JPH11115241A - Multiple led time division drive apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the control of electric current possible with a relatively simple structure for each of light emitting diodes in a time division drive circuit for light sources for an optical printer or the like having a plurality of light emitting diodes as its light sources by a method wherein a single comparison circuit is used and each of the light emitting diodes is controlled with comparison with reference value for each of lighted color. SOLUTION: A multiple LED time division drive circuit is provided at a line scan-type optical printer that forms color images with lights from each of LEDs for RGB made line-shaped and with a photosensitive paper exposed to the light at specified timing. The circuit is constructed in a structure wherein LED drive circuits for colors in red, green and blue are connected in parallel with one another to a position between a terminal Vcc at one side of a single common electric source and an earth. The LED drive circuits are constructed, being equipped respectively with transistors TR1-TR3, digital switches DS-1-DS-3 and the like. Respective cathodes of the LEDs (LED-R, LED-G and LED-B) are connected to a comparator COM, and TR's are driven in accordance with comparison with reference voltage REF for respective colors and thereby lighting is controlled for each of the LED's.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus using a plurality of light emitting diodes (hereinafter, referred to as LEDs) as light sources, for example, a predetermined timing while moving light from an RGB LED relative to a photosensitive member. The present invention relates to a time-division driving circuit for a light source such as an optical printer device that forms an image by irradiating the light.

[0002]

2. Description of the Related Art Conventionally, there has been known an optical printer device using LEDs of three colors of RGB as light sources. Thus L
When an ED is used as a light source, the electrical characteristics of the three-color LEDs are considerably different. For example, the required light quantity cannot be obtained unless R is 4 mA, G is 30 mA, and B is 10 mA. Conventionally, when LEDs having different electrical characteristics are driven in a time-division manner, a circuit for adjusting the current for each color and sequentially driving the LEDs is used. In addition, selective driving is performed according to the RGB information stored in the memory, and comparison is further performed for each color individually. A method of providing a circuit and driving sequentially has been used.

[0003]

It is permissible to carry out these different electrical characteristics with separate comparison circuits by providing a large number of circuits which are electrically simple but do not need to operate simultaneously. There is a space problem in products where the mounting space is limited.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to provide an RGB LE having different electrical characteristics.
A plurality of LEs used in an optical printer or the like which can easily control the current of D and can drive them in a time-division manner with a common comparison circuit.
It is intended to provide a D time division driving device.

[0005]

In order to achieve the above object, a multiple LED time division driving device according to the present invention includes a current control unit, a time division switch unit, and an LED. In a multiple LED time-division driving device including a plurality of LED driving circuits connected in parallel between a common power supply and sequentially driven by a time-division driving signal, each of the LEs
A current-to-voltage converter is connected between a common electrode to which one electrode of D is connected in common and one power supply terminal of a common power supply, and one common electrode has one input and the reference voltage has the other input. Is provided, and an output signal of the comparison circuit is supplied to current control means of each LED drive circuit to control an LED drive current flowing through each LED.

Further, in the multiple LED time division driving device of the present invention, the current-voltage conversion means is provided in a required number in accordance with the characteristics of the plural LEDs. Each of the current-voltage conversion means is provided with a second time division switch. It is characterized by having.

Further, in the multiple LED time division driving device of the present invention, the second time division switch provided in each of the time division switch means and the current / voltage conversion means of the plurality of LED drive circuits is controlled by the time division drive signal. The opening and closing control is performed synchronously.

Further, in the multiple LED time-division driving device according to the present invention, a voltage signal of a predetermined level range is supplied to one input of the comparison circuit by adjusting a plurality of current-voltage converting means to each characteristic of the plurality of LEDs. It is characterized in that it is supplied.

Further, the multiple LED time division driving device of the present invention is characterized in that the multiple LEDs are composed of R, G and B.

[0010] Further, the multiple LED time division driving device of the present invention is characterized in that the current-voltage conversion means is constituted by a resistance element.

Further, in the multiple LED time division driving device according to the present invention, the current control means is constituted by a transistor.

