JP2001315379A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust a light quantity by duty control in a simple circuit structure, to correct a quantity of emission light an SLED by taking all the elements causing variation in the light quantity and to prevent lowering of image quality due to the variation in the light quantity by extracting a stable light quantity region to use it. SOLUTION: It is not necessary to form a continuous triangle wave and it is possible to obtain the stable triangle wave by resetting a CR integrating filter circuit during the period except the activating term of the SLED. The variation of each of the emission points in the SLED is corrected in accordance with exposing energy measured in advance. As the correction is loaded to an SLED driving circuit upon the power-on, it is possible to superpose gradation data therewith when a density signal is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus to which a self-scanning LED is applied as a light source of exposure means for forming an image by exposing a photosensitive member.

[0002]

2. Description of the Related Art As a light source of an exposure device in an image forming apparatus, there is an SLED (Self Scanning LED). This SLED employs a thyristor structure as a portion corresponding to a switch for selectively turning on / off a light emitting point, and by applying this thyristor structure, the switch section can be arranged on the same chip as the light emitting point. Light emitting light source array.

In this SLED, the on / off timing of the switch can be selectively emitted by two signal lines, so that the data line can be shared.
Wiring can be simplified.

As shown in FIG. 12, when the trigger is set to a high level when the thyristor 10 is off, a current Itr flows to the point P, and at the same time, the transistor Q
The current Ib2 flows to the base of No. 2 (Itr ≒ Ib2).
As a result, the transistor Q2 is turned on, and the collector current of the transistor Q2 flows. That is, the base current Ib1 of the transistor Q1 flows, and the transistor Q1 is also turned on.

When the transistor Q1 is turned on, the collector current IC1 of the transistor Q1 flows, the voltage at the point P rises, and the current Itr stops flowing. However, since the collector current Ic1 of the transistor Q1 flows to the base of the transistor Q2 (current Ib2), the ON state of the transistor Q2 is maintained.

As a result, even if the trigger goes low, the transistors Q1 and Q2 maintain the on state. In this state, the voltage VEE is held and the LED
Can be turned on, and a predetermined light amount can be obtained by performing pulse width modulation.

To turn off the thyristor 10, the base current is prevented from flowing through the transistor Q2 even when the transistor Q1 is on. That is, the thyristor 10
In the self-holding state, when the voltage VEE is set to 0 V, the voltage at the point P becomes high impedance, and the electric charge stored in the parasitic capacitance is discharged through the high resistance 12, so that the transistor Q1 and the transistor Q2 are turned off.

Here, the actual operation speed is determined by the Turn On Time (rise time) and the Turn Off Time of each thyristor.
(Fall time). That is, in response to changes in the transfer control clocks (the two control signals) V1 and V2, the time (Turn O) until the thyristor is actually turned on.
n Time) cannot send a data signal (image signal). Further, since the thyristor uses the saturated state of the PNP connection, the Turn Off Time is much longer than the Turn On Time. Therefore, for example, from the Turn Off of the Nth (P is a positive integer) point P to the N + 2nd Turn O
Until n, the N-th LED is turned on until N
The third point P needs to go down.

When an array of light sources is used as in the above configuration, the variation in the light amount at the light emitting points causes streaks in the image, so that it is necessary to correct the variation in the light amount. In particular, when a SELFOC lens array is applied as an optical system, even though the light amount at the light emitting point itself does not vary, the SELFOC lens array itself has structurally irregular transmittance, and as a result, the light amount varies. I do.

For this reason, it has been proposed to turn on each LED by intensity modulation in accordance with an image signal, and to correct the drive current at this time based on correction data for unevenness in the amount of light in the SLED (Japanese Patent Laid-Open No. Hei 10 (1998)). −2970
No. 17).

[0011]

However, when the present invention is applied to a light source of an image forming apparatus or the like, it is necessary to consider variations caused by sources other than the light source (light emission point light amount and selfoc lens array). In this regard, the prior art
Since the correction data is created based on the characteristics of only the SLED, as a result, that is, it is necessary to separately provide a correction unit under image formation.

In the exposure device of the image forming apparatus, the following light amount adjustment is required. The overall light amount is adjusted based on the light amount instruction value included in the image forming process.

