# Robotica

Published by Cambridge University Press (CUP)

Online ISSN: 1469-8668

Published by Cambridge University Press (CUP)

Online ISSN: 1469-8668

Publications

Article

Over the past several decades a number of O(n) methods for forward and inverse dynamics computations have been developed in the multi-body dynamics and robotics literature. A method was developed in 1974 by Fixman for O(n) computation of the mass-matrix determinant for a serial polymer chain consisting of point masses. In other recent papers, we extended this method in order to compute the inverse of the mass matrix for serial chains consisting of point masses. In the present paper, we extend these ideas further and address the case of serial chains composed of rigid-bodies. This requires the use of relatively deep mathematics associated with the rotation group, SO(3), and the special Euclidean group, SE(3), and specifically, it requires that one differentiates functions of Lie-group-valued argument.

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Article

A nonholonomic system subjected to external noise from the environment, or internal noise in its own actuators, will evolve in a stochastic manner described by an ensemble of trajectories. This ensemble of trajectories is equivalent to the solution of a Fokker-Planck equation that typically evolves on a Lie group. If the most likely state of such a system is to be estimated, and plans for subsequent motions from the current state are to be made so as to move the system to a desired state with high probability, then modeling how the probability density of the system evolves is critical. Methods for solving Fokker-Planck equations that evolve on Lie groups then become important. Such equations can be solved using the operational properties of group Fourier transforms in which irreducible unitary representation (IUR) matrices play a critical role. Therefore, we develop a simple approach for the numerical approximation of all the IUR matrices for two of the groups of most interest in robotics: the rotation group in three-dimensional space, SO(3), and the Euclidean motion group of the plane, SE(2). This approach uses the exponential mapping from the Lie algebras of these groups, and takes advantage of the sparse nature of the Lie algebra representation matrices. Other techniques for density estimation on groups are also explored. The computed densities are applied in the context of probabilistic path planning for kinematic cart in the plane and flexible needle steering in three-dimensional space. In these examples the injection of artificial noise into the computational models (rather than noise in the actual physical systems) serves as a tool to search the configuration spaces and plan paths. Finally, we illustrate how density estimation problems arise in the characterization of physical noise in orientational sensors such as gyroscopes.

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Article

The principle of superposition introduced by Prof. S. Arimoto and his colleagues for the control of robotic hand has been shown to be applicable to the control of prehensile actions by humans. In particular, experiments have shown that static human hand actions can be viewed as a superposition of two independent synergies controlling the grasping force and the orientation of the object. Studies of elderly persons have shown that they are impaired in both synergies and show worse stabilization of the grasping force and of the total moment of forces applied by the digits to a hand-held object. Recent studies have also shown that the principle of superposition holds with respect to reactions to expected and unexpected mechanical perturbations applied to a hand-held object. Indices of the two synergies have shown different changes following a perturbation. Generalization of the principle of superposition to human prehension is an important step towards understanding the principles of control of the human hand.

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Conference Paper

Presents a formulation of the synthesis of 3D frictional form-closure grasps of n robot fingers. First, using a recursive reduction technique, we transform the problem in 6D wrench space to one in three dimensions. Then we rewrite the sufficient and necessary condition for form-closure grasps in the equivalent form of the inconsistency of each of the two sets of linear inequalities. Then we propose three conditions to check the inconsistency of the inequality system, which geometrically indicates whether the convex region formed by the inequality system is empty. We have implemented the algorithms and confirmed their real-time efficiency for the synthesis of 3D form-closure grasps

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Conference Paper

A new bending and expanding motion actuator has been developed. The actuator is composed of 40 sheets of PZT unimorph cells. Each PZT unimorph cell's electrode is divided into three sections. These cells are piled vis-a-vis. The vertically located electrodes are connected to one another with copper wire of 50 μm in diameter. The actuator is 12 mm in diameter, 20 mm in length and 6.4 g in weight. The bending angle is 3 degrees with no weight and 9.5 degrees with 115 g weight in six directions (one or two electrodes are charged), and the expansion displacement is 700 μm with no weight when three electrodes on a cell are simultaneously charged with the 150 V driving voltage. Multi-directional bending is realized by independent driving of each electrode on a cell