Further, the plural LED time division driving device of the present invention is a line scanning type light for forming an image by exposing at a predetermined timing while making the light from the plural LEDs linearly and moving relative to the photosensitive member. It is characterized by being used as a light source of a printer device.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below based on examples used in an optical printer shown in the drawings. FIG. 1 is a perspective view of a main part of an optical printer device using the present invention. Reference numeral 100 denotes an optical head, which accommodates various members of the optical system, and is scanned by the head feeding means 300 on the photosensitive paper 100 in the direction of arrow B1.

First, the configuration of the optical head 100 will be described. 110 is an LED array, R (red), G
(Green) LED elements emitting B (blue) 2
Next, the photosensitive surface 500 of the photosensitive paper 500 is arranged in two rows in the order of RGB.
They are arranged sequentially from the top in a direction perpendicular to a. Reference numeral 120 denotes a parabolic mirror that reflects light from the LED array 110 into parallel rays. Reference numeral 130 denotes a cylindrical lens, which converts the parallel light reflected from the parabolic mirror 120 to the photosensitive surface 5.
The light is focused only in the direction perpendicular to 00a, and its focus is on the photosensitive surface 500a. Reference numeral 140 denotes a reflecting mirror which transmits light from the cylindrical lens 130 to the photosensitive paper 50.
It reflects in the direction of 0. 150 is a liquid crystal shutter,
One scanning electrode and 640 signal electrodes form 640 pixels in the width direction of the photosensitive paper 6.

Next, the configuration of the head feed mechanism 300 will be described. 310 is a DC motor. 320 is low
It is a Tari encoder and includes a fin 321 and a photo interrupter 323. The fin 321 is provided with a number of openings 322 and is fixed to the rotation axis of the DC motor 310 and rotates together with the rotation axis of the DC motor 310. The photointerrupter 322 is provided with a light emitting element and a light receiving element opposed to each other with the fin 321 interposed therebetween, and the rotation of the fin 321 causes the opening 322 to interrupt light between the light emitting element and the light receiving element. An electric signal is output in synchronism with the intermittent light and a DC motor 31 is output.
A rotation angle of 0 is detected.

The rotation of the DC motor 310 is reduced by the worm gear 350 and the gears 361, 362, 363.
It is converted into linear reciprocating motion by pulleys 371 and 372 and wire 372. The wire 373 is connected to the optical head 1
00 in the scanning direction to move the optical head 10
It is fixed to a wire fixing portion 111 provided to protrude from the side surface of the “0”. As described above, the optical head 100 can be accurately moved at a low speed by the head feed mechanism 300 and the head position detection mechanism 200.

Reference numerals 210 and 220 denote position sensors comprising photointerrupters, which are fixed to the substrate 230.
The position of the optical head 100 is detected by the light shielding plate 101 blocking the position sensors 210 and 220 by the movement of the optical head 100.

Next, the operation of the present apparatus and the method of forming an image on photosensitive paper will be described. The LED array 110 has R, G,
Light is emitted in order of B in order from the top. The light reaches the parabolic mirror 120 while spreading in the width direction of the photosensitive paper. Parabolic mirror 120
A band-like light as shown in FIG. Light emitted from the LED array 110 while spreading in the width direction of the photosensitive paper 500 is converted into a light beam parallel to the width direction of the photosensitive paper 500 by the parabolic mirror 120, reflected in the direction opposite to the incident direction, and reflected by the cylindrical lens 130. Leads to. The cylindrical lens 130 transmits light from the parabolic mirror 120 to the photosensitive paper 5.
Light is condensed only in the direction perpendicular to the 00 plane. The light condensed by the cylindrical lens 130 is changed in direction by approximately 90 degrees by a flat reflecting mirror 140, and the photosensitive paper 5
The light is perpendicular to the 00 surface. Finally, the photosensitive paper 500 is exposed through the liquid crystal shutter 150. The light that has reached the photosensitive paper 500 is condensed by the cylindrical lens 130 so as to form an image on the photosensitive paper 500 with a predetermined width. Light imaged on the photosensitive paper 500 with a predetermined width is R, G, and B light in order from the scanning direction (B1).

