Flexible magnetic tactile sensor and preparation method thereof

Abstract

The invention provides a flexible magnetic tactile sensor and a preparation method thereof. The method comprises the following steps: constructing a matrix structure of a target sensor; wherein the base body structure comprises a flexible substrate and an elastic body arranged on the flexible substrate; obtaining a flexible material and a mixed material of the flexible material and a magnetic material; wherein the flexible material is used for forming a flexible substrate, and the mixed material is used for forming the elastomer; placing a flexible material in a binder jet printing device, and printing to form the flexible substrate; taking out a flexible material, placing the mixed material in the binder jet printing equipment, and printing the elastomer on a flexible substrate to form the matrix structure; carrying out magnetizing treatment on the matrix structure to form a three-dimensional detection layer; and packaging the three-dimensional detection layer and the detection chip to form the flexible magnetic tactile sensor. The sensitivity of the sensor can be improved, the preparation process is simplified, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of flexible electronic technology, and more specifically, to a flexible magnetic tactile sensor and a preparation method thereof. Background Art

[0002] At present, flexible electronic devices have broad application prospects in the fields of energy conversion, wearable devices, health care, information display, etc., due to their ability to withstand folding, bending, compression, and stretching. As one of the many flexible electronic devices, flexible tactile sensors provide the possibility for machines to interact with the surrounding environment, thus being widely used. Common tactile sensors include capacitive, resistive, and piezoelectric. However, sensors based on the above principles have shortcomings such as poor output linearity and large hysteresis, which limit the scope of use of sensors.

[0003] Due to the advantages of simple structure, high linearity and long life, magnetic field sensors have been widely used in recent years. However, since the previous method of hard permanent magnet block plus elastic matrix is ​​inconsistent with the lightness, flexibility and scalability of flexible devices, magnetic elastomers are usually used to replace the combination of permanent magnet plus magnetic film. However, this method will reduce the magnetic field strength due to the relatively dispersed magnetic material, thus affecting the performance of the sensor.

[0004] In addition, the current preparation method of flexible tactile sensors is usually based on mold molding, which greatly reduces the uniformity of the sensor and limits its application in production. Although the use of 3D printing magnetic elastomers can significantly reduce the occurrence of this situation, the mainstream 3D printing processes (such as DIW, FDM, etc.) have problems such as simple molding structure and low production efficiency. In addition, the initial magnetic field strength of the sensor is usually large and the sensitivity is low, which makes it difficult to meet high-precision sensing requirements.

[0005] Therefore, it is necessary to explore a flexible magnetic tactile sensor and a preparation method thereof to improve the sensitivity of the sensor, simplify the preparation process and improve production efficiency. Summary of the invention

[0006] In view of the above problems, the present invention provides a flexible magnetic tactile sensor and a preparation method thereof to solve the problems of simple molding structure, low production efficiency, poor sensitivity, etc. existing in the existing flexible sensors.

[0007] The method for preparing a flexible magnetic tactile sensor provided by the present invention comprises:

[0008] Constructing a base structure of a target sensor; wherein the base structure includes a flexible substrate and an elastic body arranged on the flexible substrate; and at the same time,

[0009] Obtain a flexible material and a mixed material of the flexible material and a magnetic material; wherein the flexible material is used to form the flexible substrate, and the mixed material is used to form the elastomer;

[0010] Placing the flexible material in a binder jet printing device to print and form the flexible substrate;

[0011] Taking out the flexible material, and placing the mixed material in the binder jet printing device, printing the elastomer on the flexible substrate to form the matrix structure;

[0012] Performing magnetization treatment on the base structure to form a three-dimensional detection layer;

[0013] The three-dimensional detection layer and the detection chip are packaged to form a flexible magnetic tactile sensor.

[0014] In addition, an optional technical solution is that the flexible substrate is a circular or polygonal hollow frame structure.

[0015] In addition, an optional technical solution is that when the flexible base is circular, the elastic body includes a polygonal support frame embedded in the flexible base, and a first inclined leg arranged on the polygonal support frame;

[0016] Among them, one end of different first inclined legs is respectively connected to different sides of the polygonal support frame, and the other ends of different first inclined legs intersect at one point.

