Tactile Sensing and Control of Robotic Manipulator Integrating Fiber Bragg Grating Strain-Sensor

Abstract

Tactile sensing is an instrumental modality of robotic manipulation, as it provides information that is not accessible via remote sensors such as cameras or lidars. Touch is particularly crucial in unstructured environments, where the robot's internal representation of manipulated objects is uncertain. In this study we present the sensorization of an existing artificial hand, with the aim to achieve fine control of robotic limbs and perception of object's physical properties. Tactile feedback is conveyed by means of a soft sensor integrated at the fingertip of a robotic hand. The sensor consists of an optical fiber, housing Fiber Bragg Gratings (FBGs) transducers, embedded into a soft polymeric material integrated on a rigid hand. Through several tasks involving grasps of different objects in various conditions, the ability of the system to acquire information is assessed. Results show that a classifier based on the sensor outputs of the robotic hand is capable of accurately detecting both size and rigidity of the operated objects (99.36 and 100% accuracy, respectively). Furthermore, the outputs provide evidence of the ability to grab fragile objects without breakage or slippage e and to perform dynamic manipulative tasks, that involve the adaptation of fingers position based on the grasped objects' condition.

Fiber Bragg Gratings for Medical Applications and Future Challenges: A Review

“…Then, three walking tests at three different velocities (i.e., 0.5 m/s, 1.1 m/s, and 2.2 m/s) were performed by attaching the instrumented prosthesis on the knee, showing promising results especially for the FBGs attached to the regions where the prosthesis stores and releases energy during walking. Such a study, combined with other ones focused on robotic manipulators equipped with FBGs for tactile sensing [74], [75] opens up to future applications of FBGs in bionics. Indeed, FBG-based sensory feedback could enable closedloop control of the prosthesis, improving its embodiment, amputee's recovery functions, and engagement with the surroundings going beyond the results achieved with MEMS sensors [76], [77].…”

Neuromorphic tactile sensor array based on fiber Bragg gratings to encode object qualities

“…The JPL's quadruped RoboSimian robot is equipped with an under-actuated hand (Cam-Hand) with manipulation and versatile mobility capabilities [16]. The hand consists of four aluminum fingers that were equipped with two optical fibers (running along the length of the finger) encased in a soft polymeric material in our previous work [20]. Each fiber hosted 6 FBGs.…”

“…The chosen FBG technology can be easily multiplexed (inside a single optical fiber, each grating has unique λB well separated from the others) and multiplexed FBGs provide multiple sensor sites, thus increasing sensor resolution. Figure 1 illustrates the working concept through a parallel in between the proposed neuromorphic sensor [20] encoding and human touch [9]. Experimental validation was performed by grasping cylindrical samples (30mm diameter, 150mm height).…”

“…This technology offers various advantages in terms of high sensitivity, flexibility, electromagnetic immunity, multiplexing and scalable capabilities [18,19]. For the purpose of the tactile sensing, the Fiber Bragg Gratings (FBG) were chosen for their ability to measure and localize the applied strain [20,21]. Here, the contribution of temperature is negligible, since the whole experimental session was performed at room temperature.…”

“…In particular, the proposed sensor is based on Fiber Bragg Grating (FBG) transducers [24] coupled to an Izhikevich neuron model [25]. Building on a previous implementation [20], the proposed sensor was integrated in a robotic gripper and experimentally validated by discriminating the stiffness of grasped samples made of different materials. We propose a novel neuromorphic FBG-based tactile system that is flexible, sensitive and easily adaptable for different platforms and applications.…”