In the writing, the optical head 100 is connected to the photosensitive paper 50.
When the writing position is detected by the head position detection mechanism 200, the LED of R
Emits light for a predetermined time, and exposes the photosensitive paper 500 only in a predetermined area. Next, the G LED emits light for the same time,
The photosensitive paper 500 is exposed only in an area having the same width. Similarly, the LED of B emits light for the same time, and exposes only the region having the same width as the exposure width of R and G. In this manner, by repeating this operation periodically while moving the optical head 100 with respect to the photosensitive paper 500 at a constant speed, light of three colors of R, G, and B can illuminate the same area on the photosensitive paper 500. Exposure to form a color image. Further, gradation control is performed by controlling the exposure time of the three colors R, G, and B by the liquid crystal shutter 150, so that a full-color image can be obtained. Then, the writing of all image data is completed, and the position sensor 210
The scanning of the optical head 100 is completed at the position where is turned off, and the optical head 100 is returned to the head retract position again.

Light of three colors is applied to photosensitive paper 50 in accordance with image data.
It must be accurately illuminated at a predetermined position on zero.
Therefore, in this apparatus, the light emission timing of the LED array 110 and the opening / closing timing of the liquid crystal shutter 150 are synchronized with the output of the rotary encoder 320.

FIG. 2 is a block diagram related to head speed running control and exposure timing control of the optical printer apparatus shown in FIG. The optical head 100 is moved by a predetermined scanning distance by the head feed mechanism 300, and
Although an image is formed at 0, a solid line indicates a write start position and a dotted line indicates a write end position. 600 is deco-
The output of the position sensors 210 and 220 is decoded by
Active pulses are output only when both of these position sensors are ON, when the position sensor 210 is ON, and when the position sensor 210 is OFF. I do. 610 is a motor drive circuit incorporating a PLL circuit,
620 is a controller, 630 is a counter, 640 is a control circuit for controlling the driving of the liquid crystal shutter 150 and the LED array 110, and 650 is a reference clock. In this apparatus, it is necessary to irradiate each of the R, G, and B lights on a predetermined area of the photosensitive paper 500 at a predetermined speed. For this reason, the head 10
For the feed rate of 0, the PLL control circuit 610 is
The output pulse of the tally encoder 320 is applied to the reference clock 65.
Compared with 0, the DC motor 310 is controlled at a constant rotational speed. The LED emission timing and the liquid crystal shutter opening / closing timing are controlled by counting the output pulses of the rotary encoder 320 with a counter 630 and controlling the LED emission and the liquid crystal shutter opening / closing timing in synchronization with the output at a predetermined value. doing.

FIG. 3 is a view showing the structure of the LED array of the optical printer. LED array mounting board 111
Red (R) LEDs 113 and 11 on the mounting surface 112 of
4, green (G) LEDs 115 and 116, blue (B) LE
D117, 118, a total of six LEDs, the axis (B5-B
6) Symmetrically in two rows (two rows in the width direction of photosensitive paper 500)
In each row, the components are mounted in an RGB array in order from the direction of arrow B5 to the direction of arrow B6. Each LE
D113 to D118 have a substantially rectangular shape, one of which is a light emitting surface 113a, 114a, 115a, 116.
a, 117a and 118a. The electrodes 113b, 114b, and 115 are provided at the centers of the respective light emitting surfaces.
b, 116b, 117b and 118b are provided, and the other electrode (not shown) is also provided on the surface opposite to the light emitting surface. The LEDs 113 to 118 emit light when a predetermined voltage is applied between these two opposing electrodes. This light is emitted radially from almost each light emitting surface.

