Drillstring vibration is detrimental to drilling operations. It is crucial to understand the underlying mechanisms to circumvent these vibrations and to help improve drilling performance. This paper presents a six degrees-of-freedom (DOF) finite element method (FEM) model to characterize the drillstring dynamics. In addition, a comprehensive bit-force model is developed and included as a boundary condition to the model, corresponding to the vibrations in axial, lateral, and torsional directions. This bit-force model considers the bottom hole assembly (BHA) eccentricity, mud damping, bit–rock interaction, and their coupling mechanisms. Simulation results have shown good agreement with field observations and experimental data in the literature. The utility of this modeling framework is demonstrated in the paper through case studies for normal operation, stick–slip vibration, and whirl vibration.

Parallel turning is an excellent candidate for keeping up with current trends set by manufacturing industry, namely, to increase accuracy and productivity simultaneously. In the field of manufacturing of cylindrical parts, these cutting processes offer huge potential in increasing productivity, since they ensure high material removal rates and appropriate accuracy at the same time. The above benefits can yet only be harvested if the process is free of chatter vibration, which affects the workpiece surface quality. In this study, it is shown that by means of tuning the dynamical properties of cutting tools, it is possible to expand the stable machining parameter regions in order to eliminate adverse chatter. A parallel turning system is investigated, where tuning of the system is realized by varying the overhang of one of the tools, that is, by modulating the frequency ratio of the cutters. Measurements have been carried out for the validation of the theoretical predictions of robustly stable chip width limits, below which the turning operation is stable for all spindle speed values.

Parallel kinematic machines (PKMs) have been proposed as an alternative solution for high-speed machining (HSM) tool for several years. However, their dynamic characteristics are still considered an issue for practice application. Considering the three prismatic–revolute–spherical (3-PRS) PKM design as a typical compliant parallel device, this paper applies substructure synthesis strategy to establish an analytical elastodynamic model for the device. The proposed model considers the effects of component compliances and kinematic pair contraints so that it can predict the dynamic characteristics of the 3-PRS PKM. Based on eigenvalue decomposition of the characteristic equations, the natural frequencies and corresponding vibration modes at a typical configuration are analyzed and verified by numerical simulations. With an algorithm of workspace partitions combining with eigenvalue decompositions, the distributions of lower-order natural frequencies throughout the workspace are computed to reveal a strong dependency of dynamic characteristics on mechanism's configurations. In addition, the effects of the radii of the platform and the base along with the cross section of the limb on lower-order natural frequencies are analyzed to provide useful information during the early design stage. At last, frequency response analysis for the tool center point (TCP) is worked out based on the elastodynamic model to provide primary guideline for cutting chatter avoidance.

In machining process, chatter is an unstable dynamic phenomenon which causes overcut and quick tool wear, etc. To avoid chatter, traditional methods aim to optimize machining parameters. But they have inherent disadvantage in gaining highly efficient machining. Active magnetic bearing (AMB) is a promising technology for machining on account of low wear and friction, low maintenance cost, and long operating life. The control currents applied to AMBs allow not only to stabilize the supported spindle but also to actively suppress chatter in milling process. This paper, for the first time, studies an integrated control scheme for stability of milling process with a spindle supported by AMBs. First, to eliminate the vibration of an unloaded spindle rotor during acceleration/deceleration, we present an optimal controller with proper compensation for speed variation. Next, the controller is further enhanced by adding an adaptive algorithm based on Fourier series analysis to actively suppress chatter in milling process. Finally, numerical simulations show that the stability lobe diagram (SLD) boundary can be significantly expanded. Also, a practical issue of constraints on controller output is discussed.

In this article, we address the problem of synthesizing communication networks for unmanned aerial vehicles (UAVs) in the presence of resource constraints. UAVs can be deployed as backbone nodes in ad hoc networks that can be central to civilian and military applications. The cost of operation of the network depends on the resources that are used such as the total power consumption associated with the network and the number of communication links in the network. The objective of the problem is to synthesize a communication network that maximizes connectivity subject to the cost of operation being within the specified budget for the resources. It is known that algebraic connectivity is a measure of robust connectivity and hence, it is chosen as an objective for optimization. We pose the network synthesis problem as a mixed-integer semidefinite program (MISDP): (1) provide an algorithm for computing optimal solutions using cutting plane methods; (2) develop lower bounds by posing the problem as a binary semidefinite program; and (3) construct feasible solutions using heuristics and estimate their quality. The network synthesis problem is a nondeterministic polynomial--time (NP)-hard problem. We provide some computational results to corroborate the performance of the proposed algorithms.

The motion accuracy of a heavy duty parallel manipulator is usually low due to time lag and the difficulty to real-time measure the position of the end-effector. In this paper, a dynamic modeling of this system with consideration of the link flexible deformation is proposed, and a double-feedforward control is presented. The link deformation is considered in the kinematic model. Taking link deformation into account, the dynamic model is derived for real-time application, and the inverse dynamic compensator is designed. The zero phase error tracking controller (ZPETC) is introduced as the second compensator. The system stability is investigated by simulations. The control method is compared with the kinematic-based control without consideration of link deformation. The results show that the maximum contouring error reduces from 7.5mm to 10μm. Thus, the tracking performance is improved when using the method proposed in this paper.

