JPH03234075A - Laser driver - Google Patents

Abstract

PURPOSE:To perform a dense and pale printing of high quality by providing a plurality of constant-current generating means, controlling quantities of lights at respective light quantity levels, and then emitting lasers at several levels of light quantities by a plurality of image signals. CONSTITUTION:A laser forcible lighting signal LDON1 is set to 'L' simultaneously upon starting of an APC, a latch input data 20 is incrementally increased to gradually raise the voltage of the output signal APC1 of a D/A converter 4, thereby increasing a laser driving current Il1. When the laser output exceeds a specific value of low quantity of light, a latch circuit 2 latches the input data of the converter 4, and sets a laser forcible lighting signal LDON2 to 'L' while a laser current is flowing to a semiconductor laser 10. The input data of the circuit 2 is incrementally increased to raise a laser driving current Il2, and when the quantity of the laser reaches a specific value of high quantity of light, the input data of a D/A converter 5 is latched to a latch circuit 3. Thereafter, video signals VIDEO1, VIDEO2 are input, and the laser 10 varies a density while varying the quantity of light to high or low to print it.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser driving device suitably implemented in, for example, an image recording device that emits a laser beam to record an image on a photoreceptor.

[Prior Art] Conventionally, a semiconductor laser that emits a laser beam has been used as a light source employed in this type of image recording apparatus 1, such as a laser beam printer, or has been put into practical use.

This semiconductor laser has a unique light quantity characteristic (I-characteristic) as shown in FIG. 8 between the drive current I and the light quantity pattern.

A semiconductor laser does not emit laser light (LED light emitting region) until a driving current that exceeds a certain threshold (I th) is applied, and starts emitting laser light when the above threshold (I th) is exceeded. do. In the laser emission region, the relationship between the drive current I and the amount of light has a certain slope. In addition, the vertical axis in FIG. 8 shows the amount of light, and the horizontal axis shows the drive current I.

As can be seen from this figure, in the laser emission region,
The relationship between the amount of light and the current has a certain slope (slope efficiency α).

By the way, in this type of image recording device, the laser power is set to a non-emission state (power "
O”). Then, the output power of the laser is monitored and the laser current is controlled to determine the laser current Ia so as to achieve a desired specified amount of light. And the specified light amount I
By driving the laser current Ia corresponding to LT at a constant current, the specified light amount or A is kept constant.

However, in the 1-1 characteristic of a semiconductor laser, even if it initially has the characteristic A, it is conceivable that the I-1 characteristic changes to B or C due to a change in the temperature of the semiconductor laser chip. Therefore, in a laser beam printer, in order to always print with the desired prescribed light intensity, the constant current drive circuit clears the laser power once before starting the printing operation of each page and controls the light intensity (APC). I am doing it.

The method for determining the current value of the constant current drive circuit described above is as follows:
There is a control method using a D/A converter 101 that converts digital values into analog values as shown in FIG.

In FIG. 9, 102 is a laser drive circuit, and a constant current circuit 10 determines the current flowing through the semiconductor laser 105.
4 and an image signal VIDEO from a controller (not shown)
It is composed of a switching circuit 103 that turns on and off the current flowing to the laser.

Next, the operation of the light amount control (APC) will be explained step by step.First, from the laser light amount control circuit (CPU) 100 to the D/A
An 8-bit signal 109 is sent to the converter 101, and the corresponding analog voltage 110 is sent to the D/A converter 1.
01 and determines one current setting for the constant current circuit 104. Next, it is set to "tow" and output to the line 113, and the semiconductor laser 105 is set to the current I! by the constant current circuit 104. ; Press L to force the light on. A current is passed through the PIN photodiode 106 that is irradiated with the laser beam, and a monitor voltage VW proportional to the amount of laser beam is applied to the line 111.
occurs in

The monitor voltage VM is input to the A/D board of the laser light amount control CPU 100 via the voltage follower 107, converted into a digital value inside the CPU 100, and compared with the digital value corresponding to the target light amount, until the target light amount is reached. If not, 8-bit D/A converter input signal 10
If the operation is 0 or more by incrementing 9/A converter input signal or 00H (laser current 0 [mA]), repeat this in order until the target light amount is reached.

The D/A converter input signal is incremented, for example, as shown in FIG. 10, so that the amount of increase decreases as it approaches the target value.

[Problems to be Solved by the Invention] However, in the conventional example, the laser light intensity is set at one level, and it is not possible to emit light at a plurality of light intensity levels.

Therefore, for example, when outputting a laser beam with multiple levels of light intensity to perform gradation recording, it is not possible to set the laser light intensity for each level, which deteriorates the recording quality when performing gradation recording. There was a problem.

An object of the present invention is to provide a laser drive device that solves the above technical problems and can perform high-quality gradation recording when recording using laser light.

