Asian Research Consortium

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1 Asian Research Consortium Asian Journal of Research in Social Sciences and Humanities Vol. 6, No. 6, June 2016, pp Asian Journal of Research in Social Sciences and Humanities ISSN A Journal Indexed in Indian Citation Index DOI NUMBER: / Category: Science and Technology Machine Tool Chatter Suppression Techniques in Boring Operation A Review Dr. S. Balamurugan*; Dr. T. Alwarsamy** Abstract *Professor and Head, Mechanical Engineering Department, Mahendra Engineering College, India. **Professor, Mechanical Engineering, Liaison Officer Directorate of Technical Education, Tamil Nadu, India. Chatter is a problem of instability in the metal cutting process. The phenomenon is characterized by violent vibrations, loud sound and poor quality of surface finish. Chatter causes a reduction of the life of the tool and affects the productivity by interfering with the normal functioning of the machining process. The problem has affected the manufacturing community for quite some time and has been a popular topic for academic and industrial research. Since then many researchers investigated to identify, characterize and suppress the tool chatter in boring operation. This paper presents a review of some of the significant contributions in the field of tool chatter suppression with a focus in boring operation. Keywords: tool chatter, boring operation, review paper, suppression techniques. 1. Introduction Vibration is an undesirable phenomenon in machining processes because it results in the reduction of material removal rate (MRR), poor surface finish and increased tool wear. Two major types of vibration occurring in machining are forced vibrations and self-excited vibrations. The imbalance of rotating members, servo instability, or force on a multi-tooth cutter may result in forced 2175

2 vibration. The cutting tool oscillates at the frequency of the cutting force. When this frequency is close to a natural frequency of the tool, large amplitude vibrations due to resonance occur. Selfexcited vibration or chatter is the most important type of vibration in machining processes. Two mechanisms known as regeneration and mode coupling are the major reasons for machine tool Chatter. The former, as shown in Figure1, is due to the interaction of the cutting force and the workpiece surface undulations produced by preceding tool passes. Regenerative chatter occurs when cuts overlap and the cut produced at time t leaves small waves in the material that are regenerated during each subsequent pass of the tool. The regenerative type is found to be the most detrimental to the production rate in most machining processes [1]. If regenerative vibrations become large enough that the tool does not contact the workpiece, another type of chatter known as multiple-regenerative chatter occurs. Figure 1 Instability Caused by Regeneration Mode coupling is produced by relative vibration between the tool and the workpiece that occur simultaneously in two different directions in the plane of cut. In fact, mode coupling usually occurs when there is no interaction between the vibration of the system and undulated surface of the workpiece. In this case, the tool traces out an elliptic path that varies the depth of cut in such a way as to bolster the coupled modes of vibrations (as shown in Figure 2). The amplitude of self-excited vibration increases until some non-linearities in the machining process limit this amplitude. Selfexcited frequency is usually close to a natural frequency of the cutting system. Figure 2 Instability Caused by Mode Coupling 2176

3 R.A. Mahdavinejad [2] calculated the critical cutting width based on regenerative mechanism in machining process by the following equation. a lim 1 2 kg ( ) (1) f c Where, k f G and are shearing strength and the real part of vibration conversion function of the system. According to the chattering theories, chatter vibrations occur at high frequencies, which are close to one of vibration modes of system. Regenerative chatter is due to a closed loop interaction between two independent entities: the machine tool structural dynamics and the dynamics of the cutting process. Any method of chatter suppression tries to influence one of the two entities, so that the ultimate goal of higher stability is achieved. Many works have been carried out to suppress regenerative chatter using both passive and active vibration absorbers. 2. Passive Chatter Suppression Passive chatter suppression is simple in structure, but the dynamic parameters of the damper used cannot be adjusted during the machining process and this leads to poor performance of damping system when the working condition changes. 3. Semi Active Chatter Suppression It is defined as passive device in which the properties like stiffness, damping, etc., can be varied in real time with a low power input. As they are inherently passive, they cannot destabilize the system. Semi active chatter suppression is superior to passive chatter suppression techniques and has limitations compared with active chatter suppression. 4. Active Chatter Suppression Controlling the vibration during machining process itself is called active vibration control. The aim of this strategy is to reduce the relative displacements between the tool and the workpiece and thus suppress chatter. Active chatter suppression allows for continuously adjustable dynamic parameters based on the feedback signals. In active damping techniques, the tool chatter has to be predicted in advance and the control signal is to be given to damper in order to suppress the chatter in on-line basis. This review paper presents of some of the significant contributions in the field of tool chatter suppression with a focus on boring operation. The vibration of the boring bar is influenced by three parameters, feed rate, cutting depth and cutting speed [3]. 2177

