TouchRoller: A Rolling Optical Tactile Sensor for Rapid Assessment of Textures for Large Surface Areas

Tactile sensing is important for robots to perceive the world as it captures the physicalsurface properties of the object with which it is in contact and is robust to illumination and colourvariances. However, due to the limited sensing area and the resistance of their fixed surface when theyare applied with relative motions to the object, current tactile sensors have to tap the tactile sensoron the target object a great number of times when assessing a large surface, i.e., pressing, lifting up,and shifting to another region. This process is ineffective and time-consuming. It is also undesirableto drag such sensors as this often damages the sensitive membrane of the sensor or the object. Toaddress these problems, we propose a roller-based optical tactile sensor named TouchRoller, whichcan roll around its centre axis. It maintains being in contact with the assessed surface throughout theentire motion, allowing for efficient and continuous measurement. Extensive experiments showedthat the TouchRoller sensor can cover a textured surface of 8 cm × 11 cm in a short time of 10 s, muchmore effectively than a flat optical tactile sensor (in 196 s). The reconstructed map of the texture fromthe collected tactile images has a high Structural Similarity Index (SSIM) of 0.31 on average whencompared with the visual texture. In addition, the contacts on the sensor can be localised with alow localisation error, 2.63 mm in the centre regions and 7.66 mm on average. The proposed sensorwill enable the fast assessment of large surfaces with high-resolution tactile sensing and the effectivecollection of tactile images.