NL2015995B1 - Fabric touch and force sensor. - Google Patents
Fabric touch and force sensor. Download PDFInfo
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- NL2015995B1 NL2015995B1 NL2015995A NL2015995A NL2015995B1 NL 2015995 B1 NL2015995 B1 NL 2015995B1 NL 2015995 A NL2015995 A NL 2015995A NL 2015995 A NL2015995 A NL 2015995A NL 2015995 B1 NL2015995 B1 NL 2015995B1
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Abstract
The disclosure relates to a sensor comprising a stacked layer structure. The stacked layer structure comprises an outer nonconductive layer, a first conductive layer and a second conductive layer, and a deformable layer arranged between the first and second conductive layer. The sensor comprises a measurement device connected to the first conductive layer and the second conductive layer. The measurement device is configured to measure a characteristic time associated with an electrical circuit comprising the stacked layer structure. Furthermore, the measurement device is configured to sense a touch on the sensor from a first change of the characteristic time when the deformable layer is substantially undeformed by the touch. The measurement device is also configured to sense a force from a second change of the characteristic time wherein the force causes a substantial deformation of the deformable layer. The disclosure further relates to a stacked layer structure, and a measurement device to be used in the sensor and a product comprising the sensor.
Description
Fabric touch and force sensor
FIELD OF THE INVENTION
The invention relates to a touch and force sensor, to a stacked layer structure, to a measurement device of the sensor and to a product comprising such a sensor. More particularly, the invention relates to a combined touch and force sensor comprising a layer structure having a deformable layer. More particularly, the sensor is a fabric touch and force sensor.
BACKGROUND
The interest for flexible electronics has grown rapidly over the past years. Researchers are continuously searching for new ways to integrate flexible electronics in everyday products that are soft and/or flexible, such as clothing. An important development in this field is the emergence of flexible conductive fibers that can be woven into textile sheets. Examples are known of devices for measuring the pressure exerted at different points of a flexible, pliable and/or extensible fabric capable of being worn as a garment, lapel, or the like. US 2014/0150573 discloses such a device that is provided with three stacked layers including a first insulating layer comprising an arrangement of insulating fibers and rows of conductive yarns in contact with a first surface of a piezo-resistive layer of fibers of a piezo-resistive material, and a second insulating layer comprising an arrangement of insulating fibers, including rows of conductive yarns, in contact with a second surface of the piezo-resistive layer, and an electronic circuit capable of measuring the electric resistance variation when a pressure is exerted on the fabric, the pressure being a function of the resistance variation.
While this type of device is able to measure the pressure exerted on the fabric, it cannot sense a sole touch, wherein no significant pressure is exerted on the device.
SUMMARY
It is an object of the present invention to provide an improved sensor that is configured to combine touch and force sensing.
To that end, on aspect of the disclosure pertains to a sensor comprising a stacked layer structure. The stacked layer structure comprises an outer nonconductive layer, a first conductive layer and a second conductive layer, and a deformable layer arranged between the first and second conductive layer. The sensor comprises a measurement device connected to the first conductive layer and the second conductive layer. The measurement device is configured to measure a characteristic time associated with an electrical circuit comprising the stacked layer structure. Furthermore, the measurement device is configured to sense a touch on the sensor from a first change of the characteristic time when the deformable layer is substantially undeformed by the touch. The measurement device is also configured to sense a force from a second change of the characteristic time wherein the force causes a substantial deformation of the deformable layer.
Applicant has realized that the sensor may be comprised in an electrical circuit and that this electrical circuit is associated with a characteristic time. Applicant has further realized that this characteristic time changes when the sensor is touched without deformation of the deformable layer and that the characteristic time may further change when this deformable layer in the stacked layer structure is deformed by a force acting on the sensor. By configuring a measurement device to measure the characteristic time of the electrical circuit comprising the stacked layer structure, the measurement device can sense a touch and sense a force based on changes in the characteristic time.
It should be appreciated that the sensor may be a flexible sensor, wherein each of the layers of the layer structure is a flexible layer.
The first change of the characteristic time may be caused by a touch. It should be appreciated that "first change" and "second change" do not indicate a sequentiality of the changes.
