An underground safety charging method for the battery pack of a coal mine inspection robot

Abstract

The present invention relates to a method for safely charging a battery pack of a coal mine inspection robot underground, belonging to the field of electronic circuits. The method includes the following steps: connecting a fixed charging station and an intrinsically safe charging circuit carried by a mobile inspection robot; using an intrinsically safe power source allowed to be used underground as the power source, with the circuit being safe and reliable; isolating and connecting multiple intrinsically safe power sources in series to increase the output voltage to achieve the purpose of increasing power, and the number of intrinsically safe power sources can be flexibly configured to achieve different powers; having a sequential startup function to prevent the voltage reverse charging phenomenon caused by different startup times of multiple power sources; the circuit has voltage and current control modes to ensure that the power supply output does not exceed the designed voltage and current.

Description

Technical Field

[0001] The present invention belongs to the field of electronic circuits and relates to a method for safely charging a battery pack of a coal mine inspection robot underground. Background Art

[0002] Coal mine underground robots are an effective measure to reduce the number of underground coal mine workers and are of great significance to the coal mine enterprise in reducing staff and increasing efficiency and improving safety. With the increasing development of artificial intelligence technology and robot technology, inspection robots are widely used in various fields and can replace or assist humans in performing repetitive, time-consuming, and labor-intensive inspection work.

[0003] Coal mine underground belt track inspection robots are increasingly widely used. According to the walking mode, they are mainly divided into wire rope traction type and self-driving type. The self-driving inspection robot is powered by a battery pack, and the output power supply is used for the robot walking motor. It has the advantages of autonomous walking along the track or wheel type, autonomous charging, long-term fixed-point staying, and low installation cost. The battery pack uses lithium batteries or nickel-metal hydride batteries, which have the advantages of high energy density and long life. When the battery pack has insufficient power, the inspection robot needs to be charged to replenish energy.

[0004] Due to the safety and explosion-proof requirements of coal mines, currently, the more studied charging methods for coal mine inspection robots include ground charging, underground wireless charging, underground explosion-proof interface charging, underground electromechanical conversion charging, etc.

[0005] 1) Ground charging has no explosion-proof requirements for the charging device and charging interface, can charge with a large current, and has high charging efficiency. When the battery power of the coal mine underground inspection robot is insufficient, if the inspection robot is close to the ground, it can walk back to the ground for charging from underground, or the battery pack of the inspection robot is designed to be detachable, and the battery pack is disassembled manually and then taken to the ground for charging. The ground charging method is relatively flexible and can be wireless or wired charging. After charging is completed, the battery pack with insufficient power is replaced underground manually.

[0006] 2) Underground wireless charging has a small power and slow charging speed. Since the electromagnetic wave emitted wirelessly may cause induced current in metal pipes, wires, and equipment near the antenna, restricted by the underground explosion-proof environment, the allowable charging capacity is smaller than that on the ground. The threshold power of the continuously emitting radio frequency source should not exceed 6W, which cannot meet the fast charging requirements of the inspection robot; this method is suitable for small inspection robots with full intrinsic safety design.

[0007] 3) Underground explosion-proof interface charging is currently the most important charging method, which is carried out in a dedicated charging chamber or charging cabin during charging. The charging device and the battery are designed with explosion-proof type, and explosion-proof structures such as explosion-proof cavity docking and explosion-proof ball valves are used to achieve electrical and mechanical charging interlock protection. The explosion-proof charging device and the explosion-proof battery should ensure the formation of independent explosion-proof cavities in the docking state, charging state and separation state; there are independent safety interlock mechanisms in the docking state, charging state and separation state to ensure that the charging interface of the robot and its charging device is not energized before the charging interface is not reliably connected and the charging explosion-proof cavity is not formed, so as to avoid generating electric arcs, electric sparks and dangerous temperatures and detonating gas. Charging device.

[0008] 4) Underground electromechanical conversion charging mainly includes charging methods such as mechanical rotation power generation, wind power generation, and hydraulic power generation. The explosion-proof motor rotates, and mechanical energies such as wind power and hydraulic power drive the explosion-proof generator to generate electricity, and the battery pack carried by the robot is charged through a dedicated charging device.

