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Actuators in Robotics and Automation Systems
Published in Bogdan M. Wilamowski, J. David Irwin, Control and Mechatronics, 2018
Choon-Seng Yee, Marcelo H. Ang
For large load capacities in a compact space, harmonic drives are very useful in robots [1,2]. Harmonic drives provide very high speed reductions (e.g., off-the-shelf units available for 64:1 to 320:1 [2]) and can therefore provide very high torque. The principle of operation of a harmonic drives is shown in Figure 35.35. The harmonic drive consists of a rigid spline (circular spline) with internal teeth that forms the housing of the drive, an annular spline (“flexspline”) that has external teeth that meshes with the internal teeth of the housing, and a wave generator that is driven by the actuator. The external radius of the annular spline is slightly smaller than the internal radius of the circular spline (housing). The annular spline is also called a flexspline because it undergoes elastic deformation during the meshing process. The wave generator is the input side of the drive and is coupled to the actuator; the flexspline or the circular spline are the output side of the drive and is coupled to the load. When the wave generator is rotated by an actuator, the flexspline is deformed thus engaging teeth in diametrically opposite points coincident with the major axis of the elliptical wave generator and disengaging points at the minor axis. The wave generator has a double-ended cam in place that achieves the rotation of the major and minor axes of the ellipse. If the circular spline is fixed and the load is coupled to the flexspline, rotation of the wave generator would produce a reverse rotation of the flexspline; and if the rigid spline has 202 teeth and flexspline 200 teeth, then a single revolution of the wave generator will precess the flexspline backward two teeth resulting in a velocity ratio of 100:1. If the flexspline is fixed and the load is coupled to the circular spline, then the input and output shafts rotate in the same direction. The relationship between input and output angular velocities is [2]: ωinωout=NoNc−Nf
Back-Support Exoskeletons for Occupational Use: An Overview of Technological Advances and Trends
Published in IISE Transactions on Occupational Ergonomics and Human Factors, 2019
Stefano Toxiri, Matthias B. Näf, Maria Lazzaroni, Jorge Fernández, Matteo Sposito, Tommaso Poliero, Luigi Monica, Sara Anastasi, Darwin G. Caldwell, Jesús Ortiz
Active exoskeletons employ actuators whose action is controlled during operation by a computer program based on sensor information. For this reason, they are considered to be potentially more versatile (relying on underlying control strategies, as expanded in Section “Control Strategies”). Most active exoskeletons use electric motors, but examples of pneumatic actuation exist (e.g., Muscle Suit (Aida, Nozaki, & Kobayashi, 2009), AB-Wear (Inose et al., 2017)). Electric motors are used in combination with reduction gears to achieve the necessary forces/torques. Harmonic Drive (Harmonic Drive AG, Germany) reduction gears enable very compact designs and are therefore used commonly despite their relatively high costs. Geared motors, however, introduce undesirable dynamics on the user due to added friction and large resulting inertia. To enable the use of less powerful geared motors, and thus mitigate their drawbacks, mechanical arrangements of elastic components with electric motors have been proposed (Hara & Sankai, 2012; Toxiri, Calanca, Ortiz, Fiorini, & Caldwell, 2018). One example of a parallel arrangement from Toxiri, Calanca et al. (2018) is shown in Figure 2. More comprehensive references on the use of the parallel spring-motor arrangement on exoskeletons may be found in Wang, Van Dijk, and Van Der Kooij (2011) and Beckerle et al. (2017).
Mechanics of humanoid robot
Published in Advanced Robotics, 2020
The most commonly used reducer for humanoid robots is the strain wave gearing such as Harmonic Drive® [18]. Harmonic Drive® strain wave gearing utilizes a unique operating principle which is based upon the elastic mechanics of metals. The unique operating principle allows extremely high reduction ratio in a very compact and lightweight package. The high performance attributes of this gearing technology including zero backlash, high torque, compact size, excellent positional accuracy and repeatability are all a direct result of the unique operating principle. Although planetary gears and cycloidal gears are also the candidates, there are few applications to humanoid robots due to their weight and space-consuming compared to the strain wave gearing.