Patent Description:
Conventionally, the following Patent Literature <NUM> discloses that whether or not a slip has occurred on a contact surface is determined on the basis of (i) a change amount in a center position of the pressure against the contact surface and (ii) gripping force of a gripping unit that grips a target object body.

Patent Literature <NUM>: <CIT> Other background references include <CIT> which discloses detecting a slip on the basis of a calculated movement value of a pressure center position according to the preamble of claim <NUM>, and <CIT>.

A which discloses a resilient gripper pad storing deformation energy.

Detection of a partial slip is effective in a case where a robot or the like grips an object. The partial slip is a phenomenon that occurs before a whole slip in which a relative position with respect to an object deviates and the object slips off, and in which a part of a contact surface starts to slip. In this case, in a state of the partial slip, a deviation of a relative position with respect to an object does not occur.

However, a technology disclosed in the above-mentioned Patent Literature <NUM> employs a method for detecting a whole slip when an object starts to slip, so that a gripping force is not able to be controlled unless the object starts to slip. Thus, in the technology disclosed in the above-mentioned Patent Literature <NUM>, it is difficult to control a gripping force before an object starts to slip so as to perform a stable grip. Moreover, in the first place, the fact is that there presents no effective technology for detecting a partial slip. When a partial slip is to be detected, shear deformation of a contact part which occurs before a partial slip is detected, and thus it is difficult to decide the minimum gripping force on the basis of the partial slip. Moreover, in a case where pressure distribution is uniform, for example, when an object is hard or when an object surface is plane, progress of a partial slip is rapid, so that detection of the partial slip becomes difficult.

Thus, it has been desired to detect a slip of an object with high accuracy by detecting a partial slip.

As described above, according to the present disclosure, it is possible to detect a slip of an object with high accuracy by detecting a partial slip.

The above-described effects are not necessarily limited, and any effects indicated in the present specification or other effects that can be understood from the present specification may be exerted together with or instead of the above-described effects.

The following describes preferable embodiments of the present disclosure in detail with reference to the attached drawings. In the present specification and the drawings, overlap of descriptions will be avoided by providing the same reference symbols for constituent elements having substantially the same functional configuration.

Descriptions will be constituted in the following order.

For example, when a robot grips an object with a hand thereof, it is desirable that the object is gripped with a moderate force having an extent to which the object does not slip off from the hand. Thus, the object is able to be reliably gripped without breaking the object due to a gripping force. Particularly, when an object having the flexibility is gripped, breakage and deformation of the object is able to be reduced. The present disclosure relates to a technology that detects, in gripping an object, a state of "partial slip" before occurrence of a state of "whole slip" in which the object starts to slip, so as to grip the object with an appropriate gripping force.

<FIG> is a diagram illustrating a configuration of a hand <NUM> of a robot according to one embodiment of the present disclosure. The hand <NUM> is arranged at a leading end of an arm <NUM> of a robot. As illustrated in <FIG>, the hand <NUM> includes a body <NUM>, a link <NUM> and a link <NUM> constituting a first finger <NUM>, and a link <NUM> and a link <NUM> constituting a second finger <NUM>. Joints <NUM>, <NUM>, <NUM>, and <NUM> are provided with respective actuators. The link <NUM> is turned with respect to the link <NUM> by driving force of an actuator of the joint <NUM>, and the link <NUM> is turned with respect to the body <NUM> by driving force of an actuator of the joint <NUM>. Similarly, the link <NUM> is turned with respect to the link <NUM> by driving force of an actuator of the joint <NUM>, and the link <NUM> is turned with respect to the body <NUM> by driving force of an actuator of the joint <NUM>.

The arm <NUM> as one example includes multiple joints, and a plurality of links is turnably connected by the joints. Driving force of an actuator provided to each of the joints causes corresponding links to turn with respect to each other. Thus, the multiple-joint arm <NUM> is configured to have a predetermined degree of freedom, and further to be able to move the hand <NUM> to a desired position.

In <FIG>, there is illustrated a state where the first finger <NUM> and the second finger <NUM> grip an object (target gripped object) <NUM>. Distribution pressure sensors <NUM> and <NUM> are arranged inside (on object <NUM> side) of the link <NUM> of the first finger <NUM>. A first flexible layer <NUM> is arranged inside of the distribution pressure sensor <NUM>, and a second flexible layer <NUM> is arranged further inside of the distribution pressure sensor <NUM>. Similarly, distribution pressure sensors <NUM> and <NUM> are arranged inside (on object <NUM> side) of the link <NUM> of the second finger <NUM>. The first flexible layer <NUM> is arranged inside of the distribution pressure sensor <NUM>, and the second flexible layer <NUM> is arranged inside of the distribution pressure sensor <NUM>. The first flexible layer <NUM> and the second flexible layer <NUM> are made of an elastic material having one or both of the viscosity and the elasticity, are further made of a material that is easily deformed by a load applied from the outside, and made of material such as urethane gel and silicone gel. The first flexible layer <NUM> is made of a material whose friction coefficient is smaller than that of the second flexible layer <NUM>. A slip detecting device according to the present embodiment is constituted of the first and the second flexible layers <NUM> and <NUM> and the distribution pressure sensors <NUM> and <NUM>. The first and the second flexible layers <NUM> and <NUM> and the distribution pressure sensors <NUM> and <NUM> may be directly attached to the arm <NUM>. The first and the second flexible layers <NUM> and <NUM> and the distribution pressure sensors <NUM> and <NUM> may be attached to a leg of a robot so as to detect a slip state between the leg and the ground (floor). As described above, the first and the second flexible layers <NUM> and <NUM> and the distribution pressure sensors <NUM> and <NUM> may be attached to a working part with which a robot works on an object.

<FIG> is a diagram illustrating a state in which the first and the second flexible layers <NUM> and <NUM> of the first finger <NUM> are in contact with the object <NUM>. Note that the object <NUM> illustrated in <FIG> is spherical-shaped, on the other hand, the object <NUM> exemplified in <FIG> is rectangular parallelepiped-shaped. A direction of the x-axis illustrated in <FIG> is a direction (or direction in which object <NUM> is going to slip) in which the object <NUM> relatively slips with respect to the first and the second flexible layers <NUM> and <NUM>. As illustrated in <FIG>, the two flexible layers <NUM> and <NUM> are arranged such that the second flexible layer <NUM> and the first flexible layer <NUM> are arranged in this order in a slipping direction of the object <NUM>, and thus according to this arrangement, difference in an occurrence timing of a whole slip between the first flexible layer <NUM> and the second flexible layer <NUM> is able to be enlarged. In the example illustrated in <FIG>, the x-axis direction corresponds to the gravity direction.

As illustrated in <FIG>, a force Ft is applied to the object <NUM> in the x-axis direction. When the x-axis direction is the gravity direction, the force Ft corresponds to the gravity. A force Fn is applied to the object <NUM> in the y-axis direction that is perpendicular to the x-axis direction. The force Fn corresponds to a reaction force when the object <NUM> is gripped by the first finger <NUM> and the second finger <NUM>.

As illustrated in <FIG>, the force Ft is applied to the object <NUM> in the x-axis direction. In a case where the gravity direction is the x-axis direction, when a gripping force is weak with which the first finger <NUM> and the second finger <NUM> are gripping the object <NUM>, the object <NUM> slips off in the gravity direction. Transition from a state where the object <NUM> is stopped to a state where the object <NUM> starts to slip is able to be explained by phenomenon of "whole slip" and "partial slip".

The "whole slip" is a state in which a relative position between the object <NUM> and the flexible layer deviates, and thus an object is slipping off. The "partial slip" is a phenomenon that occurs before the "whole slip" and in which a part of a contact surface between the object <NUM> and the flexible layers <NUM> and <NUM> is slipping. In the present embodiment, "partial slip" is detected in which the object <NUM> is gripped with the minimum force having an extent to which the object <NUM> does not slip off when the object <NUM> is gripped.

