EP2176632A1 - Conformant and flexible tactile sensor and method therefor - Google Patents

Conformant and flexible tactile sensor and method therefor

Info

Publication number
EP2176632A1
EP2176632A1 EP08788913A EP08788913A EP2176632A1 EP 2176632 A1 EP2176632 A1 EP 2176632A1 EP 08788913 A EP08788913 A EP 08788913A EP 08788913 A EP08788913 A EP 08788913A EP 2176632 A1 EP2176632 A1 EP 2176632A1
Authority
EP
European Patent Office
Prior art keywords
layer
light
support layer
sensing
sensing elements
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP08788913A
Other languages
German (de)
French (fr)
Inventor
Alessandro Persichetti
Fabrizio Vecchi
Maria Chiara Carrozza
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Scuola Superiore di Studi Universitari e di Perfezionamento SantAnna
Original Assignee
Scuola Superiore di Studi Universitari e di Perfezionamento SantAnna
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Scuola Superiore di Studi Universitari e di Perfezionamento SantAnna filed Critical Scuola Superiore di Studi Universitari e di Perfezionamento SantAnna
Publication of EP2176632A1 publication Critical patent/EP2176632A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
    • G01L1/247—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet using distributed sensing elements, e.g. microcapsules
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J13/00—Controls for manipulators
    • B25J13/08—Controls for manipulators by means of sensing devices, e.g. viewing or touching devices
    • B25J13/081—Touching devices, e.g. pressure-sensitive
    • B25J13/084—Tactile sensors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/22—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring the force applied to control members, e.g. control members of vehicles, triggers
    • G01L5/226—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring the force applied to control members, e.g. control members of vehicles, triggers to manipulators, e.g. the force due to gripping
    • G01L5/228—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring the force applied to control members, e.g. control members of vehicles, triggers to manipulators, e.g. the force due to gripping using tactile array force sensors
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/011—Arrangements for interaction with the human body, e.g. for user immersion in virtual reality
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/042—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by opto-electronic means
    • G06F3/0421—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by opto-electronic means by interrupting or reflecting a light beam, e.g. optical touch-screen

Definitions

  • the present invention relates to a tactile sensor adapted to detect a contact with an external body, discriminating shape, intensity of the tactile action, position of the application of the same action and slip.
  • an artificial skin with the aforesaid characteristics.
  • Possible applications concern the cases in which a mechanical interaction between two physic systems is expected, such as body-body, body-machine, body-environment, machine-machine, and machine-environment.
  • Possible fields of application are prosthetic robotics and orthotics, humanoid robotics, technological aids.
  • a tactile sensor that, in addition to giving information as output, which relates to the type of contact, intensity, position and slip, it has the exterior aspect of a sensing skin, flexible and applicable on a surface, adapted to provide sensory information similar to the human skin when contacting it.
  • Such sensors are expected to have high characteristics and performances in terms of functionality, sensibility, conformance, flexibility, softness and density.
  • Devices with tactile functionalities are known, such as that described in JP61041938, having a structure of rigid base on which an array of optoelectronics components is arranged, comprising a plurality of light elements and sensing elements placed on two different overlapped planes. For each light element a couple of sensing elements is provided that can be reached by the light emitted from light sources. The light elements emit radiations in a direction orthogonal to the plane of the base structure.
  • Such device has the disadvantage of being not flexible and therefore not adaptable to the shape of the object to cover, and therefore it is not usable in order to cover a curved surface, in particular a surface that changes its shape with time, such as an orthosis or a robotic prosthesis.
  • Another disadvantage of the aforesaid known device is that, since it requires a great number of light sources, it causes a high consumption of electric current.
  • a further disadvantage of the aforesaid known device it is that it presents a large thickness that inhibits its use as artificial skin.
  • any electromagnetic radiation source visible by an optical sensor is provided, and therefore extending even beyond the radiation range that is visible by a human eye.
  • Another object of the present invention is to provide an optoelectronic tactile sensor having an elevated robustness to impacts and to pressures applied even for long period.
  • a further object of the present invention is to provide a tactile sensor that has an high density of sensing elements and therefore a good spatial resolution.
  • Another object of the present invention is to provide a tactile sensor adapted to measure a wide range of pressures.
  • Another object of the present invention is to provide a method for producing such a tactile sensor.
  • a tactile sensor having an extended sensing surface adapted to detect the contact with an external body, characterized in that it comprises:
  • a flexible support layer parallel to said sensing surface comprising:
  • the support layer is made of a flexible material.
  • the elastic material is selected from the group comprised of:
  • - viscoelastic material in particular silicone rubber; plastic material; synthetic rubber;
  • Such tactile sensor can be used as artificial skin adapted to perceive the shapes, since the sensor can provide as autput a sort of image of the surface that is touching the entire array, taking advantage of the great conformance that the elastic material possesses, in particular silicone rubber.
  • said array of light sensing elements comprises a plurality of elements placed according to a predefined pattern, said at least one light source being arranged peripherally regarding said matrix of sensing elements, preferably along the border of said array.
