Analysis of the characteristics of the particle spring model

Collision detection is a precondition for calculating the deformation of human tissue. The fast and accurate collision detection algorithm directly affects the authenticity of human-computer interaction. An obvious feature of the particle-spring model is that when subjected to force, it is automatically treated as a point-to-point interaction. When the virtual device acts on the liver tissue, the model directly assigns the stressed area to an adjacent particle, rather than a Face.

The collision between the PHANTOM device and the virtual object is a point-to-body collision detection model, and the contact with the tissue is limited to the apex of the joystick. In view of this, taking into account the irregularity of the liver model, the complexity of constructing the bounding box and the difficulty of updating the bounding box after deformation, we propose the following collision detection algorithm: the top of the surgical instrument is represented by a three-dimensional point, through the sense of touch The delivery engine obtains the position mpos of the virtual instrument in real time, and then calculates the distance from the static mass point on the liver model in turn. When the distance is less than or equal to zero, it is determined that the collision occurs, and the vertex sequence number of the collided particle is returned.

No collision is detected, the position of the "agent" is consistent with the position displayed on the display by the surgical instrument. Once the collision is detected, the position of the "agent" is the actual position of the device "piercing" the liver tissue in the display. The surgical instrument seen by the human eye stops at the collision point, the Surface Contact Point (SCP). At this time, the distance between the "agent" and the surface contact point is that the device "presses" the surface of the liver. Depth, from which the feedback force can be calculated.

The deformation effect of liver force is applied by virtual surgical instruments to the same model at the same node. The displacements of the model at the same node are recorded, and the quadratic curve is fitted to bear the external force of equal size. The more the number of discrete particles in the liver model, the smaller the displacement produced. Conversely, under the same displacement, as the number of discrete particles in the liver model increases, the resultant force of the node also increases significantly.

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