Mini UAV whole attitude stability augmentation system design and implementation (1)

O introduction

With the domestic and international terrorism situation increasingly grim and all kinds of emergencies occur frequently, the armed police in all kinds of complicated, dangerous environment, quickly and efficiently complete tasks and set higher requirements.

Traditional reconnaissance means no longer meet the needs of the situation, such as major natural disasters, causing relief work cannot expand; counter-terrorism or assist in the capture time cannot effectively track suspects. The emergence of unmanned reconnaissance aircraft to patrol officers brought the convenience, but in reconnaissance UAV itself during the vibration makes photographing a jitter and therefore influence to a large extent to the commanders of the correct decision. Traditional self-driving adopts inertial measurement unit for aircraft attitude information, including the angular velocity meter (gyro) and accelerometer. Gyro used to measure aircraft attitude and angular velocity; accelerometer is used to measure the General gravity acceleration down two horizontal projection, through triangular relationships can be converted by the vehicle's current attitude is pitching and rolling angle. However, the use of accelerometers for measuring attitude information very vulnerable to vibration and tactical aircraft flying at its acceleration, measurement accuracy error is generally relatively large, poor stability, makes the reconnaissance effect is affected. To tackle UAV flight stability, of a three-axis gyro and tilt sensor consisting of the whole attitude stability augmentation system for improved UAV in carrying out its mandate.

1 system features

By gyro and tilt sensor constitute whole attitude stability augmentation control loop.

Gyroscope measurements of the angular velocity information as augmentation feedback control, make the aircraft control up and become more "retarded", thereby leveraging angle sensor measured aircraft rolling and pitching. And then the gyro measured angular rate information and tilt sensor measuring attitude to strap operation, get the attitude information integration. This more complex strap algorithm can make the gesture precision is greatly improved.

2 attitude stability augmentation hardware design control law

UAV attitude stability augmentation control belong to the inner loop control, it includes attitude to maintain and control, speed control mode.

Inner loop control is in a three-axis gyro and tilt sensor gets UAV flight attitude, through the elevator and rudder control, to complete the flight attitude of stability and control. Inner loop control as the core of the flight control circuit, is flying height, track, and so on the basis of outer loop control. Outer loop control is based on GPS location, heading and altitude sensor pressure height signal to a datum, it passed the navigation control method to calculate the aircraft's scheduled routes and actual route.

UAV in loop control as the outer loop control based on its ability to stabilize the flight plays a vital role.

The system, the inner loop is a three-axis gyro and tilt sensor constitute posture stability augmentation control loop. Mainly by the main control chip, A/D sampling chip, three-axis gyroscope and tilt sensor. Main control chip through SPI serial bus with A/D sampling chip connected through A/D sampling chips get three-axis gyroscope angular rate and angle sensor of roll and pitch angle, and then make the attitude information fusion, UAV pitch and roll attitude information. Main interface connection as shown in Figure 1.

Figure l, AD7888 is a high-speed, low power consumption of 12-bit analog to digital converters, can reach 125 KSPS transmission rate, has 8 analog input channels.

CS PIN for chip selected, the PIN has two functions that initiate AD7888 converters and developed serial data transfer, and microcontroller pins PB0 (SS). SCLK pin for the serial clock input, through an external MCU ATmegal28 pin PBl (SCK) provides serial clock signal. DIN is a logical data input, data for logical DOUT output pin with ATmegal28 PB2 (MOSI) and PB3 (MISO) connected.

External reference voltage Vref is the range of ~ VDD (Vref = 1.2 V).

In order to obtain a stable reference voltage, composed by TL431 reference voltage circuit. Texas Instruments ' (TI) production of TL431 is a good thermal stability of adjustable shunt reference source. Its output voltage resistance R2 and R3 can be set to Vref = 2.5 V to Vref = 36 V range of any value.

SCM ATmegal28 and AD7888 via serial interface SPI, are configured to host and from the machine.

SPI bus allows ATmegal28 and peripheral high-speed synchronous data transfer.

Three-axis gyroscope is mainly used to measure the UAV in flight pitch angle, roll and yaw angle, angular velocity and angular velocity integral angle according to the changes.

The system adopts the EWTS82 Ribensongxiagongsi (hereinafter S82), the principle is the rotation of the Earth tuning fork shock force deflection (Creole, force) converted to electrical signals. The three-axis gyro sensor parts, tuning fork driver circuit and signal processing circuit. The gyro is a simulator, with + 80 ~-80 (°)/s measuring range, single-supply (+ 5 V DC) power supply, suppression of better zero drift, and other advantages. In addition, its low prices can significantly reduce development costs.

Tilt sensor with Finland VTI Technologies company is a manufacturer of high precision dual-axis tilt sensor SCAl00T, the sensor's small size and light weight.

Its interior contains a Silicon sensitive capacitive sensor and an ASIC ASIC, both have internal temperature measurement and compensation function, with auto-detection, single-axis maximum output range of around-40 ~ + 40 ° c, the effective output ranges from-30 to + 30 degrees centigrade. When sampling frequency of 8 Hz and below, you can obtain 0.002 ° output resolution. Serial peripheral interface SPI output frequency at 500 kHz, passedSensilla component control frequency response, can withstand greater than 20 000g mechanical vibration. It has features: x, y-axis measurement of high resolution bi-directional, single power supply (+ 5 V DC) power supply, operating current small (3 mA), low noise, the operating temperature range (-40 to + 125 ° c).

3 attitude stability augmentation control software design

The entire amount of the entry flight control system is the sensor's acquisition of flight status value, the output of the aircraft State equation control variables (rudder and engine thrust), so the flight control system is essentially a multi-channel control system, that is, multiple input/multiple output control system.

Of these, the core of the flight control system is a control loop to attitude (pitch angle/rolling angle) on the basis of the feedback signals constitute flight attitude stabilization and control circuit, i.e. within the loop.

, Circuit, and the introduction of highly maintained, outside of the track control circuit.

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