  • Such a configuration allows to have a high density of sensing elements and therefore a high spatial resolution, since no further space has to be provided among them in order to house the light sources.
  • such a configuration allows to use a reduced number of light sources, involving a constructive simplification and an energy saving, therefore reduced costs.
  • said array of sensing elements, said at least one light source and said circuit are substantially on a same plane.
  • said circuit is obtained by means of photo- etching of a copper layer on one face or on both faces of a support layer of polyimide, and said array of sensing elements and said at least one light source are applied on said circuit.
  • said prefixed angle with respect to said support layer is comprised between 0° and 90°, in particular between 0° and 45°, preferably 0°.
  • Such angle depends on the results that are sought and on the desired characteristics of sensitivity.
  • said shielding cover is in particular white, and an external face of dark colour, in particular black, in order to prevent that an external light disturbs the device or that the internal radiation disperses in the environment.
  • the shielding cover presents, furthermore, a reflecting inner surface, in particular white, which causes an internal reflection of the light.
  • a further external layer that covers said external face of said cover can be provided, made of a soft material that mimics the colour of the human skin.
  • At least one transparent soft layer interposed between said elastic transparent layer and said shielding cover is provided, said transparent soft layer being softer than said elastic transparent layer.
  • said transparent soft layer is selected from the group comprised of:
  • a plurality of transparent soft layers is provided that are overlapped to each other between said elastic transparent layer and said shielding cover, said transparent soft layers having different stiffness, in particular arranged in increasing order of stiffness from said cover towards said support layer.
  • the support has at least an aperture and a layer of adhesive material is provided, for example silicone rubber, arranged adjacent to the support opposite to the layer of transparent material.
  • a layer of adhesive material is provided, for example silicone rubber, arranged adjacent to the support opposite to the layer of transparent material.
  • the layer of adhesive material extends through said, or each, aperture up to contacting said layer of transparent material. This way, the layer of adhesive material causes said support layer to fix to said layer of transparent material.
  • the adhesive layer can be made of a silicone rubber having stiffness greater than that of silicone rubbers used to make other layers of the sensor.
  • a further layer external to the adhesive layer opposite to the support layer can be provided.
  • the possible external stimulus causes a deformation of the silicone rubber cover, and consequently the amount of light seen by the sensing elements in correspondence of the stimulus changes.
  • One delicate contact can be detected thanks to the fact that the first layer under the cover is constituted by a very soft elastic transparent layer (or air) , such that the silicone rubber can easily be compressed to vary the inner light. If the external force is high, such very soft silicone rubber layer (or air) is completely compressed and the underlying elastic transparent layer, in the same way, deforms and causes the sensing elements to detect a decrease of the intensity of light.
  • every sensing element has an analog or digital output, deriving for example from a photodiode, a phototransistor or a photoresistor, depending on which optocomponent is used as sensing element.
  • the analog output varies proportionally to the amount of light that it receives, and consequently, it varies proportionally to the compression of the silicone rubber chamber through which the light emitted by light sources is transmitted.
  • said correlating means associated to said electronic circuit in order to correlate the light intensity received from said array of sensing elements and the deformation of said support layer, comprises computing means that determine the variation of the light signal received by each sensing element.
  • the sensor like a detector of shapes, using for example neural networks.
  • a tactile apparatus having an extended sensible surface adapted to detect the contact by an external body comprises a plurality of tactile sensors as above described arranged on a determined surface. This way, the data detected by each sensor are sent to a computing unit that stores and computes them tracing a map of the whole surface .
  • said sensors are arranged close to each other, in particular contiguous to each other.
  • the aforesaid objects are achieved by a method to obtain a tactile sensor having an extended sensing surface adapted to detect the contact with an external body, said method comprising the steps of:
  • the aforesaid objects are achieved by a method detecting a contact with a body by means of a tactile sensor having an extended sensing surface adapted to detect the contact with said body, said method comprising the steps of: arranging a support layer parallel to said sensing surface; arranging on said support layer an array of light sensing elements;
  • said elastic transparent layer is obtained with a step of depositing a succession of overlapping transparent soft layers, said transparent soft layers being placed in increasing order of stiffness starting from said sensing surface towards said support layer.
  • the adhesive layer and the elastic transparent layer are polymers that are cured contemporaneously.
  • a further step can be provided of arranging an external layer on the adhesive layer opposite to the support layer.
  • figure 1 shows perspective exploded view of a sensor according to the invention in which a plurality of overlapped layers is shown;
  • figure 2 shows a top plan view of a support layer on which the optoelectronic components contained in the device are integrated;
  • figure 3 shows a cross sectional view of such sensor;
  • figures 4, 5 and 6 show an application of such device during the contact with a human finger, in which in 4 figure the finger touches slightly the sensing surface, in figure 5 the finger compresses only a softer transparent layer and in figure 6 the finger applies a greater force compressing both the softer transparent layer and the less soft transparent layers;
  • figures from 7 to 9 show an exploded view, a top plan view and a cross sectional view, respectively, of a different embodiment of the sensor of figure 1;
  • figure from 10 to 13 show further embodiments of the sensor of figure 1;
  • figure 14 shows a block diagram that describes the operation of a device according to the
  • FIG 1 an exploded view is shown of a possible embodiment of a tactile sensor having an extended sensing surface 5' capable of detecting the contact with an external body.
