JPH0761721B2 - Laser diode control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a control device for a laser diode that generates a laser beam used in a laser printer or the like.

<Prior Art> Generally, the output characteristics of a laser diode are as shown in FIG. 2, and the output of the laser diode can be increased or decreased by the current supplied to the laser diode.

<Problems to be Solved by the Invention> On the other hand, when a current supplied to the laser diode exceeds a predetermined value, the control element or the like may be destroyed. Therefore, conventionally, it was necessary to provide a plurality of circuits for limiting the current supplied to the laser diode.

The present invention has been made in view of the drawbacks of the related art. When the laser diode outputs light of a predetermined value or more, it is detected and the circuit for supplying a current to the laser diode is forcibly cut off. Therefore, it is an object of the present invention to provide a control device that prevents destruction of a control element and the like without providing a complicated circuit, and also enables highly accurate laser diode output control with a simple circuit.

<Means for Solving Problems> A laser diode control device of the present invention includes a storage means for storing a value for driving the laser diode in order to supply an appropriate current to the laser diode for recording. Drive means for controlling the amount of current supplied to the laser diode according to the value stored in the storage means, monitor means for monitoring the output of the driven laser diode, and the output value of the monitor means in advance Comparing means for comparing with a predetermined reference value, and increasing / decreasing the amount of current supplied to the laser diode so that the output of the laser diode matches the output corresponding to the reference value, according to the comparison result by the comparing means. And a control means for controlling the current, wherein the control means monitors the current in a proper state supplied to the laser diode during non-recording. In order to achieve this, an initial value corresponding to the initial drive current amount of the laser diode is stored in the storage means, and the output value of the laser diode driven according to the value stored in the storage means and the proper light emission. And a calculation unit that adds or subtracts a value obtained by dividing the initial value into two with respect to the value stored in the storage unit according to a comparison result with a reference value
In order to store the calculation result in the storage means and repeat the calculation by the calculation means a predetermined number of times, based on the comparison result of the comparison means, the value to be added or subtracted is divided by 2 minutes. The value obtained after the predetermined number of times of calculation is stored in the storage means, and it is detected that the light emission amount of the driven laser diode exceeds the upper limit. A detection means and a means for stopping the operation of the drive means for controlling the amount of current to the laser diode in response to the detection signal from the detection means, and according to the proper value stored in the storage means during recording. The laser diode is driven via the driving means.

<Operation> According to the apparatus of the present invention, the control means monitors the output of the laser diode during non-recording and drives the laser diode with a current amount according to the initial value in order to drive the laser diode with a proper current for proper light emission. To drive. At this time, the output value of the laser diode is monitored by the monitor means, and the output value,
Based on the result of comparison with a reference value for proper light emission, an initial value (N) corresponding to the initial amount of current and a value obtained by dividing the initial value by two are calculated by the calculating means as N ± N / 2. And store it in the storage means.

Then, the laser diode is driven again with the amount of current according to the value stored in the storage means, and the value added / subtracted last time is output according to the comparison result between the output value and the reference value as in the monitor means.
The calculation means performs calculation of N ± N / 2 ± N / 4 by using a value obtained by further dividing N / 2 into two, as an addition or subtraction value. This is repeated a predetermined number of times to gradually decrease the addition or subtraction value divided into two,
The calculated result is stored in the storage means as an appropriate value.

At this time, when the light emission state of the driven laser diode exceeding the upper limit is monitored by the monitoring means, the monitored output value is detected by the detection means,
The current supplied to the laser diode driven by the current amount of current is forcibly prohibited. This allows
It is possible to prevent the laser diode from being damaged during the monitoring of the proper light emission and the damage to each element accompanying it, and to monitor the proper light emission.

