In this study, a parametric study on material properties and friction coefficient of mechanical components are investigated through simulating the real working conditions by a numerical method. As the screw rotors are the key components in an air compressor system, the rotors are exposed to complicated loading conditions during operation. The objective of this study is to investigate the effects on the input moment, peak Von Mises stress and the mechanical efficiency of the air compressor system subjected to varying parameters of the material properties of the female rotor and friction coefficients. From the simulation results, the peak Von Mises stress is greatly affected by the parameters of the material property of the female rotor, and the input moment and the mechanical efficiency are slightly influenced in the first condition. And, the peak Von Mises stress is significantly affected by the parameters of the friction coefficients, in the decreasing trend. The input moment is also increased with the increasing parameters of the friction coefficients. The mechanical efficiency is inversely correlated with the input moment, whereby efficiency is greatly reduced with an increase in input moment. The study shows that the proposed numerical method is efficient and suitable to establish the parameters study on the twin screw rotors, and provides an effective approach to investigate the twin screw rotors and improve the design of the system.

To enable the smart technologies, such as the GPS, suspension active and semi-active controls and electromagnetic braking system, on the railway freight vehicles, the electricity is required and in needed. In this paper, we proposed a rack-pinion based freight train suspension energy harvester with mechanical-motion-rectifier (MMR) mechanism, to harvest the energy that usually dissipated and wasted during suspension vibration. The special mechanism with one way clutches engagement and disengagement during the working period makes the harvester convert the bi-direction suspension linear motion into a generator unidirectional rotation, which improve the transmission reliability and increase the energy harvesting efficiency. Nonlinear model of the energy harvester is established in this paper to analyze the dynamic characteristic of the freight train energy harvester and bench test are carried out to experimentally characterize the proposed energy harvester. The results show that under a certain freight vehicle suspension vibration condition, the proposed energy harvester can get a peak 292W and an average 34W power, which has a much better energy harvesting performance than any other existing energy harvesting technology used for the railway vehicles. Moreover, the proposed energy harvester can reach a 70% mechanical efficiency, which shows that the MMR’s advantage in improving the energy harvesting efficiency.

The lubrication performances of cycloid drives affect the dynamic characteristics, the mechanical efficiency and the contact fatigue behavior of the system. To maintain tranmission precision it is required to minimum the times of disassebly, hence grease lubrication is often applied where starvation might occur in service. Starved lubrication performance of a cycloid gear drive is studied using a numerical finte line starved-elastohydrodynamic lubrication model. The parameter of the inlet oil film thickness is chosen to represent the starved status. Effects of the inlet film thickness on the centralfilm thickness, the friction coefficient and the frictional power loss are investigated. In addition, effects of different shape of inlet oil-supply layer in the same starved degree on lubrication performance are studied. Under the same inlet oil supply volume, the convex type profile would present a better oil film within the nominal contact zone compared with other four different shapes of the inlet film supply.

Mechanical (load-dependent) power losses of a planetary gear set occurs primarily along its lubricated rolling-sliding interfaces at the external and internal gear meshes, and planet bearings. The gear mesh originated portion of these losses are influenced by all key gear parameter, tooth profile correction and other parameters dictating the fluid film formation. In this study, a systematic planetary gear design search algorithm is combined with an efficiency formulation to (i) quantify the sensitivity of gear mesh mechanical losses of planetary gear sets to the basic gear design parameters and (ii) investigate the compromise that must take place between the mechanical efficiency and other functional attributes associated with durability and noise performance of the gear set. An example design study is presented at the end to demonstrate both of these points.

Advanced robotics requires a new generation of actuators able to exhibit a number of desirable characteristics ranging from high power density and high efficiency, high positioning resolution, high torque capacity and torsional stiffness, lightweight designs and low-cost packages. In this paper, we present the development and the experimental evaluation of a new actuator, aimed at improving the torque density and mechanical efficiency of actuated robotic joints, and enhancing the portability and effectiveness of robotic systems engaged in biomechanical applications such as rehabilitation robots and wearable exoskeletons. The new actuator, called the Gear Bearing Drive (GBD), consists of a two-stage planetary gear arrangement coupled through the planets and driven by an external rotor brushless motor that is inscribed within the input stage sun gear. This planetary configuration enables for incredible high-speed reductions and allows for embedding the motor directly within the gearbox saving significant space on the actuator length. Our initial experimental prototypes have demonstrated impressive performance with the potential to deliver more than 30Nm of continuous torque with 85% mechanical efficiency and 0.0005 degree of backlash, and up to 200 rpm maximum output speed in a highly compact and robust package.

We introduce a dual input Parallel Force/Velocity Actuation (PFVA) concept in this paper to enable variable response manipulation. The objective of this paper is to develop an analytical model for power flow in PFVA systems. We studied the functional dependence of external and internal power flow phenomena on two dimensionless parameters we define in this paper, namely Relative Scale Factor ( ρ ) and Velocity Mixing Ratio ( λ ). We observed that overall mechanical efficiency of the PFVA decreases approximately 16% from the basic efficiency when the RSF was increased 5x and the VMR was increased 10x. For a specified load torque of −100 Nm at the output of a positive-ratio PFVA and a fixed VA angular velocity of 150 RPM, the Futile Power Ratio (FPR) was observed to increase by approximately 40% when the RSF was increased by 5x and the FA velocity was increased from 0–80 RPM. Based on our analytical development we suggest some design and operational guidelines for PFVA based systems.

