Equilibrium, Stability, and Robustness in Underactuated Grasping

2007 ◽  
Author(s):  
Gert A. Kragten ◽  
Just L. Herder
Keyword(s):  
Degrees Of Freedom ◽  
Equilibrium Configuration ◽  
Performance Measure ◽  
Equilibrium Stability ◽  
Equilibrium Conditions ◽  
Design Decisions ◽  
Grasp Stability ◽  
Movable Object ◽  
Passive Compliance ◽  
Freely Moving

This paper aims to develop a performance measure for underactuated grasping devices, which is useful in making design decisions to obtain an optimally performing device. Underactuated fingers, defined as having more degrees of freedom than degrees of actuation, intrinsically adapt their shape to the object. However, the equilibrium configuration and grasp forces of these fingers are not fully controllable, which may limit their performance. The grasp performance measure defined in this paper consists of three aspects: (1) the ability to grasp objects, which is limited by the equilibrium conditions and constraints of both the underactuated fingers and the freely movable object; (2) the grasp stability, which takes the passive compliance of the fingers into account; (3) the ability to oppose disturbance forces on the grasped object by passively adapting the frictional grasp forces. This measure was applied to optimize a planar grasping device with two underactuated fingers, each consisting of two phalanges, able to grasp freely moving circular objects.

Geometric Design of Three-Phalanx Underactuated Fingers

2005 ◽  
Vol 128 (2) ◽  
pp. 356-364 ◽  
Author(s):  
Lionel Birglen ◽  
Clément M. Gosselin
Keyword(s):  
Control Strategy ◽  
Degrees Of Freedom ◽  
Equilibrium Configuration ◽  
Contact Forces ◽  
Transmission Mechanism ◽  
Static Equilibrium ◽  
Object Size ◽  
Complex Control ◽  
Transmission Mechanisms ◽  
Grasp Stability

This paper studies the grasp stability of two classes of three-phalanx underactuated fingers with transmission mechanisms based on either linkages or tendons and pulleys. The concept of underactuation in robotic fingers—with fewer actuators than degrees of freedom—allows the hand to adjust itself to an irregularly shaped object without complex control strategy and sensors. With a n-phalanx finger, n contacts (one for each phalanx) are normally required to statically constrain the finger. However, some contact forces may be lacking due to either the transmission mechanism, or simply the object size and position. Thus, one may define an ith order equilibrium, when the finger is in static equilibrium with i missing contacts. In this paper, the case for which n=3 is studied with a particular emphasis on the cases for which i=1 and i=2. The fact that some contact forces do not appear or are negative, can lead in some cases to the ejection of the object from the hand, when no equilibrium configuration is achieved.

Study of grasp-energy based optimal distribution of contact forces on a humanoid robotic hand during object grasp

Robotica ◽  
2021 ◽  
pp. 1-26
Author(s):  
Sourajit Mukherjee ◽  
Abhijit Mahapatra ◽  
Amit Kumar ◽  
Avik Chatterjee
Keyword(s):  
Optimization Algorithm ◽  
Degrees Of Freedom ◽  
Simulated Data ◽  
Performance Measure ◽  
Contact Forces ◽  
Contact Model ◽  
Robotic Hand ◽  
Net Energy ◽  
Optimal Distribution

Abstract A novel grasp optimization algorithm for minimizing the net energy utilized by a five-fingered humanoid robotic hand with twenty degrees of freedom for securing a precise grasp is presented in this study. The algorithm utilizes a compliant contact model with a nonlinear spring and damper system to compute the performance measure, called ‘Grasp Energy’. The measure, subject to constraints, has been minimized to obtain locally optimal cartesian trajectories for securing a grasp. A case study is taken to compare the analytical (applying the optimization algorithm) and the simulated data in MSC.Adams $^{^{\circledR}}$ , to prove the efficacy of the proposed formulation.

Analysis and Validation of a Flexible Planar Two Degrees-of-Freedom Parallel Manipulator With Structural Passive Compliance

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Genliang Chen ◽  
Zhuang Zhang ◽  
Lingyu Kong ◽  
Hao Wang
Keyword(s):  
Parallel Manipulator ◽  
Degrees Of Freedom ◽  
Interaction Force ◽  
Flexible Manipulator ◽  
End Effector ◽  
Flexible Links ◽  
Wide Range ◽  
Pick And Place ◽  
Passive Compliance ◽  
Large Deflection Problem

