JPH06105208B2 - High speed MTF measuring device for LED array - Google Patents

Description

The present invention relates to an MTF (modulation transfer function) measuring device for an LED array used as a light source for an LED printer device or the like.

[Prior Art] A printer head of an LED array is composed of an LED array in which a large number of minute light emitters are linearly arranged, and a SELFOC lens array which is opposed to the LED array with a certain distance. There is an optical system.

Next, the configuration of the LED printer device will be described with reference to FIG.

In FIG. 14, 1 is an LED array incorporated in the printer head, 11 is an electrostatic photosensitive drum, 12 is a corona charge, 13 is toner, 14 is a tray, 15 is a toner transfer section, and 16 is a heat fixing section.

When the light of the LED array 1 is applied to the electrostatic photosensitive drum 11 charged by the corona charge 12, only the place where the light hits is discharged.

On the paper sent from the tray 14, the toner 13 is transferred to the position corresponding to the charged portion of the electrostatic photosensitive drum 11 by the toner transfer unit 15, and the toner 13 is fixed on the paper by the heat fixing unit 16.

Next, the relationship between the LED array 1 and the electrostatic photosensitive drum 11 shown in FIG. 14 will be described with reference to FIG.

In FIG. 15, 17 is a Selfoc lens array, and 18 and 19 are gap rollers.

When the light beam of the LED array 1 is applied to the electrostatic photosensitive drum 11, if there is variation in the amount of light emitted from the LED array 1 or variation in the distance between the LED array 1 and the SELFOC lens array 17, variation will occur. It leads to deterioration of print quality. Therefore, it is necessary to measure the irradiation intensity of each beam emitted from the LED array 1 and inspect the variation in the light amount.

Next, the configuration of a conventional LED array MTF measuring device will be described with reference to FIG.

In FIG. 16, a slit plate 3 that receives the irradiation light of the LED array 1 and an optical power sensor 9A that receives the amount of light that has passed through the slit 3A are fixed to the moving table 2, and the LED array 1 is set as one light emitter (hereinafter, Light is emitted in a blinking pattern every other dot, and the moving table 2 is moved in parallel with the LED array 1.

Next, the waveform appearing in the waveform observing means 10 of FIG. 16 will be described with reference to FIG.

In FIG. 17, a voltage waveform proportional to the irradiation light of the LED array 1 is obtained as the measurement output of the optical power meter 9. The MTF is calculated from the maximum received light intensity Imax and the minimum received light intensity Imin in Fig. 17 by the following equation.

MTF = (Imax−Imin) / (Imax + Imin) (1) [Problems to be Solved by the Invention] In the conventional apparatus of FIG. 16, the measurement output from the optical power meter 9 is observed by the waveform observing means 10 to obtain the MTF. Although it is calculated by visual calculation, the operation is complicated, it is difficult to obtain the measurement accuracy, and it is difficult to determine the MTF in the case where the light beam of the LED array 1 has large and small variations and the emission failure is included. There are problems such as that it takes time to prepare and an oscilloscope must be prepared.

This invention is an electronic circuit of a MAX hold circuit, a MIN hold circuit, an analog operation circuit, and a sample hold circuit.
An MTF control circuit and an MTF cycle detection circuit that control the electronic circuit by following the operating speed of a moving table equipped with an MTF sensor consisting of a slit plate and a light receiving element are adopted in the device that automatically determines the MTF. , MT even for dots with defective light emission over all dots in the LED array
It is an object of the present invention to provide an MTF measuring device for an LED array, which can obtain an F calculated value at high speed.

[Means for Solving the Problem] In order to achieve this object, in the first invention, the light emission of the LED array is received through a slit that moves in parallel to the arrangement direction of the LED array via a SELFOC lens array, The amount of light passing through the slit is detected by the detecting means, the waveform is observed by the waveform observing means, and the MTF of the LED array is obtained.
In the MTF measuring device, a MAX hold circuit for holding the MAX of the output voltage of the detection means, a MIN hold circuit for holding the MIN of the output voltage of the detection means, and the MAX
An MTF control circuit that controls the MTF measurement of the defective light emitting array by detecting the maximum value period of the hold circuit, and an MTF period detection circuit that causes the integrating means to generate an MTF period that follows the moving speed of the slit.

