Roberto Strada

A Novel in Field Method for Determining the Flow Rate Characteristics of Pneumatic Servo Axes

Several strategies, in order to improve an actuator’s control and to increase the bandwidth, consider the relationship between the valve’s driving signal and the air flow rate. Such an approach to the control strategy takes advantage of the evaluation of the valve’s characteristic parameter, known as sonic conductance. The sonic conductance can be measured following the procedure stated by the standard ISO 6358. Nevertheless, the measurement carried out according to this standard is very expensive in terms of time and air consumption. In this paper, an alternative method to evaluate the sonic conductance is presented. The method is based on a new practical approach: the sonic conductance is evaluated leaving the valve mounted on the actuator and using only the piston’s position transducer. The steady state piston’s motion allows us to determine the sonic conductance. The new approach allows us to get the conductance in a very short time, without the need to use a proper test bench and pressure transducers. Moreover, performing the measurements directly on the pneumatic axis allows us to characterize not only the valve but the duct connecting the valve to the actuator’s chamber too.

Nonlinear modeling and experimental validation of uni-Axial servo-hydraulic shaking table

An effective way for the testing of a large number of systems is using single and multi-Axis shaking tables. Among the possible applications, the civil engineering field stands out for the testing of structures, or part of them, both on a reduced and on a full scale. However, design a high performance controller for a servo-hydraulic shaking table is a difficult problem due to its non-linarites and large friction forces. The goal of this pa- per is to develop and experimentally validate a robust numerical model that simulates the acceleration behavior of a uni-Axial servo-hydraulic shaking table system with considering three friction models, the LuGre model, the modified LuGre model and the new modified LuGre model. First, a full system model of servo- hydraulic system is developed based on fluid mechanical expressions and then the friction force of hydraulic cylinder is modeled and validated on the real shaking table. Data of the experiment are gathered from input command valve, and the output acceleration and position of the table. All models are simulated by using MATLAB and SIMULINK computer program. The parameters of the system and the friction models are estimated by using least square method (LSM). Finally, the comparisons of simulated reults with experimental ones show that the model of the system with considering third model of the friction can predict accurately the shaking tables behaviors.

Design and development of a Cartesian plotter as a way to teach Mechatronics to Mechanical Engineering students

The need for interdisciplinary skills in mechanics, electronics, control theory and computer science was recognized as becoming more and more important for mechanical designers. At this aim, it is since the academic year 2002/2003 that a course on Mechatronic Systems is delivered at Bergamo University as an option in the BS curriculum for mechanical engineering students. The course is mainly based on project oriented learning activities; actually a practical project is developed each year. This paper mainly deals with the description of the mechatronics education activity at Bergamo University, with reference to the 2005/2006 academic year course project: a Cartesian plotter driven by stepper motors

Gray-box acceleration modeling of an electro hydraulic servo shaking table with neural network

An effective way for the testing of a large number of systems is using single and multi-axis shaking tables. Among the possible applications, the civil engineering field stands out for the testing of structures, or part of them, to high natural dynamic forces. However, due to nonlinearities and structured and unstructured uncertainties of the hydraulic systems, the acceleration signal of these systems with respect to sine input are distorted. This paper is focused on identification of a gray-box acceleration model of a uni-axial servo hydraulic shaking table with respect to sine input signal with different frequencies and amplitude. First, a full system model of servo hydraulic system is developed based on fluid mechanical expressions and steady state friction. Second, for each input frequencies the unknown parameters of the friction, bulk modulus and leakage of the system are identified based on nonlinear least square method. Then, the identified parameters are used to develop a dynamic feed forward neural network model. The gray-box model uses online short fast Fourier transform harmonic identification method to identify the harmonic and amplitude of input signal and the neural network model produces parameters of the system. Finally, the comparison between the experimental results of the acceleration signal and the simulation one demonstrates the accuracy of the model.

An Unified Design Procedure for Flying Machining Operations

One of the most important aspects of the design of “flying machining” operation is the choice of the proper law of motion of the slave axis. In literature, technical reports and papers can be found concerning this subject, but they deal with specific problems and the solutions or suggestions proposed are specific as well, suitable for those cases. In order to try to overcome this limitation, in this paper we analyze the subject of the flying machining operations from a wider point of view. We propose a unified design procedure that has general validity being suitable for the choice of the slave axis’ law of motion for whatever “flying machining” operation. Moreover the unified design process proposed includes also methodologies for the choice of motor and transmission.

