CN112449458A - LED drive circuit and drive method, and liquid ejection observation device and method - Google Patents

LED drive circuit and drive method, and liquid ejection observation device and method Download PDF

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Publication number
CN112449458A
CN112449458A CN202010625207.3A CN202010625207A CN112449458A CN 112449458 A CN112449458 A CN 112449458A CN 202010625207 A CN202010625207 A CN 202010625207A CN 112449458 A CN112449458 A CN 112449458A
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China
Prior art keywords
circuit
led
signal
output
high level
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CN202010625207.3A
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Chinese (zh)
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原千弘
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Toshiba TEC Corp
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Toshiba TEC Corp
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/015—Ink jet characterised by the jet generation process
    • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
    • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
    • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
    • B41J2/0451—Control methods or devices therefor, e.g. driver circuits, control circuits for detecting failure, e.g. clogging, malfunctioning actuator
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
    • Y02B20/40—Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

Provided are an LED drive circuit and a drive method, and a liquid discharge observation device and method, which realize a long life of an LED without providing a solution for coping with heat. The LED drive circuit of the embodiment is an LED drive circuit for lighting an LED and is provided with a lighting timing control circuit. The lighting timing control circuit has an RC circuit to which a rectangular signal is input, and lights the LED for a predetermined time determined by a comparison result between an output of the RC circuit and a preset threshold value from a rise of the rectangular signal, and lights the LED out after the predetermined time has elapsed.

Description

LED drive circuit and drive method, and liquid ejection observation device and method
Technical Field
Embodiments of the present invention relate to an LED driving circuit and a liquid discharge observation device.
Background
The following techniques exist: an image (droplet image) is acquired by irradiating a droplet (ink droplet) discharged from a nozzle with a flash light source that is turned on with a pulse waveform, and the discharge state of the droplet is evaluated. The droplet image is used for the calculation of "ejection speed" and "ejection volume", and the observation of "non-ejection" and "ejection abnormality".
The time for irradiating the droplet with light, that is, the light emission time of the flash light source, is set to an appropriate time. For example, when the light emission time is longer than the appropriate light emission time, the image of the droplet may be stretched due to the movement of the droplet during exposure and light emission. Further, for example, when the light emission time is shorter than the appropriate light emission time, a sufficient amount of light may not be obtained. That is, the appropriate light emission time is required to be a time at which the image is not stretched and a sufficient amount of light can be obtained.
For example, when a flash light source includes a Light Emitting Diode (LED) as a light source, there is a problem that a sufficient amount of light cannot be obtained with a light emission time of 1(μ sec) or less. Therefore, it is considered to use a high-power LED that supplements the shortage of the light amount per unit light emission time by flowing a large current, thereby securing the light amount. In a normal operation, the duty ratio of the light emission time is about 1/100, and therefore heat generation does not become a problem. Therefore, the heat dissipation member is not required in the normal operation.
However, there is a possibility that an abnormal operation in which the power LED is turned on for a long time may occur due to an erroneous operation of the CPU, a setting error of the user, or the like. If the power LED is turned on for a long time, the life of the LED may be shortened due to heat generation. Therefore, there is a problem that a heat dissipation member needs to be provided in advance as a solution for coping with heat at the time of abnormal operation.
Disclosure of Invention
Problems to be solved by the invention
The invention aims to provide an LED drive circuit and a liquid ejection observation device which realize the long service life of an LED without a scheme for coping with heat.
Means for solving the problems
The LED drive circuit of the embodiment is an LED drive circuit for lighting an LED and is provided with a lighting timing control circuit. The lighting timing control circuit has an RC circuit to which a rectangular signal is input, and lights the LED for a predetermined time determined by a comparison result between an output of the RC circuit and a preset threshold value from a rise of the rectangular signal, and lights the LED out after the predetermined time has elapsed.
Drawings
Fig. 1 is an explanatory diagram of an example of the configuration of the liquid ejection observation device according to the first embodiment.
Fig. 2 is an explanatory diagram of an example of the configuration of the liquid ejection observation device according to the first embodiment.
Fig. 3 is an explanatory diagram of an example of the configuration of the LED driving circuit according to the first embodiment.
Fig. 4 is an explanatory diagram of an example of a timing chart of signals in the LED driving circuit of the first embodiment.
Fig. 5 is an explanatory diagram of an example of the configuration of the LED driving circuit according to the second embodiment.
Fig. 6 is an explanatory diagram of an example of a timing chart of signals in the LED driving circuit of the second embodiment.
Fig. 7 is an explanatory diagram of an example of the configuration of the LED driving circuit according to the third embodiment.
Fig. 8 is an explanatory diagram of an example of a timing chart of signals in the LED driving circuit of the third embodiment.