[0017] In addition, an optional technical solution is that when the flexible base is a polygon, the elastic body includes a circular support frame embedded in the flexible base, and a second inclined leg arranged on the circular support frame;

[0018] One end of each second inclined support leg is connected to the circular support frame, and the other end intersects at one point.

[0019] In addition, an optional technical solution is that the ends of the different second inclined legs connected to the circular support frame are evenly spaced on the circular support frame.

[0020] In addition, an optional technical solution is to perform magnetization treatment on the base structure to form a three-dimensional detection layer, including:

[0021] The base structure is extruded and limited by a preset limiting mold; wherein the inclined legs of the extruded base structure are parallel to each other and fit together; wherein the inclined legs include the first inclined legs and the second inclined legs;

[0022] Magnetizing the inclined legs in the limiting mold in the same direction;

[0023] The magnetized inclined legs are taken out from the limiting mold to form a three-dimensional detection layer.

[0024] In addition, an optional technical solution is that the limiting mold includes a bracket and a limiting hole arranged on the bracket, and the shape of the limiting hole is adapted to the shape of the inclined legs that are fitted together;

[0025] The inclined supporting leg is inserted into the limiting hole for limiting.

[0026] In addition, an optional technical solution is that after forming the base structure and before magnetizing the base structure, it also includes:

[0027] Low-temperature baking is performed on the base structure, and the baked base structure is cleaned;

[0028] The cleaned substrate structure is vacuum dried; wherein,

[0029] The temperature of the vacuum drying is lower than the melting point of the flexible material.

[0030] In addition, an optional technical solution is that the flexible material includes: at least one of TPU, TPE, SBS and SEBS;

[0031] The magnetic material includes at least one of neodymium iron boron and samarium iron nitrogen.

[0032] On the other hand, the present invention further provides a flexible magnetic tactile sensor, which is prepared using the above-mentioned flexible magnetic tactile sensor preparation method.

[0033] By utilizing the above-mentioned flexible magnetic tactile sensor and its preparation method, a flexible material is used to form the flexible substrate of the sensor, and a mixed material is used to form an elastomer on the flexible substrate. The two are respectively printed and formed by a binder jet printing device, and finally the formed base structure is magnetized. This can achieve a more complex sensor structure and improve production efficiency. The magnetization process is controllable, which can achieve the effect of improving the sensitivity of the sensor.

[0034] In order to achieve the above and related purposes, one or more aspects of the present invention include the features that will be described in detail later. The following description and the accompanying drawings describe some exemplary aspects of the present invention in detail. However, these aspects indicate only some of the various ways in which the principles of the present invention can be used. In addition, the present invention is intended to include all these aspects and their equivalents. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] By referring to the following description in conjunction with the accompanying drawings, and with a more comprehensive understanding of the present invention, other objects and results of the present invention will become more apparent and easy to understand. In the accompanying drawings:

[0036] Figure 1 is a flow chart of a method for preparing a flexible magnetic tactile sensor according to an embodiment of the present invention;

[0037] Figure 2 is a schematic diagram of the three-dimensional structure of a three-dimensional detection layer according to an embodiment of the present invention;

[0038] Figure 3 is a side view of a three-dimensional detection layer according to an embodiment of the present invention;

[0039] Figure 4 A schematic diagram of the magnetization direction of a three-dimensional detection layer according to an embodiment of the present invention;

[0040] Figure 5 is a schematic structure of a flexible magnetic tactile sensor according to an embodiment of the present invention;

[0041] Figure 6 is a magnetic field intensity distribution diagram of a flexible magnetic tactile sensor according to an embodiment of the present invention;

[0042] Figure 7 A magnetic field distribution diagram showing a change in magnetic field direction in a central area of ​​a flexible magnetic tactile sensor according to an embodiment of the present invention as the distance changes;

[0043] Figure 8 is a stress-strain diagram of the flexible magnetic tactile sensor during compression according to an embodiment of the present invention;

[0044] Fig. 9 Schematic diagram of the packaging structure of the inclined legs according to an embodiment of the present invention.

[0045] The reference numerals include: flexible substrate 1 , polygonal support frame 2 , first inclined leg 3 , base layer 4 , pin header 5 , detection chip 6 , PCB 7 , and elastomer 10 .

