PARAMETRIC TRAJECTORY OPTIMISATION FOR INCREASED PAYLOAD

The load-carrying capacity of manipulators is often considered to be the same throughout their workspace. However, the actual capacity of manipulators largely depends on their posture, their velocity, their acceleration and the limits of their actuators. In this paper, a method is proposed to increase the payload capacity of manipulators through trajectory optimisation. This optimisation is performed on a task basis and therefore, the load-carrying capacity varies from task to task. An extensive analysis of the method is conducted based on its application on a planar RR serial two degree-of-freedom manipulator. This analysis evaluates the ability of the method to find feasible trajectories and compares the results with those obtained using Bang-bang type methods. It is shown that, although the trajectories produced by the proposed method are not time optimal, the method is much more versatile and much simpler to implement than its Bang-bang counterparts.

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Design of a Two Degree-of-Freedom Compliant Tool Tip for a Handheld Powered Surgical Tool

Journal of Medical Devices ◽

10.1115/1.4034879 ◽

2016 ◽

Vol 11 (1) ◽

Cited By ~ 6

Author(s):

Karthik Chandrasekaran ◽

Asokan Thondiyath

Keyword(s):

Carrying Capacity ◽

Compressive Load ◽

Degree Of Freedom ◽

Stainless Steel Tube ◽

Load Carrying Capacity ◽

Compliant Joints ◽

Surgical Tool ◽

Load Carrying ◽

Command Input ◽

Two Degree Of Freedom

A novel monobloc design of a two degree-of-freedom (DOF) compliant tool tip for a handheld powered surgical tool is presented in this paper. The monobloc tool tip can pitch and yaw using corner-filleted flexure hinge-based compliant joints and has an integrated compliant grasper. The 2DOF of the tool tip is realized by six compliant joints placed in an alternating fashion, orthogonal to each other. The tool is externally powered and consists of a drive box, a stainless steel tube, and a compliant tool tip at the distal end. The drive box houses a thumb joystick for command input, three servo actuators, and a microcontroller. The microcontroller maps surgeon's command input to the tool tip orientation and grasper actuation. By design, the graspers of the tool tip are actuated by tensile forces conveyed by the tethers, which exert a compressive load on the 2DOF compliant joints. Since the compressive load-carrying capacity of slender flexure-based compliant joints is limited, a design to enhance the compressive load-carrying capacity of the compliant joints with a circular guide is presented. A finite-element simulation was done to verify the design of the compliant joints. Experiments were carried out to assess the relationship between the force input by the servo actuators and joint deflection. Additional experiments were carried out to determine the maximum pinching force that can be exerted by the compliant graspers. A prototype of the complete surgical tool was built to demonstrate the utility of the proposed compliant tool tip as an alternative to traditional tool tip for a handheld powered surgical tool.

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Design and Development of a Two Degree-of-Freedom Rotational Flexure Mechanism for Precise Unbalance Measurements

Journal of Mechanisms and Robotics ◽

10.1115/1.4036610 ◽

2017 ◽

Vol 9 (4) ◽

Author(s):

Zhao Hongzhe ◽

Ren Siyuan ◽

Li Ming ◽

Zhang Shuqing

Keyword(s):

Calibration Procedure ◽

Degree Of Freedom ◽

Load Carrying Capacity ◽

Shape Parameters ◽

Rotational Stiffness ◽

Element Analysis ◽

Flexure Mechanism ◽

Leaf Springs ◽

Load Carrying ◽

Two Degree Of Freedom

To measure unbalanced moments, the knife-edge is used as a support module in traditional platforms, but performances rapidly deteriorate as the edge is worn down. In this paper, considering the requirements of measurements, a two degree-of-freedom (DOF) flexure mechanism is, thus, presented to overcome this drawback. First, off-axis stiffness and manufacturability are improved qualitatively by means of configuration analysis. Then, four generalized cross-spring pivots are exploited in the 2DOF flexure mechanism, and the geometric parameters are analyzed to achieve approximately constant rotational stiffness and reduced center shift simultaneously, which benefits calibration procedure and measurement precision. Models are further developed to determine the shape parameters of leaf-springs and transducer performances. Therefore, a low rotational stiffness is obtained to ensure a high resolution for measurements, and a high load-carrying capacity is achieved via strength checking. Finally, finite element analysis (FEA) is carried out to validate the proposed design, and experimental results demonstrate that the developed platform is capable of unbalance measurements with a high precision and resolution.

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Modeling and Applications of a Family of Five-Degree-of-Freedom Parallel Mechanisms With Kinematic and Actuation Redundancy

Journal of Mechanisms and Robotics ◽

10.1115/1.4040462 ◽

2018 ◽

Vol 10 (5) ◽

Cited By ~ 3

Author(s):

Long Kang ◽

Wheekuk Kim ◽

Byung-Ju Yi

Keyword(s):

Carrying Capacity ◽

Screw Theory ◽

Degree Of Freedom ◽

Load Carrying Capacity ◽

Parallel Mechanisms ◽

Actuation Redundancy ◽

Moving Platforms ◽

Load Carrying ◽

Dynamic Simulator ◽

Schönflies Motion

This paper introduces a family of statically balanced five-degree-of-freedom (5DOF) parallel mechanisms (PMs) with kinematic and actuation redundancy. Moving platforms of this family of PMs can provide 4DOF Schönflies motion. Three applications are considered in this work. The first and second applications use kinematic redundancy to avoid parallel singularities and perform an auxiliary grasping task in sequence. The third application incorporates actuation redundancy into a kinematically redundant manipulator to increase the load-carrying capacity. Screw theory was used to derive the Jacobian of the 5DOF PM with kinematic and actuation redundancy. Parallel singularities can be completely alleviated by controlling the orientation of the redundant link, thereby obtaining a large rotational workspace, and actuation redundancy increases the load-carrying capacity. Using a commercially available multibody dynamic simulator, an example of trajectory was performed to illustrate the large rotational workspace of the first and second applications and compare the Euclidean norm of the vector of actuation torque of nonredundant and redundant PMs. Three prototypes were also developed to demonstrate the output motion and static balancing property.