  • the described invention is obtained by optoelectronics means.
  • the sensor provides a support layer 1, for example of a flexible material and very thin, which is a printed circuit on which all the necessary optoelectronics components are welded: an array of sensing elements 7, whose number depends on the dimension and spatial resolution that is desired, as well as light sources ⁇ , which emit light in directions that are parallel with the plane of circuit 1 towards sensing elements 7, and placed along the sides of the array.
  • light sources 6 can be mounted also at an angle with respect to the plane, for example between 0° and 45°.
  • the optoelectronic elements are embedded within a layer of transparent elastic material, for example a thin transparent silicone rubber layer 2.
  • the whole is covered by a silicone rubber coating, for example formed by two united layers 4 and 5: the inner layer 4 is white in order to allow inner reflection of the light, the outer layer 5 is black in order to avoid that the external light disturbs the device. It is not mandatory the use of black colour, and also another dark colour can be used, as well as it is possible to make an ulterior external layer, not shown, of silicone rubber that mimics the colour of the human skin, for example for applications on a limb prosthesis.
  • the presence of the inner white layer is optional, for example in an alternative embodiment to that shown in fig. 7.
  • At least a further much softer transparent silicone rubber layer 3 may be present, or alternatively an air layer is provided.
  • Such intermediate soft transparent layer 3, even if not necessary, permits to increase the resolution in pressure that is detectable by the sensor, and also several planes of different sensibility can be provided, for example in increasing order of stiffness from sensing surface 5' to support layer 1.
  • the possible external stimulus causes a deformation of the silicone rubber cover layers 4 and 5, and consequently the amount of light seen by sensing elements 7 in correspondence of a stimulus changes.
  • FIGS 4-6 the application of a sensor according to the invention is shown during the contact with a finger 10.
  • a soft contact can be detected thanks to the fact that transparent layer 3 under cover layers 4 and 5 is constituted by highly soft transparent silicone rubber (or air) , and consequently the silicone rubber can easily flex to vary the inner light.
  • transparent layer 3 of soft silicone rubber (or air) is completely compressed and the underlying transparent elastic layer 2 deforms itself accordingly and enables sensing elements 7 to detect a decrease of the light amount.
  • the chosen materials for the transparent layers confer to the device a high conformance and then a local deformability responsive to a stimulus, in particular locally following the external profile of the finger that is applying a pressure.
  • FIG 10 a cross sectional view is shown of sensor 50 according to the invention, applied to a curved surface, more precisely a tubular duct 70.
  • This embodiment is possible thanks to the use of a highly flexible material that confers a high overall flexibility degree to sensor 50, thus increasing the field of possible applications .
  • sensor 50 at support layer 50, touches a rod 80 for measuring flexional forces .
  • FIG. 13 A further embodiment of the invention is shown in figure 13. In this case, a determined number of sensors, - IA -
  • sensors 50a-50h are arranged close to each other on a determined surface, up to closely approach them.
  • the data detected by each sensor 50a-50h are sent to a computing unit 100 which stores and processes them.
  • computing unit 100 processes the data received by tactile sensors 50a-50h, for creating a map of the whole surface.
  • the data processed by computing unit 100 can be sent to a control system, not shown, adapted to provide output signals for operating a mechanic or mechatronic device.
  • a sensor can be provided for example having a square shape with a side of 24 mm and a thickness of 3,20 mm.
  • sensors can be made according to the invention with sizes also very different among them, without departing from the invention.
  • an array of sensing elements can be provided distributed on the support layer, for example an array of 5x5 sensing elements.
  • the number of light sources 6, for each side of the array shown in figure 2 can vary according to the width of the array.
  • the distances between the light sources 6 and the array and the distances between the sensing elements 7 can vary according to design requirements.
  • Figures from 7 to 9 show a different embodiment of the sensor of figure 1.
  • support 1 is equipped with a series of through holes 15 and an adhesive layer 16 is provided, for example of silicone rubber, arranged adjacent to support 1 opposite to transparent layer 2.
  • Adhesive layer 16 has the task of anchoring transparent layer 2, and then the entire upper portion of the sensor, to support 1. More in detail, a step is provided of depositing the adhesive layer Ib on face Ib of support 1. During this step, the adhesive material passes through holes 15 and contacts transparent layer 2. A successive curing step of the silicone rubber of layer 16 causes support 1 and transparent 2 to adhere to each other. In order to ensure a steady engagement between support 1 and transparent layer 2, the silicone rubber of transparent layer 2 and the adhesive material of adhesive layer 16 are cured contemporaneously.
  • a lower external layer 17 can be provided attached to adhesive layer 16 opposite to support layer 1.