<FIG> is a diagram schematically illustrating chronological change in a contact state between the flexible layers <NUM> and <NUM> and the object <NUM> from a state a to a state f during a time interval from a time at which the object <NUM> is gripped to a time at which the object <NUM> starts to slip in a model illustrated in <FIG>. In <FIG>, an upper surface of each of the flexible layers <NUM> and <NUM> is divided into a plurality of rectangular regions, and a contact state with the object <NUM> is classified into two of "sticking" and "slipping" by using two types of dots provided to the rectangular regions. In a rectangular region of "sticking", a slip does not occur between the object <NUM> and the flexible layers <NUM> and <NUM>, and thus the object <NUM> and the flexible layers <NUM> and <NUM> stick to each other. On the other hand, in a rectangular region of "slipping", a slip has occurred between the object <NUM> and the flexible layers <NUM> and <NUM>. The states of the rectangular regions may be obtained by analysis using simulation, for example. Hereinafter, on the basis of illustration of <FIG>, a state will be explained in which "partial slip" and "whole slip" occur during a time interval from a time at which the object <NUM> is gripped to a time at which the object <NUM> starts to slip.

A flexible layer arranged on the distribution pressure sensors <NUM> and <NUM> is divided into, for example, two parts of the first flexible layer <NUM> and the second flexible layer <NUM>, and by the division, the first flexible layer <NUM> and the second flexible layer <NUM> are aligned in a slipping direction (x-axis direction) of the object <NUM>. In the state a illustrated in <FIG>, all of the rectangular regions of upper surfaces of the first flexible layer <NUM> and the second flexible layer <NUM> are in a "sticking" state. Next, in the state b, rectangular regions in the upper surface of the first flexible layer <NUM> which are close to the second flexible layer <NUM> are changed into a "slipping" state. The other regions are in a "sticking" state.

Next, in the state c illustrated in <FIG>, in the upper surface of the first flexible layer <NUM>, rectangular regions in a "slipping" state have enlarged. In the next state d, all of the rectangular regions in the upper surface of the first flexible layer <NUM> are changed into a "slipping" state, and a part of rectangular regions in the upper surface of the second flexible layer <NUM> is changed into a "slipping" state. In the next state e, in the upper surface of the second flexible layer <NUM>, rectangular regions in a "slipping" state have enlarged. In the next state f, all of the rectangular regions in the upper surface of the second flexible layer <NUM> are changed into a "slipping" state.

When all of the rectangular regions in each of the first flexible layer <NUM> and the second flexible layer <NUM> are changed into a "slipping" state, a corresponding "whole slip" state appears. The first flexible layer <NUM> is turned into a "whole slip" state in the state d, and remains the "whole slip" state in the states e and f after the state d. On the other hand, the second flexible layer <NUM> is turned, later than the first flexible layer <NUM>, into a "whole slip" state in the state f.

As described above, in each of the first flexible layer <NUM> and the second flexible layer <NUM>, "slipping" regions are enlarged over time to turn into a "whole slip" state, and it is found that a timing at which the first flexible layer <NUM> having a low friction coefficient is turned into a "whole slip" state is earlier. In other words, when friction coefficients of the two flexible layers <NUM> and <NUM> are different from each other, it is possible to generate difference in an occurrence timing of a whole slip.

In the state f where a whole slip simultaneously occurs in two regions of the first flexible layer <NUM> and the second flexible layer <NUM>, a whole slip has occurred in all of the regions including the first flexible layer <NUM> and the second flexible layer <NUM>. In the state, the object <NUM> relatively moves with respect to both of the first flexible layer <NUM> and the second flexible layer <NUM>, and in <FIG>, the object <NUM> is slipping in the x-axis direction.

In the present embodiment, the states d and e in each of which a whole slip occurs in a region of one of the first flexible layer <NUM> and the second flexible layer <NUM>, and a whole slip does not occur in a region of the other are defined as a state where "partial slip" has occurred in all of the regions including the first flexible layer <NUM> and the second flexible layer <NUM>. In the states d and e in which "partial slip" has occurred, the object <NUM> does not relatively move with respect to the first flexible layer <NUM> and the second flexible layer <NUM>. In <FIG>, in order to indicate that the states d and e are in a "partial slip" state, the states d and e are surrounded by bold lines.

When focusing on a region of one of the first flexible layer <NUM> and the second flexible layer <NUM>, it may be interpreted that in a region of the first flexible layer <NUM> under the states b and c, or in a region of the second flexible layer <NUM> under the states d and e, a partial slip has occurred. However, in the present embodiment, when all of the regions including the first flexible layer <NUM> and the second flexible layer <NUM> are focused on, the states d and e in which a whole slip has occurred in a region of one of the flexible layers <NUM> and <NUM> and a whole slip has not occurred in a region of the other are defined as a state where "partial slip" has occurred in all of the regions.

Each of the states a to c in which a whole slip has not occurred in the first flexible layer <NUM> or the second flexible layer <NUM> is a state in which all of the regions including the first flexible layer <NUM> and the second flexible layer <NUM> are sticking to the object <NUM>.

Thus, each of the states d and e in which "partial slip" has occurred is a state just before the object <NUM> starts to slip, and the object <NUM> does not relatively move with respect to the first flexible layer <NUM> and the second flexible layer <NUM>. Thus, when a "partial slip" state is detected and an object is gripped with a gripping force having an extent to which a partial slip occurs, deformation and breakage of the object <NUM> is able to be reduced, and the object <NUM> is able to be gripped with an appropriate force with which the object <NUM> does not slip.

In the present embodiment, that "partial slip" or "whole slip" has occurred in all of the regions including the first flexible layer <NUM> and the second flexible layer <NUM> is determined on the basis of pressure-center positions obtained from the distribution pressure sensors <NUM> and <NUM>.

<FIG> is a characteristic diagram illustrating a state where a pressure-center position changes in each of regions of the first flexible layer <NUM> and the second flexible layer <NUM> in the states a to f illustrated in <FIG>. A pressure-center position Xcop is obtained from the following formula (<NUM>). Each of the distribution pressure sensors <NUM> and <NUM> includes a plurality of nodes for detecting the pressure, which is arranged in a matrix. In the formula (<NUM>), N is the number of sensor nodes of each of the distribution pressure sensors <NUM> and <NUM>, xi is a coordinate of an i-th node, and p(xi) is a pressure detected by the i-th node. The pressure-center position Xcop is a value obtained by dividing, by a total of pressure values, a total of values that are obtained by multiplying the pressure values by coordinates, and is a value indicating the pressure center of each of the distribution pressure sensors <NUM> and <NUM>.

In <FIG>, from the left, change in a pressure-center position of the second flexible layer <NUM>, change in a pressure-center position of the first flexible layer <NUM>, and change in the pressure-center positions of the first and the second flexible layers <NUM> and <NUM> are indicated in this order. In the three characteristic diagrams, a lateral axis is a number indicating the number of time steps, and a vertical axis indicates a pressure-center position. A pressure-center position of the vertical axis corresponds to a position in the x-axis direction illustrated in <FIG>. In the characteristic of the first flexible layer <NUM>, the origin of the vertical axis corresponds to the origin illustrated in <FIG>, and in the characteristic of the second flexible layer <NUM>, the origin of the vertical axis corresponds to a coordinate of -L illustrated in <FIG>. Assume that a length in the x-axis direction of the first flexible layer <NUM> and that of the second flexible layer <NUM> are the same (= L).

In <FIG>, a to f provided to the characteristic of a pressure-center position respectively correspond to the states a to f illustrated in <FIG>.