In the second invention, the light emission of the LED array is received through a slit that moves in parallel to the arrangement direction of the LED array via the SELFOC lens array, and the amount of light passing through the slit is detected by the detection means, and the waveform observation means is used. Observe the waveform,
In an MTF measuring device for obtaining the MTF of the LED array, a MAX hold circuit for holding the MAX of the output voltage of the detecting means and an M hold circuit for holding the MIN of the output voltage of the detecting means.
IN hold circuit, MTF control circuit that detects the minimum value cycle of the MIN hold circuit and controls MTF measurement of defective light emitting array, and MTF cycle that generates an MTF cycle that follows the moving speed of the slit by integrating means. And a detection circuit.

[Operation] Next, a block diagram of a high speed MTF measuring device for an LED array according to the present invention will be described with reference to FIG.

FIG. 2 is a perspective view showing the MTF measurement principle of FIG. 1, and the slit plate 3 and the light receiving element 4 are attached to the movable table 2 of FIG.

The moving table 2 in FIG. 1 moves in parallel with the array arrangement direction of the LED array 1. The moving speed of the moving table 2 is a variable speed shown in FIG. 3, such as the operating speed of an elevator.

FIG. 4 is a waveform showing the irradiation intensity of each light beam train from the LED array 1 which is passed through the slit 3A and received by the light receiving element, and the output of the amplifier 5 is taken out. The light intensity is at the center position of each dot. It becomes the maximum, and becomes the minimum in the middle of each dot or the position of the extinction dot.

The waveform cycle in FIG. 4 is inversely proportional to the moving speed of the moving table 2,
It decreases as the movement speed increases.

FIG. 5 is a block diagram of an embodiment of the MTF calculator 6 of FIG.

No.4 to Vin of MAX hold circuit 51 and MIN hold circuit 52
A voltage proportional to the received light intensity shown in the figure is input. The MAX hold circuit determines the maximum value of the waveform input to Vin (hereinafter, M
AX), and the MIN hold circuit 52 sequentially holds the minimum value of the waveform (hereinafter referred to as MIN).

The MTF control circuit 53 receives the start signal and the cycle abnormality signal from the MTF cycle detection circuit 55 as input, and the MAX hold circuit 51 and MIN
By controlling the hold timing of the hold circuit 52, the waveform MAX is held in the MAX hold circuit 51, and the waveform MIN is held in the MIN hold circuit 52, and when the waveform MAX is detected once, the waveform moves. When the MAX of the next waveform is not detected even after the time corresponding to the MTF cycle determined by the moving speed of the table 2 has elapsed, the MTF sample signal is logically supplied to the sample hold circuit 57, and the analog operation circuit
Sample and hold the MTF calculation output from 56.

The analog operation circuit 56 calculates MTF = (MAX−MIN) / (MAX) from the MAX output from the MAX hold circuit 51 and the MIN output voltage output to the MIN hold circuit 52.
+ MIN) is calculated and output.

FIG. 8 is a circuit diagram of an embodiment of the MTF cycle detection circuit 55 of FIG. 5, in which the motor drive pulse supplied to the pulse motor 2A by the motor control circuit 8 for operating the moving base 2 is used as a clock pulse input. Given.

The F / V converter 81 in FIG. 8 converts the voltage into a voltage proportional to the clock pulse frequency, and the constant current generating circuit 82 inputs the voltage from the F / V converter into a constant current proportional to the voltage. The converted constant current is charged in the capacitor 83, and when the charging voltage of the capacitor becomes a constant voltage by the Schmitt trigger 84, a logic level “1” is output to the Schmitt trigger.
To get

In other words, the MTF cycle detection circuit shown in FIG.
Is a time integration circuit that is inversely proportional to the moving speed of the capacitor, and the charging terminal side of the capacitor is grounded via the diode 85 so as to discharge the charging charge before starting the timed operation.

[Example] FIG. 4 is an output voltage waveform diagram of the amplifier 5 obtained when the LED array 1 of FIG. 1 is caused to emit light and the moving table 2 is moved, and passes through the slit 3A of the slit plate 3. It is proportional to the amount of light.

FIG. 2 shows the slit plate 3 and the SELFOC lens array 17
It is a perspective view showing a positional relationship with the LED array 1.

The SELFOC lens array 17 is arranged in the middle of a fixed distance connecting the LED array 1 and the slit plate 3 and is fixed to the LED array 1 side.

