While most optical tactile sensors rely on measuring surface displacement, insights from continuum mechanics suggest that measuring shear strain provides key information for tactile sensing. In this work, we introduce an optical tactile sensing principle based on shear strain detection. A silicone rubber layer, dyed with color inks, is used to quantify the shear magnitude of the sensing layer. This principle was validated using the NUSense camera-based tactile sensor. The wide-angle camera captures the elongation of the soft pad under mechanical load, a phenomenon attributed to the Poisson effect. We tested the robustness of the sensor by subjecting the outermost layer to multiple load (8 N) cycles using a 5 mm in radius ball head indenter. The physical and optical properties of the inked pad proved essential and remained stable over time, exhibiting only low variance.

The prompt and robust detection of tactile information is a relevant and challenging problem, and a considerable research effort is, thus, being put into innovative transduction methods for tactile sensors. In this article, we investigate the possibility of using event-based cameras to sense contact forces applied to objects by a robot end effector. The proposed optical tactile sensor incorporates a soft hemispherical pad made of silicone rubber with imprinted markers and a pulsewidth modulation light source that emits optical pulses, allowing robust detection of the markers to track deformations of the pad. To test the effectiveness of our sensor, experiments were carried out attaching it to a teleoperated robot arm to finely control it when out of the user's field of view, as accurately as if the user could see it. In the experiments, an augmented reality display and a haptic device were used to convey the force detected by the event-based tactile sensor back to the human operator. The experiments included a practical application of a soft tissue puncturing tool, and psychophysical test results from ten participants were recorded, to validate efficacy and usability of the system.

We report findings from initial exploration into using electrotactile stimulation, on the surgeon's tongue, as a potential lower-latency and less mechanically-complex way to provide force-feedback to the operator of robot-assisted surgery. We conducted a pilot feasibility study wherein participants attempted to teleoperate a robot to grasp and lift chicken eggs without breaking or dropping them. The force measured by the robot's gripper was displayed differently based on the experimental condition: visually only, or visually with electrotactile tongue stimulation. Participants were more successful lifting eggs with tongue stimulation. Data from this preliminary study, along with insights from informal interviews, suggest that tongue stimulation has potential to enhance the efficacy and safety of robot-assisted surgery.

Traditionally vibrotactile feedback delivered by haptic interfaces is used to provide additional support for visual interaction via prehensile object manipulation using fingers. Nevertheless, haptic stimuli can be also applied for non-prehensile interaction that involves movements of the elbow joint. In this paper, we have designed a table-top haptic device that provides vibrotactile stimulation to the user’s fingertips. This stimulation creates a kinesthetic illusion of the user’s forearm pivot movement with respect to the elbow joint. The vibrotactile stimulation is amplified by the pseudo-haptic effect delivered through a head-mounted display (HMD). The efficacy of the approach was validated in experiments with human subjects. The results show that the combination of pseudo-haptic and haptic illusion effects can be used to render various soft and rigid virtual objects.

The sense of touch is essential for reliable mapping between the environment and a robot which interacts physically with objects. Presumably, an artificial tactile skin would facilitate safe interaction of the robots with the environment. In this work, we present our color-coded tactile sensor, incorporating plastic optical fibers (POF), transparent silicone rubber and an off-the-shelf color camera. Processing electronics are placed away from the sensing surface to make the sensor robust to harsh environments. Contact localization is possible thanks to the lower number of light sources compared to the number of camera POFs. Classical machine learning techniques and a hierarchical classification scheme were used for contact localization. Specifically, we generated the mapping from stimulation to sensation of a robotic perception system using our sensor. We achieved a force sensing range up to 18 N with the force resolution of around 3.6 N and the spatial resolution of 8 mm. The color-coded tactile sensor is suitable for tactile exploration and might enable further innovations in robust tactile sensing.

Tactile sensing arrays are used to detect contacts of robotic systems with the environment. They are particularly useful for scenarios in which vision-based sensors cannot be used. Thanks to the presence of multiple sensing elements, tactile arrays also provide spatial information about the contact location. In this work, we present our series elastic tactile array to enable tactile exploration for position-controlled robot manipulators. Sixteen compliant sensing elements are arranged as a 4×4 array. This allows the position-controlled robot to explore objects via palpation. Tactile sensing was accomplished by measuring the change of the magnetic field caused by neodymium magnets embedded into the series elastic elements. We demonstrate the efficacy of our sensor with two sets of experiments involving physical interaction scenarios. Firstly, we show that the sensor can be used to differentiate between rigid and deformable objects. Secondly, we show that point clouds of objects can be generated quickly with our sensor module attached to a position-controlled robot manipulator as an end-effector.