bluuebunny/crossref_metadata_2025_split huggingface dataset:
Initial Experiments on the End-Point Control of a Flexible One-Link Robot
Authors: Cannon Robert H. , Schmitz Eric 
Published: March 2007

It has been known for some time ( Gevarter 1970) that if a flexible structure is controlled by locating every sensor exactly at the actuator it will control, then stable operation is easy to achieve. Nearly all commercial robots are controlled in this way, for this reason. So are most flexible spacecraft. Conversely, when one attempts to control a flexible struc ture by applying control torques at one end that are based on a sensor at the other end, the problem of achieving stability is severe. Solving it is an essential step for better control in space: the space-shuttle arm is a cogent example. The next generation of industrial robots will also need such control capability, for they will need to be much lighter in weight ( to achieve quick response with modest energy), and they will need to achieve greater precision by employing end-point sensing. A set of experiments has been constructed to demonstrate control strategies for a single-link, very flexible manipulator, where the position of one end is to be sensed and precisely positioned by torquing at the other end. The objective of this first set of experiments is to uncover and solve problems related to the control of very flexible manipulators where sen sors are not colocated with the actuator. The experimental arrangement described here is also a test bed for new designs for flexible-structure controllers, designs that use insensitive, reduced-order control and adaptive control methods, for example. This paper describes the experimental arrangement, model identification, control design, and first experimental results. Some interesting results are the following. First, good stability can be achieved for such noncolocated systems, and reponse can be achieved that is effectively three times faster than the first natural cantilever period of the system: but a good model of the system dynamics and rather sophisticated control algorithms are essential to doing so. Even then, the system will always be conditionally stable. In addition to the tip sensor, a colocated rate sensor and nearly colocated strain gauges have been found to be very useful for achieving good closed-loop performance, that is, high gain and high band width. Second, there is an ultimate physical limit to achiev able response time, namely, the time required for a wave to travel the length of the member. Well-designed controllers can approach this limit. Third, the use of end-point sensing makes less critical the elaborate dynamic conditioning of position-command signals— "model-following " differentia tors, feed-forward, and the like—such as are typically needed in present-generation robots that use "dead reckoning" in lieu of end-point sensing. With end-point sensing, feedback alone ( suitably conditioned) is sufficient to whip the tip to the commanded position and hold it there precisely. Even more important, a shift in, for example, workpiece with respect to robot base, no longer produces an error.
A New Actuator of a Joint Mechanism Using TiNi Alloy Wire
Authors: Kuribayashi Katsutoshi 
Published: March 2007

A new actuator of a joint mechanism is proposed, composed of two TiNi alloy wires. First, the static and dynamic properties of the TiNi alloy wire that were not known are analyzed. Then the mathemati cal model of the actuator is induced. Next, the control sys tems of the actuator are synthesized by pulse width modu lated (PWM) controllers, and the mathematical models of the control systems are then obtained. Finally, the experiments of the position and force control systems of the actuator are carried out. It is proved that the theoretical models obtained are valid and that the position and force controls of this actuator are possible. Moreover, the unknown characteristics of the other well- known type of actuator composed of a TiNi alloy wire and an ordinary spring are also analyzed by the above procedure. The mathematical models are presented.
Optimization of Mechanisms for Force Generation by Using Pulleys and Spring
Authors: Okada Tokuji 
Published: March 2007

A link mechanism is proposed for force generation by using pulleys and springs (FGPS) based on a scissors structure having two arms, which are effective in energy saving, simpli fication, and miniaturization of a total system of force gener ation. The relationship between the motion of the mechanism and its output force is analyzed for optimization of structure and dimensions. For optimization of pulley shapes, analyti cal and approximate methods are discussed. Experimental results show that eccentric noncircular pulleys are more effective than circular pulleys in producing a force sufficiently accurate to satisfy conditional relations between the force and the displacement of the mechanism. The mechanism is useful in fulfilling various kinds offorce versus displacement characteristics requirements.
Type Selection of Robot and Gripper Kinematic Topology Using Expert Systems
Authors: Erdman Arthur G. , Thompson Thomas , Riley Donald R. 
Published: March 2007

Robots are used for many different applications including underwater recovery, welding, inspection, pick-and-place operations, space exploration, and assembly. Each task im parts different functional demands on the robot topology including the gripper. An improper choice of the basic kine matic chain may demand sophisticated control algorithms to undo poor type selection. This paper suggests techniques of type synthesis based on graph theory and expert systems that will aid in proper kine matic topology. This new area of kinematic research has high potential for aiding the robot designer.
Sensor Models and Multisensor Integration
Authors: Durrant-Whyte Hugh F. 
Published: March 2007

