EP3352953A1

EP3352953A1 - Sensorized coating for detection of pressures

Info

Publication number: EP3352953A1
Application number: EP16801296.1A
Authority: EP
Inventors: Gastone Ciuti; Alessandro DIODATO; Tommaso MAZZOCCHI; Arianna Menciassi; Nicola Vitiello
Original assignee: Scuola Superiore di Studi Universitari e di Perfezionamento SantAnna
Current assignee: Scuola Superiore di Studi Universitari e di Perfezionamento SantAnna
Priority date: 2015-09-25
Filing date: 2016-09-26
Publication date: 2018-08-01
Also published as: WO2017051394A1; ITUB20153909A1

Abstract

A sensorized coating device (100) configured for measuring external pressures acting on it, said sensorized coating device (100) comprising a flexible sensor (110) having shape substantially laminar and comprising a plurality of sensitive areas A_i,j, said flexible sensor (110) being configured for measuring, at said sensitive areas A_i,j, the presence of corresponding external pressures P_{i, j} ^EXT· The flexible sensor (110) comprises a first layer (111) comprising a number i of strips of conductive material (111') alternate to strips of non-conductive material (111'') and a second layer (112) comprising a number j of strips of conductive material (112') alternate to strips of non-conductive material (112''). The first layer (111) and said second layer (112) are arranged in a position such that the i strips of conductive material (112') of the second layer (112) overlap without physical contact to the j strips of conductive material (111') of the first layer (111) at the said sensitive areas A_i,j. The strips of conductive material (111') of the first layer (111) and the strips of conductive material (112') of the second layer (112) are connected to an electrical circuit (115). The strips of conductive material (111') of the first layer (111) are arranged to come into electrical contact with the strips of conductive material (112') of the second layer (112) at determined sensitive areas A_i,j in consequence of determined external pressures P_{i, j} ^EXT acting on the determined sensitive areas A_i,j, said electrical contact closing the electrical circuit (115) and generating a voltage at the ends of two strips of conductive material (111', 112') in electrical contact to each other, in order to generate contact signals reporting information about the presence of said external pressures P_{i, j} ^EXT and their spatial position on the flexible sensor (110).

Description

TITLE

SENSORIZED COATING FOR DETECTION OF PRESSURES

DESCRIPTION Field of the invention

The present invention relates to the field of textile sensors for detecting external forces.

In particular, the invention relates to a textile sensor for coating a solid body, natural or artificial, for detecting external pressures that interact with it.

Description of the prior art

As known, in recent years it is spreading widely the use of robotic structures in environments where there are human operators or fragile equipment, as for example in the field of surgical or industrial. In these areas it is therefore essential that the robotic structures interact safely with the environment around them.

They are therefore developing several advanced systems for sensing such robotic structures in order to avoid or manage unpredictable collisions that can cause harm to humans or expensive and/or brittle equipment.

A possible solution presented by Rethink Robotics is to use robotic joints provided with torque sensors that allow to detect unforeseen torque variations. However, this solution requires a very complex mechanical design and control algorithms, making it very expensive and unreliable. Another possible solution is to use visual recognition algorithms of the collision, but also this solution presents problems of accuracy in crowded environments or where visibility is impaired.

A more effective approach is to use flexible pressure sensors that allow to cover a robotic structure (similar to human skin) , so as to locate and measure the intensity of external forces acting on the robot.

There are different types of pressure sensors, such as resistive, capacitive, optical, ultrasonic and magnetic sensors .

However, both the optical and capacitive sensors, although accurate and adaptable to complex surfaces, are currently poorly suited to cover large surfaces.

Moreover, the optical sensors are composed for example of a polymeric matrix in which optical fibers are inserted that allow to detect changes in light intensity. This makes these systems very expensive and not very suitable for large surface extensions.

Finally, the magnetic sensors, generally very accurate, however, are highly susceptible to the presence of metal objects that can to vary much sensitivity.

