JPS6310293Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a light emitting element (hereinafter referred to as LED) array drive circuit for an optical printer, which is a type of non-impact recording device.

Generally, thermal recording devices, electrophotographic recording devices, and the like are known as non-impact recording devices.

A thermal recording device is equipped with a thermal head consisting of a large number of heating elements, and by controlling the supply of electricity to each heating element, the thermal paper is colored using the heat generated by the heating element itself to form a desired recorded image. Low noise and low cost are expected, but in order to provide enough heat to color thermal paper, the time required to energize each heating element is usually 5 to 10 msec.
A certain amount of time is required. In order to achieve high-speed recording in a thermal recording device, it is conceivable to instantaneously apply a large current to each heating element to increase the peak value of the thermal pulse. However, the heating characteristics of the heating elements themselves, especially the rise and fall Characteristics are number
At present, it is quite difficult to perform high-speed recording with a thermal recording device, considering the fact that the thermal paper is large (msec), there are limits to the thermal response characteristics of thermal paper, and the lifespan of the heating element is adversely affected.

On the other hand, an electrophotographic recording device uses a recording light source to irradiate light onto the surface of a photoreceptor to form an electrostatic latent image.
The following is a series of electrophotographic processes: phenomenon, transfer,
A recorded image is formed on plain paper through a fixing process.

One type of electrophotographic recording device is an optical printer that uses an LED array as a recording light source.
This optical printer integrates approximately 128 LEDs.
Equipped with a recording head consisting of approximately 10 LED arrays arranged in the main scanning direction for the width of the recording paper, each LED is selectively driven and controlled to form an electrostatic latent image on the surface of the photoreceptor. However, the energization time to each LED at that time is 1 msec or less, and the electrostatic latent image formation time for one dot line in the main scanning direction is
Approximately 1msec has been achieved.

In this way, optical printers have an advantage over thermal recording devices in terms of high-speed recording.

By the way, the LED array recording heads used in optical printers and the thermal heads used in thermal recording devices usually have recording element sections arrayed in the main scanning direction, and are line-type recording in which recording is performed every one dot line in the main scanning direction. It's a head. In this type of line-type recording head, when recording one dot line, there is a method in which a large number of recording elements is divided into a plurality of blocks and drive control is performed for each block in a time-division manner, or a method in which all recording elements are controlled in a time-division manner. There is a method that controls the drive all at once. In a drive control method in which the recording element sections are driven all at once, the energization time for each recording element is approximately equal to the recording time for one dot line.On the other hand, in a drive control method in which the recording element sections are driven in time division for each block, the time division The recording time for one dot line increases by several minutes, making it unsuitable for high-speed printing. Thermal recording devices usually use a time-division drive control method due to power capacity constraints, and from this point of view as well, they are not suitable for high-speed recording. On the other hand, optical printers are not limited by power supply capacity because the power consumption of LEDs is small, and can be controlled simultaneously. Therefore, it is desirable for optical printers to adopt a simultaneous drive control system in order to perform high-speed recording.

Incidentally, LED arrays used in optical printers have different brightness characteristics due to differences in manufacturing lots, and it is also difficult to select LED arrays with the same characteristics. LEDs with such variations in brightness characteristics
When a recording head is configured using multiple arrays (for example, about 10 arrays) and is driven using a simultaneous drive control method,
Since the light emission time of each LED is the same, there is a problem in that printing density varies depending on the brightness characteristics of each LED array.

The present invention was developed to solve the above problems, and by individually controlling the light emitting time of each LED array that is driven almost simultaneously, the amount of light given to the photoreceptor of an optical printer (this amount of light is The purpose of this method is to keep the luminance of the light-emitting element multiplied by the light emitting time substantially constant, and to obtain the same effect as when the luminance characteristics of each LED array are made the same, and will be explained in detail below.

1 and 2 are wiring diagrams showing one embodiment of the present invention, and FIG. 3 is a signal diagram of each part thereof. In Figure 1, ₁₁ to ₁₁₀ each consist of 128 LEDs.
LED array, 2 ₁ to 2 ₁₀ are current amplifiers each consisting of 128 pairs of stabilizing resistor R and transistor Tra, 3 ₁
~3 ₁₀ is its current supply terminal, and 4 is a 1280-stage shift register.

