser diode 17 is Ib, and constant current drive is performed.

  In the APC circuit in which such bias APC is performed, the relationship between the pulse width of the PWM signal for pulse driving the laser diode 17 and the amount of light output from the laser diode 17 will be described below.

  FIG. 10 is a diagram showing the relationship between the pulse width of the PWM signal for driving the laser diode 17 in pulse and the amount of light (integrated value) output from the laser diode 17.

  In the figure, a graph G1 represents characteristics when the bias APC is not performed, that is, when the bias current Ib = 0. As can be seen from this graph G1, the relationship between the pulse width of the PWM signal and the amount of light (integrated value) output from the laser diode 17 is not linear but nonlinear. A non-linear curve such as the graph G1 is called a γ curve. In this graph G1, when the pulse width of the PWM signal is 10% or less, the laser diode 17 does not respond and the amount of light is zero. When the pulse width becomes 10% or more, the laser diode 17 starts to light up, and the light quantity also increases linearly sequentially. When the pulse width is 90% or more, the amount of light suddenly increases, and the amount of light is saturated at 100%.

  A graph G2 represents characteristics when bias APC is performed and the bias current Ib is set to any value between 0 and the threshold value Ith. In this graph G2, when the pulse width of the PWM signal is 5% or less, the laser diode 17 does not respond and the amount of light is zero. When the pulse width becomes 5% or more, the laser diode 17 starts to light, and the light quantity also increases linearly sequentially. When the pulse width is 90% or more, the amount of light suddenly increases, and the amount of light is saturated at 100%.

  A graph G3 represents characteristics when bias APC is performed and the bias current Ib is set to the threshold value Ith. In this graph G3, when the pulse width of the PWM signal is 5% or less, the laser diode 17 does not respond and the amount of light is zero. When the pulse width becomes 5% or more, the laser diode 17 starts to light, and the amount of light increases rapidly. When the pulse width becomes 10% or more, the amount of light gradually increases linearly. When the pulse width becomes 95% or more, the amount of light suddenly increases, and the amount of light is saturated at 100%.

  In this way, when bias APC is performed and the bias current Ib is set to an appropriate value, the proportion of the linear region of the PWM characteristic shown in FIG. 10 can be increased. By adopting an APC circuit that performs such bias APC in the apparatus, a high-quality gradation image can be created.

  FIG. 11 is a block diagram showing a configuration of a conventional PWM circuit that generates a PWM signal from image data (see, for example, Patent Document 1).

In the figure, image data composed of 4-bit parallel signals is input to a register 601 from an image processing controller (not shown). The image data temporarily stored in the register 601 is synchronized with the image clock, and is input to the digital / analog (D / A) conversion circuit 602 to be converted into an analog voltage. The converted analog voltage is input to the comparator 603. The comparator 603 compares the analog voltage with the triangular wave output from the triangular wave generation circuit 604, so that a PWM signal having a pulse width corresponding to the level of the analog voltage is obtained. Is output. The PWM signal is supplied via a buffer 605 to a laser diode drive circuit (not shown).
JP-A-6-297761

  However, in the conventional APC circuit in which the bias APC is performed, as can be seen from the graph G3 shown in FIG. 10, the ratio of the linear region of the PWM characteristic of the laser diode 17 is set by setting the bias current Ib to an appropriate value. Although it can be increased, there can still be a non-linear part.

  In the APC control, the laser beam output intensity is detected immediately before the horizontal scanning of image exposure, and this detection signal is fed back to the laser drive circuit to control the laser beam output intensity to be always equal to the set value. However, such APC control is not performed at every scanning. Therefore, it cannot be said that the correction of the laser beam output intensity is realized in real time with respect to the constantly changing temperature environment.

  The present invention has been made in view of such problems, and an object thereof is to provide an image forming apparatus, an image forming method, and a program capable of always obtaining a stable high-quality gradation image. .

To achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus which forms an image based on the inputted multi-valued image data, storage means for storing the multivalued image data, the storage means Generating means for generating a pulse signal in accordance with the multi-valued image data stored in the light source, light emitting means for flashing light emission based on the pulse signal generated by the generating means, and continuing lighting of the light emitted by the light emitting means detecting means for detecting the pulse width is the period, a data conversion means for converting the pulse width detected by said detecting means into digital data, said digital data converted by said data converting means, said storage means and a calculating means for the difference between the stored the multilevel image data and the comparative image data, said generating means, said multi-value image data From the look-up table in which pulse width data corresponding to the multi-value image data and the comparison image data is held using the address value of the upper bits and the comparison image data as the address value of the lower bits, the multi-value image data The pulse width data is read in accordance with the comparison image data, and the pulse signal is generated based on the pulse width data .

The image forming method according to the present invention is an image forming method for forming an image based on the inputted multi-valued image data, a storage step of storing the multi-value image data in the storage means, stored in said storage means and a generation step of generating a pulse signal in response to the multi-valued image data, wherein the light emitting step which is flash emission in the light emitting means based on the pulse signal generated by the generating step, the lighting of the light emitted by said light emitting step A detection step for detecting a pulse width that is a duration, a data conversion step for converting the pulse width detected by the detection step into digital data, the digital data converted by the data conversion step, and the storage means a calculating step to a comparison image data difference between the stored the multivalued image data into A, wherein in the generation step, the multi-valued image data as the address value of the upper bits, the comparison image data as the address value of the lower bits, the pulse width data corresponding to said multi-value image data and the comparison image data The pulse width data is read in accordance with the multi-value image data and the comparison image data from a look-up table in which is stored, and the pulse signal is generated based on the pulse width data .

Further, the program according to the present invention is a program for causing a computer to execute an image forming method for forming an image based on input multi-value image data, and storing the multi-value image data in a storage means. A generation step of generating a pulse signal according to the multi-valued image data stored in the storage means, a light emission step of flashing and emitting light to the light emission means based on the pulse signal generated by the generation step, and the light emission step A detection step of detecting a pulse width that is a lighting continuation period of the light emitted by the step, a data conversion step of converting the pulse width detected by the detection step into digital data, and the data converted by the data conversion step Digital data and the multi-value image data stored in the storage means And calculating the difference between the multi-value image data, the multi-value image data in the generation step, the multi-value image data as the address value of the upper bits, and the comparison image data as the address value of the lower bits. And the pulse width data according to the multi-value image data and the comparison image data from a lookup table in which pulse width data according to the comparison image data is held, and based on the pulse width data, the pulse width data is read out. A pulse signal is generated .

  According to the present invention, a pulse signal corresponding to the input multivalued image data is generated based on a predetermined generation condition, and the light emitting means is caused to blink and emit light based on the pulse signal. A pulse width which is a lighting continuation period of the light emitted by the light emitting means is detected, and the pulse width is converted into digital data. A difference between the digital data and the input multi-value image data is detected, and the predetermined generation condition is changed based on the difference.

  As a result, the image forming apparatus can always output a stable high-quality gradation image.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing an electric circuit configuration in the image forming apparatus according to the first embodiment of the present invention. The image forming apparatus is an electrophotographic image forming apparatus that performs image exposure with laser light, and an image forming apparatus that outputs a full-color gradation image corresponding to multi-value image data.

  In the figure, reference numeral 700 denotes a printer, which is a laser beam printer capable of printing a full color image. The printer 700 includes a printer controller 701 and a printer engine 702. The printer controller 701 expands the image code sent from an external device, a scanner, or the like into, for example, 4-bit image data PVDO (0.3) corresponding to yellow, magenta, cyan, and black toners. The printer engine 702 performs printing by pulse width modulation (PWM) based on the developed image data PVDO (0.3). In the following description, the resolution of the printer 700 is described as 600 dpi, but the present invention is not limited to this.

  Main signals exchanged between the printer controller 701 and the image processing unit 703 of the printer engine 702 are image data PVDO_Y / M / C / K (0.3) corresponding to each color and an image signal transfer clock PVCLK. , Printer horizontal synchronization signal PHSYNC_Y / M / C / K for each color, operation timing signal PSTART sent from a scanner (not shown) at the time of copying, scanning start reference signal (BD signal) PBD_Y / M / C / for each color in the main scanning direction K, an image data request signal PVREQ for each color by the printer engine 702 to the printer controller 701, and an operation timing signal PSCNST sent from the printer engine 702 to a scanner (not shown) at the time of copying. Signals exchanged between the image processing unit 703 and the laser unit 704 in the printer engine 702 are a pulse width modulation signal PVDC and a modulation signal PD output from the laser unit 704.

