JP2003072141A - Halftone dot image exposure apparatus and light source driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a halftone image exposure apparatus capable of exposing and forming an image with high quality. SOLUTION: The light source comprises a driving circuit 1 for driving a light emitting element L according to a driving signal, a monitor circuit 2 for monitoring the light quantity of the light emitting element L or the driving current and outputting a monitor signal M corresponding thereto, a driving control circuit 3 that feeds back the monitor signal M output from the monitor circuit 2 and outputs a driving signal to the driving circuit 1 corresponding to a deviation between the monitor signal M and a light quantity command signal S, and an offset input circuit 4 that makes the light quantity to be zero when the light quantity command signal S is zero by adding an offset signal OS having a polarity opposite to the light quantity command signal S to the light quantity command signal S input to the driving control circuit 3. A diode D1, a resistor, or a transistor is inserted between the monitor signal M fed back to the driving control circuit 3 from the monitor circuit 2 and the output signal output to the driving circuit 1 from the driving control circuit 1 to form a light source driving circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a halftone dot image exposure apparatus and a light source drive circuit, and more particularly, to a light source drive circuit with improved responsiveness of state change from a saturated state to a control state with a light quantity = 0, and a light source drive circuit including the same. The present invention relates to a halftone image exposure device.

[0002]

2. Description of the Related Art Conventionally, light from a light source is made into a minute spot light by using an optical system, and this minute spot light is irradiated onto an exposed surface of a recording material, and a light emitting element is turned on / off.
There is known a halftone dot image exposure apparatus that forms an image by a set of minute halftone dots by scanning while repeating continuously.

In such a halftone image exposure apparatus, a high-quality image can be formed by exposure by irradiating the exposed surface of the recording material with a sharp minute spot light to make the edges of each halftone stand out. desired.

By the way, as the light source of the image exposure apparatus,
Generally, a light emitting element including a semiconductor laser or an LED (light emitting diode) is used, and when recording and forming an image, the light emitting element is turned on / off by using one or more constant light amount values. Is common. Therefore,
In order to record and form a high quality image, it is necessary to control the amount of light emitted from the light emitting element to be constant.

In order to keep the amount of light emitted from the light emitting element constant, APC (Automatic Power Control) has been conventionally used.
A circuit is provided to stabilize the optical output, and ACC (Automa
A technique for controlling the current value flowing in the light emitting element to be stabilized by providing a ticCurrent Control) circuit is often adopted.

FIG. 4 shows an example of a light source drive circuit provided with an APC circuit. As shown in the figure, in the light source drive circuit provided with the APC circuit, a part of the light emitted from the light emitting element 100 is received by the light receiving element 101 such as a photo sensor,
The I / V conversion circuit 102 converts a current signal when light is received by the light receiving element 101 into a voltage signal to be a monitor signal of light quantity, and the monitor signal is used as the OP amplifier 10.
By negatively feeding back to 3, the drive of the light emitting element is controlled so that the light amount command signal input to the OP amplifier 103 and the monitor signal match.

Further, FIG. 5 shows an example of a light source drive circuit provided with an ACC circuit. As shown in the figure, in the light source drive circuit provided with the ACC circuit, a part of the drive current flowing in the light emitting element 200 is taken out as a monitor signal from the emitter of the transistor 201 which drives the light emitting element 200, and this monitor signal is output. By negatively feeding back to the OP amplifier 202, the drive of the light emitting element is controlled so that the light amount command signal input to the OP amplifier 202 and the monitor signal match.

In a general light source drive circuit provided with such an APC circuit or ACC circuit, the light emitting element may slightly emit light even when the light amount command signal = 0 due to the influence of an error such as the OP amplifier-offset voltage. is there.

To solve this problem, in the prior art, for example, taking a light source drive circuit provided with the ACC circuit of FIG. 5 as an example, as shown in FIG. 6, the light amount command signal to the OP amplifier 202 is changed to the light amount command signal. A method of adding an offset signal having a polarity opposite to that of is used. According to this, since the offset signal is a negative voltage, the light amount can be set to 0 when the light amount command signal = 0.

[0010]

However, in this method, when the light quantity command signal = 0, the signal (light quantity command signal + offset signal) input to the OP amplifier 202 becomes a negative voltage, and therefore the output of the OP amplifier 202 is output. Is negative. This is because the OP amplifier 202 works to match the light amount command signal and the monitor signal by making the output negative.

