A common way to manipulate heavy objects is to maintain at least one point of the object in contact with the environment during the manipulation. When the object has a cylindrical shape or, in general, a curved edge, not only sliding and pivoting motions but also rolling the object along the edge can effectively satisfy this condition. Edge-rolling offers several advantages in terms of efficiency and maneuverability. This paper aims to develop a novel approach for approximating the prehensile edge-rolling motion on any path by a sequence of constant screw displacements, leveraging the principles of screw theory. Based on this approach, we proposed an algorithmic method for task-space-based path generation of object manipulation between two given configurations using a sequence of rolling and pivoting motions. The method is based on an optimization algorithm that takes into account the joint limitations of the robot. To validate our approach, we conducted experiments to manipulate a cylinder along linear and curved paths using the Franka Emika Panda manipulator.Video— https://youtu.be/MX1-MAR9ubc

This article presents an analytical method to modulate the dynamic response of a robotic manipulator interacting with its environment when performing impedance-related robotic tasks, through the choice of stiffness and damping parameters. By joint space analysis of vibration and experiments, we prove that in order to preserve a desired dynamic behavior of the robot in the Cartesian space, neither a stiffness nor damping matrix can be arbitrarily chosen; this choice has to meet the desired dynamic criteria for any given configuration. After mapping the parameters (matrices) into the joint space, we analyze the vibratory dynamics of the robot and identify the proper way of suppressing of the vibration modes by specific elements in the Cartesian damping matrix without need of trial and error. Our method is especially useful for redundant robots. We show and compare experimental results from two different 7 degrees of freedom robotic manipulators.

This paper presents an analytical methodology and experimental study to identify quantitatively the zero-potential-energy (ZP) motion due to the stiffness matrices in Cartesian impedance control of redundant manipulators. This mode of motion, analogous to the rigid-body mode in classic mechanical systems, shows up as a result of the redundancy of the robot and creates a steady-state deviation from its initial configuration after it reaches equilibrium when subject to a perturbation, because of the principle of least energy for dynamic systems. We determine such ZP motion(s) by utilizing a vibration-based closed-form solution recently developed. We identify and provide experimental validation of the existence of the ZP motions on a 7 DoF Panda robot.

A rigid plate end-effector at the tip of a high-speed manipulator can remotely manipulate an object without grasping it. This paper discusses a dynamic nonprehensile manipulation strategy to rotate thin deformable objects on a rigid plate with two degrees of freedom (DOFs). The deformation of the object due to dynamic effects is exploited to produce fast and stable rotation. By varying the frequency of the rotational component of the plate's motion, we show that the dynamic behavior of the object mimics either a sliding, walking, or running gait of a biped. We introduce a model to simulate this type of system in which the object is constructed of multiple nodes that are connected by viscoelastic joint units with three DOFs. The joint's viscoelastic parameters are estimated experimentally in order to model real food. Afterward, simulation analysis is used to investigate how the object's rotational behavior and its angular velocity change with respect to the plate's motion frequency. We show how the object's behavior during rotation is analogous to bipedal sliding, walking, and running gaits and then obtain optimal plate motions leading to the maximal angular velocity of the object. We also reveal that an appropriate angular acceleration of the plate is essential for a dynamically stable and fast object's rotation. We further show that the friction coefficient that maximizes the object's angular velocity depends on its gait.

This paper presents an experimental study of the bio-inspired artificial skin consisting of silicone and embedded strain gages, in which silicone imitates the epidermis and dermis, and strain gages mimic corpuscles. The strain gages are embedded in silicone under different configurations like corpuscle in humans skin. Both static displacement and dynamic excitations are applied in arbitrary positions, with different magnitudes and frequencies. The responses are observed by measuring the output signals from strain gages. Comparison with FEM simulation of static displacement shows intuitive agreement. The responses to dynamic excitation in typical frequency range of human somatosensors are obtained both experimentally and with simulation of dynamic modeling. We found that each configuration has advantages and disadvantages. This paper shows how strain gages embedded in silicone will behave in response to both static and dynamic excitations, and suggests modeling and fundamental concepts to design a bio-inspired artificial skin sensor.

