Aircraft door closing impact force control device and method based on lvdt

Abstract

The application discloses a kind of LVDT-based aircraft cabin door closing impact force control device and method, including LVDT signal conditioning circuit, speed feedback acquisition circuit, motor phase current acquisition circuit, FPGA main control circuit.After closing approach to position, cabin door lower edge protruding part and LVDT sensor start contact, until cabin door edge is completely compressed sealing strip, full displacement is converted into voltage signal through signal conditioning circuit, while monitoring the speed feedback and motor phase current of rotary variable sensor, according to algorithm in main control circuit inside Generation meets the speed instruction of impact force, send to closing speed control device.The control and regulation of impact force of the application are faster, there is a leap in reliability index, and do not increase the cost of cargo door actuating system, easy to realize.

Description

TECHNICAL FIELD

[0001] The application relates to an LVDT-based aircraft cabin door closing impact force control device and method, and belongs to the technical field of cabin door control. BACKGROUND

[0002] An aircraft cabin door mainly includes boarding doors (including boarding doors with door-ladder integrated boarding doors) and service doors, and is mainly composed of a cabin door structure, a mechanism, an alarm indication, a driving device, a sealing device and the like. In order to meet the requirements of passenger personal luggage transportation, container cargo holds or bulk cargo holds are arranged at different positions of a large civil aircraft body, and belong to service doors. There are cargo doors and openings of different sizes, shapes, functions and bearing modes on the aircraft body, generally, large cargo doors are arranged on the front aircraft body, and large cargo doors and bulk cargo doors are often arranged on the middle and rear aircraft body. The cabin doors on the aircraft are not only numerous, but also have a very large self weight. For example, the front cargo door of a Boeing 737-800 weighs 3558 Kg, and the rear cargo door weighs 4850 Kg. The self weight of the front and rear cabin doors of some civil aircrafts is close to 20000 Kg, which inevitably requires the application of an auxiliary driving device. Meanwhile, safety is the first priority in the development of the civil aviation industry, and is also the first consideration in the design of a civil aircraft.

[0003] A cabin door actuating system is an auxiliary driving device for cabin doors, and relevant enterprises at home and abroad are developing advanced and safe cabin door actuating systems. Saab Aircraft Structures has developed a new type of electromechanical actuating system to replace the traditional hydraulic actuating system, thereby reducing the cost in the maintenance process and ensuring that the cabin door weight and cost remain basically unchanged. Curtiss-Wright provides a rotary actuator for opening and closing of a cabin door, which is widely used in Airbus A380, and the technology focuses on reducing noise and vibration when opening and closing the lower cargo door of the aircraft body, and a patented transmission design is adopted, which is similar to the transmission device on the surface of a control flight control table. SUMMARY

[0004] The application solves the technical problem of overcoming the deficiencies of the prior art, and proposes an LVDT-based aircraft cabin door closing impact force control device and method, which controls the closing of the cabin door and keeps the impact force below a threshold value when the cabin door is closed.

[0005] The technical solution of the application is as follows:

[0006] An LVDT-based aircraft cabin door closing impact force control device, comprising an LVDT sensor, an LVDT signal conditioning circuit, a speed feedback acquisition circuit, a phase current acquisition circuit and an FPGA main control circuit.

[0007] The LVDT sensor is installed at the lower edge of the aircraft door frame, and is used to sense the thickness of the sealing strip on the door frame, i.e. the distance between the door frame and the door, and convert the distance information into an alternating feedback signal;

[0008] The LVDT signal conditioning circuit generates an excitation signal and sends it to the LVDT sensor, receives the alternating feedback signal of the LVDT sensor and outputs a voltage quantity linearly related to the distance quantity, and sends the voltage quantity to the FPGA master control circuit;

[0009] The phase current acquisition circuit acquires the phase current of the motor used to control the movement of the door, and sends it to the FPGA master control circuit after digital-to-analog conversion;

[0010] The speed feedback detection circuit measures the rotational speed of the motor, converts the thickness sensed by the LVDT sensor into the movement speed of the door and sends it to the FPGA master control circuit;

[0011] The FPGA master control circuit generates a speed command according to the received current voltage quantity, phase current and door movement speed, and outputs it to the door electromechanical actuator controller, so as to control the impact force by adjusting the movement speed of the door.