Longwall mining is an underground coal mining method that is widely used. A shearer traverses the coal panel to cut coal that falls to a conveyor. Operation of the longwall can benefit from knowledge of the cutting forces at the coal/shearer interface, particularly in detecting pick failures and to determine when the shearer may be cutting outside of the coal seam. It is not possible to reliably measure the cutting forces directly. This paper develops a method to estimate the cutting forces from indirect measurements that are practical to make. The structure of the estimator is an extended Kalman filter with augmented states whose associated dynamics encode the character of the cutting forces. The methodology is demonstrated using a simulation of a longwall shearer and the results suggest this is a viable approach for estimating the cutting forces. The contributions of the paper are a formulation of the problem that includes: the development of a dynamic model of the longwall shearer that is suitable for forcing input estimation, the identification of practicable measurements that could be made for implementation and, by numerical simulation, verification of the efficacy of the approach. Inter alia, the paper illustrates the importance of considering the internal model principle of control theory when designing an augmented-state Kalman filter for input estimation.

Chatter is an undesirable dynamic phenomenon in machining processes, which causes cutting disturbance, overcut, quick tool wear, etc., and thus seriously impairs workpiece quality. To mitigate chatter, traditional methods called passive control focus on optimizing working spindle speeds and depths of cut. But they have inherent disadvantages in gaining highly efficient machining. On the contrary, the research in this paper is along the line of active control. Specifically, an adaptive algorithm is developed based on Fourier series analysis to deal with the so-called regenerative cutting force which causes chatter. As a result, chatter is remarkably mitigated. The performance improvement is illustrated by numerical simulation in terms of both stability lobes diagram (SLD) and surface location error (SLE).

A sensor module that integrates a thin film polyvinylidene fluoride (PVDF) piezoelectric strain sensor and an in situ data logging platform has been designed and implemented for monitoring of the feed and transverse forces in the peripheral end milling process. The module, which is mounted on the tool shank, measures the dynamic strain(s) produced in the tool and logs the data into an on-board card for later retrieval. The close proximity between the signal source and the PVDF sensor(s) minimizes the attenuation and distortion of the signal along the transmission path and provides high-fidelity signals. It also facilitates the employment of a first principles model based on the Euler–Bernoulli beam theory and constitutive equations of the piezoelectric sensor material to relate the in situ measured PVDF sensor signals to the feed and transverse forces acting on the tool. The PVDF sensor signals are found to compare well with the force signals measured by a platform-type piezoelectric force dynamometer in peripheral end milling experiments.

In this paper, the fractionalized differentiating method is implemented to reduce commensurate fractional order models complexity. The prominent properties of this method are its simplicity and guarantee of preserving the stability of a specific class of fractional order models in their reduced counterparts. The presented reduction method is employed in simplifying complicated fractional order controllers to a fractional order PID (FOPID) controller and proposing tuning rules for its parameters adjustment. Finally, the efficiency of the FOPID tuning rule obtained based on the proposed reduction method is shown in the temperature control of a cutting process.

A normalized chatter detection index, which is independent of cutting conditions, is critical for machining process monitoring and control. This paper introduces a novel method for on-line machine-tool chatter detection. The method characterizes the significant transition in the cutting dynamics at the onset of chatter by the changes in the instantaneous energy of the machining system. This technique utilizes the relation between the Teager–Kaiser nonlinear energy operator and time-frequency (Wigner) distribution to develop a normalized chatter detection index. The validity of this technique is demonstrated with the actual experimental cutting data obtained from turning and milling processes.

This paper presents a dynamically compensated Spindle Integrated Force Sensor (SIFS) system to measure cutting forces. Piezo-electric force sensors are integrated into the stationary spindle housing. The structural dynamic model between the cutting forces acting on the tool tip and the measured forces at the spindle housing is identified. The system is first calibrated to compensate the influence of spindle run-out and unbalance at different speeds. Using the cutting force signals measured at the spindle housing, a Kalman Filter is designed to filter the influence of structural modes on the force measurements. The frequency bandwidth of the proposed sensor system is significantly increased with the proposed sensing and the signal processing method.

To reduce work in progress in the plastic industry, integrated CNC punching and cutting machines have been used recently to combine a number of individual operations into one operation. Application of such integrated machines is confronted with a challenging problem of synchronizing two-axis motions. In this paper, an adaptive coupling controller is utilized to synchronize punching and cutting operations of the integrated CNC machine. The controller incorporates cross-coupling technology into adaptive control design, through feedback of position errors of two motion axes and the differential position error between two axes. It has been shown that the proposed controller guarantees asymptotic convergence to zero of both position errors and the synchronization error. Implementation of this new controller in real-time operations of commercial integrated CNC machines, highlights advantages of the proposed approach.

