JP3019334B2 - Electrophotographic printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] An electrophotographic printer capable of adjusting an output image density according to an increase or a decrease in power of a light source that outputs a light beam. The driving means for driving and controlling the light source according to the video signal is intended to provide
First and second delay circuits for delaying a video signal, an inversion circuit for inverting an output of the second delay circuit, and a first gate to which the delay output of the first delay circuit and the video signal are input Circuit, an AND gate circuit to which an output of the inverting circuit and a video signal are inputted, and a transistor for supplying a drive current to the light emitting source, wherein an output of the first gate circuit is inputted to a base side of the transistor. The output of the AND gate circuit is input to the collector of the transistor.

[Industrial applications]

The present invention relates to an electrophotographic printer, and more particularly, to an electrophotographic printer capable of adjusting an image density according to an increase or a decrease in power of a light source that outputs a light beam.

(Prior art)

Electrophotographic printers capable of adjusting the image density as described above have been proposed in JP-A-61-28966 and JP-A-61-25161.

[Problems to be solved by the invention]

However, in the above-described electrophotographic printer, if the cycle of the basic clock is shortened to cope with the high speed, and the drive current at the time of the rising of the pulse drive signal is increased to compensate for the response delay of the light source such as the semiconductor laser, There is a problem that the aspect ratio of the line width changes according to the increase or decrease of the power for driving the light source, and the image quality is deteriorated.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic printer in which an aspect ratio of a line width does not change in view of the above-described conventional problems.

[Means for solving the problem]

The object is to provide an endless photoconductor, a charging unit for charging the photoconductor, a light source for generating a light beam,
Driving means for controlling the driving of the light source according to a video signal; scanning means for scanning the light beam along a charged photoreceptor to form an electrostatic latent image; and developing the electrostatic latent image An electrophotographic printer comprising: a developing unit; and a transfer unit that transfers the developed image onto a sheet, wherein the driving unit includes first and second delay circuits that delay the video signal, An inverting circuit for inverting the output of the second delay circuit; a first gate circuit to which the delayed output of the first delay circuit and the video signal are input; and an output of the inverting circuit and the video signal. An AND gate circuit that is input, a transistor that supplies a drive current to the light emitting source,
Wherein the output of the first gate circuit is input to the base of the transistor, and the output of the AND gate circuit is connected to the collector of the transistor.
This is achieved by providing an electrophotographic printer characterized by the following.

[Action]

That is, in the present invention, the time for increasing the drive current is set by the first delay circuit, and the time for adjusting the beam diameter is set by the second delay circuit. The line width ratio between the vertical line and the horizontal line does not change according to the change in the driving power, and the printing quality does not deteriorate.

〔Example〕

(A) Description of the configuration of the electrophotographic printer FIG. 3 is an overall configuration diagram of the electrophotographic printer to which the present invention is applied.

As shown in the figure, the electrophotographic printer includes a paper feeding unit 1 for feeding paper, a printing unit 2 for printing on fed paper PP using an electrophotographic method, and The apparatus includes a discharge unit 3 that discharges sheets and a stacker 4 that stores the discharged sheets.

The paper cassette 10 stores paper PP to be printed (for example, cut paper) PP, and the paper cassette 10 is provided so as to be able to be inserted and removed in the left direction in the figure.

The paper PP in the paper cassette 10 is fed out by the pick roller 11, and then is fed to the printing unit 2 through the feeding path 15 by the feeding rollers 12, 13, and 14.

The feeding path 15 is a path that feeds the paper PP from the paper cassette 10 to feeding rollers (referred to as standby rollers) 13 and 14,
On the other hand, the insertion port 16 is for an operator to manually insert a print medium such as paper into the position of the feeding path 15 and the standby roller 13.

The photosensitive drum 20 is rotatably provided in the direction of the arrow, and forms an electrostatic latent image on the photosensitive layer on the surface. The charger 21 uniformly charges the photosensitive drum 2 in the axial direction thereof, and the optical unit 22 scans the laser light from a laser light source modulated in accordance with a video signal along the axial direction of the photosensitive drum 20. Irradiates the charged photosensitive drum 20 to form an electrostatic latent image.