[0009] The advantages and disadvantages of several charging methods are compared as shown in Table 1.

[0010] Table 1 Comparison of Charging Methods for Coal Mine Inspection Robots

[0011]

[0012] 1) Ground charging has no explosion-proof requirements for the charging device and the charging interface, but the inspection robot needs to walk a certain distance from the underground to the ground for charging, which consumes the energy of the battery pack additionally and takes a long round-trip time, and is not suitable for robots far from the ground; if the method of manually replacing the battery pack is adopted, it will additionally increase the labor consumption and reduce the automation degree of the inspection robot.

[0013] 2) Underground wireless charging has a small power and slow charging speed. Since the electromagnetic waves emitted wirelessly may cause induced currents in metal pipes, wires, and equipment near the antenna, limited by the underground explosion-proof environment, the allowable charging capacity is smaller than that on the ground and cannot meet the fast charging requirements of the inspection robot;

[0014] 3) Underground explosion-proof interface charging has very strict requirements for the flatness, gap, etc. of the joint surface of the explosion-proof shell structure, so the accuracy requirements for motion control during the docking process are also very high. The underground environment of coal mines is harsh, and explosion-proof equipment is relatively heavy. Dust, mechanical impact, roadway deformation, etc. will all affect the docking accuracy, and it is difficult to ensure that the explosion-proof surface can maintain high precision for a long time to meet the safety requirements.

[0015] 4) There are problems with the efficiency of mechanical energy-electrical energy conversion in underground electromechanical conversion charging, and the overall charging efficiency of the charging device is average. The inspection robot itself is equipped with an explosion-proof generator, which cannot work during normal inspections. The weight and volume of the explosion-proof generator occupy a certain proportion of the robot, causing a certain amount of energy loss and weakening the battery life.

[0016] In summary, each charging method for inspection robots has its own advantages and disadvantages, and all have certain limitations, and cannot meet the application requirements of autonomous, intelligent, and fast charging of inspection robots. Summary of the invention

[0017] In view of this, the purpose of the present invention is to provide a method for safe underground charging of a battery pack of a coal mine inspection robot, which uses a small-power intrinsically safe power supply allowed for use underground in coal mines to obtain a high voltage after isolation and series connection, thereby achieving the purpose of high-power safe and fast charging.

[0018] In order to achieve the above object, the present invention provides the following technical solutions:

[0019] A method for safely charging a battery pack of a coal mine inspection robot underground, the method comprising the following steps:

[0020] Connect the fixed charging station and the intrinsically safe charging circuit carried by the mobile inspection robot;

[0021] The fixed charging station is composed of multiple intrinsically safe power supplies and a single-chip microcomputer controller, which outputs 4 intrinsically safe power supplies for use by the mobile inspection robot. The outputs of multiple intrinsically safe power supplies are collected at the charging end for docking with the power receiving end of the mobile inspection robot. When the inspection robot needs to be charged, it moves autonomously to the vicinity of the fixed charging station, and the power receiving end of the inspection robot docks with the charging end of the charging station. After the single-chip microcomputer controller of the charging station detects that the docking is successful, it turns on switches S1 to S4 to output 4 intrinsically safe power supplies, and the charging circuit of the inspection robot works to charge its own battery pack. After the charging station receives the charging completion signal of the inspection robot through wireless, it turns off S1 to S4 to cut off the output of the 4 intrinsically safe power supplies, and the charging process is completed.

[0022] The intrinsically safe charging circuit carried by the mobile inspection robot consists of an isolation circuit and a charging circuit. The isolation circuit isolates each input intrinsically safe power supply, and after isolation, they are connected in series to charge the battery pack through the power conversion power supply;

[0023] The battery pack charging circuit of the mobile inspection robot realizes the isolation and conversion of 4 intrinsically safe power supplies and the battery charging function; the intrinsically safe power supply realizes the electrical isolation of the intrinsically safe circuit and the non-intrinsically safe circuit through isolation and conversion; the 4 isolated power outputs are connected in series to increase the output voltage to obtain a high-power power supply, and the BUCK power supply is converted through the single-chip microcomputer, while the battery pack charging voltage, charging current, and temperature information are collected to realize the control and management of the battery pack charging process;

[0024] The charging circuit carried by the mobile inspection robot includes a power-on buffer circuit, a primary push-pull conversion circuit, a rectification circuit, a voltage feedback loop, a current feedback loop, and a sequential start control circuit; the circuit adopts a potting method to meet the safety requirements for capacitors and inductors in "GB3836-2021 Explosive Environment".