[0012] Preferably, the FPGA master control circuit generates a speed command according to the received current voltage quantity, phase current and door movement speed, and outputs it, specifically including:

[0013] According to the current door movement speed, it is judged whether the following formula is satisfied:

[0014]

[0015] In the formula, V is the current door movement speed; f d is the force of the self-weight of the aircraft door converted to the extrusion of the door sealing strip; f m is the closing force actively applied by the electromechanical actuator, which is obtained by converting the current phase current; f x is the elastic deformation extrusion force of the sealing strip, which is obtained according to the current voltage quantity; m is the total mass of the door and the actuating mechanism; and Δt is the closed-loop period of the motor control driver;

[0016] If the formula is satisfied and the door movement speed is greater than the set minimum speed, the FPGA master control circuit does not output a speed adjustment command;

[0017] If the formula is satisfied and the door movement speed is less than the set minimum speed, the FPGA master control circuit outputs a speed adjustment command and sends a speed increase command to the motor control driver, and the value after the speed increase is greater than the set minimum speed;

[0018] If the formula is not satisfied, the FPGA master control circuit outputs a speed adjustment instruction, and sends a speed reduction instruction to the motor control driver.

[0019] Preferably, the elastic deformation extrusion force f of the sealing strip is calculated x :

[0020]

[0021] Wherein:

[0022]

[0023]

[0024]

[0025] L is the thickness of the sealing strip, which is converted according to the voltage; Delta L is the deformation amount of the sealing strip in the extrusion direction; C mn is the Mooney material model parameter, which is obtained by data fitting, m and n are the expansion coefficients under the second-order model, C 00 is 0.

[0026] Preferably, the speed feedback detection circuit comprises a rotary variable sensor, which obtains the rotation angle of the motor, and obtains the cabin door moving speed according to the reduction ratio of the speed reducer connected with the motor and the thickness sensitive to the LVDT sensor.

[0027] Preferably, the FPGA master control circuit converts the output torque of the motor through the current phase current, motor parameters and working state, and obtains the door closing force actively applied by the electromechanical actuator.

[0028] Preferably, the LVDT sensor is installed at the lower edge of the aircraft cabin door frame, and there is a wedge-shaped protrusion at the corresponding position of the lower side of the cabin door in the closed state. During the closing process, the protrusion starts to contact the end of the spring strut of the LVDT, extrudes the strut, the strut extrudes the sealing strip, and the LVDT sensor sensitively senses the current thickness of the sealing strip in real time.

[0029] An aircraft cabin door closing impact force control method based on LVDT is applied to an aircraft cabin door closing impact force control device, comprising:

[0030] The LVDT sensor is powered on, and the cabin electromechanical actuator receives the instruction to control the cabin door to perform the closing action.

[0031] The FPGA master control circuit monitors the distance data sensitive to the LVDT sensor. When the distance data reaches a preset first threshold value, the FPGA master control circuit sends a start instruction, and the LVDT signal conditioning circuit, the speed feedback acquisition circuit and the phase current acquisition circuit start working.

[0032] The FPGA master control circuit estimates the door closing force of the door frame according to the received current voltage, phase current and door moving speed. If the door closing force exceeds a preset maximum allowable threshold value, the FPGA master control circuit sends an emergency braking instruction to the door electromechanical actuator controller, and the door stops moving. Otherwise, the FPGA master control circuit generates a speed instruction and outputs it to the door electromechanical actuator controller, and the door electromechanical actuator controller controls the motor output current, and the door continues to perform the door closing action.

[0033] When the FPGA master control circuit monitors that the door moving speed is less than a set closing-to-position speed and the phase current is greater than a set closing-to-position current, it is determined that the door has been closed to position, and the FPGA master control circuit sends a to-position instruction to the door electromechanical actuator controller, and the door stops moving.

[0034] Preferably, the FPGA master control circuit performs multi-objective optimization of fast door closing at maximum speed and maximum reduction of impact force, generates a speed instruction every period, and the specific method is as follows:

[0035] The FPGA master control circuit generates a speed instruction in the first period t0, adjusts the door closing speed to the maximum allowed value, calculates the door closing force actively applied by the electromechanical actuator in the next period t1, and if the door closing force is less than the preset maximum allowable threshold value, no speed instruction is output in the current period. Otherwise, the door closing speed is adjusted downward, and a speed instruction is generated.

