System and method for judging air ground state of unmanned helicopter

Abstract

The invention provides a system and a method for judging the air ground state of an unmanned helicopter. The system comprises a skid type undercarriage, a satellite navigation sensor, a near-earth height sensor, a ground touch sensor, a flight control computer and a servo operation system. The skid type undercarriage is connected with the unmanned helicopter body through the ground contact sensor; the satellite navigation sensor provides positioning, direction finding and speed measuring for the unmanned helicopter and provides altitude data for high-altitude flight. The near-earth height sensor is used for measuring the relative height between the unmanned helicopter and the ground; the ground contact sensor is used for measuring the tension and pressure conditions borne by the undercarriage. The satellite navigation sensor, the near-earth relative height sensor and the ground touch sensor are used for redundancy design, sensor data are automatically switched and used according to the flight height, the system is used for judging the air ground state, and the system is suitable for flat ground, inclined field and ship-borne swing take-off and landing application and is high in reliability and engineering application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of unmanned aerial vehicle control, and in particular relates to a system and method for judging the air-ground state of an unmanned helicopter. Background Art

[0002] Unmanned helicopters have the advantages of vertical take-off and landing, fixed-point hovering, and flexible maneuverability. They are modular, easy to operate, simple to maintain, and have wide applicability. They have excellent performance in terms of endurance, flight ceiling, cruising speed, and mission payload. They can operate in specific areas for a long time and can be widely used in many fields such as emergency rescue, forest fire prevention, agricultural and forestry plant protection, maritime monitoring, material transportation and delivery, communication relay, power inspection, electronic reconnaissance, land surveying and mapping, meteorological and hydrological detection, etc.

[0003] Usually, the take-off and landing sites of unmanned helicopters are relatively narrow, and high control accuracy is required for take-off and landing, especially during the landing phase. Large control deviations may cause the unmanned helicopter to crash. The take-off and landing phases of unmanned helicopters are close to the ground. Due to the strong ground effect caused by the downwash of the main rotor acting on the ground, the airflow disturbance is enhanced, the power is reduced, and large position control deviations are caused. In order to improve the accuracy of take-off and landing control, it is necessary to distinguish between the control laws and control strategies for high-altitude and near-ground flights, and design control laws and control strategies based on the characteristics of near-ground flight airflow disturbances. Therefore, it is very necessary to establish a near-ground judgment system for unmanned helicopters and a ground-to-air state recognition system. Summary of the invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to provide a system and method for judging the ground state of an unmanned helicopter in the air in view of the deficiencies in the prior art, so as to realize the judgment of the unmanned helicopter's near-ground flight, the judgment of the unmanned helicopter's lift-off state during takeoff, and the judgment of the unmanned helicopter's landing during landing, provide data for the design of near-ground flight control laws and control strategies, and improve the take-off and landing precision control, flight safety, and reliability of the unmanned helicopter.

[0005] The present invention provides an unmanned helicopter air-ground state judgment system, comprising a skid-type landing gear, a satellite navigation sensor, a ground proximity sensor, a ground contact sensor, a flight control computer and a servo operating system;

[0006] The skid landing gear comprises an arched beam, left and right skid tubes and a push wheel bracket, the front and rear ends of the left and right skid tubes are respectively connected to the arched beam, the arched beams are connected through an intermediate connecting tube, and the push wheel bracket is installed on the left and right skid tubes corresponding to the center of the rotor main shaft of the unmanned helicopter;

[0007] The skid-type landing gear is a load-bearing component of the unmanned helicopter, and bears the entire weight and impact load of the unmanned helicopter during each take-off and landing;

[0008] The satellite navigation sensor is used for unmanned helicopter navigation, providing single-point positioning, differential positioning, altitude, speed and interference source detection data for the unmanned helicopter;

[0009] The ground proximity sensor is used to measure the relative ground height when the unmanned helicopter is flying close to the ground and when taking off and landing. The ground proximity sensor measurement is effective when the relative ground height is less than or equal to X meters, and is judged as the ground proximity when the relative ground height is less than or equal to Y meters. The ground proximity sensor is suitable for use in grass, cement, sand and water surfaces.

[0010] The ground contact sensor replaces the connecting piece between the skid-type landing gear and the fuselage of the unmanned helicopter in situ, and is conformally designed with the skid-type landing gear. On the one hand, it realizes the connection and fixation between the fuselage of the unmanned helicopter and the skid-type landing gear; on the other hand, it senses the tensile pressure loaded on the skid-type landing gear to judge the take-off and landing of the unmanned helicopter during the take-off and landing phases; from the perspective of the unmanned helicopter as a whole, the number, weight and cost of the whole machine parts can be reduced.

[0011] The satellite navigation sensor comprises a satellite antenna, a satellite receiver and a first communication module; the satellite antenna is connected to the satellite receiver via a radio frequency cable, and the satellite receiver is connected to the first communication module via a serial bus.