That is, in the image forming process, the output light amount of the exposure device is generally reduced in order to keep the output density from changing over time due to a change in sensitivity due to abrasion of the photosensitive member or a change in sensitivity of the photosensitive member due to temperature and humidity. It is necessary to shift. Each light emitting point exposure amount is adjusted according to the gradation signal. In the exposure device using the light emitting array, the light amount variation of the light emitting point is corrected. Image surface unevenness of charging, development and transfer is corrected by the amount of light.

In consideration of the above facts, the present invention enables light quantity adjustment by duty control with a simple circuit configuration, and incorporates all the factors that cause light quantity unevenness, thereby achieving SLE.
It is an object to obtain an image forming apparatus capable of correcting the amount of light emission of D.

In addition to the above objects, an object of the present invention is to provide an image forming apparatus capable of preventing image quality deterioration due to uneven light amount by extracting and using a more stable light amount region.

[0016]

According to the present invention, there is provided an image forming apparatus using a self-scanning LED as a light source of an exposing means for forming an image by exposing a photosensitive member, wherein the self-scanning LED is turned on. To adjust the overall light amount while the main power supply is driven by a constant voltage circuit whose voltage is variable according to a control signal or a constant current circuit whose current is variable according to a control signal. Means, an exposure amount adjusting means for adjusting the exposure amount of each LED based on a gradation signal of each dot corresponding to the image signal, and a correcting means for correcting variation in the light amount of each LED. ing.

In the present invention, the exposure amount adjusting means may output a triangular wave in synchronism with a light emission period of one dot, and the triangular wave may be a triangular wave using a tone signal of each dot as a threshold value. And a pulse width modulation means for emitting light during a period corresponding to the width of the intersection between two sides sandwiching the vertex.

Further, the present invention is characterized in that the triangular wave is a sawtooth wave having the end of each dot as an edge.

According to the present invention, there is provided a constant voltage circuit which varies a main power supply of a self-scanning LED according to a control signal.
Alternatively, it is driven by a constant current circuit that is variable in current according to a control signal, and for example, the entire light amount is adjusted to be constant based on the measurement result of the light amount (density) at the final stage of the device process. Thereby, it is possible to adjust the overall light amount in the machine.

Next, a gradation signal of each dot is generated according to the image signal, and the exposure of each LED is adjusted based on the gradation signal. Further, the variation of the light amount of each LED is corrected by the correction means.

By applying a self-scanning LED,
Since the light quantity control according to each factor can be performed using a common signal line, the device configuration is simplified and high-precision image formation is possible.

Here, the exposure amount adjusting means outputs a triangular wave in synchronism with the emission period of one dot, and a vertex of the triangular wave is set by using a tone signal of each dot as a threshold value. Pulse width modulation means for emitting light during a period corresponding to the width of the intersection between the two sides sandwiched,
The control of the light emission period corresponding to each dot can easily adjust the pulse width by the combination of the triangular wave and the gradation signal.

At this time, a more stable light amount can be obtained by using the latter half of the light emitting period of one dot. That is, the amount of light immediately after the rise of each LED may be unstable, whereas the amount of light is stable immediately before the fall.

[0024]

FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus 100 according to the present embodiment.

The image forming apparatus 100 includes a casing 102
, And the upper surface also serves as the discharge tray unit 104.

In the casing 102, a photosensitive roller 106 is provided at the center thereof. Around the photosensitive drum 106, a charging unit 108 for uniformly charging the surface of the photosensitive drum 106 in a counterclockwise direction from slightly above and rightward, and a self-scanning LED (hereinafter, referred to as SLED) are used. The light source array 110 and the toner tanks 112 of the respective colors of CMYK are provided, and the rotary developing unit 116 and the plurality of rollers 12 are capable of sequentially rotating the toner rolls 114 of the respective colors with the photosensitive drum 106 by rotating.
The intermediate transfer belt 122 and the cleaning unit 12 are wound around the intermediate transfer belt 122 and driven in the direction of arrow A in FIG.
4 is provided.

The photosensitive drum 106 is rotated in the direction of arrow B in FIG.
0, each process of the rotary developing unit 116, the intermediate transfer belt 122, and the cleaning unit 124 is performed.

The lower end of the intermediate transfer belt 124 is a part of a conveyance path of an image forming sheet (hereinafter simply referred to as sheet) 126. At the lower end, the sheet 126
The sheet is nipped and conveyed between the intermediate transfer belt 122 and the roller 118.