Description of the symbols
1. A liquid ejection observation device; 11. a system controller; 12. a communication interface; 13. a head drive circuit; 14. an ink jet head; 15. an LED drive circuit; 15A, LED driver circuit; 15B, LED driver circuit; 16. a flash light source; 17. a camera drive circuit; 18. a camera; 19. an image processing circuit; 21. a processor; 22. a memory; 41. an objective lens; 51. a first Schmitt trigger inverter; 52. a lighting timing control circuit; 52A, a lighting timing control circuit; 52B, a lighting timing control circuit; 53. a gate drive circuit; 61. an RC circuit; a 61A, RC circuit; a 61B, RC circuit; 62. a second Schmitt trigger inverter; 63. an AND circuit; a 64A, XOR circuit; 71. a low voltage source; c1, a capacitor; c2, a capacitor; c3, a capacitor; d1, a diode; d2, a diode; r1, resistance; r2, resistance; r3, resistance; r4, resistance; s1, a switch; LEDs, light emitting diodes.
Detailed Description
Hereinafter, an LED driving circuit and a liquid discharge observation device according to an embodiment will be described with reference to the drawings.
(first embodiment)
Fig. 1 and 2 are explanatory views showing a configuration example of the liquid ejection observation device 1 according to the first embodiment. The liquid ejection observation device 1 is a device that ejects liquid droplets from an inkjet head and acquires images of the ejected liquid droplets.
The liquid discharge observation device 1 includes: a system controller 11, a communication interface 12, a head drive circuit 13, an inkjet head 14, an LED drive circuit 15, a flash light source 16, a camera drive circuit 17, a camera 18, and an image processing circuit 19.
The system controller 11 controls the liquid ejection observation device 1. The system controller 11 includes, for example, a processor 21 and a memory 22.
The processor 21 is an arithmetic element (e.g., CPU) that performs arithmetic processing. The processor 21 is a main body of the operation of the system controller 11. The processor 21 performs various processes based on data such as a program stored in the memory 22. The processor 21 functions as a control unit capable of executing various operations by executing a program stored in the memory 22.
The memory 22 is a storage device that stores programs and data used by the programs. Further, the memory 22 temporarily stores data and the like in processing by the processor 21. The memory 22 is configured as a nonvolatile memory.
The communication interface 12 is an interface for communicating with a client apparatus or the like that provides a print job via the internet.
The head drive circuit 13 is a circuit for controlling the operation of the inkjet head 14. The head driving circuit 13 operates the inkjet head 14 to eject the liquid droplets (ink droplets) 31 from the inkjet head 14. The head driving circuit 13 supplies a driving signal and a power supply voltage to the inkjet head 14.
The inkjet head 14 is configured to eject droplets 31. The inkjet head 14 includes: a plurality of nozzles 32, an actuator not shown in the drawing, and a drive IC not shown in the drawing. The actuator constitutes a pressure chamber filled with ink for each nozzle. The drive IC drives the actuator based on the drive signal and the power supply voltage supplied from the head drive circuit 13. Thereby, the actuator is deformed, and the ink in the pressure chamber is ejected from the nozzle 32 as the droplet 31.
The LED drive circuit 15 is a circuit for controlling the operation of the light emitting diode LED of the flash light source 16. The LED driving circuit 15 emits light to the liquid droplets 31 ejected from the inkjet head 14 by causing the light emitting diode LED of the flash light source 16 to emit light. The light emission trigger signal is input from the system controller 11 or the head drive circuit 13 to the LED drive circuit 15. The light emission trigger signal is a signal synchronized with a driving signal input to the inkjet head 14. That is, the light emission trigger signal is a signal synchronized with the ejection of the liquid droplets 31 from the inkjet head 14. The LED drive circuit 15 generates a light emission signal for causing the light emitting diode LED of the flash light source 16 to emit light based on the light emission trigger signal.
The flash light source 16 irradiates the liquid droplets 31 ejected from the inkjet head 14 with light. The flash light source 16 includes a light emitting diode LED and a circuit for lighting the light emitting diode LED based on a light emission signal from the LED drive circuit 15. The light emitting diode LED is a light emitting diode (so-called high power LED) capable of obtaining a sufficient amount of light even in a short exposure time by flowing a large current.
The camera drive circuit 17 is a circuit for controlling the operation of the camera 18. The camera drive circuit 17 inputs a signal for causing the camera 18 to perform shooting. The camera drive circuit 17 inputs a signal to the camera 18 to perform photographing in synchronization with the lighting timing of the light emitting diode LED of the flash light source 16. The camera drive circuit 17 may input various parameters for shooting (such as shutter speed, aperture value, and ISO sensitivity) to the camera 18.
