The kinematic analysis of a 6-DOF (six-degree-of-freedom) force sensor whose design is based on the mechanism of the Stewart platform is presented. The force sensor is used to measure forces/torques and to provide pas...
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The kinematic analysis of a 6-DOF (six-degree-of-freedom) force sensor whose design is based on the mechanism of the Stewart platform is presented. The force sensor is used to measure forces/torques and to provide passive compliance during part assembly. It is mainly composed of two platforms, the payload platform and the end-effector platform, coupled by six spring-loaded pistons whose length variations are measured by six linear voltage differential transformers mounted along the pistons. The forces and torques applied to the end-effector platform are computed by using the inverse and forward kinematic transformations of the Stewart platform, the known spring constants, and the piston length variations. Results of experiments conducted to evaluate the sensing capability of the force sensor used during the mating and demating of space-rated connectors are reported.< >
A recent discrete-time robotic model is employed and linearized to develop three different LQ-type robot controllers, namely optimal time-varying linear-quadratic controller (OTVLQ), OTVLQ controller with steady-state...
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A recent discrete-time robotic model is employed and linearized to develop three different LQ-type robot controllers, namely optimal time-varying linear-quadratic controller (OTVLQ), OTVLQ controller with steady-state error elimination, and one-step ahead optimal LQ controller. These controllers require moderate computational effort and are suitable for microprocessor-based implementation. Experimental results on a KUKA IR 160/15 robotic model verified the success and efficiency of the controllers.
A turning gait is proposed for a quadruped walking robot. The proposed scheme makes it possible to control the translation and orientation of the walking robot simultaneously. First, feasible leg sequences which guara...
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A turning gait is proposed for a quadruped walking robot. The proposed scheme makes it possible to control the translation and orientation of the walking robot simultaneously. First, feasible leg sequences which guarantee positive longitudinal gait stability margin for each direction of movement are found. A method for finding the lifting time of each leg of a feasible leg sequence and selecting an optimal gait among feasible gaits is then suggested. The proposed gait can be applied to control the posture of walking robots and to generate an optimal gait for a desired movement of translation and rotation of the walking robot systematically.< >
The authors present the mechanical design of a robotic end-effector which has six degrees of freedom and was built to study autonomous robotic assembly in space. The end-effector's design is based on the mechanism...
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The authors present the mechanical design of a robotic end-effector which has six degrees of freedom and was built to study autonomous robotic assembly in space. The end-effector's design is based on the mechanism of the Stewart platform. The end-effector consists mainly of two platforms coupled by six linear actuators driven by DC motors. Position feedback is achieved by six linear displacement transducers (LDTs) mounted along the actuators to measure their length variations. Computations are performed to select proper DC motors, ballscrews, LDTs, and platform parameters so that a set of design specifications, including resolution of platform, accuracy, speed, and lifting capability, is satisfied.< >
The authors consider the problem of efficient computation of the forward kinematics of a six-degree-of-freedom robot manipulator built to study autonomous assembly of parts in space. The manipulator, based on the Stew...
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The authors consider the problem of efficient computation of the forward kinematics of a six-degree-of-freedom robot manipulator built to study autonomous assembly of parts in space. The manipulator, based on the Stewart platform mechanism, consists mainly of two platforms and six linear actuators. The closed-form solution of the inverse kinematics is formulated in such a way as to optimize the computation efficiency of the iterative solution of the forward kinematics using the Newton-Raphson method. A modified Jacobian matrix which relates length velocities to Cartesian translational velocities and time rates of change of roll-pitch-yaw angles is introduced. Computer simulation is performed to evaluate the computation efficiency of the developed computation schemes.< >
The design and control of an efficient two-joint, two-link flexible arm are described. This efficient arm was designed and built to use most of the energy (provided by the motors) in performing the tasks instead of mo...
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The design and control of an efficient two-joint, two-link flexible arm are described. This efficient arm was designed and built to use most of the energy (provided by the motors) in performing the tasks instead of moving the arm structure. The arm has most of the mass concentrated at the tip and uses a special mechanical configuration to decouple radial tip motions from angular tip motions. An important problem when controlling lightweight flexible arms is the large Coulomb friction of the motors. A two-nested-loop multivariable controller is used to control the lightweight flexible arm with friction in the joints. The inner loop controls the position of the motors while the outer loop controls the tip position. The resolved acceleration method is generalized to control this flexible arm. The compliance matrix is used to model the oscillations of the structure and is included in the decoupling/linearizing term of this controller. Experimental results are presented.< >
An adaptive learning control approach is proposed which combines a mechanism to improve the control input sequence as well as to improve the learning control scheme based on the knowledge learned about the unknown sys...
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An adaptive learning control approach is proposed which combines a mechanism to improve the control input sequence as well as to improve the learning control scheme based on the knowledge learned about the unknown system and environment. The iterative learning control problem is treated from the 2D system point of view. A 2D model for a class of iterative learning control system is formulated. A learning gain estimator algorithm based on the 2D model is presented. The overall learning control system structure is given. The proposed learning control scheme does not require prior knowledge of the controlled system and has the ability to generalize the knowledge learned from one task operation to other tasks. This scheme can be applied to nonlinear system control problems. To demonstrate the feasibility of the proposed learning algorithm, simulation results on learning control for a three-water-tank system are given. The results show an excellent learning performance, even for nonrepetitive tasks.< >
An adaptive learning control approach is proposed that combines a mechanism to improve control input sequence as well as to improve the learning control scheme based on the knowledge learned about unknown system and e...
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An adaptive learning control approach is proposed that combines a mechanism to improve control input sequence as well as to improve the learning control scheme based on the knowledge learned about unknown system and environment. First, the iterative learning control problem is treated from the 2-D system point of view. A 2-D model for a class of iterative learning control systems is formulated. Then a learning gain estimator algorithm based on the 2-D model is presented. The overall learning control system structure is given.< >
All linear multirate controllers for a given multirate sampled-data system plant are parameterized in terms of a single parameter Q(z) that is allowed to be any stable transfer matrix provided that certain causality c...
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All linear multirate controllers for a given multirate sampled-data system plant are parameterized in terms of a single parameter Q(z) that is allowed to be any stable transfer matrix provided that certain causality conditions are met. The result parallels a well-known parameterization result for single-rate sampled-data plants. The parameterization suggests architectures for multirate controllers.< >
The kinematic and dynamic modelling of robot manipulators are of such computational complexity that control schemes embodying on-line calculation of the robot model have previously been impossible at an economic cost ...
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The kinematic and dynamic modelling of robot manipulators are of such computational complexity that control schemes embodying on-line calculation of the robot model have previously been impossible at an economic cost in terms of computer hardware. However, the recent development of the transputer has transformed this situation, as shown in the paper. On-line schemes using transputers are shown to be feasible as solutions for two significant computational problems in manipulator control: computing the dynamic model, and computing a time-optimal path.
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