For the data storage industry, disk drive manufacturers expand the capacity and performance of computer hard disk drives by increasing track density (in the number of tracks per inch) and disk rotation speed (in the number of revolutions per minute). As the magnetic density increases, the distance between two adjacent tracks becomes smaller. Therefore, the allowable deviation error of the read/write head and the magnetic track, which is called misalignment in the disk drive industry, is also reduced accordingly, so that the hard disk is easily damaged. His working principle determines that it must use anti-harsh environment reinforcement technology, and it mainly implements reinforcement for the mechanical physical environment and the climatic environment. For disk storage devices, the most severe mechanical and physical environment is vibration and shock environments. This paper adopts external reinforcement active control theory and technology, uses electromagnetic active control technology for external reinforcement of computer external equipment (microdisk) vibration and shock, and builds a digital active control system with DSP as the hardware platform.
2 Hardware design of digital control system
Since TI (Texas Instruments, USA) introduced the universal programmable DSP chip in 1982, DSP technology has achieved rapid development.
2.1 Principle of control system
The digital signal processor (DSP) has real-time signal processing capabilities and powerful arithmetic functions. The working principle of the system is that the basic acceleration sensor picks up the basic vibration and shock acceleration signal, and then sends it to the preamplifier. After the charge amplifier output signal is sampled by A/D by the DSP, the signal is integrated (converted into a speed signal) and Two-time integration (converted into displacement signal) operation, the two integration results are summed, and then the result is input to the power amplifier after D/A conversion, and finally the power amplifier output signal is added to the actuator in the form of a control voltage Above, the actuator will generate corresponding power to offset the vibration and impact from the foundation. Because the DSP chip integrates 10b A/D, the analog signal can be directly connected to the DSP. Figure 1 is the block diagram of the entire digital control system.
2.2 DAC interface and external memory expansion
The D/A device in the system selects DAC761l of URR-BROWN Company. Because the voltage input range of 10bA/ within the DSP is 0-5V, the input signal is converted from A/D by a value of 0-1 023 (decimal number) to correspond to the voltage signal of 0-5V respectively. Therefore, the input signal of DSP is no longer a positive and negative symmetrical signal, and the output range of DAC7611 in the system is 0～4.095V, and the input of the power amplifier in the latter stage of the system should be zero-averaged, so it is necessary to use an operational amplifier for the DAC output signal. Level conversion.
In addition, DAC7611 has very strict requirements for clock signals. He requires the rising edge of its clock signal to occur during the transmission of each bit of data. The SPI (Serial Peripheral Interface) of TMS320F243 is a high-speed, synchronous serial I/O port. It can set the number of bits (1-16 bits) of the serial data stream generated each time, and the bit transmission speed can also be Programming control. The SPI clock output signal line SPICLK can provide 4 types of clock signals. Among them, there is a rising edge clock with delay, which enables SPI to send data in the half period before the rising edge or receive data after the rising edge of the SPICLK signal. This happens to meet the requirements of the DAC7611 clock signal.
Due to the limited resources on the DSP chip, RAMCY71021, which is used to store data, is expanded outside the chip in the design. The read and write time is 12ns, which matches the speed of the DSP. And the chip will automatically adopt a low-power working mode when it is not being operated. When using DSP's serial peripheral interface to transmit data to D/A, the system also uses optocoupler devices to isolate digital and analog circuits. The peripheral interface circuit is shown as in Fig. 2.
After the system is powered on, the program is first executed from the FLSH program ROM on the chip, so the pin MP/MC must be connected to the microprocessor mode.
3 Software design of digital control system
3.1 Control algorithm
After in-depth research and a lot of analysis and calculation, the electromechanical dynamics model of the system is as follows:
The system's sensing detection equation:
Among them: u is the basic vibration acceleration:
c1, k1 are the second-order integral and the first-order integral coefficient respectively related to the fundamental vibration.
Let u be the charge amplification signal of u. According to the control requirements, the system mainly uses DSP to complete the following operations:
And use the mean value compensation method to correct the integration result to realize the control of the digital system. Discretize the above formula to generate:
Obviously this requires 2 integration operations, and the operation process is as follows:
Among them: m1 (n), m2 (n) are the mean value of the first and second integral operations respectively.
3.2 System software design and implementation
The main function of the system header file (extension .h) is to correspond the name of each special function register inside the DSP to its default address. During the execution of assembly language, the DSP pointer will directly access the address specified in the header file according to the register name. The command file (extension .cmd) is actually the resource configuration file of the DSP. On the PAGE0 page (program space), it defines the starting address and space length of each program module. The definition of the table, etc.; in the PAGE1 page (data space), he defines the starting address and space length of each data module, such as the definition of the internal and external data areas of various parameters. In addition, attention should be paid to comply with the DSP actual memory and storage space conventions.
Since the system mainly communicates with its peripheral devices through the ADC module and SPI module of the DSP, their operating modes need to be configured in the software design. Regarding the working mode of the on-chip ADC: first determine the startup mode of the ADC, and then make the ADC reach a sampling rate of 10kHz. In order to ensure an accurate sampling rate, an interrupt is generated by the internal counter of the DSP as the starting method of the ADC. Because the machine instruction cycle of TMS320F243 is 50ns, it can run at most about 2,000 instruction cycles within the two sampling time interval, otherwise real-time operations cannot be completed. For the SPI module: first set its communication mode as the main mode, so that the data is removed from the SPISIMO pin according to the timing; then set the number of bits of serial data transmitted each time, clock signal mode, transmission rate, etc. Because the D/A device outside the DSP chip is 12b, and the data bus bit of the DSP is 16b, the final calculation result must be adjusted accordingly and then sent out by the SPI.
In addition, the A/D inside the DSP corresponds to the input voltage signal of 0 to 5V by the value 0 to 1 023 (decimal number), so the value of 511 should be used to represent the zero mean point, which should be paid special attention to during mean value compensation. The system program flow chart is shown as in Fig. 3.
4 Conclusion
Using DSP to directly realize electromechanical control is a technology that has only been developed in recent years, and it has distinct advantages over traditional control methods. Experiments show that the digital control system with DSP as the core can realize real-time control, and the phase error of the low frequency band is very small, and at the same time, it can take into account the higher frequency band and has a large application range. In addition, it has good stability, high accuracy, and easy control of complex models.
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