JPH07214818A - Light emitting device voltage control system - Google Patents

Abstract

PURPOSE:To make the driving control of a light emitting element more stable and energy conservation possible by providing a control circuit, etc., which makes a voltage regulator operative when first and second signals are generated at the same time. CONSTITUTION:A V1 monitor 51 makes a monitoring to determine whether or not non-stabilizing voltage V1 exceeds a predetermined value and, if the voltage V1 is not below the predetermined value, a level-on signal is supplied to and retained in an AND circuit 53 and, in the converse case, a level-off signal S51 is supplied to and retained in the AND circuit 53. A V2 monitor 52 makes a monitoring to determine whether or not the voltage V2 for APC control circuit exceeds a predetermined value and, if the voltage V2 is not below the predetermined value, a level-on signal is supplied to and retained in the AND circuit 53 and, in the converse case, a level-off signal S52 is supplied to and retained in the AND circuit 53. The AND circuit 53 when both level-on signals S51 and S52 are input, supplies a level-on signal S53 to an OR circuit 55. The OR circuit supplies a control signal S55 to a laser voltage regulator 50.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element voltage control system suitable for laser voltage control in a semiconductor laser driving circuit used in an electrophotographic laser printer or a copying machine.

[0002]

2. Description of the Related Art Some electrophotographic color laser printers and the like use a semiconductor laser as a means for forming an electrostatic latent image on a photosensitive member according to an image signal.

FIG. 4 shows an example of the overall construction of a conventional one-drum multiple transfer color laser printer. In FIG. 4, the paper 102 fed from the paper feed unit 101 is held by the gripper 103 f of the transfer drum 103 at the front end of the paper and is held on the outer periphery of the transfer drum 103.

The latent images formed from the optical unit 107 on the photosensitive member 1 for each color are developed by the respective color developing devices Dy, Dc, Dm,
It is developed by Db and transferred to the outer peripheral paper of the transfer drum 103 a plurality of times to form a multicolor color image. Thereafter, the paper 102 is separated from the transfer drum 103, fixed by the fixing unit 104, and ejected from the paper ejection unit 105 to the paper ejection tray unit 106.

Here, each of the color developing devices has a rotary support shaft 110 at both ends thereof, and each of the developing devices is held by a developing device selecting mechanism portion 108 rotatable about the shaft, and its posture is as shown in FIG. The rotation for selecting the developing device is performed while maintaining the constant value.

After the selected developing device is moved to the developing position, the developing device selecting mechanism portion 108 is integrated with the developing device, and the selecting mechanism holding frame 109 is connected to the solenoid 109 around the fulcrum 109b.
The photosensitive member is moved and positioned in one direction by a. here,
The rotary support shaft 110 is configured to be fixed to the main body of the device.

A detector 4 is a developing device selecting mechanism 1
The home position of the developing device selecting mechanism unit 108 is detected by detecting the H portion protruding on the circumference of 08. Therefore, the printer controller (not shown) confirms the position of each color developing device with reference to the H portion, determines the rotation angle of the developing device selecting mechanism unit 108, and selects a desired developing device.

Image exposure obtained by a laser beam scanner device is used as image exposure in the above-mentioned device. The image exposure means shown in FIG. 5 represents a specific example inside the optical unit 107 of FIG. This laser beam scanner device has a semiconductor laser (light emitting element) 41,
The semiconductor laser 41 is optically modulated according to the color separation image of the image signal.

The laser beam emitted from the semiconductor laser 41 is deflected by a rotating polyhedron (polygon mirror) 38 via a collimator lens 31 and a cylindrical lens 32. The deflected laser beam is imaged by the f-Θ lens composed of the spherical lens 33 and the toric lens 34, and the beam path of the beam is turned back by the reflection mirror 35 to irradiate the photoconductor 1.

By scanning the surface of the photoconductor 1 at a constant speed in the predetermined direction a with the laser beam, image exposure corresponding to the color separation image is performed. Further, a part of the laser beam is reflected by the horizontal synchronizing mirror 36, and an index signal indicating the starting direction of the scanning line of the laser beam is detected by the optical fiber 37.
The image writing timing of the line is determined.

