Improved system software and hardware design based on DSP chip to realize compaction measurement

introduction

In the late 1980s, domestic research on compaction meters began, and airborne compaction meters were also developed. Due to the use of digital tube display, advanced computer technology was not used. Although the cost is low, it is in practical application. The effect is not ideal. The real-time performance of the instrument is not strong, and the displayed value and the actual measured value cannot correspond well.

Based on the existing domestic and foreign testing methods, this article improves the existing compaction measurement system. The advanced DSP chip is used as the main controller, and the high-speed computing capability of the DSP is fully utilized to achieve real-time and accurate measurement of the degree of compaction of the compacted road.

  working principle

The pressing principle of modern rollers can be divided into static rollers, vibratory rollers and impact rollers. Among them, the vibratory roller is a kind of compaction machinery widely used in China, which is mainly composed of an engine, a transmission system, an operating system, a walking device and a frame. The vibrating wheel is a driven wheel and also a compacting wheel, which adopts an unbalanced eccentric block structure. When the vibratory roller is in operation, the vibrating wheel drives the eccentric block to rotate at a high speed, and the centrifugal force generated by the eccentric block becomes an interference force. The vibrating wheel transfers this interference force to the soil, causing the roadbed to vibrate. Under the action of the vibrating wheel’s own gravity and impact, the friction and cohesive force between the roadbed soil particles are overcome, and the small particles are filled into the large particles of soil. In the gap, the degree of compaction of the roadbed increases.

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The 　　 vibratory roller model is shown in Figure 1. In a compaction system composed of a vibratory roller and a roadbed, the change of the dynamic parameters of the vibrating wheel is closely related to the stiffness of the road surface, and the stiffness of the road surface is positively related to the degree of compaction. Therefore, the dynamic parameter changes of the vibrating wheel and the compaction The actual degree is closely related. Through the analysis of the dynamic parameters of the vibrating wheel, the change in the degree of road compaction can be reflected.

In the initial stage of compaction, the subgrade filling is relatively loose, the degree of compaction is low, and the elastic stiffness of the subgrade is small, so the damping is large and the response of the vibrating wheel is small. As the number of compactions increases, the stiffness of the roadbed increases, the damping becomes smaller, and the response of the vibrating wheel becomes larger.

When the degree of compaction of the road surface is increased to a certain extent, due to the imbalance and nonlinearity of the eccentric mass system, the vibratory roller can generate bounce, thus generating special sub-harmonic components. And the higher the degree of compaction, the higher the sub-harmonic component. By calibrating the ratio of the fundamental wave to the second harmonic and the degree of compaction, an accurate measurement of the degree of compaction can be achieved.

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Hardware system design

The basic principle of integrated system hardware design is: safe and reliable: hardware equipment must meet the temperature, humidity, vibration, dust and other requirements of the use environment. Sufficient anti-jamming capability: The hardware system has complete anti-jamming measures, which is a necessary condition to ensure the normal operation of the system. Economical and reasonable: The computer and external equipment should be reasonably selected and designed on the basis of the speed, storage capacity, compatibility, and reliability of the test system.

In view of the many sampling parameters involved in the system, the large amount of calculation, and high real-time requirements, it is difficult to meet the system design requirements with ordinary single-chip microcomputers. Therefore, this system uses Texas Instruments (TI) TMS320LF2407A (hereinafter referred to as LF2407A) processor as the main control chip.

The basic structure of the hardware system is shown in Figure 2. The acceleration sensor is installed on the bearing of the compaction wheel of the vibratory roller to collect the vertical acceleration signal of the vibrating wheel. This signal contains interference waves from the bearing, the excitation motor, etc. After being amplified by the charge amplifier, it is divided into two paths. One path is filtered by a filter, after removing the interference wave signal, it is sent to A/D sampling channel 2; the other is sent to A/D sampling channel 3 through a harmonic filter, where the function of the harmonic filter is to only vibrate The generated harmonics pass. In the LF2407A, A/D conversion is performed on the two signals first, and then the digital signals are respectively subjected to fast Fourier transform, and finally a value proportional to the degree of compaction of the roadbed is obtained. By calibrating the value and the degree of compaction, It can be used to accurately represent the change in the degree of compaction value.

The speed sensor is installed on the wheel, and the collected signal is input to A/D sampling channel 1, which is used to calculate the driving speed and mileage of the vibratory roller.

The keyboard is used to input user instructions. It is a key component in the system. Through the keyboard button response and LCD menu selection, it can realize the functions of detecting mileage setting, roller parameter setting, vibration frequency display, saving, printing and so on.

software system design

Software is the key to realize various functions of integrated system. The basic principles of software design are:

①The structure is reasonable. The program adopts structural modular design. This is not only conducive to the further expansion of the program, but also conducive to the modification and maintenance of the program.

②Good operation performance. When designing the software system, it is necessary to consider reducing the requirements for operator knowledge as much as possible, so that the system interface is concise and easy to operate.

③With certain self-diagnosis function. The system designs corresponding detection procedures so that when a failure occurs, it is easy to find the fault location.

Support assembly language and C language programming. When using C language programming, the code optimization rate can reach 90%. And assembly language can be embedded in the programming process, so programming is flexible and convenient.

The software design process is shown in Figure 3. Among them, the button service subroutine includes: detection mileage setting, roller parameter setting, soil type setting, continuous dynamic detection setting, save, print, exit, etc.

Conclusion

The system discussed in this article uses advanced DSP based on the existing detection technology, and the driver can view the compaction situation, vibration frequency, and operating speed from the display at any time, and can achieve real-time control of compaction quality with high and real-time performance. Strong.