As illustrated in <FIG>, as time passes, each of pressure-center positions of the first and the second flexible layers <NUM> and <NUM> moves in the x-axis direction illustrated in <FIG>. In this case, a pressure-center position of the first flexible layer <NUM> having a lower friction coefficient moves faster than that of the second flexible layer <NUM>. In the first flexible layer <NUM>, at a time point when the number of time steps exceeds <NUM>, movement of a pressure-center position stops to be turned into a steady state in which the pressure-center position is a constant value. On the other hand, in the second flexible layer <NUM>, at a time point when the number of time steps exceeds <NUM>, movement of a pressure-center position stops to be turned into a steady state in which the pressure-center position is a constant value.

As illustrated in <FIG>, a state where movement of a pressure-center position is stopped in each of the first flexible layer <NUM> and the second flexible layer <NUM> corresponds to a "whole slip" state. On the other hand, a state where movement of a pressure-center position is not stopped in each of the first flexible layer <NUM> and the second flexible layer <NUM> is a state where the corresponding pressure-center position is moving due to shear deformation and a partial slip of the first flexible layer <NUM> or the second flexible layer <NUM>. In the state where movement of a pressure-center position is not stopped, a relative movement does not occur between the object <NUM> and the first flexible layer <NUM> and the second flexible layer <NUM>. On the other hand, in a state where movement of a pressure-center position is not stopped, in some cases, an absolute position of the object <NUM> is changed due to shear deformation of the first flexible layer <NUM> or the second flexible layer <NUM>. As described above, when friction coefficients of the two flexible layers <NUM> and <NUM> are different from each other, it is possible to generate difference in an occurrence timing of a whole slip, as obvious from <FIG>, an occurrence timing at which a whole slip of the second flexible layer <NUM> is later than that of the first flexible layer <NUM>.

The characteristic diagram illustrated on the right side of <FIG> is a characteristic diagram obtained by overlapping the characteristic diagram illustrated on the left side of <FIG> and the characteristic diagram illustrated in the center of <FIG>. In the present embodiment, on the basis of change in a pressure-center position, a state where a whole slip has occurred in the first flexible layer <NUM> in which a whole slip occurs earlier and a whole slip has not occurred in the second flexible layer <NUM> is determined to be a state where "partial slip" has occurred in a whole region including the first flexible layer <NUM> and the second flexible layer <NUM>. Furthermore, on the basis of change in a pressure-center position, a state where a whole slip has occurred in both of the first flexible layer <NUM> and the second flexible layer <NUM> is determined to be a state where "whole slip" has occurred in a whole region including the first flexible layer <NUM> and the second flexible layer <NUM>. Furthermore, on the basis of change in a pressure-center position, a state where a whole slip has not occurred in both of the first flexible layer <NUM> and the second flexible layer <NUM> is determined to be a sticking state.

As described above, when a pressure-center position is calculated in a region of each of the first flexible layer <NUM> and the second flexible layer <NUM>, a whole slip in the corresponding region is able to be detected. In the above-mentioned example, the number of regions is two, and thus when a whole slip simultaneously occurs in the two regions, the state is determined that a whole slip has occurred in a whole region including the first flexible layer <NUM> and the second flexible layer <NUM> (state f). When a whole slip has occurred in one of the regions, the state is determined that a partial slip has occurred in a whole region (states d and e). When a whole slip has not occurred in any of the regions, the state is determined that a whole region is in a "sticking state" (states a, b, and c).

Assume that a rate of a non-detection region of "whole slip" with respect to a whole region (contact region of target object <NUM>) including the first flexible layer <NUM> and the second flexible layer <NUM> is a sticking rate. In <FIG>, in the state f, with respect to a whole region including the first flexible layer <NUM> and the second flexible layer <NUM>, both of a region of the first flexible layer <NUM> and a region of the second flexible layer <NUM> are in a state of a whole slip, and thus a sticking rate is <NUM>%. In the states d and e, with respect to a whole region including the first flexible layer <NUM> and the second flexible layer <NUM>, a region of the first flexible layer <NUM> is in a state of a whole slip, and thus a sticking rate is <NUM>%. In the states a, b, and c, with respect to a whole region including the first flexible layer <NUM> and the second flexible layer <NUM>, none of a region of the first flexible layer <NUM> and a region of the second flexible layer <NUM> are in a state of a whole slip, and thus a sticking rate is <NUM>%.

In the present embodiment, a gripping force by the hand <NUM> is controlled in accordance with a sticking rate. As a sticking rate is larger, a gripping force by the hand <NUM> is more reduced, and as a sticking rate is smaller, a gripping force by the hand <NUM> is more increased. Thus, the object <NUM> is able to be gripped with the bare minimum force, so that it is possible to prevent breakage and deformation of the object <NUM>.

As the number of division in a region of the flexible layer is larger, the resolution of a sticking rate is larger, and further the accuracy of gripping force control is higher. Moreover, as the number of division in a region of the flexible layer is larger, with respect to a smaller object and an object having concavity and convexity, a sticking rate is able to be detected. For example, in a case where the number of division in the flexible layer is three, when a sticking rate is obtained by a method similar to the above-mentioned one, a sticking rate is able to be calculated with four steps of <NUM>%, <NUM>%, <NUM>%, and <NUM>%.

For example, in a case where the number of division in the flexible layer is three and a friction coefficient of each of the divided flexible layers are different from each other, when a whole slip has occurred in all of the flexible layers, a sticking rate is <NUM>%. When a whole slip has occurred in a region of a flexible layer whose friction coefficient is the smallest and a region of a flexible layer whose friction coefficient is the second smallest, and a whole slip has not occurred in a region of a flexible layer whose friction coefficient is the largest, a sticking rate is <NUM>%. When a whole slip has occurred in a region of a flexible layer whose friction coefficient is the smallest, and a whole slip has not occurred in a region of a flexible layer whose friction coefficient is the second smallest and a region of a flexible layer whose friction coefficient is the largest, a sticking rate is <NUM>%. Furthermore, when a whole slip has occurred in all of the regions of the flexible layers, a sticking rate is <NUM>%. From a similar viewpoint, as the number of division in a region of a flexible layer is more increased, a state of a partial slip is able to be detected with a higher accuracy.

<FIG> is a characteristic diagram illustrating, for comparison with <FIG>, a case where a friction coefficient of the first flexible layer <NUM> and that of the second flexible layer <NUM> are equalized to each other. Conditions other than a friction coefficient and an indicating method of characteristic diagrams are similar to those illustrated in <FIG>. As illustrated in <FIG>, when a friction coefficient of the first flexible layer <NUM> and that of the second flexible layer <NUM> are the same to each other, there presents no difference in an occurrence timing of a whole slip between a region of the first flexible layer <NUM> and a region of the second flexible layer <NUM>, and thus it is difficult to detect a partial slip in a whole region including the first flexible layer <NUM> and the second flexible layer <NUM>. Thus, a state according to the present embodiment illustrated in <FIG> where a sticking rate is <NUM>%, in other words, a state where "partial slip" has occurred in a whole region including the first flexible layer <NUM> and the second flexible layer <NUM> is not able to be detected. According to the present embodiment, a state where "partial slip" has occurred is able to be detected in a whole region including the first flexible layer <NUM> and the second flexible layer <NUM>, and thus a gripping force is able to be controlled with high accuracy on the basis of a sticking rate corresponding to a state of a partial slip.

Thus, when friction coefficients of the first flexible layer <NUM> and the second flexible layer <NUM> are different from each other, it is possible to generate difference in an occurrence timing of a whole slip between the first flexible layer <NUM> and the second flexible layer <NUM>, so that it is possible to detect a partial slip in a whole region including the first and the second flexible layers <NUM> and <NUM>. As difference in an occurrence timing of a whole slip between the first flexible layer <NUM> and the second flexible layer <NUM> is larger, a time interval during which a partial slip occurs in a whole region including the first and the second flexible layers <NUM> and <NUM> is longer, so that it is possible to easily control a gripping force.

