Patent Description:
Various tactile sensors that simulate a human feeling in an engineering manner have been developed. Especially, a tactile sensor that is made by semiconductor micromachining techniques and can read a lot of sensor signals with less wiring allows a lot of sensor parts to be arranged in high density, and advantageously has high positional resolution.

As the tactile sensors made by semiconductor micromachining techniques, for example, a tactile sensor that utilizes deformation of a thin silicon diaphragm (<CIT>) and a tactile sensor that utilizes deformation of hinge structure (<CIT>) are known. Each of these conventional tactile sensors disclosed in <CIT> and <CIT> uses the surface of a substrate as a sensing surface, and is configured to make the surface of the substrate come in contact with a measuring object to read the deformation by the force applied in a vertical direction to the substrate. Therefore, such sensing structure is configured in a thickness direction of the substrate.

However, such a tactile sensor with the surface of the substrate used as a sensing surface allows little displacement due to the limitation of material properties and/or thickness of the substrate. Further, the flexibility in designing a tip shape of a contact of a tactile sensor is limited because the contact is vertically arranged to the substrate, and thus the tip shape appropriate to various measuring objects cannot be designed. Therefore, the problem is that such a tactile sensor is poor in detection performance with regard to fine ruggedness on the surface of a measuring object, and thus has difficulty in evaluating a fine touch feeling.

Moreover, stable detection of tactile sense and/or feeling requires that a tactile sensor performs sensing while keeping applying force (contact surface pressure) constant to a measuring object. However, it is difficult for conventional tactile sensors to keep such a measuring condition.

<CIT> discloses a microelectromechanical ("MEMS") load sensor device for measuring a force applied by a human user. The load sensor device has a contact surface in communication with a touch surface which communicates forces originating on the touch surface to a deformable membrane, on which load sensor elements are arranged, such that the load sensor device produces a signal proportional to forces imparted by a human user along the touch surface. The load sensor device has an overload protection ring to protect the load sensor device from excessive forces. The load sensor device has embedded logic circuitry to allow a microcontroller to individually address load sensor devices organized into an array. The load sensor device has electrical and mechanical connectors such as solder bumps designed to minimize cost of final component manufacturing.

Taking into consideration the problem described above, the object of the invention is to provide a tactile sensor that allows a contact to be displaced largely and can detect fine ruggedness, flexibility, and other features of a surface of a measuring object.

Another object is to provide a tactile sensor that can perform sensing while keeping applying force (contact surface pressure) substantially constant to a measuring object and that can perform stable measurement.

Yet another object is to provide a method for evaluating a touch feeling based on the data acquired by a tactile sensor.

According to an aspect of the present invention, a tactile sensor is provided as set forth in claim <NUM>. Moreover, according to other aspects of the present invention, a method of using the tactile sensor for evaluating a touch feeling of a measuring object based on data rows including surface shapes and frictional forces of the measuring object, Preferred embodiments of the present invention may be gathered from the dependent claims.

According to the invention as defined in claim <NUM>, since the contact is disposed so that the tip of the contact projects from the reference surface (as a sensing surface), and the contact coming in contact with the measuring object is displaced vertically and/or horizontally to the reference surface. The sensor part can be configured widely in a planar manner, and thus, design change can be performed easily through pattern designing and the structure has high flexibility of design. As a result, the structure allows the contact to be displaced largely and allows detection of fine ruggedness, flexibility and other features of the surface of the measuring object. Further, the contact is disposed so that the tip of the contact projects from the reference surface, and thus, force applied to the measuring object can be kept substantially constant during sensing, and the stable and sustainable contact between the contact and the measuring object allows stable measurement. The first strain detection element can detect strain of the contact in the pressing direction, and the second strain detection element can detect strain of the contact in the side slippage direction. Based on the displacement in the pressing direction and/or the displacement in the side slippage direction of the contact, the measuring object can be measured in surface shape, surface roughness, frictional force, flexibility and other features.

According to the invention as defined in claim <NUM>, when the tactile sensor is slid while being pressed to the measuring object, the contact is displaced following ruggedness of a comparable wavelength band to a radius of the tip of the contact. Thus, the surface shape of the measuring object can be measured by selecting a wavelength band with a radius of the tip of the contact.

According to the invention as defined in claim <NUM>, since the contacting face is arranged on the frame, the frame can limit the displacement of the contact to a predetermined amount or less, which prevents the sensor part from being broken due to excessive displacement of the contact.

According to the invention as defined in claim <NUM>, since the pair of contacting faces is inclined so as to spread toward the side face of the substrate, the gap between the contacting faces and the contacted faces becomes narrower when the contact is pressed in. In accordance with the width of the narrowed gap, the displacement of the contact in the side slippage direction can be further limited, which prevents the sensor part from being braked due to excessive displacement of the contact.

According to the invention as defined in claim <NUM>, when the tactile sensor is slid while being pressed to the measuring object, the moved distance and velocity of the tactile sensor can be measured based on the cycle of ruggedness of the measuring object measured by the sensor parts.

According to the invention as defined in claim <NUM>, since the tips of the contacts of the plurality of sensor parts are formed respectively in circular arcs having different radii, each of the contacts is displaced following ruggedness of a comparable wavelength band to the radius of the tip of the contact. Therefore, the surface shape of the measuring object can be measured through being decomposed into respective wavelength bands by the sensor parts. The surface roughness of the measuring object can be detected by use of the surface shape decomposed into respective wavelength bands as an index. In addition, the flexibility of the measuring object can be measured based on the difference between the displacement in the pressing direction of the contact having the tip with a small radius and the displacement in the pressing direction of the contact having the tip with a large radius when the tactile sensor is pressed to the measuring object.

