- Why cobot?
In the future robots should share their workspace with humans and work in unstructured environments, and for safety and to perform adaptive tasks, a rich set of sensors is needed in such scenarios. Tactile sensors on the robot's surface can provide the most detailed and direct information about the contacts with the environment, and are therefore a crucial component. Yet, the fact that they should be spread over the surface makes the implementation difficult.
When designing tactile skin sensors, we consider that they should have the following characteristics: (i) soft, (ii) distributed, (iii) sensing the 3-axis force vectors and (iv) integrated electronics.
Softness of the robot’s skin adds to the safety of the robot, because it adds a level of security that cannot be achieved with other methods. Active control schemes alone are typically too slow for impacts. Compliant joints help, and are a crucial component as they can typically absorb more energy than soft skin, but they can only decouple the various links of the robot, while the inertia of the robot segments in contact with the human could still lead to harmful forces. Only soft skin can absorb impact energy directly at the collision site. Furthermore, soft skin in robot hands can enhance the grasp stability, and our group has found that soft skin also aids during manipulation.
Distributed skin sensors provide detailed information about the contacts with the environment, which can be used for example for tasks like tactile servoing or tactile object recognition. Alternatives exist, like force sensors in the robot's joints, but they provide less information, as each sensor can only measure the sum of all the forces acting on it.
(iii) Sensing the 3-axis force vectors
While most distributed skin sensors only measure single axis force, measuring the force vector is required for tasks such as tactile servoing, and our group has used such information for example for robust in-hand manipulation. Distributed force vector measurements are useful in scenarios with more than one contact, a situation that is typically challenging for existing solutions that cannot measure distributed force vectors.
(iv) Integrated electronics
When distributing many sensors in the robot’s surface, without integrated electronics, a lot of wires would be required, which would require a lot of space and which would make the integration in the robot and their maintenance challenging. Distributed electronics can help, and several sensors should share a data line. Sending digital instead of analog information also makes the sensor signals less prone to interference from the environment.