Regarding the resistive sensors, an example is described in "A Novel Highly-Twistable Tactile Sensing Array using Extendable Spiral Electrodes" published by M-Y name Cheng et al . on 25/01/2009. The described sensor is composed of a plurality of copper wires arranged in a spiral around the corresponding nylon threads arranged in a matrix so as to identify a plurality of intersection points. The sensor is able to locate the presence of an external force to effect an elongation of such copper wires in one of the crossing points. Furthermore, the stretching deformation to which the copper wires are subjected will change, as well known, its resistivity and consequently the resistance that the material offers to the passage of electric current. Such variation of resistance, being proportional to the aforesaid deformation, which in turn is proportional to the effort to which is subjected the material, allow to identify not only the point of application of the external force but also its intensity.

However, this solution is very complex and expensive both in production and in mounting step.

In addition, you have a poor detection sensitivity of the intensity of the force in the event that the area covered by the sensor is slightly deformable. In this case, in fact, the stretching deformation of the copper wires is necessarily limited by the fact that the wires can not penetrate the underlying surface. A further drawback is given by the presence of the conductive polymer, in the form of liquid or gel, in which the wires of copper and nylon are immersed. Such a polymer prevents the sensor transpiration. This does not allow, for example, the wearing of the sensor by a human user.

The problem of breathability can be overcome through the sensor described in "The OLR artificial skin step I: Uniting sensitivity and collision tolerance" published by Strohmavr M. W. et al . on 06/05/2013. However, also in this document it remains the problem of a stretching deformation of the resistor element, with the consequences described above in terms of the pressure measurement accuracy.

Summary of the invention

It is therefore a feature of the present invention to provide a pressure flexible sensor which allows to detect and handle unpredictable collisions between a solid body and the external environment..

It is also a feature of the present invention to provide a pressure flexible sensor enabling the wearability either by a robotic structure by a human user..

It is also a feature of the present invention to provide such a pressure flexible sensor that is not expensive and suitable to cover a large surface area, such as a robotic arm or a complex structure.. It is still a feature of the present invention to provide a pressure flexible sensor that is transpiring in order to coat a surface that need to breath..

It is also a feature of the present invention to provide such a pressure flexible sensor that allows the damping of possible collisions with the external environment .

It is also a feature of the present invention to provide such a pressure flexible sensor that allows the multi-touch detection of more than one agent contact simultaneously on the sensor itself.

It is still a feature of the present invention to provide such a pressure flexible sensor that allows easy customization to adapt to the various needs of use..

It is also a feature of the present invention to provide a robotic structure that comprises such a pressure flexible sensor.

These and other objects are achieved by a sensorized coating device configured for measuring external pressures acting on it, said sensorized coating device comprising a flexible sensor having shape substantially laminar and comprising a plurality of sensitive areas Ai , said flexible sensor being configured for measuring, at the sensitive areas A^j, the presence of corresponding external pressures said flexible sensor comprising:

— a first layer comprising a number i of strips of conductive material alternate to strips of non- conductive material;

— a second layer comprising a number j of strips of conductive material alternate to strips of non- conductive material;

said first layer and said second layer arranged in a position this in such a way that the i strips of conductive material of the second layer overlap without physical contact to the j strips of conductive material of the first layer at the sensitive areas A j,

said strips of conductive material of the first layer and said strips of conductive material of the second layer being connected to an electrical circuit,

said strips of conductive material of the first layer arranged to come into electrical contact with the strips of conductive material of the second layer at determined sensitive areas Ai in consequence of determined external pressures P ^T acting on the determined sensitive areas Ai , said electrical contact closing the electrical circuit and generating a voltage at the ends of two strips of conductive material in electrical contact to each other, in order to generate contact signals reporting information about to the presence of the external pressures Pff^T and their spatial position on the flexible sensor,

whose main feature is that, between the first layer and the second layer, a resistor material is provided having an electrical resistivity of value p variable with the deformation, said flexible sensor having laminar shape and being configured in such a way that, when the electrical circuit closes in consequence of the external pressures Pff^T , the resistor material reduces its own thickness at the sensitive areas Ai on which act the external pressures Pff^T , changing proportionally value p, said variation of value p allowing deriving the intensity of the external pressures P f^T .

