  Tactile sensing is important for robots to perceive the world as it captures
the texture and hardness of the object in contact and is robust to illumination
and colour variances. However, due to the limited sensing area and the
resistance of the fixed surface, current tactile sensors have to tap the
tactile sensor on target object many 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 undesirable to drag such sensors as
this often damages the sensitive membrane of the sensor or the object. To
address these problems, we propose a cylindrical optical tactile sensor named
TouchRoller that can roll around its center axis. It maintains being in contact
with the assessed surface throughout the entire motion, which allows for
measuring the object continuously and effectively. Extensive experiments show
that the TouchRoller sensor can cover a textured surface of 8cm*11cm in a short
time of 10s, much more effectively than a flat optical tactile sensor (in
196s). The reconstructed map of the texture from the collected tactile images
has a high Structural Similarity Index (SSIM) of 0.31 on average, when compared
with the visual texture. In addition, the contacts on the sensor can be
localised with a low localisation error, 2.63mm in the center regions and
7.66mm on average. The proposed sensor will enable the fast assessment of large
surfaces with high-resolution tactile sensing, and also the effective
collection of tactile images.
