Initial force and postural adaptations when pushing and pulling on floor surfaces with good and reduced resistance to slipping

The objective of the present study was to determine whether differences in the frictional properties of a floor surface may affect the kinematics and kinetics of pushing and pulling. Eight male participants were required to push and pull a four-wheeled trolley over two level surfaces, on which were mounted floor coverings with good (safety floor) and reduced (standard floor) frictional properties. A psychophysical approach was used to determine the initial maximum acceptable horizontal force required to move the trolley over a short distance (3 m). Three-dimensional (3D) hand and ground reaction forces and 3D postures were measured during initial force exertions. The results showed that psychophysically derived measures of initial horizontal force and horizontal components of hand forces did not differ significantly between floor surfaces. Despite the ability to exert similar forces, the measured maximum coefficient of friction varied according to floor surface. These changes reflected significant alterations in vertical and horizontal components of ground reaction and vertical hand forces, suggesting that participants had maximized the frictional properties available to them. Postures also changed as a consequence of floor surface, with significant changes occurring in knee flexion and trunk extension. This study has shown that handlers involved in the pushing and pulling of trolleys are capable of adjusting posture and the direction of hand and foot forces in order to compensate for reduced levels of floor friction. This has particular relevance when assessing the musculoskeletal loads imposed on the handler and the likely mechanisms of injury resulting from variations in floor conditions when workers undertake pushing and pulling tasks in the workplace.     

Initial force and postural adaptations when pushing and pulling on floor surfaces with good and reduced resistance to slipping

The objective of the present study was to determine whether differences in the frictional properties of a floor surface may affect the kinematics and kinetics of pushing and pulling. Eight male participants were required to push and pull a four-wheeled trolley over two level surfaces, on which were mounted floor coverings with good (safety floor) and reduced (standard floor) frictional properties. A psychophysical approach was used to determine the initial maximum acceptable horizontal force required to move the trolley over a short distance (3 m). Three-dimensional (3D) hand and ground reaction forces and 3D postures were measured during initial force exertions. The results showed that psychophysically derived measures of initial horizontal force and horizontal components of hand forces did not differ significantly between floor surfaces. Despite the ability to exert similar forces, the measured maximum coefficient of friction varied according to floor surface. These changes reflected significant alterations in vertical and horizontal components of ground reaction and vertical hand forces, suggesting that participants had maximized the frictional properties available to them. Postures also changed as a consequence of floor surface, with significant changes occurring in knee flexion and trunk extension. This study has shown that handlers involved in the pushing and pulling of trolleys are capable of adjusting posture and the direction of hand and foot forces in order to compensate for reduced levels of floor friction. This has particular relevance when assessing the musculoskeletal loads imposed on the handler and the likely mechanisms of injury resulting from variations in floor conditions when workers undertake pushing and pulling tasks in the workplace.     

The constructions for comparing situations with the indices <Emphasis Type="Italic">sort of</Emphasis> and <Emphasis Type="Italic">as if</Emphasis>

The Russian comparative constructions with the word combinations sort of and as if are described with the help of the apparatus of construction grammar that was suggested by Ch. Chilmor. The semantics of these constructions and their syntactic properties that are determined only by semantic differences are analyzed. In particular, it is shown that both constructions must be considered comparative, despite the syntactic differences existing between them. On the other hand, the modal-discursive uses of these constructions that may be of typological interest are analyzed.     

Proposal of a shape adaptive gripper for robotic assembly tasks

This paper proposes a novel robotic gripper used for assembly tasks that can adaptively grasp objects with different shapes. The proposed hand has a combined structure between two kinds of shape adaptive mechanisms where one is the granular jamming and the other is a multi-finger mechanism driven by a single wire. Due to the effect of the two shape adaptive mechanisms, the pose of a grasped object does not change during an assembly operation. The proposed hand has four fingers where two are the active ones and the other two are the passive ones. The pose of the grasped object can be uniquely determined since the passive fingers are used to orient an object placed on a table before the active fingers are closed to grasp it. Assembly experiments of some kinds of parts are shown to validate the effectiveness of our proposed gripper.     

Real-time reversible iterative arrays

Iterative arrays are one-dimensional arrays of interconnected interacting finite automata. The cell at the origin is equipped with a one-way read-only input tape. We investigate iterative arrays as acceptors for formal languages. In particular, we consider real-time devices which are reversible on the core of computation, i.e., from initial configuration to the configuration given by the time complexity. This property is called real-time reversibility. It is shown that real-time reversible iterative arrays can simulate restricted variants of stacks and queues. It turns out that real-time reversible iterative arrays are strictly weaker than real-time reversible cellular automata. On the other hand, a non-semilinear language is accepted. We show that real-time reversibility itself is not even semidecidable, which extends the undecidability for cellular automata and contrasts with the general case, where reversibility is decidable for one-dimensional devices. Moreover, we prove the non-semidecidability of several other properties. Several closure properties are also derived.     

