FREQUENCY DOMAIN MODELLING AND IDENTIFICATION OF 2D DIGITAL SERVO VALVE

Authors

  • Jian Ruan Department of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014, P.R. China
  • Paul R. Ukrainetz Department of Mechanical Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, Saskachewan, Canada, S7N 5A9
  • Richard Burton Department of Mechanical Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, Saskachewan, Canada, S7N 5A9

Keywords:

servo valve, digital control, dynamic modelling, frequency response

Abstract

The 2D digital servo valve studied here is a two-stage valve designed by using both rotary (angular) and linear mo-tions of a spool. The rotary motion is driven by a stepper motor operating under continual angular displacement control, while the linear motion of the spool is actuated by hydraulic servo control with feedback of the spool’s displacement, which is achieved by a unique “servo screw”.

The modelling of the 2D valve is based on linear theory and is further verified by the special experiments. Because of the extremely large hydraulic natural frequency, the control of the 2D valve is identified as being that of a first-order-system. The relation between the time constant and the structural parameters is established, accounting for the non-linearity of the pilot hydraulic bridge. For the continual control of the stepper motor, a mathematical model con-sidering the rotary motion, the rotating magnetic field and the angular control signal is established. In order to prevent the stepper motor from losing steps, the rate of the control signal is limited to a certain range. As a result, this may cause a non-linearity and, consequently, the deformation of the waveform when the input sinusoid wave is of large amplitude and high frequency. By utilizing the method of the description function, the effect of limiting the rate of the control signal is approximated as a first-order-system and the relation between the time constant and the amplitude and frequency is presented. The dynamic characteristics of the stepper motor are to a large extent dependent upon the way the power is supplied. For a constant current supply, the stepper motor can be classified as a second-order-system. The factors af-fecting the natural frequency and damping ratio are clarified. Finally, the frequency response of the 2D digital valve is experimentally measured and compared with theoretical results. Both theoretical and experimental results show that the 2D digital valve has a fairly high frequency response, especially when the valve operates near the central position. For a 25% full scale input signal, the 2D digital servo valve has at least 300 Hz under the gain of –3 dB.

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Author Biographies

Jian Ruan, Department of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014, P.R. China

Jian Ruan Born on April 4th 1963 in Fuan City of Fujiang Province, P.R. China. Receving Ph. D. from Harbin Institute of Technology in Sept. 1989. Study of electro-hydraulic (pneumatic) direct digital control compo-nents and systems. Post-doctoral fellow of FPTC, Zhejiang University. Professor of Mechanical Engineering at Zhejiang Uni-versity of Technology

Paul R. Ukrainetz, Department of Mechanical Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, Saskachewan, Canada, S7N 5A9

Paul Ukrainetz BE. 1957 U of S, M.Sc. 1960 Univ. of British Columbia, Ph.D. 1962 Purdue University Bristol Aeroplane Co. 1957 U of S Assistant Professor 1962 U of S Associate Professor 1966 U of S Full Professor 1971 Head Department of Mechanical Engineering, U of S. 1974 – 1982, Professor Emeritus, 1999 - date. Active in Fluid Power Systems since 1962.

Richard Burton, Department of Mechanical Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, Saskachewan, Canada, S7N 5A9

Richard Burton Born Sept. 6, 1947. Richard Burton is a Professor of Mechanical Engineering at the University of Saskatche-wan, Saskatoon, Canada and is now Assistant Dean of Undergraduate Studies at this same institution. He received his B.E degree in Engineering Physics and M.Sc. and Ph.D. in Hydraulic Controls from the Univ. of Sas-katchewan. He has been and continues to be active in research in the Fluid Power area. He is a member of the ASME (FPST), SAE and NCFP Advisory Boards. He is also convenor for FPN (Canada).

References

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Published

2000-10-01

How to Cite

Ruan, J., Ukrainetz, P. R., & Burton, R. (2000). FREQUENCY DOMAIN MODELLING AND IDENTIFICATION OF 2D DIGITAL SERVO VALVE. International Journal of Fluid Power, 1(2), 49–58. Retrieved from https://journals.riverpublishers.com/index.php/IJFP/article/view/651

Issue

2000: Vol 01 Iss 2

Section

Original Article