In the above explanation, friction coefficients are made different from each other between the first flexible layer <NUM> and the second flexible layer <NUM> so as to make an occurrence timing of a whole slip different between the first flexible layer <NUM> and the second flexible layer <NUM>. On the other hand, parameters other than the friction coefficients may be made different from each other between the first flexible layer <NUM> and the second flexible layer <NUM>, so as to make an occurrence timing of a whole slip different between the first flexible layer <NUM> and the second flexible layer <NUM>. As parameters other than a friction coefficient, the Young's modulus, the Poisson ratio, thickness, a curvature radius, and the like may be exemplified.

In a case of a friction coefficient, as a friction coefficient is smaller, an occurrence timing of a whole slip is earlier. In a case of the Young's modulus, as the Young's modulus is larger, an occurrence timing of a whole slip is earlier. In a case of the Poisson ratio, as the Poisson ratio is smaller, an occurrence timing of a whole slip is earlier. In a case of the thickness, as the thickness is smaller, an occurrence timing of a whole slip is earlier. In a case of a curvature radius, as a curvature radius is larger, an occurrence timing of a whole slip is earlier.

In the above-mentioned parameters, when conditions both of whose occurrence timings of a whole slip are early, or conditions both of whose occurrence timings of a whole slip are late are combined with each other, it is possible to further increase difference in an occurrence timing of a whole slip. For example, when a first flexible layer whose friction coefficient is small and thickness is small and a second flexible layer whose friction coefficient is large and thickness is large are provided, it is possible to further increase difference in an occurrence timing of a whole slip between the first flexible layer and the second flexible layer.

<FIG> are diagrams illustrating dividing directions of the flexible layer. Similarly to <FIG> and <FIG>, in <FIG>, examples are illustrated in which the first flexible layer <NUM> and the second flexible layer <NUM> are divided into two parts in a slipping direction. In <FIG>, an example is illustrated in which the first flexible layer <NUM> and the second flexible layer <NUM> are divided into two parts in a direction perpendicular to the slipping direction.

When a vertical axis (z-axis illustrated in <FIG>) of the object <NUM> to be gripped is restricted with respect to a slipping direction of the object <NUM>, there presents no difference in an occurrence timing of a complete slip between the first flexible layer <NUM> and the second flexible layer <NUM>. On the other hand, when the vertical axis is not restricted, an axial rotation is slightly generated due to friction distribution, and thus difference in an occurrence timing of a complete slip is larger when the first flexible layer <NUM> and the second flexible layer <NUM> are vertically divided with respect to a slipping direction. In an actual environment, there presents no situation in which an axis of an object is restricted, and thus a case is more preferable in which the first flexible layer <NUM> and the second flexible layer <NUM> are divided with respect to a slipping direction, as illustrated in <FIG>. Moreover, a case illustrated in <FIG> in which the second flexible layer <NUM> and the first flexible layer <NUM> are arranged in this order with respect to a slipping direction of the object <NUM> has a larger difference in an occurrence timing of a whole slip than a case illustrated in <FIG> in which the first flexible layer <NUM> and the second flexible layer <NUM> are arranged in this order with respect to a slipping direction of the object <NUM>. In other words, when the second flexible layer <NUM> having a larger friction coefficient is arranged on an upper flow side of a slipping direction, difference in an occurrence timing of a whole slip between the first flexible layer <NUM> and the second flexible layer <NUM> is able to be larger. In a case of arrangement illustrated in <FIG>, a slipping force of the first flexible layer <NUM> positioned on an upper flow side of a slipping direction is stopped by the second flexible layer <NUM> positioned on a lower flow side, and thus an occurrence timing of a whole slip in the first flexible layer <NUM> becomes comparatively late. Thus, in a case of arrangement illustrated in <FIG>, difference in an occurrence timing of a whole slip between the first flexible layer <NUM> and the second flexible layer <NUM> becomes comparatively small. On the other hand, in a case of arrangement illustrated in <FIG>, a slipping force of the second flexible layer <NUM> positioned on an upper flow side of a slipping direction is not stopped by the first flexible layer <NUM> positioned on a lower flow side, and thus a whole slip occurs at a comparatively early timing in the first flexible layer <NUM> positioned on a lower flow side. Thus, in a case of arrangement illustrated in <FIG>, difference in an occurrence timing of a whole slip is able to be larger.

The plurality of flexible layers may be arranged to be adjacent to each other. For example, as illustrated in <FIG> to be mentioned later, the first flexible layer <NUM> and the second flexible layer <NUM> may be separately and respectively arranged in different fingers of the hand <NUM>.

<FIG> is a diagram illustrating a configuration example of a control system (controller) <NUM> of a robot according to one embodiment of the present disclosure. As illustrated in <FIG>, the control system <NUM> is configured to include a recognizing/planning unit <NUM>, a gripping-force calculating unit <NUM>, and a control unit <NUM>. The recognizing/planning unit <NUM> includes a recognition unit <NUM>, a command unit <NUM>, a gripping-position deciding unit <NUM>, and an operation planning unit <NUM>. The gripping-force calculating unit <NUM> includes a pressure acquiring unit <NUM>, a touch detecting unit <NUM>, a pressure-center-position calculating unit <NUM>, a pressure-center movement-amount calculating unit <NUM>, a whole-slip detecting unit <NUM>, a sticking-rate calculating unit <NUM>, and a gripping-force controlling unit <NUM>. The control unit <NUM> includes an overall control unit <NUM> and a hand controlling unit <NUM>.

The recognizing/planning unit <NUM> recognizes the object <NUM> to be gripped by a robot, and creates a plan for gripping the object <NUM>. The recognition unit <NUM> is constituted of a camera, a Time of Flight (ToF) sensor, etc. so as to recognize a three-dimensional shape of the object <NUM>. A command from a user is input to the command unit <NUM>. The gripping-position deciding unit <NUM> decides, by using recognition result of a target object by the recognition unit <NUM>, a position of a robot for gripping the object <NUM> on the basis of a command of a user which is input to the command unit <NUM>. On the basis of a gripping position decided by the gripping-position deciding unit <NUM>, the operation planning unit <NUM> creates a plan of operation of the arm <NUM> and operation of the hand <NUM> arranged at a leading end of the arm <NUM> of the robot.

The gripping-force calculating unit <NUM> calculates a gripping force of the hand <NUM> for gripping the object <NUM> so as to control the gripping force. The pressure acquiring unit <NUM> acquires a pressure detected by the distribution pressure sensors <NUM> and <NUM>. The touch detecting unit <NUM> detects, by using a distribution pressure value acquired by the pressure acquiring unit <NUM>, contact between the first and the second flexible layers <NUM> and <NUM> and the object <NUM>. For example, when a distribution pressure value is equal to or more than a predetermined value, the touch detecting unit <NUM> detects contact between the first and the second flexible layers <NUM> and <NUM> and the object <NUM>. The pressure-center-position calculating unit <NUM> calculates, by using a distribution pressure value acquired by the pressure acquiring unit <NUM>, a pressure-center position XCOP in accordance with the above-mentioned formula (<NUM>) in a region of each of the first and the second flexible layers <NUM> and <NUM>.

The pressure-center movement-amount calculating unit <NUM> calculates, by using a pressure-center position calculated by the pressure-center-position calculating unit <NUM>, a movement amount of a pressure-center position in a region of each of the first and the second flexible layers <NUM> and <NUM>. The pressure-center movement-amount calculating unit <NUM> calculates a movement amount ΔXCOP of a pressure-center position by the following formula (<NUM>). The right side of the formula (<NUM>) indicates a difference between the pressure-center position XCOP at a time point t+<NUM> and the pressure-center position XCOP at a time point t.

