Force sensor for robot feet

Abstract

A force sensor for a robot foot that can be used in the foot of a robot is provided. [Solution] The robot foot force sensor according to the present invention includes a foot body, a sole portion provided on the sole side of the foot body, a detection element, and a detection circuit. The sole portion includes a sole body, a plurality of flexible portions connected to the sole body and having greater flexibility than the sole body, and a plurality of sole protrusions provided on the sole side of each flexible portion and protruding further toward the sole than the sole body. The detection element detects relative displacement between the foot body and the sole protrusions due to a force or moment acting on the foot body. The detection circuit outputs an electrical signal indicating the force or moment acting on the foot body based on the detection result of the detection element.

Description

[Technical Field]

[0001] The present disclosure relates to a force sensor for a robot foot. [Background technology]

[0002] Force sensors are known that output electrical signals representing forces acting in a specific axial direction and moments (or torques) acting around a specific rotation axis. Force sensors are widely used for force control in a variety of robots, including industrial robots, collaborative robots, life support robots, medical robots, and service robots.

[0003] Recently, force sensors have begun to be used in humanoid robots, such as walking robots. For example, force sensors may be used in the ankles and wrists of humanoid robots.

[0004] However, in some humanoid robots, force sensors are used not only in the ankles but also in the feet, and the structure of the force sensors used in the feet is different from that of the force sensors used in the ankles, etc. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7438569 Summary of the Invention [Problem to be solved by the invention]

[0006] The present disclosure has been made in consideration of these points, and aims to provide a force sensor for a robot foot that can be used in the foot of a robot. [Means for solving the problem]

[0007] [1] This disclosure A robot foot force sensor connected to an ankle of a robot, A foot body portion; a sole portion provided on the sole side of the foot body portion; A detection element; a detection circuit; Equipped with The sole portion includes a sole body portion, a plurality of flexible portions connected to the sole body portion and having greater flexibility than the sole body portion, and a plurality of sole protruding portions provided on the sole side of each of the flexible portions and protruding further toward the sole side than the sole body portion, the detection element detects a relative displacement between the foot body portion and the plantar protrusion due to a force or moment acting on the foot body portion; The detection circuit outputs an electrical signal indicating the force or moment acting on the foot body portion based on the detection result of the detection element. It may also be a force sensor for a robot foot.

[0008] [2] This disclosure The flexible portion includes a thin portion that is thinner than the sole body portion. The force sensor for a robot foot described in [1] may also be used.

[0009] [3] This disclosure The thin-walled portion has a circular planar shape. The force sensor for a robot foot described in [2] may also be used.

[0010] [4] This disclosure the detection elements include a plurality of displacement electrodes provided on the corresponding flexible portions, and a plurality of fixed electrodes provided on the sole body portion and facing the corresponding displacement electrodes; the detection element detects a change in capacitance value between each of the fixed electrodes and the corresponding displacement electrode; The force sensor for a robot foot may be any one of those described in [1] to [3].

[0011] [5] This disclosure the foot body portion includes a plurality of body recesses that open toward the corresponding flexible portions; the fixed electrodes are disposed within the corresponding body recesses; The force sensor for a robot foot described in [4] may also be used.

[0012] [6] This disclosure the flexible portion includes a thin portion that is thinner than the sole body portion; a main body side recess is formed on the foot main body side of the thin-walled portion; The displacement electrode is disposed in the main body recess. The force sensor for a robot foot may be as described in [4] or [5].

[0013] [7] This disclosure The front-to-rear direction of the robot is defined as an X-axis direction, and the direction perpendicular to the X-axis direction in a plan view is defined as a Y-axis direction, the plurality of sole protrusions include a first sole protrusion and a second sole protrusion disposed at a position different from that of the first sole protrusion in the X-axis direction; The detection circuit outputs an electrical signal indicating a moment about the Y-axis acting on the foot body portion based on the relative displacement between the foot body portion and the first plantar protrusion and the relative displacement between the foot body portion and the second plantar protrusion. The force sensor for a robot foot may be any one of those described in [1] to [6].

[0014] [8] This disclosure The detection element detects the relative displacement in a state where the plantar protrusion is in contact with the ground. The force sensor for a robot foot may be any one of those described in [1] to [7].

[0015] [9] This disclosure Further provided with a cushioning member provided on the sole side of the sole portion, The force sensor for a robot foot may be any one of those described in [1] to [8].

