SENSOR AND SENSOR MANUFACTURING METHOD

A sensor includes: a sensor section including a conductive structure made up of a three-dimensionally continuous unit lattices, each including a plurality of columnar beams; and output connectors that output a resistance value of the sensor section, the resistance value changing at least when the conductive structure is compressed by an external force. A method for manufacturing a sensor includes forming the sensor section by stacking using a 3D printer. The sensor and method for manufacturing the sensor enable the adjustment of the repulsive force against compression to an input member and thus appropriately setting the change in resistance value against external force according to the device, in which the sensor is to be incorporated and the mode of use.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-74664, filed on Apr. 28, 2022, the entire contents of which are hereby incorporated by reference.

BACKGROUND

Field

The present invention relates to a sensor and a method for manufacturing a sensor.

Description of Related Art

Sensors using a material that is deformed by an external force are being developed to detect the external force and magnitude of the external force from the deformation. These sensors are used for many input devices, and have a high affinity with devices that a user pushes or grips, for example. Patent Document 1 discloses one of these sensors. The sensor measures a resistance value of a porous structure, which is deformable by external force and impregnated with conductive ink to have conductivity, so that the resistance value changes with the deformation of the porous structure. The sensor detects the motion of a user based on the measurement.

SUMMARY

There are high expectations for the application of these sensors that are deformable by compression because once the sensor is assembled well in a device, it detects various motions of the user. The materials that can be used, however, are limited, so that the sensors fail to have expected functions. For instance, when using commercially available foamed materials or porous materials, it is difficult to adjust the amount of deformation caused by external forces. This results in difficulty to correctly set a change in resistance value relative to the external force according to the device in which a sensor is incorporated and the mode of use.

To solve these problems, the present invention provides a sensor enabling the adjustment of a repulsive force against compression of the sensor as an input member and thus appropriately setting the change in resistance value against external force according to the device, in which the sensor is to be incorporated, and the mode of use.

A sensor according to the first aspect of the present invention includes: a sensor section including a conductive structure made up of a three-dimensionally continuous unit lattices, each including a plurality of columnar beams; and output connectors that output a resistance value of the sensor section, the resistance value changing at least when the conductive structure is compressed by an external force.

A method for manufacturing a sensor according to the second aspect of the present invention includes forming the sensor section by stacking using a 3D printer.

The present invention provides a sensor enabling the adjustment of the repulsive force against compression of the sensor as an input member and thus appropriately setting the change in resistance value against external force according to the device, in which the sensor is to be incorporated, and the mode of use.

DETAILED DESCRIPTION

[0010] The following describes some embodiments of the present invention, with reference to the attached drawings. In the attached drawings, like numbers indicate like components. When a drawing illustrates a plurality of structures with the same or similar configuration, a reference numeral may be given to some of the structures and may not be given to the other structures, in order to avoid the complexity. Not all of the elements described in the embodiments are indispensable as means for solving the problems.

FIG.1is a perspective view showing the overall configuration of a sensor100according to the present embodiment. The sensor100, also known as a soft sensor, includes a soft material as the sensing member. This embodiment describes an example of a cubic sensor with a side of about 30 mm when not subjected to external force.

The sensor100mainly includes a sensor section110and two output connectors120. The sensor section110, which will be described in details later, is a structure made up of three-dimensionally continuous unit lattices111, each including a plurality of columnar beams. The sensor section110deforms in accordance with the magnitude of an external force applied, and has elasticity to return to its original shape as soon as the external force is removed. The output connectors120are for outputting a detection signal indicating the resistance value of the sensor section110to a detection circuit, and are press-fitted into gaps of the unit lattices111to be fixed to the sensor section110.

Cables200transmit a detection signal output from the output connectors120to the detection circuit, and each have a connector pin210at the end. The connector pin210is inserted into and removed from the output connector120.

As shown in the drawings, x-, y-, and z-axes are defined. That is, the direction in which the output connectors120receive their connector pins210is x-axis direction, and the direction in which the two output connectors120are placed side by side is y-axis direction. The direction orthogonal to x-axis and y-axis is z-axis direction. Some of the following drawings show the same coordinate axes as in the state inFIG.1, thus indicating the orientation of the structure shown in each drawing.

FIG.2shows the sensor100during external force detection. This embodiment assumes a usage mode in which the user presses the sensor100with fingertips.