A plurality of rollers 118 are disposed on the transport path of the paper 126, and the uppermost paper 126 stacked on the paper feed tray 128 is taken out by the sheet-feeding device 130, and the lower end of the intermediate transfer body 124 is removed. The sheet is conveyed while being contacted by the printer, and is sent out to the discharge tray section 104 via the fixing section 132.

A density sensor 134 is provided at a position facing a part of the conveyance path of the intermediate transfer belt, for example, to detect the density of a test patch (a sample of color and density).

As shown in FIG. 2, the light source array 110
Are a plurality of LEs along the axial direction of the photosensitive drum 106.
It is configured by further arranging a plurality of LED arrays 152 in which D150s are arranged in series. The lighting of the light source array 110 is controlled by a drive circuit 156 (see FIG. 3) which is controlled in the same casing 154.

FIG. 3 shows a driving circuit 1 for the light source array 110.
56 details are shown.

Since the driving circuit 156 is basically a combination of the single driving circuit shown in FIG. 12, a detailed description of the thyristor 10 and the like will be omitted here.

As a trigger for lighting the SLED, the voltage VS is applied to the point P1 (the number following the point P indicates the order of the arranged LEDs) via the resistor 158. Point P of all steps including this point P1
(1 to N (N is a positive integer)) are connected to the base line 161 via the resistors 160, respectively. Base line 1
Reference numeral 61 is designed to maintain a predetermined voltage in the first stage, and to have a potential (Φga) that decreases by a predetermined potential (Vf) as going to each stage.

The points P (1 to N) are connected to the LED 150 on the anode side. Note that the cathode side of the LED 150 is connected to a gradation signal line 163 described later.

Here, as shown in FIG. 4, Φga is the APC based on the detection signal from the density sensor 134.
(Auto power control) 162 is driven by a constant current in response to a light amount instruction value (a constant current drive circuit). That is, the light amount instruction value is converted into an analog value by the DA converter 164, and is connected to the negative input terminal of the first comparator 168 via the resistor 166. The positive input terminal of the first comparator 168 is grounded (GND). The output terminal of the first comparator 168 and the negative input terminal are connected to a resistor 17.
0. As a result, the output of the first comparator 168 changes according to the light amount instruction value and becomes a predetermined voltage.

Here, this output voltage is connected to the plus-side input terminal of the second comparator 172, the minus-side input terminal is connected to the reference voltage source VSS via the resistor 174, and the second comparator 172 Is connected to the MOS transistor 176, a constant current flows through the MOS transistor 176.

In FIG. 4, the driving circuit for Φga is a constant current driving circuit 178, but may be a constant voltage driving circuit 180 as shown in FIG. The circuit configuration may use the output of the first comparator 168 in FIG.
The same reference numerals are given and the description of the configuration is omitted.

As shown in FIG. 3, the emitter of the odd-numbered transistor Q2 is connected to the first control line (V1) 182, and the emitter of the even-numbered transistor Q2 is connected to the second control line (V2) 184. Have been. Further, the points P (1 to N) of each stage are connected to one end of the LED 150,
The other end of the LED 150 is connected to a gradation signal line 163 that outputs a pulse wave serving as a gradation signal of each stage. When the gradation signal line 163 is at a low level (L), if the points P (1 to N) have a predetermined potential, the LED is turned on.

FIG. 6 shows a circuit 200 for generating a pulse waveform sent to the gradation signal line 163.

A floor output from an image processing unit 202 (for example, converting various types of images sent from a recording medium or a communication line into a format corresponding to the image forming apparatus 100 of the present embodiment). The tuning signal (12 bits) is calculated by the integrator 2
04 is input. The correction data (4 bits) held in the correction data holding unit 206 is also input to the integrator 204, and the light emitting point unevenness of each LED 150 is corrected.

The correction gradation signal to which the correction data is added by the integrator is converted into an analog signal (density signal) by the DA converter 208, and the plus of the comparator 210 is input to the input terminal.

On the other hand, branch lines 182A and 184A are connected to control signal lines V1 (Φ1) and V2 (Φ2) output from the timing generation section 212, respectively, and these branch lines 182A and 184A are input to an OR circuit 186. I do. Therefore, the output of the OR circuit 186 becomes active when one of V1 and V2 is active (here, low level). Synchronously with this active period, the triangular wave generating circuit 188 generates a triangular wave,
The signal is input to the negative input terminal of the comparator 210.

This operation is shown in the time chart of FIG. That is, OR of V1 (Φ1) and V2 (Φ2)
A triangular wave is formed in accordance with the signal obtained by taking At this time,
Between each triangular wave, a space a occurs, which is an odd LE.
At the lighting timing of D and the even-numbered LEDs, an interval for sequentially lighting one by one is provided.

