LED constant current lighting system of industrial endoscope and industrial endoscope

Abstract

The application relates to an LED constant-current lighting system of an industrial endoscope and the industrial endoscope, which comprises a microcontroller unit, a digital-analog converter, an LED lamp, a switching constant-current driving module connected with a power supply respectively, a low-dropout linear regulator, a differential sampling operation unit and a charge pump converter; the microcontroller unit is connected with the digital-analog converter through an I2C communication bus; the digital-analog converter is connected with the constant-current driving module; the constant-current driving module is connected with the anode of the LED lamp, and the cathode of the LED lamp is directly grounded; the low-dropout linear regulator is connected with the microcontroller unit and the digital-analog converter respectively, and the differential sampling operation unit is connected in series between a constant-current output end and the LED lamp; the charge pump converter provides a negative power supply for the differential sampling operation unit; and the endoscope adopting the system is disclosed. The application can provide stable, non-flickering, color-faithful and intelligently-adjustable lighting for the industrial endoscope.

Description

Technical Field

[0001] This invention relates to the field of industrial endoscopes, and in particular to an LED constant current illumination system for an industrial endoscope and an industrial endoscope. Background Technology

[0002] Industrial endoscopes are crucial tools for inspecting the interiors of industrial equipment (such as engine pipes, condensers, castings, etc.) for defects, wear, or assembly problems. Their working environment is typically completely dark and confined, relying entirely on a miniature illumination source integrated into the front-end camera. Existing endoscope illumination solutions mostly use LED lights, but their driving methods have significant drawbacks: Simulating dimming by changing the amplitude of the LED drive current over a large current range can cause LED color temperature shifts, affecting image color accuracy and potentially masking actual defects; while PWM dimming solves the color shift problem, low-frequency PWM dimming is prone to producing visible flicker or scan lines at camera shutter speeds, severely interfering with image quality and resulting in unclear, stable images during photography or video recording; it cannot compensate for the light decay and color shift caused by LED heat generated during prolonged operation, and the illumination brightness may gradually decrease during long-term inspections, affecting the consistency of inspection results. Summary of the Invention

[0003] To address the shortcomings of existing systems, this invention provides an LED constant current illumination system for an industrial endoscope and an industrial endoscope.

[0004] The application adopts the technical scheme that a LED constant current lighting system of an industrial endoscope comprises a microcontroller unit, a digital-analog converter, an LED lamp, a switching constant current driving module connected with a power supply respectively, a low dropout linear regulator, a differential sampling operation unit and a charge pump converter; the microcontroller unit is connected with the digital-analog converter through an I2C communication bus; the constant current driving module is provided with a feedback input end, a function signal end and a constant current output end, the output end of the digital-analog converter is connected with the function signal end; the constant current output end is connected with the anode of the LED lamp, and the cathode of the LED lamp is directly grounded; the output end of the low dropout linear regulator is connected with the microcontroller unit and the digital-analog converter respectively, the differential sampling operation unit comprises a sampling resistor connected in series between the constant current output end and the LED lamp, and a differential operation circuit capable of forming a closed loop negative feedback connected in parallel with the sampling resistor, and the operation output end of the differential operation circuit is connected with the feedback input end; the differential operation circuit comprises an operational amplifier, the operational amplifier is provided with a positive power supply pin, a negative power supply pin, an operation output end, a same phase input end and an inverse phase input end; the positive power supply pin is connected with the power supply, the negative power supply pin is connected with the output end of the charge pump converter, and the sampling resistor is arranged between the same phase input end and the inverse phase input end; a first resistor is arranged between the inverse phase input end and the operation output end, a second resistor is connected on the circuit connected with the inverse phase input end and the first resistor, and one end of the second resistor away from the first resistor is connected on the circuit in which the sampling resistor and the anode of the LED lamp are connected; a third resistor connected in series with the feedback input end is further connected on the circuit in which the first resistor and the operation output end are connected; an operational amplifier filter is connected in series between the same phase input end and the sampling resistor; the operational amplifier filter comprises a fourth resistor and a fifth resistor arranged in parallel, the fifth resistor is connected in series with a filter capacitor, and the filter capacitor is grounded; the total equivalent resistance of the same phase input end is equal to the total equivalent resistance of the inverse phase input end, the resistance value of the first resistor is equal to the resistance value of the fourth resistor, and the resistance value of the second resistor is equal to the resistance value of the fifth resistor; the charge pump converter provides a negative power supply for the differential operation circuit.