FIG. 6 shows the configuration of the light quantity control-related part of the laser drive circuit used in the optical unit 107. In FIG. 6, reference numeral 40 denotes a laser unit, which includes a laser diode (semiconductor laser) 41 and a photodiode 42 arranged in the vicinity thereof. A part of the laser beam in the laser diode 41 is received by the photodiode 42, and a signal S40 proportional to the light emission amount of the laser beam is received.
Is obtained.

Next, the signal S40 is sent to the signal comparator 44,
It is compared with a preset laser beam target light amount setting reference signal Vt level. And the signal comparator 44
The output signal S44 is output to the next-stage control circuit 45 as a signal corresponding to the error between the signal S40 and Vt. The control circuit 45 outputs a count operation control signal S45 to the counter 46 according to the error signal S44.

Next, the counter 46 performs an up-down operation according to the control signal S45, and outputs the count signal S46 to the next stage D / A converter 47. And the D / A converter 47
Then, the digital signal S46 is converted into an analog signal S47, and S47 is output to the next stage laser drive circuit 48.

Although the signal S1 is also input to the laser drive circuit 48, the signal S1 is an image signal output from an image signal control unit (not shown). The laser drive circuit 48 sets the light emission amount of the laser beam by the signal S47, generates the laser drive signal S48 whose on / off operation of the laser is controlled by the image signal S1, and outputs the laser drive signal S48 to the laser diode 41.

In this way, the APC (Aut) is used to stabilize and stabilize the light emission amount of the laser diode 41 within a predetermined range.
In the following description, it is abbreviated as APC.

The necessity of providing the circuit for stabilizing the laser light amount in the optical unit 107 in this way is as follows.
That is, the temperature characteristic of the laser is very bad, and the laser light amount is not stable under environmental conditions in which the ambient temperature changes.

When the direction a in FIG. 5 in which the laser beam scans the photosensitive member 1 is the main scanning direction and the direction b in which the photosensitive member 1 rotates is the sub scanning direction, the APC control is performed in the main scanning direction and the sub scanning direction. Performed in non-image areas. More specifically, the non-image area includes a pre-processing period during which the first image signal recording operation is performed after power is turned on, a vertical blanking period between printing sheets (including a space between colors in multicolor printing), and a line being printed. It is classified into the horizontal blanking period between.

Here, it is ideal that the APC operation is performed over the entire non-image area. However, since the laser diode 41 is forcibly emitted during the APC operation, the life of the laser is taken into consideration for each device. APC only for an arbitrary period of non-image area
Is configured to control.

Hereinafter, the APC in the pre-processing period will be referred to as an initial APC, and the APC in a horizontal blanking period (hereinafter referred to as an unblanking period) between printing papers (including a space between colors) will be referred to as an unblanking APC.

FIG. 7 shows a timing chart when the unblanking APC is executed. The TOP signal in the figure means the home position signal of the developing device selecting mechanism section 108 in FIG. 4, and corresponds to the vertical synchronizing signal of the image signal. The BD signal means a print paper writing line reference signal and corresponds to a horizontal synchronizing signal of the image signal. Further, the UBL signal is a signal which is active only during the main scanning unblanking period, and the unblanking APC is executed during this active period.

Next, referring to FIG. 6, the actual APC operation will be described separately for the non-printing period and the printing period. First, during the non-printing period, the laser diode 41 is forcibly turned on during a predetermined APC control period, and the following control operation is performed. A signal S40 proportional to the amount of laser light detected by the photodiode 42 is input to the signal comparator 44, compared with the target emission amount setting reference signal Vt of the laser and operated as follows according to the comparison result.

