Design and Implementation of a Robot Force and Motion Server

A robot manipulator is a force and motion server for a robot. The robot, interpreting sensor information in terms of a world model and a task plan, issues instructions to the manipulator to carry out tasks. The control of a manipulator first involves motion trajectory generation needed when the manipulator is instructed to move to desired positions. The procedure of generating the trajectory must be flexible and efficient. When the manipulator comes into contact with the environment such as during assembly, it must be able to comply with the geometric constraints presented by the contact in order to perform tasks successfully. The control strategies for motion and compliance are executed in real time by the control computer, which must be powerful enough to carry out the necessary computations. This thesis first presents an efficient method for manipulator motion planning. Two fundamental modes of motion, Cartesian and joint, are considered and transition between motion segments is uniformly treated to obtain an efficient and simple system. A modified hybrid control method for manipulator compliance is then proposed and implemented. The method overcomes the problems existing in previous approaches such as stiffness control and hybrid control. Finally, a controller architecture is studied to distribute computations into a number of processors to satisfy the computational requirement in a cost-effective manner. The implementation using Intel\u27s single board computers is also discussed. Finally, to demonstrate the system, the motion trajectory. and the modified forced/motion control scheme are implemented on the controller and a PUMA 260 manipulator controlled from a multi-user VAX/Unix system through an Ethernet interface

Method and apparatus for configuration control of redundant robots

A method and apparatus to control a robot or manipulator configuration over the entire motion based on augmentation of the manipulator forward kinematics is disclosed. A set of kinematic functions is defined in Cartesian or joint space to reflect the desirable configuration that will be achieved in addition to the specified end-effector motion. The user-defined kinematic functions and the end-effector Cartesian coordinates are combined to form a set of task-related configuration variables as generalized coordinates for the manipulator. A task-based adaptive scheme is then utilized to directly control the configuration variables so as to achieve tracking of some desired reference trajectories throughout the robot motion. This accomplishes the basic task of desired end-effector motion, while utilizing the redundancy to achieve any additional task through the desired time variation of the kinematic functions. The present invention can also be used for optimization of any kinematic objective function, or for satisfaction of a set of kinematic inequality constraints, as in an obstacle avoidance problem. In contrast to pseudoinverse-based methods, the configuration control scheme ensures cyclic motion of the manipulator, which is an essential requirement for repetitive operations. The control law is simple and computationally very fast, and does not require either the complex manipulator dynamic model or the complicated inverse kinematic transformation. The configuration control scheme can alternatively be implemented in joint space

Impact of end effector technology on telemanipulation performance

Generic requirements for end effector design are briefly summarized as derived from generic functional and operational requirements. Included is a brief summary of terms and definitions related to end effector technology. The second part contains a brief overview of end effector technology work as JPL during the past ten years, with emphasis on the evolution of new mechanical, sensing and control capabilities of end effectors. The third and major part is devoted to the description of current end effector technology. The ongoing work addresses mechanical, sensing and control details with emphasis on mechanical ruggedness, increased resolution in sensing, and close electronic and control integration with overall telemanipulator control system

Robot Manipulator Control and Computational Cost

In this paper robot control algorithms are considered from the point of view of computational complexity. All the algorithms provide for hybrid position and force control which is appropriate to unstructured environments. Both joint coordinate and generalized coordinate motion schemes are considered. The findings are interesting in that the peripheral processing involved in all methods, sometimes, swamps the orders of magnitude differences in computation involved in the inner loops. It is also interesting to note the similarity in complexity between direct methods and differential. Between joint coordinate methods and generalized coordinate methods there is a general two to one ratio in complexity. In general a 0.75 M Flop, 1.25 Mip machine is required to provide for a control rate of 250 hz

Control Software of Robot Compliant Wrist System

The compliant wrist combining passive compliants and sensor has been developed in GRASP laboratory. The device provides the robot system the necessary flexibility which accommodates transitions as the robot makes contact with the environment, corrects positioning error in automatic assembly, avoids high impact forces and protects the surface from damage. The device also supplies the displacement sensing of the passive compliance so that active feedback control is possible. This report is intended to serve as a reference material to introduce the control software of the robot compliant wrist system developed and implemented in the lab. The detail discussion on system performance and parameters selection can be found in the thesis [3]. The rest of material is organized as follows. Section 2 introduces the compliance control methods of robot manipulators. The historic development of both passive and active compliance method is discussed. The advantages and disadvantages of the methods are investigated. Based on the unsolved problems in this issue, the six-degree freedom compliant wrist is developed, and the design feature is presented. Section 3 discusses the hybrid position/force control scheme using the sensing information from the device. The positioning error due to load or external force when robot moves in free space is compensated for, so that the effective stiffness is increased. In force control when robot is constrained by environment, the trajectory is modified by sensed force, so that the effective stiffness is decreased. Section 4 deals with the implementation of the control scheme. Various programs have been developed to perform the hybrid control operations, such as hybrid control demonstration, surface tracking, edge tracking, insertion and pulling out, and writing operation. The programs have been successfully implemented in the experiments. Definition and selection of the parameters in the programs are discussed. Section 5. is the source code of control scheme which has been implemented in PUMA 560 with index machine in GRASP Laboratory. The control is executed on a MicroVax I1 using the RCI primitives of RCCL