[0036] In the subsequent period, the FPGA master control circuit judges:

[0037]

[0038] In the formula, V is the current door moving speed; f d is the force of the self-weight of the aircraft door converted to the extrusion of the sealing strip; f m is the door closing force actively applied by the electromechanical actuator, which is obtained by converting the current phase current; f x is the elastic deformation extrusion force of the sealing strip, which is obtained according to the current voltage; m is the total mass of the door and the actuator mechanism; and Δt is the closed-loop period of the motor control driver.

[0039] If the formula is satisfied and the door moving speed is greater than a set minimum speed, the FPGA master control circuit does not output a speed adjustment instruction in the current period.

[0040] If the formula is satisfied and the cabin door moving speed is less than the set minimum speed, the FPGA master control circuit outputs a speed adjustment instruction in the current period, sends a speed increasing instruction to the motor control driver, and the speed after increasing is greater than the set minimum speed;

[0041] If the formula is not satisfied, the FPGA master control circuit outputs a speed adjustment instruction in the current period, sends a speed decreasing instruction to the motor control driver, and the speed after decreasing satisfies the formula and is not less than the set minimum speed.

[0042] Preferably, the door closing speed is decreased or increased, and the decrease value or increase value is 20% of the current moving speed.

[0043] Preferably, the FPGA master control circuit monitors distance data sensitive to the LVDT sensor, and when the distance data reaches a preset first threshold, the FPGA master control circuit sends a starting instruction, and the first threshold is that the distance between the door frame and the cabin door is 4mm-6mm.

[0044] Compared with the prior art, the application has the following advantages:

[0045] (1) Compared with the traditional hydraulic scheme, the application has faster response speed of generating speed instructions, faster control and adjustment of impact force, and great improvement in reliability indicators, without increasing the cost of the cargo door actuating system and being easy to implement.

[0046] (2) The application introduces the elastic deformation of the rubber sealing ring as a parameter to more accurately measure the cabin door impact force.

[0047] (3) The application installs an LVDT sensor at the lower edge of the aircraft cabin door frame to realize real-time monitoring of the relative position of the cabin door and the door frame. BRIEF DESCRIPTION OF DRAWINGS

[0048] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments and are not intended to limit the scope of the application. Moreover, like reference numerals designate like parts throughout the several views in the drawings. In the drawings:

[0049] Figure 1 The figure is a principle block diagram of the cabin door actuating system of the embodiment of the application;

[0050] Figure 2 The figure is a collision control sub-circuit block diagram of the embodiment of the application;

[0051] Figure 3 The figure is a collision control method flowchart of the embodiment of the application. DETAILED DESCRIPTION

[0052] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0053] This invention proposes an aircraft cabin door closing impact force control device based on LVDT (Low-Level Transformer), comprising an LVDT signal conditioning circuit, a speed feedback acquisition circuit, a motor phase current acquisition circuit, an FPGA main control circuit, and a speed command generation algorithm. During closing, as the door approaches its final position, the protruding part of the lower edge of the door begins to contact the end of the LVDT spring rod until the door edge completely compresses the sealing strip. The entire displacement is converted into a voltage signal by the signal conditioning circuit. Due to the parallel computing characteristics of the FPGA, the speed feedback from the resolver sensor and the motor phase current are monitored simultaneously. Within the main control circuit, a speed command satisfying the impact force is generated according to the algorithm and sent to the door closing speed control device. When the calculated impact force exceeds a preset threshold, a cut-off command is immediately sent, and the door is brought to an emergency stop and held stationary.

[0054] The aircraft door closing impact force control device is located inside the control actuator of the aircraft's actuation system. The aircraft actuation system, such as... Figure 1 As shown, it includes an actuator mechanism, a motor, a control driver, a sensor, and mounting fixtures. The control driver is connected to the airborne power supply and airborne equipment, collects sensor information and ground crew operation commands, and outputs alternating current through an inverter to control the motor to run at a certain speed and torque, thereby driving the hatch to open or close.

[0055] Aircraft door closing impact force control device, such as Figure 2 As shown, it includes an LVDT sensor, an LVDT conditioning circuit, a phase current acquisition circuit, a speed feedback detection circuit, and an FPGA main control circuit.

