JP2007083652A - Driving device, led array, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the rate of the contribution of each driving pulse to an exposure energy amount from varying by making a driving current waveform have a sufficient pulse width to a rising time and a fall-down time, and to prevent a large difference from being generated between gradation data to be printed and actual printing result. <P>SOLUTION: This driving device has a gradation data arranging means, a selecting means, and a driving means. In this case, the gradation data arranging means arranges data on first and second lines which are set in a subsidiary scanning direction in response to the gradation data which have been transmitted from a higher rank device. The selecting means selects driving energy which drives an element to be driven in response to the first and second lines. The driving means drives the element to be driven corresponding to the data arranged by the gradation data arranging means for a specified period of time based on the driving energy which has been selected by the selecting means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a driving device, an LED array, and an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic printer, an LED including an LED array in which a plurality of LED (Light Emitting Diode) elements are arranged in order to form an electrostatic latent image based on image data on a photoconductor. A head is used as a light source for exposure. In this case, the LED driving device realizes gradation printing by changing the amount of exposure energy by varying the accumulated time for each driving dot in accordance with a plurality of driving signals having different driving times. It was. A combination of each pulse is selected corresponding to the gradation data of each bit to generate Sd, Sc, Sb, and Sa signals (see, for example, Patent Document 1).

  2 is a diagram showing a circuit structure of a conventional LED head, FIG. 3 is a time chart showing drive control of the conventional LED head, and FIG. 4 is a time chart showing a drive current waveform of the conventional LED element.

  As shown in FIG. 3, a strobe signal HD-STB-N having different pulse widths T8, T4, T2, and T1 is input to the LED head as shown in FIG. 2 from a control circuit (not shown). . When the strobe signal HD-STB-N is received, the CNT circuit of the LED head generates Sd, Sc, Sb, and Sa signals corresponding to the pulse widths T8, T4, T2, and T1, respectively. The logical product of each of these Sd, Sc, Sb and Sa signals and each of the outputs LT1d, LT1c, LT1b and LT1a from the latch circuit is taken, and an LED drive signal is created. In the example shown in FIG. 3, the LED drive signals corresponding to the pulse widths T8 and T1 are generated by the outputs LT1d, LT1c, LT1b, and LT1a from the latch circuit.

FIG. 4 shows the LED drive current waveform in correspondence with the strobe signal HD-STB-N. In this case, four LED drive current pulses are generated according to the different pulse widths T8, T4, T2, and T1.
JP 2001-54959 A

  However, in the conventional driving apparatus, as shown in FIG. 4, there are four LED driving current waveforms according to the pulse widths T8, T4, T2 and T1 of the command pulse of the strobe signal HD-STB-N. It has been divided into. Therefore, there is no problem if the rise time and fall time of the LED drive current are sufficiently smaller than the pulse widths T8, T4, T2, and T1, but otherwise, the LED current waveform of each drive pulse is not affected. Due to the influence of the transition time, as shown by T1 in FIG. 4, a desired current for each drive pulse cannot be obtained. As a result, the ratio of contribution to the exposure energy amount of the image forming apparatus to the photoreceptor varies.

  As a result, a large difference occurs between the gradation data to be printed and the actual printing result, so that it becomes impossible to print with good reproducibility using the gradation data.

  The present invention solves the problems of the conventional drive device, and assumes that the drive current waveform has a pulse width sufficiently large with respect to the rise time and fall time of the drive current, and exposes each drive pulse. Provided are a driving device, an LED array, and an image forming apparatus in which a contribution ratio to an energy amount does not fluctuate and a large difference does not occur between gradation data to be printed and an actual printing result. For the purpose.

  Therefore, in the driving device of the present invention, gradation data arrangement means for arranging data on the first and second lines set in the sub-scanning direction according to the gradation data transmitted from the host device, Selection means for selecting drive energy for driving the driven elements according to the first and second lines, and data arranged by the gradation data arrangement means based on the drive energy selected by the selection means Driving means for driving the driven element corresponding to the predetermined time.