First, if the comparison results are equal, the control circuit 4 sends a request signal S44 for maintaining the current laser drive signal.
5, and the output signal S47 (current state) of the D / A converter 47 is latched. Next, as a result of the comparison, if the target light quantity is not reached, the request signal S4 for increasing the laser light quantity
4 and outputs a request signal S44 for reducing the laser light amount to the control circuit 45 when the target light amount is exceeded. Then, the counter is operated up or down by the control signal S45 of the counter 46 from the control circuit 45 to output the count signal S46 composed of a plurality of bits to the D / A converter 47.

Then, the D / A converter 47 converts the input signal S46 into a laser driving analog signal S47 and outputs the laser driving analog signal S47 to the laser driving circuit 48, so that the light emission amount of the laser diode 41 changes. The above series of control operations are repeated until the detection signal S40 of the photodiode 42 converges near the target emission amount setting reference signal Vt of the laser.

Next, in the printing period, the control circuit 45 causes the laser drive signal S4 converged by the APC operation in the non-printing period.
In order to maintain 8, the control signal S45 that stops the counting operation and latches is output to the counter 46.
Therefore, the amount of laser light during the printing period is held at the amount of light converged by the APC operation immediately before printing, so that stable printing density can be secured.

[0025]

However, the power supply voltage V1 of the laser diode 41 drive circuit (48 in FIG. 6) is set.
And the APC control circuit (44, 45, 46, 47 in FIG. 6) has a risk of destroying the worst case laser diode 41 in the following cases due to the difference in the rising time of the power supply voltage V2 when the power is turned on.

(1) The laser diode 4 immediately after the power is turned on and before V1 reaches a stable voltage value over a predetermined voltage value.
When a voltage is supplied to the laser diode 1, the laser diode 41 is damaged by a surge voltage or the like and is destroyed in the worst case.

(2) When the power supply voltage V2 reaches a stable voltage value by a predetermined voltage value or more before V1, a normal voltage is not supplied to the laser diode 41, that is, a signal from the photodiode 42. Since the APC control is started even if S40 is minute or unstable, the laser drive signal S47 is set to be larger than the control value when the normal voltage is supplied to the laser diode 41.

Therefore, the APC convergence error becomes large.

In the worst case, when the APC control is started from a state where the laser diode 41 is not emitting any light, the photodiode 4 corresponding to the setting of the laser drive signal S47.
Since the response signal of the signal S40 from 2 does not react, the laser emission value does not reach the target even if the APC control is repeated a predetermined number of times, resulting in an APC error.

(3) In general, the APC control circuit is operated by a power supply voltage of 5V system, whereas the laser drive circuit is different in some devices from the viewpoint of dynamic range balance and high-speed response in which Vf of the laser diode 41 is subtracted. A power supply voltage of 5V system or 12V system is generally used.

In this case, in particular, when the power supply voltage of the laser drive circuit is a 12 V system, the content of (2) becomes a problem due to the difference in the power supply voltage of the laser drive circuit and the APC control circuit.

When the printer is in the standby state,
The laser diode does not emit light, but the current set by the APC flows through a path other than the laser for the following reasons, so the average power consumption of the laser drive unit is the same as that during the printing operation.

(4) Since the laser drive circuit switches by the modulation signal, it is generally composed of a differential circuit. Therefore, when the printer device is in the standby state, no modulation signal is supplied to the laser and no light is emitted, but the laser drive constant current set by the APC control flows through the other drive element to which the laser element is not connected, so that the laser drive circuit. The average power consumption of the parts is the same as during printing.

Therefore, this is an obstacle to realizing energy saving when the printer is on standby.

In view of the above points, the present invention has an object of providing a light emitting element voltage control system capable of further stabilizing drive control of the light emitting element and contributing to energy saving. And

[0036]

In order to achieve such an object, the invention of claim 1 stabilizes the power supply to the light emitting element drive circuit by a voltage regulator, and the light emitting element drive circuit is provided with an APC control circuit. A light emitting element voltage control system for APC control by means of: a first monitor circuit for monitoring a first voltage applied to the voltage regulator, and generating a first signal when the first voltage is within a specified range; Monitoring a second voltage applied to the APC control,
A second monitor circuit that generates a second signal when the second voltage is within a specified range; and a voltage regulator that can operate when both the first signal and the second signal occur. And a control circuit for controlling.

