JPH06105206B2 - LED array MTF measuring device - 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. 7, 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. 7 will be described with reference to FIG.

In FIG. 8, 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, a conventional MTF measuring device for an LED array will be described with reference to FIG.

In FIG. 9, an image sensor 20 for receiving the irradiation light of the LED array 1 is placed at a position separated from the SELFOC lens array 17 by a certain distance, and one LED emitter 1 (hereinafter, referred to as 1
Called a dot. ) Flashes every other pattern.

The light receiving intensity distribution on the light receiving surface of the image sensor 20 is observed with an oscilloscope or the like as a waveform as shown in FIG. 2, and the MTF is obtained from the maximum light receiving intensity Imax and the minimum light receiving intensity Imin by the following equation.

MTF = (Imax−Imin) / (Imax + Imin) (1) [Problems to be solved by the invention] In the conventional device of FIG. 9, the image sensor 20 is expensive and the drive circuit of the image sensor 20 is complicated. To be
Image sensor 20 is the range where the MTF of LED array 1 can be measured.
This is the length of the light receiving surface of the LED 1, and there is a problem that the image sensor 20 must be moved in the length direction of the LED array 1 in order to measure the MTF over the entire length of the LED 1.

The present invention is an LED array control circuit that generates a slit plate that moves in parallel with the arrangement direction of the LED array 1, a pattern that blinks the LED array 1 every other dot, and a pattern that causes the LED array 1 to continuously emit light. By providing an apparatus including the above, the irradiation state of the light beam by the LED array 1 can be measured over the entire light emitting region of the LED array 1 as the MTF of the overlapping state of each beam and the separated state. The purpose is to

[Means for Solving the Problems] In order to achieve this object, in the present invention, the LED array 1
The movable table 2 that moves parallel to the arrangement direction of the LED array 1 and the movable table 2 are attached to the movable table 2, and the slit 3A is opened in the direction orthogonal to the arrangement direction of the LED array 1, and the slit 3A is at a constant distance from the light emitting surface of the LED array 1. The slit plate 3 that is held, the light receiving element 4 that receives the light amount of the LED array 1 that has passed through the slit 3A of the slit plate 3, the amplifier 5 that amplifies the light output current of the light receiving element 4, and the output voltage of the amplifier 5 are An MTF measurement circuit 6 that calculates and converts into an MTF measurement value, an LED array control circuit 7 that generates a pattern for blinking the LED array 1 every other dot, and a pattern for continuously emitting light from the LED array 1.
With.

Next, the structure of the LED array MTF measuring device according to the present invention will be described with reference to FIGS.

In FIG. 1, 1 is an LED array to be measured, 2 is a movable table that moves in parallel with the light emitting surface of the LED array 1, and 3 is attached to the movable table 2, and is arranged at a certain distance from the light emitting surface of the LED array 1. The slit plate, 4 is a light receiving element that receives the amount of light that has passed through the slit 3A of the slit plate 3, 5 is an amplifier that amplifies the optical output current of the light receiving element 4, 6 is the output voltage of the amplifier 5, and MTF measurement is performed. An MTF measuring circuit for converting the value into a value, and 7 is an LED array control circuit for generating a pattern in which the LED array 1 blinks every other dot and a pattern in which the LED array 1 continuously emits light. 8 and 9 in FIG. 3 are gap rollers.

[Function] The LED array 1 is made to emit light in a blinking pattern every other dot, and the slit plate 3 having the slits 3A arranged in a direction orthogonal to the arrangement direction of the LED array 1 is placed at a position separated from the LED array 1 by a certain distance. When moving in parallel with the array direction of the array, the amount of light passing through the slit 3A increases as the emission output of the LED array 1 increases and the diameter of the irradiation beam passing through the slit 3A decreases.

Therefore, the amount of light passing through the slit 3A is maximized at the position facing the center of the luminescent dot, and the amount of light is minimized at the intermediate position between the luminescent dot and the luminescent dot, that is, the position of the extinction dot.

The larger the difference between the maximum and the minimum, the higher the focusing property of the beam emitted from the LED array 1, and the higher the printing resolution in the printer device.

Next, when the LED array 1 is made to emit light in a continuous light emitting pattern and the slit 3A is moved, the change in the amount of light passing through the slit 3A becomes small.

The smaller the difference in the amount of light, the higher the flatness of the beam emitted from the LED array 1 in the length direction of the LED array 1, and the clearer solid printing can be obtained in the printer device.

The present invention provides two types of light emission patterns of the LED array 1, blinking and continuous, to provide data useful for evaluating print quality of a printer device.

According to the present invention, the slit plate 3 is moved along a straight line connecting the gap rollers 8 and 9 for measurement.

