Mechanical Power Transmission Research Articles

Fuel cell drives for road vehicles

For fuel-cell driven vehicles, including buses, the fuel cell may be the main, determining factor in the system but must be integrated into the complete design process. A Low-Floor Bus design is used to illustrate this point. The influence of advances in drive-train electronics is illustrated as are novel designs for motors and mechanical transmission of power to the wheels allowing the use of novel hub assemblies. A hybrid electric power system is being deployed in which Fuel Cells produce the energy needs but are coupled with batteries especially for acceleration phases and for recuperative braking.

Optimization of travelling wave ultrasonic motors using a three-dimensional analysis of the contact mechanism at the stator–rotor interface

The present paper investigates optimization rules and new design methodologies dealing with the contact mechanics in rotative travelling wave ultrasonic motors (TWUM). The proposed approaches focus on the design of the rotor, including the friction layer that is usually deposited onto its lower surface, while the stator is supposed to be preliminary designed. Contact aspects such as the transmission of mechanical power as well as the wear mechanism of the friction layer are investigated, according to the analysis of the stator–rotor contact mechanics in both hoop and radial directions. Considering a classical wear criterion in a preliminary step, a contact ratio, that allows the mechanical power to be optimized, is pointed out in the hoop direction. In a further step, the contact conditions in the radial direction are improved through the elastic fitting of the stator and rotor radial deflexions, therefore allowing the material's wear to be decreased. Some experimental tests, that have been recently performed, give a comparison of wear marks, which occur onto optimal and non-optimal rotor geometries. A first mechanism synthesis is finally proposed in such a way to allow the mechanical architecture of the rotor (including the friction layer) to be automatically designed according to a given set of mechanical constraints.

ELECTROTHERMALLY ACTUATED BI-DIRECTIONAL LINEAR VIBROMOTOR

A compact polysilicon surface-micromachined thermal actuator-based vibromotor has been designed and fabricated. Mechanical power transmission occurs during the impact of the thermal actuators on the sides of a movable guided element (slider.) Bi-directional operation is made possible through the impact head design. The thermal actuators have been driven at frequencies up to 10 kHz. A traveling speed of 3 mm s has been demonstrated with an AC input voltage of 2.0 V at 5 kHz plus a 10.0-V DC bias offset. A polysilicon hinged vertical micromirror has been moved for a full range of 350 mu m.

Design Automation with the Aids of Multiple Artificial Intelligence Techniques

In most cases, to design a product through the process of total design is a tedious task. In order to speed up the process and hence to reduce time to market, an intelligent integrated system (IIS) approach has been developed to integrate various stages in total de sign process, including conceptual design, detail design and manufacture. The integration is achieved by blending multiple artificial intelli gent (AI) techniques and CAD/CAE/CAM packages into a single environment. The Al techniques utilised in the approach include knowledge-based systems, artificial neural networks and genetic algorithms. The IIS has been applied in mechanical power transmission system design, which approves that the approach is a powerful tool for design automation. Wthin the IIS environment, the multiple Al tech niques coexist and complement each other, and thus their drawbacks are eliminated and their advantages are maximised.

Meshing of Silent Chain and Main Cause of Noise Generation.

Chain drive has some merit in mechanical power transmissions, when the center distance of driving/driven shafts is wide and/or the same direction of rotation of driving/driven shafts is desired. The running noise and vibration of silent chain with roll-contacting rocker pins is fairly lower than normal roller chain drive or silent chain with simple joint pins, but it is still large enough to be of problem. In this report, the kinematics of the meshing of silent chain with roll contacting rocker pins with mating sprocket of involute spur gear is introduced. The simulating calculation based on this theory shows that the radial positions of successive plates of the chain around sprocket is divergent, when some slight disturbance is given for the position of the meshing in plate. This instability in the sitting position of chain plate corresponds well with the measured state of chain noise radiation and observed sitting figure of plates on the sprocket. The main cause of the chain noise and vibration is clarified.

Arrayed Electrostatic Scratch Drive Actuators: Toward Visible Effects up to the Human Scale

This paper investigates millimeter scale electrostatic motors designed through a new "bottom-up design approach." Active polysilicon sheets involving thousands of elementary scratch drive actuators are analyzed, according to the driving force superposition capabilities of distributed electrostatic actuators. Driving forces as high as 1 00,000 pIN are reported in this paper, using 6 mm2 polysilicon sheets that integrate up to 1430 elementary scratch drive actuators. The mechanical power transmission from the sheet to the external load is also investigated. Because of structural height limitations, active polysilicon sheets do not allow significant driving forces to be transmitted to the external world. Therefore, original architectures, such as tubular electrostatic motors, are proposed using the insertion of a flexible polysilicon stator within the gap of a macroscopic cylindrical joint. An original self-assembling method is used in order to develop a first generation of millimeter scale electrostatic actuators. Expected performances that are evaluated from the in situ sheet characterization (i.e., from characterization onto the silicon wafer) point out the relevance of the bottom-up design methodology proposed in this paper. For the first time, visible effects up to the human scale are conceivable from silicon-based electrostatic motors that will allow innumerable actuation applications to be performed in the near future.