The density signal is superimposed on the triangular wave, and the range of the level higher than the density signal in the triangular wave is the actual lighting time, and a pulse waveform to be sent to the gradation signal line 163 can be generated.

The lighting control in the light source array 110 according to the present embodiment in accordance with the gradation signal will be described below.

As shown in FIGS. 8 and 9, by setting Vs to the high level (H), the potential of the point P1 becomes H, and the point P2 connected from the point P1 through the LED 150 is formed.
Is P2 = Vs−Vf2 (due to the voltage drop of the LED). Similarly, point P3 = point P2-Vf, point P4 = point P3
−Vf... Point PN = Point P (N−1) −Vf However, since the saturation occurs at the Φga potential, the voltage does not drop below Φga.

Here, when V1 = low level (L), the thyristor 10 of P1 is turned on.
ΦS → 0V and the potential Φ1 → −Vf of V1. Here, the point P equivalent to the point P1, that is, the odd-numbered point P is 2V
It does not turn on because the potential has dropped in f units.

In this state, by changing VD from H to L, 1
The third LED 150 can be turned on. Also, V
By changing D from L to H, the first LED 150 is turned off, and at this time, the potential ΦD of VD becomes -Vf.

Next, by setting V2 = low level (L), the thyristor 10 of P2 is turned on, and P2 = 0V, P3
= -Vf, P4 = -2Vf. At this time, since the potential Φ2 of V2 becomes −Vf, the even-numbered thyristors 10 after P4 are not turned on.

When the thyristor 10 of P2 is turned on, V1 → H is set so that the first LED 150 is not turned on by the next data signal so that the thyristor 10 of P1 is not turned on.
Turn off 0.

In this state, by changing VD from H to L,
LED2 lights up. At this time, the potential ΦD of VD → −V
f.

Thereafter, the VD is changed from L to H to turn off the second LED 150 (VD potential φD → 0).
V).

Hereinafter, V1 controls the on (lighting) of the odd thyristor 10 (and LED 150), V2 controls the on (lighting) of the even thyristor 10 (LED 150), and sequentially converts the gradation signal to VD. The LED 150 can be set to a light amount corresponding to the gradation signal by sending the LED 150 thereon.

In the present embodiment, the APC 162 that configures the amount of light so that the potential on the surface of the photosensitive drum 106 becomes an appropriate value in accordance with the density value of the inspection patch detected by the density sensor 134 is controlled by Φga. Is going. That is, by using Φga as the voltage control constant current source, the light amount level of the entire light source array 110 can be controlled.

In addition, a so-called duty control system is adopted in which the lighting time of the SLED is controlled in accordance with the multi-gradation image signal input to the SLED, and the exposure energy is controlled to multi-gradation. In this method, a grayscale signal (12 bits) is DA-converted, pulse width modulation (duty control) is performed by a comparator signal with a triangular wave, and a light-emitting point data signal is obtained.

Here, in the case of the SLED, an interval is provided between the triangular waves because a time for shifting the light emitting point from a lighting period of a certain dot to an adjacent dot is required. Thereby, simultaneous lighting of a plurality of LEDs is prevented. The following can be said as advantages of placing an interval in a triangular wave.

That is, a triangular wave is usually obtained by passing a square wave through a CR integrating filter circuit.
If there is a component or the duty varies, the DC component of the triangular wave is affected, and it is difficult to obtain a stable triangular wave.

In this case, in this embodiment, it is not necessary to form a continuous triangular wave.
By resetting the R integration filter circuit, a stable triangular wave can be obtained.

Here, in this embodiment, an isosceles triangular triangular wave is formed as the triangular wave, and the central part of the lighting period is used. This is because the SLED requires a transfer time, and thus is in an unstable state immediately after the transfer within the lighting time of one dot. Since the end of the lighting time is more stable, the sawtooth wave having the edge of the emission time as an edge can be used for actual lighting from a stable portion of the SLED by using a triangular wave as an edge, thereby preventing malfunction. (See FIGS. 10 and 11). 10, the same components as those in FIG. 6 are denoted by the same reference numerals, and the description of the configuration will be omitted. In FIG. 10, O
A resistance 216 and a capacitor 218 provided on the downstream side of the R circuit 186, and an inversion circuit 220 and a switch 222 constitute a triangular wave (sawtooth wave) generation circuit 188.
By gradually increasing the level and turning on the switch 222 at the end, it is possible to easily generate a so-called sawtooth wave whose level drops rapidly.