It should be noted that the second change of the characteristic time may depend on the deformation of the deformable layer and, hence, a measurement of the amount of force exerted on the sensor can be derived. As an example, it may be that the change of the characteristic time depends on the degree of deformation of the deformable layer (e.g. the larger the deformation, the higher the second change of the characteristic time compared to the case wherein no force is exerted on the sensor). It should be appreciated that the deformation of the deformable layer may depend on the force. As an example, it may be that a higher force causes a larger deformation .
It should be appreciated that the force may be a pressing force applied to the sensor that may compress the deformable layer. The force may also be a pulling force applied to the sensor that may elongate the deformable layer. The force may also be a shear force with a force component affecting the deformable layer.
The outer nonconductive layer may be useful in sensing the touch as will be explained below.
The conductive layers may comprise a sheet resistance of less than 1 Ohm/cm2.
The stacked layer structure may be applied to a non-conductive substrate.
The charging and discharging of one or more capacitors in an electrical circuit is associated with a changing potential (increasing respectively decreasing) at some point in the circuit, wherein the changing potential may be relative to a ground potential of the circuit. A characteristic time associated with this changing potential may be the RC time of the circuit.
It should be appreciated that the characteristic time may comprise an RC time of the electrical circuit comprising the stacked layer structure. The characteristic time may also comprise an indication of such an RC time, for example a percentage of an RC time or another derivative of such a characteristic time. An indication of an RC time may also comprise a phase difference, for example between a periodic voltage applied to the circuit, such as a voltage sine wave, and another periodic voltage measured in the electrical circuit comprising the sensor, such as a periodic voltage across a capacitor. The characteristic time may also comprise the difference in time wherein a point in the circuit has a first potential and wherein the point has a second potential, both potentials being measured with respect to a reference potential .
It should be noted that the measurement device may be configured to measure the characteristic time of the sensor periodically, for example multiple times per second so that a change in the characteristic time may be measured rapidly.
The measurement device may be configured to measure the characteristic time by applying a voltage to an electrical circuit comprising the stacked layer structure during a time period and measuring the potential at a certain point in the electrical circuit during that time period. In an embodiment, the measurement device is configured to apply a voltage block pulse. The measurement device may also be configured to measure the characteristic time by applying a voltage sine wave. Many devices are known in the art that are configured to measure the RC time of an electrical circuit. It should be appreciated that such devices may be comprised in the measurement device.
In one embodiment the electrical circuit comprising the stacked layer structure comprises a resistance and a capacitance. The first change of the characteristic time is caused by at least one of a first change in the resistance and a first change in the capacitance. Furthermore, the second change of the characteristic time is caused by at least one of a second change in the resistance and a second change in the capacitance. The first change is different from the second change .
As mentioned above, the characteristic time may comprise an RC time of the electrical circuit comprising the stacked layer structure. Hence, any change in either the resistance or the capacitance associated with the electrical circuit may cause a change in the characteristic time. As an illustration, an RC time of an electrical circuit may change when the resistance of a resistor in that circuit is changed. Another example would be one wherein the capacitance of a capacitor is changed, resulting in a change of the RC time. A third example would be that an RC loop is added to an electrical circuit, which influences the resistance and capacitance of the electrical circuit, and which results in a changed RC time .
It should be appreciated that the touch may cause a change of the electrical circuit comprising the stacked layer structure. A finger may touch an outer nonconductive layer that may be comprised in the stacked layer structure. The finger touching the sensor may form a first plate of a capacitor, while the first or second conductive layer may form the second plate of the capacitor. Note that the plates of this capacitor may be separated by the outer nonconductive layer of the stacked layer structure. Also note that the outer nonconductive layer is useful, because without it no capacitor would be formed when a finger touches the sensor. With the touch a capacitor may be introduced in the electrical circuit comprising the stacked layer structure, or an additional RC loop may be introduced in the electrical circuit, which may cause the first change in the capacitance and resistance associated with the electrical circuit. It may be that a touch causes an increase of the capacitance of the electrical circuit and, hence, an increase of the characteristic time.