  • FIG 14 a block diagram that describes the operation of a device according to the invention is shown.
  • a stimulus of pressure 30 acts on the sensing surface of flexible tactile sensor 31
  • the array of sensing elements receives an amount of light that depends on the compression of the transparent flexible layers, and each sensing element produces a signal proportional to the pressure of the stimulus.
  • An array of n signals 32 is obtained.
  • Such signals are then transmitted to an acquisition system 33 that can send the output signals to a PC 35 to obtain a graphical 3D map 37 that allows to outline the pressure distribution on the tactile sensor.
  • the output signals coming from the acquisition system can be sent to a control system 34 that can possibly interact with PC 35 and provide output command signals for a mechanic or mechatronic device 36.

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  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Human Computer Interaction (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Robotics (AREA)
  • Force Measurement Appropriate To Specific Purposes (AREA)
  • Pressure Sensors (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Abstract

A tactile sensor, in particular with function of artificial skin, having a sensing extended surface (5' ) adapted to detect contact and pressure with an external body (10), comprising a support layer (1), for example of flexible material, extending parallel to the sensing surface (5' ), having at least a light source that emits light at a prefixed angle with respect to the support layer (1) towards the sensing elements, an electronic circuit that connects the sensing elements and said at least one source, a layer of elastic transparent material (2) laid on the support layer (1) embedding the sensing elements, the light sources and the circuit; a shielding cover (4 e 5) that coats externally the layer of elastic transparent material, having externally to it said sensing surface (5' ). When an external body (10) presses on the sensing surface (5') an elastic deformation of the cover (4 e 5) and of the underlying layer of transparent material (2) is caused thus decreasing the intensity of light seen by the sensing elements.

Description

TITLE
CONFORMANT AND FLEXIBLE TACTILE SENSOR AND METHOD THEREFOR
DESCRIPTION Field of the Invention
The present invention relates to a tactile sensor adapted to detect a contact with an external body, discriminating shape, intensity of the tactile action, position of the application of the same action and slip.
In particular it is referred to an artificial skin with the aforesaid characteristics. Possible applications concern the cases in which a mechanical interaction between two physic systems is expected, such as body-body, body-machine, body-environment, machine-machine, and machine-environment. Possible fields of application are prosthetic robotics and orthotics, humanoid robotics, technological aids.
Background of the invention
The need is felt to supply a tactile sensor that, in addition to giving information as output, which relates to the type of contact, intensity, position and slip, it has the exterior aspect of a sensing skin, flexible and applicable on a surface, adapted to provide sensory information similar to the human skin when contacting it. Such sensors are expected to have high characteristics and performances in terms of functionality, sensibility, conformance, flexibility, softness and density.
Devices with tactile functionalities are known, such as that described in JP61041938, having a structure of rigid base on which an array of optoelectronics components is arranged, comprising a plurality of light elements and sensing elements placed on two different overlapped planes. For each light element a couple of sensing elements is provided that can be reached by the light emitted from light sources. The light elements emit radiations in a direction orthogonal to the plane of the base structure.
Such device has the disadvantage of being not flexible and therefore not adaptable to the shape of the object to cover, and therefore it is not usable in order to cover a curved surface, in particular a surface that changes its shape with time, such as an orthosis or a robotic prosthesis.
Another disadvantage of the aforesaid known device is that, since it requires a great number of light sources, it causes a high consumption of electric current. A further disadvantage of the aforesaid known device it is that it presents a large thickness that inhibits its use as artificial skin.
Summary of the invention
In the following description as light source any electromagnetic radiation source visible by an optical sensor is provided, and therefore extending even beyond the radiation range that is visible by a human eye.
It is an object of the present invention to provide a tactile sensor having an extended surface adapted to detect the contact and the pressure with an external body, by measuring the intensity of the tactile action, position of application of the same action, and also adapted to recognize the typology, the shape of the same body and the slip, using such flexible and conformant sensor as artificial sensing skin.
Another object of the present invention is to provide a tactile sensor adapted to give to the person who enters in contact with it, a sensation similar to that of the contact with the human skin. Further object of the present invention is to provide a tactile sensor that requires a reduced energy for its operation.
Another object of the present invention is to provide an optoelectronic tactile sensor having an elevated robustness to impacts and to pressures applied even for long period.
A further object of the present invention is to provide a tactile sensor that has an high density of sensing elements and therefore a good spatial resolution.
It is still an object of the present invention to provide an optoelectronic tactile sensor of simple and therefore economic fabrication.
Another object of the present invention is to provide a tactile sensor adapted to measure a wide range of pressures.
Another object of the present invention is to provide a method for producing such a tactile sensor.
These and other objects are achieved by a tactile sensor having an extended sensing surface adapted to detect the contact with an external body, characterized in that it comprises:
— a flexible support layer parallel to said sensing surface, comprising:
- an array of light sensing elements;
- at least one light source that emits a light radiation at a prefixed angle with respect to said support layer;
- an electronic circuit that connects said sensing elements to said at least one source;
— an elastic transparent layer deposited on said flexible support layer and that embeds said sensing elements, said at least one light source and said circuit;
— a shielding cover that coats externally said elastic transparent layer, said shielding cover having said sensing surface on its external side;
- correlating means associated to said electronic circuit for correlating the light intensity received from said array of sensing elements and the deformation of said elastic material layer.
