During the turning production process, a material is cut by using a specified material removal strategy in order to produce the desired final form and dimension. Tool chatter is a widespread undesired dynamic instability that arises during fundamental machining processes such as milling, drilling, and turning. The dynamic interaction of the components of the cutter tool and the surface of the material being cut is just one of the numerous process variables that can result in chatter vibrations. Usually, the vigorous turning that quickly releases the metal chip causes the cutter to oscillate excessively with respect to the workpiece. Tool chatter can result in excessive wear, a shorter tool life, poor surface quality, and misaligned geometry. Due to the poor quality of the surface finish, this can consequently result in greater prices, postponed deliveries, and even lost orders. The ability of a gain modulation-based control strategy to improve the product finish in robotic turning has been examined in this investigation along with a number of other process parameters. A two-link manipulator dynamical model has been used and numerical outcomes are presented for the efficacy of the control toward achieving an improved product surface finish.

The ultimate purpose of ongoing investigations is to clarify the similarities and differences of the deformation behavior between the metal spinning and the incremental sheet forming processes. With this research, we primarily aimed to develop and test an effective forming machine on which we can perform the dual task of metal spinning and incremental sheet forming processes to facilitate the proposed comparisons vigorously in the future. The conceptual design of the proposed machine has been decided after comprehensive comparisons between the two processes. The intended utility has been experimentally tested on shear spinning of truncated cone using position/force control.

To clarify differences between metal spinning process and incremental sheet forming process classified in incremental forming method, we developed a novel machine tool. The processing characteristics are similar on the both process. Although, it has been difficult to perform both processes on a single machine due to physical requirements are not satisfied on another process. We designed a vertical-lathe like machine equipped with an angle-controlled spindle and six-axis force sensor, according several results of structural analysis. The effectiveness of applied positional PD control with feed-forward compensations of gravity and coulomb/viscous frictions, was evaluated by shear spinning of a truncated-cone product from an aluminum disc.

Feedback control strategies are desirable for disturbance rejection of human-induced vibrations in civil engineering structures as human walking forces cannot easily be measured. In relation to human-induced vibration control studies, most past researches have focused on floors and footbridges and the widely used linear controller implemented in the trials has been the direct velocity feedback (DVF) scheme. With appropriate compensation to enhance its robustness, it has been shown to be effective at damping out the problematic modes of vibration of the structures in which the active vibration control systems have been implemented. The work presented here introduces a disturbance observer (DOB) that is used with an outer-loop DVF controller. Results of analytical studies presented in this work based on the dynamic properties of a walkway bridge structure demonstrate the potential of this approach for enhancing the vibration mitigation performance offered by a purely DVF controller. For example, estimates of controlled frequency response functions indicate improved attenuation of vibration around the dominant frequency of the walkway bridge structure as well as at higher resonant frequencies. Controlled responses from three synthesized walking excitation forces on a walkway bridge structure model show that the inclusion of the disturbance observer with an outer loop DVF has potential to improve on the vibration mitigation performance by about 3.5% at resonance and 6-10% off-resonance. These are realised with hard constraints being imposed on the low frequency actuator displacements.

This paper presents a new method to eliminate deviation in positioning caused by coil’s heat generation in magnetostrictive actuators. The advantages of the proposed system are compactness, high controllability and high reliability. The actuator package consists of Galfenol as active element and a magnification mechanism combined with a Peltier element or thermoelectric cooler (TEC). By using the temperature sensor, a thermoelectric cooler (TEC) is activated to reduce the temperature of the coil. However, the reduction of temperature by TEC alone is not enough to eliminate the error and controlling of applied voltage is also required. A simple PI controller for coil’s current is combined with TEC and by reducing the temperature and current simultaneously, the positioning error is vanished completely.

Purpose – This paper aims to investigate a novel giant magnetostrictive (GM) force sensor using Terfenol-D rod. Design/methodology/approach – First of all, principle of GM force sensor based on positive magnetostriction of Terfenol-D is presented. Then, design procedure of the GM force sensor is stated. Magnetic properties such as B-H curve and permeability of Terfenol-D are measured by a novel experimental setup and the results are used in analytical model, sensitivity estimation and numerical simulations. Then, an analytical model is presented and a numerical simulation using CST Studio Suite 2011 software is done. So as a result of numerical simulations, optimum geometry of the GM force sensor is obtained related to the condition in which the GM force sensor has highest sensitivity. After that, the sensor is fabricated using the simulation results and is tested by means of an experimental setup. Characteristic curve of the GM force sensor in several conditions is measured and the optimum operational condition is obtained considering highest sensitivity condition of the sensor. Also operational diagrams of the GM force sensor is plotted in loading and unloading conditions. Characteristics of the GM force sensor in optimum condition are presented. Findings – It was found that the GM force sensor has maximum sensitivity and maximum linearity in 0.8A current, which can be known as optimum condition of application. In this sensor, maximum sensitivity is 0.51 mV/N (while current is 0.8A), which is highest among older investigations. Originality/value – At last, theoretical, numerical and experimental results are compared and the criteria for magnetostrictive sensor design are presented.