Present building-block synthesis techniques for compliant mechanisms [4–7] account for the kinematic behavior of the mechanism alone, leaving the stiffness, manufacturability and mechanical efficiency to be determined by the shape-size optimization process. In this effort, we aim to generate practical and feasible conceptual designs by designing for kinematics and stiffness simultaneously. To enable this, we use a lumped spring-lever model, which intuitively characterizes the stiffness and the kinematics of a deformable-complaint building block with distinct input and output points. This model aids in the understanding of how the stiffness and the kinematics of building blocks combine when concatenated to form a mechanism. We use this understanding to synthesize compliant mechanisms by combining building blocks of known motion characteristics. A simple compliant-dyad building block is characterized for its lumped values of stiffness and kinematics. The concatenation of these dyad-building blocks is solved in detail, and guidelines for conceptual synthesis are proposed. Two practical examples are solved; a motion amplifier for a piezo-stack and a compliant energy storage mechanism for a staple-gun. The conceptual designs obtained from this approach are very close to the kinematic and the stiffness requirements of the application, thus minimizing the role of shape and size optimization to achieve the problem specification. The model, when extended to higher dimensions may be used to solve for precision positioning and other applications.

Compared with common speed reducers, the cycloidal ones (also known as cycloid drives) cover a wider range of transmission ratios, have a higher load-carrying capacity, are smaller, exhibit a smoother running and a good efficiency. These characteristics make them attractive for industrial applications, especially for robotics applications, machine tools and linear axis positioning in assembly machinery. In this paper, a theoretical and experimental investigation on an innovative cycloidal speed reducer will be presented. The typical cycloid drive has a planet wheel, the profile of which is the inner offset of an epitrochoid, meshing with cylindrical rollers connected to the case. This reducer, on the contrary, has an external ring gear, the transverse profile of which is the external offset of an epitrochoid, and engages with the planet wheel by means of cylindrical rollers. This paper will investigate the structural characteristics and the kinematical principles of this type of reducer. A theoretical approach based on the envelope theory (following Litvin’s approach) will be developed and compared with a development of Blanche and Yang’s approach. Furthermore, a simplified procedure to calculate force distribution on cycloid drive elements, as well as its power losses and theoretical mechanical efficiency will be presented. The effects of design parameters on the values of the forces will be studied, for an optimal design of this type of reducer. The theoretical model will be then tuned using the results of tests on a specific rig. As a result of the experimental tests, the reducer mechanical efficiency dependency on speed and torque will be described. The aim of this work is to perform the fine tuning of a theoretical model in order to predict the operating behavior of the cycloid drive, and to improve its design procedure.

There are several geometric and working parameters, besides offset, that have minor effects on hypoid gears efficiency (i.e. spiral angle, pressure angle, lubricant type & temperature, surface finish, etc.). Some theoretical analyses of mechanical efficiency of hypoid gears show that surface finish has considerable effect on hypoid gear efficiency. This is due to a high sliding to rolling ratio in these types of gears. In this paper, a study on measuring of surface finish of both ring gear and pinion will be presented. Moreover, the effects of lapping and superfinishing on surface finish will be discussed. Using an accurate form-measuring machine, surface finish measurements were done on several experimentally produced hypoid gear pairs. Despite the fact that lapping is expected to improve the surface finish, measurement results show that ring gear’s surface finish becomes worse (roughness increased) after lapping while no consistent results for pinion surface finish were observed. However, it will be shown that lapping decreases transmission errors for both sides (drive and coast). Utilizing a Gleason single flank tester (SFT) 600HTT it will be shown experimentally that transmission errors up to the second harmonics for both sides will be decreased. In addition, it can be seen that lapping decreases surface finish variation among gear sets. As an expansion of the previous study [1] by the authors on lapping effects on surface finish and transmission errors, this paper will also present the effects of the superfinishing process on hypoid gears surface finish and transmission errors. This study shows the result of measurements taken before and after superfinishing, although superfinishing improves surface finish drastically it will be shown that surface finish quality will be decreased when gear sets are rolled together.

This investigation concerns with the mechanical efficiency of Cardan joints. The model includes also the effects due to manufacturing and mounting errors and the influence of rotation speed on the efficiency. The joint has been modeled as an RCCC spatial linkage and the full dynamic analysis performed by means of dual vectors algebra.

A wearable robot is a controlled and actuated device that is in direct contact with its user. As such, the implied requirements of this device are that it must be portable, lightweight and most importantly safe. To achieve these goals an actuator with a good ‘power to weight’ ratio, good mechanical efficiency, good ‘strength to weight’ ratio and that is safe is desired. The design of the standard lead screw does not normally perform well in any of these categories. The typical lead screw has low pitch angles and large radii, thereby yielding low mechanical efficiencies and high weight. However, using the design procedure outlined in this text both efficiency and weight are improved, thus yielding a lead screw system with performances that rival human muscle. The result of an example problem reveals a feasible lead screw design that has a ‘power to weight’ ratio of 277W/kg, approaching that of the DC motor driving it, at 312W/kg, as well as a mechanical efficiency of 0.74, and a maximum ‘strength to weight’ ratio of 11.3kN/kg(1154kgf/kg).

In this study, a methodology for prediction of mechanical efficiency of helical gear pairs is proposed. It combines a gear load distribution model with a friction coefficient computation model. The load distribution model is used to provide contact pressures and other contact parameters to the friction coefficient model. Two different approaches are used for the computation of the friction coefficient. The first approach employs a number of published empirical friction coefficient formulae that were typically obtained through twin-disk tests. The second approach uses a rough-surface, thermal elastohydrodynamic lubrication (EHL) model. A simplified, smooth-surface version of the EHL-based model is also proposed. The friction coefficient distributions along the tooth contact surfaces are then used to calculate the friction forces that yield the instantaneous mechanical efficiency loss of the gear pair at a given mesh angle. The model is used to study the influence of a number of design, lubricant and surface related parameters as well as load and speed on the mechanical efficiency of helical gear pairs.