JPH04239664A - Inspection device of array optical head - Google Patents

Abstract

PURPOSE:To provide the above inspection device which is used for inspection of array optical head used in an LED printer and the like and is especially capable of detecting a short circuit even when a short-circuit defect occurs between light emitting elements in the aray optical head. CONSTITUTION:Two or more LED array tips are provided in an LED head 4, and a specified number of LED elements are arranged in an array on each LED array tips and emits light in turn. The light volumes of emitted light are detected by an optical sensor 7 and stored in a memory of a computer 2 via a measuring circuit 8. The data stored in the memory are averaged for every corresponding light emitting elements according to the connection constitution between the LED array tips, thereby the light emitting element having a short-circuit defect is detected.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus using an array optical head such as an LED printer, and more particularly to an inspection apparatus for an array optical head.

0002

2. Description of the Related Art As an array optical head, for example, an LED
2. Description of the Related Art There is an apparatus that performs optical writing on a photoreceptor by arranging a large number of elements or EL elements in an array. For example, in the case of an LED printer, a L
Using an ED head, each LED element emits light by time-division driving to perform optical writing on the photoreceptor according to print data.

[0003] Fine signal lines are connected to the light emitting elements of the above-mentioned array optical head by a method such as wire bonding, and printing signals are supplied. However, since the connections of these light emitting elements are extremely fine, short-circuits at bonding portions, short-circuits and disconnections between signal lines and elements often occur.

Conventionally, after manufacturing an array optical head,
An inspection device is used to inspect the array optical head for short circuits and disconnections. In this inspection, the amount of light emitted from all the elements in the head is individually measured using a CCD sensor or the like, and it is checked whether each element satisfies a predetermined amount of light emitted. Further, this predetermined light amount value is usually set within a range of -15% to +15% compared to the normal light amount value.

[0005]

[Problems with the prior art] However, in the above-mentioned array optical head inspection device, since the amount of light emitted from each element is inspected to see if it reaches a predetermined value, if there is a short-circuit between the elements, the short-circuited element will receive an electric current. It cannot be determined that the flow is defective. That is, current flows through the short-circuited elements, and the current value is 0.8 to 0.9 times the normal current value, that is, about -20% to -10% of the normal light emission amount. In other words, since the segment driver of the LED element performs constant current drive, even if the load doubles, the current value does not double, and when converted to one element, the normal current value is 0.8 to 0. This is because it is 9 times as large. therefore,
A reduction in the amount of emitted light due to a short circuit is often not detected by conventional inspection equipment, and it has been difficult to detect defects due to short circuits between elements.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide an inspection apparatus for an array optical head that is capable of detecting short-circuit defects in light emitting elements of the array optical head.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an array of light for optical writing on a photoreceptor by arranging a plurality of chips each consisting of a plurality of light emitting elements and emitting light from each chip in turn according to print data. In the head inspection apparatus, a light emission control means for causing the light emitting elements to emit light in order with a predetermined current in each chip, a measuring means for measuring the amount of light of each light emitting element, and a storage means for storing the amount of light by the measuring means; The present invention is characterized by comprising a calculating means for calculating an average light amount within a chip, and a determining means for determining a light emitting element whose light amount is measured to be a predetermined value lower than the average light amount as a defective light emitting element.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a system block diagram of an inspection apparatus for an array optical head according to this embodiment. In the same figure,
The inspection device 1 includes a personal computer (hereinafter simply referred to as a computer) 2, a head control circuit 3, and an LED head 4.
, a motor control circuit 5, a motor 6, an optical sensor 7, a measurement circuit 8, and a rotating shaft 9. The computer 2 performs system control of the entire inspection apparatus 1 of this embodiment and manages inspection data. The computer 2 also includes a memory for storing data to be described later, and a CPU (not shown).
performs calculation processing of the average value of data, processing of comparison with data of a predetermined light amount value to be described later, processing of determining whether the LED element is good or bad, etc.