On the surface of the LED mounting board 111, one common electrode 170 and six signal electrodes 171, 172, 17
3, 174, 175, and 176 are provided. LED
113-118 are electrodes 113a-118a, electrode 113
The electrodes facing b to 118b are bonded and fixed to the common electrode 170 with a conductive adhesive (for example, silver paste). The electrodes 113b to 118b are electrically connected to the signal electrodes 171 to 176 by wires 177 made of a gold wire or the like. Then, as described above, based on the image data, a voltage is applied so that the photosensitive paper 500 is exposed at a predetermined timing, and the LED emits light. As described with reference to FIG. 1, the light emitted from the light emitting surfaces of the LEDs 113 to 118 forms RGB lines on the surface of the photosensitive paper 500. The light amounts are almost the same in the width direction.

Next, the above-described line scanning type optical printer 1 which forms a color image by exposing at predetermined timings while making the light from the RGB light emitting diodes linear and moving relative to the photosensitive paper 500 is described. L of the present invention implemented in
The ED time division driving circuit will be described. FIG. 4 is a first embodiment of an LED time-division driving circuit, and FIG. 5 is a time-division driving timing diagram thereof. In such a color printer, it is very important to balance the color of the light emitted from the R, G, and B LEDs. For this purpose, the current and voltage of each of these LEDs having different electrical characteristics are set to a desired reference value R.
It is necessary to control to match EF.

As shown in FIG. 4, this time division circuit comprises a red LED driving circuit comprising a transistor TR1, a digital switch DS-1 and an LED-R between one terminal Vcc of one common power supply and the ground. Green LED consisting of TR2, digital switch DS-2 and LED-G
Drive circuit, transistor TR3, digital switch DS
-3 and LED-B are connected in parallel, and these LED-R, LED-G, LED
-B cathodes are connected in common to form a current-voltage conversion resistor R.
0 and connected to the other end of the common power supply and to one input terminal of one comparison circuit COM. The other input terminal of the comparison circuit COM is connected to a storage circuit (not shown), and the reference voltage REF of each color is sequentially supplied. The output terminals of the comparison circuit are transistors TR1, TR2, TR3
Are connected in common. When the drive signals SW-R, SW-G, and SW-B are supplied from a drive signal source (not shown) at the timing shown in FIG.
-3, these three L
The ED-driving circuits are sequentially time-divisionally driven. The current of each drive circuit is converted into a voltage by a current-voltage conversion resistor R0 (for example, if R0 is 100 ohms, each of the currents is 0.1 V).
4 volts, 3 volts, and 1 volt) and are fed back to the comparison circuit COM. And a reference voltage R for each of R, G, and B.
EF, and the output signal is output to each transistor TR1, T
The current specified by the reference voltage REF flows through each LED by being supplied to R2 and TR3.

FIG. 6 shows a second embodiment of the multiple LED time division driving device according to the present invention. As shown in this figure, this time division circuit comprises a transistor TR1, an LED-R, a resistor R1, and two digital switches DS-1 and DS-4 between one terminal Vcc of one common power supply and an earth. Red LED driving circuit, transistor TR2, LED-G, resistor R2,
A green LED driving circuit including two digital switches DS-2 and DS-5, and a transistor TR3 and an LED
-B, resistor R3, two digital switches DS-3, D
A blue LED driving circuit composed of S-6 is connected in parallel. When the drive signal (SW-R) shown in FIG. 5 is received, the digital switches DS-1 and DS-4 are simultaneously closed,
When the drive signal (SW-G) is received, the digital switch D
S-2 and DS-5 are closed at the same time, and the drive signal (SW-
Upon receiving B), digital switches DS-3 and DS-6
Are closed at the same time.

And, these LED-R, LED-
The cathodes of G and LED-B are commonly connected and connected to one input of one comparison circuit COM. The current-voltage conversion resistors R1, R2, and R3 are adjusted so that the cathode voltage of each LED drive circuit becomes substantially constant when energized. A storage circuit (not shown) is connected to the other input terminal of the comparison circuit COM, and information (reference voltage) REF of each color is sequentially supplied. The output terminal of the comparison circuit COM is a transistor TR1,
Commonly connected to TR2 and TR3. Drive signals SW-R, SW-G, and SW-B are supplied from a drive signal source (not shown) in FIG.
Digital switches DS-1 and DS
-4, DS-2 and DS-5, DS-3 and DS-6 when sequentially supplied to these three LEDs
The drive circuits are sequentially driven in a time-division manner.

