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Knowledge of material removal behavior and generated surface characteristics are crucial to improve grinding performance. A finite element model was developed using a single grit approach with the consideration of uncut chip thick variations along the grain path. It was found that the increase in cutting speed and the decrease in rake angle led to the generation of discontinuous chips in adiabatic shearing conditions. Besides, the larger shear stresses induced by friction in the grain-chip interface contributed to the formation of chips with larger discontinuities. The enlargement of subsurface damage (SSD) depth by 23.86% and 129.42% was caused by the increase in grain edge radius from 0.5 to 2.5 μm and the rise in maximum uncut chip thickness from 0.5 to 1.5 μm, respectively. However, the SSD depth firstly decreased, and then increased with the approach to more negative rake angles and larger cutting speeds. A multi-response optimization based on analysis of variance (ANOVA) and SSD predictive model calculated the optimum combination of influential parameters as maximum uncut chip thickness of 0.719 μm, cutting speed of 80 m/s, cutting edge radius of 0.5 μm, and rake angle of − 30°. This led to the minimum SSD depth of 0.406 μm and the maximum removal rate of 57.493 mm3/mm s. The experimental results confirmed the positive contribution of an eco-friendly nanofluid minimum quantity lubrication (NMQL), containing graphene nanoplatelets with 0.3 wt% concentration within the green nanofluid, to the significant improvement of surface roughness (by 41.09%, relative to dry grinding) and morphology.

Zirconia has been used in medical applications since last few years and an optimum and cost-effective condition in grinding zirconia has drawn industrial attention. This paper aimed to improve and control the surface integrity, flexural strength and grinding cost in grinding partially stabilized zirconia (PSZ) using a diamond grinding wheel. The phase transition and grindability of PSZ were also evaluated. Ground surfaces analysis shows that all samples subjected to the grinding presented an increase in surface integrity, and the subsurface damages 100 below the surface were reduced from 3.4% to 0.9%. The flexural strength using 3 point bending test (3PB) shows that grinding increased the flexural strength more than 29% which is the result of higher surface integrity. The ground surfaces were analyzed using X-ray diffraction (XRD) and the results shows that T-M phase transition trend is in accordance with the surface integrity. In other words, XRD analyses prove that T-M phase transition results in higher flexural strength and surface integrity. It was also observed that in the best condition, the grinding cost was reduced by 72%. It can be concluded that controlling the grinding condition in grinding PSZ will result in the increase of the surface integrity and flexural strength. A mathematical model was created to find an optimum condition using response surface method (RSM). It is observed that feed rate has greater effect on the outputs rather than depth of cut.

Nowadays, in addition to technical efficiency, the demands for environmentally-friendly machining processes have increased. In this context, development of an efficient strategy for machining of ceramic matrix composites (CMCs) has found crucial importance. CMCs exhibit outstanding properties, especially under harsh and severe conditions. Machining of CMCs, however, suffers from several disadvantages such as substantial costs, high tool wear, poor surface quality and low material removal rate, highlighting the need for optimization and development of efficient machining strategies. Due to extreme hardness of the ceramic matrix, grinding with diamond abrasives is inevitable. The grinding variables and the coolant-lubricant medium play significant roles in reduction of the energy dissipation and improving the finishing quality. Among coolant-lubricant types, minimum quantity lubrication (MQL) technique, which is known as an inexpensive and environmentally-compatible grinding process, can give the best results. In comparison with dry grinding condition, 37.95% reduction in cutting force, 75.93% reduction in surface roughness, and 150% increase in grinding efficiency have been achieved by MQL method. Considering MQL as the optimum coolant-lubricant medium, four machining strategies were developed using desirability function method in which efficiency, quality, and productivity were studied. Moreover, microstructure analysis and also cutting mechanism of grinding process for different types of fiber orientation have been investigated.

Subsurface damage (SSD) is a predominant type of damage in grinding process of optical materials with direct effect on the optical components performances. A series of cup wheel grinding trials were carried out on optical glass BK7 under different grinding parameters to evaluate their impacts on SSD and surface roughness. The SSD depths of ground specimens were measured by the wedge chemo-mechanical polishing (W-CMP) method. The modified model of Lambropoulos, proposed by Li, was applied considering the ductile regime effect. Besides, a three-dimensional model was established based on the coupled finite element method (FEM) and smoothed particle hydrodynamics (SPH) to simulate the grinding-induced SSD in optical glass BK7. The experimental results were compared with the theoretical model and simulations which showed a good agreement. Therefore, both the theoretical and simulation models could be used for fast and nondestructive evaluation of SSD. Also, a novel method was applied to calculate the crack length of a SEM micrograph through image processing technique.