  FIG. 2 is an overview diagram showing the mechanical configuration of the printer 700.

  In the figure, 101 is a photosensitive drum, 102 is a roller charger, 104a to 104d are developing devices, 105 is a support for the developing devices 104a to 104d, 107 is a cleaning device for the photosensitive drum 101, 114 is a fixing device, and 109 is a fixing device. Pickup roller, 108 is a paper feed cassette, 110 is a transfer drum, 111 is a transfer charger, 116 is a separation charger, 115 is a polygon mirror (rotating polygon mirror), 113 is a vertical synchronization signal generator, and 112 is a transfer drum. A cleaning device 110 and a semiconductor laser 117 are provided.

  The operation of the printer 700 having such a configuration will be described below.

  Upon receiving the operation timing signal PSTART, the printer engine 702 drives and rotates the photosensitive drum 101 and the transfer drum 110 in the direction of the arrow in FIG. The photosensitive drum 101 is obtained by applying an organic photoreceptor or a photoconductor to the outer peripheral surface of an aluminum cylinder.

  Next, the roller charger 102 uniformly charges the photosensitive drum 101 with a predetermined potential. Next, the printer engine 702 feeds the recording paper from the paper feed cassette 108 by the pickup roller 109 and supplies it to the transfer drum 110. At the same time, the support member 105 is rotated so that the developing device 104 a having magenta toner as the first forming color among the developing devices 104 a to 104 d supported by the support member 105 is opposed to the photosensitive drum 101. The developing device 104b includes a cyan toner material, the developing device 104c includes a yellow toner material, and the developing device 104d includes a black toner material.

  For synchronization in the sub-scanning direction, the vertical synchronization signal generator 113 detects the leading edge of the recording paper supplied to the transfer drum 110, generates a vertical synchronization signal, and uses the vertical synchronization signal as a reference in the sub-scanning direction. The writing start position is synchronized. For synchronization in the main scanning direction, a BD sensor (not shown) is disposed in the vicinity of the scanning start position in the main scanning direction on the side portion of the photosensitive drum 101 or a position corresponding thereto. Laser light output from the semiconductor laser 117 and reflected by the respective reflecting surfaces of the polygon mirror 115 is detected by a BD sensor (not shown) prior to line scanning in the main scanning direction with respect to the photosensitive drum 101. The detected BD signal is input to the printer controller 701 as a scanning start reference signal PBD_Y / M / C / K in the main scanning direction. The printer controller 701 generates a printer horizontal synchronization signal PHSYNC_Y / M / C / K using this scanning start reference signal PBD_Y / M / C / K as a trigger, and sends it to the image processing unit 703. The image processing unit 703 synchronizes the writing start position of each line in the main scanning direction based on the printer horizontal synchronization signal PHSYNC_Y / M / C / K.

  Based on these vertical synchronization signal and printer horizontal synchronization signal PHSYNC_Y / M / C / K, the image processing unit 703 sends an image data request signal PVREQ to the printer controller 701. Upon receiving the first image data request signal PVREQ, the printer controller 701 sends magenta image data PVDO_M (0.3) to the image processing unit 703 in synchronization with the image transfer clock VCLK. The image processing unit 703 performs pulse width modulation according to the received image data PVDO_M (0.3), and sends the obtained pulse width modulation signal PVDC to the laser unit 704. The laser unit 704 causes the semiconductor laser 117 in the laser unit 704 to emit light according to the pulse width modulation signal PVDC. Laser light output from the semiconductor laser 117 scans the photosensitive drum 101 via the polygon mirror 115 to form a latent image on the photosensitive drum 101. The formed latent image is developed by the selected developing device 104a, and the developed magenta toner image is transferred onto the recording sheet charged by the transfer charger 111 on the transfer drum 110.

  Subsequently, the printer engine 702 rotates the support 105 so that the developing device 104b including cyan toner as the second formation color is opposed to the photosensitive drum 101. Thereafter, the cyan toner image is transferred onto the recording paper by the same procedure as that for the magenta toner image described above. Further, by the same procedure, the yellow toner image as the third formation color and the black toner image as the fourth formation color are transferred to the recording paper.

