US-12618728-B2 - Optical pressure sensor

US12618728B2US 12618728 B2US12618728 B2US 12618728B2US-12618728-B2

Abstract

An optical pressure sensor including an optical radiation source and an optical guide that may be optically coupled to the radiation source and may be configured to obtain a total internal reflection condition. The optical guide may define an interface wall. The sensor may also include an element elastically deformable and transparent to optical radiation that has a face facing said interface wall and configured so that a pressure exerted on the deformable element changes a contact area with the interface wall so that the optical guide assumes a frustrated total internal reflection condition with emission of an output optical radiation towards the first face of the deformable element dependent on the exerted pressure. The sensor may further include a photoresistor optically coupled to the second face of the deformable element and configured to provide an electrical signal dependent on the output optical radiation.

Inventors

Garbo Pierre
Andrea Zanoni
Alberto Lavatelli
Giuseppe Quaranta

Assignees

POLITECNICO DI MILANO

Dates

Publication Date: 20260505
Application Date: 20220308
Priority Date: 20210330

Claims (13)

1 . An optical pressure sensor comprising: an optical radiation source configured to emit an optical radiation; an optical guide optically coupled to the optical radiation source and configured to achieve a total internal reflection condition, the optical guide defining an interface wall to the outside; an elastically deformable element configured to be transparent to the optical radiation and having a first face that is facing the interface wall and a second face, the elastically deformable element being further configured such that in the presence of a pressure exerted on the elastically deformable element, a contact area between the elastically deformable element and the interface wall is modified so that the optical guide assumes a condition of total internal frustrated reflection with emission of an output optical radiation towards the first face of the elastically deformable element dependent on the pressure exerted and on the contact area; and a photoresistor optically coupled to the second face of the elastically deformable element and configured to provide an electrical signal dependent on the output optical radiation; wherein the optical radiation source includes at least one LED; wherein the optical guide includes a cylindrical guide optically coupled to the at least one LED; wherein the first face of the elastically deformable element hemispherical and the second face of the elastically deformable element is flat to define a second flat face, wherein the photoresistor is fixed to the second flat face; and wherein the output optical radiation is a function of an area of a contact surface between the first face of the elastically deformable element and the interface surface.
2 . The optical pressure sensor according to claim 1 , further comprising an electronic circuit connected to the photoresistor, wherein the electrical circuit is configured to: provide a readout signal to the photoresistor and receive the electrical signal dependent on the output optical radiation; and process the electrical signal dependent on the output optical radiation and provide information of interest (Sc) associated with the pressure exerted.
3 . The optical pressure sensor according to claim 1 , wherein the optical guide is a plexiglass cylinder, and wherein the elastically deformable element is made of silicone rubber.
4 . The optical pressure sensor according to claim 1 , wherein the at least one LED comprises a first LED disposed at one end of the optical guide and a second LED disposed at another end of the optical guide.
5 . The optical pressure sensor according to claim 1 , wherein the elastically deformable element comprises a plurality of elastically deformable elements; wherein the photoresistor comprises a plurality of photoresistors; wherein a second one of the elastically deformable elements is transparent to the optical radiation and has a respective first face facing the interface wall and a respective second face, wherein the presence of a pressure exerted on the second one of the elastically deformable elements, causes a modification of a corresponding contact area between the interface wall and the second one of the elastically deformable elements so that the optical guide assumes a condition of total internal frustrated reflection with emission of a further output optical radiation towards the first face of the second one of the elastically deformable elements responsive to the relative pressure exerted and on the corresponding contact area; and wherein a second one of the photoresistors is optically coupled to the second face of the second one of the elastically deformable elements and configured to provide a further electrical signal dependent on the further optical output radiation.
6 . The optical pressure sensor according to claim 5 , further comprising an electronic circuit configured to provide a further readout signal to the second one of the photoresistors and process the further electrical signal and provide a relative information of interest associated with the relative pressure exerted.
7 . The optical pressure sensor according to claim 5 , wherein the plurality of photoresistors are electrically connected in series.
8 . The optical pressure sensor according to claim 1 , further comprising: a load cell including a support structure configured to house the elastically deformable element and the photoresistor; and an outer casing configured to house the optical guide and having an opening configured to house the load cell allowing displacements relative to the optical guide under the action of the pressure exerted.
9 . The optical pressure sensor according to claim 8 , wherein the support structure includes a seat for the photoresistor and is configured such that the first face of the elastically deformable element protrudes towards the interface wall, and wherein the support structure identifies a concave surface suitable to accommodate at least part of the optical guide.
10 . The optical pressure sensor according to claim 1 , wherein the sensor is configured such that the pressure exerted is produced as a result of at least one action that includes action of a user's hand on a handle and action of a user's pelvic floor.
11 . The optical pressure sensor according to claim 10 , wherein the sensor is configured to operate as at least one of a cyclic control bar of an aircraft and a collective control bar of an aircraft.
12 . The optical pressure sensor according to claim 1 , wherein the optical pressure sensor is configured to operate in conjunction with at least one of a steering wheel of a car, input stick of a bulldozer, input stick of a construction vehicle, input stick of an aircraft or autogyro, and a power tool.
13 . The optical pressure sensor according to claim 1 , wherein the optical pressure sensor is configured to operate in conjunction with at least one of a training device and physiotherapy device.