[0012] The ground proximity sensor comprises a microstrip antenna, a transmitting branch, a receiving branch, a frequency synthesis module, a signal processing module, an MCU control module and a second communication module;

[0013] The microstrip antenna is connected to a transmitting branch and a receiving branch through a radio frequency cable, and the transmitting branch, the receiving branch, the frequency synthesis module, the signal processing module, the MCU control module and the second communication module are connected through a printed circuit board;

[0014] The ground contact sensor includes an elastic body, a strain sensor, a conditioning circuit board, a cable, an electrical connector and a cover plate;

[0015] The strain sensor is pasted in the elastomer, the strain sensor is connected to the conditioning circuit board through a cable, the conditioning circuit board is installed in the middle cavity of the elastomer, the electrical connector is connected to the conditioning circuit board through the through hole of the elastomer by a cable, and the cover plate is installed above the middle cavity of the elastomer by screws;

[0016] The ground contact sensor senses the force between the fuselage of the unmanned helicopter and the skid-type landing gear through the elastic body;

[0017] The strain sensor outputs an electrical signal, which is conditioned by a conditioning circuit board to output the real-time landing gear force condition to the flight control computer.

[0018] The flight control computer is a redundant flight control computer, comprising a power module, a data acquisition module, a central processing module and a third communication module;

[0019] The power module, the data acquisition module, the central processing module and the third communication module are connected via a printed circuit board;

[0020] The power supply module provides power excitation for the data acquisition module, the central processing module and the third communication module;

[0021] The data acquisition module acquires the tension pressure voltage signal input by the ground contact sensor, and the 12-bit ADC converts the analog signal into a digital signal and inputs it into the central processing module;

[0022] The third communication module is used to receive ground proximity sensor data and send control data to the servo controller;

[0023] The central processing module determines whether the unmanned helicopter is flying near the ground or at high altitude according to the near-ground height data, and executes corresponding control laws and control strategies;

[0024] The central processing module calculates the voltage signal input by the ground contact sensor to obtain a tension signal, compares the tension value with a preset threshold value, and determines the ground state of the unmanned helicopter in the air. The preset threshold range is 50kg to 600kg.

[0025] The central processing module calculates the servo travel setting value according to the ground altitude and the ground-air state, and sends it to the servo control system through the communication module to change the power of the unmanned helicopter to achieve take-off and landing.

[0026] The servo operating system includes a servo controller, a pitch servo, a roll servo and a tail rotor servo;

[0027] The servo controller is connected to the pitch servo, the roll servo and the tail rotor servo via cables;

[0028] The servo controller receives flight control computer control data, steering gear drive control, collects steering gear motion position, and performs built-in test (BIT) detection and fault alarm;

[0029] The pitch servo is used to control the pitch direction movement of the main rotor of the unmanned helicopter;

[0030] The roll servo is used to control the rolling direction movement of the main rotor of the unmanned helicopter;

[0031] The tail rotor servo is used to control the heading direction of the tail rotor of the unmanned helicopter;

[0032] The pitch servo and roll servo are used to control the collective pitch of the unmanned helicopter;

[0033] The servo controller controls the pitch servo, roll servo and tail rotor servo according to the control instructions of the flight control computer, adjusts the collective pitch and tail rotor pitch of the unmanned helicopter, and then adjusts the rotor lift and attitude to achieve take-off or landing of the unmanned helicopter.

[0034] The working process of the ground contact sensor includes:

[0035] Step 1, the conversion process from the tensile force to the resistance change of the resistance strain gauge, specifically includes:

[0036] When the ground contact sensor is subjected to force, the tensile pressure acts on the elastic body of the force sensor, causing the elastic body to produce tensile and compressive strains. The strain is calculated by the material mechanics formula:

[0037] ε=σ / E=F / (Α×E),

[0038] Where ε represents strain; σ represents stress; E represents the elastic modulus of the material; F represents force; Α represents the structural parameter expression;

[0039] The tensile and compressive strains cause the sensitive grid of the metal foil resistive strain sensor pasted on the elastic body to deform. The resistance R of the metal sensitive grid is proportional to the length L and inversely proportional to the cross-sectional area S, that is, R = ρL / S, where ρ represents the resistivity. When the metal sensitive grid is elongated by dL due to deformation, the cross-sectional area will be reduced by dS accordingly. d represents the differential. Differentiating R = ρL / S, the relative change of the sensitive grid resistance is dR / R = dL / L-dS / S. Because dS / S = 2dr / r, where r is the cross-sectional structural size of the metal sensitive grid, the axial strain of the metal sensitive grid is ε = dL / L, which is obtained from material mechanics: dr / r = -με,

[0040] Where μ is the Poisson's ratio of the metal sensitive gate material, so dR / R=(1+2μ)ε;

[0041] Let the sensitivity coefficient K of the resistance strain gauge be:

[0042] K=(dR / R) / ε

[0043] get:

[0044] dR=KRε,

[0045] The resistance strain gauge linearly converts the tensile and compressive strain of the elastic body caused by the tensile pressure into the change in the resistance value of the resistance strain sensor through the deformation of the sensitive grid.

[0046] Step 2, the measurement process of electrical quantities: The circuit part of the force sensor is composed of four resistance strain gauges attached to different parts of the elastic body, that is, a Wheatstone bridge. The relationship between the output voltage U0 and the power supply voltage U is:

[0047] When the tension is zero, R1=R2=R3=R4, where R1, R2, R3 and R4 are all the resistance values ​​of the strain gauge, the Wheatstone bridge is balanced, and the output voltage U0 is zero; when there is tension, the elastic body strain causes the strain gauge resistance value to change dR, the Wheatstone bridge is unbalanced, and the output voltage U0 is:

[0048] U0=U(dR4-dR3+dR2-dR1) / 4R,

[0049] Where dR1, dR2, dR3, and dR4 are the resistance changes of the resistance strain gauge;

[0050] Let dR4=-dR3=dR2=-dR1=dR, and we get: U0=U×dR / R;

[0051] The Wheatstone bridge composed of four resistance strain gauges attached to different parts of the elastic body converts the resistance change into a voltage signal output. When the force sensor senses the pulling pressure, the Wheatstone bridge outputs a voltage signal that is linearly related to the pulling pressure. The signal conditioning circuit is used to filter, amplify, and compensate the force sensor signal before output.

