Object Slippage Detection using Soft Sensor with Robotic Closed-Loop Feedback

Tactile sensing is desirable for skillful object detecting in soft robotics demonstrations. Real-time monitoring of slippage events of objects crucial for robotic interactions. This study realizes a soft sensor with a closed-loop feedback system for object-slippage event-detection in a soft robotic gripper. The sensor is fabricated of a ferroelectric polymer with nanocarbon materials because of the resulting improved crystallinity and good sensitivity. The sensor shows high performance and high-resolution and -speed response for detecting dynamic shear forces when a fragile object slips from the soft gripper. Our artificial cutaneous sensor shows high sensitivity for grasping such objects with the gripper. Further, the feedback system provides a control system for operations. Thus, demonstrating the potential of the proposed system for novel soft robotics applications such as biomimetic electronic skin.<br/>The soft sensor is fabricated from a ferroelectric polymer ideal for slip sensing due to its high-speed response. We used a ferroelectric polymeric material of P(VDF-TrFE) as a sensing layer. In our study, we combined the polymer with composite nanocarbon materials to fabricate high performance sensors. To realize the above materials system, we mixed a polar solvent with the above functional sensing materials. Moreover, a conductive polymeric material pf PEDOT:PSS was mixed with a graphene oxide to fabricate the electrode of the sensor. All sensor components were formed by a solution process of screen printing method.<br/>We measured electric performances of our soft sensor in polarization–electric field (P–E) hysteresis loop. In this study, we define the Pr value as the intersection of the polarization and the electric field curves with the zero of the coordinate systems. The loop with nanocarbon materials realized ferroelectricity of over 11.0 μC cm⁻² despite the use of the screen-printing process (current is ~7.0 μC cm⁻²). Moreover, we setup a closed-loop feedback system for object-slippage event-detection in a soft robotic gripper by our sensor. In this system, the gripper can re-grip several fragile objects automatically by high speed-response when the objects slip. The system was consisted by a personal computer (PC), digital/analog (D/A) and analog/digital (A/D) converters, air compressor, solenoid valve, 24 V power supply, air pressure gauge, co-robot, soft gripper, and proposed sensor. In this setup, the detected signal with our sensor and the signal for air supply to the soft hand are synchronized by the D/A and A/D board. The experiments showed the high sensitivity of the e-skin and demonstrated tactile sensing capabilities that allowed the robotic tactile device to interact with easily damageable objects such as fresh vegetables. By using the shear signals and threshold setting, we produced demonstration our original robotic sensing feedback loop system. Our feedback system provides a novel control system for operations without the need to train for various tasks, thus demonstrating the potential for novel soft robotics applications such as biomimetic electronic skin.