Heavy-duty robots using hydraulic actuators are expected to support rescue operations by removing heavy rubble in hostile -wet, dusty, or muddy- environments. The high friction generated by their hydraulic actuator, however, makes it difficult to use them in operations requiring high precision. The servovalves used to control a hydraulic actuator precisely are more expensive than conventional proportional valves, making it impractical to install them in all joints of heavy-duty robots having many degrees of freedom. In this paper, a new hydraulic actuator control method using a feedback modulator is proposed. The proposed controller improves the performance of hydraulic systems using conventional proportional valves, making it as good as that with servovalves. This paper also proposes exclusive control for controlling multiple joints simultaneously to prevent asynchronous joint movement under unbalanced loads. The effectiveness of the proposed method is confirmed through simulations and experiments.

1. [1] Y. Hiyama, “Rescue Robot “ENRYU”,” Proc. of 2004 SICE System Integration Division Annual Conference, Tsukuba, Japan, pp.999-1000, 2004 (in Japanese).
2. [2] N. R. Parker, S. E. Salcudean, and P. D. Lawrence, “Application of Force Feedback to Heavy Duty Hydraulic Machines,” Proc. of 1993 IEEE Int. Conf. on Robotics and Automation, Vol.1, pp. 375-381, 1993.
3. [3] S. E. Salcudean, K. Hashtrudi-Zaad, S. Tafazoli, S. P. DiMaio, and C. Reboulet, “Bilateral Matched-Impedance Teleoperation with Application to Excavator Control,” IEEE Control Systems, Vol.19, No.6, pp. 29-37, 1999.
4. [4] P. Lischinsky, C. Canudas-de-Wit, and G. Morel, “Friction Compensation for an Industrial Hydraulic Robot,” IEEE Control Systems, Vol.19, No.1, pp. 25-32, 1999.
5. [5] H. Katoh, T. Nishiumi, and T. Ichiyanagi, “Improvement of Angular Position Control Characteristics for a Hydraulic Motor with Dead Zone by Means of a Neural Network and Superimposed Small Oscillation,” Trans. of the Japan Fluid Power System Society, Vol.35, No.5, pp. 89-96, 2004. (in Japanese)
6. [6] W. S. Owen and E. A. Croft, “The Reduction of Stick-Slip Friction in Hydraulic Actuators,” IEEE/ASME Trans. on Mechatronics, Vol.8, No.3, pp. 362-371, 2003.
7. [7] B. Yao, F. Bu, J. Reedy, and T.-C. Chiu, “Adaptive Robust Motion Control of Single-Rod Hydraulic Actuators: Theory and Experiments,” IEEE/ASME Trans. on Mechatronics, Vol.5, No.1, pp. 79-91, 2000.
8. [8] G. A. Sohl and J. E. Bobrow, “Experiments and Simulations on the Nonlinear Control of a Hydraulic Servosystem,” IEEE Trans. on Control Systems Technology, Vol.7, No.2, pp. 238-247, 1999.
9. [9] A. Bonchis, P. I. Corke, and D. C. Rye, “Experimental Evaluation of Position Control Methods for Hydraulic Systems,” IEEE Trans. on Control Systems Technology, Vol.10, No.6, pp. 876-882, 2002.
10. [10] M. Ishikawa, I. Maruta, and T. Sugie, “Quantized Controller Design Using Feedback Modulators,” Transactions of the Society of Instrument and Control Engineers, Vol.43, No.1, pp. 31-36, 2007 (in Japanese).
11. [11] T. Katayama, “Introduction to System Identification,” The Institute of Systems, Control and Information Engineers, 1994 (in Japanese).