[0046] The same reference numerals throughout the drawings indicate similar or corresponding features or functions. DETAILED DESCRIPTION

[0047] In the following description, for the purpose of illustration, in order to provide a comprehensive understanding of one or more embodiments, many specific details are set forth. However, it is apparent that these embodiments may also be implemented without these specific details. In other examples, for ease of describing one or more embodiments, known structures and devices are shown in the form of block diagrams.

[0048] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0049] In order to solve the problems of simple molding structure, low production efficiency, poor sensitivity and the like in existing flexible sensors, the present invention provides a flexible magnetic tactile sensor and a preparation method thereof. A flexible substrate of the sensor is formed by a flexible material, and an elastomer on the flexible substrate is formed by a mixed material. The two are respectively printed and formed by a binder jet printing device, and finally the formed substrate structure is magnetized in a special way. This can not only realize a more complex sensor structure and improve production efficiency, but also the magnetization process is controllable, thereby achieving the purpose of improving the sensitivity of the sensor.

[0050] To describe the flexible magnetic tactile sensor and the method for manufacturing the same in detail, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0051] Figure 1 The figure shows a schematic process of a method for preparing a flexible magnetic tactile sensor according to an embodiment of the present invention.

[0052] like Figure 1 As shown, the method for preparing a flexible magnetic tactile sensor according to an embodiment of the present invention includes:

[0053] S100: constructing a base structure of a target sensor; wherein the base structure includes a flexible substrate and an elastomer disposed on the flexible substrate.

[0054] Among them, building the base structure of the target sensor can be completed through relevant modeling software. In this process, the shape and size of the flexible substrate, the structure and size of the elastomer, and the positional relationship between the flexible substrate and the elastomer can be determined for subsequent printing operations.

[0055] S200: obtaining a flexible material and a mixed material of the flexible material and the magnetic material; wherein the flexible material is used to form a flexible substrate, and the mixed material is used to form an elastomer.

[0056] Among them, the flexible material can be selected from: at least one of TPU, TPE, SBS and SEBS; the magnetic material includes: at least one of neodymium iron boron and samarium iron nitrogen. After determining the flexible material and the magnetic material, prepare the flexible material powder and the magnetic material powder, then use a sieve to remove the agglomerated material, and mix the two powders evenly in a mixer according to a certain proportion, and finally collect the mixed moderate material for use.

[0057] S300: placing a flexible material in a binder jet printing device to print and form a flexible substrate.

[0058] S400: taking out the flexible material, and placing the mixed material in a binder jet printing device to print an elastomer on the flexible substrate to form a matrix structure.

[0059] After the above materials are prepared, the printing operation can be started. First, the flexible material is placed in a preset binder jet printing device, and the flexible substrate is printed according to printing parameters such as size and shape. After the flexible substrate is printed, the printing is paused, the flexible material powder cylinder is taken out, and the pre-prepared mixed material is loaded into the powder cylinder, and the printing of the elastomer is continued.

[0060] Specifically, the relevant parameters of the binder jet printing device are preferably a single-layer inkjet volume of 0.028 μL / mm 2 The printing layer thickness is 0.05mm, and the entire base structure is cut into 100 layers for printing, so that the number of layers at which printing stops is determined according to the thickness of the flexible substrate. The specific parameters can be set according to the size and requirements of the base structure.

[0061] S500: performing magnetization treatment on the base structure to form a three-dimensional detection layer;

[0062] S600: Encapsulating the three-dimensional detection layer and the detection chip to form a flexible magnetic tactile sensor.

[0063] Among them, after the base structure is printed, it can be taken out from the binder jet printing equipment, and then undergo special magnetization treatment to form a three-dimensional detection layer. The three-dimensional detection layer and the detection chip of the sensor are then packaged at a certain detection distance to form a flexible magnetic tactile sensor.

[0064] In addition, after forming the base structure and before magnetizing the base structure, it also includes: first, low-temperature baking the base structure and cleaning the baked base structure; then, vacuum drying the cleaned base structure; wherein the vacuum drying temperature is lower than the melting point of the flexible material.