This paper discusses a nonprehensile dynamic manipulation of a deformable object, where the object is remotely manipulated on a plate attached at the tip of a bar. We have found that the object's deformation generated by dynamic effects can drastically contribute to a fast and stable object rotation. We introduce a new simulation model for a sheet-like object, where the object is constructed of multiple nodes connected by three DOFs viscoelastic joint units. We apply the model to real food after the viscoelastic parameters are estimated. Then, simulation analysis is used to show how the object's rotation behavior changes with respect to the plate's motion frequency, similar to the motion of human legs sliding, walking, and running. Finally we obtain an optimum plate motion leading to the maximal angular velocity of the object. We also reveal that an appropriate angular acceleration of the plate is essential for a dynamically stable and fast object rotation.

Viscoelastic materials are known to exhibit temporal response that changes force or displacement at the contact interface under position or force control, respectively. In this paper, we conduct experimental study using force control to explore and observe creep phenomenon in robotic grasping in order to better understand the nature of such contact interface, which has been widely used in soft robotic fingers, robotic feet, and contact surface of robotic arms. We found that the creep response under a constant external force exhibits the characteristics of exponentially increasing or decreasing temporal response. Such characteristics are similar in nature to those found in the relaxation response of viscoelastic materials when the grasping is under position control. Two different types of creep responses are found, depending on the state of grasping. Both Types I and II in creep response mirror the Types I and II in relaxation response. We also found that different loading rates under force control result in different elastic response, in addition to the temporal response. This is an interesting finding because the Fung's model postulates for an elastic response that is independent of, and can be separated from, the temporal response. The experimental results do not show such independence.

In this paper, a nonlinear latency model is presented to describe the relationship between the strain and strain rate of the temporal responses in robotic grasping that involves viscoelastic contact interface. The results from experiments and simulation are presented, and are found to match well with each other. The nonlinear latency model was able to adequately represent both Type I and Type II relaxation responses. For the successive loading and holding with a soft contact, the model describes the behavior of step-wise increase of equilibrium strain and a polynomial relationship between the strain rate and the strain. The nonlinear latency model can successfully predict and model the behavior of anthropomorphic soft contact interface in grasping and manipulation when the grasped object is held in certain posture of prehension with repeated loading and/or unloading.

Viscoelasticity is the phenomenon of time-dependent strain and/or stress in elastic solids. Various contact interfaces with anthropomorphic end-effectors and polymeric solids found in robots and manipulators are intrinsically viscoelastic. It is therefore important to model such behavior and to study the effects of such time-dependent strain and stress on the stability and sustainability of grasping and manipulation. Various models have been proposed over the years to describe such behavior of time-dependent strain and stress. Furthermore, viscoelastic solids also display typically nonlinear elastic response. Built upon a variety of literature, a new and practical latency model is proposed in this paper for the application of contact interface involving viscoelasticity in robotics. Latency model can describe various features of viscoelastic materials, such as stress relaxation, creep, and material clock. The theoretical modeling was supported by experiments in which we found two types of relaxation, depending on the loading and unloading of grasping or contact. One type is well documented in existing literature; but the other type has not been, to our best knowledge, presented before. The proposed theory can unify both types of time-dependent relaxation responses.

The latency model is an analytical model for describing the behavior of nonlinear viscoelastic contact interface in robotic grasping and manipulation. The latency model is based on experimental observation of viscoelastic materials which exhibit the behavior of both elastic and temporal responses when subject to external force or displacement. It is postulated that such materials display latency in response of external influence by the rearrangement of molecules, holes, and structures in order to achieve an equilibrium state corresponding to the instantaneous loading. As a result, we propose that there are temporal latent activities in progress before the material reaches the equilibrium state. In the previous study [21], the latent activity of strain re-distribution with a prescribed constant displacement was presented using both theoretical modeling and experimental results. In this paper, we build upon this latency model to study the behavior of viscoelastic materials under different loading rates with experimental results. The latency model is employed to explain the behavior of responses of hard and soft viscoelastic materials typically found in robotic contact and grasping.