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Conference Paper

This paper considers the problem of controlling nonholonomic
mechanical systems in the presence of incomplete information concerning
the system model and state. It is proposed that a simple and effective
solution to this problem can be obtained by first using a reduction
procedure to obtain a lower dimensional system which retains the
mechanical system structure of the original system, and then adaptively
controlling the reduced system in such a way that the complete system is
driven to the goal configuration. This approach is shown to ensure
accurate motion control without knowledge of the system dynamic model or
rate measurements. The efficacy of the proposed control strategy is
illustrated through preliminary laboratory experiments with a symmetric
nonholonomic mechanical system

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Conference Paper

This paper provides a solution to the composite adaptive output
feedback tracking control problem for robotic manipulators. The proposed
controller utilizes an update law that is a composite of a gradient
update law driven by the link position tracking error and a least
squares update law driven by the prediction error. In order to remove
the controller's dependence on link velocity measurements, a linear
filter and a new prediction error formulation are designed. The
controller provides semi-global asymptotic link position tracking
performance

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Conference Paper

Pattern recognition and object localization, using various sensors such as vision and tactile sensors, are two important areas in the application of robotic systems. This paper demonstrates the feasibility of using some relatively inexpensive pressure sensors and a neural network to achieve object localization and pattern recognition. The sensors used are force sensing resistors (FSRs), more specifically, a 16×16 array of FSRs. Because of the nonlinearities associated with a FSR, three approaches for gathering output from the sensor array are used. The neural network used consists of two 2-layer counterpropagation networks (CPNs). In addition to recognizing pre-trained patterns, this paper also demonstrates that the conventional CPN configuration can be modified to learn new patterns even when its training period is completed. Both simulated and experimental results of this paper suggest that the neural network can provide an alternative approach for object localization using tactile arrays

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Conference Paper

This paper presents a solution to the global adaptive partial
state feedback control problem for rigid-link, flexible-joint robots.
The proposed tracking controller adapts for parametric uncertainty
throughout the entire mechanical system while only requiring link and
actuator position measurements. A nonlinear filter is employed to
eliminate the need for link velocity measurements while a set of linear
filters is utilized to eliminate the need for actuator velocity
measurements. A backstepping control strategy is utilized to illustrate
global asymptotic link position tracking

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Conference Paper

In order to achieve the autonomy of mobile robots, effective localization is a necessary prerequisite. In this paper, we propose an improved Monte Carlo localization using self-adaptive samples, abbreviated as SAMCL. This algorithm employs a pre-caching technique to reduce the on-line computational burden. Further, we define the concept of similar energy region (SER), which is a set of poses (grid cells) having similar energy with the robot in the robot space. By distributing global samples in SER instead of distributing randomly in the map, SAMCL obtains a better performance in localization. Position tracking, global localization and the kidnapped robot problem are the three sub-problems of the localization problem. Most localization approaches focus on solving one of these sub-problems. However, SAMCL solves all these three sub-problems together thanks to self-adaptive samples that can automatically separate themselves into a global sample set and a local sample set according to needs. The validity and the efficiency of our algorithm are demonstrated by experiments carried out with different intentions. Extensive experiment results and comparisons are also given in this paper.

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Conference Paper

An adaptive fuzzy sliding control (AFSC) scheme is proposed to control a passive robotic manipulator. The motivation for the design of the adaptive fuzzy sliding controller is to eliminate the chattering and the requirement of pre-knowledge on the bounds of the errors associated with the conventional sliding control. The stability and convergence of the adaptive fuzzy sliding controller are proven both theoretically and practically by simulations. A three-link passive manipulator model with two unactuated joints is derived to be used in the simulations. Simulation results demonstrate that the proposed system is robust against structured and unstructured uncertainties.

