IMPEDANCE SHAPING FOR IMPROVED FEEL IN HYDRAULIC SYSTEMS

ABSTRACT Applying haptic control to mobile hydraulic equipment presents a practical yet challenging application. One criticism of newer electro-hydraulic system is a lack of "feel." To a haptics researcher this sounds like a call for haptic feedback in the human-machine interface. However, for an operator the "feel" of the system likely has more to do with how the actual system responds to forces or higher work port pressures. At some point, the high pressures slow down the system or naturally redirect flow to lower pressure circuits in a hydro-mechanical system. How this is done plays a large part in the "feel" of the system. In this paper, a paradigm is presented that tries to merge these two concepts of "feel." Instead of trying to make the system transparent, the goal is to make the system react to forces acting on the system then use haptic feedback to help alert the operator to these forces. This is done by shaping this impedance so that the system provides a response or "feel" that is closer to a typical excavator. A haptic interface is used to enhance the haptic feel. Performance is evaluated using data from human-in-the-loop testing INTRODUCTION The definition of haptics is of or relating to the sense of touch. Haptic control implies that the human-machine interface can be programmed to artificially supply the user with arbitrary force sensations. Typically the haptic force is used to relay information about the force acting on a remote or virtual environment. Haptic feedback means that information can be fed back to the operator in the form of force signals. In the case of backhoes/excavators, force signals can be generated by virtual fixtures Haptic devices can also enable coordinated motion control. Today almost all commercial backhoes/excavators are controlled by joystick commands from human operators that are mapped directly into the joint-space of the manipulator. Coordinated control is a subtle yet profound improvement over conventional hand controllers that work in joint space. Using joysticks that individ