In particular, the support layer is made of a flexible material.
In such a device mounted on any body, when a contact or pressure stimulus acts on the sensing surface, or on the shielding cover, an elastic deformation of the cover and the underlying elastic transparent layer occurs; consequently the amount of light changes that, after being emitted by the light sources and having passed through the elastic transparent layer, reaches by direct propagation the sensing elements, which detect a light variation in correspondence of the stimulus. Since such amount of light depends on the deformation of the cover and of the layer of elastic transparent layer, thanks to its measuring it is possible to understand the intensity of the applied force on the sensing surface and its point of application.
In particular, the elastic material is selected from the group comprised of:
- viscoelastic material, in particular silicone rubber; plastic material; synthetic rubber;
- natural rubber; or, a combination thereof.
Such tactile sensor can be used as artificial skin adapted to perceive the shapes, since the sensor can provide as autput a sort of image of the surface that is touching the entire array, taking advantage of the great conformance that the elastic material possesses, in particular silicone rubber.
Advantageously, said array of light sensing elements comprises a plurality of elements placed according to a predefined pattern, said at least one light source being arranged peripherally regarding said matrix of sensing elements, preferably along the border of said array. Such a configuration allows to have a high density of sensing elements and therefore a high spatial resolution, since no further space has to be provided among them in order to house the light sources. Moreover, such a configuration allows to use a reduced number of light sources, involving a constructive simplification and an energy saving, therefore reduced costs.
Advantageously, said array of sensing elements, said at least one light source and said circuit are substantially on a same plane. In this way a small total dimension is obtained in height or thickness. In particular, said circuit is obtained by means of photo- etching of a copper layer on one face or on both faces of a support layer of polyimide, and said array of sensing elements and said at least one light source are applied on said circuit.
Preferably, said prefixed angle with respect to said support layer is comprised between 0° and 90°, in particular between 0° and 45°, preferably 0°. Such angle depends on the results that are sought and on the desired characteristics of sensitivity.
Advantageously, said shielding cover is in particular white, and an external face of dark colour, in particular black, in order to prevent that an external light disturbs the device or that the internal radiation disperses in the environment.
In a different embodiment of the invention, the shielding cover presents, furthermore, a reflecting inner surface, in particular white, which causes an internal reflection of the light.
According to a possible embodiment, a further external layer that covers said external face of said cover can be provided, made of a soft material that mimics the colour of the human skin.
Advantageously, at least one transparent soft layer interposed between said elastic transparent layer and said shielding cover is provided, said transparent soft layer being softer than said elastic transparent layer.
In particular, said transparent soft layer is selected from the group comprised of:
- a layer of soft silicone rubber;
- a volume of air or gas.
Advantageously, a plurality of transparent soft layers is provided that are overlapped to each other between said elastic transparent layer and said shielding cover, said transparent soft layers having different stiffness, in particular arranged in increasing order of stiffness from said cover towards said support layer.
In a different embodiment of the invention, the support has at least an aperture and a layer of adhesive material is provided, for example silicone rubber, arranged adjacent to the support opposite to the layer of transparent material. In particular, the layer of adhesive material extends through said, or each, aperture up to contacting said layer of transparent material. This way, the layer of adhesive material causes said support layer to fix to said layer of transparent material. In particular, the adhesive layer can be made of a silicone rubber having stiffness greater than that of silicone rubbers used to make other layers of the sensor.
Advantageously, a further layer external to the adhesive layer opposite to the support layer can be provided.
The possible external stimulus causes a deformation of the silicone rubber cover, and consequently the amount of light seen by the sensing elements in correspondence of the stimulus changes. One delicate contact can be detected thanks to the fact that the first layer under the cover is constituted by a very soft elastic transparent layer (or air) , such that the silicone rubber can easily be compressed to vary the inner light. If the external force is high, such very soft silicone rubber layer (or air) is completely compressed and the underlying elastic transparent layer, in the same way, deforms and causes the sensing elements to detect a decrease of the intensity of light.
Advantageously, every sensing element has an analog or digital output, deriving for example from a photodiode, a phototransistor or a photoresistor, depending on which optocomponent is used as sensing element. The analog output varies proportionally to the amount of light that it receives, and consequently, it varies proportionally to the compression of the silicone rubber chamber through which the light emitted by light sources is transmitted.
Preferably said correlating means associated to said electronic circuit, in order to correlate the light intensity received from said array of sensing elements and the deformation of said support layer, comprises computing means that determine the variation of the light signal received by each sensing element. In particular, it is possible to identify the point where the pressure is applied and to estimate the intensity of such pressure, carrying out a 3D mapping of the array. Moreover, it is possible to use the sensor like a detector of shapes, using for example neural networks.