Noise diagnostic and reduction of a scooter engine motorcycle

This paper presents an appropriate way to reduce the noise of a scooter engine motorcycle. In order to investigate the noise contribution of each engine component, the lead covering method was used to rank the noise source. With the noise spectra from measuring the pass-by noise and releasing the lead cover on each component sequentially, the correlations between specific frequencies and each component of the engine were found. Furthermore, the noise characteristics of all components were cataloged into the airborne noise and the structure-borne noise. In this research, it was shown that the airborne noise was usually coming from the air cleaner or muffler. Additionally, the power transmission mechanism like CVT or crankcase generated the structure-borne noise. Based on the diagnostic results above, some modifications of the motorcycle had been done, for example, isolating of the CVT-cover and the crankcase-cover, fixing of high density material at the air cleaner box and adding another layer around the exhaust pipe. For the pass-by noise measurement, it was shown that the noise level of the scooter was reduced by 2.5 dB(A). [Submitted For Noise ‘‘Outstanding Young Presenter’’ Paper Award.]

Intelligent hybrid system for integration in design and manufacture

An intelligent hybrid system (IHS) approach has been developed to integrate various stages in the process of design and manufacture, including product design specification, conceptual design, detail design, process planning, costing and CNC manufacture. The IHS approach blends a rule-based system (RBS), artificial neural networks (ANNs), genetic algorithm (GA), hypermedia (HM) and CAD/CAE/CAM packages into a single environment. The design and manufacture expertise is captured by the RBS and ANNs, while the other tasks, such as numerical analysis, design optimisation, engineering drawing and data processing, are performed using GA, HM and CAD/CAE/CAM. The RBS works as a co-ordinator, controlling the whole process. As an application of the approach, an IHS for mechanical power transmission systems has been developed.

An electrostatic lower stator axial-gap polysilicon wobble motor. I. Design and modeling

This paper presents design issues and a theoretical model of electrostatically driven axial-gap polysilicon wobble motors. The motor design benefits from large axial rotor-to-stator overlap and large gear ratios, and motor designs with rotor radii of 50 and 100 /spl mu/m are capable of generating torques in the nanoNewtonmeter range at high electrostatic fields. Because of the large gear ratio, smaller angular steps and lower rotational speed are obtained, compared to radial-gap motor designs. Aspects like gear ratio, torque generation, excitation schemes and torque coverage, normal forces, friction, rotor kinetics, and dynamical behavior are addressed. The motor design is compliant to the integration of gear linkages with respect to mechanical power transmission.

Drive train configuration arrangement for gear coupled manipulators

This paper describes a methodology for the drive train configuration arrangement of gear coupled manipulators. The approach is based on the idea that the kinematic structure of a gear coupled manipulator can be described by an equivalent open-loop chain (EOLC) and mechanical power transmission lines that drive the EOLC. Conditions to select proper drive train configuration such that manipulators can possess kinematic isotropic property will be presented. Procedures to select gear ratio based on optimum dynamic performance will also be extended from two-degree of freedom (DOF) systems to three-DOF systems. From the determined drive train configuration and gear ratios, location of actuators and details of the mechanical power transmission lines can be decided accordingly. A two-DOF manipulator and a three-DOF wrist are used as illustrative examples. ©1997 John Wiley & Sons, Inc.

Parallel power paths and compactness of gear transmissions

Developments in mechanical power transmission have hinged around better materials and processes, new design ideas and effective new application of enduring scientific design principles and ideas. The current presentation aims at showing how deliberate measures to optimize load distribution have increased the compactness and capabilities of present day gear transmissions. Exploitation of parallel power paths, packing of gears in annular spaces and the effective use of epicyclic action by reducing the number of gear meshes and substituting rolling friction are explained.

A fabrication process for electrostatic microactuators with integrated gear linkages

A surface micromachining process is presented which has been used to fabricate electrostatic microactuators. These microactuators are interconnected with each other and linked to other movable microstructures by integrated gear linkages. The gear linkages consist of rotational and linear gear structures, and the electrostatic microactuators include curved electrode actuators, comb-drive actuators, and axial-gap wobble motors. The micromechanical structures are constructed from polysilicon. Silicon dioxide was used as a sacrificial layer, and silicon nitride was used for electrical insulation. A cyclohexane freeze drying technique was used to prevent problems with stiction. The actuators, loaded with various mechanisms, were successfully driven by electrostatic actuation. The work is a first step toward mechanical power transmission in micromechanical systems.