When the user pressurizes the upper surface (xy plane on the positive side on z-axis) of the sensor100downward (in the negative direction on z-axis) as indicated by the white arrow, the mutually connected unit lattices111are pressed in z-axis direction, so that the sensor section110as a whole is also pressed and compressed in z-axis direction. When the individual unit lattices111are pressed in z-axis direction, the contact area between the columnar beams making up the unit lattices111increases, so that the resistance value between the two output connectors120decreases. The resistance value between the two output connectors120is detected by transmitting a detection signal to the detection circuit described below via the cables200connected to the output connectors120.

As the amount of compression of the sensor section110by the user’s fingertips increases, the contact area between the columnar beams that make up the unit lattices111increases, so that the resistance value output from the output connectors120decreases. In other words, the sensor section100can output different resistance values in response to changes in the state of contact between the columnar beams making up the unit lattices111in accordance with the compression by the external force.FIG.2shows an example in which the upper surface (the surface on the positive side of z-axis) of the sensor section100in z-axis direction is uniformly compressed by fingertips. The upper surface may not be uniformly compressed, and at least the contact portion with fingertips may be shrunk and compressed in z-axis direction. That is, the portion of the upper surface of the sensor100in contact with the fingertips may be compressed more downward in z-axis direction (in the z-axis negative direction) than other portions of the upper surface.

FIG.3shows an example of the configuration of a sensor system that uses a detection signal from the sensor100. The cables200each having one end connected to the sensor100are connected to a detection circuit220at the other ends. The detection circuit220includes a resistance-value detection circuit and detects the resistance value of the sensor100from the detection signal received via the cables200.

The detected resistance value is A/D converted and passed to a controller230in the form of a digital signal. For instance, the controller230is a personal computer (PC), which can control software or other devices according to the detected resistance value. The sensor100can also be used as an ON/OFF switch by programming so as to turn OFF when the detected resistance value is greater than or equal to a preset threshold value, and to turn ON when the detected resistance value is less than the preset threshold value.

The controller230is not limited to a PC, which may be a portable terminal such as a smartphone or gaming device, an electrical appliance such as a vacuum cleaner, a robot, or a mobile body such as a car. In other words, the controller230may be any device that acquires a digital signal of a resistance value and controls operations, actions, etc. according to this digital signal. The detection circuit220may be included in the controller230or in the sensor100. The sensor100and detection circuit220may be incorporated into the controller230.

FIG.4is a conceptual diagram illustrating the conductive path of the sensor section110. In the example shown inFIGS.1and2, the sensor100according to this embodiment has two output connectors120placed side by side on one side face. If the entire sensor section110is a conductive structure, the straight line connecting the two output connectors120will be the shortest conductive path. In this case, the amount of change in resistance value is very small when the sensor section110is compressed in z-axis direction. Preferable sensors have a larger amount of change in output relative to a change in input because it facilitates signal processing. It is therefore preferable to place one output connector120and the other output connector120near the vertexes that are diagonal to each other, for example, in a cubic shape. The output connectors120placed in such a way, however, result in the cables200connected to them that are pulled out in radial directions that are opposite to each other with respect to the sensor section110. This not only impairs the user’s operability but also makes the routing of the cables200complicated. Therefore, it is desirable that the two output connectors120are placed on a same side face to be close to each other.

Thus, in the sensor100of the present embodiment, the sensor section110includes a conductive structure112and a non-conductive structure113to keep a conductive path of some length and to place the two output connectors120to be close to each other. The conductive structure112includes the unit lattices111that are three-dimensionally continuous, and has conductivity. The unit lattices111of the conductive structure112are formed using flexible filament made of, for example, thermoplastic polyurethane (TPU) mixed with conductive filler.

The non-conductive structure113also includes the unit lattices111that are three-dimensionally continuous, but has electrical insulating property. The unit lattices111of the non-conductive structure113are formed using flexible filament made of, for example, TPU not mixed with conductive filler. The sensor section110is formed by integrating the conductive structure112and the non-conductive structure113adjacent to each other, and TPU, which has excellent elasticity and toughness, is preferable as a material of the sensor section110which is repeatedly compressed.

More specifically, as shown inFIG.4, the sensor section110has a slit-like space extending from the lower end surface (the xy plane on the negative side of z-axis) between the two output connectors120of the conductive structure112, and the non-conductive structure113is inserted into the space.FIG.4shows the overall shapes of the conductive structure112and the non-conductive structure113by straight lines, and omits the unit lattices111.