According to a second aspect of the invention, in addition to the first aspect of the invention, a control circuit is further provided which enables the APC control circuit when both the first signal and the second signal are generated. It is characterized by that.

According to a third aspect of the present invention, in addition to the first aspect of the present invention, a control circuit, which is independent of the control circuit, enables the voltage regulator to operate in response to an external instruction. And

According to a fourth aspect of the present invention, the voltage regulator according to the first aspect, the first monitor circuit, the second monitor circuit, the control circuit, the control circuit according to the second aspect, and the third aspect. The control circuit is integrated.

[0040]

According to the first and second aspects of the present invention, when the light emitting element drive circuit starts its operation, the voltages supplied to the voltage regulator and the APC control circuit are within the specified ranges, respectively, thereby stabilizing the operation of the system. To do.

In the invention of claim 3, independently of the control of claim 1, the light emitting element drive circuit can be forcibly driven by an external instruction.

According to the invention of claim 4, power consumption is reduced by integration. Also, the mounting space can be reduced and the cost can be reduced.

[0043]

Embodiments of the present invention will now be described in detail with reference to the drawings.

An example of a semiconductor laser voltage control system to which the present invention is applied is shown in FIG. The same signal names and functional blocks as those in the conventional example shown in FIG.
In FIG. 1, reference numeral 49 denotes an APC control processing block in which the functions of 44 to 47 in FIG. 6 are combined into one block. First, the signal names used in the present embodiment, not shown in FIG. 6, will be described.

V1, V2 and V3 mean power supply voltages, and V
1, V3 are voltages supplied to the laser, and in this figure, a stabilized voltage V3 is generated from the unstabilized voltage V1. V
2 is a power supply voltage for the APC control circuit. EXTC
Is a control signal for forcibly shutting down the supply voltage of the laser from the outside, which will be described in detail later.

Next, the circuit block will be described. V
The 1 monitor 51 monitors whether or not the voltage of the unstabilized voltage V1 is equal to or higher than a predetermined value. If the voltage V1 is equal to or higher than the predetermined value, the level-on signal S is output.
51 is output to the AND circuit 53 and held.

The V2 monitor 52 is the voltage V for the APC control circuit.
It is monitored whether or not 2 is equal to or larger than a predetermined value, and if the value is equal to or larger than the predetermined value, a level-on signal S52 is output to the AND circuit 53 and held in the opposite case.

AND circuit (control circuit according to the invention of claim 1)
53 is a level-on signal (the first signal of the invention of claim 1)
When both S51 and the level-on signal (second signal of the invention of claim 1) S52 are input, the level-on signal S53 is output to the OR circuit 55. External IF circuit 54
Is an interface circuit that outputs the signal S53 and the reverse polarity signal S54 to the OR circuit 55 in response to the EXTC signal. The OR circuit 55 outputs the signal S55 for controlling whether or not the voltage V3 is supplied to the laser by the independent signals S53 and S54 to the laser voltage regulator 50 as the control circuit of the third aspect of the invention.
That is, the OR circuit 5 outputs the signal S55 that shuts down the voltage V3 to the laser when the EXTC signal is on, regardless of the signal S53, and outputs the voltage to the laser when the EXTC signal is off and the signal S53 is on. The signal S55 is output so as to supply V3.

The laser voltage regulator 50 outputs the signal S55.
When this level is turned on, operation becomes possible and this signal turns on / off.
The control by turning off supplies the stabilization voltage V3 to the laser from the non-stabilization voltage V1.

The APC permitting circuit 56 functions as a control circuit of the invention of claim 2 to enable the APC control circuit 49 to operate.
The PC control operation permission signal S56 is created based on the signal S53 and output to the APC control circuit 49. Here, it is assumed that the APC control circuit 49 is set to start later after the signal S56 becomes active (for example, level on).

A block 57 is a laser voltage control circuit in which 50 to 56 are integrated.