In the transistor 201, since the current flows only in the direction of the arrow, the OP amplifier 202 cannot match the monitor signal and the light amount command signal, and the OP
The output of the amplifier 202 is in a minus saturation state. In this minus saturation state, the output of the OP amplifier 202 has almost the same voltage level as that of the OP amplifier minus power source −Vcc,
It will be out of control.

Then, when the light quantity command signal> 0,
The output of the OP amplifier 202 becomes positive, and at this time, the monitor signal and the light amount command signal match and the control state returns.

However, when the minus saturation state (uncontrollable state) changes to the control state, the OP amplifier 202
The output of fluctuates greatly. In the transistor 201, a current flows when the base-emitter voltage reaches about 0.7 V, so that the current does not flow to the light emitting element 200 unless the output of the OP amplifier 202 exceeds 0.7 V. Power supply voltage is ± 5V
Is used, a minus saturation state (-3.5 to -4.
A voltage fluctuation of about 5V from a voltage level of about 5V) to + 0.7V or more occurs, and this change takes a very long time, which deteriorates the rising characteristic of the light output when the light emitting element 200 is driven. In FIG. 7, it takes a response time until the light output is raised as indicated by a, which deteriorates the responsiveness.

Further, since it takes time to change the state from the uncontrollable state to the control state, this also causes a delay in responsiveness.

When the response delay when driving the light emitting element is large as described above, in the halftone image exposure apparatus, it is impossible to sharply irradiate the exposed surface of the recording material with the minute spot light, and the edge is not sharp. There is a problem that it is difficult to form outstanding halftone dots by exposure. At a halftone dot with a blurred edge, the image formed thereby also has a blurred feeling, and a high-quality image cannot be formed by exposure.

Therefore, an object of the present invention is to provide a halftone image exposure apparatus capable of exposing and forming a high-quality image by irradiating the exposed surface of a recording material with a minute spot light sharply. is there.

Another object of the present invention is to provide a light source drive circuit which improves the rising characteristics of the light output of the light emitting element and improves the response.

[0018]

In order to solve the above-mentioned problems, the invention according to claim 1 scans the exposed surface of the recording material with light from a light source as minute spot light, thereby forming a halftone image on the recording material. In the halftone image exposure apparatus for recording and forming the light source, the light source monitors a drive circuit for driving the light emitting element based on a drive signal and a light amount or drive current of the light emitting element, and a monitor according to the light amount or drive current. A monitor circuit that outputs a signal; a drive control circuit that feeds back a monitor signal output from the monitor circuit and outputs a drive signal to the drive circuit according to a deviation between the monitor signal and the light amount command signal; By adding an offset signal of opposite polarity to the light amount command signal input to the control circuit,
An offset input circuit for setting the light quantity = 0 when the light quantity command signal = 0, and a monitor signal fed back from the monitor circuit to the drive control circuit and output from the drive control circuit to the drive circuit. Between the output signal,
The dot image exposure apparatus is driven by a light source drive circuit including a diode, a resistor or a transistor connected thereto.

According to a second aspect of the present invention, the light source drive circuit has a level shift circuit for changing the voltage level of the output signal at the output of the drive control circuit. It is a device.

According to another aspect of the invention for solving the above-mentioned other problems, a drive circuit for driving a light emitting element based on a drive signal and a light amount or a drive current of the light emitting element are monitored, and the light amount or the drive current is monitored. A monitor circuit that outputs a corresponding monitor signal; and a drive control circuit that feeds back the monitor signal output from the monitor circuit and outputs a drive signal to the drive circuit according to the deviation between the monitor signal and the light amount command signal. And an offset input circuit for setting the light quantity = 0 when the light quantity command signal = 0 by adding an offset signal having a reverse polarity to the light quantity command signal input to the drive control circuit. Between the monitor signal fed back from the monitor circuit to the drive control circuit and the output signal output from the drive control circuit to the drive circuit, a diode, a resistor or a transformer is provided. A light source drive circuit, characterized in that it connects the register.

The invention according to claim 4 is the light source drive circuit according to claim 3, wherein a level shift circuit for changing the voltage level of the output signal is provided at the output of the drive control circuit.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First, an embodiment of the light source drive circuit will be described. FIG. 1 shows a circuit diagram of a light source drive circuit according to the first embodiment. Here, an example in which the ACC circuit is controlled so as to stabilize the current value flowing in the light emitting element is illustrated.