In this paper, we employ Fung’s viscoelastic model discussed by Tiezzi and Kao to study the experimental data presented by Sakamoto et al. for grasping viscoelastic objects using a parallel-jaw gripper. The viscoelastic contact modeling presented in this paper is characterized by two separate responses: elastic response and temporal response. Two main and intriguing results were found in the modeling and analysis of experimental data. The first is the consistency on the normalized coefficients for the curve fitting of the temporal response during the relaxation period of the grasping. Such consistency suggests that the proposed model is applicable to the grasping task at hand. The other result is the generic pattern of the elastic response deduced from the experimental data. The pattern of elastic response represents different physical significance of grasping which involves viscoelastic contact interface.

Viscoelastic contact is a type of contact which includes, in addition to linear or nonlinear elastic response, time-dependent response due to relaxation or creep phenomena that govern the contact behavior. The characteristics of the time-dependent relaxation of such a viscoelastic contact are typically exponentially decaying functions, and exponentially growing functions for creep, respectively. Such contacts can be found in anthropomorphic robotic fingers, soft materials, viscoelastic skin with rigid core, and human fingers and feet. In this paper, the nature of viscoelastic contacts is investigated, and the evolution of their friction limit surfaces and of the pressure distributions at the contact interface are studied. Two cases commonly found in robotic grasping and manipulation are discussed. Based on the modeling formulation, it is found that the two important parameters of analysis and modeling for such contacts, i.e., the radius of contact area and the profile of pressure distribution, can be chosen using proposed coupling equations as the viscoelastic contact interface evolves with time. The new contribution of this paper includes a proposal of coupling equations between the two important parameters to describe the viscoelastic contact interface, and a study of the evolution of limit surfaces for viscoelastic contact interface due to temporal dependency, and the implication on grasp stability. It is found from the evolution of limit surfaces that when normal force is applied with typical viscoelastic contacts, grasp becomes more stable as time elapses. The modeling can be applied to the design of fingertips and the analysis of robotic grasping and manipulation involving viscoelastic fingers

Viscoelastic contact is a type of contact which includes, in addition to linear or nonlinear elastic responses, time-dependent relaxation function that governs the contact behavior. The characteristic of the time-dependent relaxation of such viscoelastic contact is typically an exponentially decaying function. Such contacts can be found in anthropomorphic soft fingers, viscoelastic skin with rigid core, and human fingers. In this paper, the nature of viscoelastic contact is investigated, as well as the resulting limit surfaces. Two cases commonly found in robotic grasping and manipulation are discussed: (i) maintaining constant area of contact after the application of normal force, and (ii) maintaining constant normal contact force after the initial contact is made. A significant yet not so intuitive result was that the two important parameters describing viscoelastic contacts can seemingly be specified independently based on theory; however, they generally follow exponentially decaying patterns. In this paper, coherent assumptions are made to correlate the two parameters. It is also found that the nature of contact interface with limit surface has a profound effect on the stability of grasping and manipulation using viscoelastic fingertips. The results can be applied to the design of fingertips and the analysis of robotic grasping and manipulation involving viscoelastic fingers

In this paper, the modeling and design for frictional loads applied by robotic fingertips through soft contact interface are investigated. The dependence of the sustainable friction forces and moments due to the normal load applied on the contact area is studied. A model that considers the dependence of both the contact area and the coefficient of friction on the application of normal load is proposed. Specimens of simplified fingertips, made with different materials and shaped with different thickness of the covering soft layer, are tested in order to validate the proposed model via designed experiments. The results obtained have very important relevance on the design of robotic hands and fingers equipped with soft pads or skins, and can help on the choice of suitable features for the different layers of contact pads or skins

Pneumatic systems are often found in manufacturing floors for automation and robotic systems. Early and intelligent faults detection and diagnosis (FDD) of such systems can prevent failure of devices that causes shutdown and loss of precious production time and profits. In this paper, we introduce analytical FDD for pneumatic systems. The diagnosis system presented in this paper focuses on the signal-based approach which employs multi-resolution wavelet decomposition of various sensor signals such as pressure, flow rate, etc., to determine leak configuration. Pattern recognition technique and analytical vectorized maps are developed to diagnose an unknown leakage based on the established FDD information using affine mapping. Experimental studies and analysis are presented to illustrate the FDD system.