The slit plate 3 moves in the array arrangement direction of the LED array 1 with a certain distance from the SELFOC lens array 17,
The light passing through the slit 3A is received by the light receiving element 4 and converted into an electric current.

Next, the facing distance from the LED array 1 to the slit plate 3 will be described.

The facing distance between the LED array 1 and the slit plate 3 is the LED array 1
It is a unique value determined by the conjugate focal length of the SELFOC lens array 17 attached to.

The LED array 1 is required to keep the distance to the electrostatic photosensitive drum 11 at this peculiar value while being incorporated in a printer device or the like.

Generally, LEDs such as the gap rollers 18 and 19 in Fig. 15 are used.
The structure provided at both ends of the array 1 is used.

Next, an embodiment circuit of the MTF calculator 6 of FIG. 1 will be described with reference to FIG.

In FIG. 5, 51 is a MAX hold circuit that holds the maximum value of the input voltage waveform, 52 is a MIN hold circuit that holds the minimum value of the input voltage waveform, and 56 is MT from the maximum value and the minimum value of the input voltage waveform.
An analog operation circuit that calculates F, 57 is an analog operation circuit 5
A sample and hold circuit that samples and holds the MTF calculation value of 6, 53 is an MTF that controls the measurement timing of the MAX hold circuit 51, the MIN hold circuit 52, and the sample and hold circuit 57.
A control circuit 55 is an MTF cycle detection circuit that variably controls the control timing of the MTF control circuit 53 in accordance with the moving speed of the moving table 2 in FIG.

In the analog operation circuit 56 of FIG. 5, 56A to 56C have a gain of -1.
Double operational amplifier, 56D is an analog divider.

Next, the MAX hold circuit 51 and the MIN hold circuit 5 shown in FIG.
2. A circuit diagram of an embodiment of the MTF control circuit 53 will be described with reference to FIG.

FIG. 12 is an operation waveform diagram when the circuit diagram of FIG. 6 is adopted in the MTF calculator of FIG. 5, and each operation of Vin and start of Start and MTF sample, MAX, and MIN of FIG. The waveforms are shown in correspondence with FIG.

Next, the MAX hold circuit 51 of FIG. 6 will be described.

The MAX hold circuit 51 in FIG. 6 is a peak hold circuit, 51A is an operational amplifier, and 51B has a small input bias current.
A FET input operational amplifier, 51C is a comparator, and 51D is an analog switch using a CMOSFET, which conducts when the control input is at the logic level "1". The input voltage Vin of the comparator 51C is
When it exceeds MAX, a logic level "0" is output.

51E is a holding capacitor, for example, a 0.1 μF capacitor.

The MIN hold circuit 52 in FIG. 6 is a bottom hold circuit, and 52A to 52E are the same as 51A to 51E.

The comparator 52C outputs a logic level "0" when the input voltage Vin exceeds MIN. The MTF control circuit 53 outputs the logic level "1" as the MTF sample timing for a certain time (T ₁ ) when both the MAX hold circuit 51 and the MIN hold circuit 52 obtain the hold state, and then the MAX hold circuit 51 is turned on. Reset for a certain time (T ₂ ).

In addition, the MAX hold circuit 51 keeps the hold state for a certain time (T
₂ ) When the MIN hold circuit 52 continues input voltage Vin
After a certain time (T _n ) has passed without detecting MIN from, a logical level “1” is output as MTF sample timing for a certain time (T ₃ ), and then the MAX hold circuit 51 is held for a certain time (T ₄ ). Reset.

53A to 53C are monostable multivibrators operating at an input logic level "0", and 53D are monostable multivibrators operating at an input logic level "1". The output pulse width of the monostable multivibrators 53A to 53D is made sufficiently smaller than the MTF cycle. In the embodiment, T _{1 to} T ₄ ≈0.2 ms.

Next, the analog operation circuit 56 and the sample hold circuit 57 shown in FIG. 5 will be described.

(MAX + MIN) is obtained at the output of the operational amplifier 56C in FIG. 5, and (MAX-MIN) is obtained at the output of the operational amplifier 56B.

These outputs are applied to the Y and X inputs of divider 56D.

The sample-hold circuit 57 sequentially holds the MTF calculation voltage obtained by the analog calculation circuit 56, so that the MTF output as shown in FIG. 12 is obtained. An A / D converter can be used instead of the sample hold circuit 57. In this case, set the MTF sample timing in Fig. 5 to A / D.
It can also be used as the conversion timing input of the converter, so that the MTF data can be digitized.

