JP6912919B2 - Tactile sensor - Google Patents

Description

The present invention relates to a cloth-like tactile sensor having piezoelectricity.

Conventionally, a tactile sensor is attached to a woven fabric such as a glove worn on a human hand to detect the pressure applied to the woven fabric, or the tactile sensor is deformed to move the woven fabric (for example). , Patent Document 1). In this tactile sensor, electrode films are formed on both sides of a string-shaped piezoelectric material whose both opposite sides are flat, and the outsides of both electrode films are covered with insulating films, respectively, and the piezoelectric fibers are formed of warp threads and weft threads. It is formed into a woven cloth by alternately weaving like this.

JP-A-2002-203996

Since such a tactile sensor needs to be in contact with the surface of the object to be detected, it is required to have flexibility that can be deformed in all directions and a property that is easily distorted by pressure. However, since the above-mentioned piezoelectric fiber is formed flat, it is easy to bend in the thickness direction, but it is difficult to bend in the width direction, and when the surface of the object to be detected is a curved surface, the contact area becomes small. There is. Further, the above-mentioned piezoelectric fiber has a problem that it is unlikely to be deformed by compression in the thickness direction or the width direction.

The present invention has been made to address the above-mentioned problems, and an object of the present invention is to provide a tactile sensor composed of a cable-shaped pressure sensor that is easily deformed in all directions and is easily distorted by an external force. be. In the following description of each constituent requirement of the present invention, in order to facilitate understanding of the present invention, the reference numerals of the corresponding parts of the embodiments are described in parentheses, but the constituent requirements of the present invention are carried out. It should not be construed as limited to the configuration of the corresponding parts indicated by the code of the form.

In order to achieve the above-mentioned object, the structural feature of the tactile sensor (10, 10a, 10b, 10c, 10d) according to the present invention is a flexible elongated cylindrical piezoelectric body (12, 32, 42, A sensor wire composed of 52), an inner conductor (13, 33, 43, 53) formed inside the piezoelectric body, and an outer conductor (14, 34, 44, 54) formed outside the piezoelectric body. The provided cable-shaped pressure sensor (11, 11a, 11b, 31, 31a, 41, 51, 61) is a tactile sensor formed by being assembled in a cloth shape, and is configured by extending the cable-shaped pressure sensor. The leader wire (16) is provided, and the piezoelectricity of the leader wire is lowered by heat treatment. According to the present invention, it is possible to prevent the leader wire from adversely affecting the sensitivity of the tactile sensor. That is, even if pressure is applied to the leader wire during the use of the tactile sensor, the detection of the object to be detected is not affected. Further, there is an advantage that the end side of the cable-shaped pressure sensor can be used as the leader wire as it is without using a separate member as the leader wire.

In the tactile sensor according to the present invention, the cross-sectional shape of the sensor electric wire constituting the cable-shaped pressure sensor is formed in a circular shape. Therefore, the cable-shaped pressure sensor can be expanded and contracted in the axial direction, and can be deformed evenly in any direction around the axis. Further, since the cross-sectional shape is formed in a circular shape, the cable-shaped pressure sensor is easily distorted when an external force is received from a direction orthogonal to the axial direction. The piezoelectric body generates a voltage according to the amount of deformation, and the larger the amount of deformation generated in the cable-shaped pressure sensor, the larger the voltage generated in the cable-shaped pressure sensor. Therefore, the tactile sensor can exhibit better detection sensitivity as the cable-shaped pressure sensor becomes more easily distorted.

Further, in the present invention, the inner conductor may be made of a metal wire or may be made of a thin layer formed along the inner surface of the piezoelectric body. When the inner conductor is composed of a thin layer, for example, a plating layer, the flexibility and elasticity of the tactile sensor can be further increased and the weight can be reduced. Further, by making the inside of the inner conductor a space, the diameter of this portion can be reduced, and thereby the tactile sensor can be made thinner. Further, when the inside of the inner conductor is made a space, the cable-shaped pressure sensor is more likely to be deformed in the radial direction, which further improves the sensitivity. In addition, if the interior is made space, it will be possible to significantly reduce costs.

Materials constituting the piezoelectric material include polylactic acid, vinylidene fluoride, vinylidene cyanide, polyamide, vinylidene cyanide, polytetrafluoroethylene and their foams and polymers, their copolymers and their laminates. , Further, a foam or the like can be used. Further, as the material constituting the inner conductor and the outer conductor, various conductive materials such as metals such as copper, silver, platinum and aluminum and alloys thereof can be used, and further, a conductive polymer and a conductive material can be used. Paint or the like can also be used. When one sensor electric wire is used, the cable-shaped pressure sensor according to the present invention is configured only by the sensor electric wire.

Yet another structural feature of the tactile sensor according to the present invention is that it is formed by assembling a cable-shaped pressure sensor in a knitted shape. According to the present invention, since the cable-shaped pressure sensors are entwined with each other so as to form a loop, the elasticity of the tactile sensor as a cloth is further increased. Therefore, even if the surface of the object to be detected is an uneven surface, the tactile sensor is partially expanded so that the surface of the object to be detected can follow the uneven surface in a good state, and the object to be detected can be detected with high accuracy. In addition, since a bent portion such as a knot is generated between the cable-shaped pressure sensors, the pressure sensor is deformed more greatly when pressure is applied, which also improves the detection sensitivity.

Yet another structural feature of the tactile sensor according to the present invention is that the cable-shaped pressure sensors (11a, 11b) in a spiral or wavy bent state are assembled in a cloth shape. According to the present invention, the cable-shaped pressure sensor constituting the tactile sensor is formed in advance in a spiral or wavy shape. Therefore, the cable-shaped pressure sensor has elasticity and flexibility like a spring, and the tactile sensor composed of such a cable-shaped pressure sensor also has high elasticity and flexibility. Further, when an external force is applied, the cable-shaped pressure sensor has a portion that is greatly deformed, which generates a large output voltage, so that the sensitivity of the cable-shaped pressure sensor is further improved.

Yet another structural feature of the tactile sensor according to the present invention is that a plurality of types of cable-shaped pressure sensors (A1, A2, B1, B2) having different thicknesses are used. According to the present invention, the sensitivity of each part can be changed according to the purpose of use of the tactile sensor. For example, use a thick cable-shaped pressure sensor for the part that requires higher sensitivity, and use a thin cable-shaped pressure sensor for the part that does not require so high sensitivity, and decide the arrangement of each cable-shaped pressure sensor. Can be done.