When applying stiffness control to redundant manipulators, three kinematic factors are considered due to the redundancy: (i) how to use the inverse kinematics to obtain the redundant joint displacement d/spl theta/ from Cartesian displacement dx, (ii) how to use the inverse kinematics to obtain Cartesian force f from redundant joint torque /spl tau/, and (iii) how to obtain Cartesian stiffness matrix K/sub p/ from joint stiffness matrix K/sub /spl theta//. This paper applies the conservative congruence transformation (CCT) to redundant manipulators, and proposes a unique and kinematically correct solution of the stiffness control for redundant manipulators. The concept of generalized instantaneous potential energy (GIPE) is introduced. Results of numerical simulation using both Cartesian-based and joint-based control schemes are presented and discussed.

In this paper, nonlinear stiffness of contact for soft fingers, commonly used in robotic grasping and manipulation, under a normal load is studied. Building upon previous research results of soft-finger contact expressed in the power-law equation, the equation for the nonlinear stiffness of soft contact was derived. This new theory relates the approach displacement (or the vertical depression) of soft fingertips with respect to the normal force applied. The nonlinear contact stiffness is found to be the product of an exponent and the ratio of the normal force versus approach displacement. Stiffness relationship of Hertzian contact for linear elastic materials is shown to be a special case of the general theory presented in this paper. Experimental results are used to validate the theoretical analysis. In addition, potential applications to fixturing are discussed.

In this paper, the Conservative Congruence Transformation (CCT), K/sub /spl theta//-K/sub g/=J/sub /spl theta///sup T/K/sub p/J/sub /spl theta//, is applied to a 3-link redundant planar manipulator. Since 3-link planar manipulator has one degree of redundancy, one constraint is allowed to be used to define the parameters of the system. Different constraints can be used to meet the specific requirements of manipulation. In this paper, two constraints are employed to obtain solution for redundant manipulation. One involves maintaining the most distal link along specific orientations; the other requires that the moment at the end-effector be always zero. In the latter case, the orientation of the distal link is decided in such a way that this constraint is satisfied. Numerical simulation and results are presented to illustrate that CCT is indeed a general and correct stiffness mapping in the analysis of redundant manipulators. The incorrect results of the conventional formulation, K/sub /spl theta//=J/sub /spl theta///sup T/K/sub p/J/sub /spl theta//, are also computed and compared with the results of the CCT theory.

In this paper, the conservative congruence transformation (CCT) for robot stiffness control is investigated by using geometrical methods. With the strategy of changing basis, it indicates that the formulation of stiffness matrix depends on the choice of coordinates. Thus, we show that the CCT can directly represent the spatial mapping relationship in robotic stiffness control. The CCT theory suggests a generalized transformation relationship in stiffness control and establishes the complete formulation of the 6/spl times/6 Cartesian stiffness matrix in the presence of external loads.

This paper presents a new conservative stiffness mapping for parallel manipulators. This new formulation properly obeys the law of the conservation of energy. The change in geometry of a parallel manipulator due to compliance is captured by an additional stiffness matrix, which has so far been neglected by other researchers. Numerical simulations of the planar and spatial Stewart-Gough platforms are conducted to verify the conservative stiffness mapping.

In this paper, the application of the conservative congruence transformation (CCT) to the stiffness mapping between non-coordinate basis and coordinate basis systems is studied and presented. Through the stiffness transformation between the 2 degree-of-freedom cylindrical and joint spaces, we illustrate that the CCT can be applied either directly or indirectly to the stiffness transformation between any two systems with either coordinate basis or noncoordinate basis. It is found that the same stiffness control for a conservative system will render a symmetric stiffness matrix with respect to a coordinate basis, but an asymmetric matrix with respect to a non-coordinate basis. The direct and indirect CCT methods are presented, with the latter requiring an intermediate coordinate system with a generalized coordinate basis. The relationships of the effective K/sub g/ matrices between the direct and indirect CCT methods are found and validated.