Further, the unevenness in the light amount at each light emitting point of the SLED is corrected in accordance with the exposure energy measured in advance. That is, at the time of measurement, the light emitting point is turned on for the nominal lighting time on the actual machine, and the exposure energy is obtained by integrating the sensor output. This makes it possible to correct variations in light emitting points due to individual electrical characteristics. The correction value based on the light amount measured in advance is E
By storing the data in a data holding unit such as an EPROM and loading the data into the SLED drive circuit when the power is turned on, the grayscale data can be superimposed when the density signal is generated.

As a modified example of the pulse waveform generation circuit 200 shown in FIG. 6, as shown in FIG. 13A, 4 bits out of 12 bits used for pulse modulation are used for correcting light amount unevenness (voltage control). By applying, the gradation can be
And the light amount unevenness can be controlled by the voltage of ΦD. FIG. 13B is a modified example in the case where the current control is used to correct the uneven light amount.

[0063]

As described above, the image forming apparatus according to the present invention is capable of adjusting the amount of light by duty control with a simple circuit configuration and incorporating all the factors that cause unevenness in the amount of light to emit light from the SLED. It has an excellent effect that the amount can be corrected.

Further, in addition to the above-described effects, by extracting and using a more stable light amount region, it is possible to prevent a decrease in image quality due to uneven light amount.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment.

FIG. 2 is a perspective view illustrating an appearance of a light source array.

FIG. 3 is a diagram of an LED drive circuit incorporated in a light source array.

FIG. 4 is a diagram of a constant current drive circuit.

FIG. 5 is a diagram of a constant voltage drive circuit.

FIG. 6 is a circuit diagram of a density signal (ΦD) generation circuit.

FIG. 7 is an operation timing chart of FIG. 6;

FIG. 8 is an operation timing chart of the LED drive circuit of FIG. 3;

FIG. 9 is a characteristic diagram illustrating an LED light emitting state of the LED drive circuit of FIG. 3;

FIG. 10 is a modified example of the density signal (ΦD) generation circuit diagram.

11 is an operation timing chart in a modified example of FIG.

FIG. 12 is a drive circuit diagram of an SLED alone.

FIG. 13 is a modified example of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 thyristor 12 high resistance 100 image forming apparatus 106 photoconductor drum 106 photoconductor roller 110 light source array 134 density sensor 156 drive circuit 161 base line 163 gradation signal line 178 constant current drive circuit 180 constant voltage drive circuit 188 triangular wave generation circuit 206 correction Data holding unit 212 Timing generation unit LED Self-scanning type

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 33/00 G03G 15/04 120 5F041 H04N 1/036 1/04 101 1/23 103 F term (reference) 2C162 AE13 AF21 AF36 AF43 AF72 FA04 FA17 2H076 AB42 AB55 DA07 DA17 DA19 DA21 EA01 5C051 AA02 CA08 DA03 DB02 DB18 DB29 DE03 DE30 5C072 AA03 BA15 CA05 CA15 FB15 5C074 AA09 BB04 CC26 DD03 DD07 DD08 EE11 BB09 5A07 BB09

Claims (3)

[Claims] 1. An image forming apparatus to which a self-scanning LED is applied as a light source of an exposing unit for forming an image by exposing a photoreceptor, wherein a main power supply for lighting the self-scanning LED is provided. , A constant voltage circuit that varies the voltage according to the control signal,
Alternatively, while being driven by a constant current circuit capable of varying current according to a control signal, a total light amount adjusting means for adjusting the total light amount, and individual LEDs based on a gradation signal of each dot corresponding to an image signal. Exposure amount adjustment means for adjusting the exposure amount, and correction means for correcting the variation in the light amount of each LED,
An image forming apparatus having: 2. The method according to claim 1, wherein the exposure amount adjusting unit outputs a triangular wave in synchronization with a light emitting period of one dot, and sandwiches a vertex of the triangular wave by using a tone signal of each dot as a threshold. 2. The image forming apparatus according to claim 1, further comprising: a pulse width modulation unit that emits light during a period corresponding to a width between intersections of the two sides. 3. The image forming apparatus according to claim 2, wherein the triangular wave is a sawtooth wave having the end of each dot as an edge.