It is understood that the UAV flight control system includes the following sections: gyroscopes, accelerometers, magnetic sensors, GPS module and a control circuit, and its main function is to automatically keep the aircraft’s normal flight attitude. Flight control system directly determines the UAV in flight stability, reliability, controllability and safety, MEMS gyroscopes, as part of this, the majority of respondents said MEMS gyroscope is expected to become UAV Flight Control System gyro standard, then, first of all to look at compared to other MEMS gyroscope gyroscope What advantages.
Wang Yi concluded: “MEMS gyroscopes advantages: (1) lower aircraft costs and promote the vigorous development of market applications; (2) reduce the weight of UAVs, reduced power consumption, improved flight time; (3) MEMS technology to integrate more sensors, is conducive to the precise attitude control deficiencies: poor compared to fiber optic gyroscopes, laser gyroscopes, MEMS gyroscope zero drift and precision. ”
Jinliang think, MEMS gyroscopes have obvious advantages, but there are some limitations. “MEMS gyroscopes to make the UAV attitude and a more stable and accurate navigation, while its power consumption is lower. And MEMS gyroscopes costs are coming down, getting smaller, and the dynamic range is expanding more. Overall, smaller and integrated sensor axes, are more conducive to the UAV attitude perception, of course, there are also disadvantages, for example not fast enough, the accuracy is not high enough, and the maximum measuring range there are some limitations. ”
Jinliang said MEMS gyroscope limitations, mainly due to the current MEMS technology. But these can not affect the MEMS gyroscope in UAV flight control system is used to achieve a balance control and auxiliary aircraft navigation of its importance.
According to the Shenzhen Otani Co., Ltd. (hereinafter referred to as “Otani Technology”) CEO Peng Mao-roots representation, in a variety of unmanned aerial vehicles, both military unmanned aerial vehicles, UAVs civilian medium, individual small aerial drones, unmanned aerial vehicles flight control system is the core, at the same time to achieve reliable control, stable and flexible one of a UAV is a measure of whether a sign of success. In order to achieve a stable and flexible flight control, UAVs must be integrated include gyroscopes, accelerometers, tilt sensors, airspeed sensors, barometric altimeter and other sensors, during the flight coprocessor their posture and precise adjustment control, which gyroscope played a significant role.
According to Wang Yi introduction, the flight control system is the sum of all parts and devices used to transfer all manipulation instruction, driving rudder movements on UAVs. Flight control system consists of airborne and ground control part two parts, which include some of the major airborne sensors, steering gear and flight controllers. Flight control system is the core part of the overall UAV airborne equipment, flight control system can work, a direct impact on a variety of performance and flight safety UAV flight.
“In the flight control system, mainly using MEMS gyroscope measurements during the flight pitch angle and roll angle, but generally require complex MEMS accelerometers, because each sensor has certain limitations.” Wang Yi explained, “For example, , MEMS gyroscope measures the angular velocity, the angle through the points in order to get in the process of integration, since the zero drift influence is bound to introduce cumulative error, the longer the integration time, the greater the error. So, which requires the use of another A MEMS sensor calibration MEMS gyroscopes. Since there is no integrated error MEMS accelerometer, so in relatively quiescent conditions can be corrected MEMS gyro error. With MEMS technology continues to mature, the current MEMS gyroscopes and accelerometers are integrated in Together, commonly referred to as 6-axis combination sensor key technologies involved in this include hardware (a combination of 6-axis sensor) and software (filtering algorithms, attitude / navigation algorithms, etc.) in two parts. ”
Xie Zhifeng also believe MEMS gyroscopes and other sensors will be used in conjunction with: “no chance at least Configuration ‘gyroscope + accelerometer’ six-axis sensor assembly, high-end configuration no chance ‘gyroscope + accelerometer + magnetic sensor’ nine-axis sensor data combination, and integrated six-axis / 9-axis fusion / attitude stabilization algorithm. “In addition to the actual accelerometer, there magnetometer and GPS assisted correction.
Similarly Jinliang said, MEMS gyroscope must be fused with other sensor data, due to the MEMS gyroscope does not provide absolute reference, therefore, how to obtain a more accurate real-time stabilized attitude information from the MEMS gyroscope with noise data become flight control systems need to break the current focus. Gyro drift will have to work long hours and integral error, short-term response to acceleration fast enough, they would receive outside interference, therefore, generally will gyroscopes and accelerometers integrated with the use, of course, there are used separately, and then by the flight control software for both complementary.
Of course, there are exceptions, Shanghai Shen Di Semiconductor Co., Ltd. (hereinafter referred to as “Deep Di”), vice president of marketing Huangyan put forward their own views, he believes that if the zero impartial stability index MEMS gyroscope low to a certain extent, then, such as low in 0.1deg / h, then the MEMS gyroscopes can be used alone, and this indicator MEMS gyroscope can also replace the magnetic sensor, by measuring the Earth’s rotation either the north.