The camera 18 is an imaging device including an optical system such as an objective lens 41 and an imaging element, for example. The camera 18 converts the light imaged through the objective lens 41 into an image (image data) by a photographing element. The camera 18 performs shooting based on a signal from the camera drive circuit 17, and acquires image data of the liquid droplets 31 (liquid droplet images).
The image processing circuit 19 performs various image processing based on the droplet image acquired by the camera 18.
In the above configuration, when the liquid droplets 31 ejected from the inkjet head 14 are imaged, the system controller 11 inputs a drive signal to the inkjet head 14 and controls the head drive circuit 13 so that the liquid droplets 31 are ejected from the inkjet head 14. Further, the system controller 11 controls the LED drive circuit 15 so that the light emission trigger signal input to the LED drive circuit 15 changes from a high level to a low level to cause the light emitting diode LED of the flash light source 16 to emit light. Further, the system controller 11 returns from the low level to the high level for a predetermined time after changing the light emission trigger signal input to the LED drive circuit 15 from the high level to the low level. Further, the system controller 11 controls the camera drive circuit to photograph the liquid droplets 31 ejected from the inkjet head 14 by the camera 18.
The system controller 11 controls the timing of inputting the light emission trigger signal to the LED driving circuit 15 and the timing of imaging by the camera 18 so as to irradiate light to the liquid droplets 31 ejected from the inkjet head 14 and image the light-irradiated liquid droplets 31. The system controller 11 performs image processing on the droplet image acquired by the camera 18 through an image processing circuit, and acquires an image processing result. Thus, the system controller 11 can calculate the ejection speed of the droplet 31, the volume of the droplet 31, and the like based on the shape of the droplet 31 in the droplet image.
Next, the detailed configurations of the LED driving circuit 15 and the flash light source 16 will be described. Fig. 3 is an explanatory diagram for explaining a configuration example of the LED driving circuit 15 and the flash light source 16.
The LED drive circuit 15 includes: a first schmitt trigger inverter 51, a lighting timing control circuit 52, and a gate drive circuit 53.
The lighting timing control circuit 52 includes: an RC circuit (resistance-capacitance circuit) 61, a second schmitt trigger inverter 62, AND an AND circuit (AND circuit) 63.
The RC circuit 61 includes a resistor R1 and a capacitor C1.
The flash light source 16 includes: switch S1, resistor R2, light emitting diode LED, diode D1 and capacitor C2.
The first schmitt trigger inverter 51 is an electronic circuit in which the output state changes with a delay with respect to a change in the input potential. The light emission trigger signal is input to the first schmitt trigger inverter 51. That is, the first schmitt trigger inverter 51 is provided on the most input side of the LED drive circuit 15. Instead of the schmitt trigger inverter, a comparator, an operational amplifier, or the like may be used.
Two terminals of the resistor R1 of the RC circuit 61 constitute an input terminal and an output terminal of the RC circuit 61, respectively. The capacitor C1 is connected between the output terminal of the RC circuit 61 and GND. An input terminal of the RC circuit 61 is connected to an output terminal of the first schmitt trigger inverter 51. The output terminal of the RC circuit 61 is connected to the input terminal of the second schmitt trigger inverter 62.
The second schmitt trigger inverter 62 is an electronic circuit in which the output state changes in a lagging manner with respect to the change in the input potential. The output terminal of the second schmitt trigger inverter 62 is connected to one terminal (terminal B) of the AND circuit 63.
The output terminal of the first schmitt trigger inverter 51 is connected to the other terminal (terminal a) of the AND circuit 63. Further, an output terminal of the AND circuit 63 is connected to the gate drive circuit 53.
The gate drive circuit 53 is a circuit that outputs a light emission signal of a predetermined voltage level to the flash light source 16 based on an output signal of the AND circuit 63. The gate drive circuit 53 is formed of, for example, a MOSFET or an IGBT. An output terminal of the gate drive circuit 53 is connected to a gate terminal of the switch S1 of the flash light source via a resistor R3. That is, the output terminal of the gate drive circuit 53 constitutes the output terminal of the LED drive circuit 15.
The switch S1 is, for example, an N-channel MOSFET (N-type MOSFET). The switch S1 may be an npn transistor, for example. As described above, the output terminal of the LED drive circuit 15 is connected to the gate terminal of the switch S1. The cathode of the light emitting diode LED is connected to the drain terminal of the switch S1 via the resistor R2. Further, the anode of the diode D1 having its cathode connected to the anode of the light emitting diode LED is connected to the drain terminal of the switch S1. GND (signal ground) is connected to the source terminal of the switch S1.
A low voltage source 71 is connected to the anode of the light emitting diode LED. Further, a capacitor C2 is connected between the anode of the light emitting diode LED and the source terminal of the switch S1.