[0065] It can be seen that the matrix structure formed by the initial printing has almost no mechanical properties. Therefore, the excess powder around the matrix structure can be removed first, and then taken out from the binder jet printing equipment, placed in a constant temperature oven at a lower temperature for a period of time, and then blown away the excess powder around with an ear bulb to complete the pre-bonding process of the matrix structure. Among them, the temperature in the pre-bonding can be set to 70-90°C, and it will not affect the material itself in the case of rapid bonding. Then, the pre-bonded and cleaned matrix structure is vacuum dried, and the vacuum oven temperature is set close to but lower than the melting point of the flexible material. The pre-bonded and powder-cleaned matrix structure is placed in the oven, baked under vacuum for a period of time, and finally taken out of the oven after cooling.

[0066] In the flexible magnetic tactile sensor of the embodiment of the present invention, the flexible substrate can be set as a circular or polygonal hollow frame structure, and the elastomer is set on the flexible substrate with a three-dimensional structure; wherein, when the flexible substrate is circular, the elastomer may include a polygonal support frame embedded in the flexible substrate, and a first inclined leg arranged on the polygonal support frame, wherein one end of different first inclined legs are respectively connected to different sides of the polygonal support frame, and the other ends of different first inclined legs intersect with a point (as shown in the attached figure) to form a force point. During the application process, external pressure acts on the force point, and a corresponding electrical signal can be generated through its deformation to complete the signal acquisition of the sensor.

[0067] Figures 2 to 4 Schematic structures of the three-dimensional detection layer according to the embodiments of the present invention are shown respectively. Figures 2 to 4 As shown together, the flexible substrate 1 is circular, and the polygonal support frame 2 adopts a square structure. At this time, four first inclined legs 3 can be provided, and one end of the four first inclined legs 3 is respectively fixed at the center position of one side of the square support frame, and the other end is inclined inward and intersects with other first inclined legs 3 to form a symmetrically distributed three-dimensional cross structure. The claw-like three-dimensional cross structure can effectively enhance the magnetic gradient effect, thereby achieving an efficient force-magnetic conversion effect.

[0068] In another specific embodiment, when the flexible substrate is polygonal, the elastomer may include a circular support frame embedded in the flexible substrate, and a second inclined leg arranged on the circular support frame; wherein one end of the different second inclined legs is connected to the circular support frame, and the other end intersects at a point.

[0069] Specifically, the deformation structure of the flexible substrate can be a square or a regular pentagon, hexagon, etc., and the support frame located therein can be set as an inscribed circle tangent to the sides of the flexible substrate polygon. At this time, three or more second inclined legs can be set, and multiple second inclined legs can be evenly distributed on the circular support frame. Through the deformation setting of the structure, that is, the multiple inclined legs, the detection range of the sensor can be improved and its scope of application can be expanded.

[0070] In addition, the flexible base and the support frame in the elastomer can also be set as a polygonal structure, and the vertices of the polygon of the support frame can be distributed at the midpoints of each side of the flexible base, while the inclined legs still use multiple claw-shaped distributions to form a three-dimensional elastic structure.

[0071] It should be noted that, in the process of magnetizing the base structure to form a three-dimensional detection layer, the base structure is extruded and limited by a preset limiting mold; wherein, the inclined legs of the extruded base structure are parallel to each other and fit together; wherein the inclined legs include a first inclined leg and a second inclined leg; then, the inclined legs in the limiting mold are magnetized in the same direction; finally, the magnetized inclined legs are taken out of the limiting mold to form a three-dimensional detection layer.

[0072] Specifically, since both the flexible substrate and the elastomer have a certain elasticity, in order to ensure the consistency of the magnetization direction and overcome the problem of low sensitivity caused by the large initial magnetic field strength of traditional sensors, during the special magnetization treatment of the substrate structure, each inclined leg is squeezed to form a structure that fits each other and has the same direction, and then magnetization is performed from the flexible substrate to the force point of the inclined leg, which can change the direction of the magnetic field at the bottom center of the substrate structure during the compression process. Subsequently, by adjusting the distance between the entire substrate structure and the detection chip, the initial magnetic field strength at a certain position is close to 0, thereby greatly reducing the value of B0 and greatly improving the sensitivity (△B / B0), where B0 represents the initial measurement value when there is no signal input, and B represents the measurement value when there is signal input.