We maintain that the key to intelligent fusion of disparate sensory information is to provide an effective model of sensor capabilities. A sensor model is an abstraction of the actual sensing process. It describes the information a sensor is able to provide, how this information is limited by the environ ment, how it can be enhanced by information obtained from other sensors, and how it may be improved by active use of the physical sensing device. The importance of having a model of sensor performance is that capabilities can be esti mated a priori and, thus, sensor strategies developed in line with information requirements. We describe a technique for modeling sensors and the information they provide. This model treats each sensor as an individual decision maker, acting as a member of a team with common goals. Each sensor is considered as a source of uncertain geometric information, able to communicate to, and coordinate its activities with, other members of the sens ing team. We treat three components of this sensor model: the observation model, which describes a sensor's measure ment characteristics; the dependency model, which describes a sensor's dependence on information from other sources; and the state model, which describes how a sensor's observa tions are affected by its location and internal state. We show how this mechanism can be used to manipulate, communi cate, and integrate uncertain sensor observations. We show that these sensor models can deal effectively with cooperative, competitive, and complementary interactions between differ ent disparate information sources.
Control of Robotic Manipulators During General Task Execution: A Discontinuous Control Approach
Authors: Mills James K. , Lokhorst David M. 
Published: March 2007

In this article, a control methodology is proposed that ad dresses the problem of control of robotic manipulators during a general class of task that requires the manipulator to make a transition from (I) noncontact motion to contact motion and (2) contact motion to noncontact motion. Specifically, the problem of control of a general n-degree-of-freedom rigid-link robotic manipulator during a general class of tasks, as described ear lier, is treated. It is assumed that during the contact phase of the assumed task, frictionless point contact is made with fixed objects in the manipulator work environment, which is modeled as a linear mechanical impedance. Furthermore, it is assumed that exact knowledge of the manipulator and work environment kinematic and dynamic parameters is available. The following closed-loop behavior is achieved with the pro posed control law: (1) the closed-loop system exhibits global asymptotic stability; (2) asymptotic trajectory tracking of gen eralized force and position inputs is achieved; and significantly, (3) on inadvertent loss of contact by the manipulator, contact is reestablished, and generalized forces and positions are again asymptotically achieved. This closed-loop behavior is achieved in the presence of collisions between the manipulator and ob jects in the manipulator work environment; such collisions may include multiple impacts as a result of bouncing on initial contact. A general mathematical framework is established to prove that the closed-loop robotic system, with a discontin uous control applied, is asymptotically stable. Experimental results performed on a two-degree-of-freedom direct-drive robot support the theoretical claims made in this work.
Periodic Motions of a Hopping Robot With Vertical and Forward Motion
Authors: M'Closkey Robert T. , Burdick Joel W. 
Published: March 2007

This article analyzes the global dynamical behavior of sim plified hopping robot models that are analogous to Raibert's experimental machines. We first review a one-dimensional ver tical hopping model that captures both the vertical hopping dynamics and nonlinear control algorithm. Second, we present a more complicated two-dimensional model that includes both forward and vertical hopping dynamics and a foot placement algorithm. These systems are analyzed using a Poincare return map. In this approach, issues of stability and global dynamical behavior are reduced to the study of the fixed points of this map. For the one-dimensional model, a closed-form return map is obtained. For the two-dimensional model, we derive an exact return map based on the first integrals of motion. Because this map can only be constructed numerically, we also derive an analytical approximation to the return map based on perturba tion methods. The approximate return map is shown to closely predict the behavior of the exact map for small forward run ning velocities. In addition, the approximate return map can be used to quantitatively explore the coupling of vertical and lat eral dynamics and to determine the effect of the foot placement algorithm on dynamical behavior The bifurcation diagrams, which capture variations in dy namical behavior with respect to the variations in system and control parameters, are also constructed. The bifurcation dia grams exhibit a period-doubling cascade. In other words, for certain system parameter values, Raibert's control algorithm can lead to an anomalous nonuniform, but stable, hopping be havior. Using the vertical model results as a guide, we interpret the interesting dynamical behavior of this system.
Kinematics and Statics of Manipulation Using the Theory of Polyhedral Convex Cones
Authors: Hirai Shinichi , Asada Haruhiko 
Published: March 2007

A new approach to the kinematic and static analysis of ma nipulative tasks performed through mechanical contacts is presented. A variety of manipulation problems, including as sembly and grasps, have been treated separately in robotics research. All of the problems are treated as ways to solve a certain class of inequalities resulting from the unidirectional nature of mechanical contacts. One of the fundamental diffi culties in the analysis of manipulative tasks is the intractable nature of inequalities. In this article, we establish an underpinning mathematical tool for dealing with a variety of manipulative tasks that are governed by unidirectional constraints. First, we introduce a coherent representation for formulating various manipulation problems. Second, we develop several procedures based on the theory of polyhedral convex cones to solve these problems in a systematic and straightforward manner. The method is then implemented on a computer and applied to a variety of manipulation problems, including grasping, fixturing, and hybrid position/force control.
Experiments in Control of a Flexible-Link Robotic Manipulator With Unknown Payload Dynamics: An Adaptive Approach
Authors: Alder Lawrence J. , Rock Stephen M. 
Published: March 2007