The non-conductive structure113inserted in this way does not make the straight line connecting the two output connectors120a conductive path, and the path bypassing the non-conductive structure113serves a conductive path as indicated by the bold line. Such a conductive path passes through more unit lattices111, which increases the difference in resistance value between when the sensor section110is compressed and when it is not compressed, and thus makes it easier to detect the amount of change in resistance value relative to the amount of compression. Thus, even in the case of a slight compression, the sensor detects the pressure more precisely. In particular, the conductive path inFIG.4is preferred for the usage mode of user’s compression of the sensor section110in z-axis direction as shown inFIG.2because of its long distance in z-axis direction.

While the sensor section110may be made by separately forming the conductive structure112and the non-conductive structure113, and then inserting the non-conductive structure113into the slit of the conductive structure112for fixing as shown inFIG.4, the present embodiment integrally forms the sensor section110using a 3D printer.FIG.5shows how a 3D printer400is used to manufacture the sensor100. Specifically, the drawing shows a process of stacking to form the sensor section110by the 3D printer400. The method of manufacturing the sensor100with the 3D printer300is not limited to the stacking, and any method such as stereolithography may be used.

The 3D printer400includes a stage410and a head420as shown, and controls the head420by a controller (not shown) to make the sensor section110on the stage410. As indicated by the white arrows, the head420is movable relative to the stage410in xy direction (planar direction) and z-axis direction (height direction).

The head420includes a conductive material nozzle421and a non-conductive material nozzle422directed toward the stage410. The conductive material nozzle421heats and melts the conductive flexible filament423by the head420supplied to the head420for discharging. The non-conductive material nozzle422heats and melts the non-conductive flexible filament424by the head420supplied to the head420for discharging. The discharge positions and amounts of the conductive material ejected from the conductive material nozzle421and the non-conductive material ejected from the non-conductive material nozzle422are controlled by the controller.

The 3D printer400discharges the conductive material and the non-conductive material by a predetermined height from the surface of the stage410upward (z-axis positive direction) for solidification. The 3D printer400repeats this for stacking to form the sensor section110. More specifically, according to the CAD data, the conductive material nozzle421discharges the conductive material at the position where the unit lattices111making up the conductive structure112are to be formed, and the non-conductive material nozzle422discharges the non-conductive material at the position where the unit lattices111making up the non-conductive structure113are to be formed.

In this embodiment, the conductive flexible filament423is made of TPU mixed with conductive filler, and the non-conductive flexible filament424is made of TPU not mixed with conductive filler, as described above. Materials are not limited to these. Any material that is resilient and tough and forms the unit lattices111can be used. For instance, one of the conductive structure112and the non-conductive structure113may be made of a polyurethane-based material, and the other may be made of a polyester-based material.

Next, the following describes a method of setting the conductive path.FIG.6shows a sensor100′ that differs from the sensor100described above and shows a method of setting to extend the conductive path. In this drawing, the portion of the cube indicated with solid lines is a conductive structure112′ and the remaining portion is a non-conductive structure113′. The conductive structure112′ has a three-dimensional shape that traces the cube along a ridge line from one end, where one output connector120is placed, to the other end, where the other output connector120is placed, while extending in z-axis positive direction, x-axis negative direction, y-axis positive direction, z-axis negative direction, x-axis positive direction, and y-axis negative direction.

The conductive structure112′ having such a three-dimensional shape allows setting of a conductive path extending in three axial directions as indicated by the thick line. Such a conductive path enables a relatively long conductive path in x-axis direction, y-axis direction, and z-axis direction. The sensor therefore detects compression both in x-axis direction and in y-axis direction with high accuracy as well as in z-axis direction as shown inFIG.2. That is, the sensor100′ detects the user’s motion regardless of where the sensor100′ is deformed. Thus, it is preferable to set such a conductive path when manufacturing sensors that are expected to be compressed in the three axial directions.

The structure of the sensor section to set a longer conductive path is not limited to this. The sensor section may be configured so that a non-conductive structure intervenes inward from the end of the conductive structure to make the distance of the conductive path between the output connectors120longer than the configuration without a non-conductive structure interposed. The conductive structure and the non-conductive structure may have complicated shapes. A method of integrally stacking the sensor section using a 3D printer allows such a sensor to be manufactured relatively easily. For instance, a sensor section having a spiral-shaped conductive structure can be manufactured with a 3D printer.

