JPH07100374B2 - Recording device - Google Patents

Description

The present invention relates to a recording device such as a laser beam printer.

[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. 7 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 to be 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 characteristics (I-l characteristics) of the amount of laser light with respect to the laser current (driving current) of a semiconductor laser that is generally used are
It is as shown in the figure. That is, as shown in FIG. 8, in the semiconductor laser, the laser current I has a certain threshold value (T _th )
However, the laser light is emitted when the threshold value is exceeded, and in the laser light 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 this time, the laser light amount I _T is kept constant by driving the laser current I _T at a constant current.

[Problems to be Solved by the Invention] However, the semiconductor laser has the ninth 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 prescribed light amount l _TA or the photosensitive drum 1 is scanned, 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 may be destroyed. May be.

Therefore, a method of providing a means for detecting the amount of laser light and determining the current to be applied to the semiconductor laser so that the amount of light detected by this detecting means becomes a desired value has been considered.

When such a method is to be realized by an analog circuit that determines the current to be applied to the semiconductor laser according to the charge amount charged in the capacitor etc., the laser light amount changes due to the change in the charged charge amount with the passage of time. The problem arises. Further, by using a D / A conversion circuit, a current corresponding to a digital value is configured to be applied to the semiconductor laser, the digital value is changed, and the light amount detected by the detection means becomes a desired value. A method of specifying the digital value is also possible.

However, in order to reduce the quantization error due to digital control, a D / A conversion circuit with a large number of bits is required, which causes a problem of a significant cost increase.

An object of the present invention is to solve the above problems and to provide a recording apparatus capable of controlling the light quantity of a beam generating means used for information recording with high accuracy without causing a significant increase in cost.

Another object of the present invention is to control the light quantity of the semiconductor laser by using the first and second D / A converting means, wherein the output from the first D / A converting means is the threshold current of the semiconductor laser. It is an object of the present invention to provide a recording device capable of determining a digital value for the first D / A conversion means so as to correspond to an appropriate current that does not exceed.

[Means and Actions for Solving Problems] In order to achieve the above-mentioned object, a recording apparatus according to the present invention comprises a beam generating means for generating a beam for recording information, and a beam generated by the beam generating means. Detecting means for detecting the amount of light, digital value outputting means for outputting the first and second digital values, and first and second D / A converting means for converting the first and second digital values into analog values, respectively. A current generating means for generating a current to be applied to the beam generating means on the basis of the outputs of the first and second D / A converting means; and a first digital value which is sequentially increased from the digital value output means. The first means for gradually increasing the applied current to the beam generating means, and the output from the detecting means due to the increase of the applied current to the beam generating means by the first means. Second means for determining whether or not a predetermined value is exceeded, and when the second means determines that the output from the detecting means exceeds a predetermined value, the output from the detecting means is predetermined. And a third means for determining a specific first digital value smaller than the digital value when the value exceeds the value of, and the specific first digital value determined by the third means being output, Fourth means for further gradually increasing the applied current to the beam generating means by causing the digital value output means to output a second digital value that increases sequentially, and an applied current to the beam generating means by the fourth means. And a control means having a fifth means for determining a specific second digital value when the output from the detection means has reached a desired value due to the increase of.

Further, in the present invention, it is preferable that the beam generating means includes a semiconductor laser, and the specific first digital value determined by the third means corresponds to a current equal to or less than a threshold current of the semiconductor laser. It is characterized by doing.

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 controls the laser light amount as shown in FIG. 2 in accordance with the control procedure shown in FIG. I do. 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 emitted 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,
The 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, and "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 a photodiode 109 built in the laser device 112, processed by a laser light amount monitor circuit 110, and a 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. A value obtained by multiplying the specified count value X _BO by a certain ratio (for example, 80%) 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, restart 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 emission current count value X _D by "1", the 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 . Semiconductor laser 108
In a state where the flash setting current I _DT is flowing to the monitor voltage V _M
Check. 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. This voltage V _O can be considered to be a voltage due to resistance division, as shown in FIG. 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. Correction value for V _O is V _O with respect to for example + 10% of the center value, or is the value of -10% or the like, the V _O corrected value as the amount of emitted light specified voltage V _D.

[Effects of the Invention] As described above, according to the present invention, it is possible to control the light quantity of the beam generating means used for information recording with high accuracy without significantly increasing the cost.

Further, according to the present invention, when the light amount of the semiconductor laser is controlled by using the first and second D / A converting means, the output from the first D / A converting means does not exceed the threshold current of the semiconductor laser. The digital value to the first D / A conversion means can be determined to correspond to the proper current.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a drive current control circuit of a laser according to 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 FIG. 7 is a conventional laser recording device. FIG. 8 is a characteristic diagram showing the relationship of the light amount with respect to the current of the semiconductor laser, and FIG. 9 is a characteristic diagram showing the relationship of the light amount with respect to the current of the semiconductor laser. 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.

 ─────────────────────────────────────────────────── ─── Continued front page (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 Within the corporation

Claims (2)

[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 invention means based on the outputs of the first and second D / A conversion means. Current generating means for generating a current to be applied, and first means for gradually increasing the current applied to the beam generating means by applying a sequentially increasing first digital value from the digital value output means, Second means for determining whether or not the output from the detecting means exceeds a predetermined value due to the increase of the current applied to the beam generating means by the first means, and the second means for detecting from the detecting means. Third means for determining a specific first digital value smaller than the digital value when the output from the detecting means exceeds a predetermined value when it is determined that the output of the above-mentioned exceeds a predetermined value.
The current applied to the beam generating means is generated by causing the digital value output means to output the second digital value which is successively increased while the specific first digital value determined by the third means is being output. And a second digital value that is specific to the output from the detection means due to an increase in the current applied to the beam generation means by the fourth means. And a control means having a fifth means for determining. 2. The beam generating means includes a semiconductor laser, and the specific first digital value determined by the third means corresponds to a current equal to or lower than a threshold current of the semiconductor laser. The recording apparatus according to claim 1.