JPH0754957B2 - Light quantity control device for recording device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light amount control device for a recording apparatus having a beam generating means for generating a beam for recording information.

[Prior Art] Conventionally, a laser beam printer is generally known as a laser recording apparatus of this type. This printer forms an electrostatic latent image by exposing and scanning a photoconductor using laser light modulated according to the input information, and visualizes this electrostatic latent image with a magnetic developer called toner. The image is transferred onto a recording material such as paper.

FIG. 10 shows an example of the above-mentioned conventional laser beam printer. In the figure, reference numeral 1 denotes a photosensitive drum which is rotatably supported in a housing H and has a semiconductor layer such as selenium or cadmium sulfide on its surface, which rotates at a constant speed in the direction of arrow A in the figure. Reference numeral 2 is a semiconductor laser that emits a laser beam L, and 2A is a control circuit that controls the laser light amount and turning on / off of the semiconductor laser 2 according to input information.

The laser light L emitted from the semiconductor laser 2 is incident on the beam expander 3 and becomes a laser light having a predetermined beam diameter. This laser light is incident on a polyhedral mirror 4 having a plurality of mirror surfaces. The polygon mirror 4 is rotated at a predetermined speed by a low-speed rotation motor (scanner motor) 5, so that the laser light emitted from the beam expander 3 is reflected by the polygon mirror 4 rotating at a constant speed and is substantially horizontal. To be scanned. Next, the laser light is imaged as spot light on the photosensitive drum 1 which is charged to a predetermined polarity by the charger 13 by the imaging lens 6 having the f-θ characteristic.

A beam detector 7 detects the laser light reflected by the reflection mirror 8. The timing of the modulation operation of the semiconductor laser 2 for obtaining the desired optical information on the photosensitive drum 1 is determined by the detection signal of the beam detector 7 described above. On the other hand, an electrostatic latent image is formed on the photosensitive drum 1 by the laser light image-formed and scanned according to the above-mentioned input information.
This latent image is visualized with toner in the developing device 9 and then transferred onto a recording material (generally, a sheet) fed from one of the cassettes 10 and 11. Thereafter, the recording material passes through the fixing device 12, so that the image is fixed on the recording material and is discharged to a discharging portion (discharge tray) not shown.

By the way, in such a laser beam printer,
The characteristic of the laser light amount (I-l characteristic) with respect to the laser current (driving current) of a semiconductor laser that is generally used is
It is as shown in FIG. That is, as shown in FIG. 11, the semiconductor laser has a laser current I with a certain threshold value (I
_{Although the} laser emission is not performed until _th ), the laser emission is performed when the threshold value is exceeded, and in the laser emission state, the laser light amount 1 with respect to the laser current I has a certain inclination α. This α is called slope efficiency.

In the laser beam printer by performing the light quantity control of the semiconductor laser 2 by the control circuit 2A, and determines the laser current I _T to be defined quantity l _T. At that time, the laser light amount I _T is kept constant by driving the laser current I _T at a constant current.

However, the semiconductor laser has the 12th characteristic in the I-l characteristic.
As shown in the figure, it initially has a characteristic of A, and when the laser current is constant current driven by I _TA in order to regulate it to a predetermined prescribed light amount l _TA , a current is passed through the semiconductor laser. Due to the increase in the chip temperature of the semiconductor laser and the like, the I-l characteristic may change to B or C after that.

Therefore, when the required specified light amount l _TA is scanned on the photosensitive drum 1, it is normal, but the I-l characteristic changes as shown in FIG. 14, and the laser current is I _T despite the laser current. When the amount of light is as small as 1 _TB as in B, the above-mentioned latent image may not be possible, and when it is as large as 1 _TC as in C, the laser chip is destroyed. There is a risk.

Therefore, conventionally, in a non-printing period such as a sheet interval of printing, a light amount control operation is performed in which the light emission amount of the semiconductor laser is detected and the drive current is controlled so that the detected light amount becomes the specified light amount l _TA . That is, by using a digital / analog converter, a driving current corresponding to the output digital value is configured to be applied to the semiconductor laser, and the digital value is sequentially counted up until the detected light amount reaches a specified light amount l _TA. , Hold the digital value when the specified light intensity l _TA is reached. During the printing period, a drive current corresponding to the held digital value is applied to the semiconductor laser according to the recording signal.