As shown in the figure, the light source drive circuit monitors the drive current supplied to the light emitting element L and the drive circuit 1 which supplies a drive current to the light emitting element L which is a light source based on the drive signal. A monitor circuit 2 that outputs a monitor signal M according to the drive current, and a drive that amplifies the deviation between the monitor signal M output from the monitor circuit 2 and the light amount command signal S and outputs a drive signal for the light emitting element L. The control circuit 3 and the offset input circuit 4 for adding an offset signal to the light amount command signal S input to the drive control circuit 3 are included.

The driving circuit 1 comprises a transistor T1, a light emitting element L connected to the transistor T1 and a resistor R1. Here, as the light emitting element L, either a semiconductor laser or an LED (light emitting diode) may be used.

The transistor T1 has a base connected to an output terminal of a drive control circuit 3 to be described later, a collector connected to a cathode electrode of the light emitting element L, and an emitter connected to a resistor R1.

A voltage of + Vcc is supplied to the anode electrode of the light emitting element L from a power source, and a drive signal from a drive control circuit 3 described later is applied to the transistor T1.
A drive current corresponding to the drive signal flows through the transistor T1 to drive the light emitting element L to emit light.

The monitor circuit 2 extracts a drive current flowing in the light emitting element L in the arrow direction between the emitter side of the transistor T1 of the drive circuit 1 and the resistor R1 and uses it as a monitor signal M as a drive control circuit 3 described later. Constitutes a feedback circuit for feedback to.

The drive control circuit 3 comprises an operational amplifier (OP amplifier) A1. The operational amplifier A1 is supplied with voltages of + Vcc and -Vcc from a power source, a light amount command signal S is input to its non-inverting input terminal, and a monitor from the monitor circuit 2 is input to its inverting input terminal. The signal M is negatively fed back and input, and the signal indicating the deviation between the light amount command signal S and the monitor signal M is inverted and amplified and output to the drive circuit 1 as a drive signal. As a result, the light emitting element L causes the light amount command signal S
And the monitor signal M coincide with each other.

The offset input circuit 4 adds an offset signal OS whose polarity is opposite to that of the light amount command signal S to the light amount command signal S which is a light amount command signal for driving the light emitting element L.

Here, as shown in FIG. 1, the monitor circuit 2
In the drive circuit 1, the monitor signal M of the drive current extracted from between the emitter side of the transistor T1 of the drive circuit 1 and the resistor R1 is branched while being negatively fed back to the inverting input terminal of the operational amplifier A1 of the drive control circuit 3. It is connected between the output side of the drive control circuit 3 and the input side of the drive circuit 1 via the diode D1.

By interposing this diode D1, when the signal input to the operational amplifier A1 is negative,
GND → resistor R1 → monitor signal M → inverting input terminal of operational amplifier A1 → diode D1 → current flows to the output terminal of operational amplifier A1 and the non-inverting input terminal of operational amplifier A1 /
It works so that the voltages at the inverting input terminals match.

The element intervening in the signal branched as described above is not limited to the diode D1, but as shown in the figure, by interposing it between the monitor signal M and the output side of the drive control circuit 3, It should function so that a current flows when the output of the operational amplifier A1 is negative, and also that it causes a potential difference between the input side and the output side or does not flow a current when the output is positive. There is no particular limitation. A resistor or a transistor may be used instead of the diode.

Next, the operation of the light source drive circuit shown in the first embodiment will be described.

First, a light amount command signal S, which is a light amount command signal for driving the light emitting element L to emit light, is input to the drive control circuit 3, and is supplied from the drive control circuit 3 to the base of the transistor T1 of the drive circuit 1 as a drive signal. When output, the collector current flows through the transistor T1, and this collector current is connected to the collector of the transistor T1.
Drive current. The light emitting element L is driven to emit light by this drive current.

The drive current of the light emitting element L flowing from the transistor T1 is taken out as the monitor signal M by the monitor circuit 2 and fed back to the inverting input terminal of the operational amplifier A1 of the drive control circuit 3. The operational amplifier A1 is
The deviation between the light amount command signal S input to the non-inverting input terminal and the monitor signal M input to the inverting input terminal is amplified and output to the base of the transistor T1 of the drive circuit 1 as a positive drive signal, and the light emitting element L Is controlled so that the current for driving light emission is kept constant.