The whole-slip detecting unit <NUM> detects, by using a movement amount of a pressure-center position calculated by the pressure-center movement-amount calculating unit <NUM>, whether or not there presents a change in movement of a pressure-center position during a preliminary-set time window. The time window is a predetermined time interval that has been preliminary set. When there presents no movement of a pressure-center position during the predetermined time interval, the whole-slip detecting unit <NUM> detects that the pressure-center position is not changed and a whole slip has occurred. The whole-slip detecting unit <NUM> monitors change in a pressure-center position for each of the regions of the two distribution pressure sensors <NUM> and <NUM>, so as to detect occurrence of a whole slip in each of the regions.

The sticking-rate calculating unit <NUM> calculates a rate of a non-detection region of a whole slip with respect to a whole region including the first flexible layer <NUM> and the second flexible layer <NUM>, and employs the calculated rate as a sticking rate. As described above, when the flexible layer is divided into two parts, the sticking rate is calculated as three-type values of <NUM>%, <NUM>%, and <NUM>%.

The gripping-force controlling unit <NUM> decides a gripping force such that a sticking rate is a constant value. The gripping-force controlling unit <NUM> controls, by feedback control, a gripping force such that a sticking rate calculated by the sticking-rate calculating unit <NUM> is a predetermined value. As one example, the gripping-force controlling unit <NUM> controls a gripping force such that a sticking rate is <NUM>%.

The control unit <NUM> controls operation of a robot. On the basis of an operation plan created by the operation planning unit <NUM>, the overall control unit <NUM> controls the arm <NUM> of the robot. On the basis of control of the gripping-force controlling unit <NUM>, the hand controlling unit <NUM> controls the hand <NUM>. Note that the gripping-force controlling unit <NUM> and the hand controlling unit <NUM> may be integrated with each other.

Each of the configuration elements of the recognizing/planning unit <NUM>, the gripping-force calculating unit <NUM>, and the control unit <NUM> of the control system <NUM> illustrated in <FIG> may be constituted of a circuit (hardware) or a center calculation processing device such as a Central Processing Unit (CPU) and a program (software) that causes the CPU to function. The program may be stored in a memory provided to the control system <NUM>, or a recording medium, such as a memory, which is connected to the control system <NUM> from the outside thereof. The same may be applied to <FIG>, <FIG>, and <FIG> to be mentioned later.

Hereinafter, a few modifications of the present embodiment will be explained.

In a modification <NUM>, physical information (rigidity) on the object <NUM> is calculated from a position of the hand <NUM> at a moment when the object <NUM> is in contact with a flexible layer and then the flexible layer is pressed against the object <NUM>, or information on a contact area and a contact force between the flexible layer and the object <NUM>. A gripping-force controlling gain is adjusted on the basis of the physical information on the object <NUM>. The gripping-force controlling gain is an increase rate when a gripping force is increased such that a sticking rate is a constant value.

<FIG> is a diagram illustrating a configuration of the gripping-force calculating unit <NUM> according to the modification <NUM>. As illustrated in <FIG>, the gripping-force calculating unit <NUM> according to the modification <NUM> includes, in addition to the configuration illustrated in <FIG>, a contact-force calculating unit <NUM>, a contact-node-number acquiring unit (contact-radius calculating unit) <NUM>, and a physical-information calculating unit <NUM>.

The contact-force calculating unit <NUM> calculates a contact force when the object <NUM> is in contact with the first and the second flexible layers <NUM> and <NUM>. The contact force is obtained by multiplying the number of contact nodes of all of the nodes of the distribution pressure sensors <NUM> and <NUM> by a force (pressure) applied to each of the contact nodes. The contact node is a node of the distribution pressure sensors <NUM> and <NUM> which is in contact with the object <NUM> via the first flexible layer <NUM> or the second flexible layer <NUM>. In other words, the contact node is a node from which a detection value (detection value is not zero) of the pressure is obtained.

On the basis of contact between the first and the second flexible layers <NUM> and <NUM> and the object <NUM> which is detected by the touch detecting unit <NUM>, the contact-node-number acquiring unit <NUM> acquires a contact node number. The contact node number corresponds to a contact area. From information on a contact area acquired from the contact-node-number acquiring unit <NUM> and information on a contact force acquired from the contact-force calculating unit <NUM>, the physical-information calculating unit <NUM> calculates rigidity as physical information on the object <NUM>.

From a contact radius a when the object <NUM> is in contact with a flexible layer, the rigidity is able to be calculated as physical information on the object <NUM>. In this case, a contact-radius calculating unit is caused to function instead of the contact-node-number acquiring unit <NUM>. From the Hertz contact theory, the contact radius a between a robot finger (first finger <NUM> or second finger <NUM>) and an object is able to be indicated by the following formula (<NUM>).

Note that r is a radius of a robot finger, and E* is an effective elastic modulus. As indicated in the following formula (<NUM>), the effective elastic modulus E* is obtained by elastic moduli Ef and Eo and respective Poisson ratios vf and vo of the robot finger and the object.

The Poisson ratio is a value that is not more than approximately <NUM> and is commonly a smaller value, and thus the Poisson ratio is able to be neglected as indicated in a formula (<NUM>) by assuming that a value of the square of the Poisson ratio does not largely affect E*.

A radius r of a robot finger and the Young's modulus Ef of the robot finger are already known, and thus on the basis of the contact radius a calculated by the contact-radius calculating unit <NUM> and information on a contact force Fn, physical information (Young's modulus Eo) on the object <NUM> is able to be calculated by the formula (<NUM>).

The rigidity as physical information on the object <NUM> is transmitted to the gripping-force controlling unit <NUM>. The gripping-force controlling unit <NUM> adjusts a gripping-force controlling gain on the basis of the physical information. As described above, a gripping-force controlling gain is an increase rate when a gripping force is increased such that a sticking rate is a predetermined constant value. When the rigidity of the object <NUM> is high, probability that deformation or breakage occurs in the object <NUM> is comparatively low, and thus the gripping-force controlling unit <NUM> sets an increase rate of a gripping force to be high when controlling a sticking rate such that the sticking rate is a target value. On the other hand, when the rigidity of the object <NUM> is low, probability that deformation or breakage occurs in the object <NUM> is comparatively high, and thus the gripping-force controlling unit <NUM> sets an increase rate of a gripping force to be low when controlling a sticking rate such that the sticking rate is a target value.

According to the modification <NUM>, the above-mentioned state of a partial slip is detected, a gripping force is able to be controlled with the bare minimum force having an extent to which the object <NUM> does not slip, and further an increase rate of a gripping force is able to be controlled in accordance with the hardness of the object <NUM>. Thus, it is possible to reliably reduce deformation and breakage of the object <NUM> in gripping.

When obtaining a rigidity of the object <NUM>, the rigidity may be obtained by relation between a position (pressed amount) of the hand <NUM> and a contact force obtained from the distribution pressure sensors <NUM> and <NUM> when a flexible layer is pressed against the object <NUM>.

In a modification <NUM>, a position and a posture of a finger are controlled in order to increase difference in an occurrence timing of a whole slip between the first flexible layer <NUM> and the second flexible layer <NUM>. Herein, as pressure distribution is steeper when the flexible layers <NUM> and <NUM> are in contact with the object <NUM>, an occurrence timing of a whole slip is later. <FIG> are characteristic diagrams illustrating examples of pressure distribution when the flexible layers <NUM> and <NUM> are in contact with the object <NUM>. <FIG>, <FIG> are aligned in the decreasing order of steepness of a pressure distribution. That a pressure distribution is steep means that a pressure gradient is large in an end part of a region (region A1 illustrated in <FIG>) in which the flexible layers <NUM> and <NUM> and the object <NUM> are in contact with each other.

