Design and development of a 3RRS wearable fingertip cutaneous device

Wearable technologies are gaining great popularity in the recent years. The demand for devices that are lightweight and compact challenges researchers to pursue innovative solutions to make existing technologies more portable and wearable. In this paper we present a novel wearable cutaneous fingertip device with 3 degrees of freedom. It is composed of two parallel platforms: the upper body is fixed on the back of the finger, housing three small servo motors, and the mobile end-effector is in contact with the volar surface of the fingertip. The two platforms are connected by three articulated legs, actuated by the motors in order to move the mobile platform toward the user's fingertip and re-angle it to simulate contacts with arbitrarily oriented surfaces. Each leg is composed of two rigid links, connected to each other and then to the platforms, according to a RRS (Revolute-Revolute-Spherical) kinematic chain. With respect to other similar cable-driven devices presented in the literature, this device solves the indeterminacy due to the underactuation of the platform. This work presents the main design steps for the development of the wearable display, along with its kinematics, quasi-static modeling, and control. In particular, we analyzed the relationship between device performance and its main geometrical parameters. A perceptual experiment shows that the cutaneous device is able to effectively render different platform configurations.