Abstract Passive compliance plays an important role in robot pick-and-place manipulation where large interaction force will be produced in response to small misalignments. In this paper, the authors report on compliance analysis and validation of a novel planar pick-and-place parallel manipulator consisting of a flexible limb. In the proposed manipulator, a planar flexible parallelogram linkage, which is coupled with a rigid one, is introduced to connect the moving and the base platforms. Since the flexible parallelogram linkage is capable of producing large deformation in both the horizontal and the vertical directions, the end effector of the manipulator can generate wide-range motions because of the flexible links. An efficient approach to the large deflection problem of flexible links is used to precisely predict the kinetostatics of the manipulator. Then, a compensation algorithm to the structural deflection of the links can be developed to actively control the position of the parallel manipulator’s end effector. The merit of the proposed flexible manipulator is its intrinsic passive compliance while performing pick-and-place tasks. A prototype is fabricated to conduct experiments for the validation of the proposed idea. The results show that the prototype has acceptable positioning accuracy, even when a large external load is exerted on its end effector. The compliance properties of the proposed flexible manipulator have also been verified in both the horizontal and the vertical directions.

scholarly journals Exploring the Dynamics of Base-Excited Structures Impacting a Rigid Stop

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Peter J. Christopher ◽  
Barnaby Dobson ◽  
Nicholas A. Alexander
Keyword(s):  
High Performance ◽  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Performance Measure ◽  
Nonsmooth Dynamics ◽  
Structural Parameter ◽  
Sigmoid Function ◽  
Stiffness Ratio ◽  
Complex Behaviour ◽  
Interstorey Drift

This paper explores the nonlinear dynamics of a multidegree of freedom (MDoF) structure impacting a rigid stop. The contact mechanics is simplified by continuous sigmoid function idealisation of a lossless spring. By introducing a smooth nonlinear formulation, we avoid the computational expense of event-driven, piecewise, nonsmooth dynamics. A large parametric study using high-performance computing is undertaken. The nondimensional equations of motion suggest one primary structural parameter, contact-to-storey stiffness ratio, and two excitation parameters, nondimensional ground amplitude and frequency. Bifurcation plots indicate an extremely rich and complex behaviour, particularly in the cases where at least two-floor degrees of freedom (DoFs) impact the stop and when the contact-to-storey stiffness ratio is large. When considering interstorey drift as a performance measure, period-1 impacting solutions are generally favourable when compared to an analogous nonimpacting case. This paper also discusses whether chaotic impacting can be favourable. Finally, we consider the question of whether higher modes are significantly excited, at a linear resonance, for impacting solutions to this system.

On two dimensional electrohydrostatic stability

1976 ◽  
Vol 349 (1657) ◽  
pp. 231-243 ◽  
Keyword(s):  
Approximate Solution ◽  
Numerical Solution ◽  
Edge Effects ◽  
Complex Variable ◽  
Equilibrium Configuration ◽  
Quantitative Agreement ◽  
Two Dimensional ◽  
Equilibrium Conditions ◽  
Conducting Membranes ◽  
Special Case

Complex variable techniques are used for the study of the electrohydrostatic stability of two dimensional charged conducting membranes, which are assumed to be fixed along their edges. The formulation of the problem is quite general, but the numerical solution presented refers to the case when the membranes are symmetrical with respect to the plane bisecting their width and carry equal and opposite charges. It is found, as expected, that for a given set of data the equilibrium configuration breaks down if the membranes are sufficiently charged. When the membranes are sufficiently apart the breakdown occurs at their edges and is manifested as inability of the system to satisfy the equilibrium conditions there. When the membranes are sufficiently close together and are charged to a certain level, they touch at their mid-points and the equilibrium breaks down. Our results are compared with an approximate solution of this problem, presented by two other authors. The approximate solution ignores the edge effects of the membranes and overestimates the amount of charge that the membranes can carry before breakdown occurs. In the special case when the gap between the membranes is much less than their width, our results are in quantitative agreement with the approximate solution but as the gap between the membranes increases, the accuracy of the approximate solution decreases.

Optimization-based posture prediction for human upper body

Robotica ◽  
2009 ◽  
Vol 27 (4) ◽  
pp. 607-620 ◽  
Author(s):  
Zan Mi ◽  
Jingzhou (James) Yang ◽  
Karim Abdel-Malek
Keyword(s):  
Performance Measures ◽  
Degrees Of Freedom ◽  
Human Performance ◽  
Computational Algorithm ◽  
Performance Measure ◽  
Upper Body ◽  
Cost Functions ◽  
Posture Prediction ◽  
Joint Limits ◽  
Digital Human

SUMMARYA general methodology and associated computational algorithm for predicting postures of the digital human upper body is presented. The basic plot for this effort is an optimization-based approach, where we believe that different human performance measures govern different tasks. The underlying problem is characterized by the calculation (or prediction) of the human performance measure in such a way as to accomplish a specified task. In this work, we have not limited the number of degrees of freedom associated with the model. Each task has been defined by a number of human performance measures that are mathematically represented by cost functions that evaluate to a real number. Cost functions are then optimized, i.e., minimized or maximized, subject to a number of constraints, including joint limits. The formulation is demonstrated and validated. We present this computational formulation as a broadly applicable algorithm for predicting postures using one or more human performance measures.