[0025] Optionally, the primary push-pull conversion circuit, the voltage feedback loop, and the rectification circuit constitute an isolated switch power conversion circuit;

[0026] U1 is a push-pull switch power control chip, which outputs two PWM signals to control Q2 and Q3 to complete the push-pull type switch power conversion; OP3A and D8 constitute a voltage feedback circuit to make the switch power output a stable voltage; D6, D7, L1, and C6 constitute a rectification circuit to rectify the pulsating voltage after isolation conversion into a DC voltage; the FB pin of the U1 chip is the inverting input terminal of the error amplifier. When the potential of this pin is high, the U1 chip stops working and shuts down the switch power voltage output. This pin is used as the enable control terminal for whether the switch power works.

[0027] Optionally, the current feedback loop includes a current detection and current comparison circuit. The current feedback loop detects the output current of the positive pole of the combined power supply and simultaneously outputs 4 feedback signals to the 4-way switch power conversion circuit, so that the output currents of the 4-way isolated switch power supplies are always kept consistent; when the output current of the combined power supply is less than the maximum output current Imax, no feedback signal is output, and each switch power supply works in voltage mode to ensure that the output voltage is stable within a certain range; Imax = 0.7 / R23; when the output current of the combined power supply reaches the output current Imax, the output feedback signal is sent to the COMP control pin of the 4-way switch power conversion control chip, and the control chip makes the output current of the combined power supply stable at Imax.

[0028] Optionally, the sequential start control circuit is an output voltage detection circuit;

[0029] When the voltage value between PWR1+ and PWR1- of the output voltage of the first-way switch power supply is greater than a certain value, the optocoupler OP3 conducts and outputs an unlocking signal. The unlocking signal is input to the working enable control terminal of the next-level switch power supply for unlocking, and then this way of switch power supply starts normally; and so on, to realize the sequential start of the 4-way isolated push-pull switch power supplies from top to bottom, so as to gradually establish the output voltage between PWR1+ and PWR4-.

[0030] Optionally, the charging circuit carried by the mobile inspection robot consists of a BUCK power conversion circuit, current detection, voltage detection, and a single-chip microcomputer;

[0031] Q6, Q7 and the peripheral drive circuit form a BUCK power conversion circuit. U4 is a synchronous drive chip, which makes Q7 work in the synchronous switching state to reduce the switching loss of the BUCK power supply; R15 is a current detection resistor, and U3 is a current amplification chip, and its output signal is used for the single-chip microcomputer to monitor the charging current; R17 and R18 are voltage dividing resistors, which are used for the single-chip microcomputer to monitor the real-time charging voltage; the single-chip microcomputer collects voltage and current signals, outputs a PWM signal to control Q6 in real time for BUCK power conversion, and completes the battery pack charging control.

[0032] The beneficial effects of the present invention are as follows:

[0033] 1) Using the intrinsically safe power supply allowed to be used underground as the power source, the circuit is safe and reliable;

[0034] 2) Using multiple intrinsically safe power supplies to be isolated and then connected in series to increase the output voltage to achieve the purpose of increasing the power, and the number of intrinsically safe power supplies can be flexibly configured to achieve different powers;

[0035] 3) Having a sequential startup function to prevent the voltage reverse charging phenomenon caused by different startup times of multiple power supplies;

[0036] 4) The circuit has voltage and current control modes to make the power supply output not exceed the designed voltage and current.