  According to the present invention, the drive current waveform has a pulse width that is sufficiently large with respect to the rise time and fall time of the drive current. For this reason, the contribution ratio of each drive pulse to the exposure energy amount does not fluctuate, and a large difference does not occur between the gradation data to be printed and the actual print result.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The drive device in the present invention is a device that selectively drives a plurality of driven elements. For example, the LED array is used as an exposure light source in an electrophotographic printer, and is used as a printer head in a thermal printer. Can be used to drive various driven devices such as a row of heating resistors, a row of display elements used in a display device, etc. Here, LEDs in an electrophotographic printer are used. The case where it is used to drive the array will be described.

  FIG. 1 is a block diagram showing the configuration of the control circuit of the image forming apparatus according to the first embodiment of the present invention, and FIG. 5 is a time chart showing the operation of the image forming apparatus according to the first embodiment of the present invention. .

  In FIG. 1, reference numeral 11 denotes a print control unit in an electrophotographic printer as an image forming apparatus, which has a microprocessor, a ROM, a RAM, an input / output port, a timer, etc., not shown, and is arranged inside the printer print unit. It is provided and controls the operation of the LED head 27 as an LED array used as a light source for exposure. The image forming apparatus according to the present embodiment is, for example, an electrophotographic printer, a facsimile machine, a copying machine, a copying machine having the functions of a printer, a facsimile machine, and a copying machine. It may be an apparatus, and may form a monochrome image or a color image. In the present embodiment, the case where the image forming apparatus is an electrophotographic printer will be described.

  The print control unit 11 performs sequence control of the entire printer by a control signal SG1, a video signal (one-dimensionally arranged dot map data) SG2 from a host controller (not shown) as a host device, and performs a printing operation. To do.

  As shown in FIG. 1, the control circuit of the image forming apparatus further includes a charging high-voltage power supply 12, a transfer high-voltage power supply 13, a developing device 14, a transfer device 15, a driver 16, a driver 17, and a development / transfer process motor. (PM) 18, paper feed motor (PM) 19, paper inlet sensor 21, paper outlet sensor 22, paper remaining amount sensor 23, paper size sensor 24, fixing device temperature sensor 25, fixing device 26 having heater 26a and LED A head 27 is provided. Each is controlled by the print control unit 11. The developing unit 14 and the transfer unit 15 are controlled by the print control unit 11 via the charging high-voltage power source 12 and the transfer high-voltage power source 13, respectively. The development / transfer process motor 18 and the paper feed motor 19 are controlled by the print controller 11 via drivers 16 and 17, respectively.

  When the print instruction is received by the control signal SG1, the print controller 11 first detects whether or not the fixing device 26 including the heater 26a is within a usable temperature range by the fixing device temperature sensor 25. If the temperature is not within the usable temperature range, the heater 26a is heated to heat the fixing device 26 to a usable temperature. Next, the print controller 11 rotates the development / transfer process motor 18 via the driver 16 and simultaneously turns on the charging high-voltage power supply 25 by the charge signal SGC to charge the developing device 14.

  Then, the presence / absence and type of paper (not shown) set is detected by the paper remaining amount sensor 23 and the paper size sensor 24, and paper feeding suitable for the paper is started. Here, the paper feed motor 19 can be rotated in both directions via the driver 17, and the set paper is set in advance until the paper suction sensor 21 detects the paper feed motor 19 in the reverse direction first. Transport the specified amount. Subsequently, the paper feed motor 19 is rotated forward to convey the paper to a printing mechanism (not shown) inside the printer.

  Subsequently, when the paper is transported to a printable position, the print control unit 11 transmits a timing signal SG3 (including a main scanning synchronization signal and a sub-scanning synchronization signal) to the host controller, and a video signal SG2 is received. The video signal SG2 edited for each page in the upper controller and received by the print control unit 11 is transferred to the LED head 27 as the print data signal HD-DATA3-0. Each of the LED heads 27 is formed by arranging a plurality of LEDs as light emitting elements that are driven elements provided for printing one dot (pixel). In the present embodiment, the LED head 27 is capable of printing gradation data consisting of 4 bits per pixel. For this reason, the LED head 27 is provided with four data lines.

  When the print control unit 11 receives the video signal SG2 for one line, the print control unit 11 transmits the latch signal HD-LOAD to the LED head 27 and holds the print data signals HD-DATA3 to 0 in the LED head 27. Thereby, the print control unit 11 can perform printing on the print data signals HD-DATA 3 to 0 held in the LED head 27 even while the next video signal SG2 is being received from the host controller. HD-CLK is a clock signal for transmitting print data signals HD-DATA 3 to 0 to the LED head 27, and HD-STB-N is a strobe signal.