The presence of the resistor material in laminar form allows to overcome the drawbacks of the prior art. In particular, in addition to being simpler and cheaper, the sensor of the present invention allows to cover slightly deformable surfaces not losing sensitivity, and also allows the wearing by human users, since the material of which the sensor is formed is integrally transpiring and flexible. These aspects allow, for example, the application of the sensor in the medical field as sensitive coating of objects, e.g. robot or moving parts, and of people. For example, the tissue can be used to safely assist the movement of a magnetic probe in the body of a patient. In fact, coating the outer guide device of the probe with the tissue above described, it allows monitoring the contact with the patient's body in a way more accurate with respect to a mere control by the operator or respect to other sensors located not at the interface between the external probe and the patient. In particular, the sensor allows the outer guide device to move in contact with the leather of the patient maintaining in an automatic way a fixed pressure and/or a predetermined and steady orientation of the outer guide device with respect to the user.

It is therefore evident how the sensor according to the present invention is extremely more versatile than the sensors of the prior art.

Advantageously, the resistor material comprises a plurality of resistive areas located at the sensitive areas Aij, said resistive areas being insulated to each other, in such a way that the contact signals do not interfere with each other.

Advantageously, the sensitive areas Ai are adapted to be located in connection to each other for making increased sensitive areas A^j, in order to adjust the resolution of the sensitivity of the flexible sensor in a way electronic. For example the sensitive areas Ai can be connected to each other by means of short circuiting the strips of conductive material .

In particular, the variation of resolution of the flexible sensor can be changed in real time by an external electronic board that allows the sensor to work in subsequent steps of detecting the outer impact.

For example, it is possible to reduce very much the resolution, up to having one or four increased sensitive areas Ai , in a starting step the impact. This way, the computation of the impact signal is extremely quick, even not precise in detecting the impact point. In a step immediately successive, triggered by the first one, the sensor will instead increase its own resolution for defining appropriately the application point and the intensity of the external pressure.

According to another aspect of the invention, a robotic structure comprises:

— a frame;

— a control unit arranged to operate the frame;

whose main feature is that it also comprises the sensorized coating device above described, in contact, in use, with the frame, said sensorized coating device also comprising at least one damping element in contact with the flexible sensor and arranged to dampen the impact of the external pressures P ^T on the frame;

said sensorized coating device arranged to send to the control unit contact signals reporting information about the presence of the external pressures P ^T detected at the sensitive areas A_j,

said control unit arranged to process the contact signals and to operate the frame according to a predetermined mode for react to the external pressures pEXT

The sensorized coating device claimed can be made of a textile material and may have the shape of a garment, for example a sock, in order to coat a wide portion of the robotic structure or the person or object, and acting substantially as a sensitive leather.

Some operating modes of the control unit can be:

a) complete and immediate stop of the robotic structure ;

b) application to pivot joints of the robotic structure of torques identical and opposite to the ones caused by the external pressures Pf^T, in order to return the frame in the starting configuration, or in order to avoid the movement of the frame;

c) handling the robotic structure along a predetermined trajectory.

The mode a) allows programing the robotic structure for acting in total safety in places wherein, with its own movement, can be caused damages to human beings or expensive and/or fragile objects, such as in the industrial or medical field.

The mode b) allows programing the robotic structure for acting in contests in that it is necessary high precision of movement, such as the surgical field.

The mode c) allows programing the robotic structure to assist the handling of it by a user, which can give it a signal of a predetermined movement with a simple contact. In particular, the structure can be programmed for moving in a predetermined direction when it senses pressures on a specific portion of the sensorized coating.

Advantageously, the sensorized coating device also comprises an electromagnetic shielding device arranged to avoid electromagnetic interferences between the flexible sensor and the electric devices present in the frame.