Minimal realizations of spatial stiffnesses with parallel or serial mechanisms having concurrent axes

This article presents a new method for the synthesis of an arbitrary spatial elastic behavior with an elastic mechanism. The mechanisms considered are parallel and serial mechanisms with concurrent axes. We show that any full‐rank spatial stiffness matrix can be realized using a parallel mechanism with all spring axes intersecting at a unique point. It is shown that this intersection point must be the center of stiffness. We also show that any full‐rank spatial compliance matrix can be realized using a serial mechanism with all joint axes intersecting at a unique point. This point is shown to be the center of compliance. Synthesis procedures for mechanisms with these properties are provided. The realizations are shown to be minimal in the sense that both the number of screw components and the total number of components are minimum. © 2001 John Wiley & Sons, Inc.     

Vision-based three-finger grasp synthesis constrained by hand geometry

This paper addresses the problem of designing a practical system able to grasp real objects with a three-fingered robot hand. A general approach for synthesizing two- and three-finger grasps on planar unknown objects is presented. Visual perception is used to reduce the uncertainty and to obtain relevant information about the objects.We focus on non-modeled planar extruded objects, which can represent many real-world objects. In addition, particular mechanical constraints of the robot hand are considered.First, a vision processing module that extracts from object images the relevant information for the grasp synthesis is developed. This is completed with a set of algorithms for synthesizing two- and three-finger grasps taking into account force-closure and contact stability conditions, with a low computational effort. Finally, a procedure for constraining these results to the kinematics of the particular hand, is also developed. In addition, a set of heuristic metrics for assessing the quality of the computed grasps is described.All these components are integrated in a complete system. Experimental results using the Barrett hand are shown and discussed.     

Safety in grammatical protection systems

In the context of operating system protection mechanisms,safety refers to the ability to decide who can obtained certain rights to resources by some future sequence of command invocations. Harrison, Ruzzo and Ullman have shown that in general safety is undecidable. On the other hand Jones, Lipton and Snyder have analyzed a simple system is which safety is decidable in time linear in the size of the system. This paper presents a large class of operating system protection mechanisms for which a polynomial time decision procedure for the safety question can be given. Extensions are then exhibited that are P-space complete andNP-complete.     

Preference-based English reverse auctions

This paper studies English reverse auctions within a unified framework for preference-based English reverse auctions. In this context, and particularly for electronic auctions, representing and handling the buyer?s preferences, so as to enable him/her to obtain the best possible outcome, is a major issue. Existing auction mechanisms, which are based on single or multi-attribute utility functions, are only able to represent transitive and complete preferences. It is well known, however, in the preference modeling literature that more general preference structures, allowing intransitivity and incomparability, are more appropriate to capture preferences. On the other hand, we must also consider properties on the evolution and, above all, on the outcome of any auction executed by an auction mechanism. These properties, as well as properties of non-dominance and fair competition defined for multiple criteria auctions, impose restrictions on the preference relation. This leaves room for interesting preference models to be implemented within English reverse auction mechanisms.     

On minimal-order inverses of linear continuous time-invariant systems

Minimal-order inverses of a linear continuous time-invariant system are defined and an algebraic algorithm for constructing them is presented. A necessary and sufficient condition for the applicability of the algorithm is shown to be the same as that for the invertibility of the given system. Some important properties of the minimal-order inverses relevant to the design of linear multivariable systems are derived. In particular the characteristic polynomials of all minimal-order inverses of a given system are shown to be identical and invariant under duality, coordinate transformations and proportional state feedback.     

Reachable zones for equicontinuous bilinear control processes†

Geometrical properties of the set of reachable states are analysed for a class of nonlinear systems termed bilinear. Admissible controls are assumed to be bounded equicontinuous functions of time. While the results are valid for the larger class of non-linear systems with linear control, it is shown that bilinear processes are of particular significance in practice.     