Grinding is one of the most complex and precise machining operations, with the performance of the grinding wheel being heavily reliant on its surface conditions. Removed chips tend to be forced back to the wheel surface due to the intense heat generated in the grinding zone. The loaded chips block the wheel's grinding capability, resulting in increased grinding force and temperature, wheel chatter, and workpiece thermal degradation. To solve these problems, this research examines the effectiveness of an auxiliary compressed air jet system during the grinding of spk tool steel with an alumina grinding wheel to clean the wheel surface of lodged chips and then the percentage of wheel loading for different tests will also be evaluated. The compressed air nozzle was examined from a variety of perspectives (0, 30, 45, and 60). Grinding with and without a cleaning system, as well as conventional cutting fluid, were also employed as comparisons. In certain output results, input parameters such as grinding wheel speed (20 m/s), cutting depth (20 m), and feed rate (100 mm/s) were maintained constant. When compared to other experiments with different cleaning nozzles, the optimal inclination angle of 45°, which allows the maximum air to reach the interface between the wheel surface and chips, removed chips by pushing them off the wheel surface. Other cleaning nozzles, such as 0°, 30°, and 60°, were less successful. The incidence angle of 45° produced the best results in terms of surface roughness, diametrical grinding wheel wear, G-ratio, tangential forces, specific energy, and wheel loading analysis. Image processing was used to detect and identify chips accumulated between abrasive grains on the wheel surface. To better understand the structure of the wheel and workpiece surface, optical and scanning electron microscopy pictures were taken and analyzed. This research adds to our understanding of the grinding wheel loading mechanism and its dynamics.

Grinding operation is one of the most complex and accurate machining processes whose performance is highly dependent on the surface conditions of the grinding wheel. As the friction between abrasive grains and the workpiece results in a large amount of heat, the use of coolant can prevent the workpiece surface from burning, microstructure alteration, subsurface damages, and hardness variation. To get better the cleaning of the abrasive grains on the surface of the wheel during the grinding process, this paper is focused on the performance of an auxiliary compressed air jet system during grinding of hard-to-grind materials. Moreover, the wheel loading of the grinding wheel will also be evaluated. Different incident angles of the compressed air nozzle (0˚, 30˚, 45˚, and 60˚) were examined. Furthermore, conventional flood coolant, as well as drying with and without a cleaning system, was applied for comparison purposes. Surface roughness, tangential forces, specific energy, wheel loading analysis, and SEM images were evaluated where the incident angle of 45˚ led to the best results. Wheel loading resulted in the accumulation of chips between abrasive grains to the top of cutting grains. Detection and identification of loading has been operated based on image processing technique.

Magnetorheological fluid is composed of micro-size carbonyl iron (CI) particles for polishing of optical substrates. In this paper, the corrosion resistance of carbonyl iron (CI) particles modified with three inorganic thin films based on rare earth elements, including cerium oxide (CeO2), lanthanum oxide (La2O3) and praseodymium oxide (Pr2O3), was investigated. The morphology and chemistry of the CI-Ce, CI-Pr and CI-La particles were examined by high resolution Field Emission-Scanning Electron Microscopy (FE-SEM), X-ray energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests were carried out to investigate the corrosion behavior of CI particles in aquatic environment. In addition, the Vibrating Sample Magnetometer (VSM) technique was utilized for determination of magnetic saturation properties of the coated particles. Afterwards, gas pycnometry and contact angle measurement methods were implemented to evaluate the density and hydrophilic properties of these particles. The results showed that deposition of all thin films increased the hydrophilic nature of these particles. In addition, it was observed that the amount of magnetic saturation properties attenuation for Pr2O3 and La2O3 films is greater than the CeO2 film. The EIS and polarization tests results confirmed that the CI-Ce had the maximum corrosion resistant among other samples. In addition, the thermogravimetric analysis (TGA) showed that the ceria coating provided particles with enhanced surface oxidation resistance.