In particular, two damping elements can be provided arranged in contact with the flexible sensor at opposite sides with respect to it. In particular, the damping element is made of polymeric material deformable with viscoelasticity differenti .

Advantageously, each damping element has a rest thickness H that can be deducted by the following equation:

wherein :

— P_∞ is the predetermined maximum pressure value that the frame can oppose to the external pressures P f^T ;

— P_th is a value greater or equal to the minimum pressure value detectable by the flexible sensor;

— d is value of the variation of thickness of the damping element owing to application of external pressures Pf^T , d being function of:

- speed v of application of the external pressures P f^T ,

- time t_a during which is carried out the deformation of the damping element owing to applying the external pressures Pf^T ,

- mechanical and dynamical features of the material of the damping element.

In particular, the thickness of the damping element has to be calibrated in order to have, on one hand, enough capacity for dampening an outer impact, allowing the robotic structure to disperse the kinetic energy by its brakes and, on the other hand, to give a sufficient sensitivity to the sensorized coating device.

Advantageously, the contact signals are sent to the control unit by means of a wireless connection.

In particular, the flexible sensor is located in contact with the frame by means of an easily removable and replaceable connection.

In particular, the connection between the flexible sensor and the frame is a magnetic or mechanical connection .

Advantageously, the magnetic connection between the flexible sensor and the frame is also an electrical connection and the contact signals are sent to the control unit by means of it.

In particular, the frame comprises a kinematical chain comprising a plurality of rotational joints activated by respective actuators, and at the rotational joints respective torque sensors are provided configured to measure the torques present on the rotational joints itself and to send a signal of torque variation to the control unit. This way, the control unit can compare the contact signals and the signals of torque variation for testing with higher precision the real status of the robotic structure. In particular, the torque sensors can provide information concerning collisions in zones of the robotic structure not coverable by the textile sensor, such as the tool of a robotic arm or the wheels for handling the structure .

In particular, the robotic structure further comprises a plurality of sensors arranged to send signals to the control unit that processes them together with the contact signals of the textile sensor.

According to another aspect of the invention, a sensorized coating device is claimed configured for measuring an interaction between a robotic structure and external pressures acting on it, said robotic structure comprising a frame and a control unit arranged to operate the frame,

the main feature of the sensorized coating device being that it comprises:

— a flexible sensor having shape substantially laminar and comprising a plurality of sensitive areas Ai , said flexible sensor being configured for measuring, at the sensitive areas A^j, the presence of corresponding external pressures pEXT .

ri '

— at least one damping element in contact with the flexible sensor and arranged to dampen the external pressures Pf^T ; said sensorized coating device arranged to send to the control unit contact signals reporting information about the presence of the external pressures P ^T detected at the sensitive areas A_j,

in such a way that the control unit can process the contact signals and operate the frame according to a predetermined mode for reacting to the external pressures Pf^T .

Brief description of the drawings

Further characteristic and/or advantages of the present invention are more bright with the following description of an exemplary embodiment thereof, exemplifying but not limitative, with reference to the attached drawings in which:

— Fig. 1 shows an exemplary embodiment of the robotic structure, according to the present invention, equipped with control unit and with the sensorized coating device;

— Fig. 2 shows a possible exemplary embodiment of the sensorized coating device;

— Fig. 3 shows a possible exemplary embodiment of the flexible sensor;

— Fig. 4 shows an exemplary embodiment of the flexible sensor alternative to that of Fig. 3; — Fig. 5 shows in diagrammatical view the matrix structure of the flexible sensor.

Description of a preferred exemplary embodiment

With reference to Fig. 1, a robotic structure 10 comprises a frame 50 and a control unit 60 arranged to operate the frame 50 by means of the rotational joints 55.

The robotic structure also comprises a sensorized coating device 100 in contact, in use, with the frame 50 and configured for measuring an interaction between the robotic structure 10 and external pressures acting on it.