[0056] The LVDT sensor is installed on the lower edge of the aircraft door frame. A wedge-shaped protrusion is located at the corresponding position on the lower side of the door when it is closed. During closing, when the distance between the protrusion and the door frame exceeds a threshold of 1, the protrusion begins to contact the end of the LVDT's spring support rod. As the closing action continues, the protrusion continuously presses against the LVDT support rod; the opening process is the reverse. To maintain structural design compatibility with traditional non-contact proximity sensors, the threshold of 1 is set to 4mm–6mm, the same detection distance as traditional sensors.

[0057] The LVDT conditioning circuit generates an excitation signal and sends it to the LVDT sensor, which converts the displacement signal into an alternating feedback signal through electromagnetic interaction, and returns it to the LVDT conditioning circuit, which processes it into a voltage quantity linearly related to the displacement quantity, which is converted into an analog quantity by the A / D circuit and sent to the FPGA main control circuit.

[0058] The phase current acquisition circuit acquires two-phase current, which is converted into an analog quantity by the A / D circuit and sent to the FPGA main control circuit. According to the motor parameters and working state, the output torque of the motor is converted, and combined with the parameters of the hatch, the force on the hatch is obtained.

[0059] The speed feedback detection circuit uses a resolver sensor and a conditioning circuit to measure the speed of the motor, and converts it into the speed of the hatch closing according to the speed reduction ratio of the mechanism and the size ratio of the connecting rod, and transmits the data to the FPGA main control circuit.

[0060] The speed feedback detection circuit calculates the speed of the hatch according to the positions L1 and L2 of T1 and T2 of the LVDT according to the formula .

[0061] The FPGA main control circuit runs the program, executes the above acquisition process according to the timing, and generates a speed command output according to an innovative algorithm, thereby controlling the impact force of the cargo hatch.

[0062] The speed command needs to meet the following conditions according to the momentum theorem:

[0063]

[0064] In the formula, V is the moving speed of the aircraft hatch; f d is the force of the self-weight of the aircraft hatch converted to the extrusion of the hatch seal strip; f m is the closing force actively applied by the electromechanical actuator, which is obtained by converting the acquired current; f x is the elastic deformation extrusion force of the hatch seal strip; m is the total mass of the hatch and the actuating mechanism; Δt is the closed-loop period of the motor control driver.

[0065] The elastic deformation of the rubber seal ring is introduced as a parameter to more accurately measure the impact force of the hatch. The constitutive model of the rubber material uses a 2nd order Mooney strain energy function,

[0066]

[0067] In the formula, W is the strain energy function; C mn is the parameter of the Mooney material model, which is obtained by data fitting, m and n are the expansion coefficients under the 2nd order model, and C 00 is 0.

[0068] For simplicity, assume that the deformation of the cabin door rubber seal is uniaxial stretching, and the engineering stress can be simplified as:

[0069]

[0070] Here:

[0071]

[0072]

[0073]

[0074] λ represents elongation, L is the thickness of the seal, and ΔL is the deformation of the cabin door seal in the direction of extrusion, which is accurately measured by the LVDT sensor.

[0075] The LVDT-based aircraft cabin door closing impact force control method, as shown in Figure 3 , includes:

[0076] (1) After power-on, run the LVDT self-checking program to confirm that the circuit is working properly. Generally, one or more channels can be detected to form redundancy. If the self-checking does not pass, a warning message is issued to remind the ground crew to pay attention and handle it according to the operation manual; if the self-checking passes, the LVDT position, i.e. the position of the aforementioned lower edge of the cabin door, is continuously monitored.

[0077] (2) When reaching the preset position threshold 1, start parallel computing, and simultaneously calculate the phase current, motor rotor angle, and cabin door moving speed, estimate the impulse on the door frame according to kinematics knowledge; if the impact force is greater than the preset threshold 1, issue an emergency braking instruction to the control driver; if the impact force is less than the preset threshold 1, compare the seal deformation force database, calculate and output the speed instruction, and perform multi-objective optimization with maximum speed to quickly close the door and minimize the impact force;

[0078] Based on the parallel computing capability of FPGA, the speed instruction can be adjusted to the maximum allowed value at t0, and the actual feedback value f m of the electromechanical actuator at the next moment t1 is compared. This value should also be within the safe value, that is, within the maximum output current capability range of the motor control driver. If not, the speed instruction is reduced, and the process is repeated. The process of cabin door extrusion takes about 1-5 seconds, which requires fast calculation, so the calculation method of speed instruction reduction and increase is simplified, that is, increase or decrease by 20% of the current value, and at the same time ensure that the maximum speed allowed value for safe operation is not exceeded.

