Highly rigid surgical robots are capable of precise positioning; however, there is a risk of injury to the surrounding organs owing to undesired contact. To solve this problem, surgeons can change their stiffness according to the desired motion by contracting and relaxing the muscles. Therefore, surgical robots that can change their stiffness according to their application, similar to a surgeon, are useful in improving safety. However, existing variable stiffness actuators cannot easily achieve a wide variable stiffness range while maintaining a small size and lightweight, which are critical factors for surgical robots. This study presents the design, fabrication, and evaluation of a variable stiffness actuator that is compact and provides a wide range of variable stiffness, with elastic elements arranged in a circumferential direction.

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