A new discovery on the stiffness control in robotics, as well as its applications in grasping and dextrous manipulation, is presented. Extended from the conservative congruence transformation (CCT) theory, the new theory accounts for the change in geometry and the non-commutative rotational property of the Cartesian stiffness in grasping and dextrous manipulation using stiffness control when the external force is applied. The theory, with the consideration of rotational effect in SE(3), as developed by using the geometrical method. The method along with an example presented in this paper provides a systematic way of constructing 6/spl times/6 Cartesian stiffness matrices in robotic grasping/manipulation and stiffness control for dextrous manipulation.

The conservative congruence transformation (CCT), K/sub /spl theta//-K/sub g/=J/sub /spl theta///sup T/K/sub p/J/sub /spl theta//, was proposed by Chen and Kao (2000) as the correct congruence transformation to replace the conventional mapping, K/sub /spl theta//=J/sub /spl theta///sup T/K/sub p/J/sub /spl theta//, proposed by Salisbury (1980). The conventional mapping was shown, to lead to physically inconsistent results when external force is present in stiffness control. Theoretical proofs are also provided to show the conservative nature of the CCT, and the non-conservative property of the conventional mapping. The CCT is established as the general and valid mapping of the stiffness matrices between the joint and Cartesian spaces of robotic manipulators. In this paper, the work of CCT is extended to a redundant planar manipulator. Numerical simulations are presented to illustrate issues related to the application of generalized inverse in the analysis of redundant manipulators.

Dextrous manipulation involves a variety of subjects in robotics, including kinematics, rolling and sliding, contact mechanics, grasping planning and optimization, dynamics, and control. It is generally postulated in the literature that contacts in all grasping and manipulation are point contacts or soft contacts. The former can be modeled as either a frictionless point contact or a frictional point contact; the latter, although being a more practical model, has not been commonly utilized. In this paper, the recent progress in the modeling of dextrous manipulation utilizing soft contacts and stiffness control is presented. The result augments the well-known Hertzian contact model from linear elastic contacts to soft contacts. In addition, the conservative congruence transformation for stiffness control in robotics, that are often used in dextrous grasping and manipulation, is presented.

The stiffness characteristics of robot systems via the conservative congruence transformation (CCT) and the conventional congruence transformation (CT) between the joint and Cartesian spaces are investigated. A stiffness matrix is conservative if: 1) the force resulting from the stiffness matrix is conservative, and 2) the work done by such force along a closed path is zero. The criteria result in the derivation of the CCT between the joint and Cartesian spaces. Numerical simulation of a two-link planar manipulator, manipulating along various closed paths with no self-intersection, is implemented. The results verify that a stiffness matrix in R/sup 3/spl times/3/ Cartesian space or joint space can be conservative if it is symmetric and satisfies the exact differential criterion. Furthermore, we also illustrate the importance of the effect of changes in geometry in grasping and manipulation using stiffness control via CCT. The results show that the CCT is the correct mapping for stiffness matrices between the joint and Cartesian spaces.

This paper presents the framework of the smart anthropomorphic contact surface technology (SACST) based upon robotics theories, to employ MEMS devices in a distributed system, and to integrate the sensory information for feedback control to import intelligence. The technology can be applied to empower intelligence to the design of seats, beds, wheelchair, shoes, and artificial skin for robot arms. SACST utilizes the soft contact model, which subsumes the Hertzian contact model (Hertz, 1882), normal force and pressure distribution at the contact interface, friction limit surface, and stiffness of contact to dynamically reshape the surface through embedded MEMS transducer systems in real time. Such designs can also implement dynamic functions such as massage or tilting of contact surfaces. We will present the ongoing development in SACST and the associated scientific principles. In the end, the framework will be able to free up users from lower level tasks in order that they can concentrate on higher level tasks.