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, in order to reduce the so-called quantization error and control the light quantity with high accuracy, if the number of bits of the digital value to be output is increased, the digital / multi-bit Since the analog converter is expensive, the cost is increased, and since the amount of change in the drive current that changes with one count-up is small, the light amount control operation takes a long time.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a light amount control device of a recording device capable of highly accurate light amount control in a short time without causing a significant increase in cost. .

[Means for Solving the Problems] In order to achieve such an object, a light quantity control device for a recording apparatus according to the present invention comprises: a beam generating means for generating a beam for information recording; and a beam generating means for generating the beam from the beam generating means. Detecting means for detecting the light quantity of the emitted beam, digital value outputting means for outputting the first and second digital values respectively, and first and second D / for converting the first and second digital values into analog values, respectively. A conversion means, a current generation means for generating a current to be applied to the beam generation means based on the outputs of the first and second D / A conversion means, and a first digital value which is sequentially increased from the digital value output means. A first means for gradually increasing the current applied to the beam generating means by outputting a value; and the detecting means for increasing the current applied to the beam generating means by the first means. Second means for determining a specific first digital value in response to the output of the reaches the first value, the second
While the specific first digital value determined by the means is being output, the second digital value that is sequentially increased is output from the digital value output means, whereby the current applied to the beam generating means is further gradually increased. Increase to the third
Means and fourth means for determining a particular second digital value in response to the output from the detecting means reaching a second value due to an increase in the current applied to the beam generating means by the third means. And a control means having the above-mentioned means, wherein the current increase amount per unit time by the first means is made larger than the current increase amount per unit time by the third means.

[Operation] In the light quantity control device according to the present invention, when the first means sequentially increases the first digital value to be output to the first D / A conversion means, the current increase amount per unit time is large, and thus the high speed The current applied to the beam generating means can be increased, and the third digital means outputs the specific first digital value determined by the second digital means. When outputting the second digital value that sequentially increases from 0 to 1, since the amount of increase in current per unit time is small, the light emission amount of the semiconductor laser can be controlled with high accuracy.

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

FIG. 1 shows a circuit configuration of essential parts of an embodiment of the present invention.

In FIG. 1, reference numeral 101 denotes a central processing unit (CPU), which controls the entire information recording process. Reference numeral 102 denotes a laser light amount comparison control circuit, which is composed of a one-chip microcomputer having an A / D (analog / digital) conversion circuit built-in, and which controls the laser light amount according to the control procedure shown in FIG.
The control shown in the figure is performed. Reference numeral 103 is a bias current control circuit having a D / A (digital-analog) conversion circuit connected to _one output B _{1 to} B _n of the laser light amount comparison control circuit 102. Reference numeral 104 denotes a bias constant current circuit controlled by the circuit 103, to which the bias current I _B is input. Reference numeral 105 denotes a light emission current control circuit having a D / A conversion circuit connected to the other outputs D _{1 to} D _n of the laser light amount comparison control circuit 102. 106
Is a light emission constant current circuit controlled by the circuit 105, and through the light emission current switching circuit 107, the light emission current I _D
Is entered.

Reference numeral 108 is a semiconductor laser, and 109 is a photodiode for receiving the laser beam of the laser 108. 110 is the photodiode 1
A laser light amount monitor circuit supplied with the detection signal from 09, and a voltage V _M corresponding to the detected light amount is output to the laser light amount comparison control circuit 102. 111 is a laser light amount setting circuit for setting the laser light amount. 121 is an AND gate and 122 is an OR gate.

Next, the operation of the above laser light amount comparison control circuit 102 will be described with reference to the flowchart of FIG.

Automatic light intensity adjustment start signal (AP) from central processing unit (CPU) 101
CST) 113 is sent (step 201), the laser light amount comparison control circuit 102 determines in step 202 the emission current control circuit.
The input signals D _{1 to} D _n and B _{1 to} B _n of the D / A conversion circuit of the bias current control circuit 103 and the bias current control circuit 103 are all cleared, whereby the semiconductor laser is passed through the light emission constant current circuit 106 and the bias constant current circuit 104. Laser current Il flowing through 108 (emission current I _D
+ Bias current I _B ) to a sufficiently small value (for example,
A laser current Il is set within the laser emission region. ). In the next step 203, a video signal (Video
(LON) signal) 116 is set to TRUE and the semiconductor laser 10
The gate of the switching circuit 107 is opened so that the light emission current flows to the switch 8.