When a light quantity command signal (light quantity command signal = 0) is given from the light quantity command signal S to extinguish the light emitting element L, the polarity is always reversed from the light quantity command signal S from the offset input circuit 4. Since the offset signal OS is added to the light amount command signal S, the light amount command signal S + the offset signal OS is input to the non-inverting input terminal of the operational amplifier A1.

At this time, the signal input to the non-inverting input terminal of the operational amplifier A1 is a negative voltage, but the monitor signal M input to the inverting input terminal of the operational amplifier A1 is the same as that of the operational amplifier A1 of the drive control circuit 3. Since it is branched while being negatively fed back to the inverting input terminal and is connected between the output side of the drive control circuit 3 and the input side of the driving section 1 via the diode D1, the inverting input terminal is connected to the operational amplifier A1. Current flows from the output terminal to the output terminal and the minus saturation state (uncontrollable state) does not occur.

Therefore, after that, when the light amount command signal = 0 is changed to the light amount command signal> 0 and the operational amplifier A1 is changed to the control state, the output change is reduced by the amount by which the voltage level is increased. . As a result, when the light emitting element L is driven, the rising characteristic of the light output is shortened by improving the response time as shown by b in FIG. 8, and the responsiveness can be improved as compared with the conventional case.

FIG. 2 shows a circuit diagram of a light source drive circuit according to the second embodiment. In this light source drive circuit, as shown in FIG.
The level shift circuit 5 is added to the light source drive circuit according to the first embodiment shown in FIG. The same components as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

The level shift circuit 5 has a diode D2 and a resistor R2. Diode D2
Is the operational amplifier A of the drive control circuit 3 at its cathode electrode.
The output terminal 1 is connected, and the anode electrode is supplied with a voltage of + Vcc from the power supply through the resistor R2. Then, the drive signal from the drive control circuit 3 is connected between the anode electrode side of the diode D2 and the resistor R2 to the base of the transistor T1 of the drive circuit 1.

The level shift circuit 5 includes an operational amplifier A
It functions to raise the output level of 1 by the forward voltage of the diode D2.

As a result, the voltage level of the output of the operational amplifier A1 is further increased as compared with the case of the above-mentioned first embodiment. Therefore, when the light amount command signal = 0 is changed to the light amount command signal> 0 and the operational amplifier A1 is changed to the control state, the output change is further reduced, and the light when the light emitting element L is driven is reduced. The rising characteristics of the output are improved with a shorter response time as shown by c in FIG. 9, and the response can be further improved.

In each of the embodiments described above, A
Although the example using the CC circuit has been described, the present invention can be similarly applied to a light source drive circuit that controls the amount of light emitted from the light emitting element using the APC circuit so as to keep it constant.

Although the transistor T1 is used for the drive circuit 1, the invention is not limited to this, and an FET or the like may be used.

Further, the drive control circuit 3 has an operational amplifier (O
However, the present invention is not limited to this, and a drive signal may be generated from a light amount command signal using a transistor or the like.

The power supply voltage may be a single power supply.

Furthermore, in the above description, the power source for driving the light source is positive, but it can be negative.

Next, an example of a halftone dot image exposure apparatus using such a light source drive circuit will be shown.

FIG. 3 is a conceptual diagram for explaining the schematic structure of the halftone image exposure apparatus. In the figure, 10 is a recording material,
Reference numeral 20 denotes a recording unit for exposing and forming a halftone dot image on the exposed surface 10a of the recording material 10 by irradiating the exposed surface 10a of the recording material 10 with light in the form of minute spots.

The recording material 10 is a photosensitive recording material having a photosensitive layer for forming an image by light exposure, and is held by a holding member such as a rotating drum (not shown) and is sub-scanning direction (vertical direction in the illustrated example). Is movably provided.

The recording unit 20 includes a light source 21 which houses the above-mentioned light source drive circuit and a light beam emitted from a light emitting element of the light source 21 as a minute spot light.
And an exposure optical system 22 including a lens group for irradiating the exposure surface 10a of
Exposure surface 10 of recording material 10 orthogonal to the sub-scanning direction
It is movable along the main scanning direction substantially parallel to a.

In the recording unit 20, the light source 21 emits a minute spot light onto the exposed surface 10a of the recording material 10 while repeating ON / OFF of the light emitting element whose light emission is controlled by the light source drive circuit in the course of scanning. Halftone dots are exposed and formed by continuous irradiation, and a desired image is recorded and formed by the set of halftone dots.