[Means and effects for solving the problem] According to the present invention, in order to generate a plurality of constant currents corresponding to a plurality of light intensity levels, a plurality of constant current generating means are provided, and APC is performed for each light intensity level. After that, laser irradiation with multiple levels of light intensity is performed using multiple image signals, making it possible to print with high quality shading.

Embodiment FIG. 1 is a block diagram of the first embodiment of the present invention. APC is performed for each level of light intensity using a laser drive circuit.

First, with reference to FIG. 2, the operation of a series of feedback systems of the D/A converter input value, laser drive current, and light emission amount monitor voltage will be described as time passes. First D/
XD [old] is input to the A converter, and a voltage corresponding to it is output from the D/A converter. In the laser drive circuit, the current In [mA] corresponding to the D/A converter output
is applied to the laser as a laser drive current. If the light emitting light amount monitor voltage VM, which is a voltage proportional to the laser light amount, has not reached the voltage VT [■ν1 corresponding to the specified light amount], the D/A converter input value XD is counted up.

When XD is counted up, the laser drive current Ill increases accordingly, and the light emission amount monitor voltage VM also increases. The above operation is repeated until the emitted light amount monitor voltage Vllll reaches the voltage 7 to [1v] corresponding to the specified light amount. At this time,
As can be seen from FIG. 2, as the count value XD increases, a time lag occurs until the light emission amount monitor voltage VM becomes stable. This is the time constant of the circuit system or
Depends on responsiveness.

Next, a series of sequences from the start to the end of APC will be explained. FIG. 3 shows a timing chart. First, low light intensity APC is performed, followed by high light intensity APC. First, at the same time as APC starts, the laser light amount control CPU shown in Figure 1
i sets all output ports Do-Dn to "L", sets strobe signals 5TBI and 5TB2 to "H" for a predetermined period of time, causes latch circuit 2 and latch circuit 3 to latch OHn, and connects D/A converter 4 and D/A converter 8 to Set the output of 5 to 0 [vl. Next, the laser forced lighting signal LDONI on line 15
is set to "L", the latch input data 20 is incremented, and the Apcxi voltage of the signal on the line 23, which is the output of the D/A converter 4, is gradually increased to increase the laser drive current IJ.
The laser drive current Ill increases by 1+[mA]
When the light emission threshold current is exceeded, laser light emission starts, and the voltage vM of the monitor voltage line 27 corresponding to the laser light intensity is inputted to the A/D port of the laser light intensity control 1 cPU1 and coated. If the code does not reach the code corresponding to the specified value of the low light amount, the CPU 1 roughly increments the latch input data.

Repeating this operation, the latch circuit 2 latches the input data of the D/A converter 4 at the time when the laser output exceeds the specified value of low light intensity, and the data is output from DO to Dn of the CPU 1.
Increment of and strobe signal 5TB on line 17
Stop I. Next, while the forced laser lighting signal U is kept at "L", that is, while the laser current that outputs the specified low light intensity is flowing through the semiconductor laser IO, the forced laser lighting signal LDON2 on the line 16 is set to "L". Then, add the laser drive current IfL.

In other words, the drive current In of the semiconductor laser 10 is 1M+ and Il
It becomes the sum of g. Then, in the same way as the above operation, the input data of the latch circuit 2 output from the CPU 1 is incremented, and the laser drive current 1flt is increased until the laser light intensity or high light intensity reaches the specified value. When the light amount reaches the specified value, the strobe signal 5TB2 on the line 28 is stopped and the input data of the D/A:ff inverter 5 is latched in the latch circuit 3.

Then, the laser forced lighting signals LDONI and LDON2 are set to H'' to end APC.

After APC is finished, the image signal VID is sent from the controller.
El and VIDEO2 are input, and in response to the image signal, the semiconductor laser 10 blinks while changing the amount of emitted light from high to low to irradiate a photosensitive drum (not shown), and print with varying density using electrophotography. In this embodiment, the relationship between the image signal and the density is as shown in the table below.

If this embodiment is used when outputting a photographic image using the dither method, the gradation will be improved, and the gradation will also be improved when outputting a photographic image by changing the pulse width of the image signal. performance is improved.

FIG. 4 is a flowchart of a series of sequences.

The sequence of this embodiment may be performed for every printed page, or every several pages, or
Also, after performing low light intensity and high light intensity PAC before printing the first page, from the second page onward, low light intensity and high light intensity A are performed between each page.
You may also do this by changing the PC.

When the APC operation is started (step S1), the laser drive current is set to a predetermined minimum value (step S2). Next, in step S3, target values for low light intensity and high light intensity are set.

Next, the low light intensity laser current I or 3 is applied and the voltage VM is checked. (Steps S4 and S5) Next, it is determined whether the voltage VM has exceeded the low light level target value or not (Step S6). If not, the input of the D/A converter 1 is incremented and the process returns to Step S5 (Step S6). S7).