In <FIG>, a region in which the pressure is high is a region in which the flexible layers <NUM> and <NUM> are in contact with the object <NUM>. In an end part of a region in which the flexible layers <NUM> and <NUM> and the object <NUM> are in contact with each other, a gradient is generated in the pressure. As the pressure gradient is larger, an occurrence timing of a whole slip is later.

For example, in a region in which the flexible layers <NUM> and <NUM> and the object <NUM> are in contact with each other, a shape of the object <NUM> has a convex surface, and as a curvature radius of the convex surface is smaller, a pressure gradient is steeper and an occurrence timing of a whole slip is later.

In the modification <NUM>, the hand <NUM> is controlled such that the first flexible layer <NUM> and the second flexible layer <NUM> are arranged in respective positions having different pressure gradients for each of the first flexible layer <NUM> and the second flexible layer <NUM>.

<FIG> is a diagram illustrating a configuration of the gripping-force calculating unit <NUM> according to the modification <NUM>. As illustrated in <FIG>, the gripping-force calculating unit <NUM> according to the modification <NUM> includes a pressure-gradient calculating unit <NUM> and an actuator controlling unit <NUM> in addition to the configuration illustrated in <FIG>.

When contact between the first and the second flexible layers <NUM> and <NUM> and the object <NUM> is detected by the touch detecting unit <NUM>, the pressure-gradient calculating unit <NUM> acquires the features illustrated in <FIG> on the basis of pressures detected by the distribution pressure sensors <NUM> and <NUM>. The pressure-gradient calculating unit <NUM> calculates a pressure gradient of the region A1 illustrated in <FIG>. Note that pressures detected by the distribution pressure sensors <NUM> and <NUM> are acquired by the pressure acquiring unit <NUM>, and are transmitted to the pressure-gradient calculating unit <NUM>.

On the basis of a pressure gradient calculated by the pressure-gradient calculating unit <NUM>, the actuator controlling unit <NUM> controls an actuator that controls the hand <NUM> or the arm <NUM>. The actuator controlling unit <NUM> controls the actuator such that the object <NUM> is gripped at a position where difference in a pressure gradient is larger in a contact part between the first flexible layer <NUM> and the second flexible layer <NUM> and the object <NUM>.

<FIG> is a diagram illustrating a specific control of the hand <NUM>. In <FIG>, a state before a position and a posture of a finger are controlled in accordance with pressure gradient is illustrated in a left part, and a state after a position and a posture of a finger are controlled in accordance with pressure gradient is illustrated in a right part. In <FIG>, the first flexible layer <NUM> and the distribution pressure sensor <NUM> are provided to the first finger <NUM>, and the second flexible layer <NUM> and the distribution pressure sensor <NUM> are provided to the second finger <NUM>. Thus, in <FIG>, an example is illustrated in which the first flexible layer <NUM> and the second flexible layer <NUM> are not divided in a slipping direction of the object <NUM>.

Before a position and a posture of a finger are controlled, a contact surface of the object <NUM> is a curved surface for each of the first flexible layer <NUM> and the second flexible layer <NUM>. On the other hand, after a position and a posture of a finger are controlled, a contact surface of the object <NUM> is a curved surface for the second flexible layer <NUM>; however, a contact surface of the object <NUM> is a plane for the first flexible layer <NUM>.

As described above, a friction coefficient of the first flexible layer <NUM> is smaller than a friction coefficient of the second flexible layer <NUM>, and thus an occurrence timing of a whole slip of the second flexible layer <NUM> is later. Additionally, after a position and a posture of a finger is controlled, a contact surface of the object <NUM> is a plane for the first flexible layer <NUM>, and a contact surface of the object <NUM> is a curved surface for the second flexible layer <NUM>. Thus, a pressure distribution in the second flexible layer <NUM> is steeper than a pressure distribution of the first flexible layer <NUM>, and thus an occurrence timing of a whole slip in the second flexible layer <NUM> is further later. Thus, difference in an occurrence timing of a whole slip is able to be larger between the first flexible layer <NUM> and the second flexible layer <NUM>.

In the above-mentioned example, the example is indicated in which a position and a posture of a finger of the hand <NUM> is controlled in accordance with pressure gradient; however, a position and a posture of a finger of the hand <NUM> may be controlled on the basis of three-dimensional information on the object <NUM> which is obtained by observing a shape of the object <NUM> by using the recognition unit <NUM>. In this case, on the basis of the three-dimensional information, the first flexible layer <NUM> may be caused to be in contact with a part having a small pressure gradient and the second flexible layer <NUM> may be caused to be in contact with a part having a large pressure gradient.

As described above, it is more preferable that the first flexible layer <NUM> and the second flexible layer <NUM> are divided in a slipping direction of the object <NUM>. In a modification <NUM>, when a plurality of slipping directions of the object <NUM> is supposed in accordance with a posture of the hand <NUM> and/or the arm <NUM>, division is executed which does not depend on a slipping direction.

<FIG> is a diagram illustrating a division example of a flexible layer. In the example illustrated in <FIG>, the Young's modulus is different for each of a plurality of flexible layers <NUM>, <NUM>, <NUM>, and <NUM>. The flexible layers <NUM>, <NUM>, <NUM>, and <NUM> are divided by circular boundaries, and the closer to the center, the smaller the Young's modulus is. According to such a division method, it is possible to correspond to slips in multiple directions which are indicated in <FIG> by using a plurality of arrows, and for each of the slipping directions, a flexible layer is divided in a corresponding slipping direction.

As described above, in a parameter that makes an occurrence timing of a whole slip different for each flexible layer, when conditions whose occurrence timings of a whole slip are early, or conditions whose occurrence timings of a whole slip are late are combined with each other, it is possible to further increase difference in an occurrence timing of a whole slip.

Thus, in the example illustrated in <FIG>, a condition of thickness and a condition of the Young's modulus are combined, and thicknesses of the flexible layers <NUM>, <NUM>, <NUM>, and <NUM> and the Young's modulus are set such that the closer to the center a flexible layer is, the larger a thickness thereof is and further the smaller the Young's modulus thereof is. Hence, the larger the Young's modulus is, the earlier an occurrence timing of a whole slip is, and the smaller a thickness is, the earlier an occurrence timing of a whole slip is, and thus in <FIG>, the closer to a periphery a flexible layer is, the earlier an occurrence timing of a whole slip is and the closer to the center of a flexible layer is, the later an occurrence timing of a whole slip is.

Regarding parameters for making an occurrence timing of a whole slip different, thickness and the Young's modulus are combined, and the peripheral flexible layer <NUM> whose Young's modulus is large is used for the heavy object <NUM> that requires a large gripping force, on the other hand, the center flexible layer <NUM> alone whose Young's modulus is small is used for gripping the light and fragile object <NUM> that does not require a large gripping force. Thus, it is possible to use an appropriate flexible layer in accordance with an object to be gripped.

<FIG> is a plan view illustrating a division example that does not depend on a position in contact with the object <NUM>. In the example illustrated in <FIG>, a flexible layer <NUM> whose Young's modulus is small and a flexible layer <NUM> whose Young's modulus is large are used. As illustrated in the plan view, the flexible layers <NUM> and the flexible layers <NUM> are alternately zigzag arranged. In <FIG>, the flexible layers <NUM> and <NUM> having different two respective Young's moduli are illustrated; however, flexible layers having different three respective Young's moduli may be arranged. In this case, when flexible layers are arranged such that in <FIG>, Young's moduli of flexible layers that are adjacent to each other in a row direction and in a column direction are different from each other, zigzag arrangement is obtained even when flexible layers having three or more different Young's moduli are arranged. When the flexible layers <NUM> and <NUM> having two different respective Young's moduli are arranged, in <FIG>, flexible layers may be arranged such that Young's moduli of the flexible layers on the same row or the same column are the same and the Young's moduli are different for each row or column.