[0079] (3) When the position threshold 2 is reached, the door closing process ends; otherwise, the above operation is continued.

[0080] When the hatch is closed to the position and the rubber seal is pressed to a certain extent, the speed will approach 0 and the current will reach a certain value. Through actual measurement, the current value, position threshold 2, is not a specific position signal, but (speed less than a certain value, current greater than a certain value). Thus, it is determined that the door closing action should not continue, that is, the door has reached the position and meets the door latch locking condition of the hatch mechanism.

[0081] The above-described embodiments are only the preferred specific embodiments of the present application, and the usual changes and replacements made by those skilled in the art within the scope of the technical solutions of the present application should be included in the protection scope of the present application.

Claims

1. An LVDT-based aircraft door closing impact force control device, characterized by, The LVDT sensor, the LVDT signal conditioning circuit, the speed feedback acquisition circuit, the phase current acquisition circuit and the FPGA main control circuit are included. The LVDT sensor is installed at the lower edge of the door frame of the aircraft cabin door and is used for sensing the thickness of the sealing strip on the door frame, i.e. the distance between the door frame and the cabin door, and converting the distance information into an alternating feedback signal. The LVDT signal conditioning circuit generates an excitation signal and sends it to the LVDT sensor, receives the alternating feedback signal of the LVDT sensor and outputs a voltage quantity linearly related to the distance, and sends the voltage quantity to the FPGA main control circuit. The phase current acquisition circuit acquires the phase current of the motor used for controlling the movement of the cabin door, performs digital-to-analog conversion and sends the phase current to the FPGA main control circuit. The speed feedback detection circuit measures the rotating speed of the motor, converts the thickness sensed by the LVDT sensor into the movement speed of the cabin door and sends the movement speed to the FPGA main control circuit. The FPGA main control circuit generates a speed instruction according to the received current voltage quantity, phase current and movement speed of the cabin door, and outputs the speed instruction to the cabin door electromechanical actuator controller, so as to control the impact force by adjusting the movement speed of the cabin door. The FPGA main control circuit generates a speed instruction according to the received current voltage quantity, phase current and movement speed of the cabin door, and outputs the speed instruction, specifically including: According to the current movement speed of the cabin door, it is judged whether the following formula is satisfied: Wherein, V is the current door moving speed; f d is the force of the self-weight of the aircraft door converted to the extrusion of the door seal strip; f m is the closing force actively applied by the electromechanical actuator, which is obtained by converting the current phase current; f x is the elastic deformation extrusion force of the seal strip, which is obtained according to the current voltage; m is the total mass of the door and the actuating mechanism; and Δt is the closed-loop period of the motor control driver. If the formula is satisfied and the movement speed of the cabin door is greater than the set minimum speed, the FPGA main control circuit does not output the speed adjustment instruction; If the formula is satisfied and the movement speed of the cabin door is less than the set minimum speed, the FPGA main control circuit outputs the speed adjustment instruction, sends the speed increasing instruction to the motor control driver, and the speed after increasing is greater than the set minimum speed; If the formula is not satisfied, the FPGA main control circuit outputs the speed adjustment instruction, sends the speed decreasing instruction to the motor control driver, and the speed after decreasing satisfies the formula and is not less than the set minimum speed.

2. The LVDT-based aircraft door closure impact force control device of claim 1, wherein, The elastic deformation extrusion force f of the sealing strip is calculated x : Wherein: λ is the elongation; L is the thickness of the sealing strip, converted from the voltage quantity; ΔL is the deformation quantity of the sealing strip in the direction of extrusion; C mn is the Mooney material model parameter, obtained by data fitting, m and n are the expansion coefficients under the second-order model, and C 00 is 0.

