Eric Paljug

The JPL Serpentine Robot: a 12-DOF system for inspection

The Serpentine Robot is a prototype hyper-redundant (snake-like) manipulator system developed at the Jet Propulsion Laboratory. It is designed to navigate and perform tasks in obstructed and constrained environments in which conventional 6-DOF manipulators cannot similarly function. This paper describes the Serpentine Robot mechanical design, a low level inverse kinematic algorithm for the joint assembly, a brief synopsis of control development to date, and the applications of this technology.

Control of multiple arms with rolling constraints

The authors present a unified formulation for the control problem of multiple arm systems which accommodates both holonomic and nonholonomic constraints. Several unique control properties of nonholonomic systems are discussed. Several useful results regarding input-output linearization and the zero dynamics in such systems are proved. The analysis and controller design are discussed for multi-arm systems. Results from computer simulations are presented to demonstrate the control algorithms. Simulation results illustrate that rolling and sliding can be effectively controlled.<<ETX>>

Control of contact conditions for manipulation with multiple robotic systems

An object much larger than a robot end-effector can not be rigidly grasped. Instead, it is necessary to support the object with multiple effectors. The effectors need not be grippers-they may be surfaces on the arm(s). Multiple arm manipulation without rigid grasps is investigated. The interaction between a robot and the object is characterized by unilateral constraints. The closed chain topology, redundancy in actuation, and the nonlinear coupled equations of motion make the problem formidable. The approach used is to utilize a minimal set of inputs to control the trajectory. The surplus inputs are used to control the contact conditions (rolling, sliding, etc.).<<ETX>>

Some important considerations in force control implementation

The authors address force control in overconstrained dynamic systems with special emphasis on robot control. Previous approaches to force control are studied, and many of these are shown to be unsuitable for dynamic force control. Practical and theoretical considerations for designing force control algorithms are discussed. Experimental and simulation results that validate the theoretical findings are presented for a single-degree-of-freedom pneumatic force controller.<<ETX>>

A cross-country teleprogramming experiment

The teleprogramming system is a supervisory control approach to time delayed teleoperation that incorporates predictive graphics and reactive skills to accomplish dexterous manipulation tasks in the presence of significant time delay. This paper presents an experimental effort to validate the teleprogramming system using the GRASP Laboratory of the University of Pennsylvania as the operator station and the TROPICS Laboratory of the Jet Propulsion Laboratory as the remote site. The teleprogramming experiment involved operator supervisory control of a robot performing puncture and slice operations on the thermal blanket securing tape of a satellite repair mission sub-task This experiment was successfully performed in August, 1994 using the Internet as the sole medium of communication. During experimentation, messages experienced time-varying time delay between three and fifteen seconds with an average delay of approximately six seconds.

Experimental study of two robot arms manipulating large objects

In this paper, we present the architecture of an experimental real-time control system called TRACS (two robotic arm coordination system) and experimental results using two PUMA 250 robot arms that perform tasks of manipulating large objects. The system uses an IBM PC-AT as the host computer which is equipped with an AMD29000 high speed floating point coprocessor. It is configured in such a way that the Intel 80286 processor performs all the input-output interface operations (interface to the sensors, arms, and user) while the AMD29000 carries out the real-time computations of feedback control algorithms. Using the system, we have successfully implemented the dynamic control algorithm developed for coordinating two robotic arms. The two arms perform the task of manipulating a large object by means of enveloping grasp. The coordinated control algorithm utilizes the full dynamics of the two arms. The results from two experimental tasks are described in detail, in which the two arms move an object while adapting the grasp configuration to the motion trajectory and to the external disturbance force. >

Control of rolling contacts in multiple robotic manipulation

When multiple arms are used to manipulate a large object, it is productive and sometimes necessary to maintain and control contacts between the object and surfaces of the robot other than those at the end-effector. Hence, the contact surface of the robot is referred to simply as its effector and includes the surface of any link of the manipulator as well as open palm-like effectors at the arms extremity. Such contacts are characterized by holonomic as well as nonholonomic (including unilateral) constraints. In this paper, the control of rolling contact is investigated. Multiarm manipulation systems are typically redundant. In the approach, a minimal set of inputs is employed to control the trajectory of the system while the surplus inputs control the rolling condition at the contacts. A nonlinear feedback scheme for simultaneous force and motion control is presented and a new approach to adaptively adjust a two-effector grasp with rolling contacts is developed. Simulations are used to illustrate the salient features in control and planning.<<ETX>>

Telerobotics for microsurgery

A telerobotic workstation for microsurgery has been developed that enables scaling down motions and filtering tremor in a surgeons hand. The system is compact and light-weight and has the potential for improving the performance of all surgeons and enabling the development of new surgical procedures currently limited by the dexterity of even the most skilful surgeons.