Here, the emission current control circuit 105 and the bias current control circuit 103 have a circuit for converting a digital value such as a D / A converter into an analog value as described above, and an output signal from the laser light amount comparison control circuit 102. By counting up or down the digital value composed of D _{1 to} D _n and B _{1 to} B _n , the laser current Il flowing through the laser through the emission constant current circuit 106 or the bias constant current circuit 104 is counted as described above. The circuit configuration is such that the amount of electricity (analog value) corresponding to up or countdown can be changed.

In this embodiment, as shown in FIG. 4A, the bias count value X _B counted by the bias current control circuit 103 is the output B ₁ of the laser light amount comparison control circuit 102 being the least significant bit (LSB). , B _n as the most significant bit (MSB) n
Considered binary bits, counting up the bias count X _B, the term counts down using. FIG. 4 (A) shows a state of counting up the bias count X _B. Here, "0" is Low level: FALSE, "1" is High level: TRUE
(True) The relationship between the above-mentioned bias count X _B and the bias current I _B is assumed to have accompanied no bias current I _B to the increase of the bias count X _B as shown in Figure No. 4 (B) increases. Further, it is assumed that the light emission count value X _D and the light emission current I _D have the same relationship as shown in FIG. 4 (B).

Further, the light emission state of the semiconductor laser 108 is photoelectrically converted by the photodiode 109 incorporated in the laser device 112, processed by the laser light amount monitor circuit 110, and the fifth state is obtained.
As the monitor voltage V _M of the light quantity-voltage characteristic as shown in the figure,
The laser light amount comparison control circuit 102 is fed back.

Now, in step 202 described above, the bias count value X
_After setting both _B and the light emission count value X _D to “0”, the bias current control is performed in steps after step 203.

Figure 2 is the bias current control (A), as shown in region A of (B), the light emission current count to X _D in a state where "0" and the bias current count X _B "1" by one count-up By doing so (step 204), a current (laser current) corresponding to the counted-up count value X _B is passed through the semiconductor laser 108 by the bias constant current circuit 104.
The detected value of the laser light amount accompanying the laser current is fed back to the laser light amount comparison control circuit 102 through the laser light amount monitor circuit 110.

The semiconductor laser 108 emits laser light when the laser current exceeds the threshold current I _th . Further, the bias current count value X _B is incremented and the semiconductor laser 108
Increase the current flowing through. After that, when the monitor voltage V _M reaches the bias current specified voltage V _BO , the count up of the bias current count value X _B is finished (step 20
Five).

The bias current count value at this time is X _BO (bias current specified count value). When X _B is X _BO , the laser 108 emits laser light, and there is a case where the laser 108 emits a sufficient amount of light to form a latent image on the photosensitive drum 1. Therefore, the bias current is the bias current. The prescribed count value X _BO is multiplied by a certain case (for example, 80%) to obtain a value, which is set as X _BT (step 206).

The laser 108 is the above-mentioned X _BT (bias current setting count value)
The current at this time is the bias setting current I _BT . While the bias setting current I _BT is flowing through the semiconductor laser 108, the monitor voltage V _M is checked and the absolute value of the value obtained by subtracting the monitor voltage V _M from the bias current specified voltage V _BO is constant at the voltage V _BO. Multiplying the ratio (α) by V _BO × α is exceeded (step 20
7), stop the laser current is set to "0" clears the bias current count X _B returns to step 202, it restarts the bias current control from the beginning. That is, the emission current control is performed with the bias setting current I _BT flowing through the semiconductor laser 108. The video signal at this time is set to TRUE, the gate of the light emission current switching circuit 107 is opened, and the light emission current _ID is made to flow to the semiconductor laser 108.

Next, if the formula | V _BO −V _M | ≦ V _B × α holds, the process proceeds from step 207 to step 208.

The emission current control at this time is performed by setting the bias current count value X _B to the bias current setting count value X _{BT as} shown in the region B of FIGS. 2A and 2B, and setting the bias setting current I _BT to the semiconductor laser 108. Perform with the flow. Light emission current count value X _D "0" from the state "1" at a time is counted up (step 208). A current I _D corresponding to the count value X _D obtained by this count-up is added to the bias specified current I _BT by the light emission constant current circuit 106. Therefore,
The laser current Il is the sum of the bias regulation current I _BT and the emission current I _D (Il = I _BT + I _D ).

