N.A. Mardi

Load and Stress Analysis for the Swash Plate of an Axial Piston Pump/Motor

In an axial piston pump design, the swash plate plays an important role in controlling the displacement of the pump, especially in a closed loop system. In this paper, the axial piston pump is incorporated into the design of a hydraulic regenerative braking system for hybrid vehicles. The pump in this configuration should function in dual mode, as a pump and as a motor. For this to occur, the swash plate should swing in two opposite directions. The swash plate presented in this paper is designed for stability and ease of control. Analytical analysis of torque and forces were conducted using MATLAB software to verify the motion of the swash plate. Furthermore, finite element analysis was also carried out to evaluate the rigidity and stress in the system. The analytical evaluation has shown that as the swash plate angle increases, the required control force and torque increase almost linearly. However, the change of the plate angle was found to have no effect on the force exerted on the X-axis and the torque exerted on the Z-axis.

Subspace-based Model Predictive Control of time-varying systems

This paper presents an approach to constrained Subspace-based Model Predictive Control (SMPC) of time-varying systems. The central ideas are to find the predictive control law recursively using a subspace identification technology, and to update the control law once a plant-model mismatch is detected. Within this framework, the proposed control law ensures that enough excitation is applied to the system when mismatch occurs, without violating the control constraints. Additionally, an implementation of a variable forgetting factor is used to facilitate faster convergence when plant changes. A simulation example is used to demonstrate the efficacy of the proposed approach.

Comparison of reconstructed rapid prototyping models produced by 3-dimensional printing and conventional stone models with different degrees of crowding

Introduction Rapid prototyping models can be reconstructed from stereolithographic digital study model data to produce hard‐copy casts. In this study, we aimed to compare agreement and accuracy of measurements made with rapid prototyping and stone models for different degrees of crowding. Methods The Z Printer 450 (3D Systems, Rock Hill, SC) reprinted 10 sets of models for each category of crowding (mild, moderate, and severe) scanned using a structured‐light scanner (Maestro 3D, AGE Solutions, Pisa, Italy). Stone and RP models were measured using digital calipers for tooth sizes in the mesiodistal, buccolingual, and crown height planes and for arch dimension measurements. Bland‐Altman and paired t test analyses were used to assess agreement and accuracy. Clinical significance was set at ±0.50 mm. Results Bland‐Altman analysis showed the mean bias of measurements between the models to be within ±0.15 mm (SD, ±0.40 mm), but the 95% limits of agreement exceeded the cutoff point of ±0.50 mm (lower range, −0.81 to −0.41 mm; upper range, 0.34 to 0.76 mm). Paired t tests showed statistically significant differences for all planes in all categories of crowding except for crown height in the moderate crowding group and arch dimensions in the mild and moderate crowding groups. Conclusions The rapid prototyping models were not clinically comparable with conventional stone models regardless of the degree of crowding. HighlightsThree‐dimensional printing (3DP) and conventional study models were compared.Measurements were generally significantly different regardless of the type of crowding.The mean biases were within ±0.15 mm (SD, <0.40 mm) but were significantly different (P <0.05).The 95% limits of agreement were beyond the acceptable clinical significance set at ±0.50 mm.The 3DP models produced were not clinically acceptable alternatives for linear measurements.

A PC-based simulation platform for a quadcopter system with self-tuning fuzzy PID controllers

Nowadays, engineers rely on simulation environments to get fast, accurate results to develop complex engineering systems. This paper presents a simulation platform that is useful for students to investigate quadcopter systems. Based on real‐time simulation results, the performance of the quadcopter under self‐tuning fuzzy PID controllers was compared and further investigated.

Motion control of a two-axis linear motor-driven stage in the micro-milling process:

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.

Transparency Improvement by External Force Estimation in a Time-Delayed Nonlinear Bilateral Teleoperation System

Teleoperation systems have been developed in order to manipulate objects in environments where the presence of humans is impossible, dangerous or less effective. One of the most attractive applications is micro telemanipulation with micropositioning actuators. Due to the sensitivity of this operation, task performance should be accurately considered. The presence of force signals in the control scheme could effectively improve transparency. However, the main restriction is force measurement in micromanipulation scales. A new modified strategy for estimating the external forces acting on the master and slave robots is the major contribution of this paper. The main advantage of this strategy is that the necessity for force sensors is eliminated, leading to lower cost and further applicability. A novel control algorithm with estimated force signals is proposed for a general nonlinear macro-micro bilateral teleoperation system with time delay. The stability condition in the macro-micro teleoperation system with the new control algorithm is verified by means of Lyapunov stability analysis. The designed control algorithm guarantees stability of the macro-micro teleoperation system in the presence of an estimated operator and environmental force. Experimental results confirm the efficiency of the novel control algorithm in position tracking and force reflection.

Investigation of layer thickness effect on the performance of low-cost and commercial fused deposition modelling printers

Abstract Rapid prototyping is one of the common technologies in additive manufacturing. The layer-by-layer mechanism of rapid prototyping allows this technology to rapidly create and print complex geometries from three-dimensional models of any objects. Fused deposition modelling is one of the common processes in rapid prototyping, and its maturity has given birth to full-scale, commercial fused deposition modelling machines, as well as low-cost, fused deposition modelling machines, which are also referred to as three-dimensional printers. This work compares the effect of layer thickness during printing on the tensile and compressive strengths of samples, for commercial and low-cost fused deposition modelling machines. Standard samples based on ASTM D638 and ASTM D695 were prepared for the tensile and compressive tests, with layer thicknesses of 0·3302 and 0·2540 mm, using acrylonitrile butadiene styrene as the printing material. From the tensile tests, specimens prepared using low-cost fused deposition modelling managed to obtain only 41·87 and 54·69% of the ultimate tensile strength of specimens prepared using commercial fused deposition modelling, for layer thicknesses of 0·3302 and 0·2540 mm. Meanwhile, from the compressive tests, specimens prepared using low-cost fused deposition modelling managed to obtain only 75·55 and 73·79% of the ultimate compressive strength of specimens prepared using commercial fused deposition modelling, for the same layer thicknesses. Ultimately, low-cost fused deposition modelling still needs more improvement in order to give better results, compared to the currently available commercial-grade fused deposition modelling printers.

Charge-based hysteresis compensation in low impedance piezoelectric actuators by a modified Prandtl–Ishlinskii model

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.

Modified robust external force control with disturbance rejection with application to piezoelectric actuators

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.

Erratum to: Evaluation of the Mechanical Properties of AA 6063 Processed by Severe Plastic Deformation

DAVOUD MASHHADI JAFARLOU, Researcher, and NOOR AZIZI BIN MARDI, Senior Lecturer, are with the Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia, and also with the Centre of Advanced Manufacturing & Material Processing (AMMP), 50603 Kuala Lumpur, Malaysia. ERFAN ZALNEZHAD, Assistant Professor, is with the Department of Mechanical Convergence Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, 133-791 Seoul, Korea. Contact e-mail: erfan@hanyang.ac.kr ABDELMAGID SALEM HAMOUDA, Professor, is with the Mechanical and Industrial Engineering Department, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar. GHADER FARAJI, Assistant Professor, is with the School of Mechanical Engineering, College of Engineering, University of Tehran, 11155-4563 Tehran, Iran. MOHSEN ABDELNAEIM HASSAN MOHAMED, Associate Professor, is with the Department of Mechanical Engineering, Faculty of Engineering, University of Malaya and Centre of Advanced Manufacturing & Material Processing (AMMP), and also with the Department of Mechanical Engineering, Faculty of Engineering, Assiut University, Assiut 71516, Egypt. The online version of the original article can be found under doi:10.1007/s11661-015-2806-7. Article published online April 7, 2015