The remaining aspect of robot simulation is calculating external force from environment. Two major subproblems of this are detecting collisions and computing collision forces. Although studied in isolation, these problems are closely related in simulation. This paper presents a method for fitting the pieces together on the rigid bodies which are formed convex polyhedron and covered with rubber-like material. We consider that the collision force between such objects is the function of the intersection of those, therefore calculating the collision force comes to finding the shape of the convex polyhedron because the intersection of two convex polyhedra is also a convex polyhedron. In order to find the shape of the convex polytope, we propose an approach based on the revised simplex method, which computational cost is approximately linear in the total number of faces.