JP2596628Y2 - Laser output stabilization circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser output stabilizing circuit for adjusting and stabilizing the amount of laser light in a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, in a laser beam printer or the like, a light amount adjusting circuit (APC) has been employed to adjust the light amount of a laser beam to a predetermined value. In order to adjust the light amount of the laser, the output light from the laser is received by a pin photodiode or the like, and a voltage corresponding to the output of the pin photodiode is used as a monitor voltage, and a monitor voltage and a reference voltage (predetermined value) are calculated. The comparison is made by a comparator as a comparison means, and the output light amount of the laser is feedback-controlled. That is, the adjustment of the laser light amount has been completed when the output (“H” level or “L” level) of the comparator is switched from one to the other.

However, when the light amount of the laser is controlled as described above, the output light amount of the laser is adjusted so that the monitor voltage substantially matches the reference voltage. In addition, there is a possibility that the monitor voltage fluctuates and the output of the comparator is inverted.

After the light quantity adjustment is completed, feedback control of the laser output light quantity is not performed, but usually, even after the light quantity adjustment is completed, the monitor voltage and the reference voltage are always applied to the comparator. Therefore, as described above, the monitor voltage fluctuates in a state where the monitor voltage and the reference voltage are close to each other, so that the comparator oscillates after the light amount adjustment is completed, which adversely affects the laser output.

Conventionally, as shown in FIG. 10, external resistors R1 and R2 are connected to an operational amplifier (operational amplifier) to which a reference voltage Vref and a monitor voltage Vm are inputted, respectively, in order to prevent the above-mentioned oscillation of the comparator. Are connected as shown in the figure and a positive feedback is applied, so that a comparator (hysteresis comparator) having a hysteresis characteristic in the comparator is generally used.

However, in the configuration shown in FIG.
Since external components are used, cost increases are inevitable. Further, since the resistance values of the external resistors R1 and R2 have individual differences, the control value of the laser output light amount differs for each printer. There was a problem.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a laser output stabilization circuit that stabilizes a laser output by using no external parts and suppressing oscillation of a comparator. It is intended to provide.

[0008]

SUMMARY OF THE INVENTION Therefore, a laser output stabilizing circuit of the present invention receives a laser beam output from a laser output unit and outputs a light receiving signal corresponding to the amount of the laser beam. Output means, comparing means for comparing the received light signal with a reference signal corresponding to a predetermined laser output light amount, and, during a predetermined light amount adjustment period, as a result of the comparison by the comparing means, the light amount of the laser light is changed to the predetermined laser light amount. Light amount control means for increasing the light amount of the laser light output from the laser output means when it is determined that the light amount is smaller than the output light amount; and the light amount of the laser light being greater than the predetermined laser output light amount during the predetermined light amount adjustment period. Switching means for switching the received light signal input to the comparing means to a predetermined signal at the time of increase. It is.

Alternatively, contrary to the above, the laser output stabilizing circuit of the present invention receives a laser beam output from a laser output unit and outputs a light receiving signal corresponding to the amount of the laser beam. Means, a comparing means for comparing the received light signal with a reference signal corresponding to a predetermined laser output light quantity, and, during a predetermined light quantity adjustment period, as a result of the comparison by the comparing means, the light quantity of the laser light is changed to the predetermined laser output quantity. Light amount control means for reducing the light amount of the laser light output from the laser output means when it is determined that the light amount is larger than the light amount; and the light amount of the laser light being smaller than the predetermined laser output light amount during the predetermined light amount adjustment period. Switching means for switching the received light signal input to the comparing means to a predetermined signal at the time when It can also be.

[0010] The comparing means can be constituted by a comparator for comparing the voltage of the light receiving signal with the voltage of the reference signal.

Further, according to the above configuration, the comparing means can be configured by a level comparator instead of a hysteresis comparator having a hysteresis characteristic by an external resistor. Further, the level comparator can be constituted by a circuit using an operational amplifier in an open loop. Further, the voltage of the predetermined signal can be set higher or lower by a predetermined amount than the voltage of the reference signal.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser output stabilizing circuit to which the present invention is applied will be described in detail with reference to FIGS.

