The Fiber Optic Sensor (FOS) developed within the SMARTHANDLE project is not merely a component, but a critical piece of intelligent dexterity that enables the secure handling of extremely sensitive items, such as the contact lenses central to the MENICON use case.
This development is part of the final prototypes for the dexterity enablers. The goal is to implement a FOS based on Fabry-Perot (FP) technology to precisely control the grasping of a contact lens using a vacuum suction cup. The development process of the sensor involved several iterations to overcome fundamental mechanical and signal noise challenges inherent in handling extremely sensitive components.
The first proposal employed the direct lens reflection of the light to estimate the vacuum. Initial implementation steps used a treated fiber optic placed axially inside a standard off-the-shelf FIPA commercial suction cup. The sensing cavity was defined by the space between the fiber tip and the contact lens surface. Testing confirmed the presence of significant noise in the signal reflected directly from the contact lens, hindering the extraction of a reliable sensing signal. Additionally, the insufficient fastening of the fiber caused vibrations when the vacuum was activated, contributing further to signal noise.
To achieve a better signal, it was done a new design where a mirror was placed inside the vacuum suction cup to reflect the optical signal properly, rather than relying on the lens surface. The mirror was positioned in the fold of the suction cup, situated between the contact lens and the fiber optic tip. After several tests, the decision was made to abandon commercial suction cups in favor of custom-designed ones that fit the mirror perfectly inside. Specifically, the final design features a double-bellows system, giving greater gain to the signal and much more stability as shown in the images.
The sensor operates by measuring the resulting deformation: when vacuum is applied and the lens is suctioned, the cup flexes, altering the length of the FP cavity (the distance between the mirror and the fiber tip). This length variation is proportional to the deformation of the contact lens caused by vacuum-induced stretching forces. A dedicated air fitting was manufactured to ensure the fiber optic was coaxial with the air duct, aiding fastening.
The primary challenge in automated contact lens production (ALP) is the safe, non-damaging manipulation of objects that are small, transparent, and deformable. Our FOS-based Tactile Sensor provides a robust control solution to this difficult manipulation task, enhancing the efficiency and reliability of the production line.
- Robust Grasping Control: The FOS is fundamental to controlling the grasping of a contact lens using a vacuum suction cup. By precisely monitoring the suction cup deformation, it ensures the applied vacuum pressure is sufficient to secure the lens but not excessive enough to inflict damage to the object.
- Real-Time Deformability Monitoring: The system works as a FP sensor that provides information in real time on the distance between the mirror and the fiber tip, which is proportional to the deformation suffered by the vacuum cup bellows. This enables the sensor to operate as a continuous monitoring system for grip control.
- Process Transition Detection: Initial tests confirmed that the signal output from the FOS is sufficiently clear to detect critical transitions in the process, such as grasping, releasing, and intentional variations in vacuum pressure. This provides necessary feedback for robotic control systems handling sensitive objects.