The aggregate motion of a flock of birds, a herd of land animals, or a school of fish is a beautiful and familiar part of the natural world. But this type of complex motion is rarely seen in computer animation. This paper explores an approach based on simulation as an alternative to scripting the paths of each bird individually. The simulated flock is an elaboration of a particle systems, with the simulated birds being the particles. The aggregate motion of the simulated flock is created by a distributed behavioral model much like that at work in a natural flock; the birds choose their own course. Each simulated bird is implemented as an independent actor that navigates according to its local perception of the dynamic environment, the laws of simulated physics that rule its motion, and a set of behaviors programmed into it by the "animator." The aggregate motion of the simulated flock is the result of the dense interaction of the relatively simple behaviors of the individual simulated birds.

/pdf/flocks-herds-and-schools-a-distributed-behavioral-model-5u7ofvq11i.pdf

Flocks, herds and schools: A distributed behavioral model

The aggregate motion of a flock of birds, a herd of land animals, or a school of fish is a beautiful and familiar part of the natural world. But this type of complex motion is rarely seen in computer animation. This paper explores an approach based on simulation as an alternative to scripting the paths of each bird individually. The simulated flock is an elaboration of a particle system, with the simulated birds being the particles. The aggregate motion of the simulated flock is created by a distributed behavioral model much like that at work in a natural flock; the birds choose their own course. Each simulated bird is implemented as an independent actor that navigates according to its local perception of the dynamic environment, the laws of simulated physics that rule its motion, and a set of behaviors programmed into it by the "animator." The aggregate motion of the simulated flock is the result of the dense interaction of the relatively simple behaviors of the individual simulated birds.

/pdf/flocks-herds-and-schools-a-distributed-behavioral-model-4uyiyjcd5y.pdf

Flocks, herds, and schools: a distributed behavioral model

The vast majority of work to date concerned with obstacle avoidance for manipulators has dealt with task descriptions in the form ofpick-and-place movements. The added flexibil ity in motion control for manipulators possessing redundant degrees offreedom permits the consideration of obstacle avoidance in the context of a specified end-effector trajectory as the task description. Such a task definition is a more accurate model for such tasks as spray painting or arc weld ing. The approach presented here is to determine the re quired joint angle rates for the manipulator under the con straints of multiple goals, the primary goal described by the specified end-effector trajectory and secondary goals describ ing the obstacle avoidance criteria. The decomposition of the solution into a particular and a homogeneous component effectively illustrates the priority of the multiple goals that is exact end-effector control with redundant degrees of freedom maximizing the distance to obstacles. An efficient numerical ...

/pdf/obstacle-avoidance-for-kinematically-redundant-manipulators-3fyn4yxbx0.pdf

Obstacle Avoidance for Kinematically Redundant Manipulators in Dynamically Varying Environments

Kinematically redundant manipulators have a number of potential advantages over current manipulator designs. For this type of arm, velocity control through pseudoinverses is suggested. Questions associated with pseudoinverse control are examined in detail and show that in some cases this control leads to undesired arm configurations. A method for distributing joint angles of a redundant arm in a good approximation to a true minimax criterion is described. In addition several numerical considerations are discussed.

Review of pseudoinverse control for use with kinematically redundant manipulators

In this paper, we describe a new scheme for redundancy control of robot manipulators. We introduce the concept of task priority in relation to the inverse kinematic problem of redundant robot manipulators. A required task is divided into subtasks according to the order of priority. We propose to determine the joint motions of robot manipulators so that subtasks with lower priority can be performed utilizing re dundancy on subtasks with higher priority. This procedure is formulated using the pseudoinverses of Jacobian matrices. Most problems of redundancy utilization can be formulated in the framework of tasks with the order of priority. The results of numerical simulations and experiments show the effectiveness of the proposed redundancy control scheme.

Task-priority based redundancy control of robot manipulators

In this paper, we have proposed a number of measures for the quantification of dexterity of manipulators. The use of such measures is especially important for kinematically redundant manipulators since they can satisfy secondary cri teria in addition to satisfying a specification of end-effector motion. We will compare several measures for the problems offinding an optimal configuration for a given end-effector position, finding an optimal workpoint, and designing the op timal link lengths of an arm.

Dexterity measures for the design and control of kinematically redundant manipulators

The loss of independent degrees of freedom at singular configurations is an inherent characteristic of robotic manipulators. Due to the unavoidable singularity of mechanical wrists, singular configurations cannot be avoided by simply restricting the bounds of the workspace. Techniques for operating at singular configurations without inducing unacceptably high joint velocities or end effector tracking errors are presented. Extensions to the damped least-squares formulation which incorporate estimates of the proximity to singularities and selective filtering of singular components are illustrated. The generality of the technique presented is illustrated in a computer simulation of a commercially available manipulator operating through singular configurations.

/pdf/numerical-filtering-for-the-operation-of-robotic-2i61tna37a.pdf

Numerical filtering for the operation of robotic manipulators through kinematically singular configurations

The evolution of legged vehicles has progressed significantly in recent years. These vehicles offer the potential of increased mobility for traversing rough terrain. The ability to maintain stability is an important consideration in the development of any control algorithm for a legged vehicle. Previous work on legged vehicle control generally assumes that the terrain is regular enough that only minimal operator interaction is necessary. However, for very irregular terrain the operator may require a guidance mode that gives maximum resolution and flexibility in control- ling body, leg, position, and orientation. Several automatic body regulation schemes that aid the operator in this important task are described. A major development is the use of an improved stability measure which can be automatically optimized. This measure, together with a consideration of constraints on the kinematic limits of individual legs, leads to the development of schemes for automatic body regulation. The automatic body regulation schemes are incorporated into the vehicle control algorithm to provide a high degree of vehicle maneuverability while reducing the operator's burden.

Charles A. Klein

Papers

Obstacle Avoidance for Kinematically Redundant Manipulators in Dynamically Varying Environments

Review of pseudoinverse control for use with kinematically redundant manipulators

Dexterity measures for the design and control of kinematically redundant manipulators

Numerical filtering for the operation of robotic manipulators through kinematically singular configurations

Automatic Body Regulation for Maintaining Stability of a Legged Vehicle