Here, in the comparison result by the comparison means, if the value by the monitoring means is larger than the reference value, the current amount supplied to the laser diode is large. At this time, if the output value of the monitor means exceeds the light emission amount that is the limit for driving the laser diode, the current supply to the laser diode is immediately prohibited as described above, and the current amount is also reduced. As described above, the value obtained by further dividing the value obtained by the addition and subtraction is subtracted, and the laser diode is driven by this to effectively monitor the proper light emission of the laser diode that matches the reference value, and at the same time, to detect the excess current. At the time of supply, the protection drive of the laser diode is immediately performed.

As described above, the driving for monitoring the appropriate light emission of the laser diode is performed by adding and subtracting while increasing the value at the initial stage and gradually decreasing the value, so it is sufficient to always make a fixed number of drive adjustments, and quickly. Appropriate light emission can be adjusted and its accuracy can be adjusted to the minimum value of addition and subtraction values.

<Examples> Hereinafter, an automatic output control device for a laser diode according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram when an embodiment of the present invention is used in a laser printer.

In the figure, 1 is a central control unit, 2 is a programmable duty control circuit, and based on a control signal input from the central control unit 1, a laser power control signal (hereinafter
PCON) pulse duty is programmable and controlled in multiple steps. 3 is pulse wide modulation (hereinafter PW) of the duty-controlled PCON.
M) is a smoothing circuit for smoothing to a DC analog signal. Reference numeral 4 denotes a current conversion circuit that controls the supply current to the laser diode 5 that emits a laser beam, and biases the lowest threshold current of the laser diode 5 and constantly supplies a predetermined current to the laser diode 5. The laser diode 5 has a built-in monitor PIN diode 5'which is a light receiving element. 6
Is a comparison circuit for comparing the output voltage from the PIN diode 5'with a reference voltage, and the output from the comparison circuit 6 is input to the central control unit 1 as a reference signal LMNT and input from the central control unit 1. The duty control circuit 2 controls the pulse duty of the PCON based on the control signal. An image signal conversion circuit 7 latches a VIDEO signal for image printing by a D-type flip-flop and outputs it as a printing signal ▲ ▼. The AND gate 8 and the transistor 9 are the above-mentioned ▲ ▼ or ▲
ON / OFF of the laser diode 5 is controlled by ▼, and the ▲ ▼ becomes high during the automatic power control period. The current flowing into the laser diode 5 increases as the High period of the PCON signal increases. Therefore, when the output of the laser diode 5 is reduced, the current flowing through the laser diode 5 is increased so that the PC
A constant laser output is maintained by increasing the ON duty of the ON signal. The laser power control signal PCON is input to the smoothing circuit 3 from the programmable duty control circuit 2 and is output to the current conversion circuit 4 as a pulse wide modulation signal PWM to control the current of the laser diode 5. The current conversion circuit 4 constantly applies a predetermined bias to the laser diode 5. This is because the optical output of the laser diode 5 is generally almost 0 in the low current region as shown in FIG. 2, and the actual control target region is only the Y portion. Therefore, it suffices to apply a bias in advance only to the X portion.

Also, the VIDEO signal is latched by the D-type flip-flop of the process control unit 7
Output as ▼. Here, in the AND gate 8, when the ▲ ▼ is High, the current of the laser diode 5 is bypassed to the transistor 9 and the laser is OF
Form F and form a non-exposed area on the photoconductor. The laser diode 5 incorporates the monitor PIN diode 5'as described above, and its output current is used for adjusting the light output and preventing destruction against excessive light emission. The output current of the PIN diode is converted into a voltage and then compared with a reference voltage by a comparison circuit 6 to generate a reference signal LMNT for automatic power control.

FIG. 3 is a flow chart showing the operation during non-recording for auto power control according to the present invention, that is, for monitoring the state of proper light emission of the laser diode, and FIG. 4 is a time chart during this operation.

First, the central controller 1 sets the enable signal ▲ ▼ for automatic power control to the low state (n
1) and programmable duty control circuit 2
The control start signal is output to. At this time, the programmable duty control circuit 2 sets the count value N (for example, 128) corresponding to the preset duty in the counter A and the counter B (n2, n3).