Still another structural feature of the tactile sensor according to the present invention is that the cable-shaped pressure sensor (61) is formed in a twisted shape by twisting a plurality of sensor electric wires (61a). According to the present invention, the cable-shaped pressure sensor is more easily bent and expanded and contracted by an external force due to the twisting, so that the cable-shaped pressure sensor has a large bending portion, which generates a large output voltage. The sensitivity of the state pressure sensor is improved. Further, by configuring the cable-shaped pressure sensor with a plurality of sensor wires, even if one of the sensor wires is broken, the other sensor wires can maintain the function as the cable-shaped pressure sensor.

Yet another structural feature of the tactile sensor according to the present invention is that flexible material layers (15, 15a, 15b) are formed on both the front and back surfaces. According to the present invention, the contact surface with the object to be detected can be softened, so that the object to be detected is not damaged. In addition, it is possible to protect the cable-shaped pressure sensor and prevent stains. Further, the sensitivity can be adjusted by appropriately selecting the material used for the flexible material layer. The flexible material layer can be composed of a cloth-like material, a film-like material, a coating layer, or the like. Further, the flexible material layer may be formed on both the front and back surfaces of the tactile sensor by providing the flexible material layer on the outer peripheral surface of each cable-shaped pressure sensor.

Yet another structural feature of the tactile sensor according to the present invention is that the hardness or thickness of the flexible material layers (15a, 15b) formed on the front and back sides are different. According to the present invention, a tactile sensor according to the purpose of use can be obtained. For example, when the soft substance layer on the front surface in contact with the object to be detected is made into a hard layer and the soft substance layer on the back surface is made into a layer softer than the soft substance layer on the front surface, the tactile sensitivity is increased, but the durability is decreased. Further, when the soft substance layer on the front surface is made a soft layer and the soft substance layer on the back surface is made a layer harder than the soft substance layer on the front surface, the tactile sensitivity is lowered, but the durability is improved. Further, when the soft substance layer on the front surface in contact with the object to be detected is made a thin layer and the soft substance layer on the back surface is made thicker than the soft substance layer on the front surface, the tactile sensitivity is increased, but the durability is lowered. Further, when the soft substance layer on the front surface is made a thick layer and the soft substance layer on the back surface is made a layer thinner than the soft substance layer on the front surface, the tactile sensitivity is lowered, but the durability is improved.

Yet another structural feature of the tactile sensor according to the present invention is that the surface hardness is set to 0 to 50 in the durometer type C as an evaluation value. According to the present invention, it is possible to obtain a flexible tactile sensor that can bend along the surface of the object to be detected. In Durometer type C (Asker C type that measures the hardness of vulcanized rubber), 0 to 50 is about the hardness of human skin, and the hardness of the surface of the cable-shaped pressure sensor is the hardness of human skin. By making the hardness or less, the tactile sensor comes into contact with the human body, for example, when it is used as a glove, it becomes comfortable to use. In this case, when the protective cover is provided on the surface of the tactile sensor, the hardness of the protective cover is 50 or less for the Asker C type, and when the protective cover is not provided, the hardness of the outer conductor is 30 or less for the Asker C type. , Preferably 20 or less. In this case, as the material constituting the outer conductor, polyurethane foam, silicon gel, urethane gel or the like can be used. The hardness of the surface described above is preferably 5 to 30 for the Asker C type, and more preferably 5 to 20.

Yet another structural feature of the tactile sensor according to the present invention is that the outer diameter of the cable-shaped pressure sensor is set to 8 μm to 800 μm. According to the present invention, it is possible to obtain a lightweight tactile sensor which is composed of an ultra-fine cable-shaped pressure sensor and has excellent flexibility and elasticity. Further, a skin having a size of 10 μm or less may be attached to this, and in that case, a polyamide, polyimide, or aramid-based material can be used. The outer diameter of the cable-shaped pressure sensor is preferably 20 μm to 500 μm, and more preferably 200 μm to 400 μm.

It is a perspective view which showed a part of the tactile sensor which concerns on 1st Embodiment of this invention. It is sectional drawing which showed the cable-shaped pressure sensor which constitutes a tactile sensor. It is a block diagram which showed the detection part provided in the robot. It is explanatory drawing which showed the position of the pressure applied to a warp and a weft, and the magnitude of the pressure. It is the schematic which showed a part of the tactile sensor which concerns on the modification 1 of 1st Embodiment. It is sectional drawing which showed the outline of the tactile sensor which concerns on the modification 2 of 1st Embodiment. It is a perspective view which showed a part of the tactile sensor which concerns on the modification 3 of 1st Embodiment. It is a side view which showed the cable-shaped pressure sensor which constitutes the tactile sensor which concerns on the modification 4 of 1st Embodiment. It is a side view which showed the cable-shaped pressure sensor which constitutes the tactile sensor which concerns on the modification 5 of 1st Embodiment. It is a top view which showed the outline of the tactile sensor which concerns on 2nd Embodiment of this invention. It is sectional drawing which showed the cable-shaped pressure sensor which comprises the tactile sensor which concerns on 3rd Embodiment. The state when pressure is applied to the tactile sensor according to the third embodiment is shown, (a) is a cross-sectional view before pressure is applied, and (b) is a cross-sectional view when pressure is applied. It is a top view which showed the piezoelectric film and the inner band-shaped layer used in the modification 1 of the 3rd Embodiment. A cable-shaped pressure sensor constituting the tactile sensor according to the second modification of the third embodiment is shown, where (a) is a side view and (b) is a cross-sectional view. It is a side view which showed the sensor central part provided in the tactile sensor which concerns on the modification 2 of the 3rd Embodiment. The cable-shaped pressure sensor constituting the tactile sensor according to the modified example 3 of the third embodiment is shown, (a) is a side view, and (b) is a cross-sectional view. It is sectional drawing which showed the piezoelectric film, the inner band-shaped layer and the outer band-shaped layer used in the modification 3 of the third embodiment. The cable-shaped pressure sensor constituting the tactile sensor according to the modified example 4 of the third embodiment is shown, (a) is a side view, and (b) is a cross-sectional view. It is sectional drawing which showed the cable-shaped pressure sensor which comprises the tactile sensor which concerns on the modification 5 of the 3rd Embodiment.