Performance Test of a Catapillar Track-Hydroturbine

Current low head and small scale hydroturbines have limitations in the minimum required head and flow rate for efficient operation. This study attempts to develop a new concept hydroturbine which is expected to run efficiently even in very low head and small flow rate, so that the limitations on the conventional small scale hydropower could be alleviated and competition with other alternative energy sources in the economic respect could be attained. A small scale catapillar track- hydroturbine was fabricated and the performance test was carried out in a water tunnel over the head range of H = 0.8 m ~ 1.26 m. The peak turbine efficiency was 41.3% at the speed ratio of 0.6, and the turbine loss was mostly due to the friction at the chain drive used for power transmission from the runner to the shafts. This type of turbine is expected to become competitive when some improvement in the power transmission mechanism is made.

粉末冶金法による超磁歪材料の開発とアクチュエータへの応用

This article presents the recent results from the study conducted by the authors on the application of giant magnetostrictive material. Tb0.3Dy0.7Fe1.95 is used to develop a novel pump which is able to feed at constant rate under high pressure. Two kinds of methods are employed for comparison purpose to fabricate the giant magnetostrictive material; Bridgman method and powder metallurgy method. The performance of the pump using each sample is closely evaluated and compared with each other. Prestress dependency of the magnetostrictive rods is also examined to illustrate distinctions between the two methods. It is found that the rod manufactured by powder metallurgy method shows less prestress dependency than that based on Bridgman method while the pump equipped with the latter sample yields a higher flow rate than the former does. It is also verified in terms of the efficacy of giant magnetostrictive materials on pumps which implies possible futuristic applications in human bodies by downsizing its power transmission mechanism.

Computer-aided selection of roller chain drives

This work presents a computer-aided analysis for the selection of roller chain drives, which are commonly used in mechanical power transmission systems. Computer programs are written and proposed to improve the traditional method of drive selection for the roller chain drives. The algorithms are mainly based on the existing equations for the mechanics of the drives, including the geometry and the power transmission capabilities. The purpose of attempting to computerize the selection procedures is to reduce the number of tables and charts that are required in traditional selection routines. In addition, it is also intended to cut down the amount of iteration and calculation work performed. To evaluate the accuracy and limitations of the proposed programs, comparisons are made with the existing examples of drive selections. It is found that the programs implemented in the present selection process are able to substitute for most of the traditional selection charts and tables. Furthermore, the selection using the proposed methodology can be performed in a shorter time owing to the computer-generated process.

Computer-Aided Optimal Design Strategy of Power Transmission Systems

A mechanical power transmission system consists of mainly shafts, gears and bearings, where each machine element can be optimally designed. However in a power transmission system each design variable such as pitch diameters of gears and diameters of bearings have certain constraints. These constraints effect the design of the other member like the shaft. A design strategy is developed for the optimal integrated design of a mechanical power transmission system including the constraints of each member and with the view to satisfy a global optimum for the system.

Dynamic Behavior of Lead Screw Mechanism with Backlash.

A lead screw is a typical power transmission mechanism and is often used in a positioning system. Fundamentally, the lead screw has backlash between a screw and a nut, which causes chattering vibration and a long positioning time. In many practical cases, the backlash is adjusted to zero by using, for example, a double nut. However, the adjustment produces a large frictional force which makes table motion slow and generates heat. The purpose of this research is to realize a high-speed and high-precision positioning system using conventional lead screw mechanisms with backlash. For the first step, dynamic behavior of the lead screw mechanism with backlash is examined using the experimental mechanism comprising a sliding screw, a table and a DC motor. In the experiments, the table position, the rotation angle of the screw and the motor current are measured. The force transmitted from the screw to the table is estimated by a disturbance observer. The frictional force between the screw and nut and the acceleration of the table and the screw are calculated from estimated values.

特集 最近の運動設計技術 不等速運動動力伝達機構

特集 最近の運動設計技術 不等速運動動力伝達機構

The Performance of a Mechanical Design ‘Compiler’

A mechanical design “compiler” has been developed which, given an appropriate schematic, specifications, and utility function for a mechanical design, returns catalog numbers for an optimal implementation. The compiler has been successfully tested on a variety of mechanical and hydraulic power transmission designs, and a few temperature sensing designs. Times required have been at worst proportional to the logarithm of the number of possible combinations of catalog numbers.

Quantitative Inference in a Mechanical Design ‘Compiler’

This paper presents the ideas underlying a computer program that takes as input a schematic of a mechanical or hydraulic power transmission system, plus specifications and a utility function, and returns catalog numbers from predefined catalogs for the optimal selection of components implementing the design. Unlike programs for designing single components or systems, this program provides the designer with a high level “language” in which to compose new designs. It then performs some of the detailed design process for him. The process of “compilation,” or transformation from a high to a low level description, is based on a formalization of quantitative inferences about hierarchically organized sets of artifacts and operating conditions. This allows design compilation without the exhaustive enumeration of alternatives. The paper introduces the formalism, illustrating its use with examples. It then outlines some differences from previous work, and summarizes early tests and conclusions.