  Thus, the recording paper on which the toner images of a plurality of colors are formed is peeled off from the transfer drum 110 by the separation charger 116, and the toner image is melted and fixed (fixed) on the recording paper by the heating by the fixing device 114. Then, the recording paper is discharged out of the machine.

  Through the above operation, a color image is formed on the recording paper by the printer 700.

  The transfer residual toner on the photosensitive drum 101 is cleaned by a cleaning device 107 having a blade unit. Further, it is preferable that the toner adhering to the transfer drum 110 is also cleaned by a cleaning device 112 having a fur brush, a web or the like, if necessary.

  Next, the image processing unit 703 in the printer engine 702 will be described.

  FIG. 3 is a block diagram showing internal configurations of the image processing unit 703 and the laser unit 704. Note that the image processing unit 703 is housed in a single integrated circuit (IC).

  In the image processing unit 703, reference numerals 41 and 42 denote line memories composed of FIFOs (A) and (B), 43 denotes a PWM width table composed of, for example, SRAM, and a lookup table storing PWM pulse width data. (LUT). 44 is a PWM circuit that performs pulse width modulation, 45 is a comparison operation unit that compares data read from the line memories 41 and 42, 47 is a pulse width detector that detects the emission pulse width of the laser beam, and 46 is The data conversion unit converts light emission pulse width data output from the pulse width detector 47 into 4-bit data.

  In the laser unit 704, 48 is a laser driver, 49 is a semiconductor laser, 50 is a photodiode, 51 is a current-voltage converter made up of, for example, a resistor, and 52 is a TTL converter that converts a signal level to a TTL level. is there.

  The operations of the image processing unit 703 and the laser unit 704 in the first embodiment having such a configuration will be described below.

  The image data PVDO sent from the printer controller 701 is written in the line memory (FIFO (A)) 41 in synchronization with the image signal transfer clock PVCLK, and read out in synchronization with the read clock RDCLK. Here, the read clock RDCLK has a frequency equivalent to the image signal transfer clock PVCLK that is the operation clock of the printer engine 702, and is a clock that is oscillated with the data storage in the line memory (FIFO (B)) 42 as a trigger. It is.

  As described above with reference to the graph G1 shown in FIG. 10, if the increase step of the pulse width of the PWM signal is constant in the APC circuit that does not perform the bias APC, the pulse width of the PWM signal and the amount of light output from the laser diode ( The relationship with the integral value is a non-linear γ curve. Therefore, in the first embodiment, in the control state of the graph G1, the entire pulse width region of the PWM signal ranging from 0 to 100% is not set to, for example, 16 increments, but the pulse width in which the light amount changes linearly. Minimum / maximum pulse width modulation is performed to make the region (10 to 90%) 16 steps. As a result, the relationship between the pulse width and the light amount becomes a gentle A curve as shown in FIG. For this reason, in the first embodiment, the PWM width table 43 stores conversion data that makes the change of the pulse width increase step non-linear like the B curve shown in FIG. By using this, a non-linear A curve is corrected to a linear C curve. FIG. 4 is a diagram showing the relationship between the pulse width of the PWM signal and the amount of light (integrated value) output from the laser diode by three curves.

  FIG. 5 is a diagram illustrating an example of conversion data stored in the PWM width table 43.

  The PWM width table 43 is a table that outputs 4-bit conversion data corresponding to an 8-bit (upper 4 bits, lower 4 bits) address value, and image data PVDO corresponds to an upper 4-bit address value. Comparative image data CVDO described later corresponds to the address value of the lower 4 bits. The PWM width table 43 in the first embodiment is for converting the image data PVDO into data along the B curve shown in FIG. 4 and outputting it as converted data.

  The 4-bit image data PVDO sent from the printer controller 701 is written to the line memory (FIFO (A)) 41 in synchronization with the image signal transfer clock PVCLK, and is output to the PWM width table 43.

  Incidentally, the image data PVDO written in the line memory (FIFO (A)) 41 is read by the input of the read clock RDCLK. On the other hand, this read clock RDCLK is a clock that is oscillated with the data storage in the line memory (FIFO (B)) 42 as a trigger. Initially, since no data is stored in the line memory (FIFO (B)) 42, the read clock RDCLK is not oscillated. Therefore, the image data PVDO written in the line memory (FIFO (A)) 41 is not compared with the comparison operation unit. 45 is not output. Therefore, comparison image data CVDO, which will be described later, is not output from the comparison calculation unit 45 to the PWM width table 43.

