JP3517584B2 - Laser light distribution analysis system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light amount distribution analysis system on a recording medium when a laser light emitting element is used to control the light amount on the recording medium.

[0002]

2. Description of the Related Art An electrophotographic system is a light quantity recording apparatus using a laser diode.

FIG. 12 is a general conceptual diagram of an LBP and a digital copying machine capable of printing a halftone image. The photodiode 21 is a semiconductor laser 2 as a laser light source.
The amount of laser light output by 0 is converted into an electric current for monitoring. The light amount control unit 18 controls the applied current to the semiconductor laser 20 based on the monitored light amount so that the output current from the photodiode 21 becomes a predetermined value. The semiconductor laser 20 and the photodiode 21 are generally combined to form a laser chip 19.

The polygon mirror 8 of the scanner is used to polarize the laser beam emitted from the semiconductor laser 20. The polygon mirror 8 is fixed to the motor shaft and rotates in the direction of the arrow in FIG. To scan. The f-θ lens 9 condenses the polarized laser beam on the photosensitive drum 10 at a constant linear velocity. B
The D mirror 11 has a mechanically fixed positional relationship with the photosensitive drum 10, and the reflected laser beam receives the light receiving diode 1
2 and is used to detect the information writing start position on the photosensitive drum 10. The output of the light receiving diode 12 is input to the horizontal synchronizing signal generating circuit 13 to generate the horizontal synchronizing signal HD. The HD signal is supplied to the pixel modulation circuit 16 and the pixel modulation data generation source 15. The blanking signal generation circuit 14 outputs BD based on the horizontal synchronization signal HD.
(Beam Detect) The mirror 11 generates a blanking signal HBL for turning on the semiconductor laser at the timing when the laser beam should be detected, and supplies the blanking signal HBL to the pixel modulation circuit 16.

The pixel modulation data DV (generally 8 bits) generated from the pixel modulation data generation source 15 is the pixel modulation circuit 1.
6 is supplied. The output signal of the pixel modulation circuit 16 is a laser driver 17 that drives and controls the semiconductor laser 20.
Is supplied to. In the detour circuit 16 for pixel editing, the horizontal synchronizing signal H
A pixel clock SCK is generated in synchronization with D, and the time base of the pixel modulation data DV is corrected based on this. In addition, a high-speed PWM signal is generated based on the pixel clock SCK and the pixel modulation data DV, and the amount of laser light can be controlled in multiple stages to enable printing of halftone images. And
When the blanking signal HBL is generated, the semiconductor laser 20 is forcibly turned on fully so that the laser beam can be supplied to the BD mirror 11 without fail so that the horizontal synchronizing signal HD can be generated. Semiconductor laser (laser diode) 2
The emission intensity output from 0 is controlled by the drive current Idrv.

FIG. 13 illustrates the amount of laser light on the photosensitive drum 10 serving as a recording medium. The horizontal axis direction is the laser scanning direction (main scanning) and the vertical axis direction is the photosensitive drum rotation direction (sub scanning), and the area S1 represents one pixel area. The instantaneous light amount distribution of the laser light output from the laser diode 20 is dispersed on an ellipse as indicated by a laser instantaneous spot 22. It is well known that the dispersed light intensity distribution has a Gaussian distribution. Pixel area S1 of the laser instantaneous light intensity distribution generated by the instantaneous light emission power
The integrated value at determines the light quantity value of the corresponding pixel, and the printing toner adheres in correlation with this light quantity value to form an image on the photosensitive drum 10. There is an increasing demand for high-speed and high-definition printing in the electrophotographic system described above. For example, one pixel region (up to 40 μm: 600 dpi) can be printed for 20 ns (50
It has become necessary to perform high-speed laser scanning of (MHz).