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Conference Paper

This paper presents a new adaptive controller as a solution to the problem of stabilizing nonholonomic mechanical systems in the presence of incomplete information concerning the system dynamic model. The proposed control system consists of two subsystems: a slightly modified version of the kinematic stabilization strategy of M'Closkey and Murray, which generates a desired velocity trajectory for the nonholonomic system, and an adaptive control scheme which ensures that this velocity trajectory is accurately tracked. This approach is shown to provide arbitrarily accurate stabilization to any desired configuration and can be implemented with no knowledge of the system dynamic model. The efficacy of the proposed stabilization strategy is illustrated through computer simulations with two nonholonomic mechanical systems

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Conference Paper

Shape memory alloy (SMA) is a device with lightweight and small
volume. It is very ideal to use SMA as actuators for micro-robots.
However, it is difficult to design a controller to handle the highly
nonlinear properties of SMA. In this paper, a fuzzy walking pattern
(FWP) is designed to control a small biped robot, using SMA as
actuators. The FWP designed in this paper can not only generate the
desired path for the biped robot, but also handle the exceptional case
when the biped robot is subject to disturbance. Experimental results
demonstrate the function of the FWP

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Conference Paper

This paper describes an automated procedure for analysing the
significance of each of the many terms in the equations of motion for a
serial-link robot manipulator. Significance analysis provides insight
into the rigid-body dynamic effects that are significant locally or
globally in the manipulator's state space. Deleting those terms that do
not contribute significantly to the total joint torque can greatly
reduce the computational burden for online control, and a Monte-Carlo
style simulation is used to investigate the errors thus introduced. The
procedures described are a hybrid of symbolic and numeric techniques,
and can be readily implemented using standard computer algebra packages

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Conference Paper

A unified force control scheme for an autonomous underwater
robotic system is proposed. This robotic system is composed of a six
degree-of-freedom autonomous underwater vehicle (AUV) and a robotic arm
that is mounted on the AUV. First, a dynamic model for the whole
underwater manipulator system considering the hydrodynamic effects is
derived. This model is then used to implement the proposed unified force
control approach, which combines impedance control with hybrid
position/force control by means of fuzzy switching to perform autonomous
underwater manipulation. This approach combines the advantages of
impedance control with hybrid control and has the potential to be
effective in underwater environment. Extensive computer simulations are
performed to verify the efficacy of the proposed control scheme, and the
results are presented

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Conference Paper

A novel design of a three dimensional localiser intended for autonomous robot vehicles is presented. A prototype is implemented in air using ultrasonic beacons at known positions, and can be adapted to underwater environments where it has important applications, such as deep sea maintenance, data collection and reconnaissance tasks. The paper presents the hardware design, algorithms for position and orientation determination (six degrees of freedom), and performance results of a laboratory prototype. Two approaches are discussed for position and orientation determination – (i) fast single measurement set techniques and (ii) computationally slower Kalman filter based techniques. The Kalman filter approach allows the incorporation of robot motion information, more accurate beacon modelling and the capability of processing data from more than four beacons, the minimum number required for localisation.

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Conference Paper

This paper proposes a new algorithm, known as the segmentation
algorithm, which provides model-based, real-time, whole-arm collision
avoidance for telerobotic applications. The work presented is an
extension and modification of potential field theory. Novel aspects of
the algorithm include the application of a hierarchical segmentation
technique to minimize on-line processing and the development of
procedures which account for workspace object translation, rotation, and
grasping. The segmentation algorithm outputs torques, which, when
applied to the control arm, prevent the teleoperator from driving the
remote arm into a collision. The teleoperator actually feels workspace
objects that are spatially close to the remote arm-an experience known
as virtual force-reflection. The segmentation algorithm's performance
has been analyzed in terms of its speed and efficiency vis a vis various
system parameters, including workspace object distribution, size, and
number. Simulation results show that the segmentation algorithm succeeds
in providing real-time collision avoidance where less elegant brute
force algorithms fail

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Conference Paper

We present a measure called collidability measure for obstacle
avoidance control of redundant manipulators. Considering moving
directions of manipulator links, the collidability measure is defined as
the inverse of sum of predicted collision distances between links and
obstacles. This measure is suitable for obstacle avoidance control since
directions of moving links are as important as distances to obstacles.
For dynamic redundancy resolution, null space control is utilized to
avoid obstacles by minimizing the collidability measure. Also, by
clarifying decomposition in the joint acceleration level, we present a
simple dynamic control law with bounded joint torques which guarantees
tracking of a given end-effector trajectory and improves a kinematic
cost function such as collidability measure. Simulation results are
presented to illustrate the effectiveness of the proposed
algorithm