[0037] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0039] Figure 1 is the functional diagram of the intrinsically safe charging method;

[0040] Figure 2 is the functional diagram of the intrinsically safe charging method;

[0041] Figure 3 is the typical power-on buffer circuit;

[0042] Figure 4 is the isolated switch power conversion circuit;

[0043] Figure 5 is the current detection and current comparison circuit;

[0044] Figure 6 is the sequential startup control circuit;

[0045] Figure 7 It is a battery charging circuit. Specific implementation manners

[0046] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the diagrams provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0047] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and should not be construed as a limitation to the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which does not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0048] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and should not be construed as a limitation to the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0049] The present invention belongs to the fields of switching power supplies and power electronics technologies, and proposes a method for safely and quickly charging a large power underground for a battery pack of an inspection robot by isolating and connecting in series multiple small-power intrinsically safe power supplies. Intrinsically safe power supplies are power equipment with relatively high safety allowed in coal mines. However, the output power of a single intrinsically safe power supply is small, and its output voltage is even less than the nominal voltage of the battery pack, making it impossible to charge the battery pack with high power. By using the method of isolating and connecting in series multiple small-power intrinsically safe power supplies, the power of the small-power power supplies is superimposed to achieve the purpose of charging the battery pack with high power.

[0050] The intrinsically safe charging method for the battery pack of the inspection robot consists of a fixed charging station and an intrinsically safe charging circuit carried by the mobile inspection robot. The functional diagram is as Figure 1 shown.

[0051] The fixed charging station consists of multiple intrinsically safe power supplies and a single-chip microcomputer controller, and can output multiple (4-way) intrinsically safe power supplies for use by mobile inspection robots. The outputs of the multiple intrinsically safe power supplies are aggregated at the charging end for docking with the power receiving end of the mobile inspection robot. When the inspection robot needs to be charged, it autonomously moves near the fixed charging station, and the power receiving end of the inspection robot itself docks with the charging end of the charging station. After the single-chip microcomputer controller of the charging station detects successful docking, it turns on switches S1 - S4 to output 4-way intrinsically safe power supplies, and the charging circuit of the inspection robot operates to charge its own battery pack. After the charging station receives the charging completion signal of the inspection robot wirelessly, it turns off S1 - S4 to cut off the output of the 4-way intrinsically safe power supplies, and the charging process is completed.

[0052] The intrinsically safe charging circuit carried by the mobile inspection robot consists of an isolation circuit and a charging circuit. The isolation circuit isolates each input intrinsically safe power supply, and after isolation, they are connected in series to charge the battery pack through a power conversion power supply.

[0053] The battery pack charging circuit of the mobile inspection robot realizes the functions of 4-way intrinsically safe power supply isolation transformation and battery charging. The intrinsically safe power supply realizes the electrical isolation between the intrinsically safe circuit and the non-intrinsically safe circuit through isolation transformation. The outputs of the 4 isolated power supplies are connected in series to increase the output voltage, thereby obtaining a high-power power supply. Through a single-chip microcomputer for BUCK power conversion, and at the same time collecting information such as the charging voltage, charging current, and temperature of the battery pack, the control and management of the battery pack charging process are realized.

[0054] The charging circuit carried by the mobile inspection robot includes a power-on buffer circuit, a primary push-pull conversion circuit, a rectification circuit, a voltage feedback loop, a current feedback loop, a sequential startup control circuit, etc. To strengthen the safety isolation and insulation level between the intrinsically safe and non-intrinsically safe circuits, the entire circuit adopts a potted encapsulation method to meet the safety requirements for capacitors and inductors in "GB3836 - 2021 Explosive Atmospheres". The specific functional block diagram is as Figure 2 shown.

[0055] (1) Power-on buffer circuit

[0056] The input end of the primary push-pull switching power supply conversion circuit needs to provide a relatively stable input voltage. Therefore, a large capacitor needs to be connected in series at the input end of the intrinsically safe power supply to stabilize the input voltage. The mine-used intrinsically safe power supply has over-current and over-voltage protection functions. Therefore, a power-on buffer circuit needs to be added during power-on to prevent the intrinsically safe power supply from entering the protection state due to the large current impact caused by the large capacitor during power-on. The power-on buffer circuit is composed of a common typical circuit, as Figure 3 shown.

[0057] (2) Primary push-pull conversion circuit, voltage feedback, rectification circuit

[0058] Since the input intrinsically safe power supply has a relatively small power, in order to achieve the maximum utilization efficiency of the power supply, a push-pull switching power supply topology is adopted. The isolated switching power supply conversion circuit is composed of a primary push-pull conversion circuit, a voltage feedback circuit, and a rectification circuit. As Figure 4 shown.