The laser light amount distribution on the photosensitive drum 10 determines the image quality, and the laser chip 19 and the laser driver 17
Also, the selection and design development of the pixel modulation circuit 16 have become factors that determine the quality of the electrophotographic system. However, the laser light amount distribution on the photosensitive drum 10 has no choice but to measure the surface potential distribution, but it is difficult to do this accurately, and in an electrophotographic system that prints a halftone image, the type of pixel light amount distribution is 256, for example. Street (8bi
There is also t) and it is not done. The actual situation is to actually print on paper and analyze mainly by visual inspection. Moreover, in the electrophotographic system of FIG. 12, only the exposure process of irradiating the photosensitive drum with laser light to form the surface potential distribution is shown, but in addition to this, the development process of attaching the printing toner based on this surface potential distribution. Since there are a transfer process for transferring the toner adhering on the photosensitive drum 10 onto the paper surface and a fixing process for thermally melting and fixing the printing toner adhered on the paper surface, in the analysis on the paper surface, there are fluctuation factors in the development stage of each process. And the exposure process cannot be analyzed accurately.

[0008]

However, there are the following problems in the method of analyzing the laser light amount distribution on the photosensitive drum which is the recording medium in the conventional electrophotographic system.

The first problem is that in the analysis using the printed image on the paper surface, the exposure process cannot be accurately analyzed due to the influence of the variable factors in the development stage of the development process, the transfer process and the fixing process.

The second problem is that in the analysis using the printed image on the paper, the number of types of pixel light amount distribution and the number of combinations with the adjacent pixels which are configured in the electrophotographic system which requires the halftone image printing are enormous, which is rapid. It is that analysis has not been completed.

Due to the above problems, an analysis system capable of seamlessly analyzing the laser light amount distribution on the photosensitive drum 10 which is a factor of the exposure process characteristic from the pixel modulation circuit 16 and the laser driver 17 so as to match the actual characteristic seamlessly. Is required.

An object of the present invention is to provide a laser light amount distribution analysis system capable of seamlessly, quickly and reliably analyzing the laser light amount distribution on a recording medium such as a photosensitive drum from an electric circuit for driving and controlling a laser diode. Especially.

[0013]

A laser light quantity distribution analysis system of the present invention is a laser light quantity distribution analysis system on a recording medium in the case of controlling a light quantity on a recording medium using a laser light emitting element. Or, it has a Gaussian filter that inputs the light emission power waveform or data that is the output of the laser diode model that represents its light emitting operation. The Gaussian filter shows a Gaussian distribution characteristic whose impulse response is similar to the instantaneous light emission distribution in the laser scanning direction. .

It is also possible to have an optical probe for observing the light emission power and input the output of the optical probe or a representative signal to the Gaussian filter.

Therefore, the light emission power waveform or data which is the output of the laser diode or the laser diode model is input to a Gaussian filter whose impulse response exhibits a Gaussian distribution characteristic similar to the instantaneous light emission distribution in the laser scanning direction, and the light quantity at that output is input. Since the distribution can be analyzed, the laser light amount distribution on the recording medium such as the photosensitive drum can be analyzed seamlessly, quickly and reliably from the electric circuit for driving and controlling the laser diode.

[0016]

FIG. 1 shows an embodiment of a laser light quantity distribution analysis system of the present invention, which comprises a laser diode model 2 and a Gaussian filter 1. Except for this, the pixel modulation circuit 16 and the laser driver 17 shown in FIG. 12 are pure electronic circuits, and therefore the characteristics can be studied comparatively easily at present with an analog simulator based on SPICE. There is.

First, the laser diode model 2 will be described.

The laser diode is shown as laser diode model 2. The laser diode is a special element that converts the driving current Idrv into the amount of emitted light, and this operation is basically shown by two rate equations regarding the carrier density N and the generated photon density Nph in the active layer.

[0019]

[Equation 1] N: Carrier density Nph: Photon density J: Injection current density D: Active layer thickness tn: Carrier lifetime tph: Photon lifetime G (N): Laser (stimulated emission) conversion gain βsp: LED (spontaneous emission) The operation represented by the conversion gains 1) and 2) in the above is the case of stimulated emission (laser operation) in which the carrier density by the drive current Idrv exceeds the critical value Nth.