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Conference Paper

This paper presents an assessment of different estimation and prediction techniques applied to the tracking of multiple robots. The main assessment criteria are the magnitude of the estimation or prediction error, the computational effort and the robustness of each method under non-Gaussian noise. Among the different techniques compared are the well known Kalman filters and their different variants (extended and unscented), and the more recent techniques relying on sequential Monte Carlo sampling methods, such as particle filters, and sigma-points filters

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Conference Paper

Significant research has been aimed at the development and control of teleoperator systems. Two controllers are developed in this paper for a nonlinear teleoperator system that targets coordination of the master and slave manipulators and passivity of the overall system. The first controller is proven to yield a semi-global asymptotic result in the presence of parametric uncertainty in the master and slave manipulator dynamic models. The second controller yields a global asymptotic result despite unmeasurable user and environmental input forces. To develop each controller a transformation encodes the coordination and passivity requirements within the closed loop system. The coordinated system is forced to track a dynamic system to assist in meeting all control objectives. Finally, continuous nonlinear integral feedback terms are used to accommodate for incomplete system knowledge for both of the controllers. Lyapunov-based techniques are used to prove that all control objectives are met and that all signals are bounded

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Conference Paper

Many studies on control of dynamic biped walking have been done in
the past two decades. While the biped dynamics is highly nonlinear, the
stability analysis, if done, was usually based on a linearized model.
The validity of the linearized model may become questionable if the
walking involves states that are too far away from the operating point.
In this paper, an approach for evaluating the robustness based on the
linearized Poincare' map is suggested and examined. The Poincare' map
technique is often used in studying periodic motion. The computational
method that results in a measurement for evaluating the robustness of
biped locomotion is developed. Our simulation study has verified that
the suggested measurement is a good indicator

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Conference Paper

In this paper we present the results obtained from the
implementation of a robust position/force controller on a
two-degree-of-freedom direct drive robot. The controller is based on the
theoretical work presented by McClamroch et al. (1988) and Grabbe et al.
(1993), which guarantees globally uniformly ultimately bounded (GUUB)
position tracking error and bounded force tracking error. The controller
accomplishes this stability result in spite of robot model uncertainty
and only requires: joint position and velocity measurements,
end-effector force measurements, and bounds on the model parameters.
Experimental results described in this paper serve to verify the
theoretical claims

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Conference Paper

A modular hierarchical model for controlling robots is presented.
This model is targeted mainly for research and development, enabling
researchers to concentrate on a certain specific task of robotics, while
using existing building blocks for the rest of the controller
application. The problems with which robotics researchers and engineers
are faced when trying to use existing commercial robots are detailed.
Based on this discussion, the authors propose TERM, a general model for
robot control. The viability of the model is demonstrated by
implementing a general-purpose robot controller. For this purpose
several building blocks were developed. Using these building blocks
three robot systems were assembled: a large system for an industrial
PUMA robot and two smaller ones for educational robots. The system is
currently used for research in nonlinear and adaptive control, path
planning and multirobot applications

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Conference Paper

In this study, a model based robust control scheme is developed for kinematically redundant robot manipulators that also enables the use of self motion of the manipulator to perform multiple sub-tasks in order to increase the manipulability and/or performance of the system. The proposed controller ensures uniformly ultimately bounded end-effector and sub-task tracking despite the parametric uncertainty associated with the dynamic model. A Lyapunov based approach has been utilized in the controller design and extension to a non minimum set of parameters for orientation representation has been presented to illustrate the flexibility of the approach. The capabilities and performance of the resulting controller is demonstrated by simulation results

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Conference Paper

A proximity sensor using a mechanical contact principle is under development for robotic applications. Good discrimination between contact loads and inertial windage loads is essential. Rugged design and easy replacement of sensing elements is also necessary. The sensor is under consideration for use on the feet of the Adaptive Suspension Vehicle.