According to a further particular aspect of the invention, a tactile apparatus having an extended sensible surface adapted to detect the contact by an external body comprises a plurality of tactile sensors as above described arranged on a determined surface. This way, the data detected by each sensor are sent to a computing unit that stores and computes them tracing a map of the whole surface .
Advantageously, to carry out a precise measurement said sensors are arranged close to each other, in particular contiguous to each other.
According to a further aspect of the present invention, the aforesaid objects are achieved by a method to obtain a tactile sensor having an extended sensing surface adapted to detect the contact with an external body, said method comprising the steps of:
- providing a support layer that extends parallel to said sensing surface;
- arranging on said support layer an array of light sensing elements;
- arranging on said support layer at least one light source that emits light at a prefixed angle with respect to said support layer towards said sensing elements; arranging on said support layer an electronic circuit that connects said sensing elements to said at least one source; arranging on said support layer an elastic _ g _
transparent layer to embed said light sources, said sensing elements and said circuit, coating externally said elastic transparent layer with a shielding cover that coats externally said plurality of transparent soft layers, said shielding cover having said sensing surface on its external side.
According to still another aspect of the present invention, the aforesaid objects are achieved by a method detecting a contact with a body by means of a tactile sensor having an extended sensing surface adapted to detect the contact with said body, said method comprising the steps of: arranging a support layer parallel to said sensing surface; arranging on said support layer an array of light sensing elements;
- arranging on said support layer at least one light source that emits light at a prefixed angle with respect to said support layer towards said sensing elements;
- arranging on said support layer an electronic circuit that connects said sensing elements to said at least one source;
- arranging on said support layer an elastic transparent layer embedding said light sources, said sensing elements and said circuit,
- coating externally said elastic transparent layer with a shielding cover that coats externally said plurality of transparent soft layers, said shielding cover having said sensing surface on its external side. detecting the received signals by each sensing element of said array; detecting the variation with time of the light signals received by each sensing element;
- determining the deformation of said cover. Advantageously, said elastic transparent layer is obtained with a step of depositing a succession of overlapping transparent soft layers, said transparent soft layers being placed in increasing order of stiffness starting from said sensing surface towards said support layer.
In a preferred embodiment of the invention the further steps are provided of:
- making at least one through-hole in said support layer;
- depositing on said support layer an adhesive layer opposite to said elastic transparent layer said adhesive layer crossing said support layer at said or each through-hole in order to contact said elastic transparent layer and make a steady connection between said support layer and said elastic transparent layer.
In particular, to achieve said steady connection between said support layer and said elastic transparent layer, the adhesive layer and the elastic transparent layer are polymers that are cured contemporaneously.
Moreover, a further step can be provided of arranging an external layer on the adhesive layer opposite to the support layer.
Brief description of the drawings
The invention will be made clearer with the following description of some exemplary embodiments, exemplifying but not limitative, with reference to the attached drawings wherein: figure 1 shows perspective exploded view of a sensor according to the invention in which a plurality of overlapped layers is shown; figure 2 shows a top plan view of a support layer on which the optoelectronic components contained in the device are integrated; figure 3 shows a cross sectional view of such sensor; figures 4, 5 and 6 show an application of such device during the contact with a human finger, in which in 4 figure the finger touches slightly the sensing surface, in figure 5 the finger compresses only a softer transparent layer and in figure 6 the finger applies a greater force compressing both the softer transparent layer and the less soft transparent layers; figures from 7 to 9 show an exploded view, a top plan view and a cross sectional view, respectively, of a different embodiment of the sensor of figure 1; figure from 10 to 13 show further embodiments of the sensor of figure 1; figure 14 shows a block diagram that describes the operation of a device according to the invention.
Description of the preferred embodiments In figure 1 an exploded view is shown of a possible embodiment of a tactile sensor having an extended sensing surface 5' capable of detecting the contact with an external body. The described invention is obtained by optoelectronics means. The sensor provides a support layer 1, for example of a flexible material and very thin, which is a printed circuit on which all the necessary optoelectronics components are welded: an array of sensing elements 7, whose number depends on the dimension and spatial resolution that is desired, as well as light sources β, which emit light in directions that are parallel with the plane of circuit 1 towards sensing elements 7, and placed along the sides of the array.
Depending on the desired results, light sources 6 can be mounted also at an angle with respect to the plane, for example between 0° and 45°. The optoelectronic elements are embedded within a layer of transparent elastic material, for example a thin transparent silicone rubber layer 2. The whole is covered by a silicone rubber coating, for example formed by two united layers 4 and 5: the inner layer 4 is white in order to allow inner reflection of the light, the outer layer 5 is black in order to avoid that the external light disturbs the device. It is not mandatory the use of black colour, and also another dark colour can be used, as well as it is possible to make an ulterior external layer, not shown, of silicone rubber that mimics the colour of the human skin, for example for applications on a limb prosthesis.
Also the presence of the inner white layer is optional, for example in an alternative embodiment to that shown in fig. 7.