Nonlinear finite element analysis is employed to study the soft-finger contact mechanics. Two fingertips of the same material but with different sizes are analyzed. The results are compared with experiments to support the power-law theory proposed by Xydas and Kao (1999). The material properties used in the FEM analysis are based upon uniaxial compression experiments conducted using the actual fingertip material. The coefficient of friction is also experimentally determined and applied in the simulation. Comparisons of numerical as well as experimental radii of contact are offered in conjunction with the power-law theory for soft fingers. The pressure distribution profile at the contact zone, obtained from the finite elements analysis, is plotted and the order of the generalized pressure distribution profile is calculated. Finally, the influence of friction over the contact area is investigated using FEM analysis.

In this paper, we study the 6/spl times/6 Cartesian stiffness matrices of conservative systems using the method of changing basis in differential geometry of the motion of the rigid body. We show that the stiffness matrix is symmetric at the unloaded equilibrium configuration. When the system is subjected to external loads, the 6/spl times/6 Cartesian stiffness matrix becomes asymmetric. The skew-symmetric part of the stiffness matrix is equal to the negative one-half of the cross-product matrix formed by the externally applied load, referenced to the inertial frame. This method presented in this paper provides a systematic way of constructing 6/spl times/6 stiffness matrix in robotic grasping/manipulation and stiffness control.

We investigate the influence of size and material properties of fingertips on the power-law equation for soft-finger contacts. Fingertips made of different materials of various sizes were tested, and the parametric relationship between normal forces and radii of contact was found. The experimental results validate that the growth of contact radius, a, is a function of the normal force, N, according to the power law, that is, a=cN/sup /spl gamma//, for nonlinear elastic soft fingers with large deformation. The experimental results suggest that /spl gamma/ is a material-dependent constant, decreasing with the hardness of the soft-finger materials and ranges from 0 to 1/3. In addition to material properties, the constant c is dependent upon the size and geometry. Overall, the constant c increases as the soft finger becomes softer and larger, and decreases when the soft finger becomes harder and smaller. An INSTRON Model 1011 equipment was employed to conduct the experiments with different fingertip materials, loading rates, and ranges of normal force.

The conservative properties of stiffness matrices via the nonconservative congruence mapping between the joint and Cartesian spaces are investigated with simulation of two fingers manipulating an object. The properties of both constant and configuration dependent stiffness matrices are presented with integration of work when manipulating along a closed path with no self-intersection. A stiffness matrix is conservative if the force resulting from the stiffness matrix is conservative, and the work done by such force along a closed path is zero, i.e., independent of the path. Both theoretical derivation and numerical simulation show that a stiffness matrix in /spl Rscr/3/spl times/3 Cartesian space or joint space with n generalized coordinates will be conservative if it is symmetric and satisfies the exact differential criterion. Simulation of two fingers manipulating an object is implemented using OpenGL with both Cartesian-based and joint-based stiffness control scheme. The results show that the congruence transformation generally results in nonconservative stiffness matrix, except for a special group configuration dependent solutions.

A new theory in contact mechanics for modeling of soft fingers is proposed to define the relationship between normal force and area of contact for soft fingers by considering the soft finger materials as nonlinearly elastic. The results show that the radius of contact is proportional to the normal force raised to the power of /spl gamma/ which ranges from 0 to 1/3. This new theory subsumes the Hertzian contact model for linear elastic materials where /spl gamma/=/3. Experiments are conducted to validate the theory using artificial soft fingers made of various materials such as rubber and silicone. This theory provides basis for constructing friction limit surface numerically. Combining the results of the contact mechanics model with the contact friction model the normalized friction limit surface is derived for anthropomorphic soft fingers.

In this paper, we study stiffness analysis as applied to human grasping. Grasp stiffness has been demonstrated to be useful for modeling and controlling robotic manipulators. The computation of general linear R/sup 3/spl times/3/ stiffness matrices for grasping, which can be decomposed into symmetric (conservative) and asymmetric (nonconservative) components, offers physical insights for stiffness control in robotics as well as human grasping. Methods of stiffness calibration, using least-squares best fits with and without symmetry constraints, are presented and applied to the force and displacement data obtained from grasping tasks to study human grasping behaviors. The results of this study show that a linear relationship between force and displacement is capable of capturing the characteristics of the experimental data of human grasps for which displacements are small (on the order of one to seven mm). Different measures, proposed and developed in the robotics literature, are employed to predict the behavior of human grasps in reacting to externally applied loads.