According to the halftone dot image exposure apparatus having the above-described light source drive circuit, the response time when driving the light emitting element of the light source 21 is improved and shortened, and the response time is improved as compared with the conventional one. The exposure surface 10a of the recording material 10 is irradiated with spot light.
Can be illuminated on. As a result, a sharp minute spot light can be emitted, and a high-quality image can be formed by exposure.

Further, when the light source drive circuit is the light source drive circuit according to the second embodiment described above, it is possible to irradiate the exposed surface 10a of the recording material 10 with a minute spot light having a further improved responsiveness. Therefore, it is possible to irradiate a sharper minute spot light, and it is possible to expose and form a higher quality image.

The light source 21 is not limited to a single light source, but has a plurality of light sources for irradiating the exposed surface 10a of the recording material 10 with light beams of R, G, and B wavelengths, for example. May be.

[0057]

According to the present invention, it is possible to provide a halftone dot image exposure apparatus capable of exposing and forming a high quality image by irradiating the exposed surface of a recording material with a sharp spot light. it can.

Further, according to the present invention, it is possible to provide a light source drive circuit in which the rising characteristic of the light output of the light emitting element is improved and the response is improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a light source drive circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a light source drive circuit according to a second embodiment of the present invention.

FIG. 3 is a conceptual diagram showing a schematic configuration of a halftone image exposure apparatus.

FIG. 4 is a circuit diagram showing a light source drive circuit having a conventional APC circuit.

FIG. 5 is a circuit diagram showing a light source drive circuit having a conventional ACC circuit.

FIG. 6 is a circuit diagram showing another light source drive circuit having a conventional ACC circuit.

FIG. 7 is a graph showing a response characteristic of a light emitting element by a conventional light source drive circuit.

FIG. 8 is a graph showing a response characteristic of a light emitting element by the light source drive circuit according to the first embodiment.

FIG. 9 is a graph showing a response characteristic of a light emitting element by the light source drive circuit according to the second embodiment.

[Explanation of symbols]

1: Drive circuit 2: Monitor circuit 3: Drive control circuit 4: Offset input circuit 5: Level shift circuit 10: Recording material 10a: exposed surface 20: Recording unit 21: Light source 22: Exposure optical system L: Light emitting element T1: Transistor R1, R2: resistance A1: Operational amplifier D1, D2: Diode S: Light intensity command signal M: Monitor signal OS: Offset signal

Claims (4)

[Claims] 1. A halftone dot image exposure apparatus for recording and forming a halftone dot image on the recording material by scanning light from a light source as a minute spot light on the exposed surface of the recording material, wherein the light source is a drive signal. A drive circuit for driving the light emitting element based on, and monitoring the light amount or drive current of the light emitting element,
A monitor circuit that outputs a monitor signal according to the light amount or the drive current, and a monitor signal output from the monitor circuit are fed back, and a drive signal is sent to the drive circuit according to a deviation between the monitor signal and the light amount command signal. A drive control circuit for outputting,
An offset input circuit for setting the light quantity = 0 when the light quantity command signal = 0 by adding an offset signal having a reverse polarity to the light quantity command signal input to the drive control circuit; It is driven by a light source drive circuit in which a diode, a resistor or a transistor is connected between a monitor signal fed back from the monitor circuit to the drive control circuit and an output signal output from the drive control circuit to the drive circuit. A halftone dot image exposure device characterized by the above. 2. The halftone image exposure apparatus according to claim 1, wherein the light source drive circuit has a level shift circuit for changing the voltage level of the output signal at the output of the drive control circuit. 3. A drive circuit for driving a light emitting element based on a drive signal, a monitor circuit for monitoring the light amount or drive current of the light emitting element, and outputting a monitor signal according to the light amount or drive current, and the monitor. A drive control circuit that feeds back a monitor signal output from the circuit and outputs a drive signal to the drive circuit according to a deviation between the monitor signal and the light amount command signal, and a light amount command signal input to the drive control circuit. On the other hand, a monitor which has an offset input circuit for setting the light quantity = 0 when the light quantity command signal = 0 by adding an offset signal of opposite polarity, and which is fed back from the monitor circuit to the drive control circuit A light source drive circuit in which a diode, a resistor or a transistor is connected between a signal and an output signal output from the drive control circuit to the drive circuit. 4. The light source drive circuit according to claim 3, wherein a level shift circuit for changing the voltage level of the output signal is provided at the output of the drive control circuit.