[0005] Preferably, the constant current driving module comprises a constant current driving chip, a first capacitor connected in series between the SW pin and the BST pin of the constant current driving chip, and an inductor connected on the circuit in which the first capacitor and the SW pin are connected; one end of the inductor away from the first capacitor is connected with the sampling resistor; a second capacitor is connected on the circuit in which the inductor and the sampling resistor are connected, and the second capacitor is grounded; the feedback input end is an FB pin arranged on the constant current driving chip, and the function signal end is an enable pin / light adjustment pin arranged on the constant current driving chip; the input pin of the constant current driving chip is connected with the power supply.

[0006] As preferred, the charge pump converter comprises a charge pump chip, a third capacitor arranged between the charge pump chip CAP+ pin and CAP- pin, an input capacitor connected to the input pin of the charge pump chip and grounded, and an output capacitor connected to the output pin of the charge pump chip and grounded; the input pin of the charge pump chip is connected to the power supply, and the digital control pin of the charge pump chip is connected to the circuit in which the input pin and the power supply are connected.

[0007] As preferred, the low dropout linear regulator comprises an LDO chip provided with two output pins and externally connected as an output end, a fourth capacitor connected to the input pin of the LDO chip and grounded, and a fifth capacitor connected to the output end of the LDO chip and grounded; the input end of the LDO chip is connected to the power supply, and the microcontroller unit and the digital-to-analog converter are connected to the output end of the LDO chip.

[0008] As preferred, the microcontroller unit is provided with a passive crystal oscillator circuit.

[0009] An industrial endoscope characterized in that the constant current illumination system according to any one of the preceding embodiments is used.

[0010] As preferred, the cathode of the LED lamp is directly connected with a grounding body for grounding, and the grounding body is a metal shell serving as an endoscope probe shell or a grounding copper foil layer arranged on an endoscope probe circuit board.

[0011] The present application has the advantages that the LED always works in a direct current constant current state, the frequency flicker problem caused by dimming is eliminated, the image definition of photographing and video recording at any shutter speed is ensured, color temperature drift is avoided, the color of the detected object is ensured to be restored truly, the heat dissipation efficiency and the brightness stability of the LED lamp are improved, the LED junction temperature is stabilized, light decay is delayed, long service life and high reliability are maintained. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a circuit diagram of the constant current driving module and the differential sampling operation unit in the embodiment of the present application;

[0013] Figure 2 is a circuit diagram of the digital-to-analog converter in the embodiment of the present application;

[0014] Figure 3 is a circuit diagram of the microcontroller unit in the embodiment of the present application;

[0015] Figure 4 is a circuit diagram of the low dropout linear regulator in the embodiment of the present application;

[0016] Figure 5 is a circuit diagram of the charge pump converter in the embodiment of the present application. DETAILED DESCRIPTION