(First Embodiment)
Hereinafter, the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a part of the tactile sensor 10 according to the present embodiment. The tactile sensor 10 is attached to, for example, a hand-shaped grip portion of a robot (not shown) for harvesting crops, and detects the pressure when the grip portion of the robot grips the crop. The grip portion is used to control the gripping force when gripping the agricultural product, and is formed in the shape of a glove covering the grip portion.

The tactile sensor 10 includes a main body formed in a woven fabric shape in which a cable-shaped pressure sensor 11 (see FIG. 2) is woven so as to form warp threads A and weft threads B, and both front and back surfaces of the woven cloth-like main body are provided. Is manufactured by sewing the material covered with the protective cover 15, which will be described later, into the shape of a glove. As shown in FIG. 2, the cable-shaped pressure sensor 11 constituting each of the warp A and the weft B has an inner conductor 13 arranged inside the cylindrical piezoelectric body 12 and an outer surface on the outer peripheral surface of the piezoelectric body 12. It is configured by arranging the conductor layer 14.

The piezoelectric body 12 is made of polyvinylidene fluoride (PVDF) and is composed of an ultrafine cylindrical body having flexibility and elasticity, and its inner diameter is set to 0.3 mm and its outer diameter is set to 0.4 mm. .. The inner conductor 13 is formed by twisting a plurality of ultrafine tin-plated annealed copper wires, and the diameter thereof is set to 0.3 mm. Like the inner conductor 13, the outer conductor layer 14 is made of a tin-plated annealed copper wire, and its thickness is set to 0.05 mm.

The piezoelectric body 12 can be formed on the outer periphery of the inner conductor 13 by, for example, the same method as the method for manufacturing a coaxial cable. In this case, the molding material made of polyvinylidene fluoride is extruded with a screw while being melted and kneaded in the cylinder of the molding apparatus, and is formed as a coating layer on the surface of the inner conductor 13 passing through the crosshead. Then, the outer conductor layer 14 is formed on the surface of the piezoelectric body 12. The outer conductor layer 14 is formed by a horizontal winding shielding method in which a tin-plated annealed copper wire is wound around the surface of the piezoelectric body 12 by aligning it in one direction.

In addition, polyvinylidene fluoride is a lightweight polymer material that produces a piezoelectric effect when a high voltage is applied and polarized, and has the property of generating a voltage when an external force is applied to it and causing distortion when a voltage is applied. ing. The piezoelectric body 12 is subjected to a polarization treatment, and when an external force is applied to the piezoelectric body 12, a voltage is induced between the inner conductor 13 and the outer conductor layer 14. Further, when a voltage is applied between the inner conductor 13 and the outer conductor layer 14, the piezoelectric body 12 is deformed (distorted).

Both the front and back surfaces of the glove-shaped tactile sensor 10 are covered with a protective cover 15 made of an insulating soft resin film. The protective cover 15 has a thickness of 20 μm to 1.2 mm, preferably 20 μm to 800 μm, more preferably 50 μm to 500 μm, and a hardness of 0 to 50 for durometer type C, that is, the hardness of human skin. Or it's a little softer. Further, the tactile sensor 10 is provided with a leader wire 16 formed by extending the cable-shaped pressure sensor 11. The leader line 16 is treated at 70 ° C. to 150 ° C. for 5 seconds to 150 seconds, preferably 80 ° C. to 120 ° C. for 5 seconds to 60 seconds, and more preferably 85 ° C. to 98 ° C. for 5 seconds to 30 seconds. By doing this, the piezoelectricity is eliminated or reduced to a level that does not cause any problem (5% or less). As a result, an amorphous layer is formed in the piezoelectric body 17 of the leader wire 16, and the piezoelectricity is lowered.

FIG. 3 shows a detection unit 20 provided in the robot to which the tactile sensor 10 is attached. In addition to the tactile sensor 10, the detection unit 20 includes a detection circuit 21, an A / D conversion circuit 22, and a CPU 23. The detection circuit 21 includes an impedance conversion circuit, an amplifier circuit, and a low-pass filter. Then, the detection circuit 21 amplifies the level of the detection signal sent from the tactile sensor 10 via the leader line 16 when the grip portion of the robot grips the agricultural product to a predetermined level, and then amplifies the system response. A component having a frequency higher than the cutoff frequency, which is the limit of the above, is attenuated and cut off, and a component having a frequency lower than the cutoff frequency is sent to the A / D conversion circuit 22.

The A / D conversion circuit 22 converts the signal sent from the detection circuit 21 into a digital signal and sends it to the CPU 23. The CPU 23 executes various processes performed by the detection unit 20. Further, the detection unit 20 is provided with a ROM for storing a program executed by the CPU 23, a RAM for temporarily storing data used for processing of the CPU 23, and the like, as well as operation buttons for operating the robot. It is equipped with an operation unit and a drive unit equipped with a switch. Here, the CPU 23 determines the positions and voltages of the warp threads A and the weft threads B that generate a voltage from the piezoelectricity generated in the warp threads A and the weft threads B constituting the tactile sensor 10 when a pressure is applied to the tactile sensor 10. By calculating the size, it is determined which part of the tactile sensor 10 and how much pressure is applied.

In this case, as shown in FIG. 4, since the plurality of warp threads A and the weft threads B are orthogonal to each other, the direction in which the warp threads A are lined up is the horizontal axis, and the direction in which the weft threads B are lined up is the vertical axis. When pressure is applied to a predetermined portion a (circled portion in FIG. 4) of the tactile sensor 10, the pressure is measured by scanning what kind of signal is generated from each of the warp A and the weft B. You can know the distribution. In this case, the intersection of the warp A and the weft B can be used as the detection point. Further, the shape of the object to be detected and the position of the pressure peak can be determined by integrating the signals detected when the warp A and the weft B are scanned for a certain period of time.

Further, the cable-shaped pressure sensor 11 generates a signal when pressure is applied and deformation occurs, but the signal is not generated when the same state under pressure continues. In such a cable-shaped pressure sensor 11, as another detection method, measurement is performed from the cable-shaped pressure sensor 11 located on the outside where no pressure is applied and no signal is generated, and the criticality with the pressure-applied portion is obtained. It is preferable to simplify the detection process by finding points.