  As described above, in the PWM width table 43 when the comparison image data CVDO is not input from the comparison operation unit 45, the image data PVDO is input to the upper 4 bits address, and corresponds to the address value, and the lower 4 bits address. Conversion data corresponding to the value “0” is output to the PWM circuit 44.

  The PWM circuit 44 generates a pulse width modulation signal PVDC having a pulse width corresponding to the converted data and outputs it to the laser unit 704. In the laser unit 704, the pulse width modulation signal PVDC is input to the laser driver 48 and converted into a pulse current, and the semiconductor laser 49 blinks and outputs the laser light in accordance with this pulse current.

  Correction of the conversion data output from the PWM width table 43 based on the optical pulse width of the laser light output from the semiconductor laser 49 is always performed during normal printing. This will be described below.

  In FIG. 3, the laser light output from the semiconductor laser 49 is detected by a photodiode 50, and the photodiode 50 outputs a current corresponding to the pulse waveform of the laser light. This current is converted into a voltage by a current-voltage converter 51. The voltage signal representing the pulse waveform of the laser beam thus obtained is converted to a TTL level by the TTL converter 52 and input to the pulse width detector 47 as the modulation signal PD.

  FIG. 6 is a timing chart showing the image signal transfer clock PVCLK, the modulation signal PD, and the sampling clock SCLK, which will be described below with reference to FIG.

  In the present embodiment, the pulse width modulation signal PVDC output from the PWM circuit 44 is output to the laser unit 704 in synchronization with the image signal transfer clock PVCLK (frequency 20 MHz, period 50 ns, FIG. 6A). The period of the modulation signal PD (FIG. 6B) is 50 ns (corresponding to one pixel). On the other hand, the frequency of the sampling clock SCLK (FIG. 6C) input to the pulse width detector 47 is 320 MHz (period 3.125 ns), and is input in synchronization with the image signal transfer clock PVCLK. In 47, the modulation signal PD is equivalently sampled. That is, it can be said that one period of the image signal transfer clock PVCLK is 16 (= 50 ns / 3.125 ns) equivalent sampling. According to this measurement accuracy, 4-bit (= 16) PWM (resolution is 1/16) can be measured sufficiently.

  The pulse width detector 47 counts the number of rising edges of the sampling clock SCLK input from the rising edge to the falling edge of the modulation signal PD, and stores the count value in a register, for example, and then sends the count value to the data converter 46. Output.

  The data converter 46 converts the count value representing the pulse width input from the pulse width detector 47 into the same 4-bit data as the image data PVDO. The 4-bit data is written in the line memory (FIFO (B)) 42 in synchronization with the image signal transfer clock PVCLK. The read clock RDCLK is oscillated using the data written in the line memory (FIFO (B)) 42 as a trigger. As a result, 4-bit image data PVDO stored in the line memory (FIFO (A)) 41 and waiting to be read out, and 4-bit detection pulse width data stored in the line memory (FIFO (B)) 42 are stored. Are read in synchronization with the read clock RDCLK. That is, the image data before laser emission and the same image data after laser emission are simultaneously read and input to the comparison calculation unit 45.

  The comparison calculation unit 45 calculates a difference between the image data PVDO read from the line memory (FIFO (A)) 41 and the detection pulse width data read from the line memory (FIFO (B)) 42, Based on this difference, 4-bit comparison image data CVDO (0.3) is generated and sent to the PWM width table 43.

  In the PWM width table 43, the conversion data corresponding to the address value of the upper 4 bits corresponding to the image data PVDO and the address value of the lower 4 bits corresponding to the comparison image data CVDO is read and output to the PWM circuit 44.

  For example, the image data PVDO read from the line memory (FIFO (A)) 41 is “0b1011”, and the detected pulse width data read from the line memory (FIFO (B)) 42 is “0b1101”. In this case, the difference calculated by the comparison calculation unit 45 is “0b0010”, and “0b0010” is sent to the PWM width table 43 as the comparison image data CVDO. Therefore, in the PWM width table 43 illustrated in FIG. 5, the upper 4 bits of the address value is “0b1011” (“B” in hexadecimal notation), and the lower 4 bits of the address value is “0b0010” (hexadecimal notation). The conversion data “0x8” that is “2”) is read out and output to the PWM circuit 44.

