JP2931051B2 - Imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time-division driving type image device, and particularly to an optical printer head used for a facsimile, a copying machine, a personal computer, and the like, and an image sensor used for a facsimile and the like. It relates to time division driving.

[Prior Art] A conventional technique will be described using an optical printer head as an example. FIG. 11 shows an example of the optical printer head. In the figure, I ₁
In is an LED chip, D _{1 to} Dn are control ICs provided for each of the chips I _{1 to} In, and 02 is a control microprocessor. led
Chip I ₁ or the like, for example, use one integrated 64 light emitting diodes in a single chip. The number n of chips is usually about 40, and the total number of light emitting diodes is, for example, 2560.

As is immediately apparent from FIG. 11, this printer head requires many control ICs, and is expensive and large.

With the increase in the output of the light emitting diode, time division driving of the printer head has become possible. In the case of FIG. 11, time division is performed for each LED chip, and one line print is divided into n pieces. As a result, the duty ratio of each light emitting diode drops to 1 / n, but printing is possible because the output of the light emitting diode is large. If time division is performed, the control ICDs _{1 to} Dn can be omitted, and the effects of miniaturization and cost reduction can be obtained.

However, the problem is that switching elements used for time division have a delay. The current consumption of the light emitting diode is large, and if these are collectively controlled by one switching element, the current flowing through the switching element becomes large. Therefore, a delay time occurs in the switching element. The delay time of the switching element is more significant when the transistor is turned on than when it is turned off. This is because it takes time to discharge the electric charge accumulated in the base of the transistor, and is a kind of inertia. When the delay time from ON to OFF is called an accumulation time, the accumulation time is about several μsec. One unit of time-division driving (on-time of each time-division LED chip) is about several tens of μm seconds, and the storage time of the switching element has a nonnegligible effect. That is, the condition for driving the LED chips I _{1 to} In in a time-division manner is to eliminate the disturbance in the time-division due to the accumulation time of the control switching element. Also, the fluctuation of the operation time of the LED chips I _{1 to} In leads to the fluctuation of the density of the image.

Here, the prior art has been described by taking an optical printer head as an example, but the problem also applies to an image input device such as an image sensor. The basic structure of a contact type image sensor is disclosed in
Nos. 1,257 and 62-285,569, all of which disclose light from an LED on a paper surface and detect the reflected light with an optical semiconductor. Again, many LEDs
Are arranged in a straight line, and high current LE
D is used. There is a common demand for driving the LEDs in a time-division manner, eliminating interference between the LEDs, and simplifying the driving circuit.

Aside from controlling the LED, the photodetector in the image input device includes a photodiode having a large dark current and a low resistance. When many photodiodes are linearly arranged to form an image sensor, the low resistance of the photodiodes and the large current consumption hinder time-division driving. That is, since the current consumption is large, the control switching elements used for the time division driving have only a long accumulation time, and the accumulation time disturbs the time division.

[Problem of the Invention] An object of the present invention is to prevent the time division of a light emitting element and a light receiving element from being disturbed due to a response delay of a switching element. If such disturbances are eliminated, the light-emitting element and the light-receiving element can be time-divided, and the size and cost of the device can be reduced. Further, it is possible to prevent a decrease in image quality due to a change in operation time of the light emitting element or the light receiving element.

[Constitution of the Invention] The present invention provides control means for dividing a large number of light emitting elements or a large number of light receiving elements into a plurality of groups, connecting switching elements to each group, and driving the switching elements in a time division manner. In addition to the above, a pulse width correction means for triggering the switching element to be turned off in a time shorter than the time allocated to each group in a time-sharing manner by a time corresponding to the response time from switching on to off of the switching element is provided. In the imaging device.