FIG. 1 is a block diagram schematically showing a laser output stabilizing circuit according to an embodiment of the present invention. In response to a control signal from the printer CPU 1, the laser drive circuit 2 drives the laser diode LD. The pin photodiode PD receives the output light of the laser diode LD, and sends a signal corresponding to the output light amount of the laser diode LD to the laser drive circuit 2. The laser drive circuit 2 outputs a monitor voltage Vm according to the output of the pin photodiode PD. The monitor voltage Vm passes through the multiplexer 4 as a switch, and is supplied to the comparator 10.
Is input to As shown in the figure, the reference voltage Vref is input to the comparator 10 in advance, and the comparator 10 compares the monitor voltage Vm with the reference voltage Vref and outputs “H”.
A signal Vo of a level or "L" level is output. The output signal Vo of the comparator 10 is input to the laser drive circuit 2 via the logic 3. Laser drive circuit 2
Controls the output of the laser diode LD according to the output Vo of the comparator. When the light amount adjustment is completed, a signal indicating the completion of the adjustment is output from the laser drive circuit 2 to the printer CPU 1. When the adjustment is completed, the laser beam is modulated according to the output data, and an exposure process is performed. There are various methods for adjusting the light amount of the laser output light, such as one for each page of exposure and one for each printing process. It can also be applied to the system type.

FIG. 2 is a flowchart showing the outline of the processing of the laser beam printer. When the power is turned on, initialization processing such as self-check and paper size setting is executed (S1). Upon completion of the initialization process, the process enters a data reception standby state (S2). When data from the host computer or the like starts to be input to the printer, a printing process is performed (S3). In the printing process, a receiving process of receiving data and storing it in a buffer, a light amount adjusting process described in detail later, and exposing a uniformly charged photosensitive drum with a laser beam whose light amount is adjusted to form a latent image Exposure processing, development processing to attach toner to the latent image, transfer processing to record and transfer the developed toner image to
A series of electrophotographic processes such as a fixing process for fixing the transferred toner image are executed.

To continue printing (S4: N
O), the process returns to the standby state, and waits for reception of the next data (S2). When printing is to be ended (S4: YE
S), the power is turned off, and the process ends.

FIG. 3 is a flowchart for explaining the operation of the laser output stabilizing circuit to which the present invention is applied.

When the printing process is started in S3 of FIG. 2 (that is, when the printing data is received), a predetermined signal is sent from the printer CPU 1 to the laser driving circuit 2 to adjust the amount of laser light (auto power control). ) Is started.

When the adjustment of the laser light amount (APC) is started, the monitor voltage Vm is applied to the comparator 10 (S10). When the APC is performed, always change the laser light amount from the minimum light amount side (comparator output is “L”).
Until the comparator output is inverted (until it changes from "L" to "H") by a predetermined amount (S11).

When the comparator output is inverted (S1
2: YES), it is considered that the reference voltage Vref and the monitor voltage Vm almost matched. However, as mentioned above,
This state is extremely unstable, and the comparator output Vo can take any value of “L” or “H” with a slight change in the monitor voltage Vm. When APC ends in this state,
Almost a predetermined amount of laser light can be obtained, but (AP
If the comparator 10 oscillates due to a slight change in the amount of laser light (after completion of C), there is a great possibility that the laser output will be adversely affected. Therefore, in the present invention,
When the comparator output Vo is inverted, the logic 3 controls the multiplexer 4 to switch the monitor voltage Vm input to the comparator 10 to the fixed voltage Vc (S13). That is, when the monitor voltage Vm substantially matches the reference voltage Vref, the input voltage of the comparator is switched to the fixed value Vc so that the comparator 10 does not oscillate, and the APC is terminated. With this control, after the light amount adjustment is completed, the comparator 10
Since the fixed voltage Vc is compared with the reference voltage Vref, the possibility that the comparator oscillates and adversely affects the laser output is extremely low.

As described above, in the laser output stabilizing circuit to which the present invention is applied, after the adjustment is completed, the monitor voltage Vm is switched to the fixed voltage Vc so that the comparator does not oscillate. For this reason, there is no need to use a hysteresis comparator in which positive feedback is applied to an operational amplifier (operational amplifier: hereinafter, abbreviated as an operational amplifier) using an external resistor as in the prior art, and as shown in FIG. Can be configured by a level comparator using the open loop. That is, with a simple circuit,
A highly reliable operation can be performed.