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Article

Two types of bending and expanding motion actuators which are composed of multilayered PZT unimorph cells have been developed. Each PZT unimorph cell's electrode is divided into three sectors and the facing sectors are connected to one another. The bending and expanding motion actuator (8 mm in diameter, 9.2 mm in length), which has three pillars on the PZT side of the unimorph cell and one pillar on the metal side, respectively, achieves a bending angle of 4.5°, and the expansion displacement is 610 μm with 100 V. The resonance frequency is 140 Hz with 25 V. Multidirectional bending is realized by controlling the driving voltage of each sector.

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Article

A kind of brand-new robot, quantum robot, is proposed through fusing quantum theory with robot technology. Quantum robot is essentially a complex quantum system and it is generally composed of three fundamental parts: MQCU (multi quantum computing units), quantum controller/actuator, and information acquisition units. Corresponding to the system structure, several learning control algorithms including quantum searching algorithm and quantum reinforcement learning are presented for quantum robot. The theoretic results show that quantum robot can reduce the complexity of O(N^2) in traditional robot to O(N^(3/2)) using quantum searching algorithm, and the simulation results demonstrate that quantum robot is also superior to traditional robot in efficient learning by novel quantum reinforcement learning algorithm. Considering the advantages of quantum robot, its some potential important applications are also analyzed and prospected.

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Article

This paper has been withdrawn. Comment: This paper has been withdrawn

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Article

The paper addresses kinematic and geometrical aspects of the Orthoglide, a three-DOF parallel mechanism. This machine consists of three fixed linear joints, which are mounted orthogonally, three identical legs and a mobile platform, which moves in the Cartesian x-y-z space with fixed orientation. New solutions to solve inverse/direct kinematics are proposed and we perform a detailed workspace and singularity analysis, taking into account specific joint limit constraints.

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Chapter

In this chapter, we developed the model for two cooperative industrial robots holding a rigid object without friction. The dynamic model for the manipulators is obtained independently from each other with the Lagrangian approach. Once the robots are holding the object, their joint variables are kinematically and dynamically coupled. These coupling equations are combined with the dynamic model of the object to obtain a mathematical description for the cooperative system. Besides, the tracking control problem for cooperative robots without velocity measurements is considered. The control law is a decentralized approach which takes into account motion constraints rather than the held object dynamics. By assuming that fingers dynamics are well known and that contact forces measurements are available, a linear observer for each finger is proposed which does not require any knowledge of the robots dynamics. Despite the fact that the stability analysis is complex, the controller and specially the observer are not. Some experiments and simulations have been carried out to test the theoretical results. The overall outcome of the mathematical model compared with the real system can be considered good, which validates the approach used.

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Article

This article synthezises the most important results on the kinematics of cuspidal manipulators i.e. nonredundant manipulators that can change posture without meeting a singularity. The characteristic surfaces, the uniqueness domains and the regions of feasible paths in the workspace are defined. Then, several sufficient geometric conditions for a manipulator to be noncuspidal are enumerated and a general necessary and sufficient condition for a manipulator to be cuspidal is provided. An explicit DH-parameter-based condition for an orthogonal manipulator to be cuspidal is derived. The full classification of 3R orthogonal manipulators is provided and all types of cuspidal and noncuspidal orthogonal manipulators are enumerated. Finally, some facts about cuspidal and noncuspidal 6R manipulators are reported.

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Article

Machine vision-based sensing enables automatic hover stabilization of helicopters. The evaluation of image data, which is produced by a camera looking straight to the ground, results in a drift free autonomous on-board position measurement system. No additional information about the appearance of the scenery seen by the camera (e.g. landmarks) is needed. The technique being applied is a combination of the 4D-approach with two dimensional template tracking of apriori unknown features.

