A dynamics-driven approach to precision machines design for micro-manufacturing and its implementation perspectives

Precision machines are essential elements in fabricating high quality micro products or micro features and directly affect the machining accuracy, repeatability and efficiency. There are a number of literatures on the design of industrial machine elements and a couple of precision machines commercially available. However, few researchers have systematically addressed the design of precision machines from the dynamics point of view. In this paper, the design issues of precision machines are presented with particular emphasis on the dynamics aspects as the major factors affecting the performance of the precision machines and machining processes. This paper begins with a brief review of the design principles of precision machines with emphasis on machining dynamics. Then design processes of precision machines are discussed, and followed by a practical modelling and simulation approaches. Two case studies are provided including the design and analysis of a fast tool servo system and a 5-axis bench-top micro-milling machine respectively. The design and analysis used in the two case studies are formulated based on the design methodology and guidelines

Hardware-in-the-loop simulator for stability study in orthogonal cutting

International audienceThe self-excited vibrations due to the regenerative effect, commonly known as chatter, are one of the major problems in machining processes. They cause a reduction in the surface quality and in the lifetime of mechanical elements including cutting tools. Furthermore, the experimental investigations of chatter suppression techniques are difficult in a real machining environment, due to repeatability problems of hard to control parameters like tool wear or position dependent dynamic flexibility. In this work, a mechatronic hardware-in-the-loop (HIL) simulator based on a flexible structure is proposed for dimensionless study of chatter in orthogonal cutting. Such system reproduces experimentally, on a simple linear mechanical structure in the laboratory, any stability situation which can be used to test and optimize active control devices. For this purpose, a dimensionless formulation is adopted and the delay related to the phase lag of the actuator and the controller employed on the HIL is compensated

Обработка деталей малых диаметров точением с высокой частотой вращения шпинделя. Проблемы и перспективы

В данной статье проанализированы возможности увеличения производительности токарной обработки для деталей малых диаметров за счет увеличения скорости резания современными режущими материалами. Выполнен обзор современных токарных обрабатывающих центров, новых инструментальных материалов ведущих производителей. Выполнен анализ факторов, влияющих на производительность обработки деталей. Уделено внимание вопросам устойчивости технологической системы в процессе резания. Основными препятствиями для повышения производительности являются низкая скорость вращения шпинделей токарных станков, связанная с балансировкой узлов станка и заготовок, и поиск зон устойчивого резания технологической системы.This article analyzed the possibility of increasing productivity for turning parts with small diameters by increasing cutting speed modern cutting materials. A review of modern turning machining centers, new tool materials from leading manufacturers. The analysis of the factors influencing the performance of machining. Paying attention to the sustainability of the technological system in the cutting process. The main obstacles to increased productivity are low speed spindle lathes associated with balancing machine components and workpieces and search zones of sustainable technological cutting system

Обработка деталей малых диаметров точением с высокой частотой вращения шпинделя. Проблемы и перспективы

В данной статье проанализированы возможности увеличения производительности токарной обработки для деталей малых диаметров за счет увеличения скорости резания современными режущими материалами. Выполнен обзор современных токарных обрабатывающих центров, новых инструментальных материалов ведущих производителей. Выполнен анализ факторов, влияющих на производительность обработки деталей. Уделено внимание вопросам устойчивости технологической системы в процессе резания. Основными препятствиями для повышения производительности являются низкая скорость вращения шпинделей токарных станков, связанная с балансировкой узлов станка и заготовок, и поиск зон устойчивого резания технологической системы.This article analyzed the possibility of increasing productivity for turning parts with small diameters by increasing cutting speed modern cutting materials. A review of modern turning machining centers, new tool materials from leading manufacturers. The analysis of the factors influencing the performance of machining. Paying attention to the sustainability of the technological system in the cutting process. The main obstacles to increased productivity are low speed spindle lathes associated with balancing machine components and workpieces and search zones of sustainable technological cutting system

Real-time performance of mechatronic PZT module using active vibration feedback control

This paper proposes an innovative mechatronic piezo-actuated module to control vibrations in modern machine tools. Vibrations represent one of the main issues that seriously compromise the quality of the workpiece. The active vibration control (AVC) device is composed of a host part integrated with sensors and actuators synchronized by a regulator; it is able to make a self-assessment and adjust to alterations in the environment. In particular, an innovative smart actuator has been designed and developed to satisfy machining requirements during active vibration control. This study presents the mechatronic model based on the kinematic and dynamic analysis of the AVC device. To ensure a real time performance, a H2-LQG controller has been developed and validated by simulations involving a machine tool, PZT actuator and controller models. The Hardware in the Loop (HIL) architecture is adopted to control and attenuate the vibrations. A set of experimental tests has been performed to validate the AVC module on a commercial machine tool. The feasibility of the real time vibration damping is demonstrated and the simulation accuracy is evaluate

Development and testing of an active boring bar for increased chatter immunity

Recent advances in smart materials have renewed interest in the development of improved manufacturing processes featuring sensing, processing, and active control. In particular, vibration suppression in metal cutting has received much attention because of its potential for enhancing part quality while reducing the time and cost of production. Although active tool clamps have been recently demonstrated, they are often accompanied by interfacing issues that limit their applicability to specific machines. Under the auspices of the Laboratory Directed Research and Development program, the project titled {open_quotes}Smart Cutting Tools for Precision Manufacturing{close_quotes} developed an alternative approach to active vibration control in machining. Using the boring process as a vehicle for exploration, a commercially available tool was modified to incorporate PZT stack actuators for active suppression of its bending modes. Since the modified tool requires no specialized mounting hardware, it can be readily mounted on many machines. Cutting tests conducted on a horizontal lathe fitted with a hardened steel workpiece verify that the actively damped boring bar yields significant vibration reduction and improved surface finishes as compared to an unmodified tool