The head control circuit 3 controls the light emission of the LED head 4 based on instructions from the computer 2. for example,
LEDs in each LED array chip arranged in an array
It controls the output of a selection signal, which will be described later, for causing the elements to emit light in order, and controls the output of a test signal. Motor control circuit 5
similarly controls the drive of the motor 6 based on instructions from the computer 2. For example, the optical sensor 7 is placed directly below the LED element that emits light in accordance with the light emission timing of the above-mentioned LED element.
It is a control to move. Note that the movement of the optical sensor 7 in the direction of the arrow is performed via a rotating shaft 9 attached to the shaft 6' of the motor 6.

The optical sensor 7 is composed of a CCD, detects the amount of light emitted from the LED element, and outputs voltage value data to the measuring circuit 8 according to the amount of received light. The measuring circuit 8 converts the input voltage value data into corresponding digital data of the light amount value, and outputs it to the computer 2. The computer 2 stores the digital data to be input into the memory, and also outputs a signal synchronized with the instruction signal output to the head control circuit 3 and motor control circuit 5 to the measurement circuit 8 to measure the voltage value output from the optical sensor 7. The measurement circuit 8 is notified of the detection timing.

Further, FIG. 2 is a diagram illustrating the configuration of the LED head 4, which is the object to be measured of the above-mentioned inspection apparatus 1. The LED head 4 described in this embodiment is used, for example, in an LED printer, and is a device that performs optical writing on a photoreceptor in the LED printer according to print data. As shown in the figure, this LED head has 64 LEDs per chip.
It has an LED array chip 10 in which elements are arranged in a row,
In addition to this LED array chip 10, the LED head 4 includes a segment driver circuit 11, segment electrodes 12, a common electrode 13, and the like.

The segment driver circuit 11 is a circuit that outputs a print signal based on print data to the LED elements in the LED array chip 10 when the segment driver circuit 11 is installed in the LED printer after being inspected by the inspection apparatus of this embodiment. however,
During the inspection operation by the inspection apparatus of this embodiment, the LED
The elements are made to emit light in sequence. This segment driver circuit 11 is supplied with a test signal from the head control circuit 3 via a terminal 11a, and is supplied with a clock signal via a terminal 11b. The segment driver circuit 11 inputs a test signal in synchronization with this clock signal. For example, when a 64-dot test signal is input, a latch signal is supplied via the terminal 11c. In synchronization with the supply of this latch signal, the 64-dot print data latched by the segment driver circuit 11 is output to the LED array chip 10 via the segment electrodes 12.

A plurality of LED array chips 10 are arranged in a line. For example, if the LED printer to which the LED head 4 of this embodiment is applied is capable of printing on up to B4 size paper, 38 LED array chips 10 are arranged in a line. 1
0-1 to 10-38 are arranged. In other words, if the print density of the LED head 4 is 240DPI, the width of B4 size paper is 257mm, so it is 257 x 240/25.
．． From the calculation formula of 4×64, 38 LED array chips 10-1 to 10-38 are required.

[0014] Moreover, this LED array chip 10-1~
The connection between 10-38 and the segment driver circuit 11 is as follows:
This is done through 64 segment electrodes 12-1 to 12-64. That is, segment electrodes 12-1 to 12-64 are connected corresponding to inputs I1 to I64 of each of the 38 LED array chips 10-1 to 10-38, and these segment electrodes 12-1 to 12-64 Outputs O1 to O of the segment driver circuit 11 corresponding to
64. Therefore, the test signal output from the output O1 of the segment driver circuit 11 is applied to the input I of all the LED array chips 10-1 to 10-38.
Similarly, test signals outputted from outputs O2 to O64 of other segment driver circuits 11 are also supplied to corresponding inputs I2 to I64 of all LED array chips 10-1 to 10-38.