It should be appreciated that the second change of the characteristic time may depend on at least one of the second change in the resistance and the second change in the capacitance. For example, a higher second change of the resistance causes a higher second change in the characteristic time. It may be that the second change in the resistance is dependent on the deformation of the deformable layer, for example such that a larger deformation causes a higher second change in the resistance. It may be that the second change in the capacitance is dependent on the deformation, for example such that a larger deformation causes a higher second change in the capacitance.
In one embodiment the deformable layer is nonconduc- tive .
It should be appreciated that the two conductive layers may form two plates of an internal capacitor of the stacked layer structure and that the deformable layer may function as an isolating layer separating the two plates.
The substantial deformation of the deformable layer may cause the second change in the capacitance of the electrical circuit. The substantial deformation may cause a change in the distance between the first conductive layer and the second conductive layer. The change in distance may change the capacitance of the capacitor formed by the first and second conductive layers. As an example, the deformable layer is compressed by a force acting on the sensor, bringing the two conductive layers closer together, which thus increases the capacity of the capacitor formed by the two conductive layers. Hence the capacitance associated with the electrical circuit comprising the stacked layer structure is increased.
It should be appreciated that a larger deformation may cause a higher second change in the capacitance of the electrical circuit, and hence a higher second change in the characteristic time.
This embodiment enables the use of cheap materials for the deformable layer. The only prerequisite in this embodiment is that the material is nonconductive and deformable.
The embodiment also allows the use of a minimal number of layers in the stacked layer structure.
In one embodiment, the deformable layer has a conductivity that is dependent on a magnitude of the deformation of the deformable layer (i.e. has a force-dependent resistivity or conductivity), and the stacked layer structure comprises a nonconductive layer arranged between the first and second conductive layer.
The deformable layer and one of the first and second conductive layers may form the two plates of a capacitor in the internal of the stacked layer structure.
It should be appreciated that the deformable layer may be a piezo-resistive layer. The deformable layer may comprise at least one of a combination of epoxy impregnated with activated carbon, textile weave impregnated with activated carbon, textile weave mixed with conductive fibers and stainless steel fibers.
It may be that a larger deformation (i.e. a larger compression) of the deformable layer causes the deformable layer to have a higher conductivity.
It should be appreciated that the deformable layer may form a variable resistor in the electrical circuit comprising the stacked layer structure. Hence the resistance associated with the electrical circuit may change depending on the deformation. Compression of the layer may increase the conductivity of the deformable layer while elongation of the layers decreases the conductivity.
This embodiment enables the sensor to be associated with a long characteristic time, e.g. a long RC time, even when no substantial deformation of the deformable layer occurs. A long characteristic time may be beneficial because it may ease the measurement. The long characteristic time is achieved by making the deformable layer (variably) conductive, so that it can form a first plate of a capacitor (possibly in conjunction with one of the first or second conductive layer). The second plate of the capacitor may then be formed by (the other) one of the first and second conductive layers. The non-conductive layer separates the two abovementioned plates of the capacitor and may be thin, so that the two plates are positioned close to each other, yielding a high capacitance of the capacitor. A high capacitance may be associated with a long characteristic time.
In one embodiment the deformable layer comprises piezo-resistive foam with a resistance between 50 Ohm and 500kOhm depending on the degree of deformation of the deformable layer by a force acting on the sensor. This embodiment enables an accurate measurement of the force with a relatively thin deformable layer.
In one embodiment at least one of the layers comprises flexible fibers. It should be noted that any number of layers in the stacked layer structure may comprise flexible fibers. It may be that all layers comprise flexible fibers. It should be appreciated that the fibers may comprise natural fibers, or synthetic fibers. The flexible fibers may also comprise textile fibers, such as cotton fibers, or polymer fibers, or any other type of flexible fibers.
The occurrence of flexible fibers in the sensor is beneficial because it allows the stacked layer structure to be flexible. An advantage of a flexible sensor is that it can be easily integrated in soft or flexible products, such as clothing or other textile products.
In one embodiment the deformable layer comprises flexible fibers that are coated with a piezo-resistive material. It should be appreciated that as a result the deformable layer may have a conductivity that is dependent on the deformation. The embodiment enables the use of fibers in the deformable layer, wherein the deformable layer has a conductivity that is dependent of the degree of deformation.