This article presents technology that extends the concept of end-point control of a flexible-link robot arm to handle payloads with unknown internal dynamics. The approach is based on merging high-performance control with an innovative identification algorithm in a self-tuning regulator framework. Payload dynamics are identified in real time using recently de veloped subspace fitting techniques. Sufficient excitation issues are addressed. End-point feedback controllers are formulated using frequency-weighted linear quadratic gaussian design methods. Experimental results demonstrating precision control of a very flexible single-link robot arm with unknown dynamic payloads are presented.
Efficient Collision Prediction Among Many Moving Objects
Authors: Hayward Vincent , Aubry Stéphane , Foisy André , Ghallab Yasmine 
Published: March 2007

We consider the problem of flagging all collisions between a large number of dynamic objects. Because the number of possible collisions grows quadratically with the number of objects, a brute force approach is not applicable with finite computational resources. Hence, we propose a scheduling mechanism that reduces the computational load by exploiting the coherence of the world throughout time. This mechanism has a very simple structure and easily lends itself to distributed processing. It considers all pairwise interactions between objects and maintains a structure that reflects the imminence, or urgency, of collision for each pair. Bounds on the urgency of collisions can be computed given minimal knowledge of the system dynamics. For example, we represent physical objects by their positions and by bounds on their relative speeds and accelerations. These are assumed to be available at all times. If the environment does not change too rapidly, the mechanism flags all collisions. False alarms may also be generated but can be eliminated with a specialized exact collision post-processor. We address the question of how often to perform the col lision checks while guaranteeing that all collisions will be caught. Given the large number of possible environments and motions, no general optimal answer can be provided. Yet the soundness and efficiency of the proposed algorithm is eaper imentally verified in the case of a simple world consisting of many spheres moving simultaneously and randomly.
Modeling Gimbal Axis Misalignments and Mirror Center Offset in a Single-Beam Laser Tracking Measurement System
Authors: Hanqi Zhuang  , Roth Zvi S. 
Published: March 2007

The calibration of robots and machine tools normally requires external pose measuring devices to provide precision cal ibration measurement data. Among the various coordinate measuring techniques, laser tracking systems based on in terferometry offer the potential for continuously producing noninvasive and highly accurate measurements over a large work volume. This article addresses the error modeling is sue for laser tracking coordinate measuring systems, which is crucial in the accuracy enhancement of such systems. Relative distance measurements provided by laser interfer ometers have an extremely high resolution. However, accuracy errors of a coordinate measuring machine based on laser tracking are dominated by geometric errors in the tracking mir ror system. Major geometric error sources include gimbal axis misalignments and mirror center offset. In this article a kine matic model for the single-beam tracker is developed in which a necessary and sufficient number of kinematic parameters are used to represent these two types of error sources for ar bitrary target positions. This model, together with its error model, which is also presented in this article, can be used for design, calibration, and control of single-beam laser tracking measurement systems.
Mobile Robot Sonar for Target Localization and Classification
Authors: Kleeman Lindsay , Kuc Roman 
Published: March 2007

A novel sonar array is presented that has applications in mobile robotics for localization and mapping of indoor en vironments. The ultrasonic sensor localizes and classifies multiple targets in two dimensions to ranges of up to 8m. By accounting for effects of temperature and humidity, the sys tem is accurate to within 1 mm and 0.1° in still air. Targets separated by 10 mm in range can be discriminated. The error covariance matrix for these measurements is derived to allow fusion with other sensors. Targets are statistically classified into four reflector types: planes, corners, edges, and unknown. This article establishes that two transmitters and two re ceivers are necessary and sufficient to distinguish planes, corners, and edges. A sensor array is presented with this minimum number of transmitters and receivers. A novel de sign approach is used such that the receivers are closely spaced so as to minimize the correspondence problem of as sociating different receiver echoes from multiple targets. A linear filter model for pulse transmission, reception, air absorption, and dispersion is used to generate a set of tem plates for the echo as a function of range and bearing angle. The optimal echo arrival time is estimated from the maximum cross-correlation of the echo with the templates. The use of templates also allows overlapping echoes and disturbances to be rejected. Noise characteristics are modeled for use in the maximum likelihood estimates of target range and bearing. Experimental results are presented to verify assumptions and characterize the sensor.
Geometric Sensing of Known Planar Shapes
Authors: Jia Yan-Bin , Erdmann Michael 
Published: March 2007