FIG. 4 shows the reference voltage Vref and the monitor voltage V
6 is a graph showing a change in m. While the comparator output Vo is at the “L” level, the amount of light is increased, and therefore the monitor voltage Vm is sequentially increased. Monitor voltage Vm is equal to reference voltage Vr
When the value exceeds ef (time Ti), the comparator output Vo is inverted from “L” to “H”. However, the monitor voltage Vm
And the reference voltage Vref is close, as shown in the figure,
The comparator output Vo repeats "H" and "L" (that is, the comparator oscillates).

Therefore, in the above embodiment, the time T
At s, the monitor voltage Vm is switched to the fixed voltage Vc. As shown in the figure, since the monitor voltage is sufficiently higher than the reference voltage, there is almost no possibility that the comparator 10 will oscillate.

In the embodiment shown in FIG. 3, the fixed voltage Vc is larger than the reference voltage Vref so that the comparator 10 does not oscillate. However, the fixed voltage Vc only needs to be separated from the reference voltage Vref so as not to oscillate, and as shown in FIG. 5, the fixed voltage Vc may be set smaller than the reference voltage Vref.

FIG. 6 shows a process for adjusting the laser light amount by decreasing it from the larger one to the smaller one, contrary to the embodiment of FIG. Also in this case, first, the monitor voltage Vm is input to the comparator 10 (S20). The laser light amount is lowered from the maximum light amount side (from the side where the comparator output Vo becomes “H”) until the comparator output Vo is inverted (until it becomes “L”) (S21, S22).
When the comparator output is inverted (S22: YE
S) After switching the monitor voltage Vm to the fixed voltage Vc (S23), the APC is terminated. Also in this case, the fixed voltage Vc can be set larger or smaller as long as the fixed voltage Vc is separated from the reference voltage Vref by such an extent that the comparator 10 does not oscillate.

In the circuit of FIG. 7, the multiplexer 5 is further added to the circuit of FIG. 1, and when the APC is completed, the monitor voltage Vm is switched to the fixed voltage Vc by the control of the logic 3 and the monitor circuit is turned off. I have.

FIG. 8 is a flowchart for explaining the operation of the embodiment of FIG. When APC is started, the multiplexers 4 and 5 are controlled by the logic 3 and the monitor voltage Vm is input to the comparator (S30), and at the same time, the monitor circuit is closed and turned on (S31).

When the APC is performed, as in the embodiment shown in FIG. 3, the laser light amount is changed from the minimum light amount side (from the side where the comparator output becomes “L”) until the comparator output is inverted (“L”). (Until it changes from "" to "H") by a predetermined amount (S32).

When the comparator output is inverted (S3
3: YES), it is considered that the reference voltage Vref and the monitor voltage Vm almost matched. However, in this state AP
When C is completed, there is a great possibility that the comparator 10 will oscillate due to a subsequent slight change in the amount of laser light as described above. Therefore, at the time when the comparator output Vo is inverted, the logic 3 controls the multiplexer 4 so that the monitor voltage Vm
Is switched to the fixed voltage Vc (S34). Further, the logic 3 controls the multiplexer 5 to turn off the circuit of the photodiode PD. That is, the monitor voltage Vm
And when the reference voltage Vref substantially matches, the input voltage of the comparator is switched to the fixed value Vc so that the comparator 10 does not oscillate, and the photodiode PD
APC is ended after turning off the monitor circuit including.

With this control, after the APC is completed, the comparator 10 outputs the fixed voltage Vc and the reference voltage Vref.
, And the possibility that the comparator oscillates is extremely low. In addition, when the light amount adjustment is not performed, the power consumption can be suppressed because the monitor circuit is turned off.

The fixed voltage Vc can be set higher or lower than the reference voltage Vref to the extent that the comparator 10 does not oscillate, as in the above-described embodiment.

FIG. 9 shows a control in the embodiment of FIG. 7 in which the adjustment is performed by decreasing the light amount from the maximum light amount side (from the side where the comparator output becomes "H") when adjusting the laser light amount. It is a flowchart which shows.

