Sensors and Actuators A 295 (2019) 512–522 Contents lists available at ScienceDirect Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna Bidirectional rotating actuators using shape memory alloy wires Youngshik Kim a,∗ , Taesoo Jang a , Hema Gurung b , Nader A. Mansour c , Bongjo Ryu a , Buhyun Shin a a Department of Mechanical Engineering, Hanbat National University, Daejeon, South Korea b Department of Mechanical Engineering, Thapar Institute of Engineering and Technology, Patiala, Punjab 147003, India c Department of Mechanical Engineering, Benha Faculty of Engineering, Benha University, Benha 13511, Egypt a r t i c l e i n f o Article history: Received 11 January 2019 Received in revised form 10 May 2019 Accepted 30 May 2019 Available online 18 June 2019 Keywords: Bidirectional Characterization Shape Memory Alloy (SMA) wire Rotating actuator Open-loop and closed-loop control system a b s t r a c t In this work, novel Shape Memory Alloy (SMA)-based actuators are proposed to provide angular dis- placements in both clockwise and counter-clockwise directions with compliance. A bidirectional SMA rotating actuator is fabricated using a rotating frame and two SMA wire-based actuating units similar to human skeletal muscle systems without any additional complicated rotational driving mechanism. These actuating units are activated independently to provide bidirectional rotary motions by using sequentially coordinated electrical inputs. The mechanical, thermal, and electrical properties of the bidirectional SMA rotating actuator are also characterized experimentally. The design and manipulation of the proposed actuator are experimentally verified with simple open-loop and closed-loop control strategies. © 2019 Elsevier B.V. All rights reserved. 1. Introduction Shape Memory Alloy (SMA) is a smart material that can mem- orize its original shape. SMA possess two thermo-mechanical properties: shape memory effect (SME) and pseudo-elasticity (PE). SMA material below its phase transformation temperature can be easily deformed by external force and hence, produce large residual strain. Through the SME, the generated strain gets fully recovered if the SMA is heated above transformation temperature. Whereas, in PE effect, above some transformation temperature loading and unloading causes strain variation. During these deformation and recovery processes, SMA material can generate large mechanical force and displacement. Thus, SMA material is used in various appli- cations providing new methods of actuation, which was difficult to achieve previously using traditional actuators such as electromag- netic motors. Comparing to electromagnetic motors, SMA actuators provide high power-to-weight ratio, clean and silent operation, compliance, small size, biocompatability and require small driving voltage. Thus, SMA actuators have been used frequently in biomed- ical, aerospace, and robotic fields [1]. Many non-invasive surgical devices [2] have used SMA material for actuation. Recently, many robotic researchers have used SMA actuators in various robotic ∗ Corresponding author. E-mail address: youngshik@hanbat.ac.kr (Y. Kim). applications which include soft and biologically inspired robots [3–7]. SMA wires have been usually used to provide one-dimensional linear or bending motion that is limited to a maximum strain of 5–8% of the original wire length [5,7–9]. However, SMA springs can provide relatively high deformation that can achieve more than 100% of its basic length depending on their resisting load and geo- metric configuration [10]. Due to difficulty in achieving rotating or folding motion using a single SMA wire or spring, researchers [11,12] have used sheets or thin plates for this purpose. Typi- cally, these SMA sheet-based folding actuators are produced by applying laser cutting process. SMA sheets [3] along with SMA springs [4,10,13] have been adopted for the rolling motion of soft or biologically inspired robots. Another novel actuator has been developed in [14] to provide rotational motion based on using a straight SMA wire that is sewed between two supporting elements. Bidirectional actuators were also presented for specific applica- tions such as a robotic fish [7] and origami [12]. However, in most of the aforementioned research, SMA actuators typically pro- vide unidirectional motion. Furthermore, a unidirectional actuator may be combined with a bias spring or an antagonistic unidirec- tional actuator to achieve bidirectional motion. Antagonistic SMA actuators can provide several advantages over spring-biased SMA actuators as mentioned in [15–17], which provides faster response, better controllability, larger displacement, linear resistance vari- ation and smaller temperature hysteresis. The use of SMA as an actuator requires a clear understanding of the thermo-mechanical https://doi.org/10.1016/j.sna.2019.05.047 0924-4247/© 2019 Elsevier B.V. All rights reserved.