Tactile Sensor

The parallel jaws of the gripper are equipped with tactile sensors for enabling tactile feedback during grasping movements. The sensor for each jaw consists of two layers of static foil sensors surrounded by several dynamic hair sensors. The static foil sensors are based on the force sensing resistor (FSR) foil developed by Interlink. Interlink has a patent on the semiconductor folio, which changes its static resistance from about 10 M$\Omega$ to about 1 k$\Omega$ exponentially with the pressure. By combining the FSR foil with a linear potentiometer it is possible to measure force and position in one dimension. The combination of two layers of orthogonally arranged FSR linear potentiometers is used to form a two dimensional sensor array sensing force and position. This static type of sensor can measure the force in a range of 0.1 - 10 N, which is only useful for controlling the grasping force in the final closing phase of the gripper.

For the detection of slightest contact, which allows to track a surface or to measure an object shape, this type of sensor is not sensitive enough. For enabling these advanced tactile skills we need a type of sensor which can measure very precisely the derivative of deformation and not the deformation itself. We achieved these advancedtactile skills by the development of a new dynamic sensor, which is based on a capacitive sensor connected with fibers for the tactile feedback. These new hair sensors are very sensitive, they even react to vibrations of the robot during the movement or to streams of air. Due to the transmission of the contact information with flexible hairs of 1 - 2 cm length, the contact force between manipulator and object is neglectable and the needed refresh rate of tactile controlled movements can be relatively low (20 Hz) in comparison with static sensors. The excelled behavior of these hair sensors are used in our tactile grasping skill and confirms us to submit this tactile method for a patent.The analog sensors are coupled to an 8-bit controller, which uses a multiplexer, a sample-hold circuit and analog-digital converter for storing the latest sensor data. The controller is equipped with a CAN-bus interface and is mounted onto the gripper module. The sensor controller is plugged into the CAN-bus and power supply cord of the manipulator and can be handled like an additional module, i.e., the sensor data can be read out through the CAN-bus interface card of the PC.

	Tactile Sensor. The sensor is a combination of static foil sensors and dynamic hair sensors.