A novel haptic model and environment for maxillofacial surgical operation planning and manipulation

This paper presents a practical method and a new haptic model to support manipulations of bones and their segments during the planning of a surgical operation in a virtual environment using a haptic interface. To perform an effective dental surgery it is important to have all the operation related information of the patient available beforehand in order to plan the operation and avoid any complications. A haptic interface with a virtual and accurate patient model to support the planning of bone cuts is therefore critical, useful and necessary for the surgeons. The system proposed uses DICOM images taken from a digital tomography scanner and creates a mesh model of the filtered skull, from which the jaw bone can be isolated for further use. A novel solution for cutting the bones has been developed and it uses the haptic tool to determine and define the bone-cutting plane in the bone, and this new approach creates three new meshes of the original model. Using this approach the computational power is optimized and a real time feedback can be achieved during all bone manipulations. During the movement of the mesh cutting, a novel friction profile is predefined in the haptical system to simulate the force feedback feel of different densities in the bone

Neural MRAC based on modified state observer

A new model reference adaptive control design method with guaranteed transient performance using neural networks is proposed in this thesis. With this method, stable tracking of a desired trajectory is realized for nonlinear system with uncertainty, and modified state observer structure is designed to enable desired transient performance with large adaptive gain and at the same time avoid high frequency oscillation. The neural network adaption rule is derived using Lyapunov theory, which guarantees stability of error dynamics and boundedness of neural network weights, and a soft switching sliding mode modification is added in order to adjust tracking error. The proposed method is tested by different theoretical application problems simulations, and also Caterpillar Electro-Hydraulic Test Bench experiments. Satisfying results show the potential of this approach --Abstract, page iv

Active tool vibration control and tool condition monitoring using a self-sensing actuator

Dissertation (PhD (Mechanical Engineering))--University of Pretoria, 2016.The studies consist of two simulations of active tool vibration control and tool condition monitoring respectively and a hardware-in-the-loop laboratory demonstration of active tool vibration control typical to turning. Besides reducing the restricting effects of tool vibrations on productivity, work-piece surface finish and tool life, it is desirable to handle lack of space at the tool tip and the cost of control systems in turning processes in an effective way. These two aspects are here considered by means of the concept of a self-sensing actuator (SSA) in the simulation of tool vibration control. In the simulation an IIRfilter represents the structure of the passive tool holder. A known pre-filtering technique was applied to the error in a feedback filtered-x LMS algorithm to maintain the stability of the control system. The self-sensing path is modelled and illustrated. The IIR-filters and their inverses were used for modelling this path, with equations resulting from the nodal displacements associated with nodes that have forces acting on them. For the cantilever type structure a considerable reduction of 93% of the displacement r.m.s. values of the tool tip, was obtained when using this control system. Signal processing using orthogonal cutting force components for tool condition monitoring (TCM) has established itself in literature. Single axis strain sensors however limit TCM to linear combination of cutting force components. This situation may arise when a single axis piezoelectric actuator is simultaneously used as an actuator and a sensor, e.g. its vibration control feedback signal exploited for monitoring purposes. Processing of a linear combination of cutting force components to the reference case of processing orthogonal components is compared. The same time-delay neural network structure has been applied in each case. Reconstruction of the dynamic force acting at the tool tip in a turning process is described. By simulation this dynamic force signal was applied to a model of the tool holder equipped with a SSA. Using a wavelet packet analysis, wear-sensitive features were extracted. The probability of a difference less than 5 percentage points between the flank wear estimation errors of abovementioned two processing strategies is at least 95 %. This study proves the basic concept of adaptive feedback active vibration control in combination with a self-sensing actuator to control tool vibrations. The structure involved is representative of a tool post clamped tool holder. The advantages that adaptive control hold when applied to non-stationary vibrations motivate this investigation. Secondly the dual functionality of a piezoelectric element is utilized for system simplification. Actuator linearization measures are considered and a model for the system’s forward path identified. The tool vibrations signal for this work is of 100 Hz bandwidth around the representative tool holder bending mode. A downscaled force based on real cutting force characteristics was artificially applied to the representative tool holder. Limited form locking contact with the tool holder restricted the actuator’s reaction to compressive forces only. Results of up to 70% attenuation of vibration induced strain on the SSA were achieved. This method clearly shows concept viability.Mechanical and Aeronautical EngineeringPhD (Mechanical Engineering)Unrestricte

Rapid Prototype Development of a Remotely-Piloted Aircraft Powered by a Hybrid-Electric Propulsion System

Remotely-Piloted Aircraft (RPA) provide users with unique mission capabilities, particularly on-demand overhead surveillance. However, a capability gap has been identified between the range and endurance of RPAs powered by internal combustion engines (ICE) and the reduced acoustic signature and smaller logistical footprint associated with electric-powered RPAs. This research, sponsored by the Office of the Secretary of Defense, aims at advancing systems engineering education by evaluating the utility of a tailored systems engineering approach. The tailored systems engineering approach used herein focuses on conducting a concept evaluation study on the rapid prototype development of a parallel hybrid-electric RPA (HE-RPA) and its ability to fill an identified mission capability gap. The concept evaluation utilizes a tailored systems engineering process to conduct a rapid prototype development and system evaluation. Two prototype RPAs and a support system are designed, integrated, and tested within a 13 month time window, in accordance with an established architectural framework. The integration of a parallel hybrid-electric system into an RPA demonstrated a potential reduction in acoustic signature and improves endurance over electric powered RPAs; however, immature technology and added system complexity result in overall performance that is currently on par with ICE-powered RPAs and only partially satisfies the capability gap