The amount of laser light accompanying the laser current Il is determined by the semiconductor laser device 11
The photoelectric conversion is performed by the photodiode 109 built in the inside of 2, and the laser light amount monitor circuit 110 performs the feedback to the laser light amount comparison control circuit 102. Therefore, by counting up the light emission current count value X _D by “1”, the light emission current I _D increases and the laser light amount increases.

Next, the increase in the laser light amount is detected by the increase in the monitor voltage V _M. That is, the emission current count value X _D is counted up, the current flowing through the laser 108 is increased, and when the monitor voltage V _M reaches the emission light amount regulation voltage V _D , the emission current count value X _D is incremented. It is ended (step 209).

The light emitting current count value at this time is _XDT (light emitting current setting count value). A current corresponding to X _DT (light emission current setting count value) is flowing through the semiconductor laser 108, and the light emission current at this time is set as the light emission setting current I _DT . The monitor voltage V _M is checked with the light emission setting current I _DT flowing through the semiconductor laser 108. That is, when the monitor voltage V _M is not within a certain range (for example, ± 5%) with respect to the emitted light amount regulation voltage V _D (step 210), the emission current count value X _D is cleared ( In step 211), the light emission current _ID is stopped, the process returns to step 208, and the light emission current control is performed again.

When the monitor voltage V _M is within a certain range with respect to the emission light amount regulation voltage V _D and the APCST signal from the central processing unit 101 is FALSE, the emission current setting count value X _DT and the bias current setting While holding the count value X _BT , close the gate of the emission current switching circuit 107,
Only the bias setting current I _BT is supplied to the semiconductor laser 108. When the above APCST signal is TRUE, the gate of the light emission current switching circuit 107 is left open, and the gate is closed when the APCST signal becomes FALSE.

The above-mentioned emission light amount regulation voltage V _D is obtained as follows. First, the laser light amount setting voltage V _{O is} set by the laser light amount setting circuit 111.
Can be decided. As shown in FIG. 6, this voltage V _O may be a voltage due to resistance division. The set voltage V _O input to the laser light amount comparison control circuit 102 is corrected by the difference in laser sensitivity of the photosensitive drum 1 in the recording device. The sensitivity of the photosensitive drum 1 is the signal indicated by CSEN1 and CSEN2 from the central processing unit 1.
Entered at 114. The correction value for V _O has a value of, for example, + 10% or −10% with respect to the central value V _O , and the value obtained by correcting V _O is defined as the emission light amount regulation voltage V _D.

In the present embodiment, as shown in FIG. 2 (A), the amount of current increase per unit time by incrementing the bias count value X _B step by step (FIG. 3A) is the emission count value X _D It is configured to be larger than the amount of increase in current per unit time by counting up by 1 step (FIG. 3B).

Incidentally, A zone in the flowchart of FIG. 2, as shown in B region, until the monitor voltage V _M is the bias specified voltage V _BO or emission light quantity setting voltage V _D, the bias count X _B and the light emitting count X _D Is incremented step by step (step 204 and step 2 in FIG. 3).
08).

Although the light quantity can be controlled with high accuracy by incrementing by one step in this way, if the number of bits of the count values X _B and X _D is increased to achieve more accurate light quantity control, , Will need more time. Usually, since the automatic light amount adjustment operation is performed between the print sheets, it does not take much time.

Therefore, in this embodiment, high-speed and high-accuracy light quantity control as shown in FIGS. 7 and 8 is performed. Next, the light amount control operation will be described with reference to the flowchart of FIG. The areas A and B of the flowchart of FIG. 3 are replaced with the procedure of FIG. Therefore, steps 203 and 207 of FIG.
After that, step 301 in FIG. 8 is executed, and the monitor voltage V _M
Is determined to be a predetermined percentage value V _BOβ (or V _Dβ ) of V _BO (or V _D ), and V _M is V
_{If BOβ} (or V _Dβ ) or less, the next step 302
Bias count value X _B (or emission count value
X _D ) count value is increased by 3 counts.

After that, when the monitor voltage V _M exceeds V _BOβ (or V _Dβ ), the process proceeds to step 303 and another predetermined ratio value V _BOα (or V _Dα ) of the monitor voltages V _M and V _BO (or V _D ) Is compared, and if the monitor voltage V _M is smaller, the count value of X _B (or X _D ) is incremented by 2 in step 304.

