William L. Cleghorn

Multiple finger, passive adaptive grasp prosthetic hand

Abstract This paper describes the mechanical features of an experimental, multiple finger, prosthetic hand which has been designed for children in the 7–11 year age group. Conventional prosthetic hands exist for this age group, but they have limited mechanical function. The experimental hand presented is able to perform passive adaptive grasp, that is, the ability of the fingers to conform to the shape of an object held within the hand. During grasping, the four fingers and thumb are able to flex inwards independently, to conform to the shape of the object. This passive design is simple and effective, not requiring sensors or electronic processing. The adaptive grasp system developed here results in a hand with reduced size and weight compared to other experimental hands, and has increased mechanical function and cosmetic appearance compared to conventional prosthetic hands.

Microassembly of 3-D microstructures using a compliant, passive microgripper

This paper describes a novel microassembly system that can be used to construct out-of-plane three-dimensional (3-D) microstructures. The system makes use of a surface-micromachined microgripper that is solder bonded to a robotic manipulator. The microgripper is able to grasp a micropart, remove it from the chip, reorient it about two independent axes, translate it along the x, y and z axes to a secondary location, and join it to another micropart. In this way, out-of-plane 3-D microstructures can be assembled from a set of initially planar and parallel surface micromachined microparts. The microgripper is 380 /spl times/ 410 /spl mu/m in size. It utilizes three geometric features for operation: 1) compliant beams to allow for deflection at the grasping tips; 2) self-tightening geometry during grasping; and 3) 3-D interlocking geometry to secure a micropart after the grasp. Each micropart has three geometric features built into its body. The first is the interlock interface feature that allows it to be grasped by the microgripper. The second is a tether feature that secures the micropart to the substrate, and breaks away after the microgripper has grasped the micropart. The third is the snap-lock feature, which is used to join the micropart to other microparts.

A mixed integer-discrete-continuous programming method and its application to engineering design optimization

An algorithm for solving non-linear programming problems containing integer, discrete and continuous variables is presented. Based on a commonly employed optimization algorithm, penalties on integer and/or discrete violations are imposed on the objective function to force the search to converge upon standard values. Examples are included to illustrate the practical use of this algorithm in the area of engineering design.

Finite element analysis of high-speed flexible mechanisms

Abstract A procedure is presented for determining the governing equations of a mechanism with physically undamped flexible links and distributed mass, operating at a prescribed input rotational speed. The procedure is illustrated by a detailed analysis of a planar 4-bar angular function generating mechanism. The set of governing equations for the deflections about the rigid body trajectory of mechanism members is derived using the Lagrange equation. These equations are discretized by the finite element method. The equations derived in this paper give a more refined mathematical model by including additional terms as compared to previous methods which represented mechanisms as a sequence of instantaneous structures. The element equations are transformed and assembled to generate the governing differential equations for the mechanism, using a connection procedure suitable for elements which are assumed axially rigid. In this manner a smaller set of global equations than those previously used is obtained.

Dynamic Modeling and Experimental Validation of a 3-PRR Parallel Manipulator with Flexible Intermediate Links

This paper presents the development of structural dynamic equations of motion for a 3-PRR parallel manipulator with three flexible intermediate links, based on the assumed mode method. Lagrange’s equation is used to derive the dynamic model of the manipulator system. Flexible intermediate links are modeled as Euler–Bernoulli beams with pinned–pinned boundary conditions. Dynamic equations of motion of a 3-PRR parallel manipulator with three flexible links are developed by adopting the assumed mode method. The effect of concentrated rotational inertia at both ends of intermediate links is included in this model. Numerical simulations of vibration responses, coupling forces and inertial forces are presented. The corresponding frequency spectra analysis is performed using the Fast Fourier Transform (FFT). Experimental modal tests are performed to validate the theoretical model through comparison and analysis of modal characteristics of the flexible manipulator system.

