Velocity Control of Hydraulic Cylinders With Only Pressure Feedback

The lack of position or velocity feedback is a very common problem particularly on construction equipment such as excavators and backhoes. The extra cost of adding position/velocity sensors is prohibitive as well as the high likelihood of sensor failure in such a harsh environment. These factors make the possibility of improving control performance with limited sensory feedback very attractive. This paper studies the velocity control of a single-rod double actuating hydraulic cylinder utilizing a programmable valve with only cylinder pressure feedback. The boom motion control of a scaled-down model of an industrial backhoe loader arm is used as a case study. The programmable valve used in this study is a unique combination of five proportional cartridge valves connected in such a way that the meter-in and meter-out flows can be independently controlled by four of the valves as well as a true cross port flow controlled by the fifth valve. The programmable valve decouples the control of the meter-in and meter-out flows providing tremendous control flexibility to control the cylinder motion while decreasing the pump energy required by utilizing the potential and kinetic energy of the load. This paper demonstrates the potential energy savings possible through the use of the programmable valve. The paper also proves that significant improvements in the velocity tracking performance of hydraulic cylinders can be attained with only pressure feedback.