[0073] To this end, the limiting mold of the embodiment of the present invention includes a bracket and a limiting hole arranged on the bracket, and the shape of the limiting hole is adapted to the appearance of each inclined leg after being bonded together; through deformation, the inclined legs are made parallel to each other and squeezed into the limiting hole for restraint and limiting, and then placed in a magnetizing device such as a strong magnetic coil for magnetization. After the magnetization is completed, each inclined leg is pulled out of the limiting hole to release the restraint, so as to obtain a three-dimensional detection layer with centripetal magnetization.

[0074] In other words, during the magnetization process of the three-dimensional detection layer, the strength of the initial magnetic field can be changed by adjusting the distance between the three-dimensional detection layer and the detection chip. The distance at which the initial magnetic field strength is close to 0 is determined by the detection chip, and the three-dimensional detection layer and the detection chip are packaged according to the distance to form a highly sensitive flexible magnetic tactile sensor.

[0075] Specifically, Figure 5 The schematic structure of a flexible magnetic tactile sensor according to an embodiment of the present invention is shown.

[0076] like Figure 5 As shown, the flexible magnetic tactile sensor of the embodiment of the present invention includes a base layer 4, a three-dimensional detection layer (including an elastic body 10) arranged on the base layer 4, a PCB 7 located below the base layer 4, a detection chip 6 located on the PCB 7, and a pin row 5 for easy insertion and positioning, wherein the detection chip 6 can be a Hall chip or the like. During the detection process, the three-dimensional detection layer will be deformed after being subjected to external pressure, and the distance between it and the detection chip 6 will change, thereby causing a change in the magnetic field strength, and finally the magnetic field strength is detected by the detection chip 6 to complete the signal detection.

[0077] Figure 6 The magnetic field intensity distribution of the flexible magnetic tactile sensor according to an embodiment of the present invention is shown. It can be seen that after special magnetization (centripetal magnetization), the magnetic field direction can change in the central area at the bottom of the three-dimensional detection layer, so that the initial magnetic field can be adjusted to near 0, thereby improving the sensitivity of the sensor. Figure 7 The figure shows the magnetic field distribution in which the magnetic field direction changes with the distance in the central area according to an embodiment of the present invention, wherein the distances of 0.5mm, 1.7mm and 2mm refer to the vertical distances between the center distance of the bottom of the three-dimensional detection layer and the detection chip, and the magnetic field strength can be adjusted by adjusting the packaging distance between the two. Figure 8 The stress and strain of the flexible magnetic tactile sensor during the compression process are shown, wherein the compression modulus is approximately 0.22 MPa in the strain range of 0-45%, and the compression modulus is approximately 1.25 MPa in the strain range of 45%-57%. It can be seen that the stress performance can be significantly improved after centripetal magnetization.

[0078] It should be noted that due to the limited modulus of the elastomer with a three-dimensional frame structure, the signal is easily saturated during mechanical testing. Therefore, when a larger signal test is required, the flexible substrate and the polygonal support frame can be removed and replaced with PDMS casting technology (the process of pouring polydimethylsiloxane PDMS material into a mold and curing it to form a microfluidic chip). Only the inclined legs are plastic-sealed and cured to form a microfluidic chip as shown in the attached figure. Fig. 9 The packaging structure shown can improve the measuring range of the elastomer to meet the needs of more application scenarios.

[0079] Corresponding to the above-mentioned method for preparing a flexible magnetic tactile sensor, the present invention further provides a flexible magnetic tactile sensor, including a flexible magnetic tactile sensor prepared by the above-mentioned method for preparing a flexible magnetic tactile sensor. It should be noted that the embodiments of the above-mentioned flexible magnetic tactile sensor can refer to the description in the embodiment of the method for preparing a flexible magnetic tactile sensor, and will not be repeated here one by one.