In one embodiment at least one of the nonconductive layers comprises a dense weave of fibers. It should be appreciated that any number of the nonconductive layers may comprise a dense weave of fabric. It may for example be that all nonconductive layers comprise a dense weave of fabric. A nonconductive layer with a dense weave of fibers is beneficial because it allows for positioning the nonconductive layer between two conductive materials and hereby preventing that the two conductive materials may contact each other causing a short circuit during compression, while the dense weave of fibers enable a flexible stacked layer structure.
In one embodiment at least one of the conductive layers comprises flexible fibers that are coated with a conductive material. It should be appreciated that any number of conductive layers may comprise flexible fibers that are coated with a conductive material. It may for example be that all conductive layers comprise flexible fibers that are coated with a conductive material. The embodiment enables the conductive layers to be flexible.
In one embodiment the sensor further comprises a vibrational motor that is configured to vibrate in response to at least one of sensing the touch and measuring the force. The embodiment enables the sensor to provide haptic feedback to a person touching or exerting a force on the sensor.
In one embodiment the sensor is machine washable.
In one embodiment the sensor comprises a plurality of stacked layer structures as defined above.. This embodiment enhances modularity of the sensor. It allows the sensor to sense a touch or sense a force at each of the plurality positions comprising a stacked layer structure using one or more measurement devices.
In another embodiment the stacked layer structures are connected to the measurement device through a bus topology. This embodiment allows for a limited number of electrical connections to be used in the sensor.
Another aspect of the invention relates to a flexible stacked layer structure comprising a first conductive layer, a nonconductive layer positioned between the first and second conductive layer, a deformable layer that has a conductivity that is dependent on a magnitude of deformation of at least part of the deformable layer and arranged between the first and second conductive layer, and a second conductive layer. It should be noted that this stacked layer structure may be used in the disclosed sensor.
Yet another aspect of the invention relates to a measurement device configured to measure a characteristic time associated with an electrical circuit comprising a stacked layer structure. The stacked layer structure comprises a first conductive layer and a second conductive layer, and a deformable layer arranged between the first and second conductive layer. The measurement device is configured to connect to the first conductive layer and the second conductive layer. The measurement device is configured to sense a touch on the sensor from a first change of the characteristic time when the deformable layer is substantially undeformed by the touch and to sense a force from a second change of the characteristic time wherein the force causes a substantial deformation of the deformable layer.
Another aspect of the invention relates to a product comprising the sensor as described above.
BRIEF DESCRIPTION OF FIGURES
Aspects of the invention will be explained in greater detail by reference to exemplary embodiments shown in the drawings, in which: FIG. 1 shows examples of implementations of the invention; FIG. 2A&B schematically depicts the sensor FIG. 3 schematically shows the measurement device; FIG. 4A&B schematically depict an embodiment of the sensor; FIG. 5 is a schematic electrical circuit comprising an embodiment of the invention; FIG. 6 is a schematic electrical circuit comprising a sensor according to the invention that is touched; FIG. 7 depicts an example of the dependency of the characteristic time on the magnitude of the applied force; FIG. 8A&B schematically show another embodiment of the sensor; FIG. 9 is a schematic electrical circuit comprising a sensor according to the invention; FIG. 10 is a schematic electrical circuit comprising a sensor according to the invention wherein the sensor is touched; FIG. 11 depicts an example of the dependency of the characteristic time on the magnitude of the applied force; FIG. 12A-B show example voltage measurements; FIG 13 shows a flexible fabric with an integrated stacked layer structure according to an embodiment; FIG. 14 schematically shows an embodiment of the invention comprising a vibrational motor; FIG. 15A and B schematically show embodiments of the invention comprising a plurality of stacked layer structures.