Ceramic matrix composites (CMCs) are a new class of high-technology materials that can be utilized in hot-zone structures and as a lightweight replacement for metallic superalloys. CMCs offer low density, high hardness, and superior thermal and chemical resistance which make them highly attractive in a vast array of applications. Nevertheless, the high hardness, as well as the inhomogeneous structure of the CMCs, causes unstable processes and high tool wear when machining. In this research, MQL grinding, known as an economical and environmentally friendly grinding process, was accomplished and its efficiency was compared with conventional fluid and dry grinding. Along with obtaining of comprehensive results, the effects of main grinding parameters, such as cutting speed, feed speed, and depth of cut, on the grinding forces, specific grinding energy, wheel wear, surface roughness, and integrity were analyzed. The results showed that MQL grinding reduced the grinding forces and specific grinding energy. As a result, wheel wear was lowered and G-ratio was increased. In addition, the surface generated by MQL grinding was smoother than fluid grinding and significantly better than dry grinding.

Piezoelectric actuators are one of the most popular actuators in micro- and nano-applications. The main deficiency of these actuators is the hysteretic behavior. Hysteresis not only can destroy the positioning accuracy, but also may lead to instability. In previous researches, hysteresis in the mechanical domain (voltage–position) has been modeled and compensated by several approaches. The limiting condition has been position measurement by a high cost, fine resolution sensor. So, an alternative idea can be compensation in the electrical domain (voltage–charge). In fact, it can be demonstrated that hysteresis compensation in the electrical domain can simultaneously compensate the mechanical one. But, experimental results depict that voltage–charge relation may be time dependent due to low internal impedances. It would lead to “time-dependent hysteresis”. As a result, conventional models cannot be applied for hysteresis identification. In this paper, a modified time-dependent Prandtl–Ishlinskii model is proposed to identify the time-dependent hysteresis in low impedance actuators. Utilizing the proposed model, experimental results validate that the mechanical hysteresis would be appropriately compensated as a result of compensation in the electrical domain.

The application of linear motor-driven stages as the feed drivers of CNC micro milling machine tools is growing. In addition to employ high speed and high precision equipment such as linear motor-driven stages, the precision of the machined contours is highly dependent on the capabilities of the servo controllers. In this paper, the design of a precise controller for a two-axis LMDS has been investigated for micro-milling applications. In such feed drives, disturbances such as friction, force ripples, and machining forces have adverse effects on the workpiece positioning precision due to the direct drive concept behind them. Therefore, in order to have an acceptable transient response and disturbance rejection properties, a two-degree-of-freedom proportional–integral–derivative controller was employed for each axis. To design this controller, the zero-placement method was used. To compensate disturbances and machining contour errors, the utilization of Kalman filter observers, neural networks, cross-coupled controllers, and different integration of them were studied. The controllers were experimentally examined for circular motions. An integrated controller consisted of a Kalman filter disturbance observer, a cross-coupled controller, and a well-designed two-degree-of-freedom proportional–integral–derivative controller resulted in a high contouring and tracking precision. The controller could also reduce the spikes caused by the friction at the motion reversal points such as the quadrants in circle trajectories.

Piezoelectric cantilever actuators are widely used in micro/nano-positioning applications due to their relatively accurate response and large operating bandwidth. One of the main obstacles in the way of implementing high-accuracy position tracking in high frequencies is the piezoelectric hysteresis phenomenon. It is known from previous research that piezoelectric materials exhibit a rate-dependent hysteresis loop. The purpose of this article is to obtain a novel hysteresis model that can accurately describe the output of the piezoelectric actuator. This is done by introducing a hysteresis model in the form of an actuated linear dynamic system. This model provides the ability to capture both rate-dependence and magnitude characteristics of the system, and it is simple and easy to implement in real-time. As a result, the proposed method accurately predicts the position of the piezo-actuated beam in a wide range of input frequencies and amplitudes. To demonstrate its effectiveness, the proposed hysteresis model is used along with a robust control loop to track the position of a piezo-actuated beam plant. It is shown using experimental results that utilizing this model leads to accurate position control in a wide range of frequencies.

The electro-hydraulic servo system (EHSS) demonstrates numerous advantages in size and performance compared to other actuation methods. Oftentimes, its utilization in industrial and machinery settings is limited by its inferior efficiency. In this paper, a nonlinear backstepping control algorithm with an energy-saving approach is proposed for position control in the EHSS. To achieve improved efficiency, two control valves including a proportional directional valve (PDV) and a proportional relief valve (PRV) are used to achieve the control objectives. To design the control algorithm, the state space model equations of the system are transformed to their normal form and the control law through the PDV is designed using a backstepping approach for position tracking. Then, another nonlinear set of laws is derived to achieve energy-saving through the PRV input. This control design method, based on the normal form representation, imposes internal dynamics on the closed-loop system. The stability of the internal dynamics is analyzed in special cases of operation. Experimental results verify that both tracking and energy-saving objectives are satisfied for the closed-loop system.