[0059] U1 is a control chip for the push-pull switching power supply, which can output two PWM signals to control Q2 and Q3 to complete the push-pull switching power supply conversion; OP3A and D8 form a voltage feedback circuit to make the switching power supply output a stable voltage; D6, D7, L1, and C6 form a rectification circuit to rectify the pulsating voltage after isolation conversion into a DC voltage; the FB pin of the U1 chip is the inverting input terminal of the error amplifier. When the potential of this pin is high, the U1 chip stops working and thus shuts down the switching power supply voltage output. This pin can be used as an enable control terminal for whether the switching power supply works.

[0060] (3) Current detection and current comparison circuit

[0061] As Figure 5 shown, the current detection and current comparison circuit forms a current feedback loop. The current feedback loop detects the output current of the positive pole of the combined power supply and simultaneously outputs 4 feedback signals to the 4-way switching power supply conversion circuit, so that the output currents of the 4-way isolated switching power supplies are always kept consistent. When the output current of the combined power supply is less than the maximum output current Imax (Imax = 0.7 / R23), no feedback signal is output, and each switching power supply works in voltage mode to ensure that the output voltage is stable within a certain range; when the output current of the combined power supply reaches the output current Imax, the output feedback signal is sent to the COMP control pin of the 4-way switching power supply conversion control chip, and the control chip makes the output current of the combined power supply stable at Imax.

[0062] (4) Sequential startup control circuit

[0063] The sequential startup control circuit is essentially an output voltage detection circuit, as Figure 6 shown.

[0064] When the output voltage of the first-way switching power supply, that is, the voltage value between PWR1+ / PWR1-, is greater than a certain value, the optocoupler OP3 conducts and outputs an unlocking signal. This signal is input to the working enable control terminal of the next-stage switching power supply for unlocking, and then this way of switching power supply can be normally started. And so on, the sequential startup of the 4-way isolated push-pull switching power supplies from top to bottom can be realized, so as to gradually establish the output voltage between PWR1+ and PWR4-.

[0065] (5) Battery charging circuit

[0066] The battery charging circuit consists of a BUCK power supply conversion circuit, current detection, voltage detection, a single-chip microcomputer, etc. As Figure 7 shown.

[0067] Q6, Q7 and the peripheral drive circuit form a BUCK power conversion circuit. U4 is a synchronous drive chip, which makes Q7 work in the synchronous switching state, reducing the switching loss of the BUCK power supply. R15 is a current sensing resistor, and U3 is a current amplification chip, and its output signal is used for the single-chip microcomputer to monitor the charging current. R17 and R18 are voltage dividing resistors, which are used for the single-chip microcomputer to monitor the real-time charging voltage. The single-chip microcomputer collects voltage and current signals, outputs PWM signals to control Q6 in real time for BUCK power conversion, and completes the charging control of the battery pack.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for safely charging the battery pack of a coal mine inspection robot underground, characterized in that: The method includes the following steps: Connect the intrinsically safe charging circuit carried by the fixed charging station and the mobile inspection robot; The fixed charging station consists of multiple intrinsically safe power supplies and a single-chip microcomputer controller, and outputs 4 intrinsically safe power supplies for the mobile inspection robot to use. The outputs of multiple intrinsically safe power supplies are gathered at the charging end for docking with the power receiving end of the mobile inspection robot. When the inspection robot needs to be charged, it autonomously moves near the fixed charging station, and the power receiving end of the inspection robot itself docks with the charging end of the charging station. After the single-chip microcomputer controller of the charging station detects successful docking, it turns on switches S1 - S4 to output 4 intrinsically safe power supplies, and the charging circuit of the inspection robot operates to charge its own battery pack. After the charging station receives the charging completion signal of the inspection robot wirelessly, it turns off switches S1 - S4 to cut off the output of 4 intrinsically safe power supplies, and the charging process is completed; The intrinsically safe charging circuit carried by the mobile inspection robot consists of an isolation circuit and a charging circuit. The isolation circuit isolates each input intrinsically safe power supply, and after isolation, they are connected in series to charge the battery pack through a power conversion power supply; The battery pack charging circuit of the mobile inspection robot realizes the functions of isolating and transforming 4 intrinsically safe power supplies and battery charging; the intrinsically safe power supply realizes electrical isolation between the intrinsically safe circuit and the non-intrinsically safe circuit through isolation transformation; the outputs of 4 isolated power supplies are connected in series to increase the output voltage to obtain a high-power power supply, and BUCK power conversion is performed through a single-chip microcomputer. At the same time, the charging voltage, charging current, and temperature information of the battery pack are collected to realize the control and management of the battery pack charging process; The charging circuit carried by the mobile inspection robot includes a power-on buffer circuit, a primary push-pull conversion circuit, a rectifier circuit, a voltage feedback loop, a current feedback loop, and a sequential start control circuit; the circuit adopts the potting method.