With the above configuration, when the light emission signal from the LED drive circuit 15 is at the high level, the switch S1 is turned on, and a current flows through the light emitting diode LED by the potential of the capacitor C2, so that the light emitting diode LED is turned on.
Next, the detailed operation of the LED driving circuit 15 will be described.
Fig. 4 is a timing chart for explaining signals in the LED driving circuit 15. Fig. 4 shows a light emission trigger signal input to the LED drive circuit 15, an output signal of the first schmitt trigger inverter 51, an input signal to the terminal a of the AND circuit 63, an output signal of the RC circuit 61, an output signal of the second schmitt trigger inverter 62, an input signal to the terminal B of the AND circuit 63, AND an output signal of the AND circuit 63, respectively.
As described above, the light emission trigger signal is a signal synchronized with the ejection of the liquid droplets 31 from the inkjet head 14. The light emission trigger signal is, for example, a signal that falls from a high level to a low level and thereafter rises from the low level to the high level. The light emission trigger signal is input to the first schmitt trigger inverter 51.
The first schmitt trigger inverter 51 has a first high level threshold ThH1 and a first low level threshold ThL1 smaller than the first high level threshold ThH 1. The first high level threshold ThH1 is a threshold value to be compared when rising. The first low level threshold value ThL1 is a threshold value to be compared when falling.
When the light emission trigger signal falls from the high level to the low level and is less than the first low level threshold value ThL1, the first schmitt trigger inverter 51 outputs a signal of the high level. In the example of fig. 4, since the light emission trigger signal is smaller than the first low level threshold ThL1 at timing t1, the first schmitt trigger inverter 51 switches the output signal from the low level to the high level.
When the light emission trigger signal rises from the low level to the high level and becomes equal to or higher than the first high level threshold ThH1, the first schmitt trigger inverter 51 outputs a low level signal. In the example of fig. 4, since the light emission trigger signal becomes equal to or higher than the first high level threshold ThH1 at timing t3, the first schmitt trigger inverter 51 switches the output signal from the high level to the low level.
Thereby, the first schmitt trigger inverter 51 makes the rise and fall of the light emission trigger signal rectangular signals (rectangular signals). The output signal of the first schmitt trigger inverter 51 is input to the terminal a of the AND circuit 63 AND the input terminal of the RC circuit 61 in a divided manner. Therefore, the input signal to the terminal a of the AND circuit 63 coincides with the output signal of the first schmitt trigger inverter 51.
The RC circuit 61 smoothes (moderates) the change in the voltage of the input signal and outputs the signal. That is, the RC circuit 61 outputs a signal that delays a change (transition) in the voltage level of the input signal, based on a circuit constant (propagation delay time) determined by the resistance value (Ω) of the resistor R1 and the electrostatic capacitance (F) of the capacitor C1. For example, as shown in fig. 4, the RC circuit 61 outputs a signal for relaxing the rise and fall of the output signal of the first schmitt trigger inverter 51. The output signal of the RC circuit 61 is input to the second schmitt trigger inverter 62.
The second schmitt trigger inverter 62 has a second high level threshold ThH2 and a second low level threshold ThL2 smaller than the second high level threshold ThH 2. The second high level threshold ThH2 is a threshold value to be compared when rising. The second low level threshold value ThL2 is a threshold value to be compared when falling.
When the output signal of the RC circuit 61 increases and becomes equal to or higher than the second high threshold ThH2, the second schmitt trigger inverter 62 outputs a low signal. In the example of fig. 4, at a timing t2 that is a predetermined time after the rise of the rectangular signal, the output signal of the RC circuit 61 becomes equal to or higher than the second high-level threshold ThH2, so the second schmitt-trigger inverter 62 switches the output signal from the high level to the low level.
When the output signal of the RC circuit 61 decreases to be smaller than the second low threshold value ThL2, the second schmitt trigger inverter 62 outputs a high signal. In the example of fig. 4, since the output signal of the RC circuit 61 is smaller than the second low level threshold ThL1 at a timing t4 after a predetermined time from the fall of the rectangular signal, the second schmitt-trigger inverter 62 switches the output signal from the low level to the high level.
The output signal of the second schmitt trigger inverter 62 is input to a terminal B of the AND circuit 63. Therefore, the input signal to the terminal B of the AND circuit 63 coincides with the output signal of the second schmitt trigger inverter 62.
When both the input signal to the terminal a AND the input signal to the terminal B are at the high level, the AND circuit 63 outputs a high-level signal. That is, when both the output signal of the first schmitt trigger inverter 51 AND the output signal of the second schmitt trigger inverter 62 are at the high level, the AND circuit 63 outputs a high-level signal. According to the example of fig. 4, the AND circuit 63 outputs a high-level signal during a period from a timing t1 when both the output signal of the first schmitt trigger inverter 51 AND the output signal of the second schmitt trigger inverter 62 are at a high level to a timing t 2.
