Attitude Angle Test Research

1 Introduction

There are many methods for testing the attitude angle of a flying object, such as magnetic sensors, high-speed cameras, accelerometers, and gyroscopes. Each method has its advantages and application limitations and is suitable for different application scenarios. A small flying object is subjected to a small overload during flight, and the attitude angle does not change much. The space available for the tester is limited. For the attitude angle test of this small aircraft, a gyroscope-based attitude angle storage test method is proposed, and the specific implementation scheme is introduced.

2 Design of attitude angle test system

The magnetic sensor method is usually only used as an auxiliary test method, and the high-speed photography method is easily affected by weather, which also limits its application. The accelerometer method has the advantages of low cost, low power consumption, and high reliability, but the theoretical calculation and installation complexity limit the application of this method. In China, most of the research is based on theory. The gyroscope method is easy to use in occasions where the overload is not too large, making it a good choice for the attitude angle test of this aircraft. The attitude motion of a flying object is the rotational motion of the flying object around its own center of mass. After introducing the concepts of rigid body assumption and coordinate system transformation, the attitude of a flying object is defined as the rotation transformation of the flying object coordinate system relative to the reference coordinate system.

2.1 Gyroscope attitude angle test principle

When analyzing the rotational motion of a rigid body, Euler angle or Cardan angle is often used. Cardan angle is suitable for occasions where the attitude angle changes slightly, so it is described with Cardan angle. Take the initial moment flight body coordinate system Oξηζ as the fixed coordinate system, and 0xyz as the moving coordinate system fixed to the flight body. The method of selecting the Cardan angle is to first rotate around the ξ axis by an angle of α to reach the position of 0x1y1zl; then rotate around the y1 axis by an angle of β to reach the position of 0x2y2z2; then rotate around the z2 axis by an angle of γ to reach the position of 0xyz. The rotation relationship is shown in Figure 1.

α, β and γ are the angular velocity components along the 0ξ axis, 0y1 axis and 0z axis respectively. The three rotations are shown in formula (1):

Here, cx represents cosx, sx represents sinx, and tgx represents tangent. The direction cosine matrices corresponding to each rotation are

The angular velocity ω of the flying body can be expressed as:

Formula (7) is the kinematic differential equation expressed by the Cardan angle, where ωx, ωy and ωz are the outputs of the gyroscope x-axis, y-axis and z-axis respectively. Integrating this formula, the Cardan angle can be obtained.

2.2 System Implementation

After studying the storage test technology, a storage test system was designed. Its most prominent features are its small size and the fact that it does not require leads during measurement, that is, it does not require electromagnetic radiation to the outside world. In the field of storage testing of dynamic parameters, the tester must move with the object being tested, requiring the test system to have the characteristics of small size, low power consumption and high overload resistance. The corresponding solutions to these requirements will be explained in conjunction with the system design below.

Whether the main control device can work normally is the key to whether the entire system can reliably obtain the measured parameters. The original level of the CPLD input and output pins can be pre-set, and the preset level can be reached when the power is turned on, and the status is clear. The signal transmission efficiency is high, which is suitable for high-speed sampling occasions. The interconnections between programmable logic macro units or logic blocks are in the same package, which is less affected by external interference and has good electromagnetic compatibility (EMC) performance. In summary, CPLD has the characteristics of strong logic, fast response time, and program not easy to run away. For this purpose, CPLD is selected as the main control device, and the internal logic of the device is designed to be as simple and reliable as possible to ensure the normal operation of the system during the entire test process. The storage capacity of this system is 512 Kx12 bit, the negative delay is 128 Kx12 bit, and the sampling frequency is 8 kHz. The principle block diagram of the test system is shown in Figure 2.

The storage test system includes four parts: gyro output, signal processing (channel switching, signal adaptation circuit, A/D converter, data storage), system control (central controller, power control) and interface circuit. The continuous sampling method is used for the three-dimensional angular velocity signal, and channel switching is required. The gyro outputs a voltage signal, and the channel switching can be performed first and then the signal adaptation can be performed, so that the area of ​​the circuit board can be reduced, and the volume of the tester can be further reduced. Through channel switching, the sensor signal is sent to the signal adaptation circuit in turn, and then sent to the A/D converter after conditioning, and the analog quantity is converted into a digital quantity and stored in the memory. When the trigger signal arrives, the test system records the preset capacity, the central controller gives an analog power off signal, the power controller stops recording, and the test system enters power saving mode. The system waits for the computer to send a reading instruction and the interface circuit reads the data. The corresponding interface circuit is designed, and the USB port and the parallel port can read the data of the test device.

2.3 System shock resistance treatment

The test system must withstand shock overload throughout the operation, and the device must be shock-resistant to protect the test device so that it can work normally in a high shock environment. In order to resist high impact overload, high overload resistant devices were specially selected. The most important main control device is XCR3064, which has a high overload resistance of 3×105g[6]. A shock-resistant mechanical shell is specially designed for the test system, and the test device is vacuum-sealed with epoxy resin to fix the test circuit in the circuit protection shell to resist high overload. After the above high overload resistance measures, the test device can well meet the test needs, ensure the normal operation of the test system, and the system can be reused.

3 Test results and measured data analysis

The storage test system has been successfully applied to the test of a small flying object, and the test data has been successfully obtained. The following is the measured curve and its analysis, the x-axis is the rotation axis, and the z-axis is the flight direction. The measured angular velocity signal during the flight process is shown in Figure 3. In Figure 3, the angular velocity curves of the three axes have a small bulge at 70 ms, which is the manifestation of the acceleration effect of the gyroscope on the curve.

The ωx, ωy, and ωz measured by the gyroscope are known. According to the kinematic differential equation shown in Expression 7, the angle is solved in MATLAB, as shown in Figure 4. After comparison, it is very consistent with the posture recorded by high-speed photography.

4 Conclusion

Aiming at the actual needs of attitude angle testing of a certain flying body, this paper studies attitude angle testing technology, proposes an attitude angle testing scheme, analyzes the theoretical basis, and conducts actual tests. The experimental results show that this scheme can meet the system usage requirements.