Next, the MTF cycle detection circuit 55 of FIG. 5 will be described with reference to the embodiment circuit of FIG. Reference numeral 81 in FIG. 8 is a frequency-voltage converter which receives a motor drive clock pulse from the motor control circuit 8 in FIG. 1 and outputs a voltage proportional to the clock frequency in the relationship shown in FIG. In the embodiment, the F / V converter 81
Uses a dedicated integrated circuit.

Reference numeral 82 is a constant current generating circuit that receives the output voltage of the F / V converter 81 and outputs a constant current. The output current is I = (R ₂ × V ₀ ) / (R ₁
X R ₃ ).

The constant current generating circuit 82 includes resistors R _{1 to} R ₃ and operational amplifiers 82A and F.
It is composed of the ET transistor 82B, and the output current with respect to the input voltage has the relationship shown in FIG.

In FIG. 8, 83 is an integrating capacitor, and 84 is a Schmitt trigger. The integrating capacitor 83 is charged by the constant current generating circuit 82, and the charging voltage of the capacitor 83 is Schmitt trigger.
When the input threshold voltage of 84 becomes high level, the output of the Schmitt trigger becomes logic level "1". 11th
The figure shows that the output of Schmitt trigger 83 is at logic level "1" after the cathode side of diode 85 is at logic level "1".
The relation of the integration time (T _n ) with respect to the charging current up to is shown.

When the circuit of FIG. 6 is used, the integration time (T _n ) set in the MTF cycle detection circuit of FIG. 8 is T when the speed of the mobile table 2 is in the constant speed region of FIG. Then, T _n ≈
Set to (T-T ₃ ). T3 is the output pulse width of the monostable multivibrator 53D shown in FIG.

The above-mentioned contents are related to the embodiment according to the first invention, and the MTF calculator of FIG. 5 can be configured by combining FIG. 6 and FIG. 8 to detect the MAX period of MTF. Then, the MTF for the defective emission dot can be calculated.

Next, an embodiment according to the second invention will be described.

In the second invention, FIG. 7 and FIG.
The MTF calculator in the figure can be configured, and the MTF for the defective light emission dot can be calculated by detecting the MIN period of the MTF.

Next, FIGS. 5 and 7 will be described.

In this embodiment, the MTF control circuit 54 of FIG. 7 can be used instead of the MTF control circuit 53 of FIG.

FIG. 13 is an operation waveform diagram of the measurement when the circuit diagram of FIG. 7 is adopted in the MTF calculator of FIG.
The operation waveforms of Vin, start, MTF sample, MAX, and MIN are shown in correspondence with FIG.

The MAX hold circuit 51 and the MIN hold circuit 52 in FIG. 7 are the same as those in FIG.

The comparators 51C and 52C shown in FIG. 7 are connected to the 51C and 52C shown in FIG. 6 by exchanging the + input and the − input.
The 51C and 52C output "1" level, which is the reverse of the output logic level when detecting MAX and MIN.

The MTF control circuit 54 outputs the logic level “1” as the MTF sample timing for a certain time (T ₁ ) when both the MAX hold circuit 51 and the MIN hold circuit 52 are in the hold state, and then the MAX hold circuit 51 is turned on. Fixed time (T ₂ )
Reset.

Further, after the MIN hold circuit 52 detects MIN from the input voltage Vin, when a certain time (T _n ) has elapsed, a certain time (T ₄ ),
After outputting the logic level "1" as the MTF sample timing, the MAX hold circuit 51 is reset for a fixed time (T ₅ ).

54A to 54E are monostable multivibrators that operate at the input logic level "1", and the output pulse width is sufficiently smaller than the MTF cycle. In the embodiment, T _{1 to} T ₅ ≈0.2 ms.

Next, when the circuit of FIG. 7 is used, the integration time (T _n ) set in the MTF cycle detection circuit of FIG. 8 is the MTF in the state where the speed of the mobile table 2 is the third constant speed region. Assuming that the period is T, the range is (T−T ₄ ) ≦ T _n <1.1T.

When _Tn is increased in the circuit of FIG. 8, the output current of the constant current generating circuit may be decreased, that is, the value of R3 may be increased.