Next, when the counter A is set to N (n4), the count value N
A PCON having a duty based on the above is issued by the programmable duty control circuit 2 (1 in PCON in FIG. 4). The counter B is a control value for automatic power control, and the control value B divides N into two (n
5) This value is added to or subtracted from the value of the counter A as described later. Then, the value of the counter A can be gradually brought close to the target value by repeating the loop of n4 to n9. That is, in n6, based on the comparison result of the comparison circuit 6, the content of the counter A is added or subtracted by the value of the counter B that stores the control numerical value that gradually changes so as to approach the reference voltage to the programmable duty control circuit 2. (Addition / subtraction is performed according to the comparison result), and finally the counter A stores a value (state of proper light emission) in the pulse width of the laser diode that matches the reference voltage.

The PCON generated from the programmable duty control circuit 2 is smoothed into a DC analog signal by the smoothing circuit 3,
The current conversion circuit 4 controls the current supplied to the laser diode 5.

The output from the laser diode 5, that is, the output of the PIN diode 5 ', and the reference voltage are compared by the comparison circuit 6 (n6). As a result, when the reference signal LMNT is High, the control signal input from the central control unit 1. The counter A of the programmable duty control circuit 2 is a value obtained by subtracting the control value N / 2 from the count value N based on Is set to (n7). If the reference number LMNT is Low, Is set to (n8). This arithmetic operation is repeated until the value of the counter B becomes 1, which is the minimum value. When the value of the counter B becomes 1 (n9), a signal of B = 1 is input from the programmable duty control circuit 2 to the central controller 1,
▲ ▼ becomes High (n10), and the laser diode 5 is turned on / off by the signal of ▼ of the process control unit 7.

The automatic power control operation is shown in FIG. 5, where the vertical axis represents the value of the counter A and the horizontal axis represents the number of times n of the automatic power control operation. As shown in the figure, when the output voltage of the laser diode 5 based on the value of counter A is smaller than the reference value, LMNT
It becomes Low, and when the output voltage of the laser diode 5 based on the value of the counter A is large, LMNT becomes High. As shown in the figure, when the automatic power control operation is repeated, A gradually approaches the target value.

As described above, according to the present invention, the output of the monitor PIN diode built in the laser diode 5 is compared with the reference voltage, and the output of the laser diode is made constant according to the preassembled operation based on the value. is there.

Although only the pre-processing until the start of recording is described in this embodiment, the comparison circuit 6 constantly compares the output voltage of the laser diode 5 with the reference voltage, and when the image is not formed, that is, ▲ ▼. Is High, press ▲ ▼
When it is set to Low, the automatic power control operation can be performed, and at the time of recording, the recording operation is performed according to the state of proper light emission of the laser diode stored in the counter A.

FIG. 6 is a diagram showing a specific configuration of the main part of FIG. 1, and its specific operation will be described below with reference to the drawings.

A bias current up to the current Ixm shown in FIG. 2 is constantly supplied to the laser diode 5 via the transistor 10 and the resistor R1.

The output from the programmable duty control circuit 2, which controls the pulse duty of the laser power unit control signal in multiple stages in a programmable manner based on the control signal input from the central controller 1, is the resistance R.
It is supplied to the current conversion circuit 4 composed of the transistor 11 and the transistor 12 and the resistor R5 through the smoothing circuit composed of 2, R3, R4 and the capacitors C1, C2, and the laser diode 5 is controlled by the current conversion circuit 4.

The light output from the laser diode 5 is detected by the feedback control diode 5 ', is input to the comparison circuit 6, and is compared with the reference voltage generated from the reference voltage circuit composed of the resistors R6, R7 and R8, The comparison value is input to the central processing unit 1.

At this time, the feedback control diode 5 '
When it is detected that the detection output of 1 is equal to or more than the Zener diode 13, the transistor 14 is turned on. Therefore, the collector potential of the transistor 14 drops regardless of control by the automatic power control (APC), and the potential of the base terminal of the transistor 11 of the current conversion circuit 4 connected to the collector of the transistor 14 also drops forcibly. , The transistor 11 is turned off. As a result, the current conversion circuit 4
The current supply operation to the laser diode 5 is prohibited.