4 Boring bars with a high length-diameter ratio (L/D) tend to chatter. The limit of stability depends not only on the boring bar, its fixation and the machine tool, but also on the selected cutting conditions. A one dimensional model of the regenerative cutting is commonly used for simulation; however, a simple model developed by F. Kuster and P.E. Gygax [4] was able to explain the influence of only a few parameters. Attempts to estimate the boundary of cutting stability by simulations with this model often give wrong results. Therefore, F. Kuster and P.E. Gygax studied more accurate cutting model at their laboratory. Besides extension to three dimensions, the model considers the radius of curvature of the cutting tool corner. This allowed the very important differentiation between roughing and finishing work. Modeling the thrust force as an infinite summation of infinitesimal forces perpendicular to the cutting edge, its direction can be calculated. Commonly the size of the forces is estimated by an exponential law depending on the thickness of the chip. Their tests showed that this assumption can be used in dynamics also, if the area of cut and the chip thickness are modeled exactly. Their paper presented a new model and illustrates its good accuracy in the estimation of the chatter stability when comparing experimental cutting test with simulation. The interface between the boring bar and the clamping house has a significant influence on the dynamic properties of the clamped boring bar. The work by Henrik Akesson et al [5] focused on the dynamic properties of a boring bar that arise under different clamping conditions of the boring bar and are introduced by a clamping house (commonly used in the manufacturing industry). A mechanical damper has been introduced to reduce tool vibrations during the high-speed milling process by Nam H. Kim et al [6]. The mechanical damper was composed of multi-fingered cylindrical inserts placed in a matching cylindrical hole in the center of a standard end-milling cutter. Centrifugal forces during high-speed rotation press the flexible fingers against the inner surface of the tool. Bending of the tool/damper assembly due to cutting forces or chatter vibration causes relative axial sliding between the tool inner surface and the damper fingers, and dissipates energy in the form of friction work. Kim Nam H et al have presented a simple numerical method to estimate the amount of friction work during tool bending. Non-linear static finite element analysis is used to estimate normal and frictional contact forces due to centrifugal forces and cutting forces and calculate the amount of frictional work dissipated by the damper. The numerical results are compared with analytical results and showed a similar trend. Parameter studies were also carried out using the numerical model to identify the best configuration to maximize the amount of friction work. In order to improve the damping capability of boring tools, Satoshi Ema et al [7], developed an impact damper consisting of a free mass and a clearance. The impact damper has the following features: (i) small and simple in construction; (ii) easy to mount on the main vibratory systems; and (iii) no need to adjust parameters of an impact damper to the vibratory characteristics of the main vibratory systems. Various methods of equipping a boring tool with an impact damper were examined. As a result, the following two ways were adopted in their study. One is to equip a ringshaped free mass on the flank face or the top face of a boring tool using a bolt and a supplementary sleeve. The other is to equip the ring-shaped free mass along the center axis of a boring tool shank. Every boring tool can accommodate an impact damper at a position 40 mm from the cutting edge. 2178