The LED-R and the resistor R1 are connected to a transistor TR.
1 is an emitter load. When the drive signal SW-R is supplied and the digital switches DS-1 and DS-4 are closed at the same time, the LED-R drive circuit operates, and when the drive current flows through the resistor R1, a voltage drop occurs.
Input to OM. The comparison circuit COM compares this with the red reference voltage R-REF, and compares the result with the transistor TR1.
To supply. As a result, the red reference voltage R-
A current matching REF flows to generate a predetermined amount of red light. When the drive signal SW-G is supplied, the digital switches DS-2 and DS-5 are closed at the same time, the LED-G drive circuit operates, and when the drive current flows through the resistor R2, a voltage drop occurs. COM. The comparison circuit compares this with the green reference voltage G-REF and supplies the result to the transistor TR2. As a result, a current corresponding to the green reference voltage G-REF flows through the LED-G to generate a predetermined amount of green light. When the drive signal SW-B is supplied, the digital switches DS-3 and DS-6 are closed at the same time, and the LED-B drive circuit operates to generate a voltage drop when the drive current flows through the resistor R3. Circuit CO
M is input. The comparison circuit compares this with the blue reference voltage BR.
The result is compared with the EF and supplied to the transistor Tr3. As a result, a current corresponding to the blue reference voltage B-REF flows through the LED-B to generate a predetermined amount of blue light. In this way, the comparator circuit supplies a common control voltage to the base of each transistor by comparing each reference voltage REF with each input of these commonly connected cathode voltages, and selecting the same. The current of the diode drive circuit is controlled.

In the second embodiment, the current-voltage conversion resistor R
3, R2 and R3 are used (for example, R1 = 20
(0 ohm, R2 = 20 ohm, R3 = 60 ohm) The control voltage generated by these and the current value of each LED-R, LED-G, LED-B is substantially constant (0.8 volt, 0 volt). .6
Volts, 0.6 volts), and the range of the control voltage supplied to the comparison circuit COM is further narrowed. By doing so, the LED
Regardless of the difference between the characteristics of -R, LED-G, and LED-B, it is easy to share one comparison circuit COM. In the first embodiment, the current-to-voltage conversion resistor R01 is shared, but in the second embodiment, the current-to-voltage conversion resistor is provided for each of them, and the range of the control voltage fed back to the comparison circuit COM is increased. It is configured to be narrower. Of course, it is also possible to use two resistors having similar characteristics according to the purpose. Sharing one comparison circuit COM means that several sets of R, G, B light emitting diodes LED-R, LED-G, L
In the case where the ED-B is driven in parallel, only one third of the comparison circuit COM is required, so that the circuit to be used and the space for mounting components are saved, and the effect is large.

FIG. 7 shows a third embodiment of the multiple LED time division driving device according to the present invention. This means that the power supply V is
The c side is grounded, and the anodes of the LEDs are connected in common and this is fed back to one input of the comparison circuit COM. This is basically the same as the two embodiments.

As described above, in the present invention, the current voltage set value of each LED is stored as a reference voltage REF in a storage circuit (not shown), and this reference voltage REF is sequentially converted from the other input terminal of the comparison circuit into a time-division signal. Synchronous supply, each L
The current flowing through the ED is controlled to be the same.
If the storage circuit and the comparison circuit have a large capacity and the output means can output a large range of output with high resolution, the feedback voltage from each LED supplied to one input of the comparison circuit may be different. For example, 1V for red and 8 for blue
In the case of V, it can be set fine even near 1V, and fine even around 8V. However, the system consists of a limited number of bits and a certain limited output range,
In the case where the output can be performed only with a limited accuracy, the accuracy becomes coarse if the output range is increased, and only the narrow range can be controlled if the output accuracy is increased. Therefore, in the present invention, fine control is enabled despite the limited storage capacity by making the voltages of the cathode and the anode uniform.