[0015] Then, 38 LED array chips 10
The selection from -1 to 10-38 is performed by a selection signal outputted from the above-mentioned head control circuit 3 via the common electrode 13. That is, when the selection signal is output to the common electrode 13-1, the LED array chip 10-1 is selected, when the selection signal is output to the common electrode 13-2, the LED array chip 10-2 is selected, and so on. LED array chips 10-3 to 10-38 can be selected by outputting a selection signal.

The inspection operation of the LED head 4 in the inspection apparatus 1 configured as described above will be explained below. First, the LED head 4, which is the object to be inspected, is set in the inspection device, the necessary signal lines are connected, and the keyboard 2' of the computer 2 is operated to instruct the LED head 4 to be inspected. An instruction signal is output to the control circuit 3 and the motor control circuit 5 at predetermined timing. Based on this instruction signal, the head control circuit 3 first
LED located at the end of the ED array chip 10-1
A test signal is output to the element (LED element connected to input I1). That is, test signals of "1000..." are sequentially outputted to the segment driver circuit 11, and these signals are supplied to the segment electrodes 12 in synchronization with the latch signal. Also, at this time, a selection signal is output to the LED array chip 10-1. By controlling in this way, the outputs O1 to O64 of the segment driver circuit 11 are synchronized with the output of the latch signal to the segment electrodes 12-1 to 1.
A test signal "1000..." is supplied to the LED array chip 10-1 via the terminal 2-64, and only the LED element located at the end of the LED array chip 10-1 emits light. At this time, under the control of the motor control circuit 5, the motor 7 is positioned directly below the LED element emitting light, and detects the amount of light emitted from the LED element. FIG. 3 is a diagram showing the light receiving state of the optical sensor 7 at this time. In addition, SELFOC lens array 1 shown in the same figure
4 is a lens for focusing the light emitted from the LED element 4 on the optical sensor 7.

The voltage value based on the amount of light received by the optical sensor 7 in this manner is output to the measuring circuit 8, converted into digital data, and stored in the memory within the computer 2. Next, the head control circuit 3 outputs a test signal "0100..." to the segment driver circuit 11 in order to emit light from the element adjacent to the above-mentioned LED element, and the corresponding LED element in the LED array chip 10-1 is outputted to the segment driver circuit 11. emits light. Then, in the same manner as described above, the motor 6 is driven to position the optical sensor 7 directly below the LED element that emits light, and the amount of emitted light is measured. In the same manner, the LED array chips 10-1 are sequentially
The light emitting element inside the head control circuit 3 emits light in accordance with the test signal output from the head control circuit 3, and the light amount value detected by the optical sensor 7 is stored in the memory of the computer 2. It is assumed that the LED array chip 10-1 is selected by the selection signal during this time.

In this way, the LED array chip 10-
After measuring the amount of light emitted from the LED elements arranged in 1,
LED array chips 10-2 and 10-3 depending on the selection signal
, . . . are performed, and during this time data on the amount of light emitted from each LED element is stored in the memory of the computer 2. When the process of measuring the amount of light emitted from all the LED elements is completed, the computer 2 reads out the data on the amount of emitted light stored in the memory, and reads out the data of the amount of emitted light stored in the memory, and
The average value of the amount of emitted light at the corresponding position of the 64 LED elements arranged at points 10-38 to 10-38 is calculated. That is, each L
The average value of the amount of light emitted from the LED elements emitting light according to the signal supplied to the input I1 of the ED array chips 10-1 to 10-38 is calculated, and the amount of light emitted from the LED element emitting light according to the signal supplied to the input I2 is calculated. The average value is calculated, and similarly, the average value (Pave) of the amount of light emitted by the LED elements emitting light is calculated according to the signal supplied to the input I64. This arithmetic processing is executed by the CPU in the computer 2, and FIG. 4 is a diagram showing the results of this arithmetic operation. Incidentally, the expression expressing the above-mentioned calculation is the following calculation expression.