5 Satoshi Ema et al carried out bending, impact and cutting tests, in order to investigate improvements in the damping capability of boring tools and suppression of chatter vibration using impact dampers. As a result the following points were clarified. 1. The damping capability of boring tools is considerably improved using impact dampers. 2. All three types of impact dampers used in the experiment can suppress considerably the vibration of boring tools in the vertical direction (principal force direction), but hardly at all in the horizontal direction (thrust force direction) where the amplitude is extremely small. 3. In practical use, the method of equipping an impact damper on the flank face of a boring tool is desirable. 4. Using an impact damper, it is possible to bore deeper holes in comparison with boring tools were on the market and to improve the efficiency of boring operations. Min Wang et al [8] proposed a new semi-active control method to suppress chatter, which was based on a novel design for a tunable-stiffness boring bar containing an electrorheological (ER) fluid. Using this boring bar chatter can be suppressed by continuously varying the stiffness of the bar in process after chatter is detected. It is shown experimentally that the effect on chatter suppression is obvious and chatter can be avoided if the chatter can be detected timely. Srinivasan, A.V. and McFarland, D.M narrated [9] that MR fluid exhibits some advantages over typical ER materials. Compared to ER fluids, which have high working voltages (2 5 kv) and narrow working temperatures (10 70 C), the power (1 2 A or 50W) and voltage (12 24 V) requirements for MR fluid activation are relatively small and the working temperatures ( 40 to 150 C) of MR fluid are relatively broadened. So MR fluids are more practical and suitable for machine tool applications. In addition, ER fluids are sensitive to impurities, which is not a problem for MR fluids. Katsuaki Sunakoda et al [10] presented the dynamic characteristics of magneto-rheological fluid damper with respect to magnetizing current. They selected MRF-128NB and MRF-132LD (magneto-rheological fluids) and established a relationship between the damping properties of the fluid and the amount of magnetizing current. This enables one to control MR-fluid s damping property which can be used in dampers to control the amount of vibration. Tony L. Schmitz et al [11] in their paper presented a finite element modeling approach to determine the stiffness and damping behavior between the tool and holder in thermal shrink fit connections. The continuous contact stiffness/damping profile between the holder and portion of the tool inside the holder is approximated by defining coordinates along the interface contact length and assigning position-dependent stiffness and equivalent viscous damping values between the tool and holder. These values are incorporated into the third generation receptance coupling substructure analysis (RCSA) method, which is used to predict the tool point frequency response for milling applications. Experimental validation was also provided. Li Chen Jung et [12] al in their paper presented a non intermittent machining processes that employ a rotating tool are modeled and analyzed in the rotational coordinates both to simplify the 2179

6 stability analysis and to permit an exact solution. Using rotating-bar boring to illustrate, the analytical results showed that the stability limits for boring with a rotating boring bar are quite different from those for boring with a stationary boring bar, and the experimental validation was also provided [12]. Y. Liu et al [13] proposed that the variable damping can be easily produced by a controllable damper, such as a fluid damper with variable orifices or a magnetorheological (MR) damper. They proposed a structure using two Voigt elements (each one composed of a controllable damper and a constant spring) in series to realize variable stiffness and damping. In the system the stiffness could be changed easily by damper. The proposed structure was experimentally implemented using two MR fluid dampers. The sinusoidal and random responses of 1-dof and 2-dof system showed that the proposed damping and stiffness on - off control system using MR fluid dampers exhibited good vibration isolation performance. However, because two controllable dampers were installed in series, the damping and stiffness could not be changed independently. Tewani et al [14] used an active dynamic absorber to suppress machine tool chatter in a boring bar; the vibrations of the system were reduced by moving an absorber mass using an active device such as piezoelectric actuator. Tanaka and Obata [15] suppressed the chatter of slender boring bar using piezoelectric actuators; chatter vibration signals detected by a pickup were fed to a computer. Marra et al [16] designed a controller to eliminate the vibrations in cutting operations with active piezoelectric actuators. Li et al [17] investigated the effects of varying spindle speed. Li and Hu [18] suppressed chatter vibration using a dynamic damper and Pan et al [19] proposed an intelligent chatter control strategies for a lathe machine. Wong et al [20] applied actively controlled electromagnetic dynamic absorbers. Rivin and Kang [21] described a systemic approach to the development of cantilever boring bar tooling structures. Deqing Mei et [22] al developed an innovative chatter suppression method based on a magnetorheological (MR) fluid-controlled boring bar for chatter suppression. The MR fluid, which changes stiffness and undergoes a phase transformation when subjected to an external magnetic field, is applied to adjust the stiffness of the boring bar and suppress chatter. The stiffness and energy dissipation properties of the MR fluid-controlled boring bar can be adjusted by varying the strength of the applied magnetic field. They established a dynamic model of a MR fluid-controlled boring bar based on an Euler Bernoulli beam model. In advancement to the above technique Yanqing Liu et al [23], proposed a new system in which the stiffness and damping can be independently and easily controlled. The responses of the system to the sinusoidal and random excitations were studied in numerical simulations and in experiments. Lonnie Houck III. et al [24], described a method to reduce tool vibrations by providing a flexible holder with dynamics tuned to match the boring bar dynamics. The flexible holder supports the boring bar and acts as a dynamic absorber for the boring bar. The flexible holder natural frequency is matched to the clamped natural frequency of the tool, thereby reducing the amplitude of vibration at the free (cutting) end of the bar. The authors presented an analytical solution, which applies Euler-Bernoulli beam theory and receptance coupling techniques, and a finite element model for the assembly dynamics. 2180