When the voltage VM exceeds the low light amount target value, the input value of the D/A converter 4 is determined (fixed) (step S8).

After this, the laser current for high light intensity is changed to 1fl,
In addition, the voltage is applied to the semiconductor laser lO, and the voltage VM is checked again (step S9510).Next, it is determined whether the voltage VM exceeds the high light intensity target value (step S511).
, if not, the input value of the D/A converter 5 is incremented and the process returns to step SIO. When the voltage VM exceeds the high light intensity target value, one line of the D/A converter 5 is stopped and the APC operation is ended (step S Is).

Second Embodiment> FIG. 5 is a block diagram of the second embodiment, and FIG. 6 is a timing chart thereof. In this embodiment, the setting of the low light intensity laser light output is performed by D/ This is done using the analog voltage 33 output from the A boat, and the high light intensity laser light output is set using the counter clock 34 output from the boat of the laser light amount control CPU 40.
The bit counter 30 is counted up, inputted to the D/A converter 31, and the output 36 is used.

Next, a series of operations of APC will be explained. First, APC15J
At the beginning of l, the CPU 40 sets the output of the D/A boat to 0[V
], the C1ear input 37 of the counter 30 is enabled and the output of the counter 30 is set to "OH". Next, set the laser forced lighting signal LDONI on line 15 to L', gradually increase the analog output of the D/A boat output 32, and when the laser light output reaches the specified low light intensity, change the D/A boat output at that time. The CPU 40 holds the counter clock 34 and then sends the counter clock 34 to the counter 30 to count up and output the D/A.
The output voltage of the converter 31 is gradually increased and the counter 30 is incremented until it reaches a specified high light intensity. When the laser light output reaches a specified high light intensity, the counter clock 34 is stopped and the output of the counter 30 is held. When the APC is completed, the laser light output is changed in magnitude as in the first embodiment, and the laser is blinked to perform shading printing.

In this embodiment, it is possible to reduce the number of ports used by the laser light amount control CPU.

<Third example> FIG. 7 shows a block diagram of the third embodiment.

In this embodiment, numeral 38 is an n-bit up/down counter which is switched between active counting and town counting via a control line 39. Next, the operation will be explained. Before printing the first sheet, APC similar to that in the second embodiment is performed. At this time, the counter 38 is set in up count mode. In the APC performed before printing the second page, the analog voltage 32 from the D/A board of the CPU 40 outputs the previous value as it is,
If the laser light monitor voltage VM is lower than the low light amount specified value, increase the D/A output 32, if higher, D/A output 32
Lower the.

Similarly, when setting the high light amount, the previous value is output as is, and if the laser light monitor voltage VM is lower than the high light amount specified value, the counter 38 counts up, and if it is higher, it counts down.

In this embodiment, it is possible to shorten the time required for APC from the second time onward.

[Effects of the Invention] As described above, by blinking the laser at a plurality of levels of light intensity set with n-bit accuracy, higher quality shading printing can be performed.

Furthermore, if Honshi-ZaDrye is used to output photographic images, images with good gradation can be obtained.

[Brief explanation of drawings]

1 is a block diagram of the first embodiment; FIG. 2 is a timing chart showing the laser drive current of the first embodiment; FIG. 3 is a timing chart showing the APC operation of the first embodiment; The figure is a flowchart of the APC operation of the first embodiment, Figure 5 is a block diagram of the second embodiment, Figure 6 is a timing chart of the second embodiment, and Figure 7 is a block diagram of the third embodiment. FIG. 8 shows the I-L characteristics of a semiconductor laser. FIG. 9 is a block diagram of a conventional example, and FIG. 10 shows a fluff of time and laser current in a conventional example. l is between laser light amount @CPU, 4 is D/A converter 1,
5 is a D/A converter 2, IO is a semiconductor laser, 11 is a Din photodiode 26 is a laser drive circuit, 27 is a laser light monitor voltage VM, 30 is a counter, and 31 is a D/A converter.
A controller/<-ta, 40(, t laser light amount u4CPU,
38 is an up/down counter.

Claims (2)

[Claims] (1) A laser driving device for generating a laser beam with a plurality of levels of light intensity from a light source, comprising: a detection means for detecting the light intensity of the laser beam emitted from the light source; a plurality of constant current generation means; and a plurality of the plurality of constant current generation means. constant current setting means provided individually corresponding to the constant current generating means and setting a constant current value of each constant current generating means based on the light intensity of the laser beam detected by the detecting means; 1. A laser driving device comprising: selection means for selectively applying a constant current generated by the current generation means to a light source. (2) In the laser driving device according to claim 1, the constant current setting means includes a counting means and an A/D conversion means for converting the counted value of the counting means into an analog signal,
A laser driving device characterized in that the constant current value is set by performing a counting operation of a counting means until the amount of light of the laser beam detected by the detection means reaches a predetermined value.