Industrial assembly involves sensing the pose (orientation and position) of a part. Efficient and reliable sensing strategies can be developed for an assembly task if the shape of the part is known in advance. In this article we investigate two problems of determining the pose of a polygonal part of known shape for the cases of a continuum and a finite number of possible poses, respectively. The first problem, named sensing by inscription, involves determining the pose of a convex n-gon from a set of m sup porting cones. An algorithm with running time O( nm) that almost always reduces to O(n + m log n) is presented to solve for all possible poses of the polygon. We prove that the number of possible poses cannot exceed 6n, given m ≥ 2 supporting cones with distinct vertices. Simulation experiments demonstrate that two supporting cones are sufficient to determine the real pose of the n-gon in most cases. Our results imply that sensing in practice can be carried out by obtaining viewing angles of a planar part at multiple exterior sites in the plane. On many occasions a parts feeder will have reduced the number of possible poses of a part to a small finite set. Our second problem, named sensing by point sampling, is con cerned with a more general version: finding the minimum number of sensing points required to distinguish between n polygonal shapes with a total of m edges. In practice this can be implemented by embedding a series of point light detectors in a feeder tray or by using a set of mechanical probes that touch the feeder at a finite number of predeter mined points. We show that this problem is equivalent to an NP-complete set-theoretic problem introduced as Discriminat ing Set, and present an O( n2m2) approximation algorithm to solve it with a ratio of 2 In n. Furthermore, we prove that one can use an algorithm for Discriminating Set with ratio c log n to construct an algorithm for Set Covering with ratio c log n + O(log log n). Thus the ratio 2 In n is asymptotically optimal unless NP ⊂ DTIME( npoly log n), a consequence of known results on approximating Set Covering. The complexity of subproblems of Discriminating Set is also analyzed, based on their relationship to a generalization of Independent Set called 3-Independent Set. Finally, simulation results suggest
Modeling Mechanisms with Nonholonomic Joints Using the Boltzmann-Hamel Equations
Authors: Cameron Jonathan M. , Book Wayne J. 
Published: March 2007

This article describes a new technique for deriving dynamic equations of motion for serial chain and tree topology mech anisms with common nonholonomic constraints. For each type of nonholonomic constraint, the Boltzmann-Hamel equations produce a concise set of dynamic equations. These equations are similar to Lagrange's equations and can be applied to mechanisms that incorporate that type of constraint. A small library of these equations can be used to efficiently analyze many different types of mechanisms. Nonholonomic constraints are usually included in a La grangian setting by adding Lagrange multipliers and then eliminating them from the final set of equations. The ap proach described in this article automatically produces a minimum set of equations of motion that do not include La grange multipliers.
Changing Divorce in Japan
Authors: Kumagai Fumie 
Published: March 2007

A century of historical perspective on divorce in Japan confirms that it occurred at an extraordinarily high rate before the turn of the century, and then declined until 1964. But with the progress of industrialization to even more ad vanced levels during the postwar era, divorce rates in Japan have gradually risen again, although not to the same high degree as in the West. For the first time, there seems to be a positive correlation between the level of industrialization and urbanization in Japan and the increasing divorce rate in the nuclear family. Recent statistics on divorce in Japan show that more and more women initiate divorce, that an increasing number of divorced women prefer to remain single, and that changing patterns of divorce have resulted in a lowering of the fertility rate, all of which may have significant implications for the demographic future of the Japanese population. With the development of industrialization and urbanization, the Westernization of lifestyles, and the growing autonomy of women in society, an increase in the divorce rate in Japanese society is likely. It is true, however, that the family is still one of the most fundamental institutions in Japan. It is to be hoped that the value traditionally accorded to the family will counteract the recent upward trend in divorce rate and reduce it in the foreseeable future.
Nonmetallic Material Flammability in Oxygen Enriched Atmospheres
Authors: Tewarson Archibald 
Published: March 2007

Nonmetallic material flammability on Oxygen Enriched Atmo spheres (OEA) is discussed with explanations based on the latest scientific un derstanding. Flammability consists of a combination of the ignition, combustion, and fire propagation behaviors of materials. Application of the newly developed test methods and advanced-engineering polymers for OEA con ditions are discussed. The test methods use high oxygen concentration, pres sure, and external heat flux to simulate large-scale fire environments. Pressure and external heat flux effects are complementary and appear to have a stronger effect on the flammability of materials than the oxygen concentration. High oxy gen concentration in combination with external heat flux provides similar heat flux exposure to materials as normal atmosphere at high pressures. Results are presented for flame heat flux transferred back to the surface of the burning materials under high pressure (normal air) and high oxygen concentra tions (at atmospheric pressure). The use of newly developed test methods is sug gested for evaluating the probability of fires in OEA facilities such as hyperbaric chambers.