In this case, first, the contour of the pressured portion a is obtained by scanning from the outer cable-shaped pressure sensor 11 in which no signal is generated, and then, when scanning, the pressure is applied to the portion a. Assuming that the pressure sensor 11 is located near the contour, the contour of the pressure-applied portion is obtained by scanning the cable-shaped pressure sensor 11. As a result, even if the range of the pressured portion a changes, the pressured portion can be sequentially obtained. In this case, the shape of the predetermined portion a described above can be obtained by time-differentiating the value obtained as the critical point. According to this, it is not necessary to scan all the cable-shaped pressure sensors 11, so that the detection time can be shortened. Further, the above-mentioned drive unit drives the grip portion of the robot under the control of the CPU 23 based on the pressure value detected by the tactile sensor 10.

As described above, the tactile sensor 10 according to the present embodiment is formed by weaving the cable-shaped pressure sensor 11 as warp threads A and weft threads B in a woven fabric shape. Each cable-shaped pressure sensor 11 has a circular cross-sectional shape. Therefore, the cable-shaped pressure sensor 11 can be easily deformed not only in the axial direction but also in any direction around the axis, and can also be deformed in the radial direction so that the cross-sectional shape changes. Then, the tactile sensor 10 has a shape of a thin woven fabric that can be deformed, and even if the surface of the crop to be detected is unevenly formed, it can be contacted over a wide area along the shape of the robot. When the gripping portion grips the crop, the force received from the crop and its distribution can be detected with high sensitivity. Further, since the surface hardness of the tactile sensor 10 is as high as that of human skin, the object to be detected is not damaged.

(Modification 1 of the first embodiment)
FIG. 5 shows a part of the tactile sensor 10a according to the first modification of the first embodiment. The tactile sensor 10a includes a warp thread A and a weft thread B composed of a cable-shaped pressure sensor 11 in the tactile sensor 10 described above, and an oblique thread C extending obliquely with respect to the warp thread A and the weft thread B. The diagonal thread C is also composed of a cable-shaped pressure sensor 11. The configuration of the other parts of the tactile sensor 10a is the same as that of the tactile sensor 10.

With this configuration, the direction in which the tactile sensor 10a can detect increases, so that the shape of the non-detected object that applies pressure to the tactile sensor 10a can be captured more accurately. The other effects of the tactile sensor 10a are the same as those of the tactile sensor 10. In FIG. 5, the diagonal thread C is arranged on the front surface side of the tactile sensor 10a, but the diagonal thread C may be arranged on the back surface side of the tactile sensor 10a, or the front and back surfaces of the tactile sensor 10a. It may be entwined with the warp A and the weft B so as to be located in a zigzag pattern. Further, the number of diagonal threads C is also set as appropriate.

(Modification 2 of the first embodiment)
FIG. 6 shows a cross-sectional view of the tactile sensor 10b according to the second modification of the first embodiment. In this tactile sensor 10b, instead of the protective cover 15 in the tactile sensor 10 described above, a thin protective cover 15a is attached to the front surface side (upper surface in FIG. 6), and the protective cover 15a is attached to the back surface side (lower surface in FIG. 6). It is configured by attaching a thick protective cover 15b. The protective covers 15a and 15b are made of the same material and hardness as the protective cover 15, and the thickness of the protective cover 15a is 20 μm to 1.2 mm, preferably 20 μm to 800 μm, and more preferably 50 μm to 500 μm. The thickness of the protective cover 15b is set to 20 μm to 1.5 mm, preferably 50 μm to 1.2 mm, and more preferably 100 μm to 800 μm. The configuration of the other parts of the tactile sensor 10b is the same as that of the tactile sensor 10.

By thinning the protective cover 15a in this way, the tactile sensitivity of the tactile sensor 10b can be increased. Further, as a modification of the tactile sensor 10b, the surface to which the protective cover 15a is attached can be used as the back surface, and the surface to which the protective cover 15b is attached can be used as the front surface. According to this, the durability of the tactile sensor 10b is improved. Further, as a modification of the tactile sensor 10b, both protective covers may have the same thickness but different hardness. In this case, if the protective cover on the front surface side is hardened, the durability can be improved, and if the protective cover on the front surface side is softened, the tactile sensitivity can be increased.

(Modification 3 of the first embodiment)
FIG. 7 shows a part of the tactile sensor 10c according to the third modification of the first embodiment of the present invention. Similar to the tactile sensor 10 according to the first embodiment described above, the tactile sensor 10c is formed by weaving warp threads A and weft threads B having the same structure as the cable-shaped pressure sensor 11, but the warp threads A have an outer diameter. Different warp threads A1 and A2 are included, and weft threads B include weft threads B1 and B2 having different outer diameters. The warp A1 and the weft B1 are composed of the same cable-shaped pressure sensor, and have an outer diameter of 0.4 mm to 1.2 mm, preferably 0.4 mm to 0.8 mm, and more preferably 0.45 mm to 0.55 mm. Further, the warp A2 and the weft B2 are composed of the same cable-shaped pressure sensor, and have an outer diameter of 0.2 mm to 0.8 mm, preferably 0.25 mm to 0.6 mm, and more preferably 0.25 mm to 0.4 mm. be. The configuration of the other parts of the tactile sensor 10c is the same as that of the tactile sensor 10.

With this configuration, the sensitivity of each part of the tactile sensor 10c can be changed. In this case, the warp A1 and the weft 1 are located in the portion where high sensitivity is required, and the warp A2 and the weft B2 are located in the portion where high sensitivity is not required. Further, the warp A1 and the weft 1 may be located in the portion where the strength is required, and the warp A2 and the weft B2 may be located in the portion where the strength is not required so much. The other effects of the tactile sensor 10c are the same as those of the tactile sensor 10.

(Modification 4 of the first embodiment)
FIG. 8 shows a cable-shaped pressure sensor 11a constituting the tactile sensor according to the fourth modification of the first embodiment of the present invention. The cable-shaped pressure sensor 11a is formed in a spiral shape like a coil spring by bending the cable-shaped pressure sensor 11 described above. The cable-shaped pressure sensor 11a is formed in a woven fabric shape by being woven as warp threads and weft threads, and constitutes a main body portion of the tactile sensor. The cable-shaped pressure sensor 11a is obtained by twisting the cable-shaped pressure sensor 11 with other fibers and then melting the other fibers or winding the cable-shaped pressure sensor 11 around a meltable core. Can be formed in a spiral shape by dissolving. The configuration of other parts of the tactile sensor using the cable-shaped pressure sensor 11a is the same as that of the tactile sensor 10.

