In most cases, the sensors fitted to robot arms and grippers are restricted to a single function. They detect objects based on either proximity or pressure. The developed ‘capacitive tactile proximity sensors’ developed by KIT unite both functions simultaneously.
Each sensor module is divided into three layers. The bottom layer consists of a flat electrode. The intermediate layer is made of a compressible insulating material, for example, foamed plastic. The top layer consists of several geometrically arranged electrodes. The number and shape of these electrodes vary, according to the specific application. The electronic control unit is separate from the sensor module. The modules can be deployed individually or as part of an interconnected sensor system.
When an object approaches the robot, it alters the electric field surrounding the sensor. The sensor uses this effect to detect the motion and proximity of the object. The mechanical compression of the intermediate layer leads to a change in the electrical capacitance between the electrodes. In this way, the sensor is able to derive tactile information.
Explains Dr Björn Hein, head of the Intelligent Industrial Robots Group (IIROB) at KIT: “The electrodes in the top layer can be freely combined. This allows us to achieve a compromise between the range and spatial resolution of the sensors.”
The modules can be combined to create sensor areas of varying sizes – small surfaces for grippers, large surfaces for a complete robot ‘skin’.
Capacitive tactile proximity sensors significantly enhance the flexibility and agility of automated industrial production. In addition, they improve the safety of human-machine interaction by detecting and localising approaching persons and emitting a warning signal as soon as they cross a predefined safety limit. In such cases, the robot slows down or stops completely. This makes a major contribution to effective human-robot collaboration in cases where humans and robots are working on the same component.
KIT will demonstrate the potential of its capacitive tactile proximity sensors at Hanover Messe 2018 (23 to 27 April).