Figure 2 shows each LED array 1 ₁ to 1 in Figure 1.
This is an energization time control section that controls the length of time for energization to each of the current supply terminals 3 ₁ to 3 ₁₀ provided corresponding to the current supply terminals 3 1 to _{3 10} . In this FIG. 2, 5 is a counter, 6 is a comparator, 7 is a counter, and 8 is an address for each LED array 1 ₁ to 1 ₁₀ using array numbers No. 1 to No. 10 of the LED arrays 1 ₁ to 1 ₁₀ as addresses. 9 is a gate circuit, 10 is a register, 11 is a current distribution circuit, and 12 ₁ to 12 ₁₀ are currents interconnected with each of the current supply terminals 3 ₁ to 3 ₁₀ in FIG. 1. It is a supply terminal, and V indicates DC voltage.
Note that each LED array 1 ₁ to 1 stored in the memory 8
1 The amount of light emission time adjustment corresponding to ₁₀ is based on each pre-measured amount.
This value is determined based on the brightness characteristics of the LED arrays 1 ₁ to 1 ₁₀ , and in this example, each LED array 1 ₁ to 1 10
₁ corresponds to a timing value for delaying the start of light emission according to its luminance characteristics. Since each light emission time of each LED array ₁₁ to ₁₁₀ is controlled by this light emission time adjustment amount, the light amount of each LED of each LED array ₁₁ to ₁₁₀ , which is expressed as the product of light emission time and brightness, is almost uniform. be converted into

Next, the overall operation of this embodiment will be explained using FIGS. 1 to 3. Note that the operation here relates to the recording operation of one line.

First, after the recording start signal _S1 , the image signal Q is stored in the shift register 4 during an extremely short data writing time _S2 . Thereafter, the maximum recording time _S3 is immediately set, and within this time _S3 , the power supply currents _E1 to _E10 having time widths _t1 to _t10 corresponding to the respective LED arrays ₁₁ to ₁₁₀ are controlled for the energization time. (FIG. 2) to each of the current supply terminals 3 ₁ to 3 ₁₀ .

Therefore, the LEDs of each LED array 1 ₁ to 1 ₁₀ are powered by the power supply current E ₁ to _{E 10} and the image signal from the shift register 4.
Light is emitted according to Q ₁ to _{Q 1280} , and the time width t ₁ to t ₁₀ in the power supply current E ₁ to _{E 10} is controlled by the energization time control unit (Fig. 2) to be the brightness of each LED array 1 ₁ to 1 ₁₀ . By making it inversely proportional, the amount of light can be made uniform.

Next, the energization time control operation of the energization time control unit shown in FIG. 2 will be described in detail below with reference to FIG. 3.

First, the counter 5 detects that the maximum recording time _S3 has been reached by a signal input to its enable terminal E, and starts counting. This counter 5
is a count value that is sequentially incremented from "1" to "256" by counting the clock _S4 within the maximum recording time _S3 , and is a count value that is sequentially incremented every time when the maximum recording time _S3 is divided into 256 equal parts. S ₅ (“1” to “256”) is output to one input terminal of the comparator 6.

On the other hand, the counter 7 is provided to specify the array numbers _{1 to 10 of the LED arrays 11} to ₁₁₀ , and is initialized to "1" each time the clock _S4 is input to the set terminal S. set, clock S ₄
Count S ₆ at 10 times the speed of “1”
Steps are performed sequentially from to "10". The count value S ₇ (“1” to “10”) is calculated for each LED array 1 ₁ to _{1 10}
The information corresponds to array numbers 1 to 10 of , and is input to the memory 8 as address information, and is also input to one input terminal of the corresponding gates 9 ₁ to 9 ₁₀ of the gate circuit 9 . As mentioned before, memory 8 has array numbers 1 to ₁₀ of LED array 1 ₁ to 1 10.
The light emission time adjustment amounts W, W ₁ to W ₁₀ corresponding to the respective LED arrays 1 ₁ to 1 ₁₀ are stored as addresses. Therefore, the count value S ₇ (“1” to
When the address information (“10”) is sequentially applied to the memory 8 as address information, the memory 8 stores the address information (“1” to
"10"), the light emission time adjustment amounts W ₁ to W ₁₀ corresponding to the respective LED arrays 1 ₁ to 1 ₁₀ are sequentially output to the other input terminal of the comparator 6. This light emission time adjustment amount W ₁ to _{W 10} is calculated when the count value S ₅ of the counter 5 is 1.
Each time it is incremented, it is output in one cycle from W ₁ to W ₁₀ .

The comparator 6 receives the count value S ₅ sequentially input from the counter 5 and the light emission time adjustment amount W ₁ corresponding to each LED array 1 ₁ to 1 ₁₀ that is continuously input while the count value S ₅ is incremented by one step. ~ Compare with W ₁₀ sequentially,
If the light emission time adjustment amounts _W1 to _W10 are smaller than the count value _S5 , "1" is output. The output signal of the comparator 6 is input to the other input terminal of each gate 9 ₁ to 9 ₁₀ of the gate circuit 9.