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Influence of Yield Strength Variability over Cross-Section to Steel Beam Load-Carrying Capacity

Nonlinear Analysis Modelling and Control ◽

10.15388/na.2005.10.2.15129 ◽

2005 ◽

Vol 10 (2) ◽

pp. 151-160 ◽

Cited By ~ 3

Author(s):

J. Kala ◽

Z. Kala

Keyword(s):

Yield Strength ◽

Cross Section ◽

Carrying Capacity ◽

Bending Moment ◽

Statistical Characteristics ◽

Load Carrying Capacity ◽

Load Carrying ◽

Strength Variability ◽

Hot Rolled ◽

Hot Rolled Steel

Authors of article analysed influence of variability of yield strength over cross-section of hot rolled steel member to its load-carrying capacity. In calculation models, the yield strength is usually taken as constant. But yield strength of a steel hot-rolled beam is generally a random quantity. Not only the whole beam but also its parts have slightly different material characteristics. According to the results of more accurate measurements, the statistical characteristics of the material taken from various cross-section points (e.g. from a web and a flange) are, however, more or less different. This variation is described by one dimensional random field. The load-carrying capacity of the beam IPE300 under bending moment at its ends with the lateral buckling influence included is analysed, nondimensional slenderness according to EC3 is λ¯ = 0.6. For this relatively low slender beam the influence of the yield strength on the load-carrying capacity is large. Also the influence of all the other imperfections as accurately as possible, the load-carrying capacity was determined by geometrically and materially nonlinear solution of very accurate FEM model by the ANSYS programme.

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Fuzzy Sets Theory in Comparison with Stochastic Methods to Analyse Nonlinear Behaviour of a Steel Member under Compression

Nonlinear Analysis Modelling and Control ◽

10.15388/na.2005.10.1.15135 ◽

2005 ◽

Vol 10 (1) ◽

pp. 65-75 ◽

Cited By ~ 5

Author(s):

Z. Kala

Keyword(s):

Fuzzy Sets ◽

Carrying Capacity ◽

Stochastic Methods ◽

Nonlinear Behaviour ◽

Load Carrying Capacity ◽

Load Carrying ◽

Input Parameters ◽

Stochastic Solution ◽

Fuzzy Solution ◽

Sets Theory

The load-carrying capacity of the member with imperfections under axial compression is analysed in the present paper. The study is divided into two parts: (i) in the first one, the input parameters are considered to be random numbers (with distribution of probability functions obtained from experimental results and/or tolerance standard), while (ii) in the other one, the input parameters are considered to be fuzzy numbers (with membership functions). The load-carrying capacity was calculated by geometrical nonlinear solution of a beam by means of the finite element method. In the case (ii), the membership function was determined by applying the fuzzy sets, whereas in the case (i), the distribution probability function of load-carrying capacity was determined. For (i) stochastic solution, the numerical simulation Monte Carlo method was applied, whereas for (ii) fuzzy solution, the method of the so-called α cuts was applied. The design load-carrying capacity was determined according to the EC3 and EN1990 standards. The results of the fuzzy, stochastic and deterministic analyses are compared in the concluding part of the paper.

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Pavement Damage Due to Conventional and New Generation of Wide-Base Super Single Tires

Tire Science and Technology ◽

10.2346/1.2174344 ◽

2005 ◽

Vol 33 (4) ◽

pp. 210-226 ◽

Cited By ~ 6

Author(s):

I. L. Al-Qadi ◽

M. A. Elseifi ◽

P. J. Yoo ◽

I. Janajreh

Keyword(s):

Carrying Capacity ◽

Material Properties ◽

Three Dimensional ◽

Fe Analysis ◽

Load Carrying Capacity ◽

Inflation Pressure ◽

3D Finite Element ◽

Load Carrying ◽

Pavement Damage ◽

New Generation

Abstract The objective of this study was to quantify pavement damage due to a conventional (385/65R22.5) and a new generation of wide-base (445/50R22.5) tires using three-dimensional (3D) finite element (FE) analysis. The investigated new generation of wide-base tires has wider treads and greater load-carrying capacity than the conventional wide-base tire. In addition, the contact patch is less sensitive to loading and is especially designed to operate at 690kPa inflation pressure at 121km/hr speed for full load of 151kN tandem axle. The developed FE models simulated the tread sizes and applicable contact pressure for each tread and utilized laboratory-measured pavement material properties. In addition, the models were calibrated and properly validated using field-measured stresses and strains. Comparison was established between the two wide-base tire types and the dual-tire assembly. Results indicated that the 445/50R22.5 wide-base tire would cause more fatigue damage, approximately the same rutting damage and less surface-initiated top-down cracking than the conventional dual-tire assembly. On the other hand, the conventional 385/65R22.5 wide-base tire, which was introduced more than two decades ago, caused the most damage.

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