The developing device 23 includes a paddle roller 230 that rotates in a counterclockwise direction for stirring the toner and the carrier constituting the developer.
A developing roller 231 that rotates clockwise to form a magnetic brush of developer and develops the electrostatic latent image on the photosensitive drum 20 with toner, a blade 232 for regulating the magnetic brush to a constant height, And with a flow path plate 233 that returns the developer regulated by the blade 232 to the paddle roller 230,
Toner replenisher 234 for replenishing consumed toner
Having.

The transfer charger 24 electrostatically transfers the toner image on the photosensitive drum 20 by giving a charge having a polarity opposite to the charge polarity of the toner to the paper PP sent through the standby roller 13. The static eliminator 25 eliminates the charge on the photosensitive drum 20 after the transfer.

The cleaning mechanism 26 is for cleaning the surface of the photosensitive drum 20, and rotates in the same direction as the photosensitive drum 20,
It has a fur brush 260 for scraping off the toner remaining on the photosensitive drum 20, a scraper 261 for scraping off the toner attached to the fur brush 260, and a discharge screw 262 for discharging the scraped toner.

The heat roller fixing device 27 fixes the paper PP on which the toner image has been transferred by heat, and includes a heat roller 27a and a backup roller 27b.

The paper guide 28 guides the paper PP holding the toner image by electrostatic attraction to the heat roller fixing device 27, and the discharge rollers 30, 31, and 32 discharge the fixed paper PP to the discharge path 33.
And discharge it to the stacker 4.

In this electrophotographic printer, first, a cut sheet PP in a paper cassette 10 is fed out by a pick roller 11 and fed to a feed roller 12.
To the feed roller 13, and in synchronization with writing on the photosensitive drum 20 of the printing unit 2, the cut sheet PP is fed by the feed roller 13.
To the printing unit 2.

In the printing unit 2, the toner image on the photosensitive drum 20 is
PP is transferred. Thereafter, the paper PP is discharged to the stacker 4 by the discharge rollers 30, 31, and 32 of the discharge unit 3.

FIG. 4 is a view showing the mechanism of the optical unit, and the same parts as those in FIG. 3 are denoted by the same reference numerals.

In FIG. 3, an optical unit frame 22a forms a frame of the optical unit 22, and includes a polygon mirror 120, a semiconductor laser 121, a collimator lens 122, an f-θ lens 123, a printed board 124, a reflection mirror 125, an optical fiber 128, and the like. Mounted.

The spindle motor 120a is provided below the optical unit frame 22a, and rotates the polygon mirror 120 by direct drive. Polygon mirror 1
The light beam 22z optically scanned by the optical unit 20 passes through the optical window 22b from the inside of the optical unit frame 22a to the outside (photosensitive drum 20).
Released in the direction. Further, the optical unit frame 22a is covered with the cover 22c, and is sealed.

The optical path length expanding mirror 129a is composed of a pair of reflecting mirrors, and turns the light beam from the f-θ lens 123 back to increase the optical path length and widen the scanning width. Output reflection mirror
Reference numeral 129b reflects the scanning light beam from the polygon mirror 120 via the f-θ lens 123 and the optical path length expanding mirror 129a, and emits it from the optical window 22b of the optical unit frame 22a to the outside.

That is, in the optical unit frame 22a, the polygon mirror 120, the semiconductor laser 121, the collimator lens 122,
An f-θ lens 123, an optical path length expanding mirror 129a, and an output reflection mirror 129b are provided as an optical scanning system, and a light beam from the semiconductor laser 121 is reflected on a mirror surface of a polygon mirror 120 via a collimator lens 122, and f -Θ lens 123,
The light is output from the optical window 22b via the optical path length expansion mirror 129a and the output reflection mirror 129b.

The reflection mirror 125 is provided at the left end of FIG. 4 (A), while one end of the optical fiber 128 is connected to the start detection position (that is, the light at the left end position of the scanning light beam from the polygon mirror 120). Position to enter through)
Is fixed at the start detection position by a fixing tool 128a fixed to the start position. The optical fiber 128 is an optical path length expanding mirror 129a.
To the lower part of the board, and the other end is printed circuit board 124.
Is fixed to the fixing device 128b.

