Transactions of the Canadian Society for Mechanical Engineering

Volume 34 (2010), Issue 2

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In aerodynamic and machine structures, one of the effective ways of dissipating unwanted vibration or noise is to exploit the occurrence of slip at the interface of structural laminates where such members are held together in a pressurised environment. The analysis and experimental investigation of such laminates have established that when subjected to either static or dynamic loading, non-uniformity in interface pressure can have significant effect on both the energy dissipation and the logarithmic damping decrement associated with themechanism of slip damping. Such behaviour can in fact be effectively exploited to increase the level of damping available in such a mechanism. What has however not been examined is to what extent is the energy dissipation affected by the relative sizes or the material properties of the upper and lower laminates? In this paper the analysis is extended to incorporate such effects. In particular, by invoking operational methods, it is shown that variation in laminate thickness may provide less efficacious means of maximizing energy dissipation than varying the choice of laminate materials but that either of these effects can in fact dwarf those associated with non-uniformity in interface pressure. To achieve this, a special configuration is required for the relative sizes and layering of the laminates. In particular, it is shown that for the case of two laminates, the upper laminate is required to be thinner and harder than the lower one. These results provide a basis for the design of such structures.

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This paper presents multi-mode vibration control and analysis of moving platform position errors of a planar 3-PRR parallel manipulator with three flexible intermediate links using PZT transducers. The active vibration controller is designed in modal space with modal filters and modal synthesizers determined from the flexible link vibration characteristics. Estimation of the moving platform position error is conducted using measurements of the flexible link deflection from PZT sensors mounted on the flexible intermediate links. An effective strategy for determining the control gains to reduce the vibrations of higher order modes is proposed through modification of the independent modal space control (IMSC) method. The proposed independent modal control strategy is experimentally implemented with first twomodes targeted for control on a parallelmanipulator with multiple flexible links. The experimental results show that the vibrations of the first two modes are effectively suppressed, and the position error of the moving platform is substantially reduced.

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This paper presents the Hamiltonian-based error analysis applied to two-dimensional elasostatic problems. The accuracy enhancement is achieved by using the p-version of finite element method. The results show that the Hamiltonian error has faster rates of convergence at lower order of interpolation polynomials to compare with the energy error, and the Hamiltonian error clearly indicates great error reductions at a certain polynomial order. This can not only obtain an accurate enough solution but also save extra computational time. Another strategy is presented by computing the residual of the Hamiltonian-based governing equations. Relative values of residuals between elements can provide an index of selecting the best polynomial orders. Illustrative examples show the validities of the two approaches.

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This study introduces a new hybrid design for a specific case of assembly lines, and proposes a multi-pass random assignment algorithm to find the minimum number of stations required. The algorithm also finds the sequence and the schedule of the tasks assigned. The new design is a combination of two-sided lines and U-shaped lines, which benefits from the advantages of both designs at the same time. One side of the line is arranged in U-shape allowing stations with crossovers, and the other side of the line is balanced like a traditional straight flow. Depending on product direction, either Left or Right side of the line can be designed in U-shape. Small and large-sized two-sided assembly line test-bed problems were solved using the algorithm. Optimal results are achieved for all small-sized problems. Due to the novelty of the design, results of largesized problems are compared to findings of studies on simple two-sided balancing. Algorithm produced better results in most of the cases.

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Developing a motor-built-in high speed spindle is an important key technology for domestic precision manufacturing industry. The dynamic analysis of the rotating shaft is the major issue in the analysis for a motor-built-in high speed spindle. One of the major concerns is how the motor rotor is mounted on the shaft, by interference (shrink) fit or else. In this study, dynamical analyses are carried out on a motor-built-in high speed spindle. The motor rotor is mounted on the spindle shaft by means of interference fit. Modal testing and numerical finite element analyses are conducted to evaluate the dynamical characteristics of the spindle. The stiffness of the shaft accounting for the interference fit is investigated for the finite element model of the spindle. This study also proposes an analysis procedure to dynamically characterize the high speed spindle with a built-in motor. Based on the results of modal testing and the numerical analyses, it may conclude that the proposed procedure is feasible for the spindle and is effective for other similar applications.

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A ray-tracing analysis was conducted on a 2-stage solar concentrator made of two parabolic mirrors created by Lunenburg Industrial Foundry & Engineering (LIFE). The effects of the secondarymirror’s focal length, the distance between the secondarymirror and the target, and the misalignment with the sun were studied. The focal length of the secondary mirror determines the maximum local solar energy flux Φ that can be achieve on the target. For the optimal focal length of 157.9", a maximum Φ = 1.2×10⁴ MW/m² was achieve compare to Φ = 1680 MW/m² for the initial LIFE’s focal length of 158.8125". The concentrator concentrates all the incident energy from the sun on the target, and that independently of the secondary mirror’s focal length (within the range studied), as long as the target position is within an 11 cm zone. Small misalignments in the order of ±2° would bring the concentration efficiency to zero.

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A hybrid approach of combining Taguchi method, principal component analysis and fuzzy logic for the tolerance design of a dual-purpose six-bar mechanism is proposed. The approach is to firstly use the Taguchi orthogonal array to carry out experiments for calculating the S/N ratios of the positional errors to the angular error of the dual-purpose six-bar mechanism. The principal component analysis is then applied to determine the principal components of the S/N ratios, which are transformed via fuzzy logic reasoning into a multiple performance index (MPI) for further analysis of the effect of each control factors on the quality of the mechanism. Through the analysis of response table and diagram, key dimensional tolerances can be classified, which allows the decision of either to tighten the key tolerances to improve mechanism quality or to relax the tolerance of non-key dimensions to reduce manufacturing costs to be made.

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This paper investigates the effect of both single-point and diamond-roll dressing techniques on the workpiece surface roughness in grinding. Two empirical surface roughness models are studied – one that incorporates single-point dressing parameters, and another that incorporates diamond-roll dressing parameters. For the experimental conditions used in this research, the corresponding empirical model coefficients are found to have a linear relationship with the inverse of the overlap ratio for single-point dressing and the interference angle for diamond-roll dressing. The resulting workpiece surface roughness models are then experimentally validated for different depths of cut, workpiece speeds and dressing conditions. In addition, the models are used to derive a relationship between overlap ratio for single-point dressing, and interference angle for diamond-roll dressing such that both dressing techniques produce a similar surface finish for a givenmaterial removal rate.