The use of fuzzy chip to implement the control of machining processes is investigated. The hardware solution can process rules in fuzzy controllers at high speed. In this paper, fuzzy-chip-based regular and self-tuning controllers are developed to maintain a constant cutting force during machining processes under time-varying cutting conditions. In the fuzzy-chip-based self-tuning controller, two knowledge bases are employed. One base is used to implement the inference of control rules and the other to execute tuning rules for adjusting the output scaling factor on line. The structure makes the proposed fuzzy-chip-based self-tuning controller different from those fuzzy adaptive controllers developed in machining. Those fuzzy-chip-based controllers are characterized by the simple structure and practical applicability for real-time implementation. Both simulation and experimental results on machining processes show that the fuzzy-chip-based controllers demonstrate feasibility, applicability, and adaptability.

Cutting brushes are used at relatively low speeds by various municipal vehicles and in particular road sweeping units. As the name suggests such brushes are designed to “cut” through debris, especially compacted sand or similar matter. The main deflection plane of a bristle (or tine) is along the mount radius, making the tines very stiff in the direction of rotation, hence the cutting action when the brush is rotated. Exploring the literature shows that very little is known, or understood, about the operation of brushes for mechanical sweeping. In this paper a pseudo-static discretized model is developed to investigate the deformations and forces acting on brushes during ideal operation of a horizontal brush on a flat plane. Due to the numerous different sweeper brushes on the market, one common configuration is used as the basis of the model and the paper will detail only the characteristics of this brush. The brush to be investigated is a “cutting brush,” introduced above, where the tines can only deflect along the mount radius. Having developed a model it is used to predict the forces and torques generated within a horizontally rotating brush. The influence of centrifugal force is analyzed although transient effects are neglected and steady state conditions assumed. The predictions of the model are compared to practical results taken from a test rig and the validity of the model is discussed. Agreement between the model and the practical results will be shown to be good, considering the complexities and practical realities involved in analyzing any system which is friction dependent.

Chatter occurring at more than 10,000 Hz frequency was found in fine boring operation, and causing reduced tool life. To identify the mechanism for the onset of high frequency chatter, cutting tests and structural dynamics examination of the boring tool have been performed. Experimental study has revealed that the regenerative effect, the penetration effect, and the X - Y looping of the tool tip are three relevant characteristics in the onset of the chatter. Those findings are included in a new chatter model of which validity is evaluated by computational analysis of energy supplied and dissipated in the vibrating system.

Chatter is an undesired phenomenon of self-excited vibrations that occurs during many machining operations. This paper analyzes mode coupling chatter from the point-of-view of the system theory. A simplified mathematical model of the cutting process is established, from which the equations of the system are obtained. Then, the eigenvalues and the eigenvectors of the system are evaluated, and a simple stability condition is formulated. The tool trajectories both in the stable and unstable case are studied. Finally, an example of mode coupling chatter in a machine for wood cutting and its stabilization is presented.

Piezoelectric dynamometers are generally used for force measuring. During transient period, their performance is limited because the signals they delivered are distorted by their dynamic behavior and then are different from applied force. This paper proposes a method to identify the dynamic characteristics of the dynamometer so that the distortion of the signal can be compensated leading to the actual force. This method is based on the interrupted cutting of a specially designed workpiece that provides a strong broadband excitation. The three components of the exciting force and the acceleration of the gravity center of the dynamometer cover plate are measured simultaneously. Although the input acceleration components are correlated in the frequency bandwidth of interest, the nine terms of the dynamometer transfer matrix are determined from only one cutting experiment. To assess the developed method, series of different pulse excitations are carried out. Then, the determined transfer matrix is used for dynamic cutting force compensation under some milling operations. [S0022-0434(00)01003-0]

An active vibration control system for a turning process is presented. The system employs a magnetostrictive actuator and a rate feedback control scheme to suppress the vibration caused by random excitation in the turning process. A specially designed tool holder is developed to implement the actuation and the control scheme effectively. A model which accounts for both the dynamic response of the cutting process and the control system is described. The effectiveness of the vibration control system is studied via simulation and a series of experiments. A disturbance force is applied to the system by a shaker and the dynamic response of the system is observed. The experimental data shows that the rate feedback control scheme adds additional damping to the system and reduces the vibration. A complete set of 2 4 factorial design cutting experiments were also conducted using the tool holder and experimentally obtained surface profiles were compared to surface profiles obtained without the vibration control. It is shown that the system can improve the surface texture generated by the turning process.

A new variational approach is presented for the MCDDSH process that leads to the optimal values of switching of machining cycles and feed rate. The problem is formulated as a nonclassical variational problem that best models the dynamics and control of a MCDDSH machine. Twist drills are used in the MCDDSH process considered here. All the control parameters like cutting forces, external disturbances, output quality, etc. are considered. Physical realization of the optimal strategy is achieved by taking into account the stochastic variation of system parameters. Control algorithms that yield maximum productivity are developed. Also investigated are the set of machining process states for the MCDDSH process and the specification of optimal switching positions of the machining cycles. These correspond to the appropriate optimal feed-rate that yields the best result.