Application of a rocket automatic tester based on embedded computer PC/104

1 Introduction

The gyro in the variable roll rate rocket is a sensitive element. Its function is to measure the yaw angle that occurs during the flight of the rocket. This yaw angle is calculated by the solution module and the controller starts the actuator to perform attitude control, thereby achieving the purpose of yaw correction. However, the gyro is a one-time product and does not work during the development and testing process. Therefore, it is necessary to simulate the gyro signal. The result of the yaw correction must also be judged to see whether it is consistent with the ideal control effect and whether there is any advance or lag phenomenon. Therefore, it is necessary to develop an automatic tester for testing. In addition to the above two important aspects, according to the development requirements and test requirements, this tester also needs to detect the secondary power supply, controller timing, main engine internal resistance test, attitude control engine internal resistance test.

This test system uses an embedded computer PC/104. PC/104 is fully compatible with the PC/AT architecture and is only 90mmX96mm in size, but it integrates almost all the functions of an ordinary desktop PC and is compatible with it. Therefore, the program developed on the PC can be run directly on the PC/104 CPU module. Compared with the single-chip system, it eliminates the need for dedicated development tools and is easy to maintain. PC/104 adopts a modular design, the hardware circuit design is simple, and the development cycle is reduced. Therefore, in this test system, we use an embedded computer PC/104.

2 System Design

2.1 Hardware Block Diagram, as shown in Figure 1:

Figure 1 Hardware Block Diagram

The central module of the system uses SCM-6456 of Shengbo Company, which uses enhanced 80486DX CPU and 32M RAM; two serial ports, the baud rate can be controlled by software, of which COM2 can be set to RS-485 mode; one parallel port; VGA supports color and monochrome LCD, EL flat panel display and analog CRT; on-board IDE and Floppy interface; the acquisition module uses ADT650 of Shengbo Company, which has 12-bit resolution, maximum 100KHz sampling rate, 16 analog input channels, and maximum 10V input; 4-channel analog output; 24-channel TTL/CMOS compatible I/O; 3 16-bit, maximum 10MHz timer/counters; the signal logic part mainly converts the signal to be tested into a signal suitable for ADT650 acquisition; in the human-machine interface, because few characters are required to be input, a 4X4 matrix keyboard is designed by ourselves, and the display results can be displayed on the monitor or printed by the printer.

2.1.1 Configuration of timer/counter

This tester requires the output frequency of 5-13Hz signal, and the period is about 200ms to 80ms. If the D/A conversion method is used with 1ms timing, the minimum output of 80 points in one period can meet the requirements of the test object for analog excitation signals after actual testing; in addition, when collecting the control signal of the actuator of the test object, the method of 1ms timing acquisition is adopted, which can also meet the requirements of the final data judgment. Therefore, the timer timing time is 1ms (that is, the output clock of the timer is 1KHz). The input clocks of the three timers on the acquisition module ADT650 are all 10MHz, which cannot meet the requirements. The cascade method can be used to connect the OUT of COUNTRT0 to the CLK input of COUNTRT1, and the OUT of COUNTRT1 to the CLK of COUNTRT2. The programming settings are as follows: (Base represents the base address of the ADT650 module, which is 0x330, the same below)

outportb (Base+15, 0x35); /＊ Timer 0 Square wave generator＊/

outportb (Base +12, 00); /＊ The low byte of the count value is sent to counter 0＊/

outportb (Base +12, 10); /＊ The low byte of the count value is sent to counter 0＊/

outportb (Base +15, 0x75); /＊ Timer 1 Square wave generator＊/

outportb (Base +13, 10); /＊ The low byte of the count value is sent to counter 1＊/

outportb (Base +13, 0); /＊ The low byte of the count value is sent to the counter 1*/,

that is, the 10MHz clock is divided by 1000 and 10 to get a 1KHz clock;

2.1.2 Design of analog gyro signal

During the development and testing of rockets, the gyro does not work, so it is required to provide an excitation signal that can simulate the gyro. There are two channels: one is the yaw signal and the other is the pitch signal; after the test, the phase difference of these two signals is 90 degrees, the frequency gradually increases from 5Hz to 13Hz, and the amplitude gradually decreases from 1V. The analog output range of ADT650 is -5V to +5V, and the resolution of D/A conversion is 12 bits. The data corresponding to -5V~+5V is 0-4095, and the output of 0V corresponds to 2048. If the period is T, the program calculates

2048+(409-40*step)*sin(2*pi*i/T)

and then calculates the bottom 8 bits (LSB) and the top 4 bits (MSB) of the DA data, and writes them into channels Base+1 and Base+2 respectively. The data is sent to the DA converter and output every 1ms to get the required signal. When enabled, step=0, where 409 means the output amplitude is 1V, that is, 1/5*2048=409. As time changes, the step increases by 1, and the amplitude gradually decreases. After a certain number of cycles are output, the frequency is increased by 1, so that the frequency gradually increases, and the corresponding T becomes smaller. The other one is 90 degrees out of phase with it, and its calculation function is

2048+(409-40*step)*sin(2*pi*(I+4/T)/T).

2.1.3 Yaw correction test

The most important content in rocket testing is to see whether the result of yaw correction is consistent with the theoretical control result. The yaw correction in the rocket is to change the attitude control engine's flame direction by switching two pairs of solenoid valves, so the tester must collect the switch signals of 4 solenoid valves. ADT650 integrates uPD71055 programmable peripheral interface, uses PA0~3 to collect the switch signal of the solenoid valve, uses 1ms interrupt to collect the signal once, and finally compares the collected control signal with the standard control signal to find out whether there is a lead or lag problem during switching, so as to determine the performance of the rocket.

2.1.4 Analog quantity acquisition

In addition to the above two important test contents, the secondary power supply, main engine internal resistance, and attitude engine internal resistance test also need to be tested. The secondary power supply mainly has 5V and 12V, and the maximum input range of ADT650 is 10V, so it must be input to the A/D input terminal after voltage division and attenuation; for the test of internal resistance, the method of converting to voltage measurement is adopted, and finally converted to the required actual resistance value in the program;

for the A/D conversion of ADT650, the direct programming method is used. First, write Base+3 to select the input channel. For multi-channel acquisition, it only needs to be set once, and the next A/D conversion will automatically switch to the next channel. After the setting is completed, write any value to Base+0 to start the A/D conversion. When the bit 0 of Base+5 becomes 0 (that is, the A/D conversion is completed), the data can be read and converted into meaningful data.

2.1.5 RS-485 communication

This test system needs to communicate with the test object. In order to ensure the reliability of data transmission, we use RS-485 communication. The SCM-6456 module has two serial ports, COM1 and COM2, of which COM2 can be set to RS485 mode through jumpers. Its application circuit is shown in Figure 2:

Figure 2 485 communication

2.2 Software design

According to the characteristics of PC/104, this system uses DOS6.22 operating system, TC2.0 environment programming, modular design, and solidifies the program in the electronic disk, and also starts from the electronic disk when starting. It mainly includes initialization module, serial communication module, data acquisition module, data processing module, etc. The program flow chart is shown in Figure 3:

Figure 3 Program flow chart

3 Conclusion

The automatic test system designed with PC/104 computer has the characteristics of small size and low power consumption, which is suitable for portable equipment and convenient for field application. This tester can also replace the signal generator and oscilloscope in the development stage to facilitate data analysis. Practical application shows that the tester is stable and reliable.