Optimization-Based Digital Human Dynamics: Santos™ Walking Backwards

2007 ◽  
Author(s):  
Hyun Jung Kwon ◽  
Yujiang Xiang ◽  
Salam Rahmatalla ◽  
R. Timothy Marler ◽  
Karim Abdel-Malek ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Optimization Problem ◽  
Joint Angle ◽  
Spline Interpolation ◽  
Performance Measure ◽  
Degree Of Freedom ◽  
Human Model ◽  
Entire Body ◽  
Joint Torques ◽  
Digital Human

An objective of this study is to simulate the backward walking motion of a full-body digital human model. The model consists of 55 degree of freedom – 6 degrees of freedom for global translation and rotation and 49 degrees of freedom representing the kinematics of the entire body. The resultant action of all the muscles at a joint is represented by the torque for each degree of freedom. The torques and angles at a joint are treated as unknowns in the optimization problem. The B-spline interpolation is used to represent the time histories of the joint angles and the well-established robotics formulation of the Denavit-Hartenberg method is used for kinematics analysis of the mechanical system. The recursive Lagrangian formulation is used to develop the equations of motion, and was chosen because of its known computational efficiency. The backwards walking problem is formulated as a nonlinear optimization problem. The control points of the B-splines for the joint angle profiles are treated as the design variables. For the performance measure, total dynamic effort that is represented as the integral of the sum of the squares of all the joint torques is minimized using a sequential quadratic programming algorithm. The solution is simulated in the Santos™ environment. Results of the optimization problem are the torque and joint angle profiles. The torques at the key joints and the ground reaction forces are compared to those for the forward walk in order to study the differences between the two walking patterns. Simulation results are approximately validated with the experimental data which is motion captured in the VSR Lab at the University of Iowa.

3D HUMAN LIFTING MOTION PREDICTION WITH DIFFERENT PERFORMANCE MEASURES

2012 ◽  
Vol 09 (02) ◽  
pp. 1250012 ◽  
Author(s):  
YUJIANG XIANG ◽  
JASBIR S. ARORA ◽  
KARIM ABDEL-MALEK
Keyword(s):  
Performance Measures ◽  
Shear Force ◽  
Degrees Of Freedom ◽  
Human Performance ◽  
Three Dimensional ◽  
Optimal Solution ◽  
Performance Measure ◽  
Maximum Pressure ◽  
Pressure Force ◽  
Digital Human

This paper presents an optimization-based method for predicting a human dynamic lifting task. The three-dimensional digital human skeletal model has 55 degrees of freedom. Lifting motion is generated by minimizing an objective function (human performance measure) subjected to basic physical and kinematical constraints. Four objective functions are investigated in the formulation: the dynamic effort, the balance criterion, the maximum shear force at spine joint and the maximum pressure force at spine joint. The simulation results show that various human performance measures predict different lifting strategies: the balance and shear force performance measures predict back-lifting motion and the dynamic effort and pressure force performance measures generate squat-lifting motion. In addition, the effects of box locations on the lifting strategies are also studied. All kinematics and kinetic data are successfully predicted for the lifting motion by using the predictive dynamics algorithm and the optimal solution was obtained in about one minute.

scholarly journals Design and Analysis of a Tendon-driven Snake-arm Robot Based on Spherical Magnet

2021 ◽  
Author(s):  
Bei Liu ◽  
Lairong Yin ◽  
Long Huang ◽  
Peng Zhang ◽  
Kefu Yi
Keyword(s):  
Degrees Of Freedom ◽  
Simple Structure ◽  
Kinematic Model ◽  
Lateral Force ◽  
Compact Structure ◽  
Multiple Degrees Of Freedom ◽  
Opposite Pole ◽  
Passive Compliance

The tendon-driven snake-arm robot can achieve multiple degrees of freedom (DOF) bending motion with a compact structure, which enables the robot to be widely applied in confined environments. However, if a conventional tendon-driven snake-arm robot is subject to a lateral force on the distal end, it will experience passive compliance. In this paper, a 2-DOF rolling joint is proposed based on the opposite-pole attraction of spherical magnets, which has a relatively simple structure than traditional joints. By serial connecting the 2-DOF rolling joints, a novel snake-arm robot is designed utilizing a tendon-driven approach. The kinematic model and workspace of the snake-arm robot are obtained, and the bending motion is validated. Based on the kinematic model, it is theoretically proved that the proposed robot can avoid passive compliance. In addition, this feature is verified through load experiments on the developed prototype.

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