Here, instead of the pulse width correction means, the supply of the image signal to the image element may be cut off in synchronization with the end of the operation time assigned to each group. In this case, even when the operation time assigned to each group ends, the switching element continues to operate during the accumulation time. However, since no image signal is supplied to the image element during this time, malfunction can be prevented. Then, the image elements of each group stop at the end of the operation time, the operation time of the image elements is kept constant, and the fluctuation of the image density can be prevented. In this case, the pause time between the operation times is made longer than the accumulation time to prevent the group assigned in the previous cycle from operating with the image signal in the next cycle.

In the present invention, a large number of light emitting elements and light receiving elements are divided into a plurality of groups, switching elements are connected for each group, and time division driving is performed by turning on / off the switching elements. What matters here is the response speed of the switching element. This is because the current consumption of the light emitting element and the light receiving element is large, and a large capacity switching element must be used. The response speed is particularly slow when the element changes from on to off. Therefore, a pulse width correction unit is provided, and the pulse width correction unit is, for example, in a time shorter by the response delay time,
Turn on the switching element. Since the switching element has a response delay time, if the switching element is turned off before the response delay time, the switching element is actually turned off in a time allocated in a time-division manner.
In this way, due to the response delay of the switching element,
Eliminate time-sharing disturbances.

When the time during which each group is operated in a time-sharing manner is called one cycle, a pause time is usually provided between cycles. If the off state of the switching element is within the range of the idle time, there is no problem even if the off state of the switching element protrudes from the cycle. Therefore, the correction signal in the pulse width correction means is not limited to the signal obtained by subtracting the response delay time from the cycle end time, and the switching element may be turned off within the idle time.

Actually, the response delay time of the switching element is not constant but varies. This variation complicates the problem. Preferably, a switching device having a uniform response delay time is selectively used for one device, and the correction by the pulse width correction means is facilitated. When the response delay time is not selected, the pulse width correction means varies the correction to the response delay time for each switching element. The correction signal in the pulse width correction means is preferably variable for each device.

Although the embodiment is described using a transistor as an example of the switching element, the present invention is not limited to this, and an arbitrary switch such as an FET switch can be used. Although a light emitting diode (LED) is shown as an example of the light emitting element, a semiconductor laser or the like may be used. The light receiving element includes a photocell and a photodiode, but the same applies to a phototransistor and a photoconductor.

In this embodiment, a switching element provided with a pulse width correction means on the control means side or a control element integrated with a pulse width correction means is shown. The pulse width correction means may be provided, for example, on the data bus side of the light emitting element, and cut off light emission data to the light emitting element by a signal of the pulse width correction means. In such an example, there is an example in which the AND gate 6 and the one-shot multivibrator 8 in FIG. 1 are moved to the data bus side.

Embodiment 1 Embodiment 1 (Optical Printer Head) FIGS. 1 to 4 show a first embodiment. In FIG. 1, I _{1 to} In are n LED chips of, for example, Ga—As type, and about 64 LED chips are integrated in one chip. Tr ₁ ~Trn the switching transistor for time division, there is accumulating time for a large signal. The accumulation time is, for example, about several microseconds.
The number of LED chips I _{1 to} In and the number of transistors Tr _{1 to} Trn are, for example, 40.

As the transistors Tr _{1 to} Trn, those having the same accumulation time are selected and used. Normally, the accumulation time is uniform within one lot, and transistors of the same lot are used. The accumulation time does not need to be the same for another printer head, but the accumulation time is made uniform for one printer head. In other words, the basic dispatch of this embodiment is to make the accumulation time uniform for each printer head and correct this. Since the correction is carried out by the same time in all of the transistor Tr ₁ ~Trn,
Make the accumulation time within one printer head uniform.

Time-division driving is performed by dividing the LED chips I _{1 to} In into 40 units. Each chip is connected to the data bus, each transistor Tr ₁ ~Trn connecting transistor control bus. There are 64 data buses and 40 transistor control buses. The 64 signal lines of the data bus are connected to 64 LED lines of each of the LED chips I _{1 to} In.
The light emitting diodes are connected to each other, and the light emitting diodes are controlled by 1/40 time division driving. 40 of transistor control bus
The signal lines are connected to a common terminal of each LED chip, and the common terminals are collectively connected to ground terminals of the light emitting diodes. Each of the transistors Tr _{1 to} Trn is connected to the LED chip I
_{1 to} In are controlled one by one.