3. The LVDT-based aircraft door closure impact force control device of claim 1, wherein, The speed feedback detection circuit includes a resolver sensor, which obtains the rotating angle of the motor, and obtains the movement speed of the cabin door according to the reduction ratio of the speed reducer connected with the motor and the thickness sensed by the LVDT sensor.

4. The LVDT-based aircraft door closure impact force control device of claim 1, wherein, The FPGA main control circuit converts the current phase current, motor parameters and working state into the output torque of the motor, and obtains the door closing force actively applied by the electromechanical actuator.

5. The LVDT-based aircraft door closure impact force control device of claim 1, wherein, The LVDT sensor is installed at the lower edge of the door frame of the aircraft cabin door, and a wedge-shaped protrusion exists at the corresponding position of the lower side of the cabin door in the closed state. During the closing process, the protrusion starts to contact the end of the spring support rod of the LVDT, extrudes the support rod, the support rod extrudes the sealing strip, and the LVDT sensor senses the current thickness of the sealing strip in real time.

6. A method for controlling the closing impact force of an aircraft door based on LVDT, applied to the aircraft door closing impact force control device of claim 1, characterized in that, Including: The LVDT sensor is powered on, and the cabin door electromechanical actuator receives the instruction to control the cabin door to perform the door closing action; The FPGA main control circuit monitors the distance data sensed by the LVDT sensor, and when the distance data reaches the preset first threshold, the FPGA main control circuit sends a start instruction, and the LVDT signal conditioning circuit, the speed feedback acquisition circuit and the phase current acquisition circuit start to work; The FPGA master control circuit estimates the door closing force of the door frame by the current voltage, phase current and door moving speed, and sends an emergency braking instruction to the door electromechanical actuator controller if the door closing force exceeds the preset maximum allowable threshold, so that the door stops moving; otherwise, a speed instruction is generated and output to the door electromechanical actuator controller, the door electromechanical actuator controller controls the motor output current, and the door continues to perform the door closing action. The FPGA master control circuit determines that the door has reached the closed position when the door moving speed is less than the set closing to position speed and the phase current is greater than the set closing to position current, and sends a to position instruction to the door electromechanical actuator controller, so that the door stops moving.

7. The aircraft door closing impact force control method according to claim 6, characterized in that, The FPGA master control circuit performs multi-objective optimization of fast closing at the maximum speed and minimizing the impact force, and generates a speed instruction every period, the specific method being: The FPGA master control circuit generates a speed instruction in the first period t0, and adjusts the door closing speed to the maximum allowed value; in the next period t1, the FPGA master control circuit calculates the door closing force actively applied by the electromechanical actuator, and if the door closing force is less than the preset maximum allowable threshold, the FPGA master control circuit does not output a speed instruction in the current period; otherwise, the FPGA master control circuit reduces the door closing speed and generates a speed instruction; In the subsequent period, if the formula is satisfied and the door moving speed is greater than the set minimum speed, the FPGA master control circuit does not output a speed adjustment instruction in the current period; Wherein, V is the current door moving speed; f d is the force of the aircraft door self-weight converted to the extrusion of the door seal strip; f m is the door closing force actively applied by the electromechanical actuator, which is obtained by converting the current phase current; f x is the elastic deformation extrusion force of the seal strip, which is obtained according to the current voltage; m is the total mass of the door and the actuating mechanism; Δt is the closed-loop period of the motor control driver; the impact force is f d +f m -f x ; If the formula is satisfied and the door moving speed is less than the set minimum speed, the FPGA master control circuit outputs a speed adjustment instruction in the current period, and sends a speed increase instruction to the motor control driver, and the speed after increasing is greater than the set minimum speed; If the formula is not satisfied, the FPGA master control circuit outputs a speed adjustment instruction in the current period, and sends a speed reduction instruction to the motor control driver, and the speed after reducing satisfies the formula and is not less than the set minimum speed. The door closing speed is reduced or increased, and the reduction value and the increase value are 20% of the current moving speed.

8. The aircraft door closing impact force control method according to claim 7, characterized in that, The FPGA master control circuit monitors the distance data sensitive to the LVDT sensor, and sends a start instruction when the distance data reaches the preset first threshold, and the first threshold is the distance between the door frame and the door of 4mm-6mm.

9. The method of claim 6, wherein, ​

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