According to the invention as defined in claim <NUM>, the flexibility of the measuring object can be measured through comparison between the displacement in the pressing direction of the contact projecting by a large projection distance and the displacement in the pressing direction of the contact projecting by a small projection distance when the tactile sensor is pressed to the measuring object. In addition, since the contacts projecting by different projection distance can apply force differently to the measuring object when the tactile sensor is slid while being pressed to the measuring object, the different touch feelings when the measuring object is slid strongly and lightly can be measured simultaneously.

According to invention as defined in claims <NUM>-<NUM>, the touch feeling can be evaluated based on the data acquired by the tactile sensor.

Some embodiments of the invention are described based on drawings.

As shown in <FIG>, a tactile sensor <NUM> of the first embodiment of the invention includes a sensor part S formed through working a substrate B such as a SOI substrate by semiconductor micromachining techniques. The sensor part S has a frame <NUM>, a contact <NUM>, and a suspension <NUM> that supports the contact <NUM> to the frame <NUM>. The size of the sensor part S is not limited to, but several millimeters square to more than ten millimeters square.

As described below, the contact <NUM> and the suspension <NUM> are formed by etching the substrate B in a predetermined pattern so as to remove unnecessary parts thereof. The frame <NUM> is the remained part of the substrate B after the unnecessary parts are removed, and has a shape enclosing the contact <NUM> and the suspension <NUM>. The sensor part S has a sensing surface (surface coming in contact with a measuring object) which is one side face of the substrate B. In the embodiment, the upper face out of the side faces of the substrate B in <FIG> is used as a sensing surface. The frame <NUM> may include the side part (upper part in <FIG>) of the substrate B having the sensing surface, but the shape thereof is not particularly limited. The face having the sensing surface out of the side faces of the frame <NUM> is referred to as a reference surface <NUM>.

The contact <NUM>, a bar-shaped member, is disposed in parallel to the substrate B, that is, on the same flat surface as the substrate B. The frame <NUM> has an opening partially on the side part having the sensing surface, and the tip of the contact <NUM> is inserted into the opening. The contact <NUM> is disposed so that the tip thereof projects outside from the reference surface <NUM> (the side of the substrate B). The contact <NUM> is also disposed so that the central axis thereof is vertical to the reference surface <NUM>.

The suspension <NUM> includes a plurality of first suspensions <NUM> and a plurality of second suspensions <NUM>. In the space surrounded by the frame <NUM>, two islands <NUM> are formed so as to sandwich the contact <NUM>. Each of the plurality of first suspensions <NUM>, a beam-shaped member, is disposed between the contact <NUM> and one of the islands <NUM>. Each of the plurality of second suspensions <NUM>, a beam-shaped member, is disposed between one of the islands <NUM> and the frame <NUM>. The contact <NUM> is supported to the frame <NUM> by the plurality of first suspensions <NUM>, the plurality of second suspensions <NUM> and the islands <NUM>.

The plurality of first suspensions <NUM> are disposed vertically to the central axis of the contact <NUM>, that is, horizontally to the sensing surface (reference surface <NUM>). Therefore, the plurality of first suspensions <NUM> allow the contact <NUM> to be displaced vertically to the sensing surface (reference surface <NUM>) (displacement in x direction in <FIG>) (hereinafter, referred to as "displacement in a pressing direction"). In the embodiment, ten first suspensions <NUM> in total are disposed so that a set of five first suspensions <NUM> is disposed in the both sides of the contact <NUM>, but the number of the first suspensions <NUM> is not particularly limited. The number and/or the width thereof may be set so as to obtain elasticity required as the first suspensions <NUM>.

The plurality of second suspensions <NUM> are disposed in parallel to the central axis of the contact <NUM>, that is, vertically to the sensing surface (reference surface <NUM>). Therefore, the plurality of second suspensions <NUM> allow the contact <NUM> to be displaced horizontally to the sensing surface (reference surface <NUM>) (displacement in y direction in <FIG>) (hereinafter, referred to as "displacement in a side slippage direction"). In the embodiment, eight second suspensions <NUM> in total are disposed so that a set of two second suspensions <NUM> is disposed in the both sides of each of the islands <NUM>, but the number of the second suspensions <NUM> is not particularly limited. The number and/or the width thereof may be set so as to obtain elasticity required as the second suspensions <NUM>.

When the sensing surface of the tactile sensor <NUM> is pressed to a measuring object, the contact <NUM> is displaced in the pressing direction (x direction). Further, when the sensing surface of the tactile sensor <NUM> is slid while being pressed to a measuring object, the contact <NUM> is displaced in the pressing direction (x direction), and in addition displaced in the side slippage direction (y direction). The sensor part S includes a displacement detector <NUM> and <NUM> in order to detect such displacement of the contact <NUM>.

Each of the displacement detectors <NUM> and <NUM> includes a first strain detection element <NUM> that detects strain of the first suspension <NUM>, or a second strain detection element <NUM> that detects strain of the second suspension <NUM>. In the embodiment, each of the first strain detection element <NUM> and the second strain detection element <NUM>, a piezoresistor, is formed on the first suspension <NUM> or the second suspension <NUM> in an integrated circuit manufacturing process such as impurity diffusion and/or ion implantation, by techniques for forming metal wiring or the like.

As shown in <FIG>, each of the first strain detection elements 41a and 41b is formed on the surface of each of two first suspensions <NUM> out of the plurality of first suspensions <NUM>. Each of the first strain detection elements 41a and 41b is formed in a shape of a step along one side face of one of the first suspensions <NUM> from the end to the center thereof and along the other side face of the first suspension <NUM> from the center to the other end thereof. In addition, the first strain detection element 41a formed on one of the first suspensions <NUM> is line-symmetric relative to the first strain detection element 41b formed on the other of the first suspensions <NUM>.