2. The underground safety charging method for the battery pack of a coal mine inspection robot according to claim 1, characterized in that: The primary push-pull conversion circuit, the voltage feedback loop, and the rectifier circuit constitute an isolated switch power conversion circuit; U1 is a push-pull switch power control chip, which outputs two PWM signals to control switch tubes Q2 and Q3 to complete the push-pull type switch power conversion; the voltage feedback circuit composed of the input end OP3A of the optocoupler and diode D8 is used to stabilize the output voltage of the switch power supply; the rectifier circuit composed of diode D6, diode D7, inductor L1, and capacitor C6 is used to rectify the pulsating voltage after isolation transformation into a DC voltage; the FB pin of the U1 chip is the inverting input terminal of the error amplifier. When the potential of this pin is high, the U1 chip stops working and thus turns off the output of the switch power supply voltage. This pin is used as the enable control terminal for whether the switch power supply works.

3. A method for safely charging a battery pack of a coal mine inspection robot underground according to claim 2, characterized in that: The current feedback loop includes a current detection and current comparison circuit. The current feedback loop detects the output current of the positive pole of the combined power supply, and at the same time outputs 4 feedback signals to the 4-way switched-mode power supply conversion circuit, so that the output currents of the 4-way isolated switched-mode power supplies are always kept consistent; when the output current of the combined power supply is less than the maximum output current Imax, no feedback signal is output, and each switched-mode power supply operates in voltage mode to ensure that the output voltage is stable within a certain range; Imax = 0.7 / R23; when the output current of the combined power supply reaches the output current Imax, the output feedback signal is sent to the control pin COMP of the 4-way switched-mode power supply conversion control chip, and the control chip makes the output current of the combined power supply stable at Imax.

4. A method for safely charging a battery pack of a coal mine inspection robot underground according to claim 3, characterized in that: The sequential startup control circuit is an output voltage detection circuit; When the voltage value between the positive and negative connection points PWR1+ and PWR1- of the output voltage of the first switched-mode power supply is greater than a certain value, the optocoupler OP3 conducts and outputs an unlocking signal; this unlocking signal is input to the working enable control terminal of the next-stage switched-mode power supply to unlock it and normally start this switched-mode power supply; And so on, to achieve the top-down sequential startup of the 4-way isolated push-pull switched-mode power supplies, so as to gradually establish the output voltage between PWR1+ and the negative connection point PWR4- of the output voltage of the fourth switched-mode power supply.

5. A method for safely charging a battery pack of a coal mine inspection robot underground according to claim 4, characterized in that: The charging circuit carried by the mobile inspection robot consists of a BUCK power supply conversion circuit, current detection, voltage detection and a single-chip microcomputer; The switching transistor Q6, the switching transistor Q7 and the peripheral drive circuit constitute the BUCK power supply conversion circuit. U4 is a synchronous drive chip to make Q7 work in the synchronous switching state to reduce the switching loss of the BUCK power supply; R15 is a current detection resistor, and U3 is a current amplification chip, and the output signal is used for the single-chip microcomputer to monitor the charging current; R17 and R18 are voltage dividing resistors for the single-chip microcomputer to monitor the real-time charging voltage; the single-chip microcomputer outputs a PWM signal to control Q6 for BUCK power supply conversion in real time by collecting voltage and current signals to complete the charging control of the battery pack.

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