In this paper we propose some simple rules for PID tuning of robot manipulators. The procedure suggested requires the knowledge of the structure of the inertia matrix and the gravitational torque vector of the robot dynamics, but only upper bounds on the dynamics parameters are needed. This tuning procedure is extracted from the stability analysis by using a suitable Lyapunov function together with the LaSalle invariance principle. We show that with this guideline, the overall closed-loop system is asymptotically stable. This procedure is illustrated for a two degrees-of-freedom robot

The control of a robot manipulator with force sensors in the gripping tips is considered. The sensors measure three components of the force. Complicated motions of the manipulator are complied from basic movements, and the paper describes how the operation of grasping an arbitrarily positioned object is constructed from the basic movements. A mathematical model of the basic procedure of keeping contact with the object is considered.

This paper presents a study of the dynamics of undersea robot manipulators in an unstructured sea water environment and a control scheme appropriate for manipulating them. Under the sea, the buoyancy and the added mass should be considered in modeling the dynamics of the robot manipulators. However, due to the complexity of the modeling of the added mass, the dynamics of the robot manipulators are treated as an unmodeled dynamics in this paper. In addition to the buoyancy and added mass/moment of inertia, disturbing forces due to drag, and current affecting the dynamics of the robot manipulators should be considered. In this paper, the forces due to the drag are defined as disturbance forces in addition to the frictional force of manipulator joints. In order to control the manipulator, a robust control scheme is devised to achieve trajectory tracking while regulating disturbance forces. A numerical example is shown.

This paper deals with an investigation of the relative importance of robotic characteristics typically associated with nonlinear manipulators. An IBM 7540 SCARA type of robot is used for simulation, and results are presented for decentralized proportional plus derivative control action applied to individual robot joints, and the use of an adaptive computed torque control strategy is illustrated. The influence of variations in payload and robot parameters on trajectory tracking is also shown.

In this paper, a joint space dynamic control scheme with an adaptive identifier is proposed for free-flying space robots. The control in Cartesian space poses a measurement problem which is critical from a point of view of implementation. In order to overcome this problem, a joint space control is developed. An inverse kinematics algorithm is proposed so as to control free-flying space robots in joint space. Since the inverse kinematic solutions for space robots depend on the dynamic parameters as well as the kinematic.parameters, the accurate estimation of all the unknown parameters is essential to make joint space control possible. Therefore, an off-line adaptive parameter identification is performed for free-flying space robots. Simulation results are given to show the validity and the effectiveness of the presented adaptive identification and dynamic control scheme.

The virtual passive control approach has recently been shown to be an effective technique for robust compensation of linear as well as nonlinear systems, when the system is open-loop stable and behaves as a block second-order plant. Mechanical systems as well as current space structure designs possess this property whereby inertia, damping and stiffness parameters characterize the dynamics.

Implementation of such controllers using digital systems may lead to instability, however, unless discretization issues are addressed. This paper presents a discrete-time representation of the Virtual Passive Approach and develops the robust controller structure for linear systems. The algorithm is then applied to a model of an actual experimental testbed; the test article is a ten-bay truss structure located at NASA Langley's Spacecraft Dynamics Branch. Results illustrate the robustness properties of the algorithm and expose issues which need to be addressed in future research activities.

A major problem in inverse kinematics algorithms is that the generated joint velocities to be fed to the joint servos may cause violation of the speed limits of the joint actuators. In this paper, it is shown how to properly cope with joint velocity limits in first-order inverse kinematics algorithms; the proposed technique guarantees tracking of the desired end-effector path. This goal is achieved by suitably slowing down the task-space trajectory when joint velocity limits are encountered. The time law is modified through a time warp such that the introduced virtual time allows fulfillment of the velocity constraints. A case study is developed to show the effectiveness of the proposed method and a kinematic control scheme based on the presented technique is implemented to demonstrate feasibility under real-time constraints.

An automated manipulating system, which performs the task of loading, positioning and holding of parts in the working area of an industrial robot is discussed in this paper. The system feeds component parts for the lifting mechanisms of electric trucks to be arc-welded by the robot and then removes them, thus completing a predetermined cycle. It is a part of an actual assembly line in a standard workshop for manufacturing electric trucks. The system's operation is described in detail, and the basic technological characteristics of the welding and peripheral equipment are given. Also, some features of an original welding torch cleaning device are described. The principal approach of planning, designing and implementing robotized cells for automatic arc-welding using a robot is also discussed.