  As a result, the difference between the actual light emission amount of the semiconductor laser 49 and the target (designated) light emission amount is fed back to the target (designated) light emission amount.

  As described above, according to the present embodiment, the laser light pulse waveform (modulation signal PD) and the image clock PVCLK can be sampled using the high-speed sampling clock SCLK that exceeds the frequency of the image clock PVCLK. Thus, the emission pulse width of the laser light can be measured. That is, the printer engine 702 measures the relationship between the image data PVDO input from the printer controller 701 and the laser light actually output from the semiconductor laser 49 based on the image data PVDO, and the pulse width of the PWM signal. And the amount of light output from the semiconductor laser 49 are linearly corrected by the PWM width table 43, thereby eliminating the influence of semiconductor laser material and product variations at the time of product shipment, environmental temperature fluctuations, and the like. Thus, the gradation of the formed image in the image forming apparatus using such a semiconductor laser is always maintained in character, and a stable high-quality print output is possible. That is, for example, in a full-color printer that forms a full-color image by superimposing toners of magenta, cyan, yellow, and black, it is possible to always obtain a stable and high-quality full-color image.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.

  Since the configuration of the second embodiment is basically the same as the configuration of the first embodiment, in the description of the second embodiment, the same parts as the configuration of the first embodiment are used. Are denoted by the same reference numerals, and the description of the first embodiment is used, and only different portions will be described.

  In the first embodiment described above, in the control state of the graph G1 shown in FIG. 10 when the bias APC is not performed, the minimum pulse width region (10 to 90%) in which the light amount changes linearly is set to 16 steps. In addition to performing the maximum pulse width modulation, the PWM width table 43 in FIG. 3 stores conversion data for making the change in the pulse width increase step non-linear as shown in the B curve in FIG. Is used to correct a non-linear A curve to a linear C curve.

  On the other hand, conventionally, by performing bias APC, a pulse width-light quantity characteristic like a graph G3 shown in FIG. 10 is obtained, and the linearity of the graph G3 is improved to 5 to 95%.

  Therefore, in the second embodiment, bias APC is performed, and minimum / maximum pulse width modulation is performed in the control state of the graph G3 shown in FIG. When minimum / maximum pulse width modulation is performed in the control state of the graph G3, the semiconductor laser exhibits a pulse width-light quantity characteristic like the B curve shown in FIG. 4, and the A curve in the first embodiment. This is the opposite of the pulse width-light quantity characteristics.

  For this reason, in the second embodiment, the PWM width table 43 stores conversion data for making the change in the pulse width increase step non-linear as shown by the A curve in FIG. Thereby, the pulse width-light quantity characteristic of the semiconductor laser can be corrected to a linear C curve.

  In the second embodiment, bias APC is performed during the initialization operation of the printer 700. The subsequent operation at the time of image formation is the same as in the first embodiment.

[Other Embodiments]
Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer of the system or apparatus (or CPU, MPU, or the like). Is also achieved by reading and executing the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention. .

  Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAM, and a DVD. -RW, DVD + RW, magnetic tape, nonvolatile memory card, ROM, etc. can be used. Alternatively, the program code may be downloaded via a network.

  Further, by executing the program code read by the computer, not only the functions of the above embodiments are realized, but also an OS (operating system) running on the computer based on the instruction of the program code Includes a case where the function of the above-described embodiment is realized by performing part or all of the actual processing.

 Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. This includes the case where the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

1 is a block diagram showing an electric circuit configuration in an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is an overview diagram illustrating a mechanical configuration of a printer. It is a block diagram which shows the internal structure of an image process part and a laser unit. It is a figure which shows the relationship between the pulse width of a PWM signal, and the light quantity (integral value) output from a laser diode with three curves. It is a figure which shows an example of the conversion data stored in a PWM width table. 4 is a timing chart showing an image signal transfer clock PVCLK, a modulation signal PD, and a sampling clock SCLK. It is a top view which shows the structure of the conventional image forming apparatus. It is a side view which shows the structure of the conventional image forming apparatus. FIG. 9 is a current-light output characteristic diagram of a laser diode showing a relationship between a current supplied to the laser diode shown in FIGS. 7 and 8 and an intensity of light output from the laser diode by the current supply. It is a figure which shows the relationship between the pulse width of the PWM signal which carries out the pulse drive of the laser diode, and the light quantity (integral value) output from a laser diode. It is a block diagram which shows the structure of the conventional PWM circuit which produces | generates a PWM signal from image data.

