Carlos López-Cajún

Kinematic isotropy and the conditioning index of serial robotic manipulators

The conditioning index of a serial robotic manipulator is de fined in this article in terms of the reciprocal of its minimum condition number. The condition number of a manipulator is defined, in turn, as that of its Jacobian matrix. Moreover, in defining the Jacobian condition number, a quadratic norm of the Jacobian matrix is needed. However, this norm, or for that matter any other norm, brings about dimensional inho mogeneities. It is shown here that by properly defining the said norm based on a weighting positive definite matrix, the dimensional inhomogeneity is resolved. Manipulators with a conditioning index of 100% are termed isotropic, a six-axis isotropic manipulator being introduced. This manipulator has all its angles between neighboring revolute axes at 90° and all its distances between neighboring axes identical; more over, these distances are identical to the offsets of those axes. The kinematic conditioning of wrist-partitioned manipulators is given due attention, and illustrated with some examples of industrial robots of this type.

Trajectory planning in robotic continuous-path applications

Trajectory planning of robot motions for continuous-path operations is formulated in configuration space, resorting to the intrinsic properties of the path traced by point of the end effector. It is shown that, by referring the orientation of the end effector to a unique orthogonal frame defined at every point of the aforementioned path, a systematic procedure for trajectory planning in configuration space is derived. The computations required to determine the angular velocity and angular acceleration of the path frame reduce to computing the Darboux vector of the path and its time derivative. >

Optimal synthesis of cam mechanisms with oscillating flat-face followers

Abstract The synthesis of the cam profile producing a given displacement program of its oscillating flat-face follower, while enclosing a minimum area is presented. The displacement program of the follower, as well as the cam profile, are generated through the use of cubic periodic splines following a method reported previously. The optimum parameters of the cam mechanism are obtained via the minimization of the cam-disk area subject to geometric constraints. It is shown that the problem reduces to finding the roots of a quartic equation, which is done explicitly using Ferraris formula. The procedure is illustrated with a fully-solved example showing its applicability to the automatic design of cam follower mechanisms.

Characterization of a Cable-Based Parallel Mechanism for Measurement Purposes#

This article describes the main characteristics of a cable-based parallel manipulator called Milli-Cassino Tracking System (Milli-CaTraSys), which was developed at LARM in Cassino. Operation models and formulations are proposed both for kinematics and statics. In particular, a procedure is proposed for error estimation to know error effects on the end-effector pose. Numerical simulations have been carried out to characterize both the procedure results and system behavior. Results of experimental tests and simulations are also compared to show the feasibility and practical efficiency of a Milli-CaTraSys prototype.

Sustainable Use of Tepetate Composite in Earthen Structure

One of the best indicators for construction sustainability is the use of earthy local materials which are completely recyclables and savers of energy during their life cycle. Tepetate is an underestimated earth-natural material, vast and economic, used only in a compacted form in backfills for layers of low resistance in pavements and platforms of buildings. This volcanic soil, named in different ways in several countries, is found in the central region of Mexico. Its resistance as compacted material is very low, of the order of 0.08 MPa. In this work, an improved sustainable-tepetate composite, using CaOH, is presented. This research includes the determination of mechanical properties as well as the physicochemical characterization of the sustainable-tepetate composite behavior. It can be concluded that the strength of the proposed composite increases significantly, immediately after treatment and with time. X-Ray Diffraction shows that all the mineralogical phases prevail in the natural tepetate and only a new phase appeared (calcite), which increases with time. This and the reaction of CaOH with clay content are very likely associated with the continuous strength increase of the composite.

Agustin Betancourt: An Early Modern Scientist and Engineer in TMM

In this paper, we have presented the personality and activity of Agustin Betancourt who can be considered among the first modern mechanical (industrial) engineers with a strong formation and expertise in TMM. Indeed his activity can be considered as a significant example of personality in the early modern developments of TMM but also how TMM formation has been useful for engineers and managers in the overcoming Industrial Revolution. In particular, Betancourt can be seen as an emblematic example of the international vision of TMM and its application, since he has been a successful scientist, engineer, and manager in Spain, France, and then Russia.Copyright

Cellular Concrete Bricks with Recycled Expanded Polystyrene Aggregate

Cellular concrete bricks were obtained by using a lightweight mortar with recycled expanded polystyrene aggregate instead of sandy materials. After determining the block properties (absorption, compressive strength, and tensile stresses), it was found that this brick meets the requirements of the masonry standards used in Mexico. The obtained material is lighter than the commercial ones, which facilitates their rapid elaboration, quality control, and transportation. It is less permeable, which helps prevent moisture formation retaining its strength due to the greater adherence shown with dry polystyrene. It was more flexible, which makes it less vulnerable to cracking walls due to soil displacements. Furthermore, it is economical, because it uses recyclable material and has properties that prevent deterioration increasing its useful life. We recommend the use of the fully dry EP under a dry environment to obtain the best properties of brick.

Cathodic Protection in Reinforced Concrete Elements, using Carbon Fibers Base Composites

A carbon fiber reinforced polymer (CFRP) composite was used as external reinforcement and as a cathodic protection (CP) system of steel in concrete elements. Different epoxy resins were tested by varying the amount and length of the carbon fibers used. The CFRP composites were glued to the concrete prisms using such selected conductive resins, then electrically connected with one of the rebars and used as impressed current anodes. A electrical current was applied between the CFRP composite (anode) and the rebar (cathode) at different current densities (50, 100, and 1000 mA/m2). The results obtained have demonstrated that the CFRP external reinforcement used in this investigation can also work as an anode in a cathodic protection system (CP). No mechanical adverse effect was found on the composite and the epoxy resin selected, although the current densities applied were greater than those used in real structures.

Synthesis of an Al-ZrO2 composite by infiltration of Zr-chelates into an Al matrix

Abstract. Aluminium-based matrix composites were prepared by infiltration with an ammoniacal zirconium chelate within an Al matrix synthesized via Aluminium powder compactation. After infiltration, this chelate can be transformed in situ by sol-gel method that leads to tetragonal phases in zirconia, which in turn, transforms to monoclinic structure on heating. Based on Differential Thermal Analysis (DTA), Fourier Transformed Infrared (FTIR), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM), we confirm the reaction sequence to obtain the tetramer, the phase transformation sequence within the Al matrix, and the development of phases that leads to the synthesis of the Al-ZrO2 composite.

Dynamic Behavior and Synchronization of an Automobile as a Complex System

A complex system is composed of many interacting components, but the behavior of the system as a whole can be quite different from that of the individual components. An automobile is an example of a common mechanical system composed of a large number of individual components that are mechanically connected in some way and hence transmit vibrations to each other. This paper proposes a variety of inter-related analytical tools for the study of experimental data from such systems. In this work, experimental results of accelerometer data acquired at two locations in the automobile for two different kinds of tests are analyzed. One test is the response to impact on a stationary vehicle, and the other is the road-response to the vehicle being driven on a flat road at different speeds. Signals were processed via Fourier and wavelet transforms, cross-correlation coefficients were computed, and Hilbert transforms and Kuramoto order parameters were determined. A new parameter representing synchronization deficit is introduced. There is indeed some degree of synchronization that can be quantified between the accelerations measured at these two locations in the vehicle.Copyright