[0017] In order to more clearly illustrate the purpose, technical solutions and advantages of the embodiments of the present application, the present application will be further described below with reference to the drawings and embodiments, and a clear and complete description will be made. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0018] The embodiments of the present application have Figures 1 to 5As shown in the middle, an LED constant current lighting system of industrial endoscope includes a microcontroller unit (MCU), a digital-to-analog converter, an LED lamp D4, a switching constant current drive module connected with a power supply respectively, a low dropout linear regulator, a differential sampling operation unit and a charge pump converter; the microcontroller unit is connected with the digital-to-analog converter through an I2C communication bus; the constant current drive module is provided with a feedback input end, a function signal end and a constant current output end, the output end of the digital-to-analog converter is connected with the function signal end; the constant current output end is connected with the anode of the LED lamp D4, and the cathode of the LED lamp D4 is directly grounded; the output end of the low dropout linear regulator is connected with the microcontroller unit and the digital-to-analog converter respectively, the differential sampling operation unit includes a sampling resistor R11 connected in series between the constant current output end and the LED lamp D4, a differential operation circuit capable of forming a closed loop negative feedback connected in parallel with the sampling resistor R11, and the operation output end of the differential operation circuit is connected with the feedback input end; the charge pump converter provides a negative power supply for the differential operation circuit. In the whole system, the low dropout linear regulator provides stable working voltage for the microcontroller unit and the digital-to-analog converter; the MCU sends instructions to the digital-to-analog converter (DAC) through the I2C bus to set the target output voltage, and the MCU can dynamically and smoothly adjust according to the preset program or real-time feedback of the user, such as quickly adjusting the brightness to prevent the lens from overexposure when checking high-reflectivity metal pipes; when checking the inside of dark and low-reflectivity castings, it can be switched to the highest brightness mode; the digital-to-analog converter outputs accurate direct current voltage to the function signal end of the constant current drive module according to the received instructions, then the constant current drive module provides the initial set current to the LED lamp D4 through the constant current output end, and the cathode of the LED lamp D4 is directly grounded, so that the sampling resistor of the differential sampling operation unit samples on the high side, and the voltages at both ends of the sampling resistor are at a relatively high common mode voltage that may change, and the differential operation circuit can suppress very high common mode voltage and accurately amplify small differential voltage, so as to accurately reflect the current value of the LED lamp D4, and the differential operation circuit outputs a feedback voltage to the constant current drive module, and the constant current drive module adjusts according to the comparison between the received feedback voltage and the set value, so as to form a closed loop negative feedback, which can compensate the influence caused by input voltage fluctuation, component temperature drift and temperature change of the LED lamp D4 itself, no matter how long the endoscope works or how the environment temperature changes, the current of the LED lamp D4 is stable at the target value, the LED lamp D4 always works in a direct current constant current state, and the brightness keeps high stability, the image brightness and contrast can keep consistent when long-time continuous detection or comparison of detection results at different times is carried out, the misjudgment or missed detection caused by illumination fluctuation is avoided, the frequency flicker problem is fundamentally eliminated, the image clarity of the photograph and video at any shutter speed is ensured, and the constant current drive also avoids color temperature drift, and ensures the true restoration of the color of the detected object.

[0019] For the differential operational circuit, as shown in Figure 1 the differential operational circuit includes an operational amplifier U5, such as an ADA4625 operational amplifier, which is provided with a positive power supply pin, a negative power supply pin, an operational output terminal, a non-inverting input terminal and an inverting input terminal; the positive power supply pin is connected with a power supply, and the negative power supply pin is connected with an output terminal of the charge pump converter, so that the operational amplifier is formed with double power supply; a sampling resistor R11 is arranged between the non-inverting input terminal and the inverting input terminal; a first resistor R5 is arranged between the inverting input terminal and the operational output terminal, that is, one end of the first resistor R5 is connected with the inverting input terminal, and the other end is connected with the operational output terminal, and the first resistor constitutes a feedback resistor; a second resistor R6 is connected with the circuit in which the first resistor R5 is connected with the inverting input terminal; one end of the second resistor R6, which is away from the first resistor R5, is connected with the circuit in which the sampling resistor R11 and the anode of the LED lamp D4 are connected; that is, one end of the second resistor R6 is connected with the circuit in which the first resistor R5 and the inverting input terminal are connected, and the other end is connected with the circuit in which the sampling resistor R11 and the anode of the LED lamp D4 are connected; a third resistor R7 is further connected with the circuit in which the first resistor R5 and the operational output terminal are connected, and the third resistor R7 is connected in series with the feedback input terminal of the constant current driving module; an operational amplifier filter is connected in series between the non-inverting input terminal and the sampling resistor R11, and the operational amplifier filter is a low-pass filter, which filters high-frequency noise and improves signal quality. At this time, the operational amplifier filter includes a fourth resistor R8 and a fifth resistor R9 which are connected in parallel; the fourth resistor R8 can prevent excessive transient current from directly impacting the operational amplifier; the fifth resistor R9 is connected in series with a filter capacitor C19, and the filter capacitor C19 is grounded; the fifth resistor R9 can avoid the non-inverting input terminal being short-circuited to the ground; high-frequency noise is bypassed to the ground by C19 and cannot reach the operational amplifier. At this time, the total equivalent resistance of the non-inverting input terminal is equal to the total equivalent resistance of the inverting input terminal, and the equivalent resistance R 并1 of the first resistor R5 and the second resistor R6 in parallel is the total equivalent resistance of the inverting input terminal, the equivalent resistance R 并2 of the fourth resistor R8 and the fifth resistor R9 in parallel is the total equivalent resistance of the non-inverting input terminal, R 并1 =R5·R6 / (R5+R6), R 并2 ==R8·R9 / (R8+R9), and R 并1 and R 并2 are equal; preferably, the resistance values of R8 and R5 are equal, and the resistance values of R9 and R6 are equal, so that common mode signals can be better suppressed.

