The recent success of deep learning in 3-D data analysis relies upon the availability of large annotated data sets. However, creating 3-D data sets with point-level labels are extremely challenging and require a huge amount of human efforts. This paper presents a novel open-sourced method to extract light detection and ranging point clouds with ground truth annotations from a simulator automatically. The virtual sensor can be configured to simulate various real devices, from 2-D laser scanners to 3-D real-time sensors. Experiments are conducted to show that using additional synthetic data for training can: 1) achieve a visible performance boost in accuracy; 2) reduce the amount of manually labeled real-world data; and 3) help to improve the generalization performance across data sets.
Force feedback coupled with a real-time physically realistic graphic display provides a human operator with an artificial sense of presence in a virtual environment. Furthermore, it allows a human operator to interact with the virtual environment through "touch". In this paper, we describe a haptic simulation system that allows a human operator to perform real-time interaction with soft 3D objects that go through large global deformations. We model and simulate such a global deformation using geometrically nonlinear finite element methods (FEM). We also introduce an efficient method that computes the force feedback, in real-time, by simulating the collision between the virtual "proxy" and the deformable object. To perceptually satisfy a human operator, haptics requires a much higher update frequency (at least 1000Hz) than graphics. We update the graphics using full simulation and interpolate the fully simulated states at a higher frequency to render haptics. The interpolation is made possible by intentionally delaying the display (both graphics and haptics) by one full simulation cycle.
Global Deformation Using Nonlinear FEM:We apply the displacement based finite element methods (FEM) to the simulation of large motions and global deformations of deformable objects. A linear strain model leads to unacceptable distortion (figure 1). To avoid this problem, we apply a quadratic strain instead (figure 1). Essentially this requires solving the following nonlinear system of differential equationswhere u is the nodal displacements; _ u and u, the respective velocities and accelerations; F, the external force; M, the mass matrix; D, the damping matrix; and Ru, the nonlinear internal force due to deformation.For a soft material such as live tissue, the material stiffness is small. This makes explicit time integration scheme appropriate because we can take large time steps. In particular We apply explicit Newmark scheme to equation (1).We diagonalize the mass matrix M and the damping matrix D.This leads to a decoupled system of nonlinear equations, which requires no matrix inversions to solve. Figure 1:The left end of the beam is fixed. The left image shows its distorted deformation under gravity, using linear strain. The right image shows the undistorted deformation, under the same gravitational force, using quadratic strain.Collision Integration Scheme: Simulating deformable object collisions using a penalty method [3] requires tiny time steps to product visually satisfactory animations. A general impulse collision [1] is considered more efficient and accurate but still requires more computation than collision-free dynamics.For deformable object collisions, the collision time can be assumed finite (unlike the instantaneous collision of rigid bodies). By recognizing this, we propose an efficient way to handle collision.Consider the collision between a deformable body with a stationary rigid body (figure 2). Assume at time tn, the node p, with velocitŷ vpn, is colliding with a rigid surface of outward normaln. Then the non-penetration constraint at node p can be enforced by setting the normal component ofvpn+1 to zero as following:If we choose 4tn+1 = 4tn for the Newmark scheme, we havê un+2 n =ûn n This shows that the non-penetration constraint is exactly enforced after two time steps, without solving a constrained problem. For a decoupled system, this collision handling scheme can be easily generalized to multiple point collision constraint. And unlike the coupled system, no explicit impulse calculation is necessary for frictionless collisions. When friction has to be considered, the equivalent impulse can be easily computed without matrix inversion. This collision-handling integration scheme can be easily generalized to collisions between a deformable body and a moving rigid body, and to collisions between deformable bodies. It is worth noting that a deformable object's resting on a surface can be handled exactly the same way. Graded Mesh: While 2D FEM has great success in achieving real time performance in computer graphics applications, the computational cost is much higher for 3D applications, main...
Abstract-Many of the most fundamental examples in probability involve the pose statistics of coins and dice as they are dropped on a flat surface. For these parts, the probability assigned to each stable face is justified based on part symmetry, although most gamblers are familiar with the possibility of loaded dice. In industrial part feeding, parts also arrive in random orientations. We consider the following problem: given part geometry and parameters such as center of mass, estimate the probability of encountering each stable pose of the part.We describe three estimators for solving this problem for polyhedral parts with known center of mass. The first estimator uses a quasistatic motion model that is computed in time O(n log n) for a part with n vertices. The second estimator has the same time complexity but takes into account a measure of dynamic stability based on perturbation. The third estimator uses repeated Monte Carlo experiments wit(15ra05-goldberg)h a mechanics simulation package. To evaluate these estimators, we used a robot and computer vision system to record the pose statistics based on 3595 physical drop experiments with four different parts. We compare this data to the results from each estimator. We believe this is the first paper to systematically compare alternative estimators and to correlate their performance with statistically significant experiments on industrial parts.
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