On the printed board 124, a light receiving element 126, a stabilizing circuit 127a, and a monitor circuit 124a which are arranged close to the other end of the optical fiber 128 are arranged.

(B) Description of one embodiment FIG. 1 is an explanatory diagram of an embodiment of the present invention, and FIG. 2 is an operation time chart.

In the figure, a print density setting switch 40 is provided on an opter panel above the insertion port 16 of the electrophotographic printer shown in FIG. 3, and is manually operated by an operator to set an image density desired by the operator. "1" ~
The value “8” is set.

Analog multiplexer 41 is specified by 3-bit output of the density setting switch 40 of the ladder resistor group each divided voltage divided by R _c (additional voltage) V _t1 ~V _t8 applied to the input terminal 01 to 08 Selectively outputs the terminal voltage as an additional voltage.

The summing amplifier 42 generates an input resistor R ₅ via an input resistor R ₆ and the base voltage V _D0 applied via adding additional voltage V _D1 ~V _D8 given by the control voltage VD.

As a result, the control voltage VD corresponding to the print density set by the operator is output from the addition amplifier 42.

On the other hand, the video signal * VIDEO supplied from the host device in synchronization with the basic clock CLK is logically inverted by the inverting circuit 43 to become a VIDEO signal.

This video signal VIDEO is at a high level when a black dot is formed on the photosensitive drum 20, and is at a low level when a white dot is formed.

Therefore, as shown in FIG. 2, time t is the time required to output one dot, and when outputting two dots, as shown by the dotted line in FIG. Thus, the semiconductor laser is driven.

In this time t, the resolution is 240 dpi (the beam diameter is about 96 μm).
m), and about 166.7 ns when the resolution is 400 dpi (beam diameter is about 53 μm).

Next, the VIDEO signal is input to delay circuits 44 and 45, respectively. The delay circuit 44 has a delay time DEL1 (duty value), and the delay circuit 45 has a delay time DEL2 (overshoot time).
have.

Since the VIDEO signal and the output of the delay circuit 44 are input to the OR circuit 46, the OR circuit 46 outputs a VDEO signal longer than the VIDEO signal by the delay time DEL1.

This VDEO signal consists of 100Ω resistors 48a, 48b and a diode.
48c adds the bias output of the addition amplifier 42 to the base of the transistor 47, and supplies the drive current i _LD from the + 49V power supply 49 to the laser diode 50.
Note that this laser diode 50 is an LT made by Sharp.
The 026MF type was used.

On the other hand, the delay output of the delay circuit 45 is inverted by the inversion circuit 51 and input to one input terminal of the AND circuit 52.

Since the VIDEO signal is input to the other input terminal of the AND circuit 52, the AND circuit 52 outputs the HVDEO signal for a delay time DEL2 from the rise of the VIDEO signal.

The HVDEO signal is input to the collector side of the transistor 47 via the 68Ω resistor 53a.

Therefore, while the HVDEO signal is at the high level, the resistor 53b of 22Ω is invalid, and during the low level, the resistors 53a and 53b are connected in parallel, the drive current i _LD of the laser diode 50 flowing through the transistor 47 increases, and the Strength can be increased.

As described above, when the time t for outputting one dot is shortened in order to cope with an increase in the speed and resolution of the electrophotographic printer, the time required for the output light level of the semiconductor laser to reach a predetermined light emission level is shortened. For this reason, a large drive current is made to flow when the VDEO signal rises.

That is, as shown in FIG. 5, when the driving characteristics of the semiconductor laser are assumed to be the driving characteristics as shown in FIG.
When a drive current having a waveform shown by a solid line in FIG. 2B is applied to the semiconductor laser, an optical output shown by a dashed line in FIG. 2C is obtained.

That is, by increasing the drive current value only during the initial overshoot time DEL2 of the drive time t of the semiconductor laser, the time during which the output level of the light beam becomes equal to or higher than the predetermined level can be made substantially equal to the time t. .