DETAILED DESCRIPTION OF FIGURES FIG. 1 shows three examples wherein a sensor according to the invention has been integrated in a product. The sensor 1 can for example be integrated in interactive children toys or in ambient living products, such as carpets. Since some embodiments of the sensor comprise flexible fibers, the invention may be smoothly integrated into soft or flexible products. The sensor 1 may also be integrated into existing technological products, such as tablet computers, smartphones and may be integrated with such technological products in a manner that allows the user to control the product through the sensor 1. The sensor may also be used to mediate social touch over a distance. FIG. 2A shows an embodiment of the sensor 1. The sensor 1 comprises a stacked layer structure 2 and a measurement device 3. Furthermore, the stacked layer structure 2 comprises two conductive layers and a deformable layer. It should be noted that further layers may be arranged between the depicted layer as indicated by the empty spaces between the depicted layers. The sensor is configured to sense a touch FI as depicted by the hand touching the sensor in FIG. 2A. The touch does not deform the deformable layer. FIG. 2B shows the same embodiment of the sensor 1 as shown in FIG. 2A. In addition to being configured to measure a touch, FI, the sensor is configured to sense a force, F2. The force at least partly deforms the deformable layer. It should be noted that the force, although not shown, may also deform at least the conductive layer at the side upon which force F2 is exerted. FIG 3 schematically shows the measurement device 3. Measurement device 3 is configured to measure a characteristic time, e.g. an RC time, of the sensor in order to sense the touch and measure the force F2 from changes in the characteristic time. The measurement device 3 comprises a power source, a switch S and a processor. The power source may for example be a current source, or a voltage source. The power source powers the sensor. Any capacitors in the electrical circuit comprising the stacked layer structure may be charged by the power source.
The processor is configured to measure the characteristic time. To this end, it may measure the potential at a point in the circuit with respect to ground, wherein the potential is increasing as a result of the charging of capacitors formed in the circuit associated with the stacked layer structure. The processor may be configured to measure the time it takes for the potential to increase from zero potential to a certain value, e.g. a rise time of the potential. The processor is further configured to sense a touch and sense a force from changes in the characteristic time. To this end, the processor measures the characteristic time e.g. periodically or at least several times per second or per millisecond. The processor may be gauged and may comprise information about the dependency of the characteristic time on the force applied to the sensor. Note that this kind of information is depicted in FIG. 7 and FIG. 11 and will be described below. The processor is further configured to relate a measured characteristic time to a touch or to a magnitude of an applied force, and hence sense a touch and measure the force.
The switch S enables the characteristic time to be measured e.g. periodically, for example multiple times per second. Once the characteristic time has been measured, for example because the potential measured by the processor has reached a certain value, the capacitors in the electrical circuit formed by the stacked layer structure are at least partly charged. To reset to the situation prior to measurement of the characteristic time, and to reset the potential of the measured point to zero potential, the switch is closed, so that a conductive layer in the stacked layer structure is short-circuited to ground and all capacitors are discharged. Once fully discharged, the switch opens up again and the characteristic time of the sensor may be measured again. FIG. 4A shows a stacked layer structure according to an embodiment of the invention wherein the deformable layer is nonconductive. The two conductive layers separated by the non-conductive deformable layer form a capacitor that may store a certain amount of energy provided by the measurement device 3 and that is associated with a capacitance. In the figure an outer nonconductive layer is schematically shown arranged adjacent to one of the conductive layers. Also a nonconductive substrate is schematically shown. In Fig 4A, the sensor, and hence the stacked layer structure, is untouched. In this situation the plates of the capacitor, i.e. the two conductive layers, are separated by a distance do. In FIG. 4B, the stacked layer is shown in a situation wherein a force F2 is applied to the sensor, and thus to the stacked layer structure. In this situation the deformable layer is compressed. As a result the distance between the two conductive layers is di, which is smaller than do. It is noted that the upper conductive layer may be deformed as well. As is generally known, a smaller distance between two plates of a capacitor yields a higher capacitance of the capacitor. Hence the stacked layer structure comprises a capacitor with a variable capacitance, wherein the variable capacitance is dependent on the deformation of the deformable nonconductive layer, and thus dependent on the force applied to the sensor. FIG. 5 shows an example of an electrical circuit representing the stacked layer structure 2 and the measurement device 3. The stacked layer structure has an identical configuration as the stacked layer shown in FIG. 4, namely with a deformable nonconductive layer positioned between the two conductive layers. As explained with reference to FIGS. 4A and 4B, the two conductive layers that are separated by the deformable nonconductive layer form a capacitor with a variable capacitance. This capacitor is indicated in FIG. 5 by Cl, wherein the arrow indicates the variability of the capacitance of Cl as a result of a deformation of the deformable layer.
