Physical interaction with a virtual knee joint - The 9 DOF haptic display of the Munich Knee Joint Simulator

In specific fields, medical education at many universities is rather theoretical and the amount of practical training is limited. A significant improvement can be achieved using virtual reality training stations with lifelike visual, acoustic, tactile, and kinesthetic feedback Particularly, when simulating procedures that require direct contact with the patient body, a realistic haptic simulation addressing tactile and kinesthetic senses can be essential for the acceptance of virtual simulation stations. A purely passive phantom may provide realistic haptic feedback, but its properties cannot be changed over time. This paper presents the haptic display of the Munich Knee Joint Simulator, which was developed to improve training and education of physical knee joint examinations. The haptic interface comprises a combination of passive phantom segments providing realistic tactile sensations, and strong actuators generating highly dynamic kinesthetic force feedback. A 3 degree of freedom (DOF) manipulator was developed in this study to drive the thigh prosthesis and one 6 DOF industrial robot was used to actuate the shank prosthesis. Both manipulators are driven by hybrid admittance-impedance controllers capable of simulating the complex dynamics of the thigh and the shank. Both actuators are equipped with a 6 DOF force torque sensor and they are virtually coupled by an analytical knee joint model. The proposed setup is capable of simulating a mechanical stiffness as high as 80 kN/m in the translatory DOF and simultaneously allows free motion in the rotatory DOF. Experimental tests of the simulator with orthopedic physicians proved the usability of the proposed concept.