Each of the gates 9 ₁ to 9 ₁₀ of the gate circuit 9 performs an AND operation between the output from the counter 7 and the output from the comparator 6, and when the result is "1", the corresponding flip-flop in the register 10 is set. . The output of this set flip-flop causes the corresponding transistor in the current distribution circuit 11 to become conductive, and power supply current is supplied to the corresponding LED array.

That is, the power supply current of each LED array 1 ₁ to _{1 10}
E ₁ to _{E 10} are the light emission time adjustment amounts W ₁ to W ₁₀ of each LED array 1 ₁ to 1 ₁₀ are count values at counter S ₅
It will rise when it becomes smaller than _S5 .
Therefore, the LEDs of each LED array 1 ₁ to 1 ₁₀ start emitting light in response to the power supply currents E ₁ to _{E 10} and the image signal from the shift register 4.

After the recording time _S3 ends, all the flip-flops of the register 10 are reset, and all the transistors of the current distribution circuit 11 become non-conducting.
The supply of power supply current to the LED arrays 1 ₁ to 1 ₁₀ is simultaneously stopped. As a result, each LED turns off.
Thereafter, a recording start signal _S1 instructing the recording operation of the next line is input, and the same operation as described above is repeated in response to this input.

As is clear from the above explanation, the conduction time width t ₁ to t ₁₀ of the power supply current E ₁ to E ₁₀ for each LED array 1 ₁ to 1 ₁₀ is inversely proportional to the brightness characteristic of each LED array 1 ₁ to 1 ₁₀ . Set the light emission time adjustment amount W ₁ to W 10 corresponding to each LED array 1 ₁ to _{1 10} as follows, and use this light emission time adjustment amount W 1 to W ₁₀ to adjust the light emission time adjustment amount W ₁ to W ₁₀ for each LED array 1 ₁ to 1.
By individually controlling the start time of energization to LEDs ₁₀ and simultaneously stopping the energization at the end of the maximum recording time _S3 , it is possible to equalize the amount of light in each LED array that emits light at approximately the same time.

As explained in detail above, according to the present invention, each
Since the LED array is driven almost all at once and the power supply time is short, it is possible to record at a much higher speed than a device such as a thermal recording device that uses time division drive and has a long power supply time to each recording element. becomes possible. In addition, according to the present invention, it is possible to correct the brightness variations of each LED array by adjusting the energization time of each LED array to uniformly expose the photoreceptor, thereby improving printing quality.

[Brief explanation of the drawing]

1 and 2 are connection diagrams showing one embodiment of the present invention, and FIG. 3 is a signal diagram of each part thereof. 4...Shift register, 5...Counter, 6...
...Comparator, 7...Counter, 8...Memory, 9...
...Gate circuit, 9 ₁ to 9 ₁₀ ...Gate, 10...
Register, 11...Current distribution circuit, 12 ₁ to 12
₁₀ ……Current supply terminal, E ₁ to E ₁₀ ……Power supply current, S ₅
... Count value of counter 5, W, W ₁ to _{W 10} ...
...Light emission time adjustment amount.

Claims (1)

[Claims for Utility Model Registration] An LED driving circuit for driving a plurality of light-emitting element arrays 1 consisting of a plurality of light-emitting elements, and a shift register in which an image signal Q is stored during a data writing time _S2 . 4, and a plurality of current amplifiers, which are provided corresponding to each of the light emitting element arrays 1 and have mutually independent current supply terminals 3, and which control the light emission of the light emitting elements according to the output of the shift register 4. circuit 2
and a control means for controlling the time length of energization to each of the current supply terminals 3, the control means having a count value that divides the maximum recording time _S3 set after the data writing time _S2 . The first outputting S ₅
a counter 5, which outputs a count value _S7 specifying an array number of each of the light emitting element arrays 1;
a second counter 7 that specifies the array number by going around for each count value _S5 of the counter 5; and a memory 8 that is addressed by the output of the second counter 7 and outputs the light emission time adjustment amount of each light emitting element array 1. a comparator 6 that compares the output of the memory 8 with the count value output of the first counter 5 and sequentially generates a binary output; Means 9 for calculating an AND, starting energizing each of the current amplifying circuits 2 according to the AND output, and then simultaneously stopping energizing all of the current amplifying circuits 2 at the end of the maximum recording time _S3 ; 11. An LED drive circuit characterized by comprising: -11.