Fault tolerance for kinematically redundant manipulators: anticipating free-swinging joint failures

English, J.D.; Maciejewski, A.A.

doi:10.1109/robot.1996.503819

Cited by 33 publications

(42 citation statements)

References 19 publications

(2 reference statements)

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“…In the event of a locked-joint failure, the actual end-effector velocity in general will not be as commanded by (6). In particular, if joint i fails, the actual end-effector velocity is given by…”

Section: Mathematical Frameworkmentioning

confidence: 99%

“…which can be obtained by combining (3), (5), and (6). Although ẋ a may not drive the end effector directly towards the desired task position, it is of interest to know whether the end effector will eventually converge to it.…”

Section: Mathematical Frameworkmentioning

confidence: 99%

“…2 Since the control of the individual joints is essentially independent in a typical robotic system, most failures affect only a single joint. While there are several ways in which a robot may fail, [3][4][5][6][7] one common failure mode is a ''locked joint,'' where the affected joint's velocity is identically zero. Such a failure may have catastrophic consequences or, at the very least, significantly degrade the system performance.…”

Section: Introductionmentioning

confidence: 99%

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Analyzing unidentified locked-joint failures in kinematically redundant manipulators

2004

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Robots are frequently used for operations in hostile environments. The very nature of these environments, however, increases the likelihood of robot failures. Common failuretolerance techniques rely on effective failure detection and identification. Since a failure may not always be successfully identified, or, even if identified, may not be identified soon enough, it becomes important to consider the behavior of manipulators with unidentified failures. This work investigates the behavior of robots experiencing unidentified locked-joint failures in a general class of tasks characterized by point-to-point motion. Based on the analysis, a procedure for workspace evaluation is developed that allows for the identification of regions in the manipulator's workspace in which tasks may be completed even with such failures. where xe R" is the position of the end effector, q eRn is the vector of joint variables, and m and n the dimensions of the task space and joint space, teepeetively. Manipulators that have more degrees of freedom (DOFs) than required for a task, i.e., n>m, are said to be redundant. 'The end-effector velocity is expressed in terms of the joint rates as where] E H m X n is the manipulator Jacobian, xis the end-effector velocity, and it is the joint velocity.If perfect servo control of the joints is assumed, then in a healthy manipulator the actual joint velodfailed, the ability of manipulators to converge to desired end-effector positions even with imperfect/ approximated lacobtana/Iacobian-inverses has been addressed in refs. 26 and 27. Therefore, we focus on the other case where a joint has actually locked, but the controller continues to command motion of that joint as though it were healthy. For a general class of tasks characterized by point-to-point motion, we examine convergence issues such as whether the manipulator comes to rest and, if so, what is the terminal position and orientation of the end-effector. The convergence analysis is restricted to purely kinematic effects, due to the fact that the dynamic effects of a failure are essentially transient in nature and do not significantly affect the convergence behavior. 18.28 -3 0 Conditions under which the manipulator converges are explicitly defined and the anomalies in behavior due to the faults explained and illustrated with examples. These conditions are used to evaluate the convergence behavior of the manipulator over the postfailure workspace. This allows for the identification of workspace regions for which task completion may be possible even with unidentified failures.The position and orientation-of the end effector of a manipulator can be expressed in terms of its joint variables by the kinematic equation "nus assumes a typical commercial robot where duplicate sensing and/or analytical redundancy does not exist.

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Section: Mathematical Frameworkmentioning

confidence: 99%

Section: Mathematical Frameworkmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Analyzing unidentified locked-joint failures in kinematically redundant manipulators

2004

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“…In previous work [14], [15], the focus has frequently been on determining the kinematic design of a robot from the local fault tolerant properties of a desired Jacobian. It is also possible to consider the dynamic properties of the robot as discussed in [16]. In This this work we start with the kinematics of a commonly used redundant robot, i.e., an anthropomorphic design like the PA-10, and try to improve its failure tolerant properties.…”

Section: Introductionmentioning

confidence: 99%

Modifying the kinematic structure of an anthropomorphic arm to improve fault tolerance

Ben-Gharbia

Maciejewski

Roberts

2015

2015 IEEE International Conference on Robotics and Automation (ICRA)

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It is well known that anthropomorphic manipulators, such as the PA-10, are intolerant to a single locked joint failure of the elbow. This is because the elbow is the only joint that can change the distance between the spherical shoulder joint and the spherical wrist. In this work, it is shown how such arms can be made significantly more fault tolerant by a minor modification to the kinematic structure of the arm. We quantify the degree of fault tolerance to locked joint failures as the minimum of the smallest singular value of the resulting seven Jacobians over all possible single failures. The DH parameters for the modified arm are designed so that the corresponding fault tolerant properties are close to those of a robot with an optimally failure tolerant Jacobian. The fault tolerance of the designed robot is evaluated for two different classes of applications, i.e., point-to-point motions and specified end-effector trajectories.Index Terms-redundant robots, robot kinematics, faulttolerant robots.

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“…These extra degrees of freedom are used to improve the ability of the manipulators. 1,2 The abilities include obstacle avoidance, 3 ᎐ 10 joint limits, singularity avoidance, 3,11,12 peak torque reduction, 13 torque optimization, 14 ᎐ 16 joint failurerfault tolerance, 17,18 etc. One main method of redundancy resolution for redundant robots is the pseudo-inverse method.…”

Section: Introductionmentioning

confidence: 99%

An improved trajectory planner for redundant manipulators in constrained workspace

Liang

Liu

1999

J. Robotic Syst.

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This article studies the trajectory planning of redundant robots performing tasks within an enclosed workspace. Configuration control of kinematically redundant manipulators using the pseudo-inverse with null-space projection method is a wellknown scheme. One advantage of this method is that the gradient of an objective function can be included in the homogeneous term to optimize the objective function without affecting the position of the end-effector. Using different objective functions, this method can achieve redundancy resolution such as obstacle or joint limits avoidance. Along this line of redundancy resolution, a switching objective function is proposed. We modify Liegeois' joint angle availability objective function so that the midpoints of each joint are switched at a series of prespecified key path points for the end-effector to achieve. These key path points are planned beforehand according to the geometry of the constrained workspace. The trajectory planning problem can then Ž . be viewed as a series of proper postures i.e., midpoints determination problems at the key path points. The proper postures are determined using a combination of the potential field method and the elastic model method that takes into account joint operating ranges and the motion tendency of the end-effector. A variable weighting technique to achieve the proper postures effectively is also presented. Simulations of a planar eight-link robot in a constrained workspace illustrate the effectiveness of the switching objective function with the variable weighting approach in trajectory planning problems. ᮊ

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Fault tolerance for kinematically redundant manipulators: anticipating free-swinging joint failures

Cited by 33 publications

References 19 publications

Analyzing unidentified locked-joint failures in kinematically redundant manipulators

Analyzing unidentified locked-joint failures in kinematically redundant manipulators

Modifying the kinematic structure of an anthropomorphic arm to improve fault tolerance

An improved trajectory planner for redundant manipulators in constrained workspace

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