The sensor100and sensor100′ are configured to have the non-conductive structure113interposed between the conductive structure112to extend the conductive path. The non-conductive structure can be used for other purposes, not just for extending a conductive path. For instance, some sensors require the conductive structure not to be exposed to the environment. In this case, the entire perimeter of the conductive structure may be covered with a non-conductive structure.

Next, the following describes a unit lattice.FIG.7explains a unit lattice. Specifically,FIG.7(a)is a perspective view of a unit lattice111of the sensor section110, andFIG.7(b)is a perspective view of a unit lattice111′ in another example.

The unit lattice111is configured so that skeletal columnar beams111aextends radially from the center of a cube with one side of 5 mm to the vertexes, which are lattice points, and the columnar beams111aare inscribed in the cube. The unit lattice111′ is configured to include, in addition to the skeletal columnar beams111ain the cube with one side of 5 mm, a frame columnar beam111bserving as a frame connecting the vertexes of the upper surface (xy plane on the z-axis positive side) and a frame columnar beam111balso serving as a frame connecting the vertexes of the lower surface (xy plane on the z-axis negative side).

A unit lattice, also called a lattice, has multiple columnar beams extending three dimensionally within a lattice space (e.g., a cube) that serves as a repeating unit. When being continuous three dimensionally, at least a part of the columnar beams abutting at their boundary is connected. The columnar beams may extend obliquely relative to the unit lattice as shown in the skeleton columnar beams111a, and may extend in a curved shape instead of in a straight line. They may have a cross-sectional shape that changes along the extending direction.

The size of the lattice space, the pattern of columnar beams, and the thickness of columnar beams may be changed, whereby physical properties, including the elasticity of the sensor section and the amount of change in resistance value during compression, can be adjusted. For instance, the columnar beams may be thicker or placed in large numbers. This makes the amount of compression smaller with a larger pressing force, so that the sensor section will provide an overall harder feel. The pattern of the columnar beams may be designed so that the adjacent columnar beams come in close contact with a slight deformation. This enhances the contact sensitivity of the sensor section.

FIG.8shows the physical properties of different unit lattices. Specifically,FIG.8(a)shows the change in load (N) versus the amount of compression (mm), andFIG.8(b)shows the change in resistance value (kΩ) versus the amount of compression. The solid line indicates the change of the sensor section A made up of the unit lattices111shown inFIG.7(a), the dotted line indicates the change of the sensor section B made up of the unit lattices111′ shown inFIG.7(b), and the dotted chain line indicates the change of the sensor section C made up of the unit lattices111′ shown inFIG.7(b)with one side changed to 6 mm in size. All of them are based on the actual measurements. All of the sensor sections have a cubic shape with one side of 30 mm in size, and has a non-conductive structure as shown inFIG.4. As shown inFIG.2, they are compressed downward (z-axis negative direction).

According toFIG.8(a), the sensor section A made up of the unit lattices having skeletal columnar beams only shows a linear change in load with respect to the amount of compression. The sensor sections B and C made up of the skeletal columnar beams and the frame columnar beams show a wave-like change. Meanwhile, according toFIG.8(b), the resistance value of each sensor section gradually decreases as the amount of compression increases. Note that the sensor sections B and C, having a high degree of occupation by the columnar beams in the lattice space, have smaller resistance values with respect to the same amount of compression than the sensor section A.

When the sensor section is formed using a 3D printer as in the present embodiment, it is easy to adjust the physical properties to meet user’s demands, for example. For instance, users’ preferences regarding elasticity may be collected via the internet in the form of a questionnaire, and the 3D printer may automatically select a unit lattice having elasticity corresponding to the collected results to form the sensor section. The 3D printer may accept data specified by the manufacturer, such as on the elasticity or the amount of change in resistance value, and automatically select a unit lattice suitable for that specification to form the sensor section. In this case, the 3D printer may store information on different unit lattices each in association with the elasticity or the amount of change in resistance value, and select a unit lattice corresponding to the acquired data, such as on the elasticity or the amount of change in resistance value, to form the sensor section.

In the sensor100described above, the sensor section110is cubic in shape. The shape of the sensor section can be changed in various ways depending on the intended use of the sensor, as long as the unit lattices are configured three-dimensional continuously. In particular, the surface of the sensor section need not be the boundary of the unit lattices, and the unit lattices may be divided on the surface. This means that a part of the sensor section may be curved or the sensor section as a whole may be spherical.