After that, when the monitor voltage V _M exceeds V _BOα (or V _Dd ), the _routine proceeds to step 305, where the monitor voltage V _M is compared with the bias specified voltage V _BO (or the light emission amount setting voltage X _B ) and If the monitor voltage V _M is small, the monitor voltage V _M
The count value of X _B (or X _D ) is incremented by 1 until it reaches V _BO (or V _D ). V _M is V _BO (or
After reaching V _D ), the routine proceeds to step 206 or step 210 in FIG. By controlling in this way,
As shown in the figure, a highly accurate automatic light quantity adjustment function can be realized in a short time. In addition, the above () corresponds to the case of the processing of the B area in FIG.

Further, Figure 8 (A), as shown (B), the increased laser current I by counting up the bias count X _B, the bias count X _B is the maximum value (MAX)
When the monitor voltage V _M does not reach the bias current specified voltage V _BO even at the time T _B , the current I _BMAX (current when the bias count value reaches MAX) or the current I _BMAX
A predetermined percentage value of _BMAX is used as the bias current.

Further, the light emission current control is performed in a state where a predetermined bias current is flowing in the light emission current. By counting up the light emission count X _D, increasing the laser current, when the monitor voltage V _M even at the time T _D which emission count X _D becomes maximum does not reach the light emission amount specified voltage V _D Ends the light emission current control in a state where the current I _DMAX (light emission current when the light emission count value reaches MAX) is supplied.

[Effects of the Invention] As described above, according to the present invention, it is possible to perform highly accurate light amount control in a short time without causing a significant increase in cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a laser drive current control circuit of an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the operation of the laser drive current control circuit of FIG. 1, and FIG. 3 is a laser of FIG. 4 is a flow chart showing the operation of the light quantity comparison control circuit, FIGS. 4 (A) and 4 (B) are diagrams showing the relationship between the bias count value (or light emission count value) and the bias current (or light emission current) in the embodiment of the present invention, FIG. 5 is a characteristic diagram showing the relationship between the laser light amount and the monitor voltage in the embodiment of the present invention, FIG. 6 is a circuit diagram showing a configuration example of the laser light amount setting circuit in FIG. 1, and FIGS. 7 (A) and 7 (B). ) Is a characteristic diagram during high speed and high precision control operation of the embodiment of the present invention, FIG. 8 is a flow chart showing high speed and high precision control operation of the embodiment of the present invention, and FIGS. 9 (A) and 9 (B) are FIG. Fig. 10 is a characteristic diagram showing the operation of the laser light amount comparison control circuit of Perspective view showing a configuration of a recording apparatus, FIG. 11 is a characteristic diagram showing the light intensity relationship to the semiconductor laser of the current, Fig. 12 is a characteristic diagram showing the light intensity relationship to the semiconductor laser of the current. 101 ... Central processing unit, 102 ... Laser light amount comparison control circuit, 103 ... Bias current control circuit, 104 ... Bias constant current circuit, 105 ... Emission current control circuit, 106 ... Emission constant current circuit, 107 ... … Light emission current switching circuit, 108 …… Semiconductor laser, 109 …… Photodiode, 110 …… Laser light quantity monitor circuit, 111 …… Laser light quantity setting circuit.

Front page continued (72) Inventor Kaoru Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takashi Seiya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-58-81329 (JP, A) JP-A-58-212256 (JP, A) JP-A-63-17582 (JP, A) JP-A-63-56060 (JP, A) Kai 60-115278 (JP, A) JP 62-32767 (JP, A)

Claims (1)

[Claims] 1. A beam generating means for generating a beam for recording information, a detecting means for detecting a light amount of the beam generated by the beam generating means, and a digital value for outputting a first and a second digital value, respectively. Output means, first and second D / A conversion means for converting the first and second digital values into analog values, respectively, and to the beam generation means based on outputs of the first and second D / A conversion means A current generating means for generating a current to be applied, and a first means for gradually increasing the applied current to the beam generating means by causing the digital value output means to output a first digital value that increases sequentially. Second means for determining a specific first digital value in response to an output from the detecting means reaching a first value due to an increase in current applied to the beam generating means by the first means; Second
While the specific first digital value determined by the means is being output, the second digital value that is sequentially increased is output from the digital value output means, whereby the current applied to the beam generating means is further gradually increased. Increase to the third
Means and fourth means for determining a particular second digital value in response to the output from the detecting means reaching a second value due to an increase in the current applied to the beam generating means by the third means. A light amount control device for a recording apparatus, wherein the amount of increase in current per unit time by the first unit is larger than the amount of increase in current per unit time by the third unit.