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Article

We give a full classification of all pentapods with linear platform
possessing a self-motion beside the trivial rotation about the platform. Recent
research necessitates a contemporary and accurate re-examination of old results
on this topic given by Darboux, Mannheim, Duporcq and Bricard, which also takes
the coincidence of platform anchor points into account. For our study we use
bond theory with respect to a novel kinematic mapping for pentapods with linear
platform, beside the method of singular-invariant leg-rearrangements. Based on
our results we design pentapods with linear platform, which have a simplified
direct kinematics concerning their number of (real) solutions.

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Article

: Navigation and collision avoidance are major areas of research in mobile robotics that involve varying degrees of uncertainty. In general, the problem consists of achieving sensor based motion control of a mobile robot among obstacles in structured and/or unstructured environments with collision-free motion as the priority. A fuzzy logic based intelligent control strategy has been developed here to computationally implement the approximate reasoning necessary for handling the uncertainty inherent in the collision avoidance problem. The fuzzy controller was tested on a mobile robot system in an indoor environment and found to perform satisfactorily despite having crude sensors and minimal sensory feedback. 1. INTRODUCTION An aim of intelligent robotics research is to develop mobile robots capable of navigating autonomously in unstructured and/or unexplored environments. This development requires intelligent control strategies capable of overcoming the uncertainties presented by the re...

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Article

. The complex domain of engineering design poses many challenges when attempting to automate the process. The frequent use of past experience by human engineers when solving new problems has led to an interest in the use of case based reasoning (CBR) to help automate engineering design. In order to create a case based reasoning system that is useful for complex domains, the problem of adaptation, or changing existing solutions to meet new problem requirements, must be addressed, as it is critical to ensure that a case based reasoner is more than just a storage and retrieval tool. In engineering design it often occurs that many past experiences must be combined to solve a new problem, and thus the process of adaptation must efficiently and systematically combine information from many sources. We have developed a methodology for case combination that allows its application across a wide range of problems by choosing a constraint satisfaction algorithm to achieve the combination. We have...

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Article

To perform dextrous manipulation efficiently, it is necessary to coordinate the interactions of many component processes. This paper investigates one approach to coordination: discrete-event systems. The applicability of discrete-event systems to the modeling of dextrous manipulation tasks is studied. Discrete-event control theory offers formal methods for determining whether a coordinator of the components can be generated. A representative dextrous manipulation task, the planar Grasp-Lift-Replace task of Howe and Cutkosky, is presented as a discrete-event process. The task is extended to include two-fingered exploratory procedures. The effectiveness of the discrete-event system approach is illustrated through simulations of several test cases. 1 Introduction In many robotics problems, robot hands must perform delicate and precise operations that include grasping and smoothly lifting an object. Robotics research has addressed many components of this dextrous manipulation problem. The...

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Article

The Orccad programming environment for robotic systems gathers control laws in continuous time at the low levels and discrete time logical aspects at higher levels. Based upon a formal deønition of robotic actions, complex applications can be designed, veriøed and generated incrementally. The approach and tools prototypes have been validated through several applications. 1 Goals and Concepts Actual robotic systems range from cooperative manipulators to autonomous vehicles. They have in common a continuously increasing complexity which makes more and more diOEcult the needed integration of issues raised by automatic control, sensor data processing and computer science areas. The goal of a control architecture is then to organize coherently all the involved subsystems so that the global system behaves in an eOEcient and reliable way to match the end-user's requirements. Robotic systems belongs to the class of hybrid reactive and real-time systems in which dioeerent methods and tools of ...

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Article

Industrial parts can be fed (oriented) using a sequence of fixed horizontal pins to topple the parts as they move past on a conveyor belt. We give an algorithm for designing a sequence of such pins for a given part. Given the n-sided convex polygonal projection of a part, its center of mass and frictional coefficients, our O(n 2 ) algorithm computes the toppling graph, a new data structure that explicitly represents the mechanics of toppling, rolling, and jamming. We verify the toppling graph analysis with experiments. Our O(n 3n ) design algorithm uses the toppling graph to design a sequence of pin locations that will cause the part to emerge in a unique orientation or to determine that no such sequence exists. Index Terms -- Manufacturing, Assembly, Part Feeding, Motion Planning. I.