With this configuration, the tactile sensor becomes highly elastic and flexible. Further, when an external force is applied, the cable-shaped pressure sensor 11a has a portion that is greatly deformed, which generates a large output voltage, so that the sensitivity of the tactile sensor is improved. The other effects of the tactile sensor using the cable-shaped pressure sensor 11a are the same as those of the tactile sensor 10. Further, as a modification of the cable-shaped pressure sensor 11a, the other fibers described above may be left as they are without being melted to be in a twisted state. According to this, the surface of the tactile sensor becomes flexible.

(Modification 5 of the first embodiment)
FIG. 9 shows a cable-shaped pressure sensor 11b constituting the tactile sensor according to the modified example 5 of the first embodiment. The cable-shaped pressure sensor 11b is formed in a wavy shape by bending the cable-shaped pressure sensor 11 described above. The cable-shaped pressure sensor 11b is formed in a woven fabric shape by weaving it as warp threads and weft threads, and constitutes the main body portion of the tactile sensor. The cable-shaped pressure sensor 11b can be formed into a corrugated shape by using a plurality of thick synthetic fibers for the warp or weft threads so as to pass through the upper and lower sides of the synthetic fibers in order to form a waveform, and then melting the synthetic fibers. The configuration of other parts of the tactile sensor using the cable-shaped pressure sensor 11b is the same as that of the tactile sensor 10. With this configuration, it is possible to obtain the same effect as that of the tactile sensor provided with the cable-shaped pressure sensor 11a described above.

(Second Embodiment)
FIG. 10 shows an outline of a part of the tactile sensor 10d according to the second embodiment of the present invention. The tactile sensor 10d is formed in a knitted shape by entwining the cable-shaped pressure sensors 11 described above so as to form loops. The other configurations of the tactile sensor 10d are the same as those of the tactile sensor 10 described above.

According to this, since each cable-shaped pressure sensor 11 is bent so as to draw a loop, the length that can be expanded and contracted in the front-rear direction or the left-right direction is greatly increased. Therefore, the tactile sensor 10d can follow the surface of the hemispherical or spherical object to be detected, and the range of the object to be detected can be expanded. Further, since each cable-shaped pressure sensor 11 is winding so as to form a knot, it is easily deformed, which improves the detection sensitivity. The other effects of the tactile sensor 10d are the same as those of the tactile sensor 10 described above. Further, as a modification of the tactile sensor 10d, a cable-shaped pressure sensor 11a or 11b may be used instead of the cable-shaped pressure sensor 11. Further, the diagonal thread C may be added to the tactile sensor 10d.

(Third Embodiment)
FIG. 11 shows a cable-shaped pressure sensor 31 constituting the tactile sensor according to the third embodiment of the present invention. The cable-shaped pressure sensor 31 is configured by forming a thin inner conductor layer 33 on the inner peripheral surface of the cylindrical piezoelectric body 32 and forming a thin outer conductor layer 34 on the outer peripheral surface of the piezoelectric body 32. The piezoelectric body 12 is made of polyvinylidene fluoride and is composed of an ultrafine cylindrical body having flexibility and elasticity, and has an inner diameter of 0.15 mm to 0.60 mm, preferably 0.3 mm, and an outer diameter of 0. It is set to .25 mm to 0.65 mm, preferably 0.32 mm. The inner conductor layer 33 is made of a thin film made of silver, and is formed on the inner peripheral surface of the piezoelectric body 32 by thin film deposition. The thickness of the inner conductor layer 33 is about 0.5 μm to 2.0 μm, preferably about 0.5 μm. Like the inner conductor layer 33, the outer conductor layer 34 is formed on the outer peripheral surface of the piezoelectric body 32 by vapor deposition of silver. The thickness of the outer conductor layer 34 is substantially the same as the thickness of the inner conductor layer 33.

The piezoelectric body 32 is formed by, for example, a known drawing method. In this case, it is set by pulling the molding material made of polyvinylidene fluoride with a gripping tool while passing through the gap between the opening of the outer diameter die having the opening and the inner diameter plug arranged inside the opening. It is molded into a cylindrical shape with a different diameter and wall thickness. Then, an inner conductor layer 33 and an outer conductor layer 34 having a thickness set on the inner surface and the outer surface of the piezoelectric body 32 are formed by a known arc vapor deposition method using a vacuum chamber. The cable-shaped pressure sensor 31 configured in this way is woven as warp threads D and weft threads E (see FIGS. 12 (a) and 12 (b)), and protective covers are attached to both the front and back surfaces thereof to provide a tactile sensor according to the present embodiment. Is configured, and its appearance is substantially the same as that of the tactile sensor 10.

As described above, the tactile sensor according to the present embodiment is formed by weaving the cable-shaped pressure sensor 31 as warp threads D and weft threads E in a woven fabric shape. Each cable-shaped pressure sensor 31 is configured by forming a thin inner conductor layer 33 on the inner peripheral surface of the cylindrical piezoelectric body 32 and forming a thin outer conductor layer 34 on the outer peripheral surface of the piezoelectric body 32. The piezoelectric body 32 is formed in an ultrafine cylindrical shape made of polyvinylidene fluoride having flexibility and elasticity. Therefore, the cable-shaped pressure sensor 31 can be easily deformed in any direction around the axis, can be expanded and contracted in the axial direction, and can be easily deformed in the radial direction so that the cross-sectional shape changes. Then, the tactile sensor becomes a thin woven fabric that can be deformed, and even if the surface of the crop to be detected is formed unevenly, it can be bent along the shape, and the grip portion of the robot is the crop. It becomes possible to detect the force received from the crop and its distribution with high sensitivity when grasping the.

Further, since the piezoelectric body 32 is made of polyvinylidene fluoride, the cable-shaped pressure sensor 31 can obtain good piezoelectricity. 12 (a) and 12 (b) show the states of the two cable-shaped pressure sensors 31 constituting the overlapping warp D and weft E when pressure is applied to the tactile sensor, and FIG. 12 (a) shows the pressure. The state before the pressure is applied, and FIG. 12B shows the state when the pressure is applied. Before pressure is applied, the cross-sectional shape of each cable-shaped pressure sensor 31 is in a state close to a perfect circle with almost no deformation, but when pressure is applied, each cable-shaped pressure sensor 31 becomes large in pressure. It is crushed accordingly and its cross-sectional shape changes to an elliptical shape.