[0052] The signal conditioning circuit comprises an input filtering circuit, a pre-stage amplifier circuit, a post-stage amplifier circuit and an output filtering circuit; the output signal of the strain gauge sensor is first filtered out of interference by the input filtering circuit, and then the pre-stage amplifier circuit composed of an instrument amplifier and a bias circuit performs pre-stage amplification and zero adjustment; the post-stage amplifier circuit composed of a rail-to-rail operational amplifier and a precision metal film resistor performs secondary amplification on the output signal of the force sensor, and the secondary amplified output signal is filtered by the output filtering circuit (second-order active filtering circuit).

[0053] The satellite navigation sensor adopts the BeiDou-3 satellite navigation system, supports single-point and differential positioning, and has an anti-spoofing function;

[0054] The ground proximity sensor is a millimeter wave radar;

[0055] The millimeter-wave radar is horizontally installed on the belly of the unmanned helicopter, with a beam width of tens of degrees, a close-range measurement accuracy of centimeters, and a working frequency band of millimeter waves.

[0056] The elastic body is a curved beam structure, the upper end of which is connected to the fuselage of the unmanned helicopter by screws, and the lower end is connected to the skid-type landing gear by screws, and the strain sensors are attached to the left and right end surfaces of the elastic body to form a Wheatstone bridge;

[0057] The strain sensor is a resistance strain sensor, which converts the push-pull force into a voltage signal by using the unbalanced Wheatstone bridge according to Hooke's law and the resistance strain principle, and outputs a millivolt voltage signal that is linearly proportional to the push-pull force;

[0058] The conditioning circuit board provides an excitation voltage for the Wheatstone bridge of the resistance strain sensor, and filters, amplifies, and compensates the millivolt voltage signal output by the resistance strain sensor and then outputs it to the flight control computer.

[0059] The present invention also provides a method for judging the ground state of an unmanned helicopter in the air, comprising: after the unmanned helicopter receives a landing instruction, it starts to execute a landing program, a flight control computer collects and receives satellite navigation sensor data, ground proximity sensor signals and ground contact sensor signals in real time, and the unmanned helicopter switches from an automatic cruise mode to an automatic landing mode when automatically landing, and the switching forms are automatic cruise flight, hovering, and autonomous landing, and the control law is vertical speed control (altitude monitoring) to landing processing; the unmanned helicopter dives down from a high altitude to near the landing height, stops and keeps hovering just above the landing point through deceleration control, and descends at a constant speed after being stable for a certain period of time. During the descent, the position holding loop and the attitude loop are both connected; the ground proximity sensor is used to observe the landing gear and The distance between the ground and the ground, when the flight altitude drops to X meters, the flight control software sets the ground proximity sensor data to be valid, and determines whether the altitude reaches the ground proximity altitude of Y meters. If it does not reach it, the high-altitude flight control law and control strategy will continue to be executed, and the flight will continue to descend. If it is determined to be near the ground, the vertical descent speed will be slowed down, the integral control will stop working, and the skid landing gear pressure will be judged by the ground contact sensor to determine whether it is greater than the threshold value Z. If it is not greater than the threshold value Z, the ground proximity landing procedure will continue to be executed. When the pressure value is greater than the threshold value Z, it is determined that the landing gear has touched the ground, and the flight control computer sends a steering gear control command to the servo control system to quickly reduce the vertical channel total distance, the longitudinal channel pitch lock, the lateral channel pitch lock, the heading channel maintains zero angular velocity and executes the parking finger procedure to complete the landing of the unmanned helicopter;

[0060] In the event of high ground wind speed, large tilt of the landing site or shaking of the landing site (such as a ship deck), the total pitch is slowly lowered. After the landing gear partially touches the ground, the flight control program automatically and in real time adjusts the propeller disc plane based on feedback from the skid-type landing gear ground contact sensor, so that the landing gear plane and the landing site plane remain dynamically approximately parallel, thereby achieving rapid landing and ensuring landing safety.

[0061] Furthermore, the system also includes control software, which includes a system layer, a management layer, an application layer and a data interface layer, wherein the system layer adopts a real-time operating system, the management layer includes interrupt priority management, clock management, task management and exception management, the application layer includes sensor signal acquisition and resolution, ground and air judgment, control law and control strategy design, servo drive control, communication, BIT detection and alarm, etc., and the data interface layer is the processing function of each functional module corresponding to the peripherals, including power interface, I / O interface, USART interface, ADC interface, etc.

[0062] The present invention has the following beneficial effects: (1) The method and system for determining the ground state of an unmanned helicopter in the air proposed in the present invention establish a near-ground determination and ground state recognition sensing system in the air, providing important support for the design of flight control laws and control strategies;

[0063] (2) The present invention solves the problem of large position control deviation caused by the downwash effect of the main rotor when the unmanned helicopter is flying close to the ground, thereby improving the take-off and landing control accuracy and safety of the unmanned helicopter;

[0064] (3) When an unmanned helicopter is landing, if the ground wind speed is high, the landing site is tilted at a large angle, or the landing site is shaking (such as a ship deck), the helicopter can slowly descend the collective pitch and, based on the landing information fed back by the ground touchdown sensor, the flight control program can automatically and in real time adjust the propeller disc plane so that the landing gear support plane and the landing site plane are dynamically kept approximately parallel, thus achieving rapid landing and ensuring landing safety.

