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At least 73 records · Page 4

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NASA NTRS1990

Stability analysis of position and force control problems for robot arms

Stability issues involving the control of a robot arm under the influence of external forces are discussed. Several different scenarios are considered: position control with the external force as an unmodeled disturbance, compliant control for a bounded external force in some subspace, and compliant control for a force due to the interaction with an environment whose dynamical behavior can be modeled. In each of these cases, a stability analysis using the Lyapunov method is presented. An explanation of instability is put forth for the case in which the environment has flexibility and the gains are inappropriately chosen. When the environment is stiff in the force control subspace, robust stability can be achieved with the integral force feedback.

Wen, John T.↗

NASA NTRS1994

Packaging Of Control Circuits In A Robot Arm

Packaging system houses and connects control circuitry mounted on circuit boards within shoulder, upper section, and lower section of seven-degree-of-freedom robot arm. Has modular design that incorporates surface-mount technology, multilayer circuit boards, large-scale integrated circuits, and multi-layer flat cables between sections for compactness. Three sections of robot arm contain circuit modules in form of stardardized circuit boards. Each module contains two printed-circuit cards, one of each face.

Kast, William↗

NASA NTRS1992

A real-time robot arm collision avoidance system

A data structure and update algorithm are presented for a prototype real-time collision avoidance safety system simulating a multirobot workspace. The data structure is a variant of the octree, which serves as a spatial index. An octree recursively decomposes 3D space into eight equal cubic octants until each octant meets some decomposition criteria. The N-objects octree, which indexes a collection of 3D primitive solids is used. These primitives make up the two (seven-degrees-of-freedom) robot arms and workspace modeled by the system. As robot arms move, the octree is updated to reflect their changed positions. During most update cycles, any given primitive does not change which octree nodes it is in. Thus, modification to the octree is rarely required. Cycle time for interpreting current arm joint angles, updating the octree to reflect new positions, and detecting/reporting imminent collisions averages 30 ms on an Intel 80386 processor running at 20 MHz.

Shaffer, Clifford A.↗

DOE OSTI2023

Arc Weld Robotic Arm & Enclosure Seismic Anchorage in B226

The Arc Weld Robotic Arm & Enclosure is adequately anchored by the details shown on sheets SKS-01 through SKS-03. Two different Hilti anchors have been provided to allow for installation flexibility. Existing documentation shows that the existing enclosure base has been anchored with 5/8”Ø Kwik Bolt TZ’s. As a result, it is believed that the existing holes are sized for that 5/8”Ø anchor. The first option is to install a 5/8”Ø Kwik Bolt TZ2, similarly to the existing conditions. The second option is to use a threaded insert anchor. Since the largest allowable diameter of HIS-N insert is 1/2”Ø based on the slab thickness, 2”x2” square plate washers with a 9/16”Ø hole will need to be installed on the top of the existing enclosure base plates to reduce the diameter of the existing holes. This is required for the anchorage to provide proper restraint in a seismic event.

42 ENGINEERING↗

NASA NTRS1994

Serpentine Robot Arm Contains Electromagnetic Actuators

Identical modules assembled into flexible robot arm configured in serpentlike fashion to manipulate objects while avoiding obstacles. Each module includes integral electromagnetic actuators energized selectively to produce variety of motions, stationary configurations, and combinations thereof.

Moya, Israel A.↗

NASA NTRS2022

First 210 solar days of Mars 2020 Perseverance Robotic Operations – Mobility, Robotic Arm, Sampling, and Helicopter

This paper includes the summary, lessonslearned, and upcoming plans for the first 210 Mars solar days(sols) of the mission. The focus of the paper is on roboticoperations which has the primary responsibility for strategicplanning, uplink commanding and downlink analysis forrover mobility and navigation, robotic arm operation, thesampling and caching capability including coring, theadaptive caching assembly and the 2nd sample handlingrobotic arm, and interface to the Mars helicopter Ingenuity.As of Sol 210 the rover has driven 2663.65 meters, executed20764 robotic arm and sampling commands, and hassuccessfully completed 13 helicopter flights covering 2382meters horizontal distance. It includes the OperationsReadiness Tests in preparation for landing, landing and initialcheckouts, strategic route planning to the science destinationand waypoints, surface checkout of all of the roboticscapability of the rover. It also discusses the strategic planningand tactical agility needed for interleaving scienceinvestigation and technology demonstration of the Marshelicopter flights where a minimum distance had to bemaintained between the rover and helicopter during flights. Itdiscusses the challenges with planning robotic operations andaddressing anomalies with the larger uncertainty presentduring early mission operations. It also discusses the impacton robotic operations from lessons incorporated fromprevious missions.