  Furthermore, transmission / reception of the video signal SG2 is performed for each print line. Here, the information printed by the LED head 27 is formed into a latent image as a dot with an increased potential on a photosensitive drum (not shown) as a photosensitive member charged to a negative potential. Then, in the developing device 27, the toner for image formation charged to a negative potential is electrically attracted to each dot by the attraction force to form a toner image.

  Thereafter, the toner image is sent to the transfer device 15. On the other hand, the positive voltage high-voltage power supply 13 is turned on by the transfer signal SG4, and the transfer device 15 transfers the toner image onto the paper that passes through the gap between the photosensitive drum and the transfer device 15. Then, the sheet having the transferred toner image is conveyed to and brought into contact with a fixing device 26 including a heater 26a, and the toner image is fixed on the paper by the heat of the fixing device 26. The sheet on which the toner image has been fixed is further conveyed and discharged from the printer printing mechanism to the outside of the printer through the sheet discharge port sensor 22.

  Note that the printing control unit 11 corresponds to the detection of the paper size sensor 24 and the paper inlet sensor 21 and transfers the voltage from the transfer high-voltage power supply 13 only while the paper is passing through the transfer device 15. Apply to. When printing is completed and the paper passes through the paper discharge sensor 22, printing of the voltage to the developing device 14 by the charging high-voltage power supply 12 is finished, and at the same time, the rotation of the development / transfer process motor 18 is stopped. When further printing is performed, the above-described operation is repeated.

  Next, the LED head 27 will be described.

  FIG. 6 is a diagram showing a circuit configuration of the LED head according to the first embodiment of the present invention.

  In the present embodiment, the LED head 27 has a plurality of, for example, 26 driver ICs 30 and LED arrays 36, and one control voltage generation circuit 40. Each driver IC 30 includes an LED drive circuit 31 as a drive unit, an AND circuit 32, a latch circuit 33, a shift register 34 as a gradation data arrangement unit, and a control circuit 35. The control voltage generation circuit 40 includes a control voltage change circuit 41, an AND circuit 42, and a control circuit 43 as selection means.

  As shown in FIG. 6, the print data signals HD-DATA 3 to 0 are input to the LED head 27 together with the clock signal HD-CLK. Here, if the printer in this embodiment is a printer capable of printing A4 size at 600 dots per inch, for example, bit data for 4992 dots is not shown in the flip-flop circuits FF1a to FF1d, FF2a to FF2d,..., FF4992a to FF4992d are sequentially transferred through the shift register 34.

  Next, a latch signal HD-LOAD is input to the LED head 27, and the bit data is latched by each latch circuit 33. Subsequently, among the light emitting elements LD1, LD2,..., LD4992 (not shown) included in the LED array 36, the bit data and the strobe signal HD-STB-N as the print drive signal are at a high level. The one corresponding to the dot data is turned on.

  Next, the control voltage generation circuit 40 will be described.

  FIG. 7 is a diagram showing a configuration of a part of the control voltage generation circuit according to the first embodiment of the present invention, and FIG. 8 shows the control voltage change circuit in the control voltage generation circuit according to the first embodiment of the present invention. It is a figure which shows a circuit structure.

  FIG. 7 shows circuit configurations of the AND circuit 42 and the control circuit 43 in the control voltage generation circuit 40, and the AND circuit 42 includes AND circuits 42a to 42d. One end of each of the AND circuits 42a to 42d is connected to each of the LED drive current control signals HD-IDAT3 to 0, and the other end is turned on / off of the LED output from the control circuit 43 that controls the LED drive time. Are connected to the signals Sa to Sd. Outputs S3 to S0 of the AND circuits 42a to 42d are input to the control voltage changing circuit 41. In addition, as shown in FIG. 14 described later, one strobe signal HD-STB-N is input to one line in the circuit shown in FIG. Are changed, thereby changing the output terminal VOUT.