[0065] (4) The present invention uses satellite navigation sensors, ground-proximate relative height sensors and ground contact sensors for redundancy design, autonomously switches to use sensor data according to flight altitude, and uses the system to determine the ground status in the air. It is suitable for flat ground, inclined sites and ship-borne swing take-off and landing applications, has high reliability and high engineering application value;

[0066] (5) The ground contact sensor in the present invention is designed to be conformal with the landing gear. The sensor is small in size and light in weight while ensuring strength, rigidity, electromagnetic compatibility and measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0068] Figure 1 The figure is a schematic diagram of the composition of the unmanned helicopter air-ground state judgment system of the present invention.

[0069] Figure 2 Workflow chart of the method for determining the air-ground state of an unmanned helicopter according to the present invention.

[0070] Figure 3 This is a structural diagram of the skid-type landing gear.

[0071] Figure 4 This is the working principle diagram of the ground contact sensor.

[0072] Figure 5 It is the relationship diagram between the output voltage U0 and the power supply voltage U. DETAILED DESCRIPTION

[0073] like Figure 1 As shown, an embodiment of the present invention provides an unmanned helicopter air-ground state judgment system, including a skid landing gear, a satellite navigation sensor, a ground proximity sensor, a ground contact sensor, a flight control computer and a servo operating system. The skid landing gear includes a bow beam (i.e. Figure 3 1, 2, 3, 4), left and right slide tubes (i.e. Figure 3 5, 6) and the push wheel bracket (i.e. Figure 3 7 and 8), for the convenience of transportation, the push wheel bracket is installed at the center of the main shaft. In order to reduce overload and better meet the requirements of buffer performance, the left and right arched beams are connected through the middle connecting pipe (i.e. Figure 39 and 10) are connected, the skid landing gear is connected to the fuselage of the unmanned helicopter through a ground contact sensor, and bears the entire weight and impact load of the unmanned helicopter; the satellite navigation sensor adopts the Beidou-3 satellite navigation system, has a four-element anti-interference antenna, and the satellite receiver (baseband chip BP2020) is integrated with the antenna and embedded in the antenna equipment to provide positioning, direction finding, speed measurement and altitude data for high-altitude flight for the unmanned helicopter; the ground proximity sensor is a millimeter wave radar, which is composed of a microstrip antenna, a transmitting branch, a receiving branch, a frequency synthesis module, a signal processing module, an MCU control module and a communication module (core device CAL77S224-HJ), and realizes the relative ground height measurement of the unmanned helicopter during close-to-ground flight, which is an important basis for the switching of the control law and control strategy of the unmanned helicopter during close-to-ground flight and high-altitude flight; the ground contact sensor is composed of an elastomer, a strain sensor (BYM350-1AA(11)N4-C), a conditioning circuit board, a cable, an electrical connector and a cover plate, and is conformally designed with the skid landing gear, as a connection between the fuselage of the unmanned helicopter and the skid. The skid landing gear connecting component senses the force between the unmanned helicopter fuselage and the skid landing gear through an elastic body, and the strain sensor outputs an electrical signal, and the real-time landing gear force condition is output to the flight control computer through conditioning of a conditioning circuit board; the flight control computer is a redundant flight control computer, which is composed of a power module, a data acquisition module, a central processing module (STM32F407) and a communication module. The data acquisition module calculates the voltage signal input by the ground contact sensor to obtain a tensile pressure signal, compares the tensile pressure value with a preset threshold value, judges the ground and air state of the unmanned helicopter, judges whether the unmanned helicopter is flying near the ground or at high altitude according to the near-ground height data, executes the corresponding control law and control strategy accordingly, and sends a control instruction to a servo operating system; the servo operating system is composed of a servo controller (main control device STM32F105), a pitch servo, a roll servo and a tail rotor servo, controls the pitch servo, the roll servo and the tail rotor servo according to the control instruction of the flight control computer, adjusts the total pitch and tail rotor pitch of the unmanned helicopter, and then adjusts the rotor lift and attitude to achieve take-off or landing of the unmanned helicopter.

[0074] The satellite navigation sensor antenna is installed on the upper surface of the tail pipe of the unmanned helicopter, keeping the antenna array horizontal and facing upward.

[0075] The front and rear ends of the left and right skid tubes of the skid landing gear are respectively connected to two arched beams, and the front and rear arched beams on the left and right sides are connected through a middle connecting pipe, and the material is titanium alloy;

[0076] Four ground contact sensors (i.e. Figure 311, 12, 13, 14) are designed in conformity with the skid landing gear. The lower end is installed on the arch beam of the skid landing gear with a ball head locking pin, and a pin spring is used to prevent loosening. The upper end is connected to the unmanned helicopter body through three M5 screws, and the skid landing gear and the unmanned helicopter body are assembled into a whole; four resistance strain sensors are pasted on the end faces of the left and right beams to form a Wheatstone bridge, which converts the tension and pressure signals into voltage signals. The working principle of the ground contact sensor is as follows Figure 4 As shown, including:

[0077] Step 1, the conversion process from tensile pressure to resistance change of resistance strain gauge (resistance strain measurement principle);

[0078] When the ground contact sensor is subjected to force, the tensile pressure acts on the elastic body of the force sensor, causing the elastic body to produce tensile and compressive strains. The strain is calculated using the material mechanics formula: ε = σ / E = F / (Α × E).