The measurement device 3 has at least two electrical terminals, one of which is connected to the top conductive layer, and the other terminal is connected to the bottom conductive layer. The measurement device may be configured to measure the potential difference between its two terminals in order to measure the characteristic time. R1 represents the sheet resistance of the top conductive layer and R2 represents the sheet resistance of the bottom conductive layer. The bottom conductive layer is connected to ground potential of the electrical circuit. FIG. 6 depicts the same sensor as FIG. 5 with the exception that the sensor 1 in FIG. 6 is touched by a finger of a person. In this situation the finger and the top conductive layer form the plates of a capacitor C2 separated by the top nonconductive layer. The finger is electrically connected to a ground potential (earth) through the body of the person which body constitutes a certain resistance Rbody. As such, the finger touching the sensor changes the electrical circuit from the perspective of the measurement device 3 of the sensor. The touch results in an additional parallel RC loop comprising Rbody and C2. Note that the variable capacitor Cl has the same capacitance in FIG. 5 and FIG. 6, because the touch does not deform the deformable layer which would change the distance between the two plates of capacitor Cl, i.e. between the two conductive layers. The additional RC loop resulting from the touch may increase the characteristic time of the electrical circuit comprising the stacked layer structure. FIG. 7 is a schematic representation of an exemplary curve of the characteristic time of a sensor comprising the stacked layer structure of the sensor depicted in FIG. 4A. On the vertical axis the characteristic time is indicated and on the horizontal axis the force F that is applied to the sensor is indicated. Note that the horizontal axis is divided in two regions. A first region I wherein the deformable layer is not substantially deformed, and a second region II wherein the deformable layer is at least partly deformed. When the sensor is not touched, no force F is applied to the sensor, the deformable layer is not deformed and no parallel RC circuit is introduced in the electrical circuit comprising the stacked layer structure. The characteristic time in this situation is indicated by to. When a finger touches the sensor, a small force may be applied, but this force is not large enough to substantially deform the deformable layer in any way. As explained with reference to FIG. 6, the touch of the finger may result in a longer characteristic time ti. The graph shows a constant characteristic time in Region I. However, it may be that the touch area of the finger increases with increased applied force, while still not deforming the deformable layer substantially. This increased touch area would result in a higher capacitance of the electrical circuit comprising the stacked layer structure and thus in an increase of the characteristic time within region I. It may even be that the capacitance already changes when a finger is very close to, but not in contact with, the sensor, which would also influence the characteristic time. It should be appreciated that the measurement device may be configured to measure a size of a touch area and/or a proximate body based on the above described changes in the characteristic time. When the force applied to the sensor 1 increases, at some point, the deformable layer will start to deform. As explained above the deformation may result in a higher capacitance of variable capacitor Cl, which increases the overall capacitance of the electrical circuit comprising the stacked layer structure, which may result in a longer RC time of the electrical circuit and thus a longer characteristic time. It should be appreciated that the parallel circuit of Rbody and C2 still exists. A larger applied force F results in a larger deformation, which results in a higher capacitance of the overall circuit.
This mechanism causes the electrical circuit to have a characteristic time that is dependent on the force exerted on the sensor as is shown by the graph wherein in region II the characteristic time increases with the force applied to the sensor. It should be appreciated that the measurement device may for example be configured to sense a touch if the measured characteristic time exceeds a threshold value, which may be lower than ti. The value of the threshold value may influence the sensitivity of the sensor. A higher threshold value may cause the sensor to be less sensitive, but also less susceptible to noise disturbance. A lower threshold value may cause the sensor to be more sensitive, but also more susceptible to noise disturbance. FIG. 8A shows another embodiment of the stacked layer structure according to the present invention. In this embodiment, the deformable layer is a layer that has an electrical conductivity that is dependent on the deformation of the deformable layer. This type of material is known as a piezo-resistive material. The larger the deformation of a piezo-resistive material, the lower its resistance becomes and the higher its conductivity. In addition, the depicted stacked layer structure comprises a nonconductive layer that is arranged between the two conductive layers. As shown in FIG. 8B, a pressing force on the stacked layer structure compresses the deformable layer, which increases the conductivity of the deformable layer. Hence the deformable layer forms a force-dependent resistor. FIG. 9 shows a stacked layer structure which is identical to the stacked layer structure depicted in FIG. 8A. R1 represents the sheet resistance of the top conductive layer and R2 represents the sheet resistance of the bottom conductive layer. The measurement device 3 has at least two terminals, one of which is connected to the top conductive layer, and one of which is connected to the bottom conductive layer. The measurement device may be configured to measure the potential difference between its two terminals in order to measure the characteristic time. The bottom conductive layer is connected to a ground potential of the electrical circuit.