Gas metal arc welding (GMAW) process is one of the most widespread welding processes in industries and using robots to manipulate the welding torch leads to excellent production quality, reliability, efficiency, and cost-effectiveness. In the previous researches, the automatic GMAW system including robotic arm, moving workpiece table and vision capability are developed for real-time seam tracking and welding of complex parts. Despite a precise tracking result achieved by the robotic methods, the welding metal deposit is uncontrolled and generates a varying bead shape on the seam. This problem comes from the variable relative speed between the torch and the curved seam and deteriorate the welded product mechanical properties. In this article, a novel approach is proposed to adjust the GMAW parameters in real-time according to the measured relative speed. Based on the process affecting parameters, a control algorithm is designed. Then some mechatronic elements are added to the system to accomplish the process control. The experimental results indicate the approach efficiency on the bead shape uniformity.

This paper presents a study on electro-hydraulic servo system for the purpose of position control using a compatible linear model. The system has high level of nonlinearity and linearization introduces extra error in system model. In order to reduce this error several methods of linearization uncertainty are discussed. In spite of applying Taylor's series for all methods, several procedures are used for considering uncertainty on linearization constants. In the first procedure, a simple bound is considered for each linearization constant. In the second procedure, a polytope is extracted for the uncertainty by a graphical method. Finally, a procedure with less conservativeness and less restriction is proposed. This procedure is used to extract the linear model of the electro-hydraulic servo system for the task of position control. The resulting model is used to synthesize an output-feedback H∞ controller for the EHSS using a Linear Matrix Inequality (LMI)-based approach. The effectiveness of the proposed method is demonstrated by simulation and experimental results. The results showed that the procedure is less conservative and has the fastest operation without any overshoot.

Electro-hydraulic servo systems (EHSS) are used in many industrial applications for position and force control. Force control with a hydraulic actuator is challenging and requires complicated control algorithms used along with high crossover frequency electro-hydraulic valves, even for simple force control tasks. In this paper, a different hydraulic structure is proposed to improve the force tracking quality and increase efficiency in the EHSS. This comes at the cost of a new model with linearization and uncertainty challenges. To address these challenges, a robust H∞ control design approach is followed to control the proposed EHSS. Model linearization uncertainties are approximated by a polytope and a robust controller is designed to keep the system stable and satisfy the H∞ performance conditions within this polytope. Experimental results verify that the objectives of the paper are satisfied after using the proposed system.

Subsurface damages and surface roughness are the two significant parameters which determine the efficiency of optical components. In this study, a cup diamond wheel is used in grinding process of the specimens made of Zerodur® glass–ceramic, to investigate the influences of grinding parameters on the SSD and SR. The grinding parameters used in this study are depth of cut, cutting speed and feed rate; and effects of these parameters are studied. The experimental results are compared with the modified model of Lambropoulos, proposed by Li, and a good accordance is observed between them. Two measuring techniques were used to study the SSD. Cross-sectional polishing method and angle polishing method; the first one, suitable for studying the material removal mechanism and the other one convenient for examining the depth of subsurface damages and distribution of micro-cracks in the ground surface, respectively. A novel technique is introduced to measure the cracks length in which the sum of all cracks in a specific area of a SEM micrograph is calculated by image processing method and regarded as a factor to study the cracks length. Also, a statistical model is developed in order to predict the surface roughness and a good agreement is observed between the experimental results and the predicted values.

Among the prevalent methods in linear bilateral teleoperation systems with communication channel time delays is to employ position and velocity signals in the control scheme. Utilizing force signals in such controllers significantly improves performance and reduces tracking error. However, measuring force signals in such cases, is one of the major difficulties. In this paper, a control scheme with human and environment force signals for linear bilateral teleoperation is proposed. In order to eliminate the measurement of forces in the control scheme, a force estimation approach based on disturbance observers is applied. The proposed approach guarantees asymptotic estimation of constant forces, and estimation error would only be bounded for time-varying external forces. To cope with the variations in human and environment force, sliding mode control is implemented. The stability and transparency condition in the teleoperation system with the designed control scheme is derived from the absolute stability concept. The intended control scheme guarantees the stability of the teleoperation system in the presence of time-varying human and environment forces. Experimental results indicate that the proposed control scheme improves position tracking in free motion and in contact with the environment. The force estimation approach also appropriately estimates human and environment forces.