Further, if the position of the slit plate 3 according to the present invention is adjusted in the vertical direction with respect to the gap rollers 8 and 9 of the LED array 1, the optimum print quality can be obtained by the MTF, that is, the largest blinking pattern (80% or more). ), The correction distance in the upper or lower direction is obtained so as to be the smallest (15% or less) in the continuous pattern, and therefore it can be useful for designing the position of the gap rollers 8 and 9.

[Embodiment] FIG. 2 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 movable table 2 is moved, and passes through the slit 3A of the slit plate 3. It is proportional to the amount of light.

FIG. 3 shows the slit plate 3 and the gap roller 8 of the LED array 1.
9 is a perspective view showing a positional relationship with 9; FIG.

The slit plate 3 moves on a straight line connecting the gap rollers 8 and 9, and 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.

The LED array 1 is required to keep the distance to the electrostatic photosensitive drum 11 at this peculiar value in a state of being incorporated in the printer device. Generally, the gap rollers 8 and 9 in FIG.
A structure provided at both ends of the LED array 1 is used like the gap rollers 18 and 19 in the figure.

Next, an example circuit of the MTF measuring circuit 6 will be described with reference to FIG.

In FIG. 4, 61 is a maximum hold circuit that holds the maximum value of the input voltage waveform, 62 is a minimum hold circuit that holds the minimum value of the input voltage waveform, 63 to 65 are DC amplifiers with a gain of −1, 66 is an analog A divider 67 is a timing control circuit that resets the maximum hold circuit 61 and the minimum hold circuit 62 with a delay of a fixed time (for example, 500 μs) after the minimum hold circuit 62 holds the minimum value.

FIG. 5 is an output voltage waveform diagram with respect to the input voltage Vin of the maximum hold circuit 61 and the minimum hold circuit 62 of FIG.
The measured value is obtained during the above-mentioned fixed time when the output voltage of the minimum hold circuit 62 holds the minimum value. Amplifier 65 of FIG.
The voltage of (Imax-Imin) is obtained at the output of, the voltage of (max + Imin) is obtained at the output of the amplifier 64, and the voltage of equation (1) is obtained at the output of the analog divider 66.

FIG. 6 is an example of MTF measurement data obtained by the apparatus of FIG. 1, where the horizontal axis is the dot number and the vertical axis is the MTF.

Fig. 6a shows the MTF when the LED array 1 is continuously illuminated.
6A is the MTF data when the LED array 1 is made to emit light every other dot.

[Effect of the Invention] According to the present invention, the slit plate is moved in parallel with the array direction of the LED array so that the LED array blinks every other dot, and the LED array 1 continuously emits light. Since it is generated by the array control circuit, L
The irradiation state of the light beam by the ED array can be measured over the entire light emitting area of the LED array as the MTF of the overlapping state of each beam and the separated state.

[Brief description of drawings]

FIG. 1 is a block diagram of an LED array MTF measuring device according to the present invention, and FIG. 2 is an output voltage waveform of an amplifier 5 obtained when the LED array 1 of FIG. FIG. 3 is a perspective view showing the positional relationship between the slit plate 3 and the gap rollers 8 and 9 of the LED array 1, FIG. 4 is a circuit diagram of an embodiment of the MTF measuring circuit, and FIG. 5 is the maximum hold of FIG. Output voltage waveform diagram for the input voltage Vin of the circuit 61 and the minimum hold circuit 62, FIG. 6 is a diagram showing MTF measurement data by the device of FIG. 1, FIG. 7 is a configuration diagram of the LED printer device, and FIG. 8 is an LED. Explanatory drawing of relationship between array and electrostatic photosensitive drum, 9th
FIG. 1 is a block diagram of a conventional LED array MTF measuring device. 1 ... LED array, 2 ... moving base, 3 ... slit plate, 3
A ... slit, 4 ... light receiving element, 5 ... amplifier, 6 ...
… MTF measurement circuit, 7 …… LED array control circuit, 8.9 ……
Gap roller.

Claims (1)

[Claims] 1. A movable table (2) which moves parallel to the arrangement direction of the LED array (1), and a slit (3A) attached to the movable table (2) in a direction orthogonal to the arrangement direction of the LED array (1). ) Is opened and the slit (3A) is held at a constant distance from the light emitting surface of the LED array (1), and the LED array (1) that has passed through the slit (3A) of the slit plate (3). Light receiving element (4) for receiving the amount of light of, and an amplifier (5) for amplifying the light output current of the light receiving element (4)
The MTF measurement circuit (6) that calculates the output voltage of the amplifier (5) and converts it to the MTF measurement value, the LED array (1) blinking every other dot, and the LED array (1) are connected continuously. An LED array control circuit (7) for generating a pattern for causing light to be emitted by an LED array MTF measuring device.