In this paper, we present fundamental properties of stiffness matrix as applied to analysis of grasping and dextrous manipulation. The investigation unveils insights of stiffness matrix which are important in grasping and manipulation for robotic hands and fingers in R/sup 3/ space. A general grasp stiffness matrix can be broken into two parts-symmetric and antisymmetric. The symmetric part is derived from a conservative quadratic potential function in the Hermitian form; while the antisymmetric part is a function of nonconservative curl vector field of the grasp. The conservative part stores and interchanges energy with the environment with which the fingers make contact. The nonconservative part dissipates or increases energy. The theory suggests that it is possible to introduce a nonsymmetric stiffness matrix in robotic control so as to have energy dissipation (damping) effects. This is useful when passive damping effects are desirable in grasping. Application of the theory to the analysis of stiffness matrix in 3D is presented for analysis of grasping and manipulation.

The author studies human grasping behavior in terms of a compliance analysis developed for modeling robot hands and fingers. The motivation is to see whether grasp compliance, which has been demonstrated to be useful for describing and controlling robotic grasps, can also capture some of the behaviors of human grasps. Force and displacement data for human grasps are used to find the stiffness matrix of the grasp by least-squares fit method. The results of this study show that the stiffness of a grasp, a linear relationship between force and displacement, is capable of capturing the experimental data of human grasps for which displacements are small (on the order of one to seven mm). Different measures, proposed and developed in the robotics literature, can be employed to predict the human grasps in reacting to externally applied loads.>

In this paper, we build upon the results of the previous sliding manipulation analysis (Kao-Cutkosky 1992,1993) developed for instantaneously dexterous motion analysis, and extend the results to finite motion analysis and trajectory planning for soft robotic fingertips. Using the method of sliding analysis with decomposed rigid-body (RB) and non-rigid-body (NRB) components, we find the trajectory and motions of the finger tips over a finite range of motions during which the RB and NRB components are updated continuously. The results show that: (i) the RB/NRB sliding analysis can be applied to finite motion planning, (ii) the relative magnitudes of RB/NRB motions can be used as an index for manipulation task, and (iii) the advantageous orientations of force/motion can be used to plan for the motions of the grasped object.>

Preliminary experiments are presented concerning the use of tactile sensing to enhance the flexibility and robustness of robotic manipulation. A simple two-fingered manipulator with very clean dynamics has been constructed to focus on tactile and force sensing in manipulation. Manipulation is characterized by constantly changing mechanical systems, as fingers make or break contact or start to roll or slide on the surface of a grasped object. It is important to detect these changes since control schemes must change to match the varying task requirements. Following the human model, it is shown that dynamic tactile sensors can reliably detect the changing contact conditions. In a simple grasp-lift-replace task, use of these sensors enables the manipulator to cope with uncertainty in object location and task forces.>

The authors express the compliance of the grasp of a robotic hand as a function of grasp geometry, contact conditions between the fingers and the grasped object, and mechanical properties of the fingers. It is argued that the effects of structural compliance and small changes in the grasp geometry should be included in the computation. Factors are then examined that can lead a grasp to become unstable, independently of whether it satisfies force closure. Finally, the authors examine the reverse problem of how to specify servo gains at the joints of a robotic hand so as to achieve, as nearly as possible, a desired overall grasp compliance. It is shown that coupling between the joints of different fingers is useful in this context.>

The authors are concerned with finding the magnitudes of applied moment and force which will cause a robot finger to slip on the surface of a grasped object. Friction and contact models used in previous grasp analyses are reviewed, and an improved model which includes torsion-shear interaction is described. Experimental measurements of the initiation of sliding as a function of loading are reported. These measurements suggest that a simple linear function of torsion and shear magnitudes will adequately predict the onset of the slip in many tasks. The use of this function is illustrated in two measures of slip susceptibility for grasp planning.>