[0016]

[10] This disclosure The sole portion includes a stopper that restricts relative displacement between the foot body portion and the sole protrusion. The force sensor for a robot foot according to any one of [1] to [9]. [Effects of the Invention]

[0017] According to the present disclosure, it is possible to provide a robot foot force sensor that can be used in the foot of a robot. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a cross-sectional view showing a force sensor for a robot foot according to this embodiment. [Figure 2] FIG. 2 is a plan view showing a cross section taken along line AA in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the first capacitance element in a state where the foot body of FIG. 1 is not in contact with the ground. [Figure 4] FIG. 4 is a cross-sectional view of the first capacitance element in a state where the foot body of FIG. 1 is in contact with the ground and a force in the Z-axis direction is acting thereon. [Figure 5] FIG. 5 is a cross-sectional view for explaining a force acting on a capacitance element when a moment about the X axis acts on the leg body portion of FIG. [Figure 6] FIG. 6 is a cross-sectional view for explaining a force acting on a capacitance element when a moment around the Y axis acts on the leg main body portion of FIG. [Figure 7] FIG. 7 is a plan view showing a strain gauge attached to a diaphragm as a modification of the present embodiment. [Figure 8] FIG. 8 is a cross-sectional view showing a force sensor for a robot foot as a modification of this embodiment. [Figure 9] FIG. 9 is a cross-sectional view showing a force sensor for a robot foot as a modification of the sensor shown in FIG. [Figure 10] FIG. 10 is a cross-sectional view showing a force sensor for a robot foot as a modification of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings attached to this specification, the scale and aspect ratios of the actual objects have been appropriately changed and exaggerated for the sake of convenience in illustration and understanding.

[0020] As used herein, geometric conditions, physical characteristics, terms specifying the extent of a geometric condition or physical characteristic, and numerical values ​​indicating a geometric condition or physical characteristic may be interpreted without being bound by strict meaning. These geometric conditions, physical characteristics, terms, and numerical values ​​may also be interpreted to include the range of extent to which similar functions can be expected. Examples of terms specifying geometric conditions include "length," "angle," "shape," "parallel," "orthogonal," and "identical."

[0021] A robot foot force sensor according to an embodiment of the present invention will be described. The robot foot force sensor is configured to be connected to the ankle of the robot. More specifically, the robot foot force sensor according to this embodiment may be connected to the leg 1 of a quadrupedal robot or a bipedal robot via the ankle 2 and used as the foot of the robot. A through-hole is formed in the ankle 2. The through-hole may be a through-hole or a screw hole. A member that exhibits joint function is inserted into the through-hole. An example of a bipedal robot is a humanoid robot.

[0022] A robot foot force sensor 10 according to this embodiment will be described below with reference to Figs. 1 to 4. Fig. 1 is a cross-sectional view showing a robot foot force sensor according to this embodiment. Fig. 2 is a diagram showing a planar cross section taken along line AA in Fig. 1. Fig. 3 is a cross-sectional view of the first capacitance element in Fig. 1 when the foot main body is not in contact with the ground. Fig. 4 is a cross-sectional view of the first capacitance element CA in Fig. 1 when the foot main body is in contact with the ground and a force in the Z-axis direction is acting thereon.

[0023] In the following explanation, an XYZ three-dimensional coordinate system is defined, with the front-to-back direction of the robot (not shown) being the X-axis direction. The direction perpendicular to the X-axis direction in a planar view is the Y-axis direction. The Y-axis direction corresponds to the left-to-right direction of the robot. The direction perpendicular to the X-axis and Y-axis directions is the Z-axis direction. The Z-axis direction corresponds to the up-down direction of the robot. A planar view means a view along the Z-axis direction.

[0024] The robot foot force sensor 10 has the function of outputting a force acting in a predetermined axial direction and a moment acting around a predetermined rotation axis as an electrical signal. However, this is not limited to this, and the sensor may be configured to output only one of the force and the moment as an electrical signal, or may be configured to output at least one axial component of the force or the moment as an electrical signal.

[0025] 1, a robot foot force sensor 10 may include a foot main body 20, a sole 30, an ankle connector 40, a detection element 50, and a detection circuit 60. Each component will be described in more detail below.

[0026] When sole protrusions 33A to 33C of sole 30, which will be described later, are in contact with the ground G (see FIG. 3) (load state), foot main body 20 receives the force or moment to be detected from robot leg 1 via ankle 2. By receiving this force, foot main body 20 moves relative to sole protrusions 33A to 33C. In the example of FIG. 1 described above, foot main body 20 is connected to ankle 2 of the robot via ankle connector 40, which will be described later, and receives the force or moment from ankle 2.

[0027] In this embodiment, as shown in FIG. 2, the foot main body portion 20 may have a rectangular planar shape. However, the planar shape of the foot main body portion 20 is not limited to a rectangle and may be circular or elliptical, and is optional. The foot main body portion 20 may be formed in a generally flat plate shape. As shown in FIG. 2, the foot main body portion 20 may include a first central axis CL1 and a second central axis CL2. The first central axis CL1 passes through the center O of the foot main body portion 20 in the Y-axis direction and extends along the X-axis direction. The second central axis CL2 passes through the center O of the foot main body portion 20 in the X-axis direction and extends along the Y-axis direction.