An output signal of the AND circuit 63 is input to the gate drive circuit 53. The output signal of the AND circuit 63 corresponds to the light emission signal output from the gate drive circuit 53. That is, the light emitting diode LED of the flash light source 16 emits light while the AND circuit 63 outputs a high-level signal, AND the light emitting diode LED of the flash light source 16 is turned off while the AND circuit 63 outputs a low-level signal. According to the example of fig. 4, the light emitting diode LED of the flash light source 16 emits light during a period from a timing t1 when a signal of high level is output from the AND circuit 63 to a timing t 2.
As described above, the LED driving circuit 15 turns on the light emitting diode LED for a predetermined time determined by the result of comparison between the output of the RC circuit 61 and the predetermined threshold (the second high level threshold ThH2 of the second schmitt trigger inverter 62) from the rise of the rectangular signal output from the first schmitt trigger inverter 51. Further, the LED drive circuit 15 can turn off the light emitting diode LED after a predetermined time has elapsed. Thus, the LED driving circuit 15 can turn on the light emitting diode LED for a time corresponding to the time constant of the RC circuit 61. Thus, even when an abnormality occurs in the output of the light emission trigger signal, the processor 21 of the system controller 11 can prevent an abnormal operation in which the light emitting diode LED is turned on for a long time. As a result, heat generation of the light emitting diode LED does not become a problem, and a long life of the light emitting diode LED can be achieved without providing a heat radiating member for radiating heat of the light emitting diode LED and a circuit in the vicinity of the light emitting diode LED.
(second embodiment)
Fig. 5 is an explanatory diagram for explaining the LED driving circuit 15A of the second embodiment. The LED driving circuit 15A of the second embodiment is different from the lighting timing control circuit 52 of the LED driving circuit 15 of the first embodiment in the configuration of the lighting timing control circuit 52A of the LED driving circuit 15A. The same components as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
The LED drive circuit 15A includes: a first schmitt trigger inverter 51, a lighting timing control circuit 52A, and a gate drive circuit 53.
The lighting timing control circuit 52A includes an RC circuit 61A and an XOR circuit (exclusive or gate) 64A.
The RC circuit 61A includes: resistor R4, capacitor C3, and diode D2.
Two terminals of the resistor R4 of the RC circuit 61A constitute an input terminal and an output terminal of the RC circuit 61A, respectively. The capacitor C3 is connected between the output terminal of the RC circuit 61A and GND. An input terminal of the RC circuit 61A is connected to an output terminal of the first schmitt trigger inverter 51. The output terminal of the RC circuit 61A is connected to one input terminal (terminal D) of the XOR circuit 64A. The diode D2 has an anode connected to the output terminal of the RC circuit 61A and a cathode connected to the output terminal of the first schmitt trigger inverter 51.
The output terminal of the first schmitt trigger inverter 51 is connected to the other input terminal (terminal C) of the XOR circuit 64A. Further, the output terminal of the XOR circuit 64A is connected to the gate drive circuit 53.
Next, the detailed operation of the LED driving circuit 15A will be described.
Fig. 6 is a timing chart for explaining signals in the LED driving circuit 15A. Fig. 6 shows a light emission trigger signal input to the LED drive circuit 15A, an output signal of the first schmitt trigger inverter 51, an input signal to the terminal C of the XOR circuit 64A, an output signal of the RC circuit 61A, a logical value of the terminal D of the XOR circuit 64A, and an output signal of the XOR circuit 64A, respectively. The light emission trigger signal and the output signal of the first schmitt trigger inverter 51 are the same as those in the first embodiment, and therefore, the description thereof is omitted.
The output signal (rectangular signal) of the first schmitt trigger inverter 51 is input in a divided manner to the terminal C of the XOR circuit 64A and the input terminal of the RC circuit 61A. Therefore, the input signal to the terminal C of the XOR circuit 64A coincides with the output signal of the first schmitt trigger inverter 51.
The RC circuit 61A smoothes (moderates) the change in the voltage of the input signal and outputs the signal. That is, the RC circuit 61A outputs a signal that delays a change (transition) in the voltage level of the input signal, based on a circuit constant (propagation delay time) determined by the resistance value (Ω) of the resistor R4 and the electrostatic capacitance (F) of the capacitor C3. For example, as shown in fig. 6, the RC circuit 61A outputs a signal for relaxing the rise of the output signal of the first schmitt trigger inverter 51. The output signal of the RC circuit 61A is input to the terminal D of the XOR circuit 64A.
