Juan Carlos Jáuregui-Correa

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.

SENSORLESS DETECTION OF TOOL BREAKAGE IN MILLING

One of the most important research topics in the area of Intelligent Manufacture Systems (IMS) is the automatic detection of tool breakage, wear of chipping during the cutting process. Sensor-based techniques are available for cutting force measurements, but there are drawbacks in this approach in cost and idle times. This work proposes a sensorless monitoring system for tool monitoring in order to detect breakage and chipping by exploiting the wavelet transform and a neural network. Previous works have made use of these tools for monitoring several machining parameters, but we propose an integrated low-cost approach to detect quickly the changes in the tool integrity for monitoring. The system output produces an accurate detection of the tool integrity that enables the system to prevent damage due to tool breakage. This approach allows for an industrial solution to be developed.

Reliable methodology for gearbox wear monitoring based on vibration analysis

Gearboxes are important components in industrial applications and its condition monitoring is relevant in industries for reducing costs and minimizing maintenance downtime. Diagnosing wear in gearboxes saves time to prepare appropriate corrective actions, and to ensure that the system does not deteriorate critically. Nowadays, for condition monitoring in gearboxes, vibration analysis is commonly used due to its high reliability. In this work, a reliable methodology for diagnosing different levels of wear in a gearbox through vibration signals, and supported by a theoretical model, is proposed. The theoretical model is based on calculating the characteristic frequencies of the gearbox, with the aim for locating the spectral components of the faults in the vibration signal. Experimentation is done to a healthy gearbox and three wear levels. Results show the reliability of this method that makes it suitable to be used in diagnosing industrial machinery such as in automotive manufacturing applications.

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

Foreground and Background Components in Separable Complex Systems

Complex systems are composed of a large number of individual components. Many of these systems are separable, i.e., they can be split into two coupled subsystems: one with foreground components and another with background components. The former leads to narrow peaks in the frequency spectrum of the system and the latter gives the broad-band part. There is coupling between the two subsystems, but they can be studied separately for purposes of modeling and for analysis of experimental data. Examples from the literature are given from the area of mechanical vibrations, but the approach is quite general and can be adapted to other kinds of problems.

Analysis of Experimental Data from Complex Multibody System

Complex mechanical systems are those that are made up of a large number of inter-connected individual components, such as a multi body system. Traditionally, interconnections among elements are assumed to be springs and dampers, in this case, weak connections are introduced to explain synchronization. The system itself is treated as a black box, but it is assumed that a number of sensors can be applied to it to obtain dynamical signals of quantities like acceleration, velocity or displacement. The methods with which these signals can be analyzed to display characteristics such as synchronization are described. Some of these methods have been applied to signals obtained in several different experiments with mechanical systems.

Experimental Analysis of the Dynamic Behavior of a Non-stationary Two Stage Planetary Gearbox

This paper presents a methodology to analyze the dynamic behavior of a two stages planetary gearbox working under non-stationary operational conditions. Experimental tests are carried out on a test bed, which consists in a motor drive that is coupled to the input shaft of a gearbox and a break system on the output shaft. The system is instrumented to measure the power consumption of the motor drive, the vibrations on the bearing next to the output shaft, the torques in both shafts, and the speed of the motor shaft. The analysis method consists in a combined use of statistical descriptors and mathematical tools in frequency and time-frequency domains, such as FFT and the continuous wavelet transform.

Method for Friction Force Estimation on the Flank of Cutting Tools

Friction forces are present in any machining process. These forces could play an important role in the dynamics of the system. In the cutting process, friction is mainly present in the rake face and the flank of the tool. Although the one that acts on the rake face has a major influence, the other one can become also important and could take part in the stability of the system. In this work, experimental identification of the friction on the flank is presented. The experimental determination was carried out by machining aluminum samples in a CNC lathe. As a result, two friction functions were obtained as a function of the cutting speed and the relative motion of the contact elements. Experiments using a worn and a new insert were carried out. Force and acceleration were recorded simultaneously and, from these results, different friction levels were observed depending on the cutting parameters, such as cutting speed, feed rate, and tool condition. Finally, a friction model for the flank friction is presented.

Determining the Coupling Source on a Set of Oscillators from Experimental Data

Complex systems are a broad concept that comprises many disciplines, including engineering systems. Regardless of their particular behavior, complex systems share similar behaviors, such as synchronization. This paper presents different techniques for determining the source of coupling when a set of oscillators synchronize. It is possible to identify the location and time variations of the coupling by applying a combination of analytical techniques, namely, the source of synchronization. For this purpose, the analysis of experimental data from a complex mechanical system is presented. The experiment consisted in placing a 24-bladed rotor under an airflow. The vibratory motion of the blades was recorded with accelerometers, and the resulting information was analyzed with four techniques: correlation coefficients, Kuramoto parameter, cross-correlation functions, and the recurrence plot. The measurements clearly show the existence of frequencies due to the foreground components and the internal interaction between them due to the background components (coupling).

Mechanical Reproduction of the Horse Movement from a Hippotherapy Cycle

In this paper, a methodology for obtaining the basic movements of a horse for children hippotherapy is presented. These were determined from actual measurements acquired from different body parts of a horse that influence the desired effects for therapy. Measuring results were analyzed to identify those movements that help the therapy. Accelerometers placed on several spots on the horse allowed recording measurements of the motion of an actual horse rider during the walking and trotting gaits of the horse. Based on those, the planar trajectory and main tilts of the motion of a horse rider were obtained. The main goal of this project is to reproduce the closest movement via a 4-DOF parallel mechanism.