Description

RELATED APPLICATIONS This application is a national phase application of, and claims priority under 35 U.S.C. § 371 to PCT application serial No. PCT/IB2022/052048, filed on Mar. 8, 2022 and titled OPTICAL PRESSURE SENSOR, which, in turn, claims priority to Italian Patent Application No. 102021000007781 filed on Mar. 30, 2021 and titled Sensore di pressione ottico. The contents of each of these applications are incorporated herein by reference except for where the content therein conflicts with the content herein. TECHNICAL FIELD The present invention relates to optical pressure sensors, and in particular to sensors that operate based on the phenomenon of frustrated total internal reflection. STATE OF THE ART As known, Total Internal Reflection (TIR) indicates the complete reflection of electromagnetic radiation within a material, in the presence of an interface with another material. The phenomenon occurs if the angle of incidence is greater than a certain limiting angle, called the critical angle, depending on the refractive indices of the two interfaced materials, according to Snell's law. Although in a TIR condition the radiation is basically completely reflected, there is a part of the electromagnetic field that crosses the interface. This field does not propagate but decays very quickly with distance from the interface. However, in the presence of another material within this distance, with a refractive index at least equal to that of the first material, some of the radiation may propagate again and the reflection will not be complete. In this case we speak of frustrated total internal reflection (in English, Frustrated TIR). The paper S. Zhu, A. Yu, D. Hawley, and R. Roy “Frustrated total internal reflection: a demonstration and review”, American Journal of Physics, vol 54, no. 7, pp. 601-607, 1986, provides a theoretical description of the FTIR phenomenon. The paper A. Lavatelli, A. Zanoni, E. Zappa, A. Cigada, “On the Design of Force Sensors Based on Frustrated Total Internal Reflection,” IEEE Transactions on Instrumentation and Measurements, vol. 68, no. 10, pp 4065-4074, 2019, describes among others, an experiment documenting the behavior of the FTIR phenomenon at the micromechanical level and proposes a Greenwood-Williamson (GW) model as a tool to predict the response of an FTIR-based pressure sensor. The paper J. Castillo, A. P. D. L. Blanca, J. A. Cabrera, A. Simón, “An optical tire contact pressure test bench,” Vehicle System Dynamics, vol 44, no. 3, pp. 207-221, 2006, describes an optical test bench for tire contact pressure measurement. U.S. Pat. No. 9,880,653 describes a pressure-sensitive tactile system consisting of a transparent sheet, with a light source and detector arranged along perimeter of the transparent sheet. SUMMARY OF THE INVENTION The present invention addresses the problem of providing an optical pressure sensor, based on the FTIR phenomenon, which is an alternative to known ones and which, in particular, is not limited to the measurement of pressures exerted on large surfaces but allows its miniaturization. The present invention relates to an optical pressure sensor as defined by independent claim 1 and particular embodiments thereof, as defined by dependent claims 2, and 4-13. BRIEF DESCRIPTION OF THE DRAWINGS The present invention is hereinafter described in detail, by way of example but not limitation, with reference to the accompanying drawings, wherein: FIG. 1 shows an example of an optical pressure sensor comprising an optical guide and a load cell with two photoresistors and two elastically deformable and transparent elements; FIG. 2 refers to another example of said optical sensor implemented as a control rod of a helicopter or a driving simulator system; FIG. 3 shows an example of an outer casing of said control bar; FIG. 4 shows load cells and optical guides housed in said enclosure; FIG. 5 shows a support base of two photoresistors with relative elastically deformable elements of one of said load cells; FIG. 6 shows one of the load cells and one of the optical guides housed in the casing of the control bar; FIGS. 7 and 8 show, respectively, a front view and a rear view of one of said load cells of the control bar; FIG. 9 shows an example of an electronic circuit that can be associated with the control bar. DETAILED DESCRIPTION In this description, similar or identical items or components will be referred to in the figures by the same identifying symbol. FIG. 1 shows an example of an optical pressure sensor 100 operating according to the principle of frustrated total internal reflection. The optical pressure sensor 100 (hereinafter, for brevity, “optical sensor”) includes at least one optical radiation source 1, an optical guide 2, at least one elastically deformable element 3, and at least one photoresistor 4. In accordance with the particular embodiment described herein, the sensor 100 is such that it generates an electrical signal dependent on the pressure exe