The laser voltage control sequence having the above configuration will be described.

In the transient state immediately after the power supply of the printer is turned on, if either of the voltages V1 and V2 is less than or equal to the predetermined value (see FIG. 3), the AND circuit 5
The output signal of 3 is level off. When the EXTC signal is not generated, the output signal S55 of the logical sum circuit 55 is turned on and the supply of the voltage V3 to the laser is shut down.

In this case, since the APC permission signal S56 is also inactive (level off), the APC control operation is not performed. As described above, in the present embodiment, the APC is supplied only when the stable voltage V3 is supplied to the laser and the voltage of the APC control circuit is secured at a predetermined value or more.
The control operation does not start. On the other hand, E
When an external instruction is input by the XTC signal, the level-on signal S54 is output as the signal S55 to the laser voltage regulator 50 regardless of the signal S53 level.
Is supplied via.

In the configuration of the present invention, the laser supply voltage V
3 (Voltage regulation from unregulated voltage V1) and APC
Although the voltage V2 for the control circuit is described as being different, it is not limited to being different in particular.

Further, although the semiconductor laser has been described as an example in the configuration of the present invention, it is not particularly limited, and LE can be used.
It is obvious that any light emitting element such as D can be applied.

The internal structure of the laser drive circuit 48 shown in FIG. 1 will be described with reference to FIG. In FIG. 2, Q1 and Q2 are transistor elements, which form a differential circuit in which their emitter terminals are commonly connected. A resistor R is connected to the collector terminal of Q1 and a laser diode 41 is connected to the collector terminal of Q2.

The buffer circuit 59 has laser diode signals S0 and S0 * with opposite polarities to the base terminals of the differential circuits Q1 and Q2 in accordance with the image signal S1 supplied from the image signal control unit (not shown). To supply.

The constant current circuit 58 holds a constant current set by the APC control so that the laser emits a predetermined amount of light. As is apparent from such a configuration, the laser drive constant current value set in the constant current circuit 58 by APC control makes either of the paths of the transistor Q1 or Q2 conductive by the laser diode signals S0 and S0 *. Will be supplied. In this case, the laser emits light when Q2 becomes conductive.

Therefore, when the laser is not emitting light, Q1
Is on, and the average power consumption of the laser drive circuit 48 is constant regardless of whether the laser emits light or not.

In addition to this embodiment, the following example can be realized.

1) In this embodiment, the AND circuit 53 is used to determine the conditions under which the laser voltage regulator 50 can operate, but if the signal level contents of the signals S51 and S52 are different, another gate circuit is used. To use. In any case, the conditions for operating the laser voltage regulator 50 are that the voltages V1 and V2 are both within the specified voltage range.

2) As the voltage regulator of FIG. 1, any constant voltage circuit may be used as long as it is a circuit for stabilizing the voltage. A comparator or the like may be used for the monitor circuit.

As described above, the voltage values of the power supply voltage V1 supplied to the laser element and the APC control circuit power supply voltage V2 are monitored, and after the stable convergence of both the voltage values of the voltages V1 and V2 to a predetermined value or more, the laser Since the power supply voltage is supplied to the element, the APC control permission signal is output, and the APC control circuit starts the APC operation by the APC control permission signal, the following effects are obtained.

(1) Since the laser element is not supplied with a voltage in a transient state where the power source voltage is unstable immediately after the power source of the device is turned on, the laser element is destroyed by a stress such as a surge during a power source voltage rising transient. There is no danger of doing so.

As shown in FIG. 3, when the voltages V1 and V2 are different, there are several rising paths of the power supply voltage, so that the effect is particularly great.

(2) Since the APC control starts after the power is supplied to the laser element without fail, the APC control circuit does not supply the voltage to the laser element or the voltage is supplied but the laser is unstable and the laser emits enough light. APC starts from the time when it does not reach the state and the APC convergence error is large,
In the worst case, there is no inconvenience such as an APC convergence failure and an error.

