1,721,051 research outputs found
On Crossley's contribution to the development of graph based algorithms for the analysis of mechanisms and gear trains
No full textThis paper celebrates a particular branch of Crossley's early work dedicated to Mechanism Science, which deals with a rigorous introduction of Graph Theory to the study of some fundamental and intrinsic properties of kinematic chains and mechanisms. Although such idea gave its main outcome in Type and Number Synthesis (which has been much better and extensively described in another paper of the present special issue) some other intriguing side effects appeared, later in Mechanism Science, which yielded several results, and are still in the center of research and industrial world interest, such as, to name but a few, the automatic generation of the equations governing kinematic, static force and dynamic analysis of mechanisms and geared trains, the power flow analysis, the computation of the efficiency and, finally, the never fully explored structure-to-function mapping, which the present contribution points out to be still a challenge in the field
Automatic sketching of planar kinematic chains
No full textIn this paper an original method for the fully automatic sketching of planar kinematic chains is described. This procedure may ease the interpretation of the results obtained during the enumeration of complex multi-loop kinematic chains. The designer is supplied with a graphical interface useful to better understand and topological properties of the kinematic chain generated, by a confortable visual inspection. The sketch of a kinematic chain is obtained by first mapping the graph in the plane and then sketching its line-graph, after deletation of extraneous edges. The graph is embedded of the graph directly leads to the deletion of the extraneous edges of the line-graph. Likewise, a straightforward original procedure converts the embedded edges of the graph into embedded vertices of the line-graph. A fully automatic drawing of the complete atlas of 1 d.o.f. planar kinematic chains with eight and ten links was obtained without any occurrence of crossing links. Finally, several examples are illustrated and some further developments discussed. © 1993
A novel method to fully suppress single and bi-modal excitations due to the support vibration by means of piezoelectric actuators
No full textVibration attenuation and control is a typical topic in mechanical, civil and aeronautical engineering. In recent years, there has been extensive research on smart materials and among all of them, the piezoelectrics seem to be the most attractive for passive and active vibration damping applications. Furthermore if multiple modes are concurrently excited, as in case of turbomachinery blades, active damping systems may remarkably increase their life-cycle and outweigh the shortcomings of implementing such systems. However the damping efficiency of the piezoelectric actuators is strictly bound to their driving voltage, size and location on the structure. In this work, a cantilever piezoelectric bimorph beam under base motion is considered and the analytical expression of the electric potential that nullifies the elastic tip displacement of the beam is derived in case of single and bi-modal excitations. The model allows to identify for every bi-modal excitations a set of solutions, each of them represented by three parameters: voltage amplitude, left and right corner positions of the piezoelectric actuators pair. As a result, designers can choose the best solution for their specific application demands. For example, if the supply voltage must to be kept as low as possible, then wider actuators should be used and vice versa. It was also found out that the control parameters do not depend on the spectral distribution between the two excited modes. Hence, even if the spectral distribution between the two coupled modes changes over time, it is not necessary to adjust either the voltage or the position of the actuator pair. The analytical predictions were compared with the results of FEM multi-physics simulations for several base motion excitations and a fair agreement was observed
Engineering-aided inventive surgery
Get PDFThis Editorial presents a new Special Issue dedicated to some old and new interdisciplinary areas of cooperation between engineering and surgery. The first two sections offer some food for thought, in terms of a brief introductory and general review of the past, present, future and visionary perspectives of the synergy between engineering and surgery. The last section presents a very short and reasoned review of the contributions that have been included in the present Special Issue. Given the vastness of the topic that this Special Issue deals with, we hope that our effort may have offered a stimulus, albeit small, to the development of cooperation between engineering and surgery
Advanced multi-body modelling of DCCSS isolators: Geometrical compatibility and kinematics
Get PDFThe effectiveness of Double Concave Curved Surface Sliders (DCCSS), which initially spread under the name of Double Friction Pendulum (DFP) isolators, was already widely proven by numerous experimental campaigns carried out worldwide. However, many aspects concerning their dynamical behavior still need to be clarified and some details still require improvement and optimization. In particular, due to the boundary geometrical conditions, sliding along the coupled surfaces may not be compliant, where this adjective is adopted to indicate an even distribution of stresses and sliding contact. On the contrary, during an earthquake, the fulfillment of geometrical compatibility between the constitutive bodies naturally gives rise to a very peculiar dynamic behavior, composed of continuous alternation of sticking and slipping phases. Such behavior yields a temporary and cyclic change of topology. Since the constitutive elements can be modelled as rigid bodies, both approaches, namely Compliant Sliding and Stick-Slip, can be numerically modelled by means of techniques typically adopted for multi-body mechanical systems. With the objective of contributing to the understanding and further improvement of this technology, a topology-changing multi-body mechanical model was developed to simulate the DCCSS. In the present work, attention is focused on details regarding geometrical compatibility and kinematics, while the complete dynamics is presented in another work. In particular, for the sake of comparison, the kinematic equations are presented and applied not only for the proposed Stick-Slip approach, but also for the currently accepted Compliant Sliding approach. The main findings are presented and discussed
A Cantilever-Based Piezoelectric MEMS for Arbitrary XY Path Generation
Get PDFThis work pertains to the design of a cantilever-based piezoelectric MEMS device that is
capable of generating arbitrary paths of its tip. The conceived device consists of a pair of rigidly
coupled piezoelectric bimorph cantilevers, and a theoretical model is developed for the analytical
evaluation of the proper voltage distribution to be supplied to the inner and outer electrodes of each
piezoelectric actuator, in order to drive the tip along any desired trajectory. Such a device could be
appealing in some microsurgical operations, i.e., the unclogging of arteries, endoluminal treatment of
obstructive lesions, but also as a 2D micropositioning stage, etc. Theoretical predictions of voltage
versus time that allow several pathways such as circles, ellipses, spirals, etc., to be accomplished have
been verified with multiphysics FEM simulations and the numerical outcomes seem to corroborate
the proposed model
Micromanipulation: A Challenge for Actuation
No full textManipulating micro objects has become an important task in several applications. Actuation is a crucial aspect of micromanipulation because there are physical restrictions which affect actuators’ performances at the micro or nano scale. One way of getting rid of these limitations is the use of an appropriate mechanical structure which enhances the elasticity of the material or provides mechanical advantage. This Special Issue of Actuators, which is dedicated to micromanipulation, offers a contribution to the development of some promising methods to actuate a microsystem for micromanipulation
A feasibility study of a novel piezo MEMS tweezer for soft materials characterization
No full textThe opportunity to know the status of a soft tissue (ST) in situ can be very useful for microsurgery or early diagnosis. Since normal and diseased tissues have different mechanical characteristics, many systems have been developed to carry out such measurements locally. Among them, MEMS tweezers are very relevant for their efficiency and relative simplicity compared to the other systems. In this paper a novel piezoelectric MEMS tweezer for soft materials analysis and characterization is presented. A theoretical approach has developed in order to carry out the values of the stiffness, the equivalent Young's modulus, and the viscous damping coefficients of the analyzed samples. The method has been validated by using both Finite Element Analysis and data from the literature
On the numerical computation of generalized burmester points
No full textThis note describes a procedure for plane higher-curvature path analysis and synthesis. All coefficients have been written in terms of elementary instantaneous invariants. This facilitates the numerical computation of Generalized Burmester Points for a moving link of a planar mechanism in a non-symmetric position. FORTRAN subroutines have been written and a numerical example is provided
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