[0079] Where ε represents strain; σ represents stress; E represents the elastic modulus of the material; F represents force; and Α represents the structural parameter expression.

[0080] The tensile and compressive strains cause the sensitive grid of the metal foil resistive strain sensor pasted on the elastic body to deform. It is known from physics that the resistance R of the metal sensitive grid is proportional to the length L and inversely proportional to its cross-sectional area S, that is, R = ρL / S, where ρ represents resistivity, R represents resistance, L represents length, and S represents cross-sectional area. When the metal sensitive grid is elongated by dL due to deformation, its cross-sectional area will be reduced by dS accordingly, and d represents differential. The change in resistivity ρ is very small and can be ignored. Differentiating R = ρL / S, the relative change in sensitive grid resistance is dR / R = dL / L-dS / S, because dS / S = 2dr / r, where r is the cross-sectional structural size of the metal sensitive grid, and the axial strain ε of the metal sensitive grid is dL / L. From material mechanics, we get: dr / r = -με,

[0081] Where μ is the Poisson's ratio of the metal sensitive gate material, so dR / R=(1+2μ)ε;

[0082] Let the sensitivity coefficient K of the resistance strain gauge (resistance strain measurement principle, i.e. resistance strain effect) be:

[0083] K=(dR / R) / ε

[0084] get:

[0085] dR=KRε.

[0086] It can be seen that the resistance strain gauge linearly converts the tensile and compressive strain of the elastic body caused by the tensile pressure into the change in the resistance value of the resistance strain gauge through the deformation of the sensitive grid.

[0087] Step 2, the measurement process of electrical quantities;

[0088] The circuit part of the force sensor, the Wheatstone bridge, consists of resistance strain gauges attached to different parts of the elastic body, such as Figure 5 As mentioned above, the relationship between the output voltage U0 and the power supply voltage U is:

[0089] When the tension is zero, R1=R2=R3=R4, the Wheatstone bridge is balanced, and the output voltage U0 is zero. When there is tension, the elastic body strain causes the strain gauge resistance to change dR, the Wheatstone bridge is unbalanced, and the output voltage U0=U(dR4-dR3+dR2-dR1) / 4R, where dR1, dR2, dR3, and dR4 are the resistance changes of the resistance strain gauge. According to the electrical principle of resistance strain measurement, let dR4=-dR3=dR2=-dR1=dR, and we can get: U0=U×dR / R.

[0090] The Wheatstone bridge composed of four resistance strain gauges attached to different parts of the elastic body converts the resistance change into a voltage signal output. When the force sensor senses the tensile pressure, the Wheatstone bridge outputs a voltage signal that is linearly related to the tensile pressure, and the signal is only at the millivolt level. Therefore, a signal conditioning circuit is required to filter, amplify, compensate, and process the force sensor signal before output.

[0091] The signal conditioning circuit is mainly composed of input filter circuit, pre-amplifier circuit, post-amplifier circuit and output filter circuit. The output signal of the strain gauge sensor is first filtered out by the input filter circuit, and then the pre-amplifier circuit composed of the instrument amplifier and the bias circuit performs pre-amplification and zero adjustment. The post-amplifier circuit composed of the rail-to-rail operational amplifier and precision metal film resistor performs secondary amplification on the output signal of the force sensor. The secondary amplified output signal is filtered by the second-order active filter circuit.

[0092] The ground contact sensor has a measuring range of 0 to 300 kg, a limit load of 600 kg, a measurement accuracy of not less than 10% F·S, an output voltage of +2V for a pressure of 300 kg, an output voltage of +8V for a tension of 300 kg, and an output of 5V when no force is applied (zero position). The power supply is +12V, and the power consumption is 2.13W. The metal material of the ground contact sensor elastic body and the upper cover plate are made of aluminum alloy 2A12-T4, and the left and right covers of the sealed sensor patch area are made of stainless steel strip 06Cr19Ni10. The resistance strain sensor R1 to R4 is made of BYM series high-precision resistance strain sensor BYM350-1AA(11)N4-C, which can be temperature self-compensated and creep self-compensated, has good environmental resistance, high sensitivity coefficient, fatigue life ≥107, and the strain limit can reach 2%. The first-stage amplifier is HRFA04M1, and the second-stage amplifier is GF158SZ. The sensor weighs 450g and has a size of 154mm×55mm×78.

[0093] The ground contact sensor conditioning circuit board provides excitation voltage for the Wheatstone bridge of the resistance strain sensor, and performs pre-amplification, post-amplification, and secondary filtering on the millivolt voltage signal output by the resistance strain sensor and then outputs it to the flight control computer; after the resistance strain sensor signal is filtered out by the input filter circuit, the pre-amplification and zero position adjustment are performed by the pre-amplification circuit composed of the instrument amplifier and the bias circuit. The post-amplification circuit composed of the rail-to-rail operational amplifier and precision metal film resistor performs secondary amplification on the signal. The secondary amplification output signal is filtered by the second-order active filter circuit and outputs a 2-8V signal. When the sensor is not under force (zero position), the output is 5V, and the excitation voltage V is +9VDC.