When the threshold value is equal to or lower than Nth, the stimulated emission term disappears and the rate equation during spontaneous emission (LED operation) is as shown in the following equation.

[0021]

[Equation 2] These two operations are continuously changed by the drive current Idrv.

FIG. 2 is an internal circuit diagram of a laser diode model 2 in which the present inventors have solved the above rate equation by an electric circuit. This internal operation is not the subject of the present invention and will be described briefly. The configuration is a spontaneous emission induction including a threshold current (Ith) setting section including a terminal lead model section 3, an inter-terminal voltage model section 4 and a current amplifier AMP1, a carrier time constant (τn) section 5 and a current-voltage conversion amplifier AMP2. Section, an induced addition section including the stimulated emission inducing section 6 and ADD1, a photon-carrier feedback section including a photon time constant section 7 and a current amplifier AMP6, and a current-voltage conversion amplifier AM.
It is composed of a light output unit composed of P7. And the anode terminal an
It has an ode, a cathode terminal cathode, a light output terminal Pout, and a carrier density terminal N_probe which does not actually exist.

The carrier density N is indicated by the voltage across the terminals of the capacitor C3 and the resistor R3, and the instantaneous light emission power is detected by the current value flowing through the coil L2 and the resistor R6. Using this model, we can easily study the operation of the laser diode. For example, a commercially available laser diode (5mW class, Ith
= 20 mA, slope efficiency = 0.3 mW / mA), and the emission characteristics are shown in FIG. 3 as a model. a)
Is the drive current Idrv (unit is 10 mA) supplied from the laser driver, b) is the emission power waveform (unit is m)
W) and c) are optical power waveforms viewed through BESSEL_LPF with a cutoff of 1 GHz, assuming observation with a commercially available optical probe (1 GHz). However, the light emission waveform of FIG. 3 is a general display of the laser energy emitted from the laser diode, and does not show the light amount distribution on the photosensitive drum.

Next, consideration of the light quantity distribution will be described.

The light quantity distribution is provided on the photosensitive drum, and it is necessary to represent it on the time axis like the emission power waveform shown on the time axis output from the laser diode (model). The laser instantaneous light amount distribution represented by a Gaussian distribution is generally represented by a spot diameter, and the spot diameter is defined by a standard value h with respect to the central value of the light amount distribution. If the light amount distribution indicated by the integrated value of the instantaneous light amount distribution in the main scanning (laser scanning) direction is analyzed, the sub-scanning (photosensitive drum rotation) direction can be easily analyzed using the crest value of the Gaussian distribution as a coefficient.

Laser light distribution (model)
Similar to the emission power waveform shown on the time axis output from
Need to be expressed on the time axis. Instantaneous emission that occurs at time to
Instantaneous light intensity distribution in the main scanning direction depending on the light center intensity p (to)
sp (to) is represented by the following formula. sp (to) = p (to) exp (-(t-t₀)²/ Σ) 3) The spot coefficient σ that defines the spot shape is
It σ == (T_sp/ 2)²/ Log_e(1 / h) 4) T_sp: Main scanning spot diameter (time converted in pixel cycle To)
(Shown in units) For example, t = 0, instantaneous light emission center intensity p (0) = 1, pixel
Period To = 20 ns, T _sp= 30 ns (main scanning spot
Instantaneous when the diameter is 1.5 pixels) and the spot standard value h = 0.2
The hourly light intensity distribution is shown in FIG. This instantaneous light intensity distribution is
This is the instantaneous light intensity distribution of the us.

Next, a basic method of generating a light amount distribution in the main scanning direction from the light emission power waveform shown in FIG. 3 will be described with reference to FIG. FIG. 5A shows a light emission power waveform composed of a data array, and FIG. 5B shows each instantaneous light amount distribution generated from the impulse light according to each data value.

Since the actual light intensity distribution SP is represented by the sum of the instantaneous light intensity distributions, it is expressed by the following equation from the equation 3).