At this time, compressive stress is generated on the inner surface side of both side portions (the left and right sides of the cross section of FIG. 12B) of the piezoelectric body 32 of the cable-shaped pressure sensor 31 deformed into an elliptical shape, and the cable-shaped pressure sensor 31 is pulled toward the outer surface side. It is distorted so that stress is generated. Therefore, when the cable-shaped pressure sensor 31 is expanded and contracted in the axial direction or the piezoelectric body 32 is compressed in the thickness direction on the left and right sides of the cable-shaped pressure sensor 31 shown in the cross section in FIG. 12 (b). Larger deformation will occur compared to.

The piezoelectric body 32 generates a voltage according to the amount of deformation. Therefore, a larger voltage is generated in the cable-shaped pressure sensor 11 which is greatly deformed by the pressure, and the tactile sensor can exhibit good detection sensitivity. Further, since the inner conductor layer 33 and the outer conductor layer 34 are composed of a silver vapor deposition layer, they can be formed into an ultrathin layer. Along with this, the diameter of the cable-shaped pressure sensor 31 can be reduced, the weight can be reduced, and the cost can be reduced. Further, as another example, the cable-shaped pressure sensor 31 may be assembled in the knitted shape shown in FIG. 10 to form a tactile sensor.

(Modification 1 of the third embodiment)
As the first modification of the third embodiment described above, the piezoelectric film 32a shown in FIG. 13 can be used to form the piezoelectric body 32. The piezoelectric film 32a is composed of an elongated rectangular sheet made of polyvinylidene fluoride, and an inner band-shaped layer 33a for forming the inner conductor layer 33 is formed in the central portion in the width direction of one of the surfaces. .. The piezoelectric body 32 is formed in a cylindrical shape by winding both edge portions 32b in the width direction of the piezoelectric film 32a so as to overlap each other, and the inner strip-shaped layer 33a is a portion of the piezoelectric film 32a excluding the overlapped both edge portions 32b. Is formed in. Then, an outer conductor layer 34 is formed on the outer peripheral surface of the piezoelectric body 32 as in the cable-shaped pressure sensor 31 described above.

When the piezoelectric film 32a is wound in a cylindrical shape, for example, the piezoelectric film 32a in which the internal band-shaped layer 33a is formed is wound around a core wire made of a material that is easily dissolved or evaporated to form a cylindrical shape, and then the core wire is formed. Can be used to dissolve or evaporate the film to remove it. The diameter of the core wire is preferably 0.15 mm to 0.55 mm, preferably 0.30 mm. The outer conductor layer 34 can be formed by vapor deposition of silver as in the third embodiment described above, but it may also be formed by using a plating layer of another metal or by applying a conductor resin. good. The conductor resin may be impregnated by utilizing the capillary phenomenon. Further, in the first modification, the width of the piezoelectric film 32a is 3.5 mm and the length is 200 m, and a cylindrical body composed of the piezoelectric body 32, the inner conductor layer 33 and the outer conductor layer 34 is formed slightly thicker. The diameter and wall thickness are set by pulling after forming into a cylindrical shape.

The dimensions of each part of the piezoelectric film 32a are as follows: length 10 mm to 1000 mm, preferably 100 mm to 500 mm, width 1 mm to 10 mm, preferably 1.5 mm to 5 mm, and thickness 8 μm to 120 μm, preferably. It is set to 15 μm to 40 μm, most preferably 20 μm. Further, when the width of the piezoelectric film 32a is 3.5 mm as described above, the width of the inner strip-shaped layer 33a is set to 1.3 mm to 1.7 mm, and the width of the edge portions 32b on both sides of the inner strip-shaped layer 33a is set. Is preferably set to 0.9 mm to 1.1 mm. In this case, the inner conductor layer 33 has a gap extending in the longitudinal direction. Further, in FIG. 13, the inner strip-shaped layer 33a is not formed at both ends of the piezoelectric film 32a in the longitudinal direction, but the inner strip-shaped layer 33a may extend to both ends of the piezoelectric film 32a in the longitudinal direction. ..

(Modification 2 of the third embodiment)
14 (a) and 14 (b) show the cable-shaped pressure sensor 41 constituting the tactile sensor (not shown) according to the second modification of the third embodiment. Similar to the cable-shaped pressure sensor 31 described above, the cable-shaped pressure sensor 41 forms a thin inner conductor layer 43 on the inner peripheral surface of the cylindrical piezoelectric body 42, and has a thin outer conductor layer 44 on the outer peripheral surface of the piezoelectric body 42. The piezoelectric body 42 and the inner conductor layer 43 are each formed in a cylindrical shape by spirally winding an elongated material.

In manufacturing the cable-shaped pressure sensor 41, a piezoelectric film having an internal band-shaped layer similar to that of the piezoelectric film 32a on which the internal band-shaped layer 33a shown in FIG. 13 is formed is used. Then, the piezoelectric film is spirally rolled into a cylindrical shape so that the inner strip-shaped layer is on the inside, and the edges of the overlapping piezoelectric films are joined to each other. As a result, the sensor center portion 41a including the piezoelectric body 42 shown in FIG. 15 and the internal conductor layer 43 (see FIG. 14B) is obtained. A spirally extending gap 43a is formed between the edges of the inner conductor layer 43 in the width direction. In this case, the piezoelectric film can also be wound by using the core wire made of the above-mentioned material that is easily dissolved or evaporated. Next, the outer conductor layer 44 is formed on the outer peripheral surface of the piezoelectric body 42 to obtain the cable-shaped pressure sensor 41. The outer conductor layer 44 can also be formed by vapor deposition of silver, plating of other metals, coating of a conductor resin, or the like.

The inner and outer diameters of the piezoelectric body 42 are substantially the same as those of the piezoelectric body 32 described above, and the thicknesses of the inner conductor layer 43 and the outer conductor layer 44 are substantially the same as the thicknesses of the inner conductor layer 33 and the outer conductor layer 34 described above. Is. The plurality of cable-shaped pressure sensors 41 configured in this way are divided into two sets, one of which is a warp and the other of which is a weft to form a woven cloth, and protective covers are attached to both the front and back surfaces. Therefore, a tactile sensor similar to the tactile sensor using the cable-shaped pressure sensor 31 can be obtained. Further, the cable-shaped pressure sensor 41 may be assembled in the knitted shape shown in FIG. 10 to form a tactile sensor.