This paper presents experimental and numerical results about the effectiveness of a beam-type twin dynamic vibration absorber for a cantilevered flexible structure carrying an unbalanced rotor. An experimental laboratory prototype setup has been built and implemented in our laboratory and numerical investigations have been performed through finite element analysis. The proposed system design consists of a primary cantilevered flexible structure with an attached dual-mass cantilevered secondary dynamic vibration absorber arrangement. In addition, an unbalanced rotor system is attached to the tip of the flexible cantilevered structure to inspect the system response under harmonic excitations. Numerical findings and experimental observations have revealed that significant vibration reductions are possible with the proposed dual-mass, cantilevered dynamic vibration absorber on a flexible cantilevered platform carrying an unbalanced rotor system at its tip. The proposed system is efficient and it can be practically tuned for variety of design and operating conditions. The designed setup and the results in this paper can serve for practicing engineers, researchers and can be used for educational purposes.

This paper presents a new analytical model for both magnetic flux density and thrust force in a DC tubular Linear Direct-Drive Motor (LDDM). Two-dimensional finite element method (FEM) is used for numerical analysis. Magnetic flux density and thrust force computed numerically shows a good agreement with the values resulted from proposed analytical model. This research, investigates the effect of some geometrical dimensions of LDDM. The sensitivity analysis of parameters highlights the influence of air gap, permanent magnet radius, coil's length of phases and thickness of back-iron. It is found that lower air gap and thinner back-iron cause higher ratio of maximum thrust force to mover's mass. Furthermore, the optimum value for coil's length is also presented. The general shape of thrust force is also confirmed by experimental results.

This paper presents a conceptual design and control of a novel Gasoline Direct Injector (GDI) using of giant magnetostricitve material, Terfenol-D, as an actuation component. Electromagnetic and fluid analyses are accomplished to investigate the influence of some parameters such as nozzle length, pressure of input fuel, cone angle of injector's needle are investigated. Experimental results obtained from fabricated GDI show a good agreement with the numerical results provided by 3D finite element analysis. Furthermore, the fabricated GDI is controlled by fuzzy and PID controllers. It is found that fuel consumption by fuzzy controller is 3.5% less than PID controller.

Chatter leaves a rough machined surface, accelerates wear of the cutter and creates unacceptably loud noise levels. A conventional approach to suppress chatter is to slow the material removal rate. Such an action is usually successful to avoid chatter, but causes increased production time and cost. Therefore, it is desirable to maintain a reasonably fast rate of production and employ a chatter control measure. In this research, a semi-active parameter control technique is investigated numerically during a robotic turning process. Investigations have been performed on a two-link robotic arm model. The control of chatter has been achieved by varying the joint stiffness in a synchronized mode with the spindle speed. Stability lobe diagrams have been compared for controlled and uncontrolled cases. Simulation results showed that significant improvements can be achieved by varying the joint stiffness of robotic structures. The proposed method is stable, effective and requires no additional hardware to implement at the actuated joints of robots.

Metal spinning is a plastic forming process in which a disk or tube of metal is rotated at high speed and forced onto a mandrel. It is widely used in industry as an efficient, modern and economical production technique. This research proposes to develop a versatile robotic forming method and expand the application areas of robotic manufacturing processes to the metal spinning area. A lathe-type laboratory setup has been built and an industrial robot manipulator has been used to implement the metal spinning process. Experiments have been conducted with enhanced cascaded trajectory tracking algorithms with an add-on vibration suppressor. The potential of the proposed method has been illustrated with extensive case studies using both constant and variable speed trajectory profiles. Analyses for the growth of wrinkles have been performed through the topographical measurements of the products and the forming forces have been inspected. Results indicate that the efficiency of the process can be significantly improved with suitably selected variable speed trajectory profiles and the process parameters. The developed scheme successfully reduces the excessive oscillations of the manipulator during the metal spinning process and it requires no additional hardware to employ. The investigations demonstrate the feasibility of robotic metal spinning using an industrial serial link manipulator.

Vibration control of a maneuvering flexible robotic arm is a challenging task in the presence of changing structural dynamics which has to deal with measurement inaccuracies and complex modeling efforts. This paper presents an effective and versatile controller for a maneuvering flexible arm. Proposed Variable Stiffness Control (VSC) is stable, due to its being dissipative in nature. The technique is suitable to be implemented as an add-on controller to existing robots, and it requires no additional hardware. Control is based on the detection of a kinematic event, peak relative displacement, rather than an accurate knowledge of structural dynamics. Hence, although there may not be a claim for the suggested control to be the most effective, it certainly represents significant practical advantages for cases where there may be structural uncertainties.