[0080] According to the flexible magnetic tactile sensor and preparation method thereof of the present invention, the binder jet printing technology is used to realize the design of more complex structures and the production of larger areas and higher efficiency. At the same time, through the combination of the elastomer design of the inclined leg structure and the special magnetization method, the direction of the magnetic field at the bottom center of the three-dimensional detection layer can be changed during the compression process. Then, by adjusting the distance between the three-dimensional detection layer and the detection chip, the initial magnetic field strength at a certain position is close to 0, and then packaging is performed, thereby greatly reducing the value of B0 and improving the detection sensitivity.

[0081] As described above, the flexible magnetic tactile sensor and the method for preparing the same according to the present invention are described by way of example with reference to the accompanying drawings. However, those skilled in the art should understand that various improvements can be made to the flexible magnetic tactile sensor and the method for preparing the same according to the present invention without departing from the content of the present invention. Therefore, the protection scope of the present invention should be determined by the content of the attached claims.

Claims

1. A method for preparing a flexible magnetic tactile sensor, characterized in that: include: Constructing a base structure of a target sensor; wherein the base structure includes a flexible substrate and an elastic body arranged on the flexible substrate; and at the same time, Obtain a flexible material and a mixed material of the flexible material and a magnetic material; wherein the flexible material is used to form the flexible substrate, and the mixed material is used to form the elastomer; Placing the flexible material in a binder jet printing device to print and form the flexible substrate; Taking out the flexible material, and placing the mixed material in the binder jet printing device, printing the elastomer on the flexible substrate to form the matrix structure; Performing magnetization treatment on the base structure to form a three-dimensional detection layer; The three-dimensional detection layer and the detection chip are packaged to form a flexible magnetic tactile sensor.

2. The method for preparing a flexible magnetic tactile sensor according to claim 1, characterized in that: The flexible substrate is a circular or polygonal hollow frame structure.

3. The method for preparing a flexible magnetic tactile sensor according to claim 2, characterized in that: When the flexible base is circular, the elastic body includes a polygonal support frame embedded in the flexible base, and a first inclined leg arranged on the polygonal support frame; Among them, one end of different first inclined legs is respectively connected to different sides of the polygonal support frame, and the other ends of different first inclined legs intersect at one point.

4. The method for preparing a flexible magnetic tactile sensor according to claim 3, characterized in that: When the flexible base is polygonal, the elastic body includes a circular support frame embedded in the flexible base, and a second inclined leg arranged on the circular support frame; One end of each second inclined support leg is connected to the circular support frame, and the other end intersects at one point.

5. The method for preparing a flexible magnetic tactile sensor according to claim 4, characterized in that: The ends of the different second inclined legs connected to the circular support frame are evenly spaced and distributed on the circular support frame.

6. The method for preparing a flexible magnetic tactile sensor according to claim 4, characterized in that: The base structure is magnetized to form a three-dimensional detection layer, including: The base structure is extruded and limited by a preset limiting mold; wherein the inclined legs of the extruded base structure are parallel to each other and fit together; wherein the inclined legs include the first inclined legs and the second inclined legs; Magnetizing the inclined legs in the limiting mold in the same direction; The magnetized inclined legs are taken out from the limiting mold to form the three-dimensional detection layer.

7. The method for preparing a flexible magnetic tactile sensor according to claim 6, characterized in that: The limiting mold includes a bracket and a limiting hole arranged on the bracket, and the shape of the limiting hole is adapted to the shape of the inclined legs that are fitted together; The inclined supporting leg is inserted into the limiting hole for limiting.

8. The method for preparing a flexible magnetic tactile sensor according to claim 1, characterized in that: After forming the base structure and before magnetizing the base structure, the method further comprises: Low-temperature baking is performed on the base structure, and the baked base structure is cleaned; The cleaned substrate structure is vacuum dried; wherein, The temperature of the vacuum drying is lower than the melting point of the flexible material.

9. The method for preparing a flexible magnetic tactile sensor according to claim 1, characterized in that: The flexible material comprises: at least one of TPU, TPE, SBS and SEBS; The magnetic material includes at least one of neodymium iron boron and samarium iron nitrogen.

10. A flexible magnetic tactile sensor, characterized in that: The flexible magnetic tactile sensor is prepared by the method for preparing the flexible magnetic tactile sensor as described in any one of claims 1 to 9.

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