As described above, the larger the number of division in a region is, the resolution of a sticking rate increases, so that the accuracy of gripping force control is improved. The larger the number of division in a region is, detection of a sticking rate is able to be executed with respect to a smaller object and an object having concavity and convexity. However, the number of division depends on a pitch width between nodes of a distribution pressure sensor, and when the number of division is to be more increased, there presents a limit in terms of hardware. Thus, as illustrated in <FIG>, in order to artificially reduce a pitch width between nodes of two distribution pressure sensors <NUM> and <NUM>, the distribution pressure sensors <NUM> and <NUM> are laminated in a displaced manner.

In the example illustrated in <FIG>, from the top, there are illustrated three methods of a case (example (a)) where the two distribution pressure sensors <NUM> and <NUM> are displaced to each other in an alignment direction (x-axis direction) of nodes, a case (example (b)) where the two distribution pressure sensors <NUM> and <NUM> are displaced to each other in alignment directions (x-axis direction and y-axis direction) of nodes, and a case (example (c)) where the distribution pressure sensor <NUM>, which is one of the two distribution pressure sensors, is rotated by <NUM>° and overlapped with the other of the two distribution pressure sensors.

In the example (a) illustrated in <FIG>, the distribution pressure sensors <NUM> and <NUM> are arranged by displacing them to each other in the x-axis direction by <NUM>/<NUM> width of a node. In the example (b) illustrated in <FIG>, the distribution pressure sensors <NUM> and <NUM> are arranged by displacing them to each other in the x-axis direction and the y-axis direction by <NUM>/<NUM> width of a node. The arrangement and the overlapping method of the distribution pressure sensors are not limited to the examples illustrated in <FIG>.

As described above, when the distribution pressure sensors <NUM> and <NUM> are arranged by displacing them to each other, it is possible to artificially reduce a pitch width between nodes and to increase the number of division in a region.

As described above, as a method for delaying an occurrence timing of a whole slip, there presents a method for increasing a thickness of the flexible layer. On the other hand, when a thickness of a flexible layer is large, there presents a problem that the sensitivity of the distribution pressure sensor is reduced.

In the modification <NUM>, as illustrated in <FIG>, a part of a thickness of a flexible layer <NUM> arranged upper than a distribution pressure sensor <NUM> is arranged lower than the distribution pressure sensor <NUM>, and thus the distribution pressure sensor <NUM> is arranged vertically between flexible layers <NUM> and <NUM>. Movement of a pressure-center position depends on a total of thicknesses of the flexible layers <NUM> and <NUM>, on the other hand, detection sensitivity depends on the flexible layer <NUM> arranged upper than the distribution pressure sensor <NUM>, and thus an occurrence timing of a whole slip is able to be delayed without reducing detection sensitivity of the distribution pressure sensor <NUM>.

<FIG> is a diagram illustrating detection sensitivity by the distribution pressure sensor <NUM> in accordance with difference in thickness of a flexible layer. In <FIG>, there are illustrated detection sensitivity (examples (a) to (c)) when three types of the flexible layers <NUM> having different thickness are arranged on the distribution pressure sensor <NUM> and detection sensitivity when the distribution pressure sensor <NUM> is arranged vertically between the flexible layers <NUM> and <NUM> (modification <NUM>).

In the example (a) illustrated in <FIG>, the flexible layer <NUM> having a thickness of <NUM> is arranged on the distribution pressure sensor <NUM>. In the example (b) illustrated in <FIG>, the flexible layer <NUM> having a thickness of <NUM> is arranged on the distribution pressure sensor <NUM>, and in the example (c) illustrated in <FIG>, the flexible layer <NUM> having a thickness of <NUM> is arranged on the distribution pressure sensor <NUM>.

In an example of the modification <NUM> illustrated in <FIG>, the flexible layer <NUM> having a thickness of <NUM> is arranged on the distribution pressure sensor <NUM>, and the flexible layer <NUM> having a thickness of <NUM> is arranged under the distribution pressure sensor <NUM>.

In <FIG>, with respect to the examples (a) to (c) and the modification <NUM>, a pressure detected by the distribution pressure sensor <NUM> and a standard deviation thereof are indicated. As indicated in the examples (a) to (c), it is found that the larger a thickness of the flexible layer <NUM> arranged upper than the distribution pressure sensor <NUM> is, the larger a standard deviation of detection values of the pressure is and the more detection sensitivity of the distribution pressure sensor <NUM> is reduced.

On the other hand, as illustrated in <FIG>, in the modification <NUM>, although a total thickness of the flexible layer <NUM> and the flexible layer <NUM> is the same as that of the example (c), a thickness of the flexible layer <NUM> arranged upper than the distribution pressure sensor <NUM> is <NUM>, and thus a standard deviation of detection values of the pressure is restrained. Thus, according to the modification <NUM>, detection sensitivity is able to be obtained, which is similar to that of at least the example (a).

<FIG> is a characteristic diagram illustrating states of the examples (a) to (c) and the modification <NUM> that are illustrated in <FIG>, in which a pressure-center position changes similarly to that of <FIG>. As indicated by the examples (a) to (c) illustrated in <FIG>, the larger a thickness of the flexible layer <NUM> arranged on the distribution pressure sensor <NUM> is, the more an occurrence timing of a whole slip delays.

As illustrated in <FIG>, an occurrence timing of a whole slip of the modification <NUM> is a timing similar to that of the example (c). Therefore, according to the modification <NUM>, a thickness of the flexible layer <NUM> arranged upper than the distribution pressure sensor <NUM> is equalized to that of the flexible layer <NUM> of the example (a), so that it is possible to ensure detection sensitivity equivalent to that of the example (a). Moreover, according to the modification <NUM>, a total thickness of the flexible layers <NUM> and <NUM> vertically between which the distribution pressure sensor <NUM> is interposed is equivalent to that of the flexible layer <NUM> of the example (c), so that it is possible to equalize an occurrence timing of a whole slip of the modification <NUM> to that of the example (c).

In the feature of the modification <NUM> illustrated in <FIG>, a moving direction of a pressure-center position is reverse to those of the examples (a) to (c). This is caused by effects of pressure applied to a top and a bottom of the distribution pressure sensor <NUM>.

<FIG> are diagrams illustrating a reason that a moving direction of a pressure-center position of the modification <NUM> is reverse to those of the examples (a) to (c). In each of <FIG>, there are illustrated a state (left part) where the object <NUM> is not gripped and a state (right part) where the object <NUM> is gripped, and a state where the object <NUM> is gripped and the corresponding flexible layer is deformed. In <FIG>, an arrow A11 indicates a direction in which the object <NUM> is going to slip. Note that, for convenience of explanation, illustration of the object <NUM> is omitted in <FIG>.

<FIG> illustrates the example (a), and a state is illustrated in which the object <NUM> is going to slip in a direction of the arrow A11 and the flexible layer <NUM> is deformed in the direction of the arrow A11. In this case, there does not present the flexible layer <NUM> in a region A3 illustrated in <FIG> and the pressure becomes small, and thus in a pressure detection value of the distribution pressure sensor <NUM>, a pressure is small in a left edge and a pressure is large in a right edge of the distribution pressure sensor <NUM>. Thus, as illustrated in <FIG>, a pressure-center position moves toward a positive direction of the x-axis.

On the other hand, the modification <NUM> is illustrated in <FIG>, and a state is illustrated in which the object <NUM> is going to slip in a direction of the arrow A11 and the flexible layer <NUM> and the flexible layer <NUM> are deformed in the direction of the arrow A11. In this case, there does not present the flexible layer <NUM> in a region A4 illustrated in <FIG> and the pressure becomes small, and thus in a pressure detection value of the distribution pressure sensor <NUM>, a pressure is small in a right edge and a pressure is large in a left edge of the distribution pressure sensor <NUM>. Thus, as illustrated in <FIG>, a pressure-center position moves toward a negative direction of the x-axis. In <FIG>, a moving direction of a pressure-center position is different from those of the examples (a) to (c) illustrated in <FIG> and <FIG>; however, a method itself for determining that a whole slip occurs at a time point when movement of a pressure-center position is stopped is similar to those of the examples (a) to (c) illustrated in <FIG> and <FIG>.