Finite element formulation of a tapered Timoshenko beam for free lateral vibration analysis

Abstract A finite element model is developed for free lateral vibration analyses of linearly tapered Timoshenko beams. The shape functions are obtained from the homogeneous solution of the governing equations for static deflections. Illustrative examples demonstrate the performance of this element, and allow comparisons of results with those obtained by elements based on different formulations.

Automatic Microassembly Using Visual Servo Control

We propose an automatic microassembly method that can be used to construct three-dimensional microelectromechanical system (MEMS) structures. A six degree-of-freedom micromanipulator, equipped with a passive microgripper, is employed to grasp, manipulate, and join the micropart using visual feedback from an optical microscope. The proposed process utilizes a two-stage alignment strategy to perform the micro-grasping and micro-joining tasks. Using a vision-based localization method, the Cartesian coordinates of the manipulated micropart in three-dimensional space are determined. Further, a vision-based contact sensor determines the contact state between two micro-components in three dimensions to facilitating the micro-joining tasks. Visual servo control is used for accurate position feedback in three Cartesian coordinates during microassembly tasks. The necessary steps towards construction of complex three-dimensional MEMS devices, i.e., grasping a micropart, manipulating it, joining it to another micropart, and finally releasing it from the microgripper, have been successfully carried out using a six degree-of-freedom micromanipulator. Experiments demonstrate both the efficiency and validity of the proposed automatic assembly approach.

Experimental Implementation on Vibration Mode Control of a Moving 3-PRR Flexible Parallel Manipulator with Multiple PZT Transducers

This paper presents the experimental implementation of active vibration control applied to a moving 3-PRR parallel manipulator with three flexible links. The active vibration control is implemented using three piezoelectric (PZT) transducer pairs applied to one flexible intermediate link based on modal strain rate feedback (MSRF) control. A real-time active vibration control system is developed using two PCs with LabVIEW Real-Time. Modal analyses are conducted, and the results demonstrate that the vibration modes of the intermediate links are dynamically coupled and the vibration frequency components are complicated and closely spaced. Simplified and efficient modal filters are developed to extract modal coordinates in real time, and a second order compensator is used to filter amplified noises and unmodeled high frequency dynamics. A MSRF controller is then designed using an independent mode space control strategy, and is implemented experimentally with the first mode targeted for control. Experimental results demonstrate that the vibration amplitude of the first vibration mode of the intermediate link is significantly reduced using three PZT control pairs. The experimental results using one PZT control pair and two control pairs are provided to justify the use of three PZT control pairs.

Optimum design of high-speed flexible mechanisms

Abstract In recent years, considerable attention has been given to the analysis of flexible mechanisms. Analysis procedures often involve representing members of a particular mechanism by finite elements, and solving the derived system of governing equations for deflections and stresses. The inverse problem, which is one of design rather than analysis, is more difficult, and only a limited amount of work has been carried out in this area. In design, one must determine mechanism parameters that will satisfy specified stress and/or deflection conditions. In this paper a new procedure is presented for designing flexible mechanisms, and it is illustrated by an example of a planar 4-bar mechanism driven at a constant input rotational speed. Results for the example problem, using this new procedure, are found to converge to the optimum solution in fewer iterations than that required for previously published optimization techniques.

Flexible fixture design with applications to assembly of sheet metal automotive body parts

Purpose – To design a reconfigureable flexible fixture for the assembly of a set of sheet metal automotive body parts. Reconfigureable fixturing permits different parts to be grasped for assembly by a fixture without the need to conduct costly redesign and fabrication of hardware fixtures, which is an industry standard in widespread use in industry. While somewhat more complex than fixtures in current use, reconfigureable fixtures provide one solution to the problem of costly redesign of fixtures due to changes in dimensions, or geometry of parts to be assembled.Design/methodology/approach – We propose a novel reconfigureable fixture for robotic assembly of a number of different parts. Motivated by the marine organism, O. vulgaris, commonly referred to as an octopus, which grasps different objects or prey using suction cups, the proposed fixture has three fingers, each equipped with a suction cup, to facilitate the grasping process and increase grasp flexibility. Using this design approach, the fixture is...