Between cover layers 4 and 5 now described and the transparent silicone rubber layer, at least a further much softer transparent silicone rubber layer 3 may be present, or alternatively an air layer is provided. Such intermediate soft transparent layer 3, even if not necessary, permits to increase the resolution in pressure that is detectable by the sensor, and also several planes of different sensibility can be provided, for example in increasing order of stiffness from sensing surface 5' to support layer 1.
In fact, the possible external stimulus causes a deformation of the silicone rubber cover layers 4 and 5, and consequently the amount of light seen by sensing elements 7 in correspondence of a stimulus changes. In figures 4-6 the application of a sensor according to the invention is shown during the contact with a finger 10. A soft contact can be detected thanks to the fact that transparent layer 3 under cover layers 4 and 5 is constituted by highly soft transparent silicone rubber (or air) , and consequently the silicone rubber can easily flex to vary the inner light. As shown in figure 6, if the external force applied by finger 10 is high, transparent layer 3 of soft silicone rubber (or air) is completely compressed and the underlying transparent elastic layer 2 deforms itself accordingly and enables sensing elements 7 to detect a decrease of the light amount.
The chosen materials for the transparent layers, for example silicone rubber, confer to the device a high conformance and then a local deformability responsive to a stimulus, in particular locally following the external profile of the finger that is applying a pressure.
In figure 10 a cross sectional view is shown of sensor 50 according to the invention, applied to a curved surface, more precisely a tubular duct 70. This embodiment is possible thanks to the use of a highly flexible material that confers a high overall flexibility degree to sensor 50, thus increasing the field of possible applications .
A particular application of the sensor according to the invention is shown in figures 11 and 12. In this case sensor 50, at support layer 50, touches a rod 80 for measuring flexional forces .
A further embodiment of the invention is shown in figure 13. In this case, a determined number of sensors, - IA -
for example sensors 50a-50h, are arranged close to each other on a determined surface, up to closely approach them.
The data detected by each sensor 50a-50h are sent to a computing unit 100 which stores and processes them. In particular, computing unit 100 processes the data received by tactile sensors 50a-50h, for creating a map of the whole surface. The data processed by computing unit 100 can be sent to a control system, not shown, adapted to provide output signals for operating a mechanic or mechatronic device.
In a possible, but not limitative, embodiment of the invention a sensor can be provided for example having a square shape with a side of 24 mm and a thickness of 3,20 mm. Obviously sensors can be made according to the invention with sizes also very different among them, without departing from the invention. In the event of a square shape, an array of sensing elements can be provided distributed on the support layer, for example an array of 5x5 sensing elements.
The number of light sources 6, for each side of the array shown in figure 2, can vary according to the width of the array. The distances between the light sources 6 and the array and the distances between the sensing elements 7 can vary according to design requirements.
According to the intensity of the involved forces it is possible to use transparent silicone rubbers with different stiffness between the shielding cover and the optoelectronics. Also the number of silicone rubber layers can be chosen in a desired way.
Figures from 7 to 9 show a different embodiment of the sensor of figure 1. In this case, support 1 is equipped with a series of through holes 15 and an adhesive layer 16 is provided, for example of silicone rubber, arranged adjacent to support 1 opposite to transparent layer 2. Adhesive layer 16, in particular, has the task of anchoring transparent layer 2, and then the entire upper portion of the sensor, to support 1. More in detail, a step is provided of depositing the adhesive layer Ib on face Ib of support 1. During this step, the adhesive material passes through holes 15 and contacts transparent layer 2. A successive curing step of the silicone rubber of layer 16 causes support 1 and transparent 2 to adhere to each other. In order to ensure a steady engagement between support 1 and transparent layer 2, the silicone rubber of transparent layer 2 and the adhesive material of adhesive layer 16 are cured contemporaneously. Moreover, a lower external layer 17 can be provided attached to adhesive layer 16 opposite to support layer 1.
In figure 14 a block diagram that describes the operation of a device according to the invention is shown. When a stimulus of pressure 30 acts on the sensing surface of flexible tactile sensor 31, the array of sensing elements receives an amount of light that depends on the compression of the transparent flexible layers, and each sensing element produces a signal proportional to the pressure of the stimulus. An array of n signals 32 is obtained. Such signals are then transmitted to an acquisition system 33 that can send the output signals to a PC 35 to obtain a graphical 3D map 37 that allows to outline the pressure distribution on the tactile sensor. The output signals coming from the acquisition system can be sent to a control system 34 that can possibly interact with PC 35 and provide output command signals for a mechanic or mechatronic device 36.
The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Claims

Claims: - 17 -
1. A tactile sensor having an extended sensing surface adapted to detect the contact with an external body, characterized in that it comprises:
- a flexible support layer parallel to said sensing surface, comprising:
- an array of light sensing elements;
- at least one light source that emits a light radiation at a prefixed angle with respect to said support layer;
- an electronic circuit that connects said sensing elements to said at least one source;
- an elastic transparent layer deposited on said flexible support layer and that embeds said sensing elements, said at least one light source and said circuit;
- a shielding cover that coats externally said elastic transparent layer, said shielding cover having said sensing surface on its external side.