[0028] As shown in Fig. 1, the foot body 20 according to this embodiment may include a plurality of main body recesses 21 that open toward the sole 30. Each of the main body recesses 21 may open toward a corresponding flexible portion 32A to 32C (described later). As shown in Fig. 2, the main body recesses 21 may have a circular planar shape. However, the planar shape of the main body recesses 21 is not limited to a circular shape and may be rectangular.

[0029] 1 and 2, at least two main body recesses 21 may be disposed at different positions in the X-axis direction. In this embodiment, the foot main body portion 20 includes three main body recesses 21. Each main body recess 21 is disposed at a position overlapping the corresponding flexible portion 32A to 32C in a plan view.

[0030] As shown in Fig. 1, the sole portion 30 is provided on the plantar side of the foot main body portion 20. The sole portion 30 may cover the entire plantar surface of the foot main body portion 20. The plantar side refers to the direction toward the ground G, which corresponds to the negative side in the Z-axis direction. The sole portion 30 may include a sole main body portion 31, multiple flexible portions 32A-32C, and multiple plantar protrusions 33A-33C.

[0031] The sole body portion 31 may be formed to be thicker than the flexible portions 32A to 32C. The sole body portion 31 may be fastened to the foot body portion 20 with bolts or the like (not shown).

[0032] The flexible portions 32A to 32C may be connected to the sole main body portion 31. The number of flexible portions 32A to 32C is arbitrary as long as it is two or more. As shown in Figures 1 and 2, in this embodiment, three flexible portions 32A to 32C are formed on the sole main body portion 31. The three flexible portions 32A to 32C may include a first flexible portion 32A, a second flexible portion 32B, and a third flexible portion 32C.

[0033] 2, the first flexible portion 32A may be disposed at a different position in the X-axis direction from the second flexible portion 32B and the third flexible portion 32C. More specifically, the first flexible portion 32A may be disposed on the positive side of the X-axis direction relative to the second central axis CL2. The second flexible portion 32B and the third flexible portion 32C may be disposed on the negative side of the second central axis CL2 in the X-axis direction. The distance from the second central axis CL2 to the first flexible portion 32A along the X-axis direction may be equal to the distance from the second central axis CL2 to the second flexible portion 32B (or the third flexible portion 32C) along the X-axis direction.

[0034] As shown in FIG. 2, the first flexible portion 32A may be disposed between the second flexible portion 32B and the third flexible portion 32C when viewed along the X-axis direction. More specifically, the first flexible portion 32A may be disposed on the first central axis CL1 described above. The second flexible portion 32B may be disposed on the positive side of the first central axis CL1 in the Y-axis direction, and the third flexible portion 32C may be disposed on the negative side of the first central axis CL1 in the Y-axis direction. The distance from the first central axis CL1 to the second flexible portion 32B along the Y-axis direction may be equal to the distance from the first central axis CL1 to the third flexible portion 32C along the Y-axis direction. In this case, the second flexible portion 32B and the third flexible portion 32C may be disposed symmetrically with respect to the first central axis CL1.

[0035] The flexible portions 32A to 32C may be more flexible than the sole main body portion 31. As shown in Fig. 4, which will be described later, the flexible portions 32A to 32C are configured to elastically deform in the Z-axis direction due to the action of a force or moment applied to the foot main body portion 20. Fig. 4 shows, as an example, an example in which when the sole protrusions 33A to 33C are in contact with the ground G, the sole main body portion 31 is also in contact with the ground G. However, even when the sole protrusions 33A to 33C are in contact with the ground G, the sole main body portion 31 does not have to be in contact with the ground G.

[0036] As shown in FIGS. 1 and 3, the flexible portions 32A to 32C may include thin portions 34 that are thinner than the sole main body portion 31. In this embodiment, the flexible portions 32A to 32C are entirely composed of the thin portions 34. The thin portions 34 may be formed along the X-axis direction and the Y-axis direction. As shown in FIG. 2, the thin portions 34 may have a circular planar shape. In this case, the thin portions 34 may be configured as diaphragms. Each of the flexible portions 32A to 32C may have the same diameter as the corresponding main body recess 21.