Design of a fatigue ski testing bench

The aim of this paper is to show the design procedure for a fatigue ski test bench. The interest in developing an equipment to test ski characteristics has greatly raised since the introduction of carving skis. The characteristics of this kind of skis allow new trajectories and promise turn easiness and fun to everyone. These features come from a correct combination of ski shape and mechanical characteristics both of which determine load distribution under the edges. To quantify ski edge load and to characterise different skis, as well as to test their fatigue behaviour, we designed a ski test bench that allows to load an edged ski against an instrumented bed and to measure load distribution along the edge as well as the shape of the deformed edge.

Online Wavelet Complementary velocity Estimator

In this paper, we have proposed a new online Wavelet Complementary velocity Estimator (WCE) over position and acceleration data gathered from an electro hydraulic servo shaking table. This is a batch estimator type that is based on the wavelet filter banks which extract the high and low resolution of data. The proposed complementary estimator combines these two resolutions of velocities which acquired from numerical differentiation and integration of the position and acceleration sensors by considering a fixed moving horizon window as input to wavelet filter. Because of using wavelet filters, it can be implemented in a parallel procedure. By this method the numerical velocity is estimated without having high noise of differentiators, integration drifting bias and with less delay which is suitable for active vibration control in high precision Mechatronics systems by Direct Velocity Feedback (DVF) methods. This method allows us to make velocity sensors with less mechanically moving parts which makes it suitable for fast miniature structures. We have compared this method with Kalman and Butterworth filters over stability, delay and benchmarked them by their long time velocity integration for getting back the initial position data.

TEACHING TYRE TESTING AND MODELLING TO UNDERGRADUATE MECHANICAL ENGINEERING STUDENTS

Tyre characterization is an important step for full vehicle dynamic simulation: main tyre companies have their own testing machines based on rotating drums or flat beds, while special vehicles are used for tyre testing on real tracks with various road conditions (wet, dry, smooth, harsh…). The use of these experimental data, during a vehicle dynamics simulation performed with a multibody code, is allowed by means of several tools, such as data interpolation, physical or empirical tyre models. Many tyre models, with different degrees of complexity, have been proposed in literature: among them we can cite, because of their widespread use, Pacejka formulas. These well-known formulas present various degrees of load interaction capabilities that, generally, can be switched on/off in Multibody codes used for vehicle simulations. Usually, these programs come with a set of example files, based on these formulas, that describe tyres with various sizes (for cars ranging from city to sport) and that can be used at academic level to perform full vehicle simulations. To foresee the behaviour of such models is not easy and the simple calculation of formula outputs with plenty of graphs is not completely satisfactory; it is more intuitive discover the tyre characteristics using a testing procedure similar to the experimental setups. To this aim a virtual model of a testing machine with serial architecture has been built using MSC Adams. Users of this virtual testing environment, in our case undergraduate Mechanical Engineering students of a course on Vehicle Dynamics at Bergamo University, can obtain quite easily tyre characteristics, varying both test rig settings (camber, slip angle, vertical load and driving torque) as well as acting on tyre models parameters (for example scale factors of Pacejka formulas). Students can also appreciate the differences in tyre behaviour that arise when various load case combinations are activated. Students, that already have some background in Multibody Dynamics, appreciated this approach and after a very short training on the lab they were able to proceed by themselves with a better understanding of tyre characteristics.

Design of Torque Balancing Mechanisms

Machines are often subjected to periodic loads, related both to the characteristics of the payload or to the kinematic chains used for motion generation, such as linkages or cam follower mechanisms. The load fluctuation can cause several inconveniences to the proper functioning of the machines, like shaking forces and moments, vibrations, severe speed fluctuations. Speed fluctuations are a main source of concern since, generally, mechanisms design and optimization is performed considering a constant main shaft speed and a departure from ideal behavior gets worse increasing machine speed. The simpler approach used to mitigate this fact consists in adopting a large flywheel and/or a massive motor, even to drive small loads. More sophisticated procedures add appropriate balancer mechanisms to the machine. This paper, starting from a review of the available literature, presents a theoretical framework to the problem of input torque balancing and defines a methodology for the synthesis of balancing mechanisms.

4-DOF redundant haptic interface: Redundancy coordination method for control system design

The present work deals with the development of a 4-DOF redundant haptic interface, with particular focus on the problem of reaching the systems mechanical limits. After a brief presentation of the main characteristics of the device, of the kinematic structure of the mechanism and of the different methods used for the resolution of the inverse kinematics, an improvement of one of the methods is shown, together with results obtained from several simulations. Being the objective of the work just the definition of a redundancy coordination method, the system, rather than an haptic interface, has been analyzed as a parallel kinematic manipulator.