  FIG. 8 shows an internal circuit of the control voltage changing circuit 41 in the control voltage generating circuit 40, where r0 to r15 are resistors and 50 is an analog multiplexer. As shown in FIG. 8, the terminal to which the reference voltage VREF is applied from a reference voltage generation circuit (not shown) is connected to one end of a series connection circuit of resistors r0 to r15, while being connected to the analog multiplexer 50 as V15. Is output.

  The analog multiplexer 50 includes inverter circuits 51 a to 51 h, and the inverter circuits 51 a to 51 h include a plurality of P channel MOS transistors 52 and N channel MOS transistors 53. Then, one of 16 voltages applied to the 16 input terminals P0 to P15 is selected according to the logic signal level input to the S0 to S3 terminals, and the voltage level is output as an analog value to the output terminal. It is an analog switch that outputs from VOUT. In the present embodiment, description will be made assuming that four voltage levels are used.

  Next, the LED drive circuit 31 will be described.

  FIG. 9 is a diagram showing a circuit configuration of the LED drive circuit according to the first embodiment of the present invention.

  In FIG. 9, 61 is an inverter circuit, 62a to 62d are NAND circuits, 63 and 64 are P-channel MOS transistors, 65 is an N-channel MOS transistor, and 66 is an LED drive electrode pad for connection to the electrode pad of the LED. .

  In this case, a command signal for LED driving corresponding to the strobe signal HD-STB-N is connected to the S terminal of the LED driving circuit 31, and the command signal is logically inverted by the inverter circuit 61, and NAND circuits 62a to 62d. Is supplied to one of the input terminals. The other input terminals of the four NAND circuits 62 a to 62 d are connected to four signals output from the latch circuit 33. Signals for this purpose are shown in FIG. 9 as D3 to D0. On the other hand, an inverter circuit is formed by P-channel MOS transistor 63 and N-channel MOS transistor 65 arranged above and below. The source terminal of the P-channel MOS transistor 63 constituting the inverter circuit is connected to the reference voltage VREF, and the source terminal of the N-channel MOS transistor 65 is connected to the potential VIN. This potential VIN is obtained from the output terminal VOUT of the analog multiplexer 50 described above.

  Each two-stage inverter circuit composed of the P-channel MOS transistor 63 and the N-channel MOS transistor 65 is connected in cascade and drives the gate terminal of the P-channel MOS transistor 64, respectively. The source terminal of the P-channel MOS transistor 64 is connected to the reference voltage VREF, and the drain terminal is connected to the D0 output pad as the LED driving electrode pad.

  Next, the operation of the drive device in the present embodiment will be described. First, static characteristics of the P-channel MOS transistor will be described.

  FIG. 10 is a graph showing the static characteristics of the P-channel MOS transistor for driving the LED in the first embodiment of the present invention.

FIG. 10 shows static characteristics under conditions where the horizontal axis represents the gate-source voltage V _GS of the P-channel MOS transistor, the vertical axis represents the drain current ID, and the drain-source voltage V _DS is constant. Is shown. The operating point of the P-channel MOS transistor is set so as to operate in the saturation region of the MOS characteristics. In this situation, the gate-source voltage V _GS and the drain current ID of the P-channel MOS transistor are expressed by the following equation (1).
ID = β (W / L) (V _GS −Vt) ² Formula (1)
Here, β is a constant, W is the gate width of the transistor Tr1, L is the gate length of the P-channel MOS transistor, and Vt is the threshold voltage of the P-channel MOS transistor.

  In the LED drive circuit 31 having the circuit configuration as shown in FIG. 9, first, assume that D0, which is an output signal of the latch circuit 33, is high level and the S terminal transitions to low level for LED drive. . Then, the output of the inverter circuit 61 becomes High level, and the output of the NAND circuit 62a transits to Low level. As a result, the gate terminal level of the P-channel MOS transistor 64 obtained via the two-stage inverter circuit becomes a low voltage level, which is almost equal to the voltage value of the terminal VIN.