[0029]

[Equation 3] Since the number of instantaneous emission intensity data is in the range of thousands to tens of thousands, it takes much time to analyze the equation (5), which is not practical. Moreover, since it is generally difficult to make the time interval of each data constant, the impulse light for each data value changes not only the peak value but also the pulse width, so it is necessary to analyze the instantaneous light intensity distribution for each impulse light. Yes, it will take more time.

Next, the analysis of the light amount distribution by the Gaussian filter will be described.

In order to speed up the analysis of the light quantity distribution, the emission intensity signal of the laser diode output is input to the Gaussian filter 1 as shown in FIG. A configuration example of the Gaussian filter 1 is shown in FIG. It is composed of filter units F1 to F12, coefficient circuits k1 to k5, and adders A1 to A3. The filter units F1 to F12 have exactly the same configuration, and the configuration is shown in FIG. The Gaussian filter is one whose impulse response exhibits a Gaussian distribution waveform. Standard value h
= 0.2, target a Gaussian impulse response with T _sp = 30 ns. The filter unit sets the following constants as BESSEL_LPF with a gentle phase characteristic. R1 = 1k R2 = 1k C1 = 1.325pF C2 = 6.635pF L1 = 3.82uHfc = 50MHz (3dB) FIG. 8 shows the impulse response waveform normalized by the maximum peak value. As can be understood from FIG. 8, the passive filter exhibits an impulse response waveform far from the Gaussian distribution due to the symmetry of the impulse response and overshoot. The process of approximating the output of the filter unit F1 exhibiting this characteristic into a Gaussian distribution waveform will be described with reference to FIG. Each coefficient value of the coefficient circuit has the following conditions. k1 = 0.5 k2 = 0.4 k3 = 0.4 k4 = 0.07 k5 = 1 / (k1 (1 + k2) (1 + k3) (1 + k
4)) = 0.954 Further, FIG. 9 shows a waveform when the maximum peak value of the final output waveform of the coefficient circuit k5 is normalized. The input impulse signal is generated at time t = 2 ns. In the figure, a)
Is F1 output, b) is A1 output, c) is A2 output, d) is A3 output, and e) is k5 output. In b) and c), the symmetry of the response waveform is corrected, in d) the overshoot is corrected, and in e), a response waveform similar to a Gaussian distribution waveform is generated.

FIG. 10 shows the degree of coincidence between the impulse response waveform of the Gaussian filter 1 and the target Gaussian distribution waveform. In the figure, a) is the target impulse response waveform (T _sp = 3).
0 ns), and the following formula derived from formula 3) is used. sp = exp (-t < ² > /1.39e < ^-20 >) 6) In the figure, b) is the corrected delay time td of the impulse response (td = 51 ns in this case).

As can be seen from FIG. 10, the impulse response of the Gaussian filter 1 closely matches the Gaussian distribution waveform. The characteristic of the Gaussian filter 1 is that the delay time td of the impulse response is obtained by analyzing the light amount distribution that requires the integral calculation represented by the equation 5) generated from the input emission power waveform.
And the time from the negligible peak point of impulse response energy is added to the analysis time and it is automatically displayed.

FIG. 11 shows an example of the result of analyzing the light quantity distribution using the light quantity distribution analysis system of FIG. In the figure,
a) shows the drive current Idrv (unit is 10 mA), b) shows the light emission power waveform (mW), and c) shows the light amount distribution in the main scanning direction. In this way, the light quantity distribution characteristics can be analyzed seamlessly, quickly, and reliably from the electrical processing circuit.

Even if the spot diameters are different, the Gauss filter 1 can be easily designed by the following method. 1) Obtain the spot diameter ratio m for T _sp = 30 ns. 2) The capacities and the inductors of the filter units F1 to F12 are each multiplied by m. 3) The delay time td is m of the delay time when T _sp = 30 ns.
Double.

The emission power waveform input to the Gaussian filter is not limited to the simulation data, but may be emission power data detected by an optical probe, for example.

The impulse response waveform of the Gaussian filter is not limited to the Gaussian distribution, but may be matched with the actual light quantity distribution characteristic of the laser diode.

In this embodiment, since the Gaussian filter is used on the simulator, it is composed of ideal elements, but it may be created by an actual filter block. In this case, the optical probe output is observed through this Gaussian filter. By doing so, the light quantity distribution on the recording medium can be analyzed in real time.

[0039]

As described above, according to the present invention, the emission power waveform or data output from the laser diode or the laser diode model has a Gaussian distribution characteristic in which the impulse response is similar to the instantaneous emission distribution in the laser scanning direction. By inputting to the filter and analyzing the light quantity distribution at the output, the analysis of the laser light quantity distribution on the recording medium such as the photosensitive drum can be performed seamlessly, quickly and reliably from the electric circuit that controls the drive of the laser diode. The effect is that you can do it.

[Brief description of drawings]

FIG. 1 is an example of an analysis system for laser light quantity distribution using the present invention.

FIG. 2 is an internal circuit diagram of a laser diode model in which the present inventors have solved the rate equation by an electric circuit.

FIG. 3 is a diagram showing light emission characteristics based on a laser diode model.

FIG. 4 is a case where t = 0, instantaneous emission center intensity p (0) = 1, pixel period To = 20 ns, T _sp = 30 ns (main scanning spot diameter 1.5 pixels), and spot standard value h = 0.2. FIG. 5 is a diagram showing an instantaneous light intensity distribution of FIG.

FIG. 5 is an explanatory diagram of a basic analysis method of a light amount distribution in a laser scanning direction. (A) It is a figure which shows the light emission power waveform which consists of a data array. (B) It is the figure which showed each instantaneous light amount distribution generated from the impulse light by each data value.

FIG. 6 is a diagram showing a configuration example of a Gaussian filter.

FIG. 7 is a diagram showing a configuration of a filter unit.

FIG. 8 is a diagram showing an impulse response waveform of a filter unit normalized by a maximum peak value.

FIG. 9 is a diagram illustrating a process of approximating the output of the filter unit F1 to a Gaussian distribution waveform.

FIG. 10 is a diagram showing a matching degree between an impulse response waveform of a Gaussian filter and a target Gaussian distribution waveform.

11 is a waveform chart showing the results of laser light amount analysis using the analysis system of FIG.

FIG. 12 is a general conceptual diagram of an LBP and a digital copying machine capable of printing a halftone image.

FIG. 13 is a diagram illustrating the amount of laser light on a photosensitive drum that serves as a recording medium.

[Explanation of symbols]

1 Gaussian filter 2 Laser diode model 3-terminal lead model section 4 terminal voltage model 5 Carrier time constant part 6 Stimulated emission inducer 7 Photon time constant part 8 Scanner polygon mirror 9 f-θ lens 10 Photosensitive drum 11 BD mirror 12 Beam detector 13 Horizontal sync signal generator 14 Blanking signal generation circuit 15 Pixel modulation data source 16 pixel modulation circuit 17 Laser driver 18 Light intensity controller 19 laser chips 20 Semiconductor laser (laser diode) 21 photodiode 22 Laser Instant Spot A1 to A3 adder F1 to F12 filter unit k1 to k5 coefficient circuit

Claims (2)

(57) [Claims] 1. An analysis system of a laser light amount distribution on a recording medium in the case of controlling the light amount on the recording medium using a laser light emitting element , wherein an emission power waveform as an output of a laser diode or
A laser diode that represents the light emitting operation of the laser diode.
Emitting power waveform data, which is the output of the Iodo model,
In the emission power waveform or the emission power waveform data
Impulse response due to the instantaneous in the laser scanning direction
Approximate to have a Gaussian distribution characteristic similar to the emission distribution
Input to the Gaussian filter and output from the Gaussian filter.
A laser light amount distribution analysis system characterized by finding the light amount distribution in the laser scanning direction by force . 2. Light emission which is the output of the laser diode.
The power waveform is the output of the optical probe that observes the emission power.
It is a signal, The analysis system of the laser light amount distribution of Claim 1 characterized by the above-mentioned.