As a method for changing a friction coefficient a flexible layer, in addition to a method for changing material, there are considered a method for micro-fabricating a surface of a flexible layer and a method for coating a surface of a flexible layer. Thus, even when a plurality of flexible layers is made of the same material, various distributions of friction coefficients are able be generated.

Furthermore, there is exemplified a method for changing a surface area of a region of each of the flexible layers in order to change the frictional force of the corresponding flexible layer. The larger a surface area of a flexible layer is, the larger the frictional force is.

<FIG> is a diagram illustrating an example in which a surface area of the flexible layer is changed. An area of a center flexible layer <NUM> is larger than an area of a peripheral flexible layer <NUM>, and thus the frictional force of the center flexible layer <NUM> is larger than the frictional force of the peripheral flexible layer <NUM>. Thus, it is possible to make an occurrence timing of a whole slip different between the flexible layer <NUM> and the flexible layer <NUM>.

Similarly to the modification <NUM> illustrated in <FIG>, <FIG> illustrates an example in which the distribution pressure sensor <NUM> is arranged vertically between the flexible layers <NUM> and <NUM>, and further illustrates a method for changing the hardness of the flexible layer <NUM> arranged lower than the distribution pressure sensor <NUM> in order to change the frictional force of the flexible layer <NUM> arranged upper than the distribution pressure sensor <NUM>. In <FIG>, the hardness of the flexible layer <NUM> arranged lower than the distribution pressure sensor <NUM> are changed into three types of low (flexible layer 572a), middle (flexible layer 572b), and high (flexible layer 572c).

When change amounts of the flexible layers 572a to 572c are constant, the reaction forces Fn generated in the flexible layers 572a to 572c are different from each other, and thus a distribution of the frictional forces Ft (= Fn × µ · Fn) generated in flexible layers 574a to 574c is able to be generated. Thus, replacement of a flexible layer in a surface is facilitated.

In a modification <NUM>, linear flexible layers are arranged instead of dividing a flexible layer. <FIG> is a diagram illustrating a configuration example using linear flexible layers <NUM> and <NUM> according to the modification <NUM>. As illustrated in <FIG>, the linear flexible layers <NUM> and <NUM> are arranged on distribution pressure sensors <NUM> and <NUM>. The flexible layer <NUM> is arranged on the distribution pressure sensor <NUM>, and the flexible layer <NUM> is arranged on the distribution pressure sensor <NUM>. The flexible layer <NUM> is made of a material whose friction coefficient is larger than that of the flexible layer <NUM>.

In <FIG>, there is illustrated a state where the object <NUM> is gripped by using the flexible layers <NUM> and <NUM>. Thus, the object <NUM> is in contact with the flexible layers <NUM> and <NUM> from thereon.

<FIG> illustrates chronological movements at a time point t1, a time point t2, and a time point t3. The time point t1 indicates a sticking state. In this state, leading ends of the flexible layers <NUM> and <NUM> are uniformly directed toward the left.

Next, the time point t2 indicates a state where a partial slip has occurred on the object <NUM>. In this state, leading ends of the flexible layers <NUM> whose friction coefficients are small are directed toward the right. On the other hand, leading ends of the flexible layers <NUM> whose friction coefficients are large keep a state directed to the left. In a case where a slip has partially occurred, when a direction of the flexible layers <NUM> that is a slipping regional portion is changed, the pressure of the region becomes small, and thus the distribution pressure sensor <NUM> is able to detect the change.

Next, the time point t3 indicates a state where a whole slip has occurred on the object <NUM>. In this state, the object <NUM> is slipping in the right direction, and leading ends of the flexible layers <NUM> and <NUM> are uniformly directed to the right.

<FIG> is a diagram illustrating a configuration of the gripping-force calculating unit <NUM> using the linear flexible layers <NUM> and <NUM> illustrated in <FIG>. The pressure acquiring unit <NUM> acquires pressure detected by the distribution pressure sensors <NUM> and <NUM>. The whole-slip detecting unit <NUM> monitors change in pressure of the linear flexible layers <NUM> and <NUM> so as to detect a slip in each of the flexible layers <NUM> and <NUM>. As described above, at the time point t2 illustrated in <FIG>, a pressure detection value of the distribution pressure sensor <NUM> alone which is corresponding to the flexible layer <NUM> is reduced, so that it is possible to detect a state of a partial slip. The sticking-rate calculating unit <NUM> calculates a rate of a non-detection region of a partial slip to all of the regions. The gripping-force controlling unit <NUM> decides a gripping force such that a sticking rate calculated by the sticking-rate calculating unit <NUM> is a constant value.

When a pressure detection value is reduced, a whole slip is able to be detected. Change in pressure in each of the linear flexible layers <NUM> and <NUM>, which is acquired by the pressure acquiring unit <NUM>, is monitored, and when the pressure exceeds a threshold value, a whole slip is detected. The sticking-rate calculating unit <NUM> calculates a rate of a non-detection region of a whole slip to all of the regions. In the example illustrated in <FIG>, a whole slip occurs in the flexible layer <NUM> alone at the time point t2, and the flexible layer <NUM> is in a sticking state. The total number of the flexible layers <NUM> and <NUM> is seven, the number of the flexible layers <NUM> is four, and thus a sticking rate is <NUM>% {= (<NUM>/<NUM>) × <NUM>}.

<FIG> is a diagram illustrating an example in which the flexible layers <NUM> and <NUM> are arranged in multiple directions in the configuration using the linear flexible layers <NUM> and <NUM> illustrated in <FIG>. As indicated by the state at the time point t1 illustrated in <FIG>, in the sticking state, leading ends of the flexible layers <NUM> and <NUM> are uniformly directed. As illustrated in <FIG>, when directions of the flexible layers <NUM> and <NUM> in a sticking state are arranged in multiple directions, a configuration capable of corresponding to multiple slipping directions is able to be realized.

As described above, according to the present embodiment, a partial slip of an object is able to be detected on the basis of a simple configuration and a simple calculating process alone, and further a gripping force of an object is able to be appropriately controlled. Moreover, an occurrence timing of a whole slip is made different in a plurality of flexible layers, so that it is possible to detect a partial slip with high accuracy even under various conditions such as in a case of a hard object or an object whose surface is plane, and a case where pressure distribution is flat.

While preferable embodiments of the present disclosure have been described above in detail with reference to the attached drawings, the technical scope of the present disclosure is not limited thereto.

For example, in the above-mentioned embodiment, the example is indicated in which a flexible layer and a distribution pressure sensor are provided to the hand <NUM> that grips the object <NUM>; however, the present technology is not limited to the example. For example, the flexible layer and the distribution pressure sensor may be arranged on a ground contact surface of a toe of walking robot so as to detect a slip of the toe. As described above, the present embodiment may be broadly applied for detecting a slip.

Claim 1:
A slip detecting device comprising:
a plurality of contact parts (<NUM>, <NUM>) having different slipping characteristics when an object (<NUM>) in contact with the plurality of contact parts is slipping; and
a plurality of sensors (<NUM>, <NUM>) that detect a pressure distribution of each of the plurality of contact parts, each sensor including a plurality of nodes that detect the pressure distribution; characterised in that
the plurality of contact parts is aligned along a slipping direction of the object, and
a contact part of the plurality of contact parts on which the object is hard to slip is arranged on an upper flow side of the slipping direction.