[0019]

[Math 1]

Here, i represents the i-th LED array chip 10, k represents the k-th LED element, and c
indicates the total number of LED array chips 10. Here, if a short circuit occurs between the LED elements in a certain LED array chip 10, as shown in FIG. Detected as a low value. That is, as explained in the conventional example, it is -20% to -10% of the normal value. Moreover, adjacent LED elements continuously emit a low amount of light. Therefore, the measurement circuit 8 is controlled by the computer 2, the head control circuit 3, and the motor control circuit 5 in the same manner as described above.
When the digital data outputted from the computer 2 is stored in the memory of the computer 2 and the average value is calculated, the calculation result as shown in FIG. 6 is obtained. In other words, the L causing the short circuit failure
Both of the ED elements are in a state where the amount of emitted light is continuously low compared to all the LED chips. The reason for this is that the segment driver circuit 11 and the LED array chip 1
0-1 to 10-38 are connected as shown in FIG. This is because the amount of light emitted by the corresponding LED element in the LED array chip 10 in which no short circuit has occurred also decreases. Then, the light amount value (Pa
ve') is expressed by the following formula.

[0021]

[Math 2]

Here, the normal light amount value of the j-th LED element of the i-th LED array chip is assumed to be P(i,j). Further, r has a value of 0.8 to 0.9. Therefore, as shown in FIG. 6, when the amount of light emitted from successive n and n+1 LED elements is below a predetermined level, the CPU determines that the device is defective, thereby easily determining a short circuit. Note that the predetermined light amount value (threshold level) shown in the figure is higher than the conventional -15%, for example, about -5%. This is the average amount of emitted light corresponding to 38 LED array chips 10, so it is shown in the conventional example (-15%
This is because it is thought that the variation will not occur as much as (~+15%).

In this embodiment, the LED array chip 10 is composed of 38 pieces, and the number of LED elements in the LED array chip 10 is 64 pieces, but the present invention is not limited to these specific numbers of elements. Of course.

Furthermore, in this embodiment, a head in which LED elements are arranged in an array has been described, but EL, PLZ
The present invention can be applied to the inspection of a head in which a light emitting element such as T is arranged and each element emits light using a constant current driver.

[0025]

As described in detail above, according to the present invention, even if a short-circuit occurs in a light emitting element, it can be detected, so that an array optical head can be reliably inspected.

In addition, since the inspection is performed using a computer or the like, inspection data can be managed efficiently. For example, this inspection data can be used to detect bonding locations where short-circuit defects are likely to occur in the array optical head. can do.

[Brief explanation of the drawing]

FIG. 1 is a system block diagram of an inspection apparatus for an array optical head according to an embodiment.

FIG. 2 is a diagram illustrating the internal configuration of an array-shaped optical head.

FIG. 3 is a diagram illustrating an inspection state of an array-shaped optical head inspection apparatus.

FIG. 4 is a diagram showing measurement results of the average value of the amount of emitted light.

FIG. 5 is a diagram illustrating the inspection state of the array optical head inspection apparatus when a short circuit occurs between elements.

FIG. 6 is a diagram showing measurement results of the average value of the amount of emitted light when a short circuit occurs between elements.

[Explanation of symbols]

1 Inspection device 2 Computer 3 Head control circuit 4 LED head 5 Motor control circuit 6 Motor 7 Optical sensor 8 Measurement circuit 9 Rotating shaft 10, 10-1 to 10-38 LED array chip 1
1 Segment driver circuit

Claims (1)

[Claims] 1. In an inspection apparatus for an array optical head that performs optical writing on a photoreceptor by arranging a plurality of chips each including a plurality of light emitting elements and causing each chip to emit light in turn according to print data, each of the light emitting elements is A light emission control means for sequentially causing the chip to emit light with a predetermined current, a measuring means for measuring the light amount of each light emitting element, a storage means for storing the light amount by the measuring means, and a calculating means for calculating the average light amount within the chip. 1. An inspection apparatus for an array optical head, comprising: a determining means for determining, as a defective light emitting element, a light emitting element whose light intensity is measured to be lower than an average light intensity by a predetermined value.