As a result, the voltage V _GS between the gate and the source applied to the P-channel MOS transistor 64 is a value obtained by subtracting the potential of the terminal VIN from the reference voltage VREF. Therefore, during LED driving, a driving current corresponding to the gate-source voltage V _GS shown in FIG. The drain current is expressed by the following equation (2) when the gate-source voltage is V _GS0 .
ID0 = β (W0 / L) (V _GS0 −Vt) ² Formula (2)
When the gate-source voltage V _GS is changed in 16 ways from V _GS0 to V _GS15 , the drain current can be changed in 16 ways for each V _GS . ) To (5) can be obtained.
ID0 = β (W0 / L) (V _GS1 −Vt) ² Formula (3)
ID0 = β (W0 / L) (V _GS7 −Vt) ² Formula (4)
ID0 = β (W0 / L) (V _GS15 −Vt) ² Formula (5)
Similarly, 16 drain currents can be obtained for each P-channel MOS transistor 64.

  Next, the operation of the print data transfer method of the LED head 27 will be described.

  FIG. 11 is a time chart showing the print data transfer method of the LED head in the embodiment of the present invention.

  As shown in FIG. 11, the latch signal LOADI is set to a low level, and gradation data consisting of 4 bits per pixel is input via each terminal of DATAI3 to DATAI0, and by 4992 clock signal (CLKI) pulses. Perform shift transfer. When the transfer is completed, a latch signal LOADI is generated, and the data transferred to the shift register 34 is latched in the latch circuit 33. Next, when the strobe signal STB-N and the LED drive current control signals HD-IDAT3 to 0 are input, the voltages corresponding to the LED drive current control signals HD-IDAT3 to 0 are set in the control voltage generation circuit 40, respectively. It is generated for each print line and supplied to the driver IC 30. The driver IC 30 generates an LED drive current according to the pulse width of the strobe signal STB-N and the line drive voltage as the voltage supplied from the control voltage generation circuit 40.

Next, a method for generating the above-described gate-source voltage V _GS will be considered. Here, as an example, a case where the gradation data indicated by 4 bits is “11” (binary “1011”) will be considered.

  In the control voltage changing circuit 41 having the circuit configuration as shown in FIG. 8, since the currents flowing through the resistors r0 to r15 are equal, the potentials of the output voltages V0 to V15 have a relationship in which the potential drops monotonously. can get. Therefore, one of the potentials of the output voltages V0 to V15 is selected and output from the output terminal VOUT, and applied to the gate of the P-channel MOS transistor 64 as the potential VIN of the LED drive circuit 31 shown in FIG. As a result, the drain current of the P-channel MOS transistor 64 can be adjusted to 16 levels. In this way, it can be seen that the LED drive current can be adjusted in 16 steps for each print line by the control signal of the LED drive current. In the present embodiment, only four voltage levels are used.

  FIG. 12 is a graph showing the relationship between exposure energy amount and print density in the first embodiment of the present invention, and FIG. 13 shows the relationship between gradation data and drive current in the first embodiment of the present invention. It is a graph.

  FIG. 12 shows the relationship between the exposure energy amount irradiated to the photosensitive drum by the LED element and the print density after printing obtained thereby, and FIG. 13 shows the input in the LED head 27 for gradation printing. The relationship between the gradation data, the LED drive current control signal, and the LED drive current obtained thereby is shown.

  In the present embodiment, the driving time of each dot of the LED head 27 is the same. Further, since the light emission power is obtained according to the LED drive current, the exposure energy amount is also determined according to the LED drive current value. Therefore, in FIGS. 12 and 13, the numerical value axis of the exposure energy amount and the numerical value axis of the drive current are shown in association with each other.

  FIG. 14 is a time chart showing the LED drive current waveform in the first embodiment of the present invention.

  FIG. 14 shows a drive current waveform of an LED element, strobe signal HD-STB-N, LED drive current control signal input to control voltage generation circuit 40, output of control voltage generation circuit 40, gradation It is shown corresponding to the data. In the present embodiment, as shown in FIG. 14, four LED drive current waveforms having the same pulse width but different current values or voltage values are generated.

  In this case, a voltage corresponding to HD-DATA3 is generated and inputted to the output terminal VOUT by the first STB of the first line. In this embodiment, since HD-DATA3 = "1", the output pad is driven by this voltage. Further, a voltage corresponding to HD-DATA2 is generated and inputted to the output terminal VOUT by the second STB of the second line. In this embodiment, since HD-DATA2 = "0", the output pad is not driven. Further, a voltage corresponding to HD-DATA1 is generated and inputted to the output terminal VOUT by the third STB of the third line. In the present embodiment, since HD-DATA1 = "1", the output pad is driven, and is matched with the driving for the HD-DATA3. Hereinafter, the same applies to the fourth STB of the fourth line.