[0032]

As is apparent from the above description,
ADVANTAGE OF THE INVENTION According to the multiple LED time-division driving device of the present invention, time-division driving with different levels can be performed by one comparison circuit, and the circuit to be used and the component mounting space can be saved. Another object of the present invention is to provide a circuit suitable for time-division driving of a circuit using a common LED circuit block, and the effect of the compact product configuration is enormous.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing the structure of an optical printer according to the present invention.

FIG. 2 is a block diagram of optical head scanning speed control and exposure timing control of the optical printer device in FIG. 1;

FIG. 3 is a perspective view of an LED array of the optical printer device in FIG.

FIG. 4 is a first embodiment of a multiple LED time division driving device of the present invention.

FIG. 5 is a timing chart of the time division driving.

FIG. 6 is a second embodiment of the multiple LED time division driving device of the present invention.

FIG. 7 is a third embodiment of the multiple LED time division driving device of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Optical head 110 LED array 111 LED mounting board 112 Mounting surface 113, 114 Red LED-R 115, 116 Green LED-G 117, 118 Blue LED-B 111a to 116a Light emitting surface 111b to 116b Electrode 120 Parabolic mirror 130 Cylindrical Lens 140 Reflector 150 Liquid crystal shutter 170 Common electrode 171 to 176 Signal electrode 177 Wire 210, 220 Position sensor 240 Shielding plate 300 Head feed mechanism 310 Motor 320 Rotary encoder 500 Photosensitive paper 600 Decorator 610 Motor Drive circuit 620 Controller 630 Counter 640 Control circuit 650 Reference clock TR1 to TR3 Current control transistor DS-1 to DS-6 Digital switch SW-R, R time division drive signal SW-G, G Split drive signal SW-B, B time division drive signal COM Comparison circuit RO, R1-R3 Current-voltage conversion resistor Vcc Positive terminal side of power supply Vss Negative terminal side of power supply REF Reference voltage R-REF Red reference voltage G-REF Green Reference voltage B-REF Blue reference voltage

Claims (8)

[Claims] 1. A plurality of LED drives, each having a current control means, a time division switch means, and an LED, connected in parallel between one common power supply, and sequentially driven by a time division drive signal. In the multiple LED time-division driving device provided with a circuit, a current-to-voltage conversion unit is connected between a common electrode that commonly connects one electrode of each LED and one power terminal of the common power source, One comparison circuit having the common electrode as one input and a reference voltage as the other input is provided, and an output signal of the comparison circuit is supplied to current control means of each of the LED drive circuits, and an LED drive current flowing through each LED is provided. LED characterized by controlling the number of LEDs
Time sharing drive. 2. The method according to claim 1, wherein the current-voltage conversion means includes a plurality of LEs.
2. The multiple LED time division driving device according to claim 1, wherein a required number of the current voltage conversion units are provided in parallel according to the characteristic of D, and each of the current-voltage conversion means is provided with a second time division switch. 3. A time-division switch provided in each of the plurality of LED driving circuits and a second time-division switch provided in each of the current-to-voltage converters are synchronously controlled to open and close by the time-division driving signal. 3. The multiple LED time division driving device according to claim 2, wherein: 4. A voltage signal of a predetermined level range is supplied to said one input of said comparison circuit by matching said plurality of current-voltage conversion means to the characteristics of each of said plurality of LEDs. 3. The multi-LED time-sharing driving device according to claim 2, wherein: 5. The multiple LED time division driving device according to claim 1, wherein the plurality of LEDs are composed of R, G, and B. 6. The multiple LED time division driving device according to claim 1, wherein said current control means comprises a transistor. 7. The multiple LED time-sharing driving circuit according to claim 1, wherein said current-voltage converting means is constituted by a resistance element. 8. A light source device of a line scanning optical printer device which forms an image by exposing at a predetermined timing while exposing at a predetermined timing while making light from a plurality of LEDs linearly move relative to a photosensitive member. The multi-LED time-sharing drive device according to claim 1, wherein: