Transactions of the Canadian Society for Mechanical Engineering

Volume 33 (2009), Issue 3

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The flow around two circular cylinders of equal diameter in tandem arrangement was investigated numerically using the finite volume method in the present study. The code was validated by comparison with previous works at the Reynolds number of 200. A systematic investigation of the relationships of Strouhal number and the aerodynamic forces with cylinder separation and Reynolds number was done. Results demonstrate not only the important combined effects cylinder separation and Reynolds number on the wake aerodynamics, but also on the relative strengths of the forces acting on the two cylinders (both mean and fluctuations).

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The mixing homogeneity of powders has a significant influence on the quality of composites fabricated from a powder metallurgy process. The factors that influence the homogeneity include the powder mixer, the medium, and the ball-milling procedure. In this paper, the influences of powder mixers and mixing media on the quality of tungsten-particle reinforced copper matrix composites are studied. Apart from dry mixing, other media used in the wet mixing process include n-butyl alcohol, camphor oil, and paraffin oil. Comparisons on mixing feature are made to a TURBULA® mixer and a Random mixer. The TURBULA® mixer is commercially available, and the Random mixer is an in-house designed machine. Our results show that using paraffin oil as the mixing medium, one may obtain optimal homogeneity in the composites. The Random mixer is superior to the TUBULA® mixer due to the fact that the Random mixer offers an avalanching motion creating pure shear forces onto the powders.

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In this paper, we present experimental results of implementing five bilateral control schemes, widely used for electro-mechanical systems, to a hydraulic actuator. The goal is to investigate the applicability of each control scheme to a hydraulic actuator and compare their performances on a common system. The considered schemes are ‘force reflection’, ‘position error’, ‘shared compliant control’, ‘force reflection with passivity’ and ‘four channels architecture’ schemes. The evaluation is conducted in terms of position tracking, force tracking, and fidelity of perceived stiffness by the operator. It is shown that force reflection and four channels architecture control schemes perform best in terms of both position tracking and force tracking during interaction with an environment emulated by different springs. Position error scheme, on the other hand, exhibits good position tracking capability, but cannot track environmental force encountered at the master site. It, however, produces a feel to the operator, based on position error between the slave and the master arms, which is potentially desirable during unconstrained motion control of the actuator.

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In this research, a buried pipe containing an external semi-elliptical crack has been modeled and investigated using finite element analysis. The interaction between the soil and pipe has been considered according to the Burns and Richard model. A few major parameters, namely, the soil height over pipe, the geometries of pipe and crack and the circumferential position of crack on pipe have been changed and their effects on elastic stress intensity factors have been studied at different positions along the crack front. The results showed that the crack experienced mixed mode loading condition and the circumferential crack position on pipe had a significant influence on the stress intensity factors.

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This paper proposed a method of representing the geometry of an imaginary disc cutter in parameter form. The undercutting condition of the imaginary disc cutter is studied, and the mathematical model of the generated gears is developed by the undercutting condition of the cutter. Through a mathematical model of the generation process, the vector equations of generated gears are established. According to the proposed method, a planetary gear mechanism and a pair of gear pump with smaller numbers of teeth are illustrated. A cutting simulation process is presented for machining the proposed gear pairs. Stress analysis for the proposed gear mechanism is performed. Finally, the proposed method is applied to determine singular points of the proposed disc cutter.

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The resolution and performance of an optical system can be characterized by a quantity known as the modulation transfer function (MTF), which is a measurement of an optical system’s ability to transfer contrast from the specimen to the intermediate image plane at a specific resolution. Accordingly, this study employs skew ray tracing based on a 4×4 homogeneous coordinate transformation matrix and Snell’s law to develop a detailed methodology for determining the spot diagram on the image plane when light rays pass through the optical system. And the authors present calculations of the MTF of an optical system by using the spot diagram on the image plane. The numerical results of the proposed methodology are demonstrated using a symmetrical optical system.

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This work is an extension of the authors’ published work on a planar four-bar motion generation search algorithm with Grashof, transmission angle and linkage perimeter conditions [1]. This latest work considers planar four-bar path generation with a coupler point load, crank static torque, crank transverse deflection and follower buckling in a modified search algorithm. As demonstrated in the example, a conventional methodology used in kinematic path generation has been expanded to consider static loading, elastic deflection and buckling in path generation. These factors must be considered in mechanical design, but are not the focus in traditional kinematic synthesis.

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A computerized approach for analyzing the tolerances in disk cam mechanisms with a flatfaced follower is presented in this paper. Based on the simulated higher-pair contact analysis, the kinematic deviation of the follower motion caused by the tolerance amount of each design parameter can be determined numerically. The method is validated by means of analyzing the case of an eccentric circular cam mechanism; such a case has an exact solution of the follower motion error. Compared with the exact solutions, the presented computerized approach is demonstrated to be able to provide excellent accuracy and sufficient efficiency no matter how large the level of the tolerance is. Then, both the offset translating oblique flat-faced follower and the oscillating flat-faced follower cases are given to illustrate the presented method. The presented computerized approach and the obtained results can be helpful for tolerance allocation tasks of disk cam mechanisms with a flat-faced follower.

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This work aims to propose a novel design for quick return mechanisms, and the new mechanism is composed by a generalized Oldham coupling and a slider-crank mechanism. First, the kinematic dimensions that affect the time ratio are found by investigating the geometry of the proposed design. By transforming into its kinematically equivalent mechanism, and then the design equations of time ratio are derived. Furthermore, a design example is given for illustration. Moreover, the design is validated by kinematic simulation using ADAMS software. Finally, a prototype and an experimental setup are established, and the experiment is conducted. The results show that proposed new mechanism is feasible and with reasonable accuracy. In addition, it is more compact and easier to be balanced dynamically than a conventional quick return linkage.

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This paper discusses a cascade decomposition method for two-time-scale systems. We decompose the two-time-scale system into slow and fast subsystems connected in cascade form. With the proposed decomposition method, fast and slow low-order subsystems can be easily extracted from the two-time-scale full order system. The longitudinal dynamics of a low speed experimental UAV is used to illustrate the proposed method. An altitude hold control structure is constructed to allow sequential designs based on the lower order fast and slow models using classical designs. The structure contains two control loops. The inner loop is for altitude rate regulation. In this control loop, we use combination of altitude rate and pitch angle as the feedback signals. A fast controller is designed to satisfy the high frequency requirements using the fast model. Following the results of the fast design, three control gains are designed to satisfy the low frequency requirements using the slow models. The design results of the inner loop are used to design the outer altitude control loop. Frequency domain analysis and computer simulations confirm the success of the proposed decomposition method and verify the effectiveness of the control law using the proposed control structure.

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This paper deals with the optimal path placement for a manipulator based on energy consumption. It proposes a methodology to determine the optimal location of a given test path within the workspace of a manipulator with minimal electric energy used by the actuators while taking into account the geometric, kinematic and dynamic constraints. The proposed methodology is applied to the Orthoglide 3-axis, a three-degree-of-freedom translational parallel kinematic machine (PKM), as an illustrative example.