According to the tactile sensor in this embodiment, since the inner conductor layer 43 is formed by the inner band-shaped layer previously formed on the piezoelectric film, the cable-shaped pressure sensor 41 can be easily formed. Further, by changing the diameter of the core wire used for winding the piezoelectric film and the winding method of the piezoelectric film, the shape, inner diameter, outer diameter, thickness, and other dimensions of each part constituting the cable-shaped pressure sensor 41 can be arbitrarily set. Therefore, the structure of the tactile sensor can be set arbitrarily. The other effects of the tactile sensor using the cable-shaped pressure sensor 41 are the same as those of the tactile sensor using the cable-shaped pressure sensor 31 described above.

(Modification 3 of the third embodiment)
16 (a) and 16 (b) show a cable-shaped pressure sensor 51 that constitutes a tactile sensor (not shown) according to the third modification of the third embodiment. The cable-shaped pressure sensor 51 is configured by forming a thin inner conductor layer 53 on the inner peripheral surface of the cylindrical piezoelectric body 52 and forming a thin outer conductor layer 54 on the outer peripheral surface of the piezoelectric body 52. In the cable-shaped pressure sensor 51, the piezoelectric body 52, the inner conductor layer 53, and the outer conductor layer 54 are all formed into a cylindrical shape or a substantially cylindrical shape by spirally winding an elongated material. The piezoelectric body 52 is formed in a cylindrical shape, but the inner conductor layer 53 and the outer conductor layer 54 are formed in a spiral shape with gaps 53b and 54b, respectively, like a coil spring.

When manufacturing this cable-shaped pressure sensor 51, first, as shown in FIG. 17, an inside made of a thin layer of silver is centered in the width direction of one surface (upper surface in FIG. 17) of the piezoelectric film 52a. The band-shaped layer 53a is formed, and an outer band-shaped layer 54a made of a thin layer of silver is formed at the center of the other surface (lower surface in FIG. 17) of the piezoelectric film 52a in the width direction to be used as the sensor material 51a. Next, the sensor material 51a is spirally rolled into a cylindrical shape so that the inner strip-shaped layer 53a is on the inside and the outer strip-shaped layer 54a is on the outside, and the edges 52b of the overlapping piezoelectric films 52a are joined to each other. As a result, a cable-shaped pressure sensor 51 composed of the piezoelectric body 52, the inner conductor layer 53, and the outer conductor layer 54 is obtained. In this case, the edges 52b of the piezoelectric film 52a are preferably bonded to each other by adhesion or crimping. Further, the sensor material 51a can be wound by using the core wire made of the above-mentioned material that is easily dissolved or evaporated.

The inner and outer diameters of the piezoelectric body 52 are substantially the same as those of the piezoelectric body 32 described above, and the thicknesses of the inner conductor layer 53 and the outer conductor layer 54 are substantially the same as the thicknesses of the inner conductor layer 33 and the outer conductor layer 34 described above. Is. The plurality of cable-shaped pressure sensors 51 configured in this way are divided into two sets, one of which is a warp and the other of which is a weft to form a woven fabric, and protective covers are attached to both the front and back surfaces. A tactile sensor can be obtained with. Further, the cable-shaped pressure sensor 51 may be assembled in the knitted shape shown in FIG. 10 to form a tactile sensor.

According to the tactile sensor according to the third modification, the inner conductor layer 53 and the outer conductor layer 54 constituting the cable-shaped pressure sensor 51 are formed of the inner band-shaped layer 53a and the outer band-shaped layer 54a previously formed on the piezoelectric film 52a. Therefore, the formation of the inner conductor layer 53 and the outer conductor layer 54 becomes easy. Further, also in this case, by changing the diameter of the core wire used for winding the sensor material 51a and the winding method of the sensor material 51a, the shape, inner diameter, outer diameter, thickness, etc. of each part constituting the cable-shaped pressure sensor 51 can be changed. Since the dimensions of the tactile sensor can be set arbitrarily, the structure of the tactile sensor can be set arbitrarily. The other effects of the tactile sensor using the cable-shaped pressure sensor 51 are the same as those of the tactile sensor using the cable-shaped pressure sensor 31 described above. Further, as another modification, instead of winding the sensor material 51a in a spiral shape, the edge portions 52b can be joined together while being straight to form a cylindrical shape.

(Modification 4 of the third embodiment)
18 (a) and 18 (b) show a cable-shaped pressure sensor 61 constituting a tactile sensor (not shown) according to the fourth modification of the third embodiment. The cable-shaped pressure sensor 61 is formed by twisting a plurality of sensor electric wires 61a into a twisted yarn shape, and each sensor electric wire 61a is configured to be the same as the cable-shaped pressure sensor 31 of the third embodiment described above. However, it needs to be extremely fine. Then, the plurality of cable-shaped pressure sensors 61 configured in this way are divided into two sets, one of which is a warp and the other of which is a weft to form a woven fabric, and protective covers are attached to both the front and back surfaces. A tactile sensor can be obtained by attaching it. Further, the cable-shaped pressure sensor 61 may be assembled in the knitted shape shown in FIG. 10 to form a tactile sensor.

In the tactile sensor according to the modification 4, since the cable-shaped pressure sensor 61 is composed of a plurality of sensor electric wires 61a, the strength is increased and the sensitivity is improved. Further, since each cable-shaped pressure sensor 61 is more easily bent by an external force and is more easily expanded and contracted in the axial direction due to the twisting, the tactile sensor composed of the cable-shaped pressure sensor 61 is more flexed along the object to be detected. It will be easier. Further, by configuring the cable-shaped pressure sensor 61 with a plurality of sensor wires 61a, even if some of the sensor wires 61a are cut, the other sensor wires 61a can maintain the function as the cable-shaped pressure sensor 61. can.

The other effects of the tactile sensor using the cable-shaped pressure sensor 61 are the same as those of the tactile sensor using the cable-shaped pressure sensor 31 described above. Further, as a modification of the cable-shaped pressure sensor 61, the sensor wire used as each sensor wire 61a may be configured by the cable-shaped pressure sensor 11, 41 or 51 instead of the cable-shaped pressure sensor 31.