The RC circuit 61A includes a diode D2 connected in parallel to the resistor R4. Therefore, when the output signal of the first schmitt trigger inverter 51 falls, the charge of the capacitor C3 is instantaneously discharged. Therefore, when the output signal of the first schmitt trigger inverter 51 falls, the output signal of the RC circuit 61A also falls in a substantially rectangular shape.
The XOR circuit 64A compares the input signal with a preset threshold value ThXOR, and processes the signal to "1 (high level)" when the signal is a value equal to or greater than the threshold value, and processes the signal to "0 (low level)" when the signal is a value smaller than the threshold value. In the example of fig. 6, the output signal of the RC circuit 61A becomes equal to or higher than the threshold value ThXOR at timing t12 after a predetermined time from the rise of the rectangular signal, and the output signal of the RC circuit 61A becomes lower than the threshold value ThXOR at timing t13 of the fall of the rectangular signal.
While the output signal of the first schmitt trigger inverter 51 is at the low level and the output signal of the RC circuit 61A is at the low level, the XOR circuit 64A outputs a low-level signal. While the output signal of the first schmitt trigger inverter 51 is at the high level and the output signal of the RC circuit 61A is at the low level, the XOR circuit 64A outputs a high-level signal. While the output signal of the first schmitt trigger inverter 51 is at the low level and the output signal of the RC circuit 61A is at the high level, the XOR circuit 64A outputs a high-level signal. While the output signal of the first schmitt trigger inverter 51 is at the high level and the output signal of the RC circuit 61A is at the high level, the XOR circuit 64A outputs a low-level signal.
In the example of fig. 6, the XOR circuit 64A outputs a low-level signal during a period from the timing t10 to the timing t11, outputs a high-level signal during a period from the timing t11 to the timing t12, and outputs a low-level signal after the timing t 12.
The output signal of the XOR circuit 64A is input to the gate drive circuit 53. The output signal of the XOR circuit 64A corresponds to the light emission signal output from the gate drive circuit 53. That is, the light emitting diode LED of the flash light source 16 emits light while the XOR circuit 64A outputs a high-level signal, and the light emitting diode LED of the flash light source 16 is turned off while the XOR circuit 64A outputs a low-level signal. According to the example of fig. 6, the light emitting diode LED of the flash light source 16 emits light during a period from a timing t11 to a timing t12 at which a high-level signal is output from the XOR circuit 64A.
As described above, the LED drive circuit 15A turns on the light emitting diode LED for a predetermined time period determined by the result of comparison between the output of the RC circuit 61A and the predetermined threshold (the threshold ThXOR of the XOR circuit 64A) from the rise of the rectangular signal output from the first schmitt trigger inverter 51, as in the LED drive circuit 15 of the first embodiment. Further, the LED drive circuit 15A can turn off the light emitting diode LED after a predetermined time has elapsed. With this configuration, even when an abnormality occurs in the output of the light emission trigger signal in the processor 21 of the system controller 11, the LED driving circuit 15A can prevent an abnormal operation in which the light emitting diode LED is turned on for a long time. Further, since the second schmitt trigger inverter 62 can be omitted as compared with the first embodiment, the cost of the components can be suppressed.
(third embodiment)
Fig. 7 is an explanatory diagram for explaining the LED driving circuit 15B of the third embodiment. The LED drive circuit 15B of the third embodiment is different from the LED drive circuit 15A of the second embodiment in the configuration of the lighting timing control circuit 52B of the LED drive circuit 15B. The same components as those of the second embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
The LED drive circuit 15B includes: a first schmitt trigger inverter 51, a lighting timing control circuit 52B, and a gate drive circuit 53.
The lighting lamp control circuit 52B includes an RC circuit 61B and an XOR circuit 64A.
The RC circuit 61B includes a resistor R4 and a capacitor C3. That is, the RC circuit 61B is different from the RC circuit 61A of the second embodiment in that it does not include the diode D2 connected in parallel with the resistor R4. Two terminals of the resistor R4 of the RC circuit 61B constitute an input terminal and an output terminal of the RC circuit 61B, respectively. The capacitor C3 is connected between the output terminal of the RC circuit 61B and GND. An input terminal of the RC circuit 61B is connected to an output terminal of the first schmitt trigger inverter 51. The output terminal of the RC circuit 61B is connected to one input terminal (terminal D) of the XOR circuit 64A.
The output terminal of the first schmitt trigger inverter 51 is connected to the other input terminal (terminal C) of the XOR circuit 64A. Further, the output terminal of the XOR circuit 64A is connected to the gate drive circuit 53.
Next, the detailed operation of the LED driving circuit 15B will be described.