Assistive devices and exoskeletons have critical importance for people with manipulative and locomotive disabilities. One of the major purposes of such devices when used for lower extremities is to help provide the postural or gait stability of the user. However, current lower extremity exoskeletons available lack the sufficient foot support area to guarantee a safe operation for the rehabilitation of patients, and normal posture/gait for users carrying heavy loads on backpack. As a result, these devices may require an intensive control effort to supply the posture or gait stability and can demand additional therapist help during rehabilitation. In this paper, we proposed a novel adaptive foot system to enhance the required stability of lower extremity exoskeletons as an add-on device. The method essentially aims to automatically extend the support area behind the heel during walking. The proposed adaptive foot system can extend passively during stance and retract during the toe rocker phase, which allows increased support areas during stance and prevent collisions to the level ground during swing. It is practical to implement and can be employed without necessitating an actuation power. The proposed wearable system will particularly be valuable in rehabilitation for enhancing the stability where safety of patients is particularly critical. It is also anticipated that the system can be a complementary device for current exoskeletons or humanoid robots to enhance their stability. A detailed description and numerical analysis of the stability in sagittal plane is presented for postural and gait cases in this paper. Experiments have been also conducted to prove the effectiveness of the adaptive wearable device for postural and gait stability.

Robotic operations have undeniable advantages of speed and precision in machining. However, such operations are generally limited by the self-excited tool chatter problem. When uncontrolled, chatter leaves a rough machined surface, accelerates wear of the cutter and creates unacceptably loud noise levels. A conventional approach to suppress chatter is to slow the waste removal rate. Such an action is usually successful to avoid chatter, but causes increased production time and cost. Therefore, it is desirable to maintain a reasonably fast rate of production and employ a chatter control measure. A simple semi-active parameter control technique is investigated numerically in this study. The proposed method is effective and requires no additional hardware to implement at the actuated joints such as those in robotic structures.

Metal spinning is a plastic forming process in which a relatively ductile metal sheet is forced onto a rotataing mandrel by using a roller tool. This study is aimed at developing a versatile and intelligent forming process and expand the application area of robotic manufacturing processes. In this research, the metal spinning process has been accomplished with an industrial robot. Trajectory control algorothms have been implemented. The effectiveness and the applicability of the proposed method have been experimentally verified. In addition, wrinkle occurences have been experimentally analyzed with repect to spinning conditions.

Traditionally, robotic manipulators have been used extensively for repetitive manufacturing processes where their power, speed and accuracy offer significant advantages over human performance. Today, industrial automation has significantly raised the expectations from the robots in terms of their functionality and diversity of application areas. This paper aims at providing a basis for the extension of robotic applications to metal spinning process and improve its performance. Numerical predictions are presented in this paper to demonstrate the effectiveness of a control technique in providing attenuation of excessive oscillations of a multi-link arm under harmonic excitations. A dynamical model has been developed considering the nonlinearity and the gravity effects of vibrations. Variable stiffness control technique has been proposed and tested for the vibration suppression of a multi-link robotic arm model. The technique is based on actively manipulating the joint resilience. It is a stable control technique due to its being dissipative in nature and it can be used as an add-on controller. Results show that the proposed controller can significantly improve the performance of robot manipulators under excessive forced vibrations.

In order to increase the adaptability of industrial robots to broader application areas, it is required to improve the fundamental control strategies with supplementary methods to a more sophisticated level. Machining processes are one of the areas that need more advanced and robust control approaches due to the steady force requirements and inevitable feedback between the task forces and dynamics of the system. With this research, it is aimed to introduce industrial robots, as a highly versatile automation tool, to the metal spinning process and expand its application areas. An industrial robot has been used to implement robotic metal spinning process and to conduct experiments. Preliminary experimental results for an enhanced trajectory tracking algorithms are presented in this paper to provide a foundation for the expansion of robotic applications. The results show that it is feasible to perform the metal spinning process by using an industrial robot with cascaded trajectory tracking algorithms. Further improvements can be observed with the proposed cascaded control technique together with an add-on vibration suppressor, in an attempt to enhance the process and attenuate the robot's joint oscillations.

We develop a four-mount active vibration isolation system (AVIS) using voice coil actuators. The flexible body modes in the upper plate of the AVIS can cause an instability problem due to control signal whose frequency is close to the resonant frequency of the flexible modes. The loop shaping technique is applied to reduce the amplitude of the control signal. We investigate the performances of the active vibration isolation system proposed in the word in the time domain and frequency domain by comparing to the passive isolation system.

Flexible robot manipulators have numerous advantages over their rigid counterparts. They have increased payload-to-weight ratio, they run at higher speeds, use less energy and smaller actuators, and they are safer during interaction with their environments. On the other hand, light design combined with external effects result in components which can oscillate with excessive amplitudes. These oscillations cause deviation from the desired path and long idle periods between tasks in order to perform the intended operation safely and accurately. This paper is on an investigation into the effectiveness of a vibration control technique for a two-link flexible robotic arm. Variable stiffness control (VSC) technique is used to control the excessive oscillations. Owing to its dissipative nature, the technique is stable, it is relatively insensitive to significant parameter changes and suitable to be implemented on existing robots. This research considers that the source of the flexibility is either the joints or the links or both. Simulation results of the response of the arm are presented to show the versatility of the proposed control technique. Experiments are performed on a laboratory prototype and the results are presented to test the validity of simulations.