Reference numeral 2 denotes a control microprocessor, and reference numeral 4 denotes a memory such as a shift register, which may be built in the microprocessor 2. 6 is an AND gate consisting of 40 AND circuits,
Reference numeral 8 denotes a pulse width correction circuit using a one-shot multivibrator. The one-shot multivibrator 8 is activated by a trigger signal (latch command) from the microprocessor 2 and sets the pulse width with an external resistor or capacitor. Reference numeral 10 denotes an external resistor for setting a pulse width.

FIG. 2 shows details of the LED chip I ₁ and the AND gate 6.
LED chip to I ₁ has the light emitting diodes LED ₁ ～LEDm of m (64 in this case), the AND gate 6 of n AND circuits A ₁
There is ~ An. The output of the one-shot multivibrator 8 controls each of the AND circuits A _{1 to} An.

FIG. 3 shows the structure of the microprocessor 2. In the figure, reference numeral 12 denotes a buffer memory for storing image data to be printed from outside such as a personal computer. Here, it is generally referred to as image data, but may be character information or image information. Shift register 4
If only the buffer memory 12 is sufficient, the buffer memory 12 is unnecessary. 14
Is a control CPU, which communicates with the outside of the personal computer or the like, 16 is a timer, and 18 is a multiplexer.

Describing the overall structure of the printer head, the light from the LED chip I ₁ -In, feeding the photosensitive drum via a SELFOC lens, etc., for printing by transferring the printing information on the photosensitive drum.

The operation of the embodiment will be described. The CPU 14 controls the buffer memory 12 and the timer 16 according to external requests. If printing of one line (2560 printing dots corresponding to 2560 LEDs) is to be performed in, for example, 1.3 ms, the operating time assigned to one LED chip is less than 30 μ. Therefore, the timer 16 operates at intervals of 32.5 μs, and the print command signal W of 30 μs is
Send out. In synchronization with the rise of the print command signal W, the shift register 4 receives the next 64 dot signals from the buffer memory and sends them out to 64 data buses. On the other hand, the print command signal W is also sent to the multiplexer 18 to select one of the transistor control buses and send it to the AND gate 6. One-shot multivibrator 8
Is activated by the print command signal W, and the pulse width is
Than the storage time ΔW. As described above, transistors Tr _{1 to} Trn having the same accumulation time are used. An external resistor is set so that the output pulse of the one-shot multivibrator 8 is shortened by the accumulation time ΔW.
Select a resistance value of 10. Print command signal W by AND gate
Of the output of the one-shot multivibrator 8 and an ON signal of W-.DELTA.W is applied to necessary transistors.

FIG. 4 shows operation waveforms. Data to be printed is sent to the data bus for a width W by a signal from the timer 16 (FIG. 4A). When the correction by the one-shot multivibrator 8 is not performed, the transistors Tr ₁ , Tr ₂ , Tr ₃ are turned on longer than the print command signal W by the accumulation time ΔW (FIG. 4) to 4)). If this is not corrected, the transistor continues to operate even with the next print command signal, and the previous chip operates with the print data for the next chip. As a result, the print was disturbed,
Necessary printing operation cannot be performed. Note that, here, printing is not limited to the case of outputting graphic data, but also includes the case of outputting character data.

The output signal from the AND gate 6 is limited by the pulse width of the one-shot multivibrator 8, and the print command signal W
A signal shorter than Δ by ΔW is applied to the transistor (FIGS. 4 and 5) to 8)). The setting of ΔW is performed by selecting the external resistor 10 for each printer head in accordance with the accumulation time of the transistor. As a result, the on-time of the transistor becomes equal to the printing command signal W (FIGS. 4 to 6) to 8)), and time division is completed. That is, the previous chip does not operate with the data for the next chip, and the disturbance of the print data is eliminated. As a result, time-division driving becomes possible, and the driving
Shift ICD _{1 to} Dn to shift register 4 or microprocessor 2
And a small, low-cost printer head can be obtained.