As shown in <FIG>, when the first suspensions <NUM> are distorted, one side of the first strain detection element 41a has smaller resistance due to compression stress, and the other side of the first strain detection element 41a has larger resistance due to tensile stress.

A circuit (not shown in <FIG> or in <FIG>) as shown in <FIG> is formed on the surface of the substrate B. In the circuit, the first strain detection elements 41a and 41b are connected in series and a voltage Vdd is applied to both ends of the series connection, and then a voltage Vout between the first strain detection elements 41a and 41b is measured. Strain of the first suspensions <NUM> can be detected by measuring a voltage Vout that varies in accordance with differential between the first strain detection elements 41a and 41b. Based on the strain, displacement of the contact <NUM> in the pressing direction (x direction) can be detected.

Similarly, each of the second strain detection elements 42a and 42b is formed on the surface of each of two second suspensions <NUM> out of the plurality of second suspensions <NUM>. Each of the second strain detection elements 42a and 42b is formed in a shape of a step. When the plurality of second suspensions <NUM> are distorted, one side of the second strain detection element 42a has smaller resistance due to compression stress, and the other side of the second strain detection element 42a has larger resistance due to tensile stress. A circuit (not shown in <FIG> or in <FIG>) is formed on the surface of the substrate B. In the circuit, the second strain detection elements 42a and 42b are connected in series and a voltage Vdd is applied to both ends of the series connection, and then a voltage Vout between the second strain detection elements 42a and 42b is measured. Strain of the plurality of second suspensions <NUM> can be detected by measuring a voltage Vout. Based on the detected strain, displacement of the contact <NUM> in the side slippage direction (y direction) can be detected.

<FIG> shows an enlarged view of the tip of the contact <NUM>. As shown in <FIG>, a contact part <NUM> having a semicircular shape is formed on the tip of the contact <NUM>. The tip of the contact <NUM> may be formed in a circular arc shape, not limited to the semicircular shape, that is, may be in a fan shape with a central angle of larger or smaller than <NUM> degrees.

The contact <NUM> is disposed in parallel to the substrate B and then etching is performed in a predetermined pattern so as to form the contact <NUM>. This can form the contact part <NUM> in a characteristic shape on the tip of the contact <NUM>. In a case of a contact part disposed vertically to the substrate, the tip of the contact part needs to be formed flat or in a square-pyramid shape by anisotropic etching, not in an arbitrarily-designed shape such as a smooth curved surface.

In a state where the contact <NUM> is not pressed in, the top of the contact part <NUM> projects by a predetermined projection distance v from the reference surface <NUM>. When the sensing surface is made come in contact with a measuring object, the contact <NUM> is displaced in the pressing direction (x direction) by the maximum amount v or less. That is, the tip of the contact <NUM> is not pressed inside lower than the reference surface <NUM>. As above, the frame <NUM> can limit the displacement of the contact <NUM> in the pressing direction (x direction) to a predetermined maximum amount or less, which can prevent the sensor part S from being braked due to excessive displacement of the contact <NUM>.

The contact <NUM> is disposed so that the tip thereof slightly projects from the reference surface <NUM>. Thus, force applied by the contact <NUM> to a measuring object (contact surface pressure) can be kept substantially constant during sensing, and the stable and sustainable contact between the contact <NUM> and the measuring object allows stable measurement.

Each of the frame <NUM> and the contact <NUM> has the following configuration so as to limit the displacement in the side slippage direction (y direction) of the contact <NUM> to a predetermined amount or less. A pair of contacting faces <NUM> and <NUM> is formed on an edge face of an opening of the frame <NUM>. The formed pair of contacting faces <NUM> and <NUM> sandwiches the contact <NUM>. A pair of contacted faces <NUM> and <NUM> facing the contacting faces <NUM> and <NUM> is formed.

The pair of contacting faces <NUM> and <NUM> is disposed substantially in a V shape. That is, the pair is inclined to the sensing surface so as to spread toward the sensing surface. Similarly, the pair of contacted faces <NUM> and <NUM> is disposed substantially in a V shape. That is, the pair is inclined to the sensing surface so as to spread toward the sensing surface. The pair of contacted faces <NUM> and <NUM> is disposed in parallel to the pair of contacting faces <NUM> and <NUM> apart by a predetermined gap width. The contacting faces <NUM> and the contacted faces <NUM> are formed by linearly etching and removing the parts between the frame <NUM> and the contact <NUM> so as to make a predetermined gap width.

In a state where the contact <NUM> is not pressed in, there is a gap between the contacting face <NUM> and the contacted face <NUM>, for example, with the minimum machinable width by etching. When the contact <NUM> comes in contact with a measuring object and is pressed in, the gap between the contacting face <NUM> and the contacted face <NUM> becomes narrower. In accordance with the width of the narrowed gap, the displacement of the contact <NUM> in the side slippage direction (y direction) is further limited. That is, this makes the width of the gap narrower than the machinable width, and thus the displacement of the contact <NUM> in the side slippage direction (y direction) can be limited to the narrowed width. As a result, this structure can prevent the sensor part S from being braked due to excessive displacement of the contact <NUM>.

In accordance with the object of measurement, the maximum value of each of the displacement of the contact <NUM> in the pressing direction (x direction) and the displacement in the side slippage direction (y direction) may be set, and further, the projection distance v of the contact <NUM> from the reference surface <NUM> and the width of the gap between the contacting face <NUM> and the contacted face <NUM> may be set. The shapes of the plurality of first suspensions <NUM> and the plurality of second suspensions <NUM> may be designed so as to allow the maximum displacement of the contact <NUM>.