Fig. 8 is a timing chart for explaining signals in the LED driving circuit 15B. Fig. 8 shows a light emission trigger signal input to the LED drive circuit 15B, an output signal of the first schmitt trigger inverter 51, an input signal to the terminal C of the XOR circuit 64A, an output signal of the RC circuit 61B, a logical value of the terminal D of the XOR circuit 64A, and an output signal of the XOR circuit 64A, respectively. The light emission trigger signal and the output signal of the first schmitt trigger inverter 51 are the same as those in the first embodiment, and therefore, the description thereof is omitted.
The output signal (rectangular signal) of the first schmitt trigger inverter 51 is divided and input to the terminal C of the XOR circuit 64A and the input terminal of the RC circuit 61B. Therefore, the input signal to the terminal C of the XOR circuit 64A coincides with the output signal of the first schmitt trigger inverter 51.
The RC circuit 61B smoothes (moderates) the change in the voltage of the input signal and outputs the signal. That is, the RC circuit 61B outputs a signal that delays a change (transition) in the voltage level of the input signal, based on a circuit constant (propagation delay time) determined by the resistance value (Ω) of the resistor R4 and the electrostatic capacitance (F) of the capacitor C3. For example, as shown in fig. 8, the RC circuit 61B outputs a signal for relaxing the rise and fall of the output signal of the first schmitt trigger inverter 51. The output signal of the RC circuit 61B is input to the terminal D of the XOR circuit 64A.
The XOR circuit 64A compares the input signal with a preset threshold value ThXOR, and processes the signal to "1 (high level)" when the signal is a value equal to or greater than the threshold value, and processes the signal to "0 (low level)" when the signal is a value smaller than the threshold value. In the example of fig. 8, the output signal of the RC circuit 61B becomes equal to or greater than the threshold value ThXOR at timing t22 a predetermined time after the start of the rise of the rectangular signal, and the output signal of the RC circuit 61B becomes smaller than the threshold value ThXOR at timing t24 a predetermined time after the start of the fall of the rectangular signal.
While the output signal of the first schmitt trigger inverter 51 is at the low level and the output signal of the RC circuit 61B is at the low level, the XOR circuit 64A outputs a low-level signal. While the output signal of the first schmitt trigger inverter 51 is at the high level and the output signal of the RC circuit 61B is at the low level, the XOR circuit 64A outputs a high-level signal. While the output signal of the first schmitt trigger inverter 51 is at the low level and the output signal of the RC circuit 61B is at the high level, the XOR circuit 64A outputs a high-level signal. While the output signal of the first schmitt trigger inverter 51 is at the high level and the output signal of the RC circuit 61B is at the high level, the XOR circuit 64A outputs a low-level signal.
In the example of fig. 8, the XOR circuit 64A outputs a low-level signal from the timing t20 to the timing t21, and outputs a high-level signal from the timing t21 to the timing t 22. The XOR circuit 64A outputs a low-level signal from the timing t22 to the timing t23, a high-level signal from the timing t23 to the timing t24, and a low-level signal after the timing t 24.
According to the example of fig. 8, the light emitting diode LED of the flash light source 16 emits light during a period from the timing t21 to the timing t22 at which the signal of high level is output from the XOR circuit 64A and during a period from the timing t23 to the timing t 24. That is, the LED drive circuit 15B turns on the light emitting diode LED of the flash light source 16 twice each time the liquid droplet 31 is ejected from the inkjet head 14. Thus, the liquid discharge observation device 1 including the LED driving circuit 15B can image one droplet 31 twice.
As described above, the LED driving circuit 15B turns on the light emitting diode LED for a predetermined time determined by the result of comparison between the output of the RC circuit 61B and the predetermined threshold (the threshold ThXOR of the XOR circuit 64A) from the rise and fall of the rectangular signal output by the first schmitt trigger inverter 51. Further, the LED drive circuit 15B can turn off the light emitting diode LED after a predetermined time has elapsed. With this configuration, even when an abnormality occurs in the output of the light emission trigger signal in the processor 21 of the system controller 11, the LED driving circuit 15B can prevent an abnormal operation in which the light emitting diode LED is turned on for a long time.
In the above-described embodiment, the lighting time of the light emitting diode LED is determined based on the time constant determined by the resistance value of the resistor of the RC circuit and the capacitance of the capacitor and the threshold value set in advance. In the case where the droplets 31 of the ink jet head 14 are photographed by the camera 18, the lighting time of the light emitting diode LED needs to be "time when the image is not extended", and "time when a sufficient amount of light is obtained". The "time during which the image does not extend" is determined by the ejection conditions (for example, ejection speed) of the droplet 31, the diameter of the droplet 31, and the allowable amount of extension of the image. The "time to obtain a sufficient amount of light" is determined by the amount of light per unit time of the light emitting diode LED, the setting of the sensitivity and the setting of the aperture in the camera 18, and the like. Thus, "the time for which the image is not stretched" and "the time for which a sufficient amount of light is obtained" are not uniquely determined. However, as described above, when the light emission time is required to be 1(μ sec) or less (for example, 100 to 500(nsec)), the RC circuit is configured using a resistance of 1000(Ω) and a capacitor of 1000 (pF). Thereby, a light emission signal having a pulse width of 500(nsec) can be output from the LED driving circuit 15.