FIG. 5 shows an example in which the AND gate 6 of FIG. 1 is moved to a bus for image data. In the figure, reference numeral 7 denotes an AND gate, which shuts off the supply of the image signal to the data bus in synchronization with the end of the print signal. Transistor Tr ₁ to Tr _n continues to operate during the even accumulated time finished printing signals, but the light emitting diode because there is no image signal do not emit light. As a result, the operation time of the light emitting diode can be made constant in synchronization with the printing signal, and unevenness in the density of an image to be formed can be prevented.

Embodiment 2 FIGS. 6 and 7 show a second embodiment. The difference from the embodiment of FIG. 1 lies in that the pulse width is corrected by the one-shot multivibrator 8 and corrected by the ROM 24. In FIG. 6, 22 is a microprocessor, 24 is
ROM and 26 are timers. ROM24 the transistor Tr ₁ ~Trn
Is stored. If the storage times are the same, only one data is required, and if the storage times are not the same, 40 data are stored. The structure and operation of the other parts are the same as in the embodiment of FIG.

The operation will be described with reference to FIG. The data bus has
The print data (image data) is sent via the shift register 4 within the width of the print command signal W (FIG. 1). When storage time of the transistor Tr ₁ ~Trn is to irregular, if not corrected, the transistor Tr ₁ ~Trn The on-time of 7 2), 3) disturbed as. In synchronization with the print command signal W, the CPU 14 addresses the ROM 24 and inputs the accumulation times ΔW _{1 to} ΔWn of the individual transistors to the timer 26. Timer 26
Has two outputs, one in the pulse width fixed printing command signal W, a signal other is obtained by correcting the accumulated time ΔW ₁ ~ΔWn (pulse width _{W-ΔW 1 ~W-ΔWn)} . The pulse having the width W-ΔW is supplied to the transistor Tr ₁ via the multiplexer 18.
TTrn to eliminate the variation in the operation time of the transistor due to the accumulation time (FIG. 7).

Modification 1 The present invention can be used not only for a printer head but also for an LED control of a contact image sensor. This example is shown in FIG. In the figure, I _{1 to} In. Are the same LED chips as described above. For example, 64 LEDs are integrated into one chip, and 40 chips are used. PC ₁ ～PCn40 the chip of the optical semiconductor is mounted photovoltaic amorphous Si or the like 64 on a single chip. The number of LEDs and the number of photovoltaic cells may be different, and the number of photovoltaic cells is usually increased.

The problem here is to simplify the control circuit by time-division driving of the LED, to reduce the size and cost of the device, and to prevent the photocell from responding to oblique incident light and causing a reading error. It is in. 64 transistors Tr _{1 to} Trm are connected to the LED chips I _{1 to} In, and the LEDs in the chip are sequentially set to 1
Light is emitted individually. Branch off the transistor control bus,
The address bus of the optical semiconductor PC _{1 to} PCn is bused, and the optical semiconductor PC _{1 to} P
Connect 40 data buses to Cn. That is, 2560 LEDs
And the photovoltaic cells are time-divisionally driven in 64 divisions.

Reference numeral 28 denotes a microprocessor, which is similar to the microprocessor 22 in FIG. 6, reference numeral 30 denotes a buffer memory for a read image, and reference numeral 32 denotes a memory for image data.

The operation of the modification will be described. At the command of the CPU 14, the accumulation time ΔW of each transistor is read from the ROM 24,
Tell The timer 26 sends a pulse having a width obtained by subtracting ΔW from the fixed width W to the multiplexer 18 and sends the pulse to the transistor determined by the CPU 14. As a result, each of the transistors Tr _{1 to} Trm is turned on with a fixed width W. This is because a control pulse that takes into account the effect of the accumulation time ΔW is added. Transistor Tr ₁
~ Trm operate by 1/64 time division drive, and each LED chip I ₁ ~ In
Turns on one LED at a time, for a total of 40
LEDs emit light simultaneously.