However, for example, when the drive current value of the semiconductor laser is changed from the value indicated by the solid line to the value indicated by the dotted line in order to change the print density or the line width, the light output level during the overshoot time is different from that at other times. The change rate is smaller than the increase amount of the light output level.

Therefore, there is a problem that the rate of change of the vertical line width differs from the rate of change of the horizontal line width, and the vertical line and the horizontal line have different line widths.

Therefore, it is necessary to set an overshoot time in which the line widths of the vertical line and the horizontal line do not differ even when the drive current value of the semiconductor laser, that is, the output power of the semiconductor laser is changed.

The present inventors have confirmed through various experiments that the optimal overshoot time is 20 ns to 25 ns regardless of the beam diameter.

That is, the devices A and B having different manufacturing times are used, and the optical unit a having a beam diameter of 96 μm and the beam diameter are
Using a 53 μm optical unit b, experiments were conducted for all combinations thereof to determine the optimal value of the overshoot time.

FIG. 6 is a diagram showing an approximation error between the straight line X _i = T _i and the OD value.

That is, first, the laser power was changed for each overshoot time and duty value, and the change in line width for each laser power was measured by the OD value.

As shown in FIG. 7, the horizontal axis represents the OD value of one horizontal dot line,
The OD value and T _i, taking the OD value of the vertical 1-dot line on the vertical axis,
This OD value was defined as X _i , and approximated to a straight line X _i = aT _i .

As is clear from FIG. 7, when the inclination a = 1, the ratio of the change in the line width due to the laser power is equal in the vertical and horizontal directions. Further, the lateral 1 OD value of the dot lines (corresponding to the laser power) and offset the OD value of the vertical 1-dot line when a "0", the inclination a of the straight line T _i obtained is "1"
And the closer the offset value is to “0”, the smaller the approximation error.

From these points, as the approximation error between the straight line X _i = T _i and the straight line X _i = aT _i obtained by the measurement is smaller, the line width of the vertical line and the horizontal line does not change even when the laser power is changed. It can be called an overshoot time and a duty value.

Therefore, as apparent from FIG. 6, it can be said that the optimum overshoot time is about 20 to 25 ns.

On the other hand, the optimum value of the duty value differs depending on the beam diameter. When the beam diameter is 96 μm, the duty value is about 80 ns and the beam diameter is 53
In the case of μm, about 50 ns is found to be optimal.

Therefore, in the drive circuit shown in FIG. 1, even if the laser power is changed according to the value input from the density setting switch 40, the delay time DEL2 of the delay circuit 45 is set to about 20 to 25 ns. The line width of vertical and horizontal lines does not change,
There is no deterioration in print quality.

At this time, if the beam diameter is 96 μm, the delay circuit
44 delay time DEL1 set to about 80ns, beam diameter 53μm
In this case, it is desirable to set the delay time DEL1 of the delay circuit 44 to about 50 ns.

(3) Description of Another Embodiment FIG. 8 is an explanatory diagram of another embodiment of the present invention, and FIG. 9 is an operation time chart thereof.

The only difference from FIG. 1 is that the OR circuit 46 is replaced by an AND circuit 54.

8, the VDEO signal rises after the delay time DEL1 of the delay circuit 44, is added to the bias output of the addition amplifier 42, is applied to the base of the transistor 47, and is driven from the + 24V power supply 49. The current i _LD is supplied to the laser diode 50.

Then, as in the embodiment shown in FIG.
Since the HVEDO signal is supplied to the open collector output of 47 only during the delay time DEL2 of the delay circuit 45, the time from the rise of the VDEO signal to the delay time DEL1-the delay time DEL2,
The drive current i _LD increases, and the light emission intensity can be increased.

This embodiment is effective when the horizontal line is thicker than the vertical line.

(4) Description of Another Embodiment FIG. 10 is an explanatory diagram of another embodiment of the present invention, and FIG. 11 is an operation time chart thereof.

As shown in the figure, a semiconductor laser which is a laser light source
The laser diode 121 is activated by the modulation circuit 60 in accordance with the video signal VIDEO.