- correlating means associated to said electronic circuit, for correlating the light received from said array of sensing elements and the deformation of said elastic material layer.
2. A tactile sensor, according to claim 1, wherein said array of light sensing elements comprises a plurality of elements placed according to a predefined pattern, said at least one light source being arranged peripherally with respect to said matrix of sensing elements, preferably along the border of said array.
3. A tactile sensor, according to claim 1, wherein said array of sensing elements, said at least one light source and said circuit are substantially on a same plane.
4. A tactile sensor, according to claim 1, wherein said prefixed angle with respect to said support layer is comprised between 0° and 90°, in particular between 0° and 45°, preferably 0°.
5. A tactile sensor, according to claim 1, wherein said shielding cover has an external face of dark colour, in particular black, adapted to prevent that an external light disturbs the device or that the internal radiation is dispersed in the environment.
6. A tactile sensor, according to claim 1, wherein said shielding cover presents, furthermore, a reflecting inner surface, in particular white.
7. A tactile sensor, according to claim 1, wherein a further external layer that covers said external face of said cover is provided, made of a soft material that mimics the colour of the human skin.
8. A tactile sensor, according to claim 1, wherein at least one transparent soft layer interposed between said elastic transparent layer and said shielding cover is provided, said transparent soft layer being softer than said elastic transparent layer.
9. A tactile sensor, according to claim 8, wherein said transparent soft layer is selected from the group comprised of:
- a layer of soft elastic material;
— a chamber containing air or gas .
10. A tactile sensor, according to claim 1, wherein a plurality of transparent soft layers is provided that are overlapped to each other between said elastic transparent layer and said shielding cover, said transparent soft layers having different stiffness, in particular arranged in increasing order of stiffness from said cover towards said support layer.
11. A tactile sensor, according to claim 1, wherein each sensing element has an output, deriving for example from a photodiode, a phototransistor or a photoresistor, depending on which optocomponent is used as sensing element.
12. A tactile sensor, according to claim 1, wherein said correlating means associated to said electronic circuit, in order to correlate the light intensity received from said array of sensing elements and the deformation of said support layer, comprises computing means that determines the variation of the light signal received by each sensing element.
13. A tactile sensor, according to claim 1, wherein the support has at least an aperture and a layer of adhesive material is provided, said layer of adhesive material arranged adjacent to the support opposite to the layer of transparent material, said layer of adhesive material extending through said, or each, aperture up to contacting said layer of transparent material to fix said layer of transparent material.
14. A tactile sensor, according to claim 1, wherein the elastic material is selected from the group comprised of:
- viscoelastic material, in particular silicone rubber;
- plastic material;
- synthetic rubber; natural rubber;
- a combination thereof.
15. A method to obtain a tactile sensor having an extended sensing surface adapted to detect the contact with an external body, wherein said method comprises the steps of:
- providing a support layer that extends parallel to said sensing surface; arranging on said support layer an array of light sensing elements;
- arranging on said support layer at least one light source that emits light at a prefixed angle with respect to said support layer towards said sensing elements;
- arranging on said support layer an electronic circuit that connects said sensing elements to said at least one source;
- arranging on said support layer an elastic transparent layer to embed said light sources, said sensing elements and said circuit,
- coating externally said elastic transparent layer with a shielding cover that coats externally said plurality of transparent soft layers, said shielding cover having said sensing surface on its external side .
16. A method for detecting a contact with a body by means of a tactile sensor having an extended sensing surface adapted to detect the contact with said body, said method comprising the steps of: arranging a support layer parallel to said sensing surface;
- arranging on said support layer an array of light sensing elements;
- arranging on said support layer at least one light source that emits light at a prefixed angle with respect to said support layer towards said sensing elements; - arranging on said support layer an electronic circuit that connects said sensing elements to said at least one source;
- arranging on said support layer an elastic transparent layer embedding said light sources, said sensing elements and said circuit,
- coating externally said elastic transparent layer with a shielding cover that coats externally said plurality of transparent soft layers, said shielding cover having said sensing surface on its external side .
- detecting the received signals by each sensing element of said array;
- detecting the variation with time of the light signals received by each sensing element; determining the deformation of said cover.
17. A method, according to claim 15 or 16, wherein said elastic transparent layer is obtained with a step of depositing a succession of overlapping transparent soft layers, said transparent soft layers being placed in increasing order of stiffness starting from said sensing surface towards said support layer
EP08788913A 2007-07-23 2008-07-23 Conformant and flexible tactile sensor and method therefor Withdrawn EP2176632A1 (en)

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IT000085A ITPI20070085A1 (en) 2007-07-23 2007-07-23 FLEXIBLE TACTILE SENSOR AND METHOD TO OBTAIN IT
PCT/IB2008/001911 WO2009013599A1 (en) 2007-07-23 2008-07-23 Conformant and flexible tactile sensor and method therefor

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