Ono, Hiro↗

NASA NTRS1987

Adaptive control of dual-arm robots

Three strategies for adaptive control of cooperative dual-arm robots are described. In the position-position control strategy, the adaptive controllers ensure that the end-effector positions of both arms track desired trajectories in Cartesian space despite unknown time-varying interaction forces exerted through the load. In the position-hybrid control strategy, the adaptive controller of one arm controls end-effector motions in the free directions and applied forces in the constraint directions, while the adaptive controller of the other arm ensures that the end-effector tracks desired position trajectories. In the hybrid-hybrid control strategy, the adaptive controllers ensure that both end-effectors track reference position trajectories while simultaneously applying desired forces on the load. In all three control strategies, the cross-coupling effects between the arms are treated as disturbances which are rejected by the adaptive controllers while following desired commands in a common frame of reference. The adaptive controllers do not require the complex mathematical model of the arm dynamics or any knowledge of the arm dynamic parameters or the load parameters such as mass and stiffness. The controllers have simple structures and are computationally fast for on-line implementation with high sampling rates.

Seraji, H.↗

NASA NTRS1989

The KALI multi-arm robot programming and control environment

The KALI distributed robot programming and control environment is described within the context of its use in the Jet Propulsion Laboratory (JPL) telerobot project. The purpose of KALI is to provide a flexible robot programming and control environment for coordinated multi-arm robots. Flexibility, both in hardware configuration and software, is desired so that it can be easily modified to test various concepts in robot programming and control, e.g., multi-arm control, force control, sensor integration, teleoperation, and shared control. In the programming environment, user programs written in the C programming language describe trajectories for multiple coordinated manipulators with the aid of KALI function libraries. A system of multiple coordinated manipulators is considered within the programming environment as one motion system. The user plans the trajectory of one controlled Cartesian frame associated with a motion system and describes the positions of the manipulators with respect to that frame. Smooth Cartesian trajectories are achieved through a blending of successive path segments. The manipulator and load dynamics are considered during trajectory generation so that given interface force limits are not exceeded.

Backes, Paul↗

NASA NTRS1989

Adaptive Control For Cooperative Dual Robot Arms

Three strategies proposed for adaptive control of two cooperative robot arms. New dual-arm control strategies implemented at low level of control hierarchy. Each arm operated independently under single-arm control scheme treating forces and torques transmitted through load as though disturbances. Yields promising results in numerical simulations, and general approach extended to greater numbers of arms.

Seraji, Homayoun↗

NASA NTRS2022

Docking the Mars 2020 Perseverance Robotic Arm

The Mars 2020 Perseverance Rover includes an innovative Sample Caching Subsystem (SCS). Two key features of SCS are the ability to collect and process rock and regolith samples for possible future return to Earth and the ability to switch between different types of drill bits for coring rocks, abrading rocks, and collecting regolith. These capabilities are enabled by a Corer mounted on the end of a Robotic Arm and a Bit Carousel mounted on the front of the rover body. Beneath the Bit Carousel, a smaller Sample Handling Arm can insert and remove sample tubes from sampling bits in the carousel. For the Corer to interface with the Bit Carousel so that it can exchange drill bits and hand off rock samples, the Robotic Arm must maneuver the Corer to dock with the Bit Carousel. Docking serves two primary purposes: it precisely aligns the Corer with the hardware inside the Bit Carousel, and it applies enough preload between the Corer and the Bit Carousel to make them stay aligned through the process of bit exchange.The docking assembly consists of four concave alignment cones mounted on a large rotating ring, through the center of which the drill can exchange bits and samples with the Bit Carousel. The coring drill includes four alignment posts which mate with the four cones on the dock. Docking uses an algorithm we call “Force-Corrected Docking”, which means it iteratively reads the force/moments reported by the FTS, performs a small motion to reduce sideload and moments while increasing preload, and repeats until reaching a deadband around the target preload. Because docking is a critical function for SCS, the dock hardware and algorithm have been tested thousands of times over 7 years in various stages of development. The culmination of this work is a reliable docking system which has been demonstrated and used in flight.

Warner, Antonia↗

NASA NTRS1987

Collision-free motion of two robot arms in a common workspace

Collision-free motion of two robot arms in a common workspace is investigated. A collision-free motion is obtained by detecting collisions along the preplanned trajectories using a sphere model for the wrist of each robot and then modifying the paths and/or trajectories of one or both robots to avoid the collision. Detecting and avoiding collisions are based on the premise that: preplanned trajectories of the robots follow a straight line; collisions are restricted to between the wrists of the two robots (which corresponds to the upper three links of PUMA manipulators); and collisions never occur between the beginning points or end points on the straight line paths. The collision detection algorithm is described and some approaches to collision avoidance are discussed.

