Transmission (mechanical device)

A transmission (also called a gearbox) is a mechanical device which uses gears to change the speed or direction of rotation in a machine. Many transmissions have multiple gear ratios, but there are also transmissions that use a single fixed gear ratio. Most currently-produced passenger cars with petrol or diesel engines use transmissions with 5-8 forward gear ratios and one reverse gear ratio. Electric vehicles typically use a single-speed or two-speed transmission. Fixed-ratio transmissions The simplest transmissions used a fixed ratio to provide either a gear reduction or increase in speed, sometimes in conjunction with a change in the orientation of the output shaft. Examples of such transmissions are used in helicopters, wind turbines and power take-offs (PTOs) for tractors. In the case of a wind turbine, the first stage of the gearbox is usually a planetary gear, to minimize the size while withstanding the high torque inputs from the turbine. Multi-ratio tr

Flexure Variable Stiffness Actuators

Frédéric Henri Vaskin Giraud, Mustafa Mete, Jamie Paik

Series elastic actuators (SEAs) and variable elastic actuators (VSAs) provide shock resistance, energy storage, and stable force control. However, they usually require extra springs, mechanical parts, and transmissions, increasing size, weight, number of moving parts, and reducing the mechanical efficiency. In particular, this mechanical complexity is one of the significant challenges in the design of wearable and scalable force feedback devices. In this article, flexure variable stiffness actuators (F-VSAs), which combine kinematic transmission, elasticity, and stiffness modulation via a network of folding patterns using flexure hinges, are presented. Thus, F-VSAs allow the creation of robots benefiting from the advantages of SEAs and VSAs without hindering form factor or mechanical efficiency. To illustrate the design strategy of F-VSAs, a 4-design-of-freedom (DoF) robot that provides stiffness and force output is presented. An analytical model that estimates the inherent stiffness and the end-effector force output for any given configuration of the folding pattern is proposed. Finally, stiffness modulation and force control of the robot are implemented and good agreement with the predictions from the model is observed. Thus, this novel design strategy allows the creation of compact and scalable robots with stiffness and force output for wearable, rehabilitation, and haptic applications.

WILEY2022

Dynamics of torque control continuously variable transmissions

Robert Fuchs

With the increasing concerns in the impact of automotive emissions of CO2 and NOx on the environment combined with today's speculation on oil crude supply, the need to find solutions reducing the fuel consumption and emission of tomorrow's cars is more than ever present. Although the first continuously variable transmissions (CVT) appeared over a hundred years ago, it is only with the recent technological improvements in material durability, lubrication oil as well as control related hardware and software, that these transmissions have proved their capabilities. Because of their ability to decouple the engine from the wheel speed, CVTs enable significant fuel gains by shifting the engine operating point for a certain power demand toward higher torque and lower speed. A CVT can be regarded as a system dedicated to converting the torque delivered by the engine to the wheels. Conversely, for the engine speed control, it can be seen as an actuator applying a load to the engine. Two control concepts of CVTs are recognized. First is the concept of ratio control, which is a natural extension to fixed gear ratio transmissions, enabling an actuation of the transmission ratio. Second and less conventional, is the torque control concept, which sets the torque to be transmitted. It is the particular mechanism of these variators that allows the transmission to automatically shift to the appropriate ratio. Torque control CVTs extend the benefits obtained with conventional ratio control CVTs as they provide a direct control of the load applied on the engine, resulting in a straightforward control of the powertrain. Moreover, when such CVTs are combined with an epicyclic gear train in a split torque arrangement to form an infinitely variable transmission (IVT), virtually no control is required for the operation at the geared neutral point (infinite or zero speed ratio depending on the definition). However, the extended ability of torque control CVTs to decouple the engine and the vehicle speeds causes strong internal interactions, which must be fully understood for their development. The objective of this thesis is to provide a comprehensive and coherent set of analytical tools for the development and operation of torque control CVT powertrains. The classical method of modeling, performance analysis and control is applied to the Torotrak IVT Series 3 and its torque control full toroidal variator. Each of these steps gives a different perspective of the dynamics involved within the variator, of the interactions of the variator with the surrounding subsystems (hydraulics and driveline) and of the powertrain control. The contribution of this work is threefold. Firstly, the most relevant dynamics involved in TC/CVT-based powertrains are described with an application to the Torotrak torque control IVT. The main technical achievements are the development and validation of a model for simulation of the full toroidal variator, an open-loop performance analysis of the powertrain and the development of a control strategy for the engine operating point based on the nonlinear input-output feedback linearization technique. Secondly, this work broadens the general theoretical knowledge base of the operation of CVT powertrains. The two control concepts are compared and formally defined resulting in a new and original classification of transmissions. Also, the problem of powertrain control is formalized with the development of high-level, low bandwidth models of the engine, the transmission and the vehicle featuring properties similar to those of the ratio control CVT powertrain model. Thirdly, the formal and progressive analysis made throughout this work shows how the classical method of modeling, performance analysis and control can be applied to complex systems. This relies most of all on the development of models of varying complexity adapted to the requirements of the system analysis, design and control.

EPFL2006

Rigid foldability and mountain-valley crease assignments of square-twist origami pattern

Huijuan Feng

Rigid foldability allows an origami pattern to fold about crease lines without twisting or stretching component panels. It enables folding of rigid materials, facilitating the design of foldable structures. Recent study shows that rigid foldability is affected by the mountain-valley crease (M-V) assignment of an origami pattern. In this paper, we investigate the rigid foldability of the square-twist origami pattern with diverse M-V assignments by a kinematic method based on the motion transmission path. Four types of square-twist origami patterns are analyzed, among which two are found rigidly foldable, while the other two are not. The explicit kinematic equations of the rigid cases are derived based on the kinematic equivalence between the rigid origami pattern and the closed-loop network of spherical 4R linkages. We also convert a non-rigid pattern into a rigid one by introducing an extra crease. The kinematic analysis of the modified pattern reveals an interesting bifurcation behaviour. This work not only helps to deepen our understanding on the rigid foldability of origami patterns and its relationship with the M-V assignments, but also provides us an effective way to create more rigidly foldable origami patterns from non-rigid ones. (C) 2020 Elsevier Ltd. All rights reserved.

PERGAMON-ELSEVIER SCIENCE LTD2020

Dynamics of torque control continuously variable transmissions

Robert Fuchs

EPFL2006