Type Synthesis of Compound Load Simulators Outputting the Bending Moment and Tension/Compression Force

A bending moment and a tension/compression force are two types of commonly used load patterns in loading test for mechanical components. A great number of simulator types available for the two loads have been reported widely. However, current types mainly focus on the single load pattern and only one-dimensional bending moment can be achieved. With the increasing demand of the mechanical part performance, it is urgent to build a more complex testing environment. In this situation, a novel compound load simulator capable of outputting single multi-dimensional load and compound load patterns gradually catches the attention of the researchers. The development of parallel mechanism (PM) supplies a new direction to the field of simulators, whereas there is still shortage of effective types and design principles. In this paper, type synthesis of the compound load simulators outputting the bending moment and tension/compression force is introduced. First of all, the relationship between load patterns and degree-of-freedom (DOF) of parallel mechanism is derived. Based on the derivation, the DOF correspondence with a two-dimensional pure bending moment is two-dimensional rotation and that with a tension/compression force is one-dimensional translation. Furthermore, a typical 3-PRS PM as a representative of the PM with 2R1T DOF is studied and the analysis reveals that there is parasitic motion during its two-dimensional rotation. The undesired parasitic motion will bring additional load to the part, such as shear force. Then the special characteristics of PM meeting the requirement of outputting pure bending moment are proposed. Finally, a graphical approach is utilized to synthesize the effective types of the compound simulator.

Classification and Type Synthesis of Deficient-DOF Parallel/Hybrid Compound Load Simulator With a Specified Load Pattern

A compound load simulator has drawn increasing attention due to the growing demand for testing of critical components in mechanical devices. However, its development is still limited owning to the shortage of corresponding design principle. Accompanied with the application of parallel mechanisms in a variety of multi-axis machine tools and motion simulators, it brings new inspiration to this field. Although existing six degree-of-freedom (DOF) parallel mechanisms such as Stewart platform can output multi-dimensional loads, it also produces the complexity of force control and inevitable collaborative error. Actually, it is enough to utilize deficient-DOF mechanisms for a majority of load patterns and practical engineering applications. Therefore, this paper mainly focuses on synthesizing deficient-DOF parallel/hybrid compound load simulators. Regular load types are summarized including one-dimensional generalized force and compound of them. Based on characteristics of each load type, DOF of the moving platform connecting to the component to be tested is determined through the mapping between force and displacement in rigid body motion. Current typical deficient-DOF parallel mechanism is enumerated to evaluate its load output characteristics. What is more important, a type synthesis procedure based on the graphic approach is presented to construct the configurations of parallel/hybrid mechanism corresponding to different compound load types, which may lead to useful load simulator configurations. The procedure also verifies that the graphic approach is a concise and effective method to synthesize the load simulators associated with a specified load pattern.

Theoretical and Experimental Study on Stiffness Characteristics of a Wire Race Ball Bearing

A new mathematical model on the stiffness matrix of the bearing was established by using the non-conforming Hertz contact theory. In this model, the case of compound load and the coupling effects was considered. The numerical arithmetic to estimate the displacements under the compound loads is discussed. As a sample, a wire race ball bearing used in a certain type of three-axis aircraft simulating rotary table was provided. The curves of axial stiffness and radial stiffness were obtained in MATLAB. The experimental system for measuring the stiffness was built. The experimental results verify the validity of the theoretical model.

Removal of Taste and Odour Compounds by Conventional Granular Activated Carbon Filtration

In recent years, musty-earthy tastes in drinking water have become a seasonal problem (September to November) for communities that draw their water from the upper St. Lawrence River. The source of the problem is attributed to the presence of geosmin and 2-methylisoborneol (MIB) at concentrations ranging from 5 to 60 ng/L. In 1997 and 1998, the Cornwall Water Purification Plant added granular activated carbon (GAC) to conventional gravity filters to control taste and odour compounds. We report on a study to test the efficiency of these conventional GAC-capped filters to reduce geosmin and MIB concentrations in finished water as a function of filter age, initial chlorine residual and contact time. GAC–capped filters removed on average 60% of the MIB and 80% of the geosmin from the source water after 2 and 12 months of filter operation. However, testing after 24 months operation showed reduced efficiency. Amounts removed ranged between 13 and 20% (15% average) for MIB and 50 to 57% (54% average) for geosmin in these filters. Testing also suggested that filter efficiency was greater with longer contact times and with higher chlorine residuals (in the range 0.1 to 0.6 mg free Cl2/L). In addition to carbon age, chlorine residual and contact time, flow channelization and slow release of the taste and odour compound load (particularly MIB) from the GAC bed may affect apparent filter efficiency.