• Authors: Dobrzynski, Michal; Halasz, Ionut; Pericet Camara, Ramon; Floreano, Dario

Typical deflection sensors like strain gauges or devices based on optical fibers require physical contact with the deflected substrate during the measurement process. Such contact, however, impacts on the softness of the substrate and may falsify the measurements. In order to overcome this drawback, a novel method of contactless deflection sensing was proposed in a recent work. It was verified that the deflection angle between two planes can be extracted using only a photosensor and a light source bearing a bell-shape angular emission profile. Yet, the range of operation was limited to concave shapes. In this paper, we introduce an alternative configuration of this light-based deflection sensing method to extend its functionality to convex surfaces. Here, a spheroidal mirror bearing a customized profile is introduced above the light source. This mirror redirects part of the emitted light towards the photosensor hindered by the bending surface during convex deflections.We make use of a ray tracing simulation method to design the mirror profiles, which are accurately reproduced in the manufactured prototypes by tuning the fabrication variables of the manufacturing process. Using a shape-sensing prototype, it is verified that the use of the mirror extends the range of detectable deflections by 55deg. to convex bendings, yielding a deviation of only 8.3% from simulated results. Our deflection sensing solution is a promising method to be used as a shape sensor in numerous applications, such as soft robotics platforms or prosthetic devices.

• Authors: Dobrzynski, Michal; Pericet Camara, Ramon; Floreano, Dario

In the emerging field of soft robotics, there is an interest in developing new kinds of sensors whose characteristics do not affect the intrinsic compliance of soft robot components. Additionally, non-invasive shape and deflection sensors may provoke improved solutions to assist in the control of mechanical parts in these robots. Herein, we introduce a novel method for deflection sensing where an LED element and a photodiode are placed on to two substrates connected physically or virtually at a deflection point. The deflection angle between the two planes can be extracted from the LED light intensity detected at the photodiode due to the bell-shaped angular intensity profile of the emitted light. The main advantage of this system is that the components are not in physical contact with the deflection region as in the case of strain gauges and similar sensing methods. The sensor is characterized in a range of deflections of 105-180 degrees, showing a near 1 degree resolution. The experimental data are compared to simulations, modeled by ray tracing. The light intensity vs. deflection angle measurements in our setup display a maximum difference of 9% and an average difference of approximately 5% with respect to the model. Finally, a shape monitoring system has been developed using the proposed concept for a flexible PCB. The system is composed of 12 deflection sensors that operate at frame rate of 33 Hz. This device could be applied to monitor the body shape of a soft robot.