In particular, the sensorized coating device 100 is adapted to send to the control unit 60 contact signals reporting information about the presence of external pressures P ^T , in such a way that the control unit 60 can process the contact signals and sending an operating signal to the frame 50 for reacting to the external pressures P ^T according to a predetermined mode.

For example, some operating modes of the control unit can be :

— complete and immediate stop of the robotic structure 10;

— application to pivot joints 55 of the robotic structure of torques identical and opposite to the ones caused by the external pressures Pff^T, in order to return the frame in the starting configuration, or in order to avoid the movement of the frame 50;

— handling the robotic structure 10 along a predetermined trajectory.

In particular, with reference even to Fig. 2, the sensorized coating 100 comprises a flexible sensor 110 and two damping elements 120 arranged in contact with the flexible sensor 110 at opposite sides with respect to it, in order to dampen the impact of the external pressures Pf^T on the frame 50.

More in detail, with reference even to Figs. 3, 4 and

5, the flexible sensor 110 comprises a first layer 111 that has a number i of strips of conductive material 111' alternate to strips of non-conductive material 111'', and a second layer 112 having a number j of strips of conductive material 112' alternate to strips of non-conductive material 112' ' . The two layers 111 and 112 are arranged in such a way that the respective strips of conductive material 111' and 112' overlap to each other generating a plurality of sensitive areas A _j .

The strips of conductive material 111' and 112' are also connected to an electrical circuit 115, in such a way that when determined external pressures Pf^T act on determined sensitive areas Ai , the respective strips of conductive material 111', 112' close the electrical circuit 115 generating a voltage, in order to generate the contact signals reporting information about the presence of the external pressures P ^T and their spatial positions on the flexible sensor 110. In Fig. 5, an example is shown where the pressures are applied closing the electrical circuit 115 at the respective sensitive areas A_2i2 and A₃₁. Detection of pressures on different points of the flexible sensor allows the sensor itself to be a multi- touch sensor.

In particular, with reference to Fig. 3, between the layers 111 and 112 a layer of resistor material 113 is provided having an electrical resistivity of value p variable with the deformation. This way, when the electrical circuit 115 closes in consequence of the external pressures P ^T , the resistor material 113 deforms changing proportionally value p . Such variation changes the voltage at the ends of the circuit 115, allowing deriving the value of the external pressures P ^T applied. Such exemplary embodiment allows therefore, not only determining the position of the external pressures Pff^T , but also the intensity.

In the exemplary embodiment of Fig. 4, the resistor material 113 is split into a plurality of resistive areas 113' , generated by strips that overlap at the sensitive areas Ai . This way, you limit the interference between contact signals obtained by an electrical contact that is carried out at adjacent sensitive areas. In a further exemplary embodiment the resistive areas 113' are generated by portions of resistive material 113 completely insulated to each other.

The foregoing description some exemplary specific embodiments 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 in various applications the specific exemplary embodiments without further research and without parting from the invention, and, accordingly, it is meant that such adaptations and modifications will have to be considered as equivalent to the specific embodiments. 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 that is employed herein is for the purpose of description and not of limitation.

Claims

1. A sensorized coating device (100) configured for measuring external pressures acting on it, said sensorized coating device (100) comprising a flexible sensor (110) having shape substantially laminar and comprising a plurality of sensitive areas Ai , said flexible sensor (110) being configured for measuring, at said sensitive areas A _j, the presence of corresponding external pressures Pf^T ;

said flexible sensor (110) comprising:

— a first layer (111) comprising a number i of strips of conductive material (111') alternate to strips of non-conductive material (111'');