As MEMS gyroscope is used in conjunction with other sensors how to balance control and auxiliary navigation, Jinliang detailed explanation to reporters: “For example, three-axis accelerometer and three-axis gyroscope (angular velocity) concurrent transmitted to the microcontroller or DSP processing, and then the posture by the microcontroller or DSP solver (such as quaternions), to solve the current aircraft pitch, roll and yaw angle of the three, and then through the PID control operation in accordance with these three angles, four PWM outputs to control four motors ( UAV in terms of four-axis) acceleration and deceleration to achieve the equilibrium state hovering UAVs. ”
Jinliang also stressed that because MEMS gyroscope capable of measuring angular velocity along one axis or several axes motion, and with the MEMS accelerometer (accelerometers) are formed complementary advantages, a combination of accelerometers and gyroscopes two sensors can be better full motion tracking and capture three-dimensional space, in the absence of GPS or GPS data update interstices, by a combination of gyroscopes and accelerometers to aid navigation.
According to Wang Yi introduced a system of independent control input dimension is less than the degree of freedom of the system, then the system is called under-drive system. Axis UAV has four separate inputs, which consists of four independent motor-driven propeller, while the fuselage with six degrees of freedom of the change, so the UAV axis is a typical under-drive system. Four-axis control algorithms for unmanned aerial vehicles, the effect relatively good linear quadratic optimal control, backstepping control, PID control, sliding mode control.
Wang Yi also explained the MEMS gyroscope is how to achieve a balance control. “Axis UAV in the air flying, aircraft flight direction and flight speed is determined by the inclination of the aircraft, the aircraft tilted towards which the aircraft will be flying in any direction, the greater the inclination angle of the flight faster. By adjusting the rotational speed can be adjusted for each propeller UAV flight attitude. “he said.
In UAV flight control system, when the use of the accelerometer MEMS gyroscopes fit, not the lack of algorithms. According 赵延辉, currently the most commonly used algorithm is complementary filter, Kalman filtering and SINS, simply means that the use of sensor fusion MEMS gyroscopes, accelerometers and magnetometers, etc., in different scenarios, using different weights calculates the pitch angle, roll angle, heading angle changes, and then through PID control to achieve balance control.
The output value can be more precisely accurate representation of the UAV flight status. According to Jin-liang introduction, UAV flight status output value of the four elements, Euler angles, direction cosine matrix of three, where the advantages of the four elements that facilitate the calculation of the difference, but unfortunately it is difficult to directly represents the rotation, and the direction cosine matrix The coefficient too much, it is difficult to interpolation; Euler angle expression, although relatively more simple, however, the problem of the existence of universal lock.
Wang Yi also introduced the flight attitude of presentation: “The UAV axis attitude control, we must first be expressed in gestures, posture currently used expressions have Euler angles and quaternion two ways, Euler angles represents more intuitive but during the rotation matrix calculations large amount of calculation, and quaternion rule overcome this disadvantage. Second, we must be detected on the attitude, the attitude detection mainly to MEMS gyroscopes, MEMS accelerometers and other sensors for the angular velocity the measurement value of the acceleration is converted to a preliminary estimate posture, and then after filtering algorithm for data integration. Finally, the appropriate choice of control algorithm to control the attitude. ”
MEMS gyroscopes known UAV in terms of essential, in combination with other sensors can be more accurately stated UAV flight attitude from the above, then, for four axis, six-axis, multi-axis unmanned eight shaft machine is concerned, to take a few MEMS gyroscope is better? Is the more MEMS gyroscopes wing more use of?
On this issue, according to Wang Yi explained that the UAV generally use a three-axis multi-axis MEMS gyroscope, the main task is to control the posture sensing and navigation. If the head is mounted for aerial photography, you can also use a MEMS gyroscope on the head, for the camera’s image stabilization shooting. In multi-axis UAV, the more the wing is not more used MEMS gyroscopes.
Jinliang also believes that, in general, the UAV is to take a MEMS gyroscope, but the use of two individual. In order to ensure that the aircraft stable in three axes. Flight control software to coordinate them. Using several gyroscope on the plane almost no relationship with the number of wings. Generally use only a three-axis multi-axis gyroscope. For example, our latest product Mirage Mirage on the use of a UAV three-axis gyroscope.
Yanhui Zhao also explained to reporters: “Usually the least use one, do body smooth control and navigation assistance there is also two and a smooth control and an auxiliary make navigation of the fuselage, a smooth control of the camera frame to do, of course. For different reasons, there are many more, such as different application scenarios, start a different range of gyroscopes. Also by a show of hands algorithms to improve reliability of the system, then you may need a 3- axially 5 gyroscope. ”
MEMS gyroscope that measures the angular velocity of the UAV, but since the output value of MEMS gyroscope angle needs to get through the integration, requiring the acceleration sensor effective to correct it. But, nevertheless, when the UAV is in flight state, the accuracy of the acceleration sensor has been reduced because they measure the gravity and external forces, therefore, reduce the vibration intensity UAVs, will be able to increase the accuracy of the MEMS gyroscope and the output value of the acceleration sensor.