(Modification 5 of the third embodiment)
FIG. 19 shows a cross section of the cable-shaped pressure sensor 31a constituting the tactile sensor (not shown) according to the modified example 5 of the third embodiment. The cable-shaped pressure sensor 31a is configured by forming an insulating sheath 35 on the outer peripheral surface of the cable-shaped pressure sensor 31 described above. The insulating sheath 35 is formed by wrapping an ultrathin polyester tape around the outer peripheral surface of the outer conductor layer 34, and has a thickness of 3 μm to 80 μm, preferably 5 μm to 50 μm, and more preferably 10 μm to 25 μm. .. Then, a plurality of cable-shaped pressure sensors 31a configured in this way are knitted into warp threads and weft threads to form a woven fabric, and protective covers are attached to both the front and back surfaces to obtain a tactile sensor. ..

In the tactile sensor according to the modified example 5, since the strength of each cable-shaped pressure sensor 31a is increased, damage can be prevented and the life can be extended. The other effects of the tactile sensor using the cable-shaped pressure sensor 31a are the same as those of the tactile sensor using the cable-shaped pressure sensor 31 described above. Further, as a modification of the cable-shaped pressure sensor 31a, the central portion may be configured by any of the cable-shaped pressure sensors 11, 41, 51, 61 instead of the cable-shaped pressure sensor 31. The cable-shaped pressure sensor 31a may be assembled in the knitted shape shown in FIG. 10 to form a tactile sensor.

In each of the above-described embodiments and modifications, the tactile sensor 10 and the like are attached to the grip portion of the robot in the form of gloves, but the tactile sensor according to the present invention can also be used for other purposes. Hereinafter, each application will be described. First, the tactile sensor can be used in non-destructive inspection to inspect the presence or absence of defects in welds such as pipes. In this case, the tactile sensor is formed in a flat cloth shape and wound around the part to be inspected of the pipe. In that state, a voltage is applied to the tactile sensor to generate vibration. At this time, the presence or absence of defects, such as cavities and cracks, can be determined from the state of vibration reflected from the inner surface after passing through the pipe. In addition, a tactile sensor is wound around a pipe, gas is introduced into the pipe, and air leaks to the outer surface of the pipe to apply pressure to the tactile sensor. It is also possible to judge whether or not it is present.

In addition, a balloon whose surface is covered with a tactile sensor is put into a pipe and inflated, and in that state, a voltage is applied to the tactile sensor to generate vibration, which is reflected from the inner surface after passing through the pipe. It is also possible to determine the presence or absence of defects, such as cavities and cracks, based on the state of vibration. Further, the tactile sensor according to the present invention is attached to the seat surface or backrest of an automobile seat and used as a pressure detection device, or is used to determine whether a person or an object is on the seat. It can also be used for. It can also be used to determine the driver's condition by attaching it to an automobile seat belt, steering wheel cover, etc. and measuring heartbeat and respiration.

The tactile sensor according to the present invention can also be used as a medical device, and can be attached to a bed sheet or a pillow cover to be a non-invasive heartbeat / respiratory sensor. Further, it can also be used as a sphygmomanometer. In this case, for example, the tactile sensor is provided with a soft portion and a hard portion, and the blood pressure can be determined according to the vibration state of each portion. In addition, it can be attached to an artificial leg or an artificial hand and used to detect a load, or can be used as a massage device for rehabilitation. In these cases, the shape of the tactile sensor should be tailored to the purpose. In short, a tactile sensor can be used as long as it is a machine or instrument that measures the pressure from the outside or achieves the purpose by deforming the piezoelectric body.

Further, the tactile sensor according to the present invention is not limited to the above-described embodiments and modifications, and can be appropriately modified and implemented within the technical scope of the present invention. For example, in each of the above-described embodiments and modifications, the protective covers 15, 15a and 15b as the flexible substance layer according to the present invention are formed on the surfaces of the tactile sensors 10, 10a and the like, respectively. The outer peripheral surface itself of each cable-shaped pressure sensor 11, 11a or the like may be formed in a flexible material layer. According to this, the protective covers 15, 15a and 15b can be omitted.

Further, the material and dimensions of each part constituting the cable-shaped pressure sensors 11, 31 and the like described above can be changed as appropriate. For example, the diameters of the cable-shaped pressure sensors 11, 11a, 11b are preferably set to arbitrary values in the range of 8 μm to 800 μm, and the diameters of the cable-shaped pressure sensors 31, 41, etc. are arbitrary in the range of 8 μm to 100 μm. It is preferable to set the value of. Further, the thickness of the insulating sheath is preferably set to an arbitrary value in the range of 5 μm to 80 μm.

10, 10a, 10b, 10c, 10d ... Tactile sensor, 11, 11a, 11b, 31, 41, 51, 61, 71 ... Cable-shaped pressure sensor, 12, 32, 42, 52 ... Piezoelectric body, 13 ... Internal conductor, 14, 34, 44, 54 ... External conductor layer, 15, 15a, 15b ... Protective cover, 16 ... Leader wire, 33, 43, 53 ... Internal conductor layer, 61a ... Sensor wire, A, A1, A2, D ... Warp , B, B1, B2, E ... Weft, C ... Diagonal thread.

Claims (9)

A cable-shaped pressure sensor including a sensor electric wire composed of a flexible elongated cylindrical piezoelectric body, an inner conductor formed inside the piezoelectric body, and an outer conductor formed outside the piezoelectric body. , A tactile sensor formed by assembling into a cloth
A tactile sensor characterized in that a leader wire formed by extending the cable-shaped pressure sensor is provided, and the piezoelectricity of the leader wire is lowered by heat treatment. The tactile sensor according to claim 1, wherein the cable-shaped pressure sensor is assembled in a knitted shape. The tactile sensor according to claim 1 or 2, wherein the cable-shaped pressure sensor in a spiral or wavy bent state is assembled in a cloth shape. The tactile sensor according to any one of claims 1 to 3, wherein a plurality of types of cable-shaped pressure sensors having different thicknesses are used. The tactile sensor according to any one of claims 1 to 4, wherein the cable-shaped pressure sensor is formed by twisting a plurality of the sensor electric wires into a twisted yarn shape. The tactile sensor according to any one of claims 1 to 5 , wherein a flexible substance layer is formed on both the front and back surfaces. The tactile sensor according to claim 6, wherein the soft material layers formed on the front and back surfaces have different hardness or thickness. The tactile sensor according to any one of claims 1 to 7, wherein the surface hardness is evaluated to be 0 to 50 in a durometer type C. The tactile sensor according to any one of claims 1 to 8, wherein the outer diameter of the cable-shaped pressure sensor is set to 8 μm to 800 μm.

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