Net-based control versus rational control The relation between ITNC vector languages and rational relations

 An Individual Token Net Controller (or ITNC) is a particular type of state-machine decomposable Petri net that can be used as a synchronization mechanism in concurrent systems consisting of a fixed number of sequential subsystems. In this paper the family of ITNC vector languages is compared to the well-known family of rational relations. On the one hand it is proved that the family of rational relations equals the family of vector languages of Generalized ITNCs, i.e. ITNCs in which the restriction of completeness is dropped. On the other hand a vector language property induced by completeness is identified that precisely characterizes the difference between ITNC vector languages and Generalized ITNC vector languages. In addition, the results are shown to carry over to the prefix-closed versions of the models. Received: 7 August 1990/6 October 1995     

A requirement specification language for configuration dynamics of multiagent systems

In agent‐mediated applications, the system configuration can change because of the creation and the deletion of agents. The behavior of such systems on the one hand depends on the dynamics of the system configuration; on the other hand, behavior of such a system consists of the information dynamics of the system. We discuss configuration and information dynamics of agent‐mediated systems and define a requirement language to express properties of those dynamics. A prototypical scenario for an agent‐mediated system is discussed and some important requirements for this system are specified. It is shown how these properties can be verified automatically to evaluate system behavior. © 2004 Wiley Periodicals, Inc.     

Sliding Mode Disturbance Observer‐based Motion Control for a Piezoelectric Actuator‐based Surgical Device

This paper presents a sliding mode disturbance observer‐based motion tracking control methodology. In particular, the methodology is applied to control a semi‐automated hand‐held ear surgical device for the treatment of otitis media with effusion. The proposed control methodology is utilised to deal with the undesirable effects in the motion system, such as non‐linear dynamics, parametric uncertainties and external disturbances. It employs a proportional‐derivative control scheme together with a sliding mode disturbance observer for rejecting the undesirable effects. The stability of the proposed control methodology is proven theoretically and its effectiveness is evaluated experimentally. In addition, promising motion tracking experimental results are shown, and it can be observed that the proposed approach offers more robust performance for controlling the hand‐held surgical device and other similar instruments.     

On the physical limitations of pattern matching

Abstract

The powerful functional capacities (Turing computability) of digital computers are, in part, responsible for fostering the notion that understanding mind is simply a matter of determining the right algorithm—the so-called ‘strong AI’ position that cognition is computation which holds that computers can have mental states and that behavioural equivalence is a sufficient test for the existence of mind (i.e. the Turing Test). John Searle's Chinese Room thought experiment (Searle 1980), however, raises the possibility that pure symbol manipulation does not capture the essence of mind (e.g. intentionaiity) because it lacks certain features—so-called ‘causal properties’. The current status of this debate borders on being a stalemate because, on the one hand, empirical verification based on behaviour is, at the very least, a long way from being decisive while, on the other hand, intuitive arguments about mind are subjective and, as such, untestable. This paper, in contrast to arguing intuitively or relying on behaviour, challenges the computational theory of mind on purely physical grounds, thereby avoiding such an impasse. In particular it is shown that digital computers are physically limited by the very process that underlies their powerful functional capacities, pattern matching. This physical limitation, it is claimed, is fundamental to deciding whether computation is sufficient for understanding mind. Pattern matching is the physical process by which symbols in computers are causal and, therefore, serves as the physical basis for information processing in computers. To demonstrate the physical limitations of pattern matching, a general, causal framework based on how physical change is brought about is introduced, enabling an analysis of the ways in which objects physically embody and transmit information. Physical interactions are causally analysed into ‘informing’ categories which are hypothesized to be Searle's causal properties. It is claimed that differences in these properties explain the cognitively-relevant physical differences between computers and brains     

The SPRING Hand: Development of a Self-Adaptive Prosthesis for Restoring Natural Grasping

Commercially available prosthetic hands are simple grippers with one or two degrees of freedom; these pinch type devices have two rigid fingers in opposition to a rigid thumb. This paper focuses on an innovative approach for the design of a myoelectric prosthetic hand. The new prosthesis features underactuated mechanisms in order to achieve a natural grasping behavior and a good distribution of pinching forces. In this paper it is shown that underactuation allows reproducing most of the grasping behaviors of the human hand, without augmenting the mechanical and control complexity.     

An insight into instrumental variable frequency-domain subspace identification

In this paper, we study instrumental variable subspace identification of multi-input/multi-output linear-time-invariant, discrete-time systems from non-uniformly spaced frequency response measurements. A particular algorithm, which does not require noise covariance function to be known a priori is shown to be strongly consistent provided that disturbances have uniformly bounded second-order moments and the frequencies satisfy a certain regularity condition. Interpolation properties of this algorithm and a related one are also studied. A numerical example illustrating the properties of the studied algorithms is presented.     

Limits of input-to-state stability

The relations between attractors, input-to-state-stability, and controllability properties are discussed. In particular it is shown that loss of the attractor property under perturbations is connected with a qualitative change in the controllability properties due to a ‘merger’ with a control set.