Motion control has been one of the main areas of focus for the development of residual vibration reduction. Its application has been widely addressed to cranes [1][2][3][4] . Extensive work has been carried out within the methods based on command generation techniques applied to discrete linear systems 5,6 : In general, the state of the flexible modes at the initial condition is considered to be null, such as in the rest-to-rest maneuvers. This is the case of a standard crane. Most of its maneuvers, that include an input shaper in its control, will start in a null initial oscillatory condition and will achieve a null residual vibration in the stationary state. However, if there is a requirement of an emergency stop while the payload is swaying during the transient, the motion profile which is generated in a standard condition does not guarantee the stop of this load with a null residual oscillation. The main objective of the current development is to provide a method to design input functions which includes the non-zero initial states of the system in its formulation and to focus on a real time application such as an emergency stop of a crane. The new method can be included within the time-domain approaches. Other literature methods among the before mentioned time-domain approaches are the signal generation by means of trigonometric series and the so-called input shapers which are the most commonly used; other methods base their formulation in the frequency-domain, such as command conventional filtering and zero-placement techniques. Within the time-domain techniques, early approaches [7][8][9] focused the definition of the transient motion profiles through trigonometric series expansion avoiding the terms related with the system natural frequency. Another technique defines the motion profiles through convolution of pulses multiplied by a negative exponential time function when damping is considered 10,11 .The zero-vibration (ZV) input shaper was firstly proposed in 1950 12 and developed later [13][14][15] : an input signal is shaped by convolving it with two impulses, properly located in time and with the appropriate amplitude. The vibration that is generated with the first impulse is suppressed with the vibration which is generated with the second one. This property remains invariable when any command signal is convolved with this impulse sequence. To provide robustness against variation of the system parameters, the zero-vibration and derivative (ZVD) and extra insensitive (EI) shapers were designed by adding one more impulse to the ZV shaper. Other approaches of this technique included: i) phasorial diagrams to reduce numerical calculations 16,17 ; ii) negative impulses to reduce the transient time 18 ; iii) an optimal trade-off between performance, measured in terms of residual vibration and speed, and robustness 19 ; iv) the cancellation of a so-called pseudo-mode with lower frequency than any of the system component modes 20 ; v) the reduction of the system response during the transient 21,22 .Frequency do...
This paper presents an adaptive algorithm to reduce residual vibrations when the feedback sensor used has the drawback of having null drift along the time. The adaptive approaches are useful to deal with large variations of the system parameters at each maneuver, such as it occurs in cranes. For the feedback sensor, the use of inertial measurement units such as Micro-Electro-Mechanical Systems (MEMS) is increasingly extended because of their cost, size, robustness and power consumption. However, the effectiveness of the adaptive input shaping algorithms is compromised because of this drift, which is a commonly raised issue in this kind of devices. For a standard crane application, this major drawback could be avoided with a frequent time-basis calibration of the sensor, but it is not a feasible solution. The study presented in this manuscript focuses on the development of an automatic compensation of this drift to obviate such frequent calibrations. It is based on a non-asymptotic algebraic identification technique, which has the advantage of not requiring initial conditions and having a short convergence time. The new formulation uses the Zero-Vibration (ZV) input shaper technique, and the null drift is added to the algorithm as a new parameter to be identified. The proposed method has been particularized for single maneuvers of cranes with a gyroscope as feedback sensor, in a real time scenario. Experimental results show the efficacy of the method with its application to a scaled crane test platform. P R E -P R I N T V E R S I O N
Due to dynamic effects, clearances, manufacturing and assembly errors in form-closed cam mechanisms, the follower jump can also occur. For conjugate cam mechanisms a technique to avoid the follower jump without the use of a spring involves making the conjugate cam profiles bigger than the kinematical ones by adding an external offset. This strategy produces an interference fit between the conjugate cam profiles and the follower train. This paper presents an ordered procedure to study the influence that the planned interference fit has on the evaluation of the contact forces, the expected fatigue life of the rollers, contact pressures and the lubrication conditions. The study is based on a conjugate cam mechanism with translational roller followers used in a real automatic process for manufacturing muselets. A three-degree-of-freedom dynamic model is proposed and the Hertzian theory for general profiles is used to model the nonlinear contact stiffness between the cams and the crowned rollers. The dynamic model predicts that it is difficult to obtain conjugate cam mechanisms with an infinite expected fatigue life of the rollers just by considering typical achievable manufacturing errors or clearances, and as happens in reality, a set-up process is highly recommended. The procedure is also tested with measured manufacturing errors on a coordinate measure machine—CMM—and with measured radial internal clearances for the rollers measured by an experimental apparatus. Also, to evaluate lubrication conditions, surface finishing measurements have been taken of the cams and the rollers with a surface profiler.
This article examines new tutoring evaluation methods to be adopted in the course, Machine Theory, in the Escola Tècnica Superior d'Enginyeria Industrial de Barcelona (ETSEIB, Universitat Politècnica de Catalunya). These new methods have been developed in order to facilitate teaching staff work and include students in the evaluation process. Machine Theory is a required course with a large number of students. These students are divided into groups of three, and required to carry out a supervised work constituting 20% of their final mark. These new evaluation methods were proposed in response to the significant increase of students in spring semester of 2010-2011, and were pilot tested during fall semester of academic year 2011-2012, in the previous Industrial Engineering degree program. Pilot test results were highly satisfactory for students and teachers, alike, and met proposed educational objectives. For this reason, the new evaluation methodology was adopted in spring semester of 2011-2012, in the current bachelor's degree program in Industrial Technology (Grau en Enginyeria en Tecnologies Industrials, GETI), where it has also achieved highly satisfactory results.
To solve the indetermination of forces existing in a form-closed cam mechanism formed by conjugate cams, where the contact between the cams and the follower rollers is constantly ensured by only the geometry of the elements, dynamic models that consider the elasticity of the elements must be proposed. Because the stiffness of the main elements is associated with the elasticity of the solids, tight variations in manufacturing and assembly errors modify the effective interference fit, which significantly affects the expected fatigue life of the mechanism, leading to a premature failure of the elements due to surface fatigue. Based on a real industrial application of a conjugate cam mechanism and using lumped-parameter models, the objectives of this paper are: first, to show that it is difficult to achieve a pure form-closed conjugate cam mechanism, with the expected fatigue life of the mechanism, by using only standard tolerance specifications; second, to compare the expected fatigue life and motor torque with other cam mechanism design strategies such as force-closed and the combination of force-closed and form-closed strategies, known as force-closed conjugate cam strategy. This paper based on simulation results demonstrates that this latest strategy can, thanks to a better control of the preload, easily achieve results very similar to the theoretical ones of a form-closed conjugate cam mechanism. A prototype of the mechanism of the force-closed conjugate cam strategy is also built.
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