Further, since the voltage supply to the laser element can be forced on / off controlled from the outside, the power supply to the laser drive circuit can be reduced by shutting down the voltage supply to the laser when the printer is on standby, and the energy saving of the apparatus can be achieved. Can contribute to.

Further, by integrating the laser voltage control unit into an integrated circuit, the mounting density is improved, the unit cost is reduced by reducing the number of parts, the mounting cost is reduced, the circuit is reused in the design of multiple models by the common module, and the design period is shortened. A great effect can be obtained for shortening.

[0070]

As described above, according to the first and second aspects of the present invention, when the light emitting element drive circuit starts operating, the voltage supplied to the voltage regulator and the APC control circuit are within the specified ranges. This stabilizes the operation of the system.

In the invention of claim 3, independently of the control of claim 1, the light emitting element drive circuit can be forcibly driven by an instruction from the outside.

Further, since the voltage supply to the laser element can be forcibly turned on and off from the outside, the power supply to the laser drive circuit can be reduced by shutting down the voltage supply to the laser when the printer is on standby. Can contribute to.

According to the invention of claim 4, power consumption is reduced by integration.

Further, by integrating the laser voltage control unit into an integrated circuit, the mounting density is improved, the unit cost is reduced by reducing the number of components, the mounting cost is reduced, and the circuit is reused in the design of multiple models due to the modularization of the circuit. A great effect can be obtained for shortening.

[0075]

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a voltage control system for a semiconductor laser according to the present invention.

FIG. 2 is a circuit diagram showing an example of a laser drive circuit inside the laser drive system in FIG.

FIG. 3 is a power supply voltage sequence diagram of a laser device and an APC control circuit.

FIG. 4 is an overall configuration diagram of a color printer suitable for application to the present invention.

FIG. 5 is a diagram of a laser beam scanner used to explain the present invention.

FIG. 6 is a system diagram of a semiconductor laser drive circuit.

FIG. 7 is a timing chart of an unblanking period in a multiple rotation color printer.

[Explanation of symbols]

 31 Collimator Lens 32 Cylindrical Lens 33 Spherical Lens 34 Toric Lens 35 Reflecting Mirror 36 Horizontal Synchronizing Mirror 37 Optical Fiber 38 Rotating Polyhedron 40 Semiconductor Laser Unit 41 Semiconductor Laser (Laser Diode) 42 Photodiode 44 Signal Comparator 45 Control Circuit 46 Counter 47 D / A converter 48 laser drive circuit 49 APC control circuit in which 44 to 48 are integrated 50 laser voltage regulator 51 voltage V1 monitor 52 voltage V2 monitor 53 AND circuit 54 external IF circuit 55 logical sum circuit 56 APC permission determination circuit 57 50 To 56 integrated laser voltage control circuit 105 paper discharge unit 106 paper discharge tray 107 scanning optical unit 108 developing device selecting mechanism 109 developing device selecting mechanism holding frame 109a Soleno Id 109b intersection

Claims (4)

[Claims] 1. A light emitting element voltage control system in which a power source applied to a light emitting element driving circuit is stabilized by a voltage regulator, and the light emitting element driving circuit is APC controlled by an APC control circuit, wherein a first voltage applied to the voltage regulator is set. Monitor and
A first monitor circuit that generates a first signal when the first voltage is within a specified range, and a second voltage that is applied to the APC control is monitored,
Second monitor circuit that generates a second signal when the voltage of the second voltage is within a specified range, and a control circuit that enables the voltage regulator when both the first signal and the second signal occur A light-emitting element voltage control system comprising: 2. The control circuit further comprises a control circuit that enables the APC control circuit when both the first signal and the second signal are generated.
The light-emitting device voltage control system according to item 1. 3. The light-emitting element voltage control according to claim 1, further comprising a control circuit that is independent of the control circuit and that enables the voltage regulator to operate in response to an instruction from the outside. system. 4. The voltage regulator according to claim 1, the first monitor circuit, the second monitor circuit, the control circuit, the control circuit according to claim 2, and the control circuit according to claim 3. A light-emitting element voltage control system characterized by being integrated.