Therefore, when there is a light output from the laser diode 5 which is equal to or more than a predetermined value in order to monitor proper light emission, this is output by the monitoring diode 5'and this output value is sent by the zener diode 13 to the laser diode. Since light emission exceeding the upper limit of 5 is detected, this detection turns on the transistor 14 that operates as drive stopping means to prevent the supply of excess current to the laser diode 5 and forcibly shuts off the current conversion circuit 4. ing. Therefore, the laser diode 5 and the diode 5'which is a control element are prevented from being destroyed. At this time, the comparison means 6 naturally performs the above-described subtraction operation for reducing the amount of current supplied to the laser diode 5, assuming that the monitor output exceeds the reference value.

On the other hand, after the proper light emission state of the laser diode 5 is controlled according to the output of the monitor diode 5'as described above, the data signal related to the recording is actually transmitted through the AND gate 8 and the transistor 9 during the actual recording. The laser diode 5 is driven by being supplied with a current in the adjusted appropriate emission state.

<Effect> As described above, according to the apparatus of the present invention, the proper light emission state by the laser diode is monitored before the start of recording, that is, at the time of non-recording, and it corresponds to the current for supplying to the laser diode in multiple stages. Since the control is performed by changing the pulse width, the accuracy is extremely high and the proper light emission state can be quickly monitored. In this case, when the amount of emitted light exceeding the limit of the laser diode to be driven is detected, the current supply to the laser diode can be immediately shut off, so damage to the laser diode and its accompanying monitor elements, etc. can be prevented. This can be prevented in advance, and at the same time, the operation for adjustment for properly emitting the laser diode can be accurately performed.

Therefore, during recording, the laser diode can be driven in an appropriate light emission state monitored during non-recording, and recording can be performed very stably.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a laser diode control device of the present invention, FIG. 2 is a diagram showing a relationship between a current value supplied to the laser diode of the device and an optical output, and FIG. 3 is an auto power of the device. Flow chart showing the control operation,
FIG. 4 is a time chart during the automatic power control operation of the same apparatus, FIG. 5 is a diagram showing the state of the counter A during the automatic power control operation, and FIG. 6 is a specific configuration of the main part of FIG. It is a figure. 1: Central control unit, 2: Programmable duty control circuit, 3: Smoothing circuit, 4: Current conversion circuit, 6: Comparison circuit.

Claims (1)

[Claims] 1. A storage means for storing a value for driving the laser diode in order to supply an appropriate current to the laser diode for recording, and the laser according to the value stored in the storage means. Drive means for controlling the amount of current supplied to the diode; monitor means for monitoring the output of the driven laser diode; comparison means for comparing the output value of the monitor means with a predetermined reference value; According to the comparison result by the means, a control means for controlling the increase or decrease of the amount of current supplied to the laser diode so that the output of the laser diode matches the output corresponding to the reference value, and the control means, In order to monitor the current in the proper state supplied to the laser diode during non-recording, the initial drive current of the laser diode is adjusted. The same initial value is stored in the storage means, and the initial value is set to 2 by the comparison result between the output value of the laser diode driven according to the value stored in the storage means and the reference value for proper light emission. A calculation means for adding or subtracting the divided value to or from the value stored in the storage means,
In order to store the calculation result in the storage means and repeat the calculation by the calculation means a predetermined number of times, based on the comparison result of the comparison means, the value to be added or subtracted is divided by 2 minutes. The value obtained after the predetermined number of times of calculation is stored in the storage means, and it is detected that the light emission amount of the driven laser diode exceeds the upper limit. A detection means and a means for stopping the operation of the drive means for controlling the amount of current to the laser diode in response to the detection signal from the detection means, and according to the proper value stored in the storage means during recording. A laser diode control device in which a laser diode is driven via the drive means.