Basta, Robert A.↗

NASA NTRS1988

Coordination of dual robot arms using kinematic redundancy

A method is developed to coordinate the motion of dual robot arms carrying a solid object, where the first robot (leader) grasps one end of the object rigidly and the second robot (follower) is allowed to change its grasping position at the other end of the object along the object surface while supporting the object. It is shown that this flexible grasping is equivalent to the addition of one more degree of freedom (dof), giving the follower more maneuvering capabilities. In particular, motion commands for the follower are generated by using kinematic redundancy. To show the utility and power of the method, an example system with two PUMA 560 robots carrying a beam is analyzed.

Suh, Il Hong↗

NASA NTRS1986

Nonlinear adaptive control of an elastic robotic arm

An approach to control of a class of nonlinear flexible robotic systems is presented. For simplicity, a robot arm (PUMA-type) with three rotational joints is considered. The third link is assumed to be elastic. An adaptive torquer control law is derived for controlling the joint angles. This controller includes a dynamic system in the feedback path, requires only joint angle and rate for feedback, and asymptotically decomposes the elastic dynamics into two subsystems representing the transverse vibrations of the elastic link in two orthogonal planes. To damp out the elastic vibration, a force control law using modal feedback is synthesized. The combination of the torque and force control laws accomplishes joint angle control and elastic mode stabilization.

Singh, S. N.↗

NASA NTRS2016

Lower Robotic Arm Assembly Having a Plurality of Tendon Driven Digits

A lower robotic arm includes a base structure, a plurality of digits, and a plurality of tendons. The digits each include first, second, third, and fourth phalanges. Each digit is operatively attached to the base structure at the respective first phalange. A first joint operatively connects the first and second phalange to define a first axis, a second operatively connects the second and third phalange to define a second axis, and a third joint operatively connects the third and fourth phalange to define a third axis, such that the phalanges are selectively rotatable relative to the adjacent phalange, about the respective axis. The tendons are operatively connected to a respective one of the fourth phalanges. Each tendon selectively applies a first torque to the respective fourth phalange to urge the respective phalanges to rotate in a first direction about the respective axes.

Guo, Raymond↗

NASA NTRS1989

Test and validation for robot arm control dynamics simulation

The Flight Telerobotic Servicer (FTS) program will require an ability to develop, in a cost effective manner, many simulation models for design, analysis, performance evaluation, and crew training. Computational speed and the degree of modeling fidelity associated with each simulation must be commensurate with problem objectives. To demonstrate evolving state-of-the-art general purpose multibody modeling capabilities, to validate these by laboratory testing, and to expose their modeling shortcomings, two focus problems at the opposite ends of the simulation spectrum are defined: (1) Coarse Acquisition Control Dynamics. Create a real time man-in-the-control-loop simulator. Provide animated graphical display of robot arm dynamics and tactile feedback sufficient for cueing the operator. Interface simulator software with human operated tactile feedback controller; i.e., the Kraft mini-master. (2) Fine, Precision Mode Control Dynamics. Create a high speed, high fidelity simulation model for the design, analysis, and performance evaluation of autonomous 7 degree-of-freedom (DOF) trajectory control algorithms. This model must contain detail dynamic models for all significant dynamics elements within the robot arm, such as joint drive mechanisms.

Yae, K. Harold↗

NASA NTRS1991

System For Research On Multiple-Arm Robots

Kali system of computer programs and equipment provides environment for research on distributed programming and distributed control of coordinated-multiple-arm robots. Suitable for telerobotics research involving sensing and execution of low level tasks. Software and configuration of hardware designed flexible so system modified easily to test various concepts in control and programming of robots, including multiple-arm control, redundant-arm control, shared control, traded control, force control, force/position hybrid control, design and integration of sensors, teleoperation, task-space description and control, methods of adaptive control, control of flexible arms, and human factors.

Backes, Paul G.↗

NASA NTRS1987

Feedback control of vibrations in a moving flexible robot arm with rotary and prismatic joints

A robot with a long extendible flexible arm which can also undergo both vertical translation and rotary motion is considered. First, A distributed-parameter model for the robot arm dynamics is developed. It is found that the extending motion could enhance the arm vibrations. Then, a Galerkin-type approximation based on an appropriate time-dependent basis for the solution space is used to obtain an approximate finite-dimensional model for simulation studies. A feedback control for damping the motion-induced vibrations is derived by considering the time rate-of-change of the total vibrational energy of the flexible arm. The authors conclude with some simulation results for a special case with the proposed control law.

Wang, P. K. C.↗

NASA NTRS1994

Dynamic Coordination Of A Two-Arm Robotic Manipulator

Report presents study of dynamical and kinematical considerations guiding selection of configuration of self-reconfigurable, two-arm robotic manipulator. Two multiple-link arms cooperate in manipulating single object, reconfiguring their mutual, cooperative structure according to changing task requirements.

Lee, Sukhan↗