In the above embodiment, the voltage value output corresponding to the light amount of the laser beam is compared with the reference voltage value, and the light amount is adjusted based on the result. However, it is also possible to use means for outputting a current corresponding to the light amount of the laser. In this case, the same control can be performed by converting a current generated according to the light amount into a voltage value.

Alternatively, a means for generating pulse data corresponding to the amount of laser light can be used.
For example, it is conceivable to use means for generating a pulse having a pulse number corresponding to the light amount or a waveform (such as a duty ratio) corresponding to the light amount. In this case, the control of the present invention can be easily applied by converting the number of pulses or the waveform into a voltage value.

In each of the above embodiments, the reference voltage and the monitor voltage are compared as analog values. However, the present invention is not limited to this, and the same effect can be obtained even when a digital comparator corresponding to the laser light amount is compared with a reference digital value using a digital comparator as the comparator.

As described above, according to the laser output stabilization circuit of the present invention, the oscillation of the comparator is achieved without using any external parts and with a simple circuit configuration (a level comparator using an operational amplifier in an open loop). Thus, a laser output stabilizing circuit that can prevent and suppress the adverse effect on the laser output can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a laser output stabilization circuit to which the present invention is applied.

FIG. 2 is a flowchart illustrating an operation of the laser beam printer.

FIG. 3 is a flowchart illustrating an APC process.

FIG. 4 is a graph showing a relationship between a monitor voltage and a reference voltage, and an output of a comparator.

FIG. 5 is a graph showing a relationship between a monitor voltage and a reference voltage.

FIG. 6 is a flowchart illustrating a modification of the first embodiment.

FIG. 7 is a block diagram showing a configuration of a laser output stabilization circuit according to a second embodiment.

FIG. 8 is a flowchart illustrating an APC process according to a second embodiment.

FIG. 9 is a flowchart illustrating a modification of the second embodiment.

FIG. 10 is a circuit diagram showing a conventional hysteresis comparator.

[Explanation of symbols]

 2 Laser drive circuit 4 Multiplexer 5 Multiplexer 10 Comparator

Claims (7)

(57) [Scope of request for utility model registration] 1. A light receiving signal output means for receiving a laser light output from a laser output means and outputting a light receiving signal corresponding to a light amount of the laser light, and a reference corresponding to the predetermined light output amount of the laser light. A comparison means for comparing with a signal, and, during a predetermined light amount adjustment period, when the light amount of the laser light is determined to be smaller than the predetermined laser output light amount as a result of the comparison by the comparison means, the signal is output from the laser output means. Light amount control means for increasing the light amount of the laser light, and when the light amount of the laser light becomes larger than the predetermined laser output light amount during the predetermined light amount adjustment period, the light reception signal input to the comparison means A laser output stabilizing circuit, comprising: switching means for switching to a predetermined signal. 2. A light receiving signal output means for receiving a laser light output by a laser output means and outputting a light receiving signal corresponding to the light amount of the laser light, and a reference corresponding to the predetermined light output amount of the laser light. A comparison means for comparing with a signal, and, during a predetermined light amount adjustment period, output from the laser output means when it is determined that the light amount of the laser light is larger than the predetermined laser output light amount as a result of the comparison by the comparison means. Light amount control means for reducing the light amount of the laser light, and when the light amount of the laser light becomes smaller than the predetermined laser output light amount during the predetermined light amount adjustment period, the light receiving signal input to the comparing means A laser output stabilizing circuit, comprising: switching means for switching to a predetermined signal. 3. The method according to claim 2, wherein the comparing unit compares a voltage of the light receiving signal with a voltage of the reference signal.
The laser output stabilizing circuit according to claim 1 or 2. 4. The laser output stabilizing circuit according to claim 1, wherein said comparing means has a level comparator. 5. The level comparator comprises a circuit using an operational amplifier in an open loop.
The laser output stabilizing circuit according to claim 4. 6. The laser output stabilizing circuit according to claim 4, wherein a voltage of the predetermined signal is higher than a voltage of the reference signal by a predetermined amount. 7. The laser output stabilizing circuit according to claim 4, wherein a voltage of said predetermined signal is lower than a voltage of said reference signal by a predetermined amount.