7 Generally the designed absorber has a fixed position while H. Moradi et al [25] dealt with optimum position of the absorber in a horizontal boring machine. The authors considered, a dynamic system containing a Tuneable vibration absorber (TVA) applied on an Euler Bernoulli beam was considered. The formulation is derived for a TVA composed of mass, spring and damper elements. The designed TVA was applied for suppression of self-excited vibrations in the boring manufacturing process in which the boring bar is modeled as a cantilever Euler Bernoulli beam. The optimum values of the absorber parameters such as spring stiffness, absorber mass and its position are determined using an algorithm based on the mode summation method. Results showed that the optimum absorber acts effectively, especially in the resonance condition. After studying the forced vibration, chatter stability was analyzed for the boring bar. The stability lobes diagrams, which indicated the critical value of width of cut, are found in the first three mode shapes of the boring bar. Results showed that at higher modes larger critical width of cut and consequently more material removal rate (MRR) can be achieved. A mechatronic system of actuators, sensors, and analog circuits is demonstrated to control the selfexcited oscillations known as chatter that occur when single-point turning a rigid workpiece with a flexible tool. The actuators and sensors must be rugged and of exceptionally high bandwidth and the control must be robust in the presence of unmodeled dynamics. Jon Robert Pratt, et al [26] presented an advanced hardware and control system design for a boring bar application to take care of nonlinear stability characterized by jump phenomenon. Critical issues related to the selection and use of piezoelectric actuators were explored and clarified by Enrico L. Colla [27] and Piotr M. Przybyłowicz [28] in their respective works. Various applications, which could inspire additional applications and new ideas involving active vibration damping with piezoelectric actuators, are presented by Enrico L. Colla in his work. Active control is a step towards realization of smart structures. These are structural entities, which in addition to serve their primary structural functionality, have integrated sensors and actuators for sensing and responding to environmental and load conditions. A typical machining scenario for an aircraft component was described by Y. Zhang and N.D. Sims [29], from which a simplified finite element model was developed. The model was used to predict the chatter stability under a variety of control regimes, and the performance compared to the openloop case. Practical issues and complications such as controller spillover and saturation are then discussed. It is concluded that active damping of thin walled workpieces could substantially improve performance when regenerative chatter is properly considered during the controller design process. The work by Amit A. Ghate [30] dealt with controlling the vibrations of a cantilever beam using piezoelectric actuators and sensors. A Finite Element Model was developed for the system taking into consideration the added mass and stiffness because of sensor/actuator mounting. Then two control strategies are applied to control the beam vibrations. These two strategies were Direct Velocity Feedback (DVF) and Modified Independent Modal Space Control (MIMSC). In the experimentation, the finite element Model was verified by comparing the natural frequencies obtained by it with those from experiments. Finally an active control experiment was performed using collocated DVF, which, within the limitations of hardware, found to add damping in the 2181

8 system as per the philosophy of DVF. The system damping was found to be increased by about 100 % with the application of control. Angela Trego et al [31] developed a technology, called Stress Coupling Activated Damping (SCAD) to reduce chatter vibration in lathe boring bar. It reduced high frequency vibrations by up to 20 db. When chatter (vibration) is introduced to the cutter, there was an immediate and visible effect on the surface being machined. L. Andren and L. Hakansson presented [32] a different method for the introduction of secondary vibration in boring bars and hence the primary vibrations produced in the tool have been reduced to some extent. One of the goals was to make the active control system applicable to a general lathe. Embedding the active parts, i.e. the actuator and accelerometer, will not only protect them from the surrounding environment but will also allow the design to be used on a general lathe provided that the mounting arrangement is relatively similar. Sanjiv G. Tewani et [33] al in their paper obtained the stability analysis of a boring bar with active dynamic absorber using the model for cutting dynamics and the theory for stability analysis. The maximum allowable width of cut was calculated as a function of the cutting speed. The threshold of stability is plotted for a typical boring bar under no control. This was then compared with the corresponding limits obtained for a boring bar with a passive absorber and with an active absorber. Emily Stone et al [34] in their paper they investigated the forces produced in dynamic metal cutting, where either the chip load varies in time, or the tool itself oscillates. They separated chatter into these two pieces by using finite element software for metal cutting developed by Third Wave Systems, Inc. called AdvantEdge, to simulate the processes. AdvantEdge is a validated software package that integrates advanced dynamic, thermo-mechanically coupled finite element numerics and material modeling appropriate for machining processes. David Singletary [35] in his paper concerned the study of vibration and chatter seen during metal cutting processes by Third Wave Systems AdvantEdge. Third Wave Systems AdvantEdge used extensively to show how force/vibration varies when altering criteria like cutting speed, depth of cut and feed rate. An AdvantEdge standard flat surface workpiece was compared to a custom made irregular surface workpiece and a custom made wavy surface workpiece [35]. L. Pettersson et al [36] found the solution to machine tool vibration in a CNC lathe by embedding piezo ceramic actuators in a standard industry tool holder and the active control of tool vibration is enabled. They explained the single-channel feedback control of tool vibration in the cutting speed direction. An alternative way to study chatter via a mechatronic simulator, without conducting actual cutting tests was presented by A. Ganguli et al [37] by the name "Hardware in the Loop". An aluminum cantilever beam is used to represent the MDOF dynamics of a turning machine and a voice coil actuator at its end generates the cutting force signal. A corner cube reflector was mounted on the other side of the tip, which was a part of a HP laser interferometer setup, acting as the displacement sensor. The 16 bit position information from the interferometer was passed on to a DSP board where the regenerative cutting process was simulated in real time. The cutting force values, thus 2182