[0094] The ground proximity sensor uses a millimeter-wave radar sensor. One sensor is installed on the outer surface of the belly of the aircraft. The antenna array is parallel to the ground, and there is no object blocking the signal transmission path within the beam width.

[0095] The millimeter wave radar sensor operates at a frequency of 76 to 81 GHz, has a transmission power of 10 dBm, 2-channel transmission, 4-channel reception, FMCW modulation, a beam width of 40 degrees, a measurement height range of 500 m, an accuracy of 0.05 m for height ≤ 30 m, and an accuracy of 0.2 m for height ≥ 30 m. The communication method is standard RS422, the weight is 0.2 kg, and the size is 100 mm × 60 mm × 20 mm.

[0096] The flight control computer is installed in the equipment cabin of the unmanned helicopter. It is a dual-redundancy flight control computer. When a flight control computer of one channel fails, it switches to another control channel and has a single fault safety capability. The power module provides power excitation for the data acquisition module, the central processing module, and the communication module; the data acquisition module collects the tension and pressure voltage signal input by the ground contact sensor, converts the analog signal into a digital signal and inputs it into the central processing module; the central processing module determines whether the unmanned helicopter is flying near the ground or at high altitude based on the ground proximity data, and executes the corresponding control law and control strategy accordingly. The central processing module calculates the tension and pressure signal input by the ground contact sensor, compares the pressure value with the preset threshold, and determines the ground and air status of the unmanned helicopter; the central processing module solves the servo travel setting value based on the ground proximity height and the ground and air status, and sends it to the servo control system through the communication module to change the power of the unmanned helicopter to achieve takeoff and landing.

[0097] The servo controller is installed in the equipment cabin of the unmanned helicopter, the pitch servo and roll servo are installed on the main rotor automatic tilt device, and the tail servo is installed in the tail rotor operator. The servo controller and the servo are both electrical double-redundant architectures, in which the servo controller receives the instructions of the flight control computer in real time, and transmits the servo instructions to each motor drive module after parsing and processing to control the 4-way servo to run to the specified position, realize the main rotor pitch direction movement, roll direction movement and tail rotor heading direction movement and unmanned helicopter collective pitch adjustment, and ensure the flight of the unmanned helicopter.

[0098] The satellite navigation sensor, ground proximity sensor, ground contact sensor, and servo control system are connected to the flight control computer through the whole machine cable to achieve data exchange.

[0099] The provision also includes control software, which includes a system layer, a management layer, an application layer and a data interface layer, wherein the system layer adopts a real-time operating system, the management layer includes interrupt priority management, clock management, task management and exception management, the application layer includes sensor signal acquisition and resolution, ground and air judgment, control law and control strategy design, servo drive control, communication, BIT detection and alarm, etc., and the data interface layer is the processing function of each functional module corresponding to the peripherals, including power interface, I / O interface, USART interface, ADC interface, etc.

[0100] like Figure 2As shown, after receiving the landing command, the unmanned helicopter starts to execute the landing procedure. The flight control computer collects and receives satellite navigation sensor data, ground proximity sensor signals and ground touchdown sensor signals in real time. When the unmanned helicopter automatically lands, it switches from automatic cruise mode to automatic landing mode. The switching form is automatic cruise flight-hovering-autonomous landing. The control law is vertical speed control (altitude monitoring) to landing processing. The unmanned helicopter swoops down from a high altitude to the landing height. Through deceleration control, it stops and keeps hovering just above the landing point. After stabilizing for a certain period of time (for example, 5 seconds), it descends at a constant speed. During the descent, the position holding loop and the attitude loop are both connected. The ground proximity sensor is used to observe the distance between the landing gear of the unmanned helicopter and the ground. When the flight altitude drops to 200 meters, the flight control software sets the ground proximity sensor data to be valid, and determines whether the altitude has reached the ground proximity altitude of 10 meters. If not, the high-altitude flight control law and control strategy will continue to be executed, and the flight will continue to descend. If it is determined to be the ground proximity altitude, the vertical descent speed will be slowed down to 0.1m / s, the integral control will stop working, and the skid landing gear pressure will be determined by the ground contact sensor to determine whether it is greater than the threshold of 50 kg. If it is not greater than the threshold, the ground proximity landing procedure will continue to be executed. When the pressure value is greater than the threshold, it is determined that the landing gear has touched the ground, and the flight control computer sends a steering gear control command to the servo control system to quickly reduce the vertical channel total distance, the longitudinal channel pitch lock, the lateral channel pitch lock, the heading channel maintains zero angular velocity and executes the parking finger procedure to complete the landing of the unmanned helicopter.

[0101] In the case of ground wind speed greater than or equal to 12 m / s (force 6 wind), landing site inclination greater than or equal to 5°, or landing site shaking (such as ship deck), the total pitch is slowly lowered. After the landing gear partially touches the ground, the flight control program automatically and in real time adjusts the propeller disc plane based on the feedback information from the skid-type landing gear touchdown sensor, so that the landing gear plane and the landing site plane dynamically remain approximately parallel, thereby achieving rapid landing and ensuring landing safety.