— a second layer (112) comprising a number j of strips of conductive material (112') alternate to strips of non-conductive material (112''); said first layer (111) and said second layer (112) arranged in a position such that said i strips of conductive material (112') of said second layer (112) overlap without physical contact to said j strips of conductive material (111') of said first layer (111) at said sensitive areas A _j,

said strips of conductive material (111') of said first layer (111) and said strips of conductive material (112') of said second layer (112) being connected to an electrical circuit (115),

said strips of conductive material (111') of said first layer (111) arranged to come into electrical contact with said strips of conductive material (112') of said second layer (112) at determined sensitive areas Ai in consequence of determined external pressures P ^T acting on said determined sensitive areas Ai_j , said electrical contact closing said electrical circuit (115) and generating a voltage at the ends of two strips of conductive material (111', 112') in electrical contact to each other, in order to generate contact signals reporting information about the presence of said external pressures P ^T and their spatial position on said flexible sensor (110),

said sensorized coating device (100) characterized in that, between said first layer (111) and said second layer (112), a resistor material (113) is provided having an electrical resistivity of value p variable with the deformation, said flexible sensor (110) having laminar shape and being configured in such a way that, when said electrical circuit (115) closes in consequence of said external pressures P ^T , said resistor material (113) reduces its own thickness at sensitive areas Ai_j on which act said external pressures P ^T , changing proportionally said value p, said change of said value p allowing deriving the intensity of said external pressures Pf^T .

2. The sensorized coating device (100), according to claim 1, wherein said resistor material (113) comprises a plurality of resistive areas (113') located at said sensitive areas A _j, said resistive areas (113') being insulated to each other, in such a way that said contact signals do not interfere with each other.

3. The sensorized coating device (100), according to claim 1, wherein said sensitive areas Ai are adapted to be connected to each other for making increased sensitive areas Ai , in order to adjust the resolution of the sensitivity of said flexible sensor (110) .

4. A robotic structure (10) comprising:

— a frame ( 50 ) ;

— a control unit (60) arranged to operate said frame ( 50 ) ;

characterized in that it also comprises a sensorized coating device (100), according to any of claims from 1 to 3, in contact, in use, with said frame (50), said sensorized coating device (100) also comprising at least one damping element (120) in contact with said flexible sensor (110) and arranged to dampen the impact of said external pressures }EXT

i.j on said frame

(50) ;

said sensorized coating device (100) arranged to send to said control unit (60) contact signals reporting information about the presence of said external pressures Pf^T detected at said sensitive areas A _j, and in that said control unit (60) is adapted to process said contact signals and to operate said frame (50) according to a predetermined mode to react to said external pressures Pf^T .

5. Robotic structure (10), according to claim 4, wherein said sensorized coating device (100) also comprises an electromagnetic shielding device arranged to avoid electromagnetic interferences between said flexible sensor (110) and electric devices present in said frame (50) .

6. Robotic structure (10), according to claim 4, wherein two damping elements (120) are provided arranged in contact with said flexible sensor (110) at opposite sides with respect to it.

7. Robotic structure (10), according to claim 4, wherein said or each damping element (120) has a rest thickness H that can be deducted by the following equation :

¹ Poo = ^Ptn+f{^d/_H) wherein :

— P_∞ is the predetermined maximum pressure value that said frame (50) can oppose to said external pressures P f^T ;

— P_th is a value greater or equal to the minimum pressure value detectable from said flexible sensor (110) ;

— d is value of the variation of thickness of said damping element (120) owing to application of external pressures Pff^T , d being function of:

- speed v of application of said external pressures P f^T ,

- time t_a during which is carried out the deformation of said or each damping element (120) owing to applying said external pressures P f^T ,

- mechanical and dynamical features of the material of said damping element (120) .

8. Robotic structure (10), according to claim 4, wherein said contact signals are sent to said control unit

(60) by means of a wireless connection.

9. Robotic structure (10), according to claim 1, wherein said flexible sensor (110) is located in contact with said frame (50) by a removable connection.

10. Robotic structure (10), according to claim 4, wherein said frame (50) comprises a kinematical chain comprising a plurality of rotational joints (55) activated by respective actuators, at said rotational joints (55) arranged respective torque sensors configured to measure the torque present on said rotational joints (55) and to send a signal of torque variation to said control unit (60) .