  Thus, the driven energy is combined by the voltages corresponding to HD-DATA 3, 1, 0, and the gradation data “11” is output.

  As described above, the LED head 27 in the present embodiment can change the control voltage for the driving device for each printing line by the control signal for the LED driving current, Can be generated.

  Thus, in the present embodiment, the LED drive current waveform has a pulse width that is sufficiently larger than the rise time and fall time of the LED drive current. Therefore, due to the influence of the transition time of the LED drive current waveform with respect to each drive pulse, the ratio of contribution to the exposure energy amount to the photosensitive drum with respect to each drive pulse rarely varies.

  Thus, there is no great difference between the gradation data to be printed and the actual printing result, and printing can be performed with good reproducibility using the gradation data.

  Next, a second embodiment of the present invention will be described. In addition, about what has the same structure as 1st Embodiment, the description is abbreviate | omitted by providing the same code | symbol. The description of the same operation and the same effect as those of the first embodiment is also omitted.

  First, the LED head 27 will be described.

  FIG. 15 is a diagram showing a circuit configuration of an LED head according to the second embodiment of the present invention, and FIG. 16 is a diagram showing a partial structure of a control voltage generating circuit according to the second embodiment of the present invention.

  As shown in FIG. 15, in the present embodiment, the control voltage generation circuit 40 further includes a latch circuit 44 and a shift register 45 in addition to the configuration of the control voltage generation circuit 40 in the first embodiment. It has the structure made. Since the configuration of other points is the same as that of the first embodiment, description thereof is omitted.

FIG. 16 shows the structures of the AND circuit 42, the control circuit 43, the latch circuit 44, and the shift register 45 in the control voltage generation circuit 40. The shift register 45 includes flip-flop circuits _{FF V3a ~FF v3d, FF v2a ~FF} v2d, consists FF _v1a to ff _V1d and _FF v0a ~FF v0d, similarly to the shift register 34 in the driver IC 30, the bit data sequentially Forward. The bit data, a latch signal HD-LOAD, the latch circuit _{LT v3a ~LT v3d, LT v2a ~LT} v2d, is latched by the LT _v1a to LT _V1d and _LT v0a ~LT v0d.

Then, the AND circuit 42a~42d are respectively located four, one end of each of AND circuits 42a~42d the latch circuit _{LT v3a ~LT v3d, LT v2a ~LT} v2d, LT v1a ~LT v1d and _LT v0a ~LT v0d The other end is connected to signals Sa to Sd for commanding on / off of the LED output from the control circuit 43 that controls the LED driving time. The outputs S3 to S0 of the AND circuit are input to the control voltage changing circuit 41. Since other configurations are the same as those in the first embodiment, description thereof is omitted.

  In the present embodiment, as shown in FIG. 15, the control signal HD-IDAT is not used. Therefore, instead of using the signal line of the control signal HD-IDAT, S0 to S4 designation data corresponding to each line is added to the head of the head data for one line and transmitted to the head.

  In this case, data corresponding to (* 1) in FIG. 14 is added to the head of the data on the first line (0111). Data corresponding to (* 2) in FIG. 14 is added to the head of the data on the second line (1011). Further, data corresponding to (* 3) in FIG. 14 is added to the head of the data on the third line (1101). Furthermore, data corresponding to (* 4) in FIG. 14 is added to the head of the data on the fourth line (1110). Data corresponding to (* 1) in FIG. 14 is added to the head of the data on the fifth line (0111).

  Next, the operation of the drive device in the present embodiment will be described. Here, the operation of the print data transfer method of the LED head 27 will be described.

  FIG. 17 is a time chart showing the operation of the LED head print data transfer method according to the second embodiment of the present invention.

  As shown in FIG. 17, the latch signal LOADI is set to a low level, and gradation data consisting of 4 bits per pixel and 4 bits of line drive voltage control data are input via the DATAI3 to DATAI0 terminals. Shift transfer is performed by 4992 + 4 = 4996 clock signal (CLKI) pulses. When the transfer is completed, a latch signal LOADI is generated, and the data transferred to the shift registers 34 and 45 is latched in the latch circuits 33 and 44. Next, when the strobe signal STB-N is input, a voltage corresponding to the line drive voltage control data is generated for each print line in the control voltage generation circuit 40 and supplied to the driver IC 30. Then, the driver IC 30 generates an LED drive current according to the pulse width of the strobe signal HD-STB-N and the line drive voltage supplied from the control voltage generation circuit 40.