As explained above, the deformable layer may function as a variable, force-dependent resistor, which is depicted by variable resistor R3. A capacitor C3 is formed by a first plate comprising the top conductive layer and a second plate formed by the lower conductive layer in conjunction with the deformable layer, which plates are separated by the nonconductive layer . FIG. 10 shows a situation wherein the sensor 1 of FIG. 9 is touched by a finger of a person. The finger and the top conductive layer are separated by the outer nonconductive layer and form a capacitor C2 as indicated. Herewith an additional parallel RC loop comprising Rbody and C2 is introduced in the electrical circuit comprising the stacked layer structure, which increases the overall capacitance of the electrical circuit and the RC time of the circuit as measured by the measurement device 3 and thus the characteristic time. Note that the touch depicted in FIG. 10 does not deform the deformable layer, thus the conductivity of the deformable layer has not changed in comparison to the situation of FIG 9. If, for example, a pressing force would compress the deformable layer, the conductivity of the deformable layer would increase, i.e. its resistance would decrease. It should be understood that this lower resistance yields a lower RC time of the electrical circuit comprising the sensor and thus may yield a shorter characteristic time of the sensor as measured by the measurement device 3. FIG. 11 shows an exemplary curve of the characteristic time of a sensor comprising the stacked layer structure of FIG. 8A. On the vertical axis the characteristic time is indicated and on the horizontal axis the force F that is applied to the sensor 1. Note that the horizontal axis is, again, divided in two regions. A first region I wherein the deformable layer is not substantially deformed, and a second region II wherein the deformable layer is substantially deformed. When the sensor is not touched, and thus no force is applied to the sensor, the characteristic time of the sensor is equal to to.
As explained with reference to FIG. 10, the touch of the finger may result in a longer characteristic time, indicated with ti. The graph shows a constant characteristic time in Region I. However, it may be that the touch area of the finger increases with increased applied force, while still not deforming the deformable layer substantially. This increased touch area would result in a higher capacitance of the electrical circuit comprising the stacked layer structure and thus in a change of the characteristic time within region I. It may even be that the capacitance already changes when a finger is very close to, but not in contact with, the sensor, which would also influence the characteristic time. It should be appreciated that the measurement device may be configured to measure a size of a touch area and/or a proximate body based on the above described changes in the characteristic time. As the force F applied to the sensor increases further, at some point, the deformable layer will start to deform. As explained above, a substantial deformation, such as a compression, of the deformable layer may lead to a shorter characteristic time of the sensor. Furthermore, the higher the applied force F, the larger the deformation of the deformable layer, which results in a lower resistance of the deformable layer and a lower characteristic time of the sensor. This is depicted in region II by the decreasing characteristic time with increasing force F applied to the sensor. Hence a magnitude of the force may be determined based on the basis of the characteristic time.
Note that the characteristic time to in FIG. 11 has a higher value than the to in FIG. 7. This may be, because the capacitor C3 in FIG. 9 and 10 may be associated with a higher capacitance than the capacitor Cl depicted in FIG. 5 and 6, because the nonconductive layer in FIG. 9 and 10 may be thin, whereas the deformable nonconductive layer in FIG. 5 preferably has a certain width so that it can be compressed by a force acting on the sensor.
It should be appreciated that the measurement device may for example be configured to sense a touch if the measured characteristic time exceeds a threshold value, which may be lower than ti. The value of the threshold value may influence the sensitivity of the sensor. A higher threshold value may cause the sensor to be less sensitive, but also less susceptible to noise disturbance. A lower threshold value may cause the sensor to be more sensitive, but also more susceptible to noise disturbance.