9 calculated were fed back through the digital to analog converter of the DSP board and a current amplifier into the voice coil. Kari Tammi [38] had established a test set up environment for active vibration control of rotors, to study the dynamics of the system, and to design a control system for controlling rotor vibrations. The principal idea was to use a non-contacting magnetic actuator without a load-carrying function. According to the simulations and experiments performed, the velocity feedback control system reduced the vibration response significantly. The controller made it possible to run the rotor across the critical speed. In boring operations, the boring bar usually have vibration components in both the cutting speed and the cutting depth direction. The introduction of the control force in different angles in between the cutting speed and the cutting depth directions have been investigated by Linus Pettersson et al [39]. Furthermore control path estimates produced when the active boring bar was not in contact with the workpiece and during continuous cutting operation are compared. Linus Pettersson s experimental results indicated that the control force should be introduced in the cutting speed direction. Although the vibrations are controlled in just the cutting speed direction the vibrations in the cutting depth direction were also reduced significantly. A. Ganguli et al [40] on their paper demonstrated the effect of active damping on regenerative chatter instability for a turning operation. Two approaches are used for this purpose. In the first approach, the traditional stability analysis technique in Altintas [Manufacturing Automation, Cambridge University Press, Cambridge, 2000] and other works is adopted and a correlation between the chip shape (which is dependent on the spindle speed) and the system damping was presented [40]. C. Mei [41] in his work proposed an active controller design from wave point of view to absorb chatter vibration energy in a broad frequency band to improve machining performance of a nonrotating boring bar. In contrast to most of the current active chatter control design, the wave controller is designed based on the real distributed cutting system model. Shuaishuai Sun et al [42] developed a novel compact shock absorber with both damping and stiffness variable characteristics. The shock absorber was developed based on MR fluid through an innovative design. A mathematical model that incorporated the Bingham model was established and an optimization method was adopted to identify the parameters. The coherence of experiments and the proposed model verified the control ability of dual damping and stiffness of the shock absorber. 5. Passive Chatter Suppression Techniques F. Kuster and P.E. Gygax studied more accurate cutting model at their laboratory. Henrik Akesson et al focused on the dynamic properties of a boring bar that arise under different clamping conditions of the boring bar. Nam H.Kim et al mechanical damper is composed of multi-fingered cylindrical insert. Satoshi Ema et al developed an impact damper consisting of a free mass and a clearance. Tony L. Schmitz et al in their paper presented a finite element modeling approach. Li 2183