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Article

The goal of concurrent mapping and localization (CML) is enable a mobile robot to build a map of an unknown environment, while concurrently using that map to navigate. This paper describes the application of the stochastic mapping approach to CML [10, 8, 3] to data from a high resolution array forward look imaging sonar [9, 7, 2]. The objective is to test the feasibility of stochastic mapping as a method for autonomous underwater vehicle (AUV) navigation. Measurements from the forward look sonar were postprocessed to yield estimates for the locations of environmental features and the trajectory of the sensor. The resulting trajectory provides an improvement in comparison to position estimates computed with an inertial navigation system. DGPS data is used as a ground-truth for comparison. The results demonstrate the potential of CML algorithms to achieve a bounded navigation error through tracking of environmental features. 1 Introduction Navigation is one of the most challenging issu...

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Article

A wheeled mobile manipulator system is modeled using Kane's dynamic equations. Kane's equations are constructed with minimum eort, are control oriented and provide both physical insight and fast simulations. The powerful tools of Kane's approach for incorporating nonholonomic motion constraints and bringing noncontributing forces into evidence are exploited. Both nonholonomic constraints associated with slipping and skidding as well as conditions for avoiding tipping over are included. The resulting equations, along with the set of constraint equations provide a safe and complete framework for developing control strategies for mobile manipulator systems. 1

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Article

This paper deals with the kinematic synthesis of manipulator. A new method based on distributed solving is used to determine the dimensional parameters of a general manipulator which is able to reach a set of given tasks speciøed by orientation and position. First, a general Distributed Solving Method (DSM) is presented in three steps : the problem statement, the objective functions formulations and the minimum parameters values determination. Then, this method is applied to solve the synthesis of Denavit and Hartenberg set of parameters of a manipulator with a given kinematic structure. In this case, the kind and the number of joints are speciøed and a set of constraints are included such as joint limits, range of dimensional parameters and geometrical obstacles avoidance. We show that if the Denavit and Hartenberg parameters (DH) are known, the synthesis problem is reduced to an inverse kinematic problem. We show also how the problem of robot base placement can be solved by the same ...

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Article

Multilink robot arms are geometrically similar to chain molecules. We investigate the performance of molecular simulation methods, combined with stochastic methods for optimization, when applied to problems of robotics. An efficient and flexible algorithm for solving the inverse kinematic problem for redundant robots in the presence of obstacles (and other constraints) is suggested. This "Constrained Kinematics / Stochastic Optimization" (CKSO) method is tested on various standard problems. e-mail: kast@pap.univie.ac.at y e-mail: ves@pap.univie.ac.at 1 1 Motivation There is an impressive arsenal of analytical and semianalytical methods for treating the mechanics of multilink manipulators [1, 2]. Generally, one attempts to set up a small (minimum?) set of internal coordinates q that determine the world coordinates x of the ultimate link (the "end effector"). A simple example would be a two-dimensional chain consisting of three links of fixed lengths, coupled by three joints (the f...

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Article

In programming robot manipulators to carry out a wide variety of tasks it would be desirable to create a cad system in which these tasks can be programmed at the task level, leaving the fine-grained detail of path planning and collision detection to the system. This paper describes the theoretical background to such a system, by providing a model in which robot motions are represented using multivariate B-splines, a standard representation for free-form shapes in the cad environment. The paper also describes algorithms which take this representation and apply it to collision detection and path-planning. 1 Introduction. Robots are typically programmed in one of two ways. The first of these is to guide the robot through a set of motions using a teach-pendant, which takes the robot out of the production line for the duration of the programming task. The second is to plan the motions using a robot programming language, possibly assisted by using a simulation package such as CimSt...

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Article

The basic robot control technique is the model based computed-torque control which is known to suffer performance degradation due to model uncertainties. Adding a neural network (NN) controller in the control system is one effective way to compensate for the ill effects of these uncertainties. In this paper a systematic study of NN controller for a robot manipulator under a unified computed-torque control frame work is presented. Both feedforward and feedback NN control schemes are studied and compared using a common back-propagation training algorithm. Effects on system performance for different choices of NN input types, hidden neurons, weight update rates, and initial weight values are also investigated. Extensive simulation studies for trajectory tracking are carried out and compared with other established robot control schemes. This work is supported in part by NITTA Corporation of Japan I Introduction For the past several years, there have been a lot of interests in applying...