[0037] As shown in FIGS. 1 and 3 , the thin-walled portion 34 may be located at a middle position in the Z-axis direction relative to the sole body portion 31. In this case, a body-side recess 35 may be formed on the foot body portion 20 side of the thin-walled portion 34, and a plantar-side recess 36 may be formed on the plantar side of the thin-walled portion 34. The sole portion 30 according to this embodiment may include three body-side recesses 35 and three plantar-side recesses 36. Each body-side recess 35 may face a corresponding body recess 21 and overlap with it in a planar view. Each body-side recess 35 may form a continuous space with the corresponding body recess 21. Each plantar-side recess 36 may overlap with the corresponding body-side recess 35 in a planar view. The body-side recess 35 and the plantar-side recess 36 may each have a circular planar shape. Each body-side recess 35 and the plantar-side recess 36 may have the same diameter as the corresponding body recess 21.

[0038] As shown in FIGS. 1 and 2, the sole protrusions 33A to 33C may be provided on the sole side of each of the flexible portions 32A to 32C. More specifically, the sole portion 30 according to this embodiment may include three sole protrusions 33A to 33C. The three sole protrusions 33A to 33C may include a first sole protrusion 33A, a second sole protrusion 33B, and a third sole protrusion 33C. The first sole protrusion 33A may be provided on the sole side of the first flexible portion 32A. The second sole protrusion 33B may be provided on the sole side of the second flexible portion 32B. The third sole protrusion 33C may be provided on the sole side of the third flexible portion 32C. As shown in FIG. 2, the first sole protrusion 33A may be located at a different position in the X-axis direction from the second sole protrusion 33B and the third sole protrusion 33C. The second plantar protrusion 33B may be disposed at a different position in the Y-axis direction from the third plantar protrusion 33C. The first plantar protrusion 33A may be disposed at a different position in the Y-axis direction from the second plantar protrusion 33B and the third plantar protrusion 33C. The first plantar protrusion 33A may be disposed between the second plantar protrusion 33B and the third plantar protrusion 33C when viewed along the X-axis direction.

[0039] As shown in FIG. 1, the sole protrusions 33A-33C may protrude further toward the sole of the foot than the sole main body 31. This allows each of the sole protrusions 33A-33C to come into contact with the ground G when the sole 30 comes into contact with the ground G. Also, as shown in FIG. 3, the dimension by which the sole protrusions 33A-33C protrude from the underside of the sole main body 31 toward the sole of the foot may be shorter than the distance d between the displacement electrodes 51A-51C and the fixed electrodes 52A-52C, which will be described later. The distance d is the distance when the sole protrusions 33A-33C are not in contact with the ground G. This prevents the displacement electrodes 51A-51C from coming into contact with the fixed electrodes 52A-52C, even when the foot main body 20 comes into contact with the ground G due to a negative Z-axis force Fz.

[0040] As shown in Fig. 2, each of the sole protrusions 33A to 33C may be disposed at the center of the corresponding flexible portion 32A to 32C in a plan view. As shown in Fig. 2, the sole protrusions 33A to 33C may have a circular planar shape. However, the sole protrusions 33A to 33C may also have a rectangular planar shape.

[0041] The sole body 31 and flexible portions 32A-32C of the sole portion 30 may be integrally formed from a continuous material. The sole body 31 and flexible portions 32A-32C may be produced by machining (e.g., cutting) or casting a single metal material. The sole body 31 and flexible portions 32A-32C may be produced from a metal material such as an aluminum alloy or an iron alloy. However, the flexible portions 32A-32C may be attached to the sole body 31 as separate parts. The sole protrusions 33A-33C may be attached to the corresponding flexible portions 32A-32C as separate parts, or may be integrally formed from a continuous material with the corresponding flexible portions 32A-32C.

[0042] As shown in FIG. 1 , the ankle connector 40 is an optional component of the robot foot force sensor 10. The ankle connector 40 may be configured to connect the foot main body 20 to the ankle 2 of the robot. The ankle connector 40 may be provided on the side of the foot main body 20 opposite the plantar side and may be fastened to the foot main body 20 with a bolt or the like. The ankle connector 40 may be located on the positive side of the X-axis direction relative to the center of the foot main body 20 in the X-axis direction. The ankle connector 40 may be located in a position overlapping the first flexible part 32A in a plan view. However, the ankle connector 40 does not have to overlap the first flexible part 32A.

[0043] As shown in FIG. 1, the detection element 50 may be configured to detect relative displacement between the foot main body 20 and the plantar protrusions 33A-33C due to a force or moment acting on the foot main body 20. The detection element 50 may detect relative displacement when the plantar protrusions 33A-33C are in contact with the ground G. A state in which the plantar protrusions 33A-33C are not in contact with the ground G corresponds to an unloaded state in which no load is applied to the robot foot force sensor 10 (see FIG. 3). A state in which the plantar protrusions 33A-33C are in contact with the ground G corresponds to a loaded state in which a load is applied to the robot foot force sensor 10 (see FIG. 4). When the robot walks, the loaded state and the unloaded state are alternately repeated. In order for the detection