As described above, the contact <NUM> is disposed in parallel to the substrate B so that the tip thereof projects from the side face of the substrate B. Thus, the side face of the substrate B functions as a sensing surface and the contact <NUM> coming in contact with a measuring object is displaced in a level parallel to the substrate B. Therefore, since the sensor part S can be configured widely in a planar manner along the substrate B as described above, design change can be performed more easily through pattern designing and the structure has higher flexibility of design, compared to the conventional case in which such structure is formed in the thickness direction of the substrate B. As a result, the structure allows the contact <NUM> to be displaced largely and can detect fine ruggedness, flexibility and other features of the surface of the measuring object. Further, the structure can prevent the sensor part S from being damaged during measurement because the measuring object does not come in direct contact with an electric circuit part thereof.

Next, the method for manufacturing the tactile sensor <NUM> with SOI substrate is described based on <FIG>.

The SOI substrate has three-layer structure of a base substrate (silicon), an oxide film layer (silicon dioxide) and an active layer (silicon) with a thickness of, for example, <NUM>.

First, the substrate is cleaned and subjected to oxidation treatment. Next, a diffusion layer pattern to be a circuit part is formed and phosphorus diffusion is performed. Then, the back surface of the substrate is subjected to sputtering to form a chrome thin-film, and the chrome film is subject to etching to form a pattern of the movable structure part (contact <NUM> and suspension <NUM>) for release. Then, the oxide film of the upper surface is removed and the movable structure part is formed by ICP-RIE etching. Finally, the intermediate oxide film and a resist are removed to release the movable structure part.

Next, a detection method by use of the tactile sensor <NUM> is described.

When performing detection by use of the tactile sensor <NUM>, the sensing surface is pressed to a measuring object, or the sensing surface is slid while being pressed to a measuring object. This displaces the contact <NUM>, and at the same time distorts the plurality of first suspensions <NUM> and the plurality of second suspensions <NUM>. Due to the strain, the first strain detection element <NUM> detects displacement in the pressing direction (x direction) of the contact <NUM>, and the second strain detection element <NUM> detects displacement in the side slippage direction (y direction) of the contact <NUM>. Based on the displacement in the pressing direction (x direction) and/or the displacement in the side slippage direction (y direction) of the contact <NUM>, the measuring object can be measured in surface shape, surface roughness, frictional force, flexibility and other features thereof. The detection method is detailed in order below.

First, the method for detecting a surface shape of a measuring object by use of the tactile sensor <NUM> is described.

As shown in <FIG>, the sensing surface of the tactile sensor <NUM> is pressed to a surface of a measuring object O so as to make the reference surface <NUM> come in contact with the measuring object O. This locates the reference surface <NUM> to the level connecting peaks of the ruggedness on the surface of the measuring object O. When the contact part <NUM> comes in contact with the surface of the measuring object O, the contact <NUM> is pressed by the reaction force of the measuring object O.

Next, as shown in <FIG>, the sensing surface of the tactile sensor <NUM> is slid along the surface of the measuring object O while being pressed to the surface of the measuring object O. This displaces the contact <NUM> in the pressing direction following the ruggedness on the surface of the measuring object O, and thus distorts the first suspensions <NUM>. The first strain detection element <NUM> detects temporal change or distance change of the displacement of the contact <NUM> in the pressing direction.

As shown in <FIG>, the surface shape (spatial waveform) of the surface of the measuring object O can be reproduced based on the detected temporal change or distance change of the displacement of the contact <NUM> in the pressing direction.

Here, the contact <NUM> is displaced following ruggedness of a comparable wavelength band to a radius of the contact part <NUM>. That is, the contact part <NUM> with a smaller radius can follow ruggedness having smaller wavelengths, and detect finer ruggedness on the surface of a measuring object. On the other hand, the contact part <NUM> with a larger radius more hardly follows fine ruggedness, and thus can detect the ruggedness having larger wavelengths (swell) regardless of fine ruggedness on the surface of the measuring object. As described above, the surface shape of the measuring object O can be measured by selecting a wavelength band (frequency band) with a radius of the contact part <NUM>.

The tip (contact part <NUM>) in a circular arc of the contact <NUM> comes in contact with the measuring object O. Thus, the contact <NUM> can move smoothly without being caught by the measuring object O during when the tactile sensor <NUM> is slid while being pressed to the measuring object O. Therefore, the contact <NUM> is displaced following the ruggedness on the surface of the measuring object, and thus accurate measurement with regard to the surface shape of the measuring object O can be performed.

Next, the method for detecting frictional force of the measuring object by use of the tactile sensor <NUM> is described.

As shown in <FIG>, the sensing surface of the tactile sensor <NUM> is slid along the surface of the measuring object O while being pressed to the surface of the measuring object O. The reaction force received from the measuring object O displaces the contact <NUM> in the pressing direction, and the displacement distorts the first suspensions <NUM>. The first strain detection element <NUM> detects the displacement of the contact <NUM> in the pressing direction. The frictional force generated between the contact part <NUM> and the measuring object O also slides the contact <NUM>, and the sliding distorts the second suspensions <NUM>. The second strain detection element <NUM> detects the displacement of the contact <NUM> in the side slippage direction.

Since an elastic modulus of the first suspensions <NUM> is known, a reaction force Fx received by the contact <NUM> can be calculated based on the displacement of the contact <NUM> in the pressing direction. Similarly, since an elastic modulus of the second suspensions <NUM> is known, a frictional force Fy received by the contact <NUM> can be calculated based on the displacement of the contact <NUM> in the side slippage direction. By use of the calculated reaction force Fx and the calculated frictional force Fy, a dynamic friction coefficient µ of the surface of the measuring object O can be calculated based on Formula <NUM> below.

An operation similar to the one described above may allow detection of the force applied in the direction parallel to the surface of the measuring object O, such as an unsmooth feeling in a case of a fibrous measuring object O.

As shown in <FIG>, a tactile sensor <NUM> of the second embodiment of the invention includes two sensor parts of a sensor part S1 and a sensor part S2. Each of the sensor parts S1 and S2 has the same configuration as the sensor part S of the tactile sensor <NUM> of the first embodiment, and thus the same codes are attached to the same members and the description thereof is omitted herein.

The sensor parts S1 and S2 are disposed so as to share a sensing surface. That is, the contact <NUM> of the sensor part S1 and the contact <NUM> of the sensor part S2 are disposed in parallel to each other and the both tips thereof are disposed on the shared sensing surface.

The tactile sensor <NUM> is slid while being pressed to the measuring object O. This allows each of the sensor parts S1 and S2 to detect the surface shape of the measuring object O. The two contacts <NUM> of the sensor parts S1 and S2 are disposed away from each other by a predetermined distance, and thus the cycles of ruggedness of the measuring object O measured by the sensor parts S1 and S2 are shifted by the distance. Based on the shift, the moved distance and velocity of the tactile sensor <NUM> to the measuring object O can be measured.

Setting different elastic moduli for the suspensions <NUM> of the sensor parts S1 and S2 allows the sensor parts S1 and S2 to perform measurement in different ranges. As a result, a single unit of the tactile sensor <NUM> can perform measurement in a wider range.

The tactile sensor <NUM> of the embodiment includes two sensor parts of the sensor parts S1 and S2. However, a tactile sensor may be configured to include three sensor parts or more.

As shown in <FIG>, a tactile sensor <NUM> of the third embodiment of the invention includes two sensor parts of a sensor part S3 and a sensor part S4. Each of the sensor parts S3 and S4 basically has the same configuration as the sensor S of the tactile sensor <NUM> of the first embodiment, and thus the same codes are attached to the same members and the description thereof is omitted herein.

As a feature of the tactile sensor <NUM> of the embodiment, the tips of the contact <NUM> of the sensor part S3 and the contact <NUM> of the sensor part S4 are formed in circular arcs having different radii. That is, a contact part <NUM> having a semicircular shape with a radius r<NUM> is formed on the tip of the contact <NUM> of the sensor part S3, while a contact part <NUM> having a semicircular shape with a radius r<NUM> which is smaller than the radius r<NUM> is formed on the tip of the contact <NUM> of the sensor part S4. The both contacts <NUM> are disposed so as to project by the same projection distance v from the reference surface <NUM>.

The radii r<NUM> and r<NUM> of the contact parts <NUM> and the projection distance v of the contacts <NUM> are not limited, and may be set in accordance with the measuring object O and/or the purpose of the measurement. For example, the radius r<NUM> is set to <NUM>, the radius r<NUM> is set to <NUM>, and the projection distance v is set to <NUM>.

Next, the method for detecting surface roughness of a measuring object by use of the tactile sensor <NUM> is described.

As show in <FIG>, the surface shape of the measuring object O may have swell components of large wavelengths and fine components of short wavelengths. The sensing surface of the tactile sensor <NUM> is slid along the surface of the measuring object O while being pressed to the surface of the measuring object O. This displaces each of the contacts <NUM> of the sensor parts S3 and S4 in the pressing direction along the ruggedness on the surface of the measuring object O.

The contact <NUM> is displaced following ruggedness of a comparable wavelength band to a radius of the contact part <NUM>. That is, the contact <NUM> having the contact part <NUM> with the large radius r<NUM> is displaced following ruggedness of a long wavelength band, and the contact <NUM> having the contact part <NUM> with the small radius r<NUM> is displaced following ruggedness of a combination of the long wavelength band and a short wavelength band.

Therefore, as shown in <FIG>, the sensor part S3 including the contact <NUM> having the contact part <NUM> with the large radius r<NUM> can measure a spatial waveform of the long wavelength band (low frequency band) free from the short wavelength band (high frequency band). That is, the sensor part S3 can extract just the swell components of the surface shape of the measuring object O.

As shown in <FIG>, the sensor part S4 including the contact <NUM> having the contact part <NUM> with the small radius r<NUM> can measure a spatial waveform of the combination of the long wavelength band (low frequency band) and the short wavelength band (high frequency band). That is, the sensor part S4 can extract the waveform combined with the swell components and the fine components of the surface shape of the measuring object O.

Then, the spatial waveform measured by the sensor part S3 (swell components) is eliminated (subtracted) from the spatial waveform measured by the sensor part S4 (combination of swell components and fine components) so as to obtain the spatial waveform only of the short wavelength band (high frequency band), that is, the fine components of the surface shape of the measuring object O, as shown in <FIG>.

As described above, since the tips of the contacts <NUM> of the sensor parts S3 and S4 are formed in the circular arcs respectively with the different radii of the radius r<NUM> and the radius r<NUM>, each of the contacts <NUM> is displaced following the ruggedness of the comparable wavelength band to the radius r<NUM> or the radius r<NUM> of the contact part <NUM>. Thus, the surface shape of the measuring object O can be measured through being decomposed into respective wavelength bands by the sensor parts S3 and S4. The surface roughness of the measuring object O can be detected by use of the surface shape decomposed into respective wavelength bands as an index.

In a case where the components of the long wavelength band are many in the spatial waveform, the surface of the measuring object O can be determined to be rough, while in a case where the components of the short wavelength band are many in the spatial waveform, the surface of the measuring object O can be determined to be smooth.

A sensor may be configured to include three sensor parts or more respectively having the tips of the contacts <NUM> with more various kinds of radii. Such a sensor can decompose the surface shape of the measuring object O into more wavelength bands (frequency bands) so as to identify the surface roughness thereof. In a case where three sensor parts respectively having contact parts <NUM> with different radii are set, such a sensor can decompose a spatial waveform for measurement into three bands of a short wavelength band (high frequency band), a middle wavelength band (intermediate frequency band), and a long wavelength band (low frequency band).

Next, the method for detecting flexibility of a measuring object by use of the tactile sensor <NUM> is described.

The sensing surface of the tactile sensor <NUM> is pressed to the surface of the measuring object O so as to detect flexibility of the measuring object O. This makes the contacts <NUM> of the sensor parts S3 and S4 come in contact with the surface of the measuring object O, and the contacts <NUM> are pressed in by the reaction force of the measuring object O.

In the embodiment, since the tips of the contacts <NUM> of the sensor parts S3 and S4 are formed in circular arcs respectively having different radii, the contacts <NUM> are differently displaced in the pressing direction in accordance with the flexibility of a measuring object O. Concretely, in a case of a hard measuring object O, both of the contact <NUM> having the contact part <NUM> with the large radius r<NUM> and the contact <NUM> having the contact part <NUM> with the small radius r<NUM> are displaced in the pressing direction by substantially the same amount. In a case of a soft measuring object O, the contact <NUM> having the contact part <NUM> with the small radius r<NUM> is easy to stick the measuring object O. Thus, compared to the contact <NUM> having the contact part <NUM> with the small radius r<NUM>, the contact <NUM> having the contact part <NUM> with the large radius r<NUM> is displaced more largely in the pressing direction.

According to the result, when the tactile sensor <NUM> is pressed to a measuring object O, the flexibility of the measuring object O can be measured based on the difference between the displacement in the pressing direction of the contact <NUM> having the tip with the small radius r<NUM> and the displacement in the pressing direction of the contact <NUM> having the tip with the large radius r<NUM>.

As shown in <FIG>, a tactile sensor <NUM> of the fourth embodiment of the invention includes two sensor parts of a sensor part S5 and a sensor part S6. Each of the sensor parts S5 and S6 basically has the same configuration as the sensor S of the tactile sensor <NUM> of the first embodiment, and thus the same codes are attached to the same members and the description thereof is omitted herein.

As a feature of the tactile sensor <NUM> of the embodiment, the projection distances from the reference surface <NUM> of the contacts <NUM> of the sensor parts S5 and S6 are set differently. That is, the contact <NUM> of the sensor part S5 is disposed to project by a projection distance v<NUM>, and the contact <NUM> of the sensor part S6 is disposed to project by a projection distance v<NUM> that is smaller than the projection distance v<NUM>. The contact parts <NUM> of the both contacts <NUM> are set to have the same radius r.

The projection distances v<NUM> and v<NUM> of the contacts <NUM> and the radius r of the contact parts <NUM> are not limited, and may be set in accordance with a measuring object O and/or the purpose of the measurement. For example, the projection distance v<NUM> is set to <NUM>, the projection distance v<NUM> is set to <NUM>, and the radius r is set to <NUM>.

The sensing surface of the tactile sensor <NUM> is pressed to the surface of the measuring object O so as to detect flexibility of the measuring object O. This makes the contacts <NUM> of the sensor parts S5 and S6 come in contact with the surface of the measuring object O, and the contacts <NUM> are pressed in by the reaction force of the measuring object O. The displacement respectively by the contacts <NUM> in the pressing direction is measured.

When the tactile sensor <NUM> is pressed to the measuring object O, the contacts <NUM> projecting from the reference surface <NUM> respectively press and deform the surface shape of the measuring object O. Each of the contacts <NUM> is displaced in the pressing direction in accordance with the balance between the elastic force generated by the strain of the first suspensions <NUM> and the elastic force generated by the deformation of the measuring object O. Thus, in a case of a hard measuring object O, the measuring object O hardly deforms and the contacts <NUM> are largely displaced in the pressing direction. In a case of a soft measuring object O, the measuring object O deforms largely and the contacts <NUM> are less displaced in the pressing direction.

In the embodiment, since the projection distances of the contacts <NUM> of the sensor parts S5 and S6 are different, the difference between the tip locations of the contacts <NUM> varies depending on the flexibility of the measuring object O. Concretely, in a case of a hard measuring object O, the measuring object O hardly deforms, and thus the difference between the tip locations of the contacts <NUM> is decreased. In a case of a soft measuring object O, the part of the measuring object O which comes in contact with the contact <NUM> projecting by the large projection distance v<NUM> deforms largely, and thus the difference between the tip locations of the contacts <NUM> is increased.

When the displacement in the pressing direction of the contact <NUM> measured by the sensor part S5 is X<NUM> and the displacement in the pressing direction of the contact <NUM> measured by the sensor part S6 is X<NUM>, the difference between the tip locations of the contacts <NUM>, that is, a strain ΔZ generated in the measuring object O, is calculated based on Formula <NUM> below. The flexibility of the measuring object O can be measured by use of the strain ΔZ as an index.

As above, the flexibility of the measuring object O can be measured through comparison between a displacement X<NUM> in the pressing direction of the contact <NUM> projecting by the large projection distance v<NUM> and a displacement X<NUM> in the pressing direction of the contact <NUM> projecting by the small projection distance v<NUM>.

Next, the method for detecting frictional force of a measuring object by use of the tactile sensor <NUM> is described.

The sensing surface of the tactile sensor <NUM> is slid along the surface of the measuring object O while being pressed to the surface of the measuring object O to detect frictional force of the measuring object O. This makes the contacts <NUM> of the sensor parts S5 and S6 come in contact with the surface of the surface of the measuring object O, and the contacts <NUM> are pressed in by the reaction force of the measuring object O. Further, the contacts <NUM> of the sensor parts S5 and S6 are also displaced in the side slippage direction by the frictional force generated between each of the contacts <NUM> and the measuring object O. The displacement in the pressing direction and the displacement in the side slippage direction of each of the contacts <NUM> are measured.

Since the contacts <NUM> of the sensor parts S5 and S6 respectively project by different projection distances, the contacts <NUM> can apply force differently to the measuring object O. Thus, each of the sensor parts S5 and S6 can measure the frictional force when a different contact surface pressure is applied to the measuring object O.

Concretely, the contact <NUM> projecting by the large projection distance v<NUM> can apply a large contact surface pressure to the measuring object O, and thus the sensor part S5 can measure the frictional force when a large contact surface pressure is applied. The contact <NUM> projecting by the small projection distance v<NUM> can apply a small contact surface pressure to the measuring object O, and thus the sensor part S6 can measure the frictional force when a small contact surface pressure is applied.

Comparing the cases when the measuring object O is slid strongly and lightly, the shape and properties of the surface of the measuring object O may be changed and thus the frictional force and a touch feeling may be changed. The different frictional forces and touch feelings when the measuring object O is slid strongly and lightly can be measured simultaneously.

In the embodiments described above, the suspension <NUM> includes the plurality of first suspensions <NUM> disposed horizontally to the sensing surface and the plurality of second suspensions <NUM> disposed vertically to the sensing surface. However other configurations may be set. In an example, suspensions may be disposed obliquely to the sensing surface.

Moreover, a displacement detector to detect the displacement of the contact <NUM> is not limited to a piezoresistor. In an example, a displacement detector may be configured to detect electrostatic capacitance between the contact <NUM> and the frame <NUM> by utilizing the change in distance between the frame <NUM> and the contact <NUM> due to the displacement of the contact <NUM>.

Further, the tip of the contact <NUM> may be formed in a different shape, not limited to a circular arc shape. For example, the tip may be formed in a tip-sharpened needle or wave shape, or asymmetrically. Alternatively, the tip of the contact <NUM> may be formed in a hook shape so as to be easily caught by a measuring object in a case of measuring an unsmooth feeling of a measuring object as an important parameter.

A contacting part formed in a different shape from the contacting face <NUM> of the embodiments described above may be set so as to limit excessive displacement of the contact <NUM>. The contacting part may be disposed so as to face the contact <NUM> apart by a prescribed gap width. That is, the contacting part may be configured to limit only the excessive displacement of the contact <NUM> in the pressing direction, or may be configured to limit only the excessive displacement of the contact <NUM> in the side slippage direction.

Further, in order to limit excessive displacement of the contact <NUM> in a thickness direction of the substrate B, a plate such as a glass plate may be attached to each of a front face and a back face of the substrate B with a prescribed gap distance to each of a front face and a back face of the contact <NUM>.

A test for detecting displacement of the contact <NUM> is performed by use of the tactile sensor <NUM> of the first embodiment described above.

The tactile sensor <NUM> is fixed horizontally (the sensing surface disposed vertically). A voltage Vdd respectively applied to the first strain detection element <NUM> and the second strain detection element <NUM> is set to 10V. A handicraft cutting mat is used as a measuring object O. The act of sliding a side face of the handicraft cutting mat while pressing the side face to the sensing surface of the tactile sensor <NUM> is repeated three times.

<FIG> shows temporal change of a voltage Vout output by the circuit including the first strain detection element <NUM> and a voltage Vout output by the circuit including the second strain detection element <NUM>. <FIG> shows change of the output voltage detected by the first strain detection element <NUM> that detects the displacement of the contact <NUM> in the pressing direction and also of the output voltage detected by the second strain detection element <NUM> that detects the displacement of the contact <NUM> in the side slippage direction. The result shows that the first strain detection element <NUM> and the second strain detection element <NUM> can detect the displacement of the contact <NUM> in the pressing direction and the displacement in the side slippage direction on the same time-axis.

A test for evaluating a touch feeling is performed by use of the tactile sensor <NUM> of the third embodiment described above.

The radius r<NUM> of the contact part <NUM> of the sensor part S3 is set to <NUM>, the radius r<NUM> of the contact part <NUM> of the sensor part S4 is set to <NUM>, and the projection distance v of the both contacts <NUM> is set to <NUM>. Further, the voltage Vdd respectively applied to the first strain detection element <NUM> and the second strain detection element <NUM> is set to 10V.

Two types of sheets of copy paper and Japanese straw paper are prepared for use as measuring objects. For a person, the copy paper feels smooth, while the straw paper feels rough. The sensing surface of the tactile sensor <NUM> is slid at a constant velocity (<NUM>/sec) while being pressed to each of the sheets for use as a measuring object.

<FIG> shows temporal change of a voltage Vout output by the circuit including the first strain detection element <NUM> of the sensor part S4 and a voltage Vout output by the circuit including the second strain detection element <NUM> of the sensor part S4. <FIG> shows a case of copy paper for use as a measuring object, while <FIG> shows a case of straw paper for use as a measuring object. The output voltage by the first strain detection element <NUM> shows the surface shape of a measuring object. The output voltage by the second strain detection element <NUM> shows the frictional force of a measuring object. The horizontal axis represents a time axis, and is also synonymous with a position coordinate on the surface of a measuring object because the tactile sensor <NUM> is moved at a constant velocity to the measuring object. As described above, the tactile sensor <NUM> can acquire data rows including surface shapes and frictional forces of a measuring object.

The output voltage of 5mV by the first strain detection element <NUM> corresponds to the amplitude of a surface shape of approximately <NUM>. <FIG> shows that the tactile sensor <NUM> can measure the amplitude of a surface shape by the resolution of approximately <NUM>. In a case of straw paper (<FIG>), both of the amplitude of the surface shape thereof and the amplitude of the frictional force thereof are larger compared to those of copy paper (<FIG>). This shows that the surface of the straw paper has larger ruggedness.

In addition, <FIG> shows that in each case the waveform of the surface shape and the waveform of the frictional force are similar to each other, and the phases of them are shifted each other. The peak of the frictional force appears immediately before the peak of the surface shape. Each arrow in <FIG> shows an example location of the peak of the surface shape or the peak of the frictional force adjacent to the peak of the surface shape. It may be considered that this happens because the contact part <NUM> is caught by a projection part of a surface of a measuring object (a peak of the surface shape), and thus frictional force is increased immediately before the projection part. Conventionally, frictional force can be measured only as an average value of an entire measuring object. The tactile sensor <NUM> can partially measure frictional force of a measuring object. In addition, the tactile sensor <NUM> can measure change in frictional force as well as change in surface shape. Therefore, new knowledge as described above can be obtained.

<FIG> shows a scatter diagram in which the horizontal axis represents surface shape and the vertical axis represents frictional force. <FIG> shows a case of copy paper for use as a measuring object, while <FIG> shows a case of straw paper for use as a measuring object. A correlation coefficient r between surface shapes and frictional forces is calculated for each of the cases. The correlation coefficient r in a case of copy paper is <NUM>, while the correlation coefficient r in a case of straw paper is <NUM>. Here, the correlation coefficient r in the data rows including coupled values {(x<NUM>, y<NUM>)}(i=<NUM>, <NUM>,. , n) is defined based on Formula <NUM> below. Other definition may be used as the definition of the correlation coefficient.

The values x and y respectively represent the arithmetic means of x={x<NUM>} and y={y<NUM>}.

The correlation coefficient of the straw paper is lower than the correlation coefficient of the copy paper. The measuring object having a higher correlation coefficient can be said to feel smooth, while the measuring object having a lower correlation coefficient can be said to feel rough. As described above, a touch feeling can be quantified by use of a correlation coefficient between surface shapes and frictional forces as an index.

As described above, the phases of the waveform of the surface shapes and the waveform of the frictional forces are shifted each other. The phases of the respective waveforms are shifted by a unit of <NUM> second in the period from zero to <NUM> second to obtain the correlation coefficients between the surface shapes and the frictional forces in various phase differences. <FIG> shows the result. <FIG> shows a case of copy paper for use as a measuring object, while <FIG> shows a case of straw paper for use as a measuring object.

<FIG> shows that in a case of no phase shifted the correlation coefficient of copy paper (<FIG>) is higher. However, the peak value of the correlation coefficient of straw paper (<FIG>) is higher. The phase difference of the peak value of the correlation coefficient of copy paper is different from that of the straw paper. The correlation coefficient of straw paper has a peak with a larger phase difference compared to the case of copy paper. The measuring object having a smaller phase difference at a peak of a correlation coefficient can be said to feel smooth, while the measuring object having a larger phase difference at a peak of a correlation coefficient can be said to feel rough. As described above, a touch feeling can be quantified by use of a phase difference at a peak of a correlation coefficient as an index.

<FIG> shows differential spatial frequency distribution with regard to surface shapes and frictional forces. <FIG> shows a case of copy paper for use as a measuring object, while <FIG> shows a case of straw paper for use as a measuring object. Information regarding a touch feeling is considered to be included in the similarity and the phase difference with regard to the waveforms of surface shapes and the waveforms of frictional forces. Thus, attention is focused on the differential spatial frequency distribution showing the similarity and the phase difference. The differential spatial frequency distribution is obtained in such a manner that a differential waveform is obtained by removing a signal waveform of frictional force from a signal waveform of a surface shape, and then a Fourier transformation is applied to the obtained differential waveform.

The distribution of a case of copy paper (<FIG>) shows that many low frequency components are included, while less high frequency components are included. The reason of the distribution is that the copy paper is made from relatively fine fibers and has a smooth surface shape, and thus the both waveforms themselves of the surface shapes and the frictional forces have less high frequency components. Another reason is that the similarity between the waveforms of the surface shapes and the frictional forces is high, and the phase difference between them is small. The distribution of a case of straw paper (<FIG>) shows that high frequency components are included, as well as low frequency components. The reason of the distribution is that the waveforms themselves of the surface shapes and the fictional forces have many high frequency components because the straw paper is made from relatively coarse fibers and thus the contact part <NUM> receives the frictional force generated when the contact part <NUM> is occasionally caught by such coarse fibers. Another reason is that the similarity between the waveforms of the surface shapes and the frictional forces is low, and the phase difference between them is large. Therefore, it can be said that the measuring object having less high frequency components feels smooth, while the measuring object having more high frequency components feels rough. As described above, a touch feeling can be evaluated by use of differential spatial frequency distribution with regard to surface shapes and frictional forces as an index.

Claim 1:
A tactile sensor (<NUM>), comprising
a sensor part (S) that is formed in a substrate (B), wherein
the sensor part (S) includes:
a frame (<NUM>) that includes a reference surface (<NUM>) coming in contact with a measuring object (O);
a contact (<NUM>) that is disposed so that a tip of the contact (<NUM>) projects from the reference surface (<NUM>);
a suspension (<NUM>) that supports the contact (<NUM>) on the frame (<NUM>); and
a displacement detector (<NUM>, <NUM>) that detects displacement of the contact (<NUM>),
wherein the suspension (<NUM>) includes:
a first suspension (<NUM>) that allows the contact to be displaced vertically to the reference surface (<NUM>);
a second suspension (<NUM>) that allows the contact to be displaced horizontally to the reference surface (<NUM>), and
an island (<NUM>) that is disposed between the first suspension (<NUM>) and the second suspension (<NUM>); and
wherein the displacement detector (<NUM>, <NUM>) includes:
a first strain detection element (<NUM>) that detects strain of the first suspension (<NUM>); and
a second strain detection element (<NUM>) that detects strain of the second suspension (<NUM>).