In micromanipulation applications, controlling the force exerted on the object is of great importance. In such cases, any uncontrolled forces may damage the object or cause system failure. However, the presence of disturbances such as impedance uncertainties and hysteresis can strongly degrade force control performance and even lead to instability. Therefore, accurate force control when internal and external disturbances occur is a significant challenge. Conventional control methods usually have a number of restrictive conditions especially on the disturbance bounds. To rectify those issues, a modified robust disturbance rejection-based force control approach is proposed in this paper. For this purpose, an appropriate disturbance observer is utilized to estimate the disturbance effect regardless of amplitude. Then a robust control method is employed to achieve the disturbance-free desired dynamic. A modification is also performed to rectify the need for acceleration measurement in the control design. Finally, the force control for an unknown environment in the presence of disturbances is accomplished. The efficiency of the proposed approach is evaluated through simulation studies and compared with the well-known PI method. The experimental results validate the force control performance for the micropositioning piezoelectric actuator.

Bimorph Piezoelectric Cantilevered (BPC) actuators have been of increasing interest in micro-manipulation processes during recent years. Due to properties such as transverse vibration, the performance and manoeuvrability have considerably improved, compared with conventional longitudinal piezoelectric actuators. Therefore, dynamic modelling of such actuators has been the centre of attraction. For this purpose, a target point on the actuator, e.g. the cantilever end tip, is usually considered as the actuator output. One degree of freedom lumped and continuous type dynamic models have been considered in prior research works. These types of modelling lead to two significant issues. First, the effect of higher vibrational modes in the actuator output is disregarded. Second, a minimum phase dynamic system is achievable for all target points regardless of position. In this paper, these two issues will be analytically and experimentally investigated. To this end, a linear continuous dynamic model for a general B...

Self-sensing actuation has been extensively used in vibration control of flexible structures over the last three decades. Positive position feedback controller has been commonly used in this field due to the robustness against spillover phenomena. Piezoelectric clamped capacitance is the most important parameter that affects the performance of this technique. In this study, the effect of capacitance change on performance and stability of a self-sensing system with positive position feedback controller is investigated. Based on this analysis, some modifications are suggested to increase the stability of the closed-loop system against capacitance change. An online Fourier transform–based capacitance measurement method is used, which guarantees good performance and stability of closed-loop system in the presence of capacitance change. Experimental results are also presented to show the effectiveness of this method in vibration control of cantilever beam.

Precise control of piezoelectric actuators used in micropositioning applications is strongly under the effect of internal and external disturbances. Undesired external forces, unmodelled dynamics, parameter uncertainties, time variation of parameters and hysteresis are some sources of disturbances. These effects not only degrade the performance efficiency, but also may lead to closed-loop instability. Several works have investigated the positioning accuracy for constant and slow time-varying disturbances. The main concern is controlling performance and also the presence of time-varying perturbations. Considering unknown source and magnitude of disturbances, the estimation of the existing disturbances would be inevitable. In this paper, a compound disturbance observer-based robust control is developed to achieve precise positioning in the presence of time-varying disturbances. In addition, a modified disturbance observer is proposed to remedy the effect of switching behaviour in the case of slow time variations. A modified Prandtl–Ishlinskii (PI) operator and its inverse are utilized for both identification and real-time compensation of the hysteresis effect. Experimental results depict that the proposed approach achieves precise micropositioning in the presence of estimated disturbances.

Wheel loading entails chip accumulation in porosities between grains or welding to the top of cutting grains. It is considered one of the most prevalent problems in grinding nickel-based super alloys. Utilizing separate jet cleaning systems can significantly reduce wheel loading. In this study, a separate high-pressure coolant was supplied through a nozzle towards the wheel surface to flush out the chips. The effects of various wheel cleaning parameters on the loaded area to wheel surface ratio in relation to grinding performance were examined. It was observed that the lowest wheel loading was achieved at a nozzle standoff distance of 70 mm from the wheel’s surface. Nozzle stream direction had no significant effect. Increasing flow rate and jet speed led to a significant decrease in wheel loading and corresponding specific energy until a threshold value was reached. Furthermore, the loaded area to wheel surface ratio was reduced by 100 % and the corresponding specific energy by up to 30 % when the wheel cleaning system was employed.