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Article

A new neural network (NN) control technique for robot manipulators is introduced in this paper. The fundamental robot control technique is the model-based computed-torque control which is subjected to performance degradation due to model uncertainty. NN controllers have been traditionally used to generate a compensating joint torque to account for the effects of the uncertainties. The proposed NN control approach is conceptually different in that it is aimed at prefiltering the desired joint trajectories before they are used to command the computed-torque-controlled robot system (the plant) to counteract performance degradation due to plant uncertainties. In this framework, the NN controller serves as the inverse model of the plant, which can be trained on-line using joint tracking error. Several variations of this basic technique is introduced. Back- This work is supported in part by NITTA Corporation of Japan propagation training algorithms for the NN controller have been develop...

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Article

Let P = {p 1 , p 2 ,..., p n } and Q = {q 1 , q 2 ,..., q m } be two simple polygons monotonic in directions q and j, respectively. It is shown that P and Q are separable with a single translation in at least one of the directions: q + p / 2, j + p / 2. Furthermore, a direction for carrying out such a translation can be determined in O(m + n) time. This procedure is of use in solving the FIND-PATH problem in robotics. 1. Introduction Spurred by developments is spatial planning in robotics, computer graphics and VLSI layout, considerable attention has been devoted recently to the problem of moving polygons in the plane without collision. 1-11 A typical problem in robotics is the FIND-PATH problem, 12 where a robot must determine if an object, modeled as a polygon in the plane, can be moved from a starting position to a goal state without collisions occurring between the object being moved and the obstacles. Much work has been done on the problem of hypothesizing channel...

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Article

An analytical method is presented to obtain all surfaces enveloping the workspace of a general n degree-of-freedom mechanism with non-unilateral constraints. The method is applicable to kinematic chains that can be modeled using the Denavit-Hartenberg ...

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Article

D. Zhang and F. Zhang addressed the issue of designing and analyzing totally decoupled 3-DOF spherical parallel manipulators (SPMs) and concluded that the SPMs in Figs. 5(a) and 5(b) of ref. [1] are completely decoupled and fully isotropic (see Abstract, Section 5, and Conclusions in ref. [1]). This topic is of great interest to researchers working in the general area of parallel mechanisms. However, we disagree with the authors of ref. [1] on their conclusion.

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Article

The main goal of this paper is the design of 4PUS+1PS parallel manipulator, using an optimization problem that takes into accounts the characteristics of the workspace and dexterity. The optimization problem is formulated considering constraints on actuated and passive joint limits. A comparison between quantum particle swarm Optimization (QPSO) and PSO is developed. Two numerical examples are presented, which reveal the advantages of QPSO to PSO. Moreover, it is shown that by introducing the dexterity index as a quality measure throughout the workspace, the parallel manipulator is improved at the cost of a minor reduction in its workspace.

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Article

Based on the Lie-group-algebraic properties of the displacement set and intrinsic coordinate-free geometry, several novel 4-dof overconstrained hybrid parallel manipulators (HPMs) with uncoupled actuation of three spatial translations and one rotation (3T-1R) are proposed. In these HPMs, three limbs are those of Cartesian translational parallel mechanisms (CTPMs) and the fourth limb includes an Oldham-type constant velocity shaft coupling (CVSC). The Lie subgroup of Schoenflies (X) displacements of the displacement Lie group and its mechanical generators with nine categories of their general architectures are recalled. A comprehensive enumeration of all possible Oldham-type CVSC limbs is derived from X-motion generators. Their constant velocity (CV) transmissions are verified by group-algebraic approach. Then, combining one CTPM and one CVSC, we synthesize a lot of uncoupled 3T-1R overconstrained HPMs, which are classified into nine distinct classes of general architectures. In addition, all possible architectures with at least one hinged parallelogram or with one cylindrical pair are disclosed too. At last, related non-overconstrained HPMs are attained by the addition of one idle pair in each limb of the previous HPMs.

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