Then, the following describes some application examples of the sensor100in the present embodiment. The drawings for the following application examples illustrate the overall shape while omitting their unit lattices.FIG.9is an overall view of the sensor500according to a first application example. The sensor500has a duck-like outer shape as a whole and is small enough to fit in both palms of an adult. The sensor500is served as a child’s toy, for example.

The sensor500is almost entirely formed of a conductive structure512, and a non-conductive structure513intervenes at a position corresponding to the abdomen of the duck so as to be inserted from below. The two output connectors120are placed adjacent to each other on a side face of the abdomen with the non-conductive structure513interposed therebetween. The sensor500is connected to a detection circuit and a controller via cables (not shown) connected to the output connectors120. For example, when the sensor500is compressed in the direction indicated by the white arrows, the controller detects the change in the resistance value to emit a sound that imitates the quacking of a duck. The loudness of the duck’s quack can be changed according to the extent to which the sensor500, having the shape of a duck, is compressed.

FIG.10is an overall view of a stylus pen690with a sensor600incorporated, according to a second application example. For instance, the stylus pen690is a device that is wirelessly connected to a tablet terminal and that transmits movement of the pen tip in accordance with user’s operation to the tablet terminal.

The sensor600has an overall cylindrical shape and is attached to a grip of the stylus pen690. The sensor600is almost entirely formed of a conductive structure612, and a non-conductive structure613intervenes to be inserted at a part of the cylindrical shape corresponding to a certain central angle. The two output connectors120are placed adjacent to each other close to the central axis of the stylus pen690with the non-conductive structure613interposed therebetween.

The stylus pen690has an internal detection circuit, and the output connectors120are connected to a connection terminal at the detection circuit. The stylus pen690also functions as a controller, and determines the presence or not of a set input according to the change in resistance value detected by the detection circuit. For instance, when the user presses the sensor section in the direction indicated by the white arrows, the stylus pen690determines that a click operation has been performed.

FIG.11is an overall view of a sensor700according to a third application example. Specifically,FIG.7(a)is an overall perspective view looking down on the upper surface, andFIG.7(b)is an overall perspective view looking down on the lower surface. The sensor700has a crisscross shape as a whole and functions as a cross button with protruding portions in the four directions, each serving as an independent pressed portion.

In the sensor700, the protruding portions in the four directions are mainly formed with conductive structures712, and they are divided into a first conductive part715, a second conductive part716, a third conductive part717, and a fourth conductive part718, each of which is subject to compression. A non-conductive structure713is placed in the center of the cross so as to partition these conductive parts. In each conductive part, a non-conductive structure713is placed from the lower surface toward the upper surface so as to divide the conductive part in two in the protruding direction. On the lower surface of each conductive part, two output connectors120are placed adjacent to each other with the non-conductive structure713, extending in the protruding direction, interposed therebetween. That is, the sensor700is connected to eight cables. The sensor700is connected to a detection circuit and a controller via cables (not shown) connected to the output connectors120, and when each of the conductive parts is compressed in the direction indicated by the white arrows, the controller detects the change in the resistance value to determine which conductive part is pressed.

In addition to the application examples described above, the sensor according to the present embodiment is applicable in various ways. The sensor may be incorporated as at least part of the insole or sole of a shoe so that the sensor can detect weight shift (change in weighting) during walking. The sensor may be incorporated into a grip of a motorcycle, for example, so that the sensor detects the direction and amount of twisting of the grip by the driver to adjust the accelerator.

That is descriptions of some sensors according to the present embodiment, which can be modified in various ways as long as the sensor includes: a sensor section having a conductive structure with a three-dimensionally continuous unit lattices; and an output connector that outputs a resistance value that changes with compression of the sensor section. For instance, the unit lattices making up the conductive structure and the non-conductive structure may have different sizes and shapes. Each of the conductive and non-conductive structures may include a plurality of types of unit lattices combined, instead of single continuous unit lattices. For example, they may include unit lattices of the same shape but different sizes from each other.

The conductive and non-conductive structures may be colored differently from each other. For instance, the sensor section may have a hard material serving as a base that is embedded in the central portion. The output connector is not limited to a type that receives a connector pin, and may have a structure in which a lead wire is simply pulled out as long as it can output a resistance value to the detection circuit.