The semiconductor laser 121 is a monitor diode (photodetector) 50a that monitors and receives the light emitted from the laser diode 50.
Is built-in.

The light receiving output of the monitor diode 50a is sampled for a certain section outside the image forming area, and the drive current in the modulation circuit 60 is set based on the value.

That is, first, the received light output of the monitor diode 50a is amplified by the amplifier 61. Thereafter, the comparator 62 compares the output of the amplifier 61 with a light output control signal PC which has been adjusted and set in advance so as to obtain a predetermined image density. The comparator 62 outputs “1” when the output of the amplifier 61 is larger than the optical output control signal PC, and outputs “0” when the output of the amplifier 61 is smaller than the optical control signal PC.

Then, the comparison output of the comparator 62 is sampled by the gate circuit 63 only during the period when the start signal (BD signal in FIG. 11) is BDON.

This start signal is a signal received by the light receiving element 126 as described above, and is input to the gate circuit 63 via a start signal detection circuit (not shown).

The output of the comparator 62 passes through the gate circuit 63 to the light output control unit.
Given to 64. As a result, when the output of the gate circuit 63 is “1”, the light output control unit 64 supplies a drive current value to the modulation circuit 60 so that the light amount level of the output light of the semiconductor laser 121 becomes low (see FIG. ) To change the light control signal LCS). On the other hand, when the output of the gate circuit 63 is “0”, the light output control unit 64 changes the drive current value so that the light amount level increases. Then, the light output control unit 64 holds the drive current value for one scanning period and supplies it to the modulation circuit 60. That is, the BDON period in FIG. 11 is the start of scanning of the light beam and corresponds to a certain period outside the image forming area, and the sample is taken during this period. With this configuration, even if the periphery of the semiconductor laser 121 changes, the semiconductor laser 1
21 light output levels can be kept constant.

In the electrophotographic printer using the semiconductor laser driving circuit configured as described above, when changing the print density, the output of the print density setting circuit 65 is input to the light output control unit 64, and the light output control unit 64 By amplifying the drive current value given to the modulation circuit 60 in accordance with the value specified by the density setting circuit 65, the density can be adjusted.

FIG. 12 is a detailed circuit diagram of the embodiment shown in FIG.

In the figure, the same parts as those in FIGS. 1 and 10 are denoted by the same reference numerals, and the description thereof will be omitted. In addition, the optical output control unit 64 includes an operational amplifier 170 for voltage addition and resistors 171 and 17
It has an addition circuit 17a composed of 2,173,174.

Then, the addition circuit 17a adds the voltage appearing at the terminal Z and the voltage appearing at the terminal Y, and provides an addition output to the base of the transistor 47 in the modulation circuit 60.

The voltage held by the capacitor 180 that holds the voltage for controlling the light output appears at the terminal Y of the adder circuit 17a. This capacitor 180 is composed of a transistor 181 and discharge current setting resistors 182, 183,
Discharge is performed by the discharge circuit 17b composed of the circuit 184.

This capacitor 180 is a charging circuit 1 comprising a transistor 191 and resistors 192, 193, 194 for setting charging and discharging current.
Charging is performed by 7c.

The output of the AND circuit 151 forming the gate circuit 63 is connected to the base of the transistor 191 of the charging circuit 17c via the resistor 192.

A signal obtained by inverting the output of the comparator 62 by the inverting circuit 153 is input to one input terminal of the AND circuit 153, and a BD signal is input to the other input terminal.

Therefore, the AND circuit 151 outputs "1" only when the output of the comparator 62 is "0" during the period when the BD signal is BDON, and the charging circuit 17c charges the capacitor 180 only at this time.

The AND circuit 152 has an inverting circuit 1
The output of the inversion circuit 154 for further inversion is input to the output of 53, and the BD signal is input to the other input terminal.

Therefore, the AND circuit 152 outputs “1” only when the output of the comparator 62 is “0” during the period when the BD signal is BDON, and the discharge circuit 17 b discharges the capacitor 180 only at this time.