[0102] The present invention provides an unmanned helicopter air-ground state judgment system and method. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. An unmanned helicopter air-ground state judgment system, characterized in that: It includes skid landing gear, satellite navigation sensor, ground proximity sensor, ground contact sensor, flight control computer and servo operating system; The skid landing gear comprises an arched beam, left and right skid tubes and a push wheel bracket, the front and rear ends of the left and right skid tubes are respectively connected to the arched beam, the arched beams are connected through an intermediate connecting tube, and the push wheel bracket is installed on the left and right skid tubes corresponding to the center of the rotor main shaft of the unmanned helicopter; The skid-type landing gear is a load-bearing component of the unmanned helicopter, and bears the entire weight and impact load of the unmanned helicopter during each take-off and landing; The satellite navigation sensor is used for unmanned helicopter navigation, providing single-point positioning, differential positioning, altitude, speed and interference source detection data for the unmanned helicopter; The ground proximity sensor is used to measure the relative ground height when the unmanned helicopter is flying close to the ground and when taking off and landing. When the relative ground height is less than or equal to X meters, the ground proximity sensor measurement is effective, and when the relative ground height is less than or equal to Y meters, it is determined to be the ground proximity height; The ground contact sensor replaces the connecting piece between the skid-type landing gear and the fuselage of the unmanned helicopter in situ, and is conformally designed with the skid-type landing gear. On the one hand, it realizes the connection and fixation between the fuselage of the unmanned helicopter and the skid-type landing gear; on the other hand, it senses the tensile pressure loaded on the skid-type landing gear, and is used for judging the take-off and landing of the unmanned helicopter during the take-off and landing phases.

2. The system according to claim 1, characterized in that The satellite navigation sensor comprises a satellite antenna, a satellite receiver and a first communication module; the satellite antenna is connected to the satellite receiver via a radio frequency cable, and the satellite receiver is connected to the first communication module via a serial bus.

3. The system according to claim 2, characterized in that The ground proximity sensor comprises a microstrip antenna, a transmitting branch, a receiving branch, a frequency synthesis module, a signal processing module, an MCU control module and a second communication module; The microstrip antenna is connected to a transmitting branch and a receiving branch through a radio frequency cable, and the transmitting branch, the receiving branch, the frequency synthesis module, the signal processing module, the MCU control module and the second communication module are connected through a printed circuit board.

4. The system according to claim 3, characterized in that The ground contact sensor includes an elastic body, a strain sensor, a conditioning circuit board, a cable, an electrical connector and a cover plate; The strain sensor is pasted in the elastomer, the strain sensor is connected to the conditioning circuit board through a cable, the conditioning circuit board is installed in the middle cavity of the elastomer, the electrical connector is connected to the conditioning circuit board through the through hole of the elastomer by a cable, and the cover plate is installed above the middle cavity of the elastomer by screws; The ground contact sensor senses the force between the fuselage of the unmanned helicopter and the skid-type landing gear through the elastic body; The strain sensor outputs an electrical signal, which is conditioned by a conditioning circuit board to output the real-time landing gear force condition to the flight control computer.

5. The system according to claim 4, characterized in that The flight control computer is a redundant flight control computer, comprising a power module, a data acquisition module, a central processing module and a third communication module; The power module, the data acquisition module, the central processing module and the third communication module are connected via a printed circuit board; The power supply module provides power excitation for the data acquisition module, the central processing module and the third communication module; The data acquisition module acquires the tension pressure voltage signal input by the ground contact sensor, and the 12-bit ADC converts the analog signal into a digital signal and inputs it into the central processing module; The third communication module is used to receive ground proximity sensor data and send control data to the servo controller; The central processing module determines whether the unmanned helicopter is flying near the ground or at high altitude according to the near-ground height data, and executes corresponding control laws and control strategies; The central processing module calculates the voltage signal input by the ground contact sensor to obtain a tension pressure signal, compares the tension pressure value with a preset threshold value, and determines the ground state of the unmanned helicopter in the air; The central processing module calculates the servo travel setting value according to the ground altitude and the ground-air state, and sends it to the servo control system through the communication module to change the power of the unmanned helicopter to achieve take-off and landing.

6. The system according to claim 5, characterized in that The servo operating system includes a servo controller, a pitch servo, a roll servo and a tail rotor servo; The servo controller is connected to the pitch servo, the roll servo and the tail rotor servo via cables; The servo controller receives flight control computer control data, steering gear drive control, collects steering gear motion position, in-machine test detection and fault alarm; The pitch servo is used to control the pitch direction movement of the main rotor of the unmanned helicopter; The roll servo is used to control the rolling direction movement of the main rotor of the unmanned helicopter; The tail rotor servo is used to control the heading direction of the tail rotor of the unmanned helicopter; The pitch servo and roll servo are used to control the collective pitch of the unmanned helicopter; The servo controller controls the pitch servo, roll servo and tail rotor servo according to the control instructions of the flight control computer, adjusts the collective pitch and tail rotor pitch of the unmanned helicopter, and then adjusts the rotor lift and attitude to achieve take-off or landing of the unmanned helicopter.

