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This paper discusses the effect of friction in tool-tissue interaction of surgical simulation. The focus of this research is on mitral valve repair by robot-assisted surgery (RAS) method with tactile feedback. Heart tissue is considered to be touched by a tactile sensor with considering the friction effect. A regularized Coulomb law analogous to elastoplastic theory is used to represent the friction. Since the heart tissue is subjected to repeated loading condition, a generalized standard solid chain is chosen for modeling the heart tissue. To implement the generalized standard solid chain in finite element analysis (FEA), a new splitting strategy is presented. The splitting strategy avoids the complicated conversion procedure from creep function to relaxation function by dividing the total problem into several subproblems. The penalty method is used in the derivation of continuum model for the interaction between the tactile sensor and the tissue. By performing linearization for the continuum model, the discrete model for the FEA is obtained. Numerical results are obtained by using the constitutive parameters of tissue and friction coefficient, which were found experimentally.

Different from the general 6-SPS Stewart platform, 6-PUS parallel mechanism is a kind of fully parallel mechanism whose actuators are all fixed at the frame. The advantages of this mechanism are light movable mass, small inertia and good dynamic characteristics. This paper is focused on the singularity analysis of the 6-PUS parallel mechanism. Based on the Jacobian matrix which is derived from the kinematical equation, the analytic singularity locus equations are obtained and the three types singularities of the parallel mechanism are analyzed. Moreover, the position-singularity of the mechanism is discussed through some specific examples.

This paper describes two aspects of multibody system (MBS) dynamics on a generalized mass metric in Riemannian velocity space and recursive momentum formulation. Firstly, we present a detailed expression of the Riemannian metric and operator factorization of a generalized mass tensor for the dynamics of general-topology rigid MBS. The derived expression allows a clearly understanding the components of the generalized mass tensor, which also constitute a metric of the Riemannian velocity space. It is being the fact that there does exist a common metric in Lagrange and recursive Newton-Euler dynamic equation, we can determine, from the Riemannian geometric point of view, that there is the equivalent relationship between the two approaches to a given MBS. Next, from the generalized momentum definition in the derivation of the Riemannian velocity metrics, recursive momentum equations of MBS dynamics are developed for progressively more complex systems: serial chains, topological trees, and closed-loop systems. Through the principle of impulse and momentum, a new method is proposed for reorienting and locating the MBS form a given initial orientation and location to desired final ones without needing to solve the motion equations.

The parallel structure of the sensor, which based on Stewart platform, has a direct impact on the technical quota. This article uses Genetic Algorithm to parameterize the model of the sensor. Take the isotropy target of the sensor as objective function, and take five basic structural parameters of the Stewart platform as design variables. Then it optimizes the structure of the sensor. Then apply the virtual prototype technology of ADAMS to simulate. At last, it found the transformation relation between the isotropy target of the sensor and each parameter. It can offer an important gist for optimizing the structure of the sensor.