As described above, the optical output control unit 64 sets the BD signal to a high level (BDO
If the output of the monitor diode 50a amplified by the amplifier 61 during the period of N) is larger than the optical output control signal PC,
The holding voltage of the capacitor 180 is reduced by the operation of the discharging circuit 17b, and when the output of the monitor diode 50a amplified by the amplifier 61 is smaller than the optical output control signal PC, the holding of the capacitor 180 is performed by the operation of the charging circuit 17c. Increase the voltage.

The holding voltage of this capacitor 180 and the print density setting circuit 65
Are input to the operational amplifier 170 via the addition constant setting resistors 174 and 173, respectively, and are added.

Therefore, the output of the operational amplifier 170 changes according to the output of the addition amplifier 42 corresponding to the print density set by the print density setting switch 40, and the light emission level of the laser diode 50 can be changed.

(5) Description of Still Another Embodiment FIG. 13 is an explanatory diagram of still another embodiment. The difference from FIG. 12 is that the value of the light output control signal PC is changed to the print density setting circuit 65.
In that a gain changing circuit 66 for changing the output according to the output is provided.

This gain changing circuit 66 includes resistors R ₈ and R ₉ and a transistor 67.
The gain of the optical output control signal input to the comparator 62 is changed according to the output of the addition amplifier 42.

(6) Description of Other Embodiments In the embodiment described above, an example in which the invention is applied to an electrophotographic printer has been described. However, the present invention is not limited to this, and a semiconductor laser drive circuit for optical communication, or The present invention can be applied to a drive circuit of another light beam output device.

It goes without saying that the output of the print density setting circuit 65 may be used as it is as the light output control signal.

〔The invention's effect〕

As described above, according to the present invention, the aspect ratio of a light beam can always be kept constant even when the intensity of the light beam changes. The line width between the line and the horizontal line can always be kept in a constant relationship, and the printing quality does not deteriorate.

[Brief description of the drawings]

1 is an explanatory view of one embodiment, FIG. 2 is an operation time chart thereof, FIG. 3 is an explanatory view of a configuration of an electrophotographic printer, FIG. 4 is an explanatory view of an optical unit of FIG. 3, and FIG. FIG. 6 is a diagram illustrating the approximation error between the straight line X _i = Y _i and the OD value. FIG. 7 is a diagram illustrating the relationship between the straight line X _i = Y _i and the straight line X _i = aY _i. FIG. 8 is an explanatory view of another embodiment, FIG. 9 is an operation time chart thereof, FIG. 10 is an explanatory view of another embodiment, FIG. 11 is an operation time chart thereof, FIG. FIG. 10 is a detailed circuit diagram of FIG. 10, and FIG. 13 is an explanatory diagram of still another embodiment. In the figure, 44, 45... Delay circuit 46... OR circuit 47... Transistor 50... Laser diode 51.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/23-1/31 B41J 3/00

Claims (2)

(57) [Claims] An endless photoreceptor; a charging unit for charging the photoreceptor; a light source for generating a light beam; a driving unit for driving and controlling the light source in response to a video signal; Scanning means for scanning along the photoreceptor thus formed to form an electrostatic latent image, developing means for developing the electrostatic latent image, and transfer means for transferring the developed image onto paper. An electrophotographic printer, wherein the driving unit comprises: a first and a second delay circuit for delaying the video signal; an inversion circuit for inverting an output of the second delay circuit; and the first delay circuit. A first gate circuit that receives the delayed output of the inverting circuit and the video signal, an AND gate circuit that receives the output of the inverting circuit and the video signal, and a transistor that supplies a drive current to the light emitting source. The first Electrophotographic printer output of the gate circuit is input to the base side of the transistor, characterized in that formed by input to the collector of the transistor output of the AND gate circuit. 2. A drive circuit for driving a light emitting source in accordance with an on / off signal, comprising: first and second delay circuits for delaying the on / off signal; and inverting an output of the second delay circuit. An inverting circuit, a gate circuit to which the delay output of the first delay circuit and the on / off signal are input, and an AND gate circuit to which the delay output of the inverting circuit and the on / off signal are input, A driving circuit for driving the light emitting source, wherein an output of the gate circuit is input to a base side of the transistor, and an output of the AND gate circuit is connected to a collector side of the transistor.