It should also be appreciated that the measurement device may be configured to only be able to sense a force during a measurement if the measurement device has already sensed a touch during the measurement, or in other words if the measurement device has measured a characteristic time longer than the above mentioned threshold value during the measurement. A measurement may be defined as the time period between measurement of a characteristic time equal or longer than the threshold value and a time at which the characteristic time stabilises around to, which occurs when the sensor is no longer touched. An advantage of the above may be that the sensor is less prone to erroneously sensing a force when a change in the characteristic time is caused by noise instead of an actual applied force. FIG. 12A shows two examples of the measured potential build-up associated with the charging of the capacitors in the electrical circuit representative of the sensor. The potential increases exponentially. If the power source keeps supplying power to the circuit, eventually the potential will reach a maximum voltage depicted by Vmax.
The graph shows two curves, curve 1 and curve 2.
Curve 1 depicts a typical increase of the potential with time in a situation wherein the sensor is not touched. In this example, the characteristic time is defined as the time it takes for the potential to increase from zero to a value of 0.63Vmax, which is in fact the RC time of the circuit. Note that the value of 0.63 is derived from the mathematical constant e by 0.63 = 1-e-1. The characteristic time in this situation is t0 as shown.
Curve 2 depicts a situation wherein the sensor is touched. The potential increases more slowly and it only reaches the value of 0.63Vmax at time ti. The characteristic time in this case is thus larger. FIG. 12B shows again two curves of an increasing voltage, curve 1 and curve 3. Curve 1 is identical to curve 1 in FIG. 12A and depicts the situation wherein the sensor is not touched. Again the characteristic time is defined as the time it takes the potential to increase from zero to the value Of 0.6 3 Vmax ·
Curve 3 depicts the situation wherein a force F2 is applied to the sensor that deforms at least part of the deformable layer. It takes much less time for the potential to reach the 0.63Vmax value, namely a time t2. This could be because the force increased the conductivity of the deformable layer leading to a shorter characteristic time as explained above . FIG. 13 depicts a piece of fabric that comprises the sensor. The stacked layer structure is flexible and is integrated in the piece of fabric. FIG. 14 is a schematic view of the sensor, wherein the sensor comprises a vibrational motor 4 that is connected to the measurement device 3. The vibrational motor may be configured to vibrate in response to a touch (haptic feedback) sensed by the sensor 1 or a force measured by the sensor 1.
The vibrational motor may vibrate more heavily in response to higher measured forces. FIG. 15A shows an embodiment of the invention wherein the sensor is integrated in a sleeve S that is worn on an arm A of a person. As shown, the sensor comprises a plurality of stacked layer structures 2. The stacked layer structures are positioned at different locations so that the measurement device is able to sense a touch and sense a force at separate locations. The sleeve and all stacked layer structures 2 are made of flexible fibers, so that the sleeve can be worn comfortably.
Fig. 15B schematically shows an embodiment of the sensor that comprises three stacked layer structures, 2a - 2c, that are each connected to the measurement device through a bus topology 5.
Claims (16)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL2015995A NL2015995B1 (en) | 2015-12-21 | 2015-12-21 | Fabric touch and force sensor. |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL2015995A NL2015995B1 (en) | 2015-12-21 | 2015-12-21 | Fabric touch and force sensor. |
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| Publication Number | Publication Date |
|---|---|
| NL2015995B1 true NL2015995B1 (en) | 2017-06-30 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| NL2015995A NL2015995B1 (en) | 2015-12-21 | 2015-12-21 | Fabric touch and force sensor. |
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| Country | Link |
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| NL (1) | NL2015995B1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109470386A (en) * | 2018-11-09 | 2019-03-15 | 福州大学 | A kind of power/position touch sensor detection system and detection method |
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2015
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109470386A (en) * | 2018-11-09 | 2019-03-15 | 福州大学 | A kind of power/position touch sensor detection system and detection method |
| CN109470386B (en) * | 2018-11-09 | 2020-11-10 | 福州大学 | Force/position touch sensor detection system and detection method |
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| MM | Lapsed because of non-payment of the annual fee |
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