  Since other operations of the drive device in the present embodiment are the same as those in the first embodiment, the description thereof is omitted.

  As described above, the LED head 27 according to the present embodiment can change the control voltage for the drive device for each print line according to the drive voltage control data included in the print data, so that the drive currents of different magnitudes can be obtained. It can be generated for each printing line. Further, gradation can be expressed by the applied data without using the signal line of the control signal HD-IDAT, and the control becomes easy.

  Thus, in the present embodiment, the LED drive current waveform has a pulse width that is sufficiently larger than the rise time and fall time of the LED drive current. Therefore, due to the influence of the transition time of the LED current waveform with respect to each drive pulse, the ratio of contribution to the exposure energy amount to the photosensitive drum with respect to each drive pulse rarely varies.

  Thus, there is no great difference between the gradation data to be printed and the actual printing result, and printing can be performed with good reproducibility using the gradation data.

  In this embodiment, the same effect as in the first embodiment can be realized with a smaller number of external input signals.

  In the first and second embodiments, in addition to the LED array in the electrophotographic printer described above, a column of exothermic antibodies in a thermal printer or a column of display elements in a display device is selectively used. It can also be used with respect to a driving device to be driven.

  The present invention is not limited to the above-described embodiment, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a control circuit of the image forming apparatus according to the first embodiment of the present invention. It is a figure which shows the circuit structure of the conventional LED head. It is a time chart which shows the drive control of the conventional LED head. It is a time chart which shows the drive current waveform of the conventional LED element. 3 is a time chart illustrating the operation of the image forming apparatus according to the first embodiment of the present invention. It is a figure which shows the circuit structure of the LED head in the 1st Embodiment of this invention. It is a figure which shows the structure of a part of control voltage generation circuit in the 1st Embodiment of this invention. It is a figure which shows the circuit structure of the control voltage change circuit in the control voltage generation circuit in the 1st Embodiment of this invention. It is a figure which shows the circuit structure of the LED drive circuit in the 1st Embodiment of this invention. It is a graph which shows the static characteristic of the P channel MOS transistor for LED drive in the 1st Embodiment of this invention. It is a time chart which shows the print data transfer method of the LED head in embodiment of this invention. It is a graph which shows the relationship between the exposure energy amount and printing density in the 1st Embodiment of this invention. It is a graph which shows the relationship between the gradation data and drive current in the 1st Embodiment of this invention. It is a time chart which shows the LED drive current waveform in the 1st Embodiment of this invention. It is a figure which shows the circuit structure of the LED head in the 2nd Embodiment of this invention. It is a figure which shows the structure of a part of control voltage generation circuit in the 2nd Embodiment of this invention. It is a time chart which shows operation | movement of the printing data transfer method of the LED head in the 2nd Embodiment of this invention.

Explanation of symbols

27 LED head 31 LED drive circuit 34 shift register 36 LED array 41 control voltage change circuit

Claims (6)

(A) gradation data arrangement means for arranging data on the first and second lines set in the sub-scanning direction according to the gradation data transmitted from the host device;
(B) selection means for selecting drive energy for driving the driven element according to the first and second lines;
(C) a driving device having driving means for driving a driven element corresponding to the data arranged by the gradation data arranging means for a predetermined time based on the driving energy selected by the selecting means; . The drive device according to claim 1, wherein the selection unit selects a magnitude of a drive voltage. The driving apparatus according to claim 1, wherein the selection unit selects a magnitude of a driving current. (A) gradation data arrangement means for arranging data on the first and second lines set in the sub-scanning direction according to the gradation data transmitted from the host device;
(B) selection means for selecting drive energy for driving the light emitting element according to the first and second lines;
(C) An LED array comprising driving means for driving a light emitting element corresponding to the data arranged by the gradation data arranging means for a predetermined time based on the driving energy selected by the selecting means. An image forming apparatus using the driving device according to claim 1. An image forming apparatus using the LED array according to claim 4.

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