[0020] For the constant current driving module, as shown in Figure 1As shown, the constant current drive module includes a constant current drive chip U6, a first capacitor C17 connected in series between the SW pin and the BST pin of the constant current drive chip, and an inductor L1 connected to the circuit connecting the first capacitor C17 and the SW pin. One end of the first capacitor C17 is connected to the SW pin of the constant current drive chip, and the other end is connected to the BST pin of the constant current drive chip. The end of the inductor L1 away from the first capacitor C17 is connected to the sampling resistor R11. A second capacitor C18 is connected to the circuit connecting the inductor L1 and the sampling resistor R11. The second capacitor C18 is grounded, that is, one end of the second capacitor C18 is grounded, and the other end is connected to the circuit connecting the inductor L1 and the sampling resistor R11. The feedback input terminal is the FB pin on the constant current drive chip, and the function signal terminal is the enable pin EN / dimming pin DIM on the constant current drive chip. The input pin of the constant current drive chip is connected to the power supply.

[0021] like Figure 5 As shown, the charge pump converter includes a charge pump chip U8, a third capacitor C26 disposed between the CAP+ and CAP- pins of the charge pump chip, an input capacitor C22 connected to the input pin of the charge pump chip and grounded, and an output capacitor C23 connected to the output pin of the charge pump chip and grounded. The input pin of the charge pump chip is connected to the power supply, that is, one end of the input capacitor C22 is directly grounded, and the other end is connected to the circuit connecting the power supply and the input pin, which is indirectly connected to the input pin of the charge pump chip. The digital control pin SD of the charge pump chip is connected to the circuit connecting the input pin and the power supply.

[0022] like Figure 4 As shown, the low dropout linear regulator includes an LDO chip U1 with two output pins VOUT connected externally as output terminals, a fourth capacitor C1 connected to the input pins of the LDO chip and grounded, and a fifth capacitor C2 connected to the output terminal of the LDO chip and grounded. The input pins of the LDO chip are connected to the power supply, and the microcontroller unit and the digital-to-analog converter are connected to the output terminal of the LDO chip. That is, the two output pins VOUT of the LDO chip are first connected and then connected to the fifth capacitor C2, the microcontroller unit and the digital-to-analog converter respectively.

[0023] like Figure 3 As shown, the microcontroller unit is equipped with a passive crystal oscillator circuit to provide a stable and accurate clock signal to the MCU; the passive crystal oscillator circuit includes capacitor C3, capacitor C8 and quartz crystal Y2.

[0024] The industrial endoscope adopts the constant current illumination system as any one of the preceding, that is, the circuit system for controlling illumination in the existing industrial endoscope adopts the constant current illumination system to realize constant current illumination, and solves the problem of stroboscopic effect. At this time, the cathode of the LED lamp is directly connected with a grounding body for grounding, and the grounding body is a metal shell serving as an endoscope probe shell or a grounding copper foil layer arranged on an endoscope probe circuit board. The topology of directly grounding the LED cathode makes the heat generated by the LED directly conducted to the stainless steel shell of the endoscope front probe or the large-area grounding copper foil layer on the internal circuit board of the endoscope probe, so that the heat dissipation efficiency is improved in the limited probe space, and the improvement of the heat dissipation efficiency can meet the demand of using a larger power LED to obtain brighter illumination, while ensuring stable LED junction temperature, delaying light decay, maintaining long service life and high reliability.

[0025] Although the present application has been described in detail with general description and specific embodiments above, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, all belong to the scope of the present application claimed.