While several embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These embodiments can be implemented in other various forms, and various omissions, substitutions, and changes can be made without departing from the spirit of the invention. These embodiments and modifications are included in the scope and spirit of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Claims (10)

1. An LED drive circuit for lighting an LED,
the LED drive circuit includes a lighting timing control circuit having an RC circuit to which a rectangular signal is input, and turns on the LED for a predetermined time determined by a comparison result of an output of the RC circuit and a preset threshold value from a rise of the rectangular signal, and turns off the LED after the predetermined time has elapsed.
2. The LED driver circuit of claim 1,
the lighting timing control circuit further includes:
an inverter circuit that outputs a high level during a period in which an output of the RC circuit is less than the threshold; and
an AND circuit that outputs a high level during a period in which the rectangular signal AND the output of the inverter circuit are at a high level,
the LED driving circuit further includes a gate driving circuit that turns on the LED when the output of the AND circuit is at a high level.
3. The LED driver circuit of claim 1,
the lighting timing control circuit further includes an XOR circuit that outputs at a high level during a period in which the output of the RC circuit is smaller than the threshold value and the rectangular signal is at a high level, or during a period in which the output of the RC circuit is equal to or larger than the threshold value and the rectangular signal is at a low level,
the LED drive circuit further comprises a gate drive circuit which enables the LED to be lightened when the output of the XOR circuit is in a high level.
4. The LED driver circuit according to any of claims 1 to 3,
the inkjet head further includes a Schmitt trigger inverter that makes a signal synchronized with a drive signal that is emitted by the LED and ejects a droplet from the inkjet head be the rectangular signal.
5. A liquid discharge observation device includes:
an ink jet head which ejects liquid droplets in accordance with a drive signal;
an LED for irradiating the liquid droplet ejected from the ink jet head with light;
a camera to acquire an image of the droplet; and
an LED drive circuit for lighting the LED,
the LED drive circuit includes a lighting timing control circuit having an RC circuit to which a rectangular signal synchronized with the drive signal is input, and lights the LED for a predetermined time determined by a comparison result of an output of the RC circuit and a preset threshold value from a rise of the rectangular signal, and lights the LED out after the predetermined time has elapsed.
6. An LED driving method for lighting an LED by an LED driving circuit,
the LED driving method includes turning on the LED for a predetermined time determined by a comparison result between an output of the RC circuit and a preset threshold from a rise of a rectangular signal by a lighting timing control circuit having the RC circuit to which the rectangular signal is input, and turning off the LED after the predetermined time has elapsed.
7. The LED driving method according to claim 6,
an inverter circuit provided in the lighting timing control circuit outputs a high level while the output of the RC circuit is less than the threshold,
a high-level output is performed during a period in which the output of the inverter circuit AND the rectangular signal are at a high level by an AND circuit provided in the lighting timing control circuit,
the LED is turned on by a gate drive circuit provided in the LED drive circuit when the output of the AND circuit is at a high level.
8. The LED driving method according to claim 6,
performing, by an XOR circuit included in the lighting timing control circuit, high-level output during a period in which the output of the RC circuit is smaller than the threshold and the rectangular signal is at a high level or during a period in which the output of the RC circuit is equal to or larger than the threshold and the rectangular signal is at a low level,
and the LED is lightened by the gate drive circuit of the LED drive circuit when the output of the XOR circuit is at a high level.
9. The LED driving method according to any one of claims 6 to 8,
the signal synchronized with the drive signal for emitting the liquid droplets from the inkjet head by the light emitted from the LED is made to be the rectangular signal by a schmitt trigger inverter provided in the LED drive circuit.
10. A liquid ejection observation method comprising:
ejecting a droplet by an inkjet head according to a driving signal;
irradiating light to the liquid droplet ejected from the inkjet head by an LED;
acquiring an image of the droplet by a camera;
enabling the LED to be lightened through an LED driving circuit; and
the lighting timing control circuit includes an RC circuit to which a rectangular signal synchronized with the driving signal is input, and the LED driving circuit turns on the LED for a predetermined time determined by a comparison result between an output of the RC circuit and a predetermined threshold from a rise of the rectangular signal, and turns off the LED after the predetermined time has elapsed.
CN202010625207.3A 2019-09-05 2020-07-02 LED drive circuit and drive method, and liquid ejection observation device and method Withdrawn CN112449458A (en)

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