[Effect of the Invention] According to the present invention, an analog electronic circuit composed of a MAX hold circuit, a MIN hold circuit, an analog operation circuit, and a sample hold circuit can be freely followed by the moving speed of a slit attached to a moving table. Since the MTF of the LED array is calculated by the MTF calculator that has the MTF control circuit and the MTF cycle detection circuit that logically processes the measurement timing control and the dot defect detection, the waveform observation means of the prior art is not required, and the defective light emission is eliminated. Even when including, it is possible to obtain MTF data for all dots of the LED array in a short time and provide a high-speed MTF measuring device.

[Brief description of drawings]

FIG. 1 is a block diagram of a high speed MTF measuring device for an LED array according to the present invention, and FIG. 2 is a perspective view showing the MTF measuring principle of FIG.
FIG. 3 is a diagram showing the moving speed of the movable table 2, FIG. 4 is a waveform diagram showing the irradiation intensity of each light beam train from the LED array 1, and FIG. 5 is an embodiment of the MTF calculator 6 of FIG. Fig. 6 shows the MAX hold circuit 51 and MIN hold circuit 52 in Fig. 5.
Circuit diagram of an embodiment of the MTF control circuit 53, FIG. 7 is a circuit diagram of another embodiment of FIG. 6, FIG. 8 is a circuit diagram of an embodiment of the MTF cycle detection circuit 55 of FIG. The figure shows the F / V converter 81 in Fig. 8.
Fig. 10 shows the relationship between input frequency and output voltage of Fig. 8
FIG. 11 is a diagram showing the relationship between the input voltage and the output current of the constant current circuit 82, and FIG. 11 is the constant current generation circuit 82 and capacitor 83 of FIG.
Diagram of the charging current by the diode 85 and the integration time,
12 is an operation waveform diagram when the circuit of FIG. 6 is adopted for the MTF calculator 6 of FIG. 5, and FIG. 13 is a waveform diagram when the circuit of FIG. 7 is adopted for the MTF calculator 6 of FIG. Operating waveform diagram, Fig. 14 is LE
D printer device configuration diagram, FIG. 15 is LED array 1 in FIG.
And FIG. 16 is an explanatory view of the relationship between the electrostatic photosensitive drum 11 and FIG. 16, FIG. 16 is a configuration diagram of a conventional LED array MTF measuring device, and FIG. 17 is a waveform diagram appearing in the waveform observing means 10 of FIG. 1 ... LED array, 2 ... moving base, 2A ... pulse motor, 3 ... slit plate, 3A ... slit, 4 ... light receiving element, 5 ... amplifier, 6 ... MTF calculator, 7 ... LED array control circuit, 8 ... Motor control circuit, 51 ... MAX hold circuit, 52 ... MIN hold circuit, 53 ... MTF control circuit, 54
...... MTF control circuit, 55 …… MTF cycle detection circuit, 56 …… Analog operation circuit, 57 …… Sample hold circuit.

Claims (2)

[Claims] 1. Light emitted from an LED array is received through a slit that moves parallel to the arrangement direction of the LED array via a SELFOC lens array, the amount of light passing through the slit is detected by a detection means, and a waveform is observed by a waveform observation means. Observe the above
In an MTF measuring device for determining the MTF of an LED array, a MAX hold circuit that holds the MAX of the output voltage of the detection means, a MIN hold circuit that holds the MIN of the output voltage of the detection means, and a maximum value of the MAX hold circuit LED array characterized by including an MTF control circuit for detecting the cycle of MTF control of the defective light emitting array and controlling the MTF measurement of the defective light emitting array, and an MTF cycle detection circuit for generating an MTF cycle following the moving speed of the slit by an integrating means. High speed MTF measuring device. 2. The light emitted from the LED array is received through a slit that moves parallel to the arrangement direction of the LED array via a SELFOC lens array, the amount of light passing through the slit is detected by a detecting means, and a waveform is observed by a waveform observing means. Observe the above
In an MTF measuring device for determining the MTF of an LED array, a MAX hold circuit that holds the MAX output voltage of the detection means, a MIN hold circuit that holds MIN of the output voltage of the detection means, and a minimum value of the MIN hold circuit LED array characterized by including an MTF control circuit for detecting the cycle of MTF control of the defective light emitting array and controlling the MTF measurement of the defective light emitting array, and an MTF cycle detection circuit for generating an MTF cycle following the moving speed of the slit by an integrating means. High speed MTF measuring device.