The number of LEDs that emit light simultaneously is one for each chip, and there is no risk of the photocell malfunctioning due to oblique light. A switch is connected to each photovoltaic cell, and the switch is turned on by the data of the address. As a result, the output of the photovoltaic cell immediately above the emitting LED appears on the data bus via the switch. This data is stored in the buffer memory 30, and is transferred to the memory 32 by an address command from the CPU. And in 64 cycles,
The LED and all the photovoltaic cells operate, and the reading of the image data for one row is completed.

Modification 2 FIGS. 9 and 10 show a modification relating to time-division driving of a photodiode. An object of the modification is to drive a large-current photodiode in a time-division manner to reduce the size and cost of the attached circuit. Reference numeral 28 denotes a microprocessor similar to the modification shown in FIG. 8, and it is assumed that the transistor array has n (here, 40) transistors arranged in parallel as in the case of FIG. There are 40 transistor control buses. PD _{1 to} PDn are 40 photodiode arrays,
For example, 64 photodiodes are integrated. The photodiode array PD ₁ ~PDn, consisting 64 signal lines, connecting the data bus.

The operation of the device is shown in FIG. Multiplexer 18, RO
An operation pulse (width W-ΔW) in which the accumulation time ΔW has been compensated is sent to the individual transistor with the data of M24 (FIG. 10, FIG. 10). When the accumulation times are not equal, the width of the operation pulse differs for each transistor, and when the accumulation times are equal, the width of the operation pulse is common. With this operation pulse, the transistors are turned on with a common width W (FIG. 10). This is because the width of the operation pulse is W-ΔW and the accumulation time is ΔW. As a result, the photodiode arrays PD _{1 to} PDn operate one chip at a time, and output the data from the data to the buffer memory.
Input to 30 (Fig. 10 3)).

[Effects of the Invention] According to the present invention, disturbance of time division due to response delay of a switching element is eliminated, and time division of a light emitting element or a light receiving element is enabled. As a result, the size and cost of the device can be reduced. In addition, it is possible to prevent a change in image density and the like, and to improve image quality.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment, FIG. 2 is a detailed circuit diagram showing an LED chip and an AND gate of the embodiment, FIG. 3 is a detailed circuit diagram showing a microprocessor of the embodiment, FIG. 8) are operation waveform diagrams of the embodiment, FIG. 5 is a circuit diagram of an embodiment obtained by modifying the embodiment of FIG. 1, FIG. 6 is a circuit diagram of the second embodiment, FIG. 8) is a circuit diagram of a modification, FIG. 9 is a circuit diagram of a second modification, FIGS. 10) 1) to 3) are operation waveform diagrams thereof, FIG. Is a circuit diagram of a conventional example. In the figure, I _{1 to} In: LED chip, Tr _{1 to} Trn: switching transistor, PC _{1 to} PCn: optical semiconductor chip, PD _{1 to} PDn: photodiode array.

Claims (3)

(57) [Claims] 1. A large number of light-emitting elements are divided into a plurality of groups, switching elements are connected to each group, and control means for driving the switching elements in a time-division manner are provided. An image apparatus provided with pulse width correction means for triggering a switching element to be turned off in a time shorter than a time corresponding to a response time from an on state to an off state of the switching element. 2. A plurality of light-emitting elements are divided into a plurality of groups, switching elements are connected to each group, and control means for driving the switching elements in a time-division manner are provided. An image device provided with means for interrupting supply of image data to a light emitting element in synchronization with the end of time. 3. A large number of light-receiving elements are divided into a plurality of groups, switching elements are connected to each group, and control means for driving the switching elements in a time-division manner are provided. An image apparatus provided with pulse width correction means for triggering a switching element to be turned off in a time shorter than a time corresponding to a response time from an on state to an off state of the switching element.