Research On Key Technology Of High Accuracy Servo Turntable

High accuracy servo turntable is a kind of key device for the inertial instruments testing and it should be improved by one order of magnitude compared with the instruments to be tested,only in this way tests will make sense. The precision of the angular measurement system and the control system are main factors which detemine the precision of the system. In regard to the developing high accuracy servo turntable which precision of the angular measurement is 0.5 arc sec, it is very difficult to realize to use inductosyn as angular sensor,so I used circular grating as the angular measuring component.In my article I used a single-axis turntable in my lab as the experimental platform and I reseached the key technology to improve the precision of servo turntable,it include the subdivision of grating signal,the multiple readheads structure to eliminate errors and the corresponding design promblems of discrete repetitive controller system.It is the key of the grating subdivision and distinguish direction to improve the precision of measurement. First the article introduced the structure and the work principle of grating,then analysed the quadrature characteristic of grating output signal and it is essential to distinguish direction circuit. And then briefly introduced the common grating signal subdivision, and the characteristics of these types of subdivision were compared to select the appropriate of the system.In order to increase the reading accuracy, the paper has studied in the multiple readheads structure of the measurement equipment. First the article introduced and analyzes the principle of eliminating error of the optical scale's multiple readheads structure, then explained separately from two aspects the principle of its multiple readheads structure to eliminated error according to the difference of the circle grating's output signal. As a result of the craft and other aspect's reason, the actual system usually only places two readheads to the diameter position,but if the readheads were not installed to diameter's twoterminals, it will affect the reading value. In order to confirm the superiority of the double readheads structure in the actual angular measurement system, the paper analysed and compared the test data of the angulat measurement error between single readhead and double readheads structure.The paper then introduced control system structure and working principle of the turntable,and specified the design and implementation of he hardware circuit. The system uses DSP to achieve real-time control, and use an FPGA chip to complete the functions such as grating's subdivision,distinguish direction, counter and latch and so on.Last, the turntable control system was designed according to the mathematical models and performance specification of the system. First I designed the phase-lead controller and filter and then obtained the corresponding digital controller after selecting a reasonable sample time. To reject the periodic disturbances in mid-frequency band effectively,and further improve the rate accuracy,the article raised a design scheme which inserts repetitive controller in the phase-lead controller,and discussed the corresponding design promblems of discrete repetitive controller system and selected the structure and parameters of the controller. Through simulation a conclusion had been obtained that repetitive controller can reject periodic interference more effectively.