7. The system according to claim 6, characterized in that The working process of the ground contact sensor includes: Step 1, the conversion process from the tensile force to the resistance change of the resistance strain gauge, specifically includes: When the ground contact sensor is subjected to force, the tensile pressure acts on the elastic body of the force sensor, causing the elastic body to produce tensile and compressive strains. The strain is calculated by the material mechanics formula: ε=σ / E=F / (Α×E), Where ε represents strain; σ represents stress; E represents the elastic modulus of the material; F represents force; Α represents the structural parameter expression; The tensile and compressive strains cause the sensitive grid of the metal foil resistive strain sensor pasted on the elastic body to deform. The resistance R of the metal sensitive grid is proportional to the length L and inversely proportional to the cross-sectional area S, that is, R = ρL / S, where ρ represents the resistivity. When the metal sensitive grid is elongated by dL due to deformation, the cross-sectional area will be reduced by dS accordingly. d represents the differential. Differentiating R = ρL / S, the relative change of the sensitive grid resistance is dR / R = dL / L-dS / S. Because dS / S = 2dr / r, where r is the cross-sectional structural size of the metal sensitive grid, the axial strain of the metal sensitive grid is ε = dL / L, which is obtained from material mechanics: dr / r = -με, Where μ is the Poisson's ratio of the metal sensitive gate material, so dR / R=(1+2μ)ε; Let the sensitivity coefficient K of the resistance strain gauge be: K=(dR / R) / ε get: dR=KRε, The resistance strain gauge linearly converts the tensile and compressive strain of the elastic body caused by the tensile pressure into the change in the resistance value of the resistance strain sensor through the deformation of the sensitive grid; Step 2, the measurement process of electrical quantities: The circuit part of the force sensor is composed of four resistance strain gauges attached to different parts of the elastic body, that is, a Wheatstone bridge. The relationship between the output voltage U0 and the power supply voltage U is: When the tension is zero, R1=R2=R3=R4, where R1, R2, R3 and R4 are all the resistance values ​​of the strain gauge, the Wheatstone bridge is balanced, and the output voltage U0 is zero; when there is tension, the elastic body strain causes the strain gauge resistance value to change dR, the Wheatstone bridge is unbalanced, and the output voltage U0 is: U0=U(dR4-dR3+dR2-dR1) / 4R, Where dR1, dR2, dR3, and dR4 are the resistance changes of the resistance strain gauge; Let dR4=-dR3=dR2=-dR1=dR, and we get: U0=U×dR / R; The Wheatstone bridge composed of four resistance strain gauges attached to different parts of the elastic body converts the resistance change into a voltage signal output. When the force sensor senses the pulling pressure, the Wheatstone bridge outputs a voltage signal that is linearly related to the pulling pressure. The signal conditioning circuit is used to filter, amplify, and compensate the force sensor signal before output. The signal conditioning circuit comprises an input filtering circuit, a pre-stage amplifier circuit, a post-stage amplifier circuit and an output filtering circuit; the output signal of the strain gauge sensor is first filtered out by the input filtering circuit to remove interference, and then the pre-stage amplifier circuit composed of an instrument amplifier and a bias circuit performs pre-stage amplification and zero adjustment; the post-stage amplifier circuit composed of a rail-to-rail operational amplifier and a precision metal film resistor performs secondary amplification on the output signal of the force sensor, and the secondary amplified output signal is filtered by the output filtering circuit.

8. The system according to claim 7, characterized in that The satellite navigation sensor adopts the Beidou-3 satellite navigation system, supports single-point and differential positioning, and has an anti-spoofing function; The ground proximity sensor is a millimeter wave radar; The millimeter wave radar is horizontally installed on the belly of the unmanned helicopter.

9. The system according to claim 8, characterized in that The elastic body is a curved beam structure, the upper end of which is connected to the fuselage of the unmanned helicopter by screws, and the lower end is connected to the skid-type landing gear by screws, and the strain sensors are attached to the left and right end surfaces of the elastic body to form a Wheatstone bridge; The strain sensor is a resistance strain sensor, which converts the push-pull force into a voltage signal by using the unbalanced Wheatstone bridge according to Hooke's law and the resistance strain principle, and outputs a millivolt voltage signal that is linearly proportional to the push-pull force; The conditioning circuit board provides an excitation voltage for the Wheatstone bridge of the resistance strain sensor, and filters, amplifies, and compensates the millivolt voltage signal output by the resistance strain sensor and then outputs it to the flight control computer.

10. A method for determining the ground state of an unmanned helicopter in the air using the system according to any one of claims 1 to 9, characterized in that: include: After receiving the landing command, the unmanned helicopter starts to execute the landing procedure. The flight control computer collects and receives satellite navigation sensor data, ground proximity sensor signals and touchdown sensor signals in real time. When the unmanned helicopter automatically lands, it switches from automatic cruise mode to automatic landing mode. The switching form is automatic cruise flight, hovering, and autonomous landing. The control law is vertical speed control until landing processing; the unmanned helicopter dives down from a high altitude to near the landing height, stops and keeps hovering just above the landing point through deceleration control, and descends at a constant speed after stabilizing for a certain period of time. During the descent, the position holding loop and the attitude loop are both connected; the ground proximity sensor is used to observe the distance between the landing gear of the unmanned helicopter and the ground. When the flight altitude drops to X meters When the flight control software sets the ground proximity sensor data to be valid, it determines whether the height has reached the ground proximity height Y meters. If not, it continues to execute the high-altitude flight control law and control strategy and continues to descend. If it is determined to be the ground proximity height, the vertical descent speed is slowed down, the integral control stops working, and the skid landing gear pressure is judged to be greater than the threshold value Z through the ground contact sensor. If it is not greater than the threshold value Z, the ground proximity landing procedure continues to be executed. When the pressure value is greater than the threshold value Z, it is determined that the landing gear has touched the ground, and the flight control computer sends a steering gear control command to the servo control system to quickly reduce the vertical channel total pitch, the longitudinal channel pitch lock, the lateral channel pitch lock, the heading channel maintains zero angular velocity and executes the parking finger procedure to complete the landing of the unmanned helicopter.

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