Claims

1. An LED constant current illumination system for industrial endoscopes, characterized in that, The application relates to a constant current drive module for LED lamps, which comprises a microcontroller unit, a digital-analog converter, an LED lamp, a switch-type constant current drive module, a low-drop linear voltage stabilizer, a differential sampling operation unit and a charge pump converter, and is characterized in that the microcontroller unit is connected with the digital-analog converter through an I2C communication bus; the constant current drive module is provided with a feedback input end, a function signal end and a constant current output end, the output end of the digital-analog converter is connected with the function signal end; the constant current output end is connected with the anode of the LED lamp, and the cathode of the LED lamp is directly grounded; the output end of the low-drop linear voltage stabilizer is connected with the microcontroller unit and the digital-analog converter respectively; the differential sampling operation unit comprises a sampling resistor connected in series between the constant current output end and the LED lamp, a differential operation circuit capable of forming a closed loop negative feedback connected in parallel with the sampling resistor, and the operation output end of the differential operation circuit is connected with the feedback input end; the differential operation circuit comprises an operational amplifier, the operational amplifier is provided with a positive power supply pin, a negative power supply pin, an operation output end, a same-phase input end and an inverse-phase input end; the positive power supply pin is connected with the power supply, the negative power supply pin is connected with the output end of the charge pump converter, and the sampling resistor is arranged between the same-phase input end and the inverse-phase input end; a first resistor is arranged between the inverse-phase input end and the operation output end, a second resistor is connected on the circuit connected with the inverse-phase input end and the first resistor, and one end of the second resistor away from the first resistor is connected on the circuit in which the sampling resistor and the anode of the LED lamp are connected; a third resistor connected in series with the feedback input end is further connected on the circuit in which the first resistor and the operation output end are connected; an operational amplifier filter is connected in series between the same-phase input end and the sampling resistor; the operational amplifier filter comprises a fourth resistor and a fifth resistor arranged in parallel, the fifth resistor is connected in series with a filter capacitor, and the filter capacitor is grounded; the total equivalent resistance of the same-phase input end is equal to the total equivalent resistance of the inverse-phase input end, the resistance value of the first resistor is equal to the resistance value of the fourth resistor, and the resistance value of the second resistor is equal to the resistance value of the fifth resistor; the charge pump converter provides a negative power supply for the differential operation circuit.

2. The LED constant current illumination system for industrial borescopes as defined in claim 1, wherein, The constant current drive module comprises a constant current drive chip, a first capacitor connected in series between the SW pin and the BST pin of the constant current drive chip, and an inductor connected on the circuit in which the first capacitor and the SW pin are connected; one end of the inductor away from the first capacitor is connected with the sampling resistor; a second capacitor is connected on the circuit in which the inductor and the sampling resistor are connected, and the second capacitor is grounded; the feedback input end is an FB pin arranged on the constant current drive chip, and the function signal end is an enable pin / light adjustment pin arranged on the constant current drive chip; the input pin of the constant current drive chip is connected with the power supply.

3. The LED constant current illumination system for industrial borescopes as defined in claim 1, wherein, The charge pump converter comprises a charge pump chip, a third capacitor arranged between the charge pump chip CAP+ pin and CAP- pin, an input capacitor connected to the input pin of the charge pump chip and grounded, and an output capacitor connected to the output pin of the charge pump chip and grounded; the input pin of the charge pump chip is connected to a power supply, and the digital control pin of the charge pump chip is connected to a circuit in which the input pin and the power supply are connected.

4. The LED constant current illumination system for industrial borescopes of claim 1, wherein, The low dropout linear regulator comprises an LDO chip provided with two output pins and externally connected as an output end, a fourth capacitor connected to the input pin of the LDO chip and grounded, and a fifth capacitor connected to the output end of the LDO chip and grounded; the input end of the LDO chip is connected to a power supply, and the microcontroller unit and the digital-to-analog converter are connected to the output end of the LDO chip.

5. The LED constant current illumination system for industrial borescopes as defined in claim 1, wherein, The microcontroller unit is provided with a passive crystal oscillator circuit.

6. An industrial endoscope characterized by comprising: The constant current lighting system according to any one of claims 1-5 is adopted.

7. The industrial endoscope according to claim 6, characterized in that, The cathode of the LED lamp is directly connected with a grounding body for grounding, and the grounding body is a metal shell serving as an endoscope probe shell or a grounding copper foil layer arranged on an endoscope probe circuit board.

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