Presents the application of an image registration method for a mobile manipulator. The robot is used for scanning natural terrain and detecting metal objects hidden beneath the terrain surface (e.g., landmines) using a metal detector. The range image may be interpreted for visual servoing, map building and path planning, or object recognition. In the work, the image is used to build a terrain map for obstacle free path planning. Because the working area of the robot is extremely dynamic (i.e., not only the robot travels but also the environment is also subject to change) an active range sensing method is selected to provide the range image. The range values are acquired using a laser range finder with a rotating mirror for scanning so that sensor fusion in the form of collecting sensor readings over an extended period of time is required. In addition, range readings of two ultrasonic range finders are fused at signal level to tackle both sensor imperfection and environmental illumination that induce uncertainty at the system. We explain the use of a real-time programming platform that executes an online map-building process in parallel for robot manipulation and control.

Experimental evaluation of various task-space control algorithms shows that significant deviations from desired trajectories may occur, especially at higher speeds, or in the vicinity of singularities. The experiments on a modular reconfigurable robotic setup confirmed this conclusion: the lateral deviations may range up to several centimeters from the closest point on the desired trajectory. The main reason is that the control output often reaches the saturation value of an actuator. The lateral error is also found very dangerous in obstacle cluttered environments due to possible damage of the manipulator arm while hitting an obstacle at high speed. This paper is devoted to solve this problem. Widely used task space control algorithms such as the resolved-rate and the resolved-acceleration algorithms are modified by introducing monitoring on the control output, and, accordingly, modifying the commanded control signal so that the end-effector is prevented from leaving the programmed path. As a consequence, the manipulator tip may slowdown along the path due to limited actuator power, but it will be accelerated after that to reach the desired position as soon as possible. The algorithms also take into account the presence of singularities to avoid uncontrollable excursions of the manipulator tip. Hundreds of experiments have been carried out to confirm the concept. Some of those with a desired trajectory reaching both the regular and the singular region of the workspace are provided to illustrate the method.

In this paper the application of the damped least-squares method to the resolved-acceleration control is experimentally examined on a 2-DOF planar manipulator In order to decrease the position error introduced by the damping, only small singular values are damped. The symbolical expressions of the singular value decomposition of the Jacobian matrix were utilized in order to decrease the computational burden. Position error along the work-space boundary was only 15% greater than along the trajectories inside the reachable workspace.>

The authors present two novel parallel algorithms for computing robot inverse dynamics and control laws starting from the customized symbolic robot models. The first algorithm resolves the scheduling problem for an array of pipelined processors. The second algorithm is devoted to parallel processors connected by a complete crossbar interconnection network. The main feature of the algorithms is that they take into account the communication delays between processors and minimize both the execution time and the communication cost. The algorithms were verified by experiments on an INMOS T800 transputer-based system. The experimental results showed that the most complicated dynamic control laws could be executed in a submillisecond range.>

The authors extend the idea of a fourth-order model of an elastic link and introduce two complementary ways of controlling such systems. In the case of measurable joint forces/torques, they propose a control law based on a deterministic observer whose job is to recover immeasurable components of the state vector. If the forces/torques are not measurable, they propose a Kalman filter technique which uses the manipulator's model to recover the unknown states of the system. Simulation results are presented. The example used is a 6-link manipulator, UMS-2. The results encourage implementation of these control structures on a real system.>

The structure of SYM, a program package for manipulator modeling, control law synthesis, and simulation, is described. SYM's research and educational aims are emphasized. The control law synthesis in symbolic form and the system simulation are discussed in detail. Several examples of SYM outputs which depict the main steps in the manipulator control system creation process, namely, manipulator structure as a 3-D scheme, control law definition form, and system simulation results as 2-D plots are presented.>

An algorithm is presented for generating numerically efficient manipulator models in symbolic form, i.e., as computer programs written in a high-level language such as C or FORTRAN. The algorithm does its job in two main steps. First, a suboptimal symbolic model, which is the input for the second step, is generated. The first step has been explained in the authors' previous papers (1989). The main emphasis in this study is put on the second step: generating analytical expressions of output variables in the form of so-called structural matrices and their reconstruction into a program again.>

The authors address the problem of the optimal evaluation of robot inverse dynamics on array processors. The inverse dynamics models used are the symbolic customized models with near-minimum numerical complexity, which are computer-generated given the robot arm parameters. Such models represent the input for a proposed scheduling algorithm that distributes the computation of the model over several multipliers and adders. The scheduling algorithm is automatic and minimizes the number of microcycles. The algorithm was tested on several standard robots, and processor efficiency up to 84% was achieved. Experimental results on a 30 MFLOPS array processor showed that the inverse dynamics of a three-link PUMA-like robot requires 25.5 mu s. For a six-link robot, the computation of the inverse dynamics and the control law takes about 100 mu s on this processor. Thus, the control of high-speed robots could be achieved by attaching low-cost array processors (10 MFLOPS) to the control processor of the robot controller.>

An algorithm for constructing dynamic models of single-arm robots is presented in this paper. Motion equations of robots in analytical form are derived applying a fully automated procedure. It is shown that the solution of direct and/or inverse problem based on the analytical model requires considerably fewer floating- -point multiplications/additions that is the case with previously developed numerical methods. The developed method is therefore very suitable for real-time application of the dynamic models of robots. The developed program package is illustrated using the example of Stanford manipulator.