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This research is motivated by the problem of regenerative chatter vibration, which is a pronounced problem in machining. The problem of chatter vibration is especially critical in the internal turning process, where the material is removed from the inner part of a rotating workpiece using a slender bar. Active mechatronic solutions to the problem of regenerative chatter vibration in internal turning are mostly given by means of piezoelectric actuators embedded into the boring bar. However, due to the volume needed for accommodation of the actuators, it is difficult to apply these solutions to narrow bars. This paper presents a novel actuation approach with a potential application for active control of regenerative chatter vibration in internal turning. This approach involves a bar whose clamping has an ability to move perpendicularly to the bar axis. In addition, it involves two actuators: one of them is placed near the bar clamping, and another one is placed at the bar clamping. The presented actuation approach is compared to the related approaches in the literature. Additionally, this paper presents a method for robustness analysis of the actively controlled cutting process, which is based on the structured singular value methodology. Experiments performed on a specially designed testbed imitating the internal turning process demonstrate the potential applicability of the introduced actuation approach, as well as the utility of presented robustness analysis method.

In this paper, Simple Adaptive Control (SAC) is applied to a Single Degree of Freedom (SDOF) Active Magnetic Bearing (AMB) testbed. The plant on which SAC is applied is required to be Almost Strictly Positive Real (ASPR). Therefore, Parallel Feedforward Configuration (PFC) design proves to be the most important step in the algorithm implementation. Here, PFC design guidelines, based on classical SISO tools (bode plots and step response), are proposed and validated experimentally. Additionally, a slowly varying, unknown disturbance rejection method is suggested within the framework of the SAC algorithm. The proposed method is also validated experimentally, on a SDOF AMB testbed.

The motivation behind this study is the problem of regenerative chatter vibration in internal turning. Regenerative chatter is an extremely undesired phenomenon in machining. This is since, in addition to causing surface finish degradation and cutting tool wear, regenerative chatter imposes a fundamental limitation on the material removal rate. In internal turning, due to the relatively low internal damping of the boring bar, regenerative chatter is especially undesired. Another factor, which reduces the material removal rate, as well as surface accuracy, is machining error. Machining error is very common in internal turning due to low boring bar stiffness. At the same time, machining error compensation has received little attention in the literature hitherto. This study proposes a control methodology for chatter vibration suppression with simultaneous compensation of the machining error in internal turning. The proposed methodology consists of three components. The first component is a newly developed method for the identification of the cutting force model parameters. The second component, which utilizes the cutting force model parameters identified in the previous step, is a robust stabilizing controller synthesis developed to address the key issues arising in the context of regenerative chatter control in the internal turning process. In contrast to the corresponding control methods reported in the literature, the control approach developed in this study accounts explicitly for the time-delayed term associated with the regenerative feature of chatter, as well as uncertainty in both cutting force and the flexible boring bar models. The last third component of the presented control methodology is a novel approach for machining error compensation, which is based on a feedforward term designed to eliminate the bar tip deflection. Every single component of the proposed control methodology can be utilized separately in the context of active control in internal turning. The potential applicability of the control methodology presented in this study is demonstrated experimentally, using an active slender bar demonstrator imitating the internal turning process. In particular, it is demonstrated that: (i) given the identified model of the boring bar, the proposed method for cutting parameters estimation allows to obtain reasonable estimations of the cutting coefficient and the overlap factor, (ii) the presented robust control system synthesis procedure allows to obtain controllers which increases the chatter immunity of the actively controlled cutting process, and (iii) the presented method for machining error compensation counteracts successfully the error due to flexible bar deflection caused by the DC component of the cutting force model.

This paper considers the set-point control problem of an uncertain six-degree-of-freedom precision positioning system, where only position measurements are available. As a solution, we present an iterative output feedback control algorithm whose learning mechanism is based on the concept of contraction mapping. Besides stability and convergence, the presented analysis includes practical aspects associated with the algorithm implementation. In particular, it is shown that: 1) the system response due to the iterative process converges to an arbitrarily small neighborhood of the desired equilibrium point, and 2) the steady-state response after each iteration is bounded inside the system traveling range. The presented control algorithm is demonstrated experimentally.

This research is motivated by the problem of regenerative chatter vibration, which is an extremely harmful phenomenon in machining in general, and in internal turning in particular. In addition to limiting the production rate and accelerating the tool wear, regenerative chatter deteriorates the surface finish, which is especially undesired in the context of precision machining. This paper presents an active control design method for slender bars with delayed excitation which can be applied to the problem of active control of regenerative chatter in internal turning. The presented control method is based on the delay-dependent output feedback controller synthesis. The contribution of the presented design approach stems from incorporating into the design procedure the delayed dynamics of the regenerative chatter, the flexible bar model uncertainty, and the hardware limitations. Furthermore, the delay dynamics is taken explicitly in the synthesis of an H ∞ output feedback controller by linear matrix inequalities. The resulting controller is tested by simulations and experiments using a testbed imitating the dynamics of the internal turning process. The results demonstrate the effectiveness of the presented controller synthesis method in comparison to the commonly used approaches.

AMB (Active Magnetic Bearing) technology based multi-degree-of-freedom positioning systems is a very promising solution to many precise motion problems. In some applications, such as the photolithography process, AMB based positioning system can be used to carry tools of unknown geometry and mass. To avoid the positioning stage tracking performance degradation due to unknown payload, adaptive control methods should be used. Although the subject of adaptive control algorithms for the AMB based rotating machinery was widely studied in the past, due to some differences, the available results can not be applied in a straight-forward manner to the precise AMB based positioning systems. This paper contributes to the field of precise AMB based positioning stages by presenting design and implementation of an adaptive control algorithm for a 1DOF (degree-of-freedom) AMB based suspension system. In this study we assume that the payload and electromagnetic coefficient values of the plant are unknown and only the output measurements are available as a feedback. In addition, the control currents computed by the presented algorithm are free of a bias term. The control law in this papers solves the trajectory tracking problem, and its effectiveness was verified experimentally.

This paper presents the concept and the practical implementation of a switch-mode power driver for the use in Active Magnetic Bearings (AMB). The switch-mode driver consists of a full-bridge capable of operating in 2-level, 3- level, or phase-shifted PWM mode. An optimal digital current- programmed mode controller lays out the foundations to a proximate-optimal, robust, large-signal dynamic response of the system under extreme cases of loading and parameters variations. In particular, the developed power driver is capable of following the desired reference for large inductance variations (due to displacement). The power stage combines a newly developed, efficient, passive-based current sensor that is capable of sensing bi-directional and near-zero currents, while being robust to exter- nal disturbances and maintaining simple and efficient structure. Performance evaluation of the power driver has been verified experimentally on a closed-loop design for a single-axis AMB platform using a dual channel prototype, controlled using a single 16-bit, low-cost microcontroller. I. INTRODUCTION