10 and Hu suppressed chatter by using a dynamic damper and Rivin and Kang developed a cantilever boring bar tooling structures. These techniques belong to the passive chatter suppression methods. 6. Semi Active Chatter Suppression Techniques Min Wang et al proposed a new semi-active control method to suppress chatter. Srinivasan, A.V. and McFarland, D.M narrated the development of semi active damper based on MR fluid. H. Moradi et al dealt with optimum position of the absorber in a horizontal boring machine considering a dynamic system containing a Tuneable vibration absorber. 7. Active Chatter Suppression Techniques Y. Liu. et al, proposed that the variable damping can be easily produced by a controllable damper. Deqing Mei et al developed an innovative chatter suppression method based on a magnetorheological (MR) fluid-controlled boring bar for chatter suppression. The chatter suppression methods based on the effects of varying spindle speed, piezoelectric actuator, magnetorestrictive actuator and actively controlled electromagnetic dynamic absorber belong to active chatter suppression method. 8. Conclusion Self excited vibration or chatter is the most important type of vibration in machining process. Chatter occurs when the cutting forces are modulated by changes in the uncut chip thickness, which in turn results in greater variations in the uncut chip thickness of the next tooth pass. It limits cutting depth (as a result, productivity), adversely affects surface finish and causes premature tool failure. This review paper described the various available techniques to suppress the chatter vibrations. The paper summarized active vibration control, semi active vibration and passive vibration control techniques that are available as on today in the field of machine tool chatter. To provide better understanding some of the techniques are listed for each category in the above sections. Comparing all the techniques active chatter suppression techniques are superior. Hence to provide enhanced chatter control it is necessary to follow active chatter suppression techniques in all future works. 7. References H. Moradi, F. Bakhtiari-Nejad and M.R. Movahhedy, Tuneable vibration absorber design to suppress vibrations: An application in boring manufacturing process, Journal of sound and vibration 318 (2008) pp R.A. Mahdavinejad, A step forward to chatter analysis in turning machines, 13th International Scientific conference on achievements in mechanical and material Engineering, Linus Andren, Lars Hakansson, Anders Brandt and Ingvar Claesson, Identification of Dynamic Properties of Boring Bar Vibrations in a Continuous Boring Operation, Journal of Mechanical Systems & Signal Processing 18 (2004) pp

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13 Y. Zhang and N.D. Sims, Experimental Investigation of Active Damping for Regenerative chatter suppression in high-speed milling, Proceedings of ICMEM2005: International Conference on Mechanical Engineering and Mechanics, Nanjing, China (2005) pp Amit A. Ghate, Seshu. P Active vibration control of a smart beam, Proceedings of the SPIE 5062 (2003) pp Angela Trego, Paul F. Eastman, William F. Pratt, and C. G. Jensen, Reduced boring bar vibrations using damped composite structures, Proceedings of the 1995 Design Engineering Technical Conferences 3 (1995) pp Linus Andren, Lars Hakansson, Anders Brandt and Ingvar Claesson, Identification of Dynamic Properties of Boring Bar Vibrations in a Continuous Boring Operation, Journal of Mechanical Systems and Signal Processing, Vol. 18(2004) pp Sanjiv G. Tewani, Keith E. Rouch and Bruce L. Walcott, A Study of cutting process stability of a boring bar with active dynamic absorber, International Journal of Machine Tools & Manufacture 35 (1995) pp Emily Stone, Suhail Ahmed, Abe Askari & Hong Tat, Investigations of Process Damping Forces in Metal Cutting, Journal of Computational Methods in Science and Engineering (2005) David Singletary, Vibration and Chatter Analysis Using Third Wave Systems AdvantEdge, Engineering Seminar MANE6900HEG, Rensselaer Hartford, Spring (2006) pp Linus Pettersson, Lars Hakansson, Ingvar Claesson, Sven Olsson, Active Control of Machine-Tool Vibration in a CNC Lathe Based on an Active Tool Holder Shank with Embedded Piezo Ceramic Actuators The 8th International Congress on Sound and Vibration, Hong Kong SAR, China( 2001). A. Ganguli, A. Deraemaeker, M. Horodinca and A. Preumont, Active damping of chatter in machine tools Demonstration with a "Hardware in the Loop" simulator, Proceedings of Institution of Mechanical Engineers, Part I: Journal of systems and control Engineering 219 (2005) pp Kari Tammi, Jari Hatonen and Steve Daley Novel adaptive repetitive algorithm for active vibration control of a variable-speed rotor, Journal of Mechanical Science and Technology 21 (2007) pp Linus Pettersson, Lars Hakansson, Ingvar Claesson and Sven Olsson, Active Control of Boring Bar Vibration in Cutting Operations, International Conference on Sound and Vibration 9, Orlando, Florida, USA (2002). A. Ganguli, A. Deraemaeker and A. Preumont, Regenerative chatter reduction by active damping control, Journal of sound and vibration 300 (2007) pp C. Mei, Active regenerative chatter suppression during boring manufacturing process, Journal of Robotics and Computer -integrated manufacturing 21 (2005) pp

14 Shuaishuai Sun, Huaxia Deng, Haiping Du, Weihua Li, Jian Yang, Guiping Liu, Gursel Alici, and Tianhong Yan, A Compact Variable Stiffness and Damping Shock Absorber for Vehicle Suspension, IEEE/ASME transactions on Mechatronics October