A novel variable stiffness scotch yoke series elastic actuator for enhanced functional stiffness
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TECHNICAL PAPER
A novel variable stiffness scotch yoke series elastic actuator for enhanced functional stiffness Seung Ho Lee1 • Hyuk Jin Lee1 • Kyeong Ha Lee1 • Kyung Tae Nam2 • Ja Choon Koo1 Received: 30 October 2019 / Accepted: 18 May 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This paper presents a new design and modeling of a novel variable stiffness scotch yoke series elastic actuator (VSY-SEA) mechanism that can achieve variable stiffness values with a linear relationship between torque and displacement. The main goal of this study was to design the yoke’s shape in the scotch yoke mechanism for a system with the desired stiffness. The word ‘‘variable’’ in VSY-SEA does not simply mean that the system has different random stiffness, but rather that the system has the stiffness of the functional form desired by the designer. Yoke shapes in the scotch-yoke mechanism were designed by calculating the relationship between external torque and rotation angle of VSY-SEA, and the simulations were performed using CAD models with various yoke designs. A prototype of the model was built and the calculations were verified through experiments.
1 Introduction Presently, as robot operations follow not only pre-defined paths of movement, but also unknown tasks, it becomes very important to absorb, measure, and control the unknown external forces that a robot receives. Rehabilitation robots, service robots, and wearable robots are typical examples, which have compliance structures as a part of their mechanism for interacting with their environments and users (Pratt and Williamson 1995; Lee et al. 2017; Sergi et al. 2013; Albu-Scha¨ffer et al. 2007; Woo et al. 2017; Veneman et al. 2006). There are many methods for measuring external torque and giving passive compliance to a system such as measuring torque with many kinds of torque sensors and controlling stiffness by control algorithms (Pugi et al. 2016; Allotta et al. 2009; Pulcinelli et al. 2018). The series elastic actuator (SEA) is one of that methods and it is widely used in robots for its merit which can act as both torque sensor and passive compliance, the two objectives can be mechanically achieved, reducing the complexity of the control. It acts as a torque sensor that & Ja Choon Koo [email protected] 1
School of Mechanical Engineering, Sungkyunkwan University, Suwon 16419, Korea
2
KITECH (Korea Institute of Industrial Technology), Applied Robot R&D Department, Ansan, Korea
measures external torque and enables control when an external force is applied. Alternatively it works as a passive compliance device that absorbs impact to the robot when an external torque is applied. When the SEA acts as a torque sensor, it is important to define the relationship between the rotation angle of the robot joint and the external torque. In the role of passive compliance, the SEA must have the stiffness characteristic curve desired by users according to the local environment. Many previous studies in the f
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