Study On Driving Technology Of Piezoelectric In Vertical Pendulum Tiltmeter

Observation of Earth’s solid tide not only provides a window to understand the Earth’s internal structure, and provides important research data for modern contemporary space geodesy, precision gravity measurements and astronomical longitude and latitude measurements. Vertical pendulum tiltmeter is the relatively representative one of which are used to observe and study the Earth’s solid tide.On one hand, the traditional vertical pendulum tiltmeter has advantages in construction,installation, operation, maintenance and so on. On the other hand, it has some shortcomings of small measuring range, nonlinear error and so on. In this paper, we will use the capacitance-to-angle sensors, ADC ads8556, FPGA chip, DAC ad5745R, driving circuit,piezoelectric to form an angle feedback to increase measurement range and reduce nonlinear error of vertical pendulum tiltmeter.The vertical pendulum tiltmeter detects tilt signal by the variety of relative position between the pendulum and its bracket. The pendulum and the plates fixed around the floor form a pair of differential capacitances, In a horizontal state, the values of the two capacitances are equal, but in a state of imbalance, there will be a corresponding difference between the two capacitances, and then the difference can be transformed to voltage by the capacitance-to-angle sensors, and ADS8556 collects the voltage which will be uploaded to PC software. On this basis, this paper will design feedback vertical pendulum tiltmeter, and the voltage collected by ADS8556 will be sent to PID program modules and former piezoelectric feed-forward control module to get the driving amount which will be exported by DAC AD5745. The output of AD5745 will be amplified by the drive circuit to drive the piezoelectric. The output of the drive circuit can drive piezoelectric reach a certain expected displacement which can make the vertical pendulum tiltmeter resume the horizontal state.Driving voltage reflects the amount of tilt. Since the pendulum position deviating from its equilibrium in vertical pendulum tiltmeter with feedback is smaller than those in the tiltmeter without feedback, the nonlinear error of pendulum caused by too much deviation from the equilibrium position will be reduced, and measurement range has also been increased.In order to control the piezoelectric, this article established a relatively accurate piezoelectric polycyclic hysteresis model, and designed the method based on the inverse model to control the expected displacement of piezoelectric. To improve the control performance of the system and reduce the tracking error, this paper introduced the digital PID controller to form a compound control scheme composed of piezoelectric inverse model and digital PID. The control scheme uses verilog hardware description language as the carrier eventually be realized in FPGA, the parameter of control system is obtained by using simulation.In order to display and storage the running results of vertical pendulum tiltmeter with feedback, we used Labview to design PC software which can display, storage, convert and draw constantly the data of FPGA uploaded by the Serial ports. In this process, the paper also solves the problem that the RS232 serial port can’t simultaneously transmit data with 16 bits.The paper debugged all parts of vertical pendulum tiltmeter including its mechanical structure, hardware circuits and controlling algorithm and PC software. Finally, we did some experiments to test the vertical pendulum tiltmeter with feedback and analyze the experimental data, and the results show that the design of the titlmeter achieved the desired results.