Explanation of symbols

41 line memory (FIFO (A), first storage means)
42 Line memory (FIFO (B))
43 PWM width table (generation means)
44 PWM circuit (generation means)
45 Comparison operation part (change means)
46 Data converter (data converter)
47 Pulse width detector (detection means)
48 Laser driver (light emitting means)
49 Semiconductor laser (light emitting means)
50 Photodiode (detection means)
700 Printer 701 Printer Controller 702 Printer Engine 703 Image Processing Unit 704 Laser Unit

Claims (7)

In an image forming apparatus that forms an image based on input multivalued image data,
A storage means for storing the multivalued image data,
Generating means for generating a pulse signal according to the multi-value image data stored in the storage means ;
A light emitting means for flashing and emitting light based on the pulse signal generated by the generating means;
Detecting means for detecting a pulse width which is a lighting continuation period of light emitted by the light emitting means;
Data conversion means for converting the pulse width detected by the detection means into digital data;
Wherein a data converting means and said digital data converted by the calculating means to the comparison image data difference between the multi-valued image data stored in said storage means,
The generation means stores the pulse width data corresponding to the multi-value image data and the comparison image data, with the multi-value image data as an upper bit address value and the comparison image data as a lower bit address value. An image forming apparatus, wherein the pulse width data is read from the look-up table according to the multi-value image data and the comparison image data, and the pulse signal is generated based on the pulse width data . The image forming apparatus according to claim 1, wherein the generation unit and the calculation unit are housed in the same integrated circuit. The detection means includes
Conversion means for receiving the light emitted by the light emitting means and converting it into an electrical signal;
And sampling pulse generating means for generating a sampling pulse having a period shorter than the period of said pulse signal generated by said generating means,
In the lighting duration is detected based on the electrical signal obtained by the conversion means, and the pulse width detection means for detecting the pulse width by counting the number of the sampling pulses generated by said sampling pulse generating means The image forming apparatus according to claim 1, further comprising: 4. The image forming apparatus according to claim 3 , wherein the data conversion unit converts the count value obtained by the pulse width detection unit into data having the same property as the multi-value image data. The image forming apparatus according to claim 1, wherein the generation unit outputs a pulse width modulation signal as the pulse signal according to the pulse width data . In an image forming method for forming an image based on input multi-value image data,
A storing step of storing the multi-value image data in the storage means,
A generation step of generating a pulse signal in accordance with the multi-value image data stored in the storage means ;
A light emitting step which is flash emission in the light emitting means based on the pulse signal generated by said generating step,
A detection step of detecting a pulse width that is a lighting duration of the light emitted by the light emission step ;
A data conversion step of converting the pulse width detected by the detection step into digital data;
A calculation step using a difference between the digital data converted by the data conversion step and the multi-value image data stored in the storage means as comparison image data ,
In the generation step, pulse width data corresponding to the multi-value image data and the comparison image data is held using the multi-value image data as an upper bit address value and the comparison image data as a lower bit address value. An image forming method comprising: reading out the pulse width data from the look-up table according to the multi-valued image data and the comparison image data, and generating the pulse signal based on the pulse width data . In a program for causing a computer to execute an image forming method for forming an image based on input multivalued image data ,
A storing step of storing the multi-value image data in the storage means,
A generation step of generating a pulse signal in accordance with the multi-value image data stored in the storage means ;
A light emitting step which is flash emission in the light emitting means based on the pulse signal generated by said generating step,
A detection step of detecting a pulse width that is a lighting duration of the light emitted by the light emission step ;
A data conversion step of converting the pulse width detected by the detection step into digital data;
A calculation step using a difference between the digital data converted by the data conversion step and the multi-value image data stored in the storage means as comparison image data ,
In the generation step, pulse width data corresponding to the multi-value image data and the comparison image data is held using the multi-value image data as an upper bit address value and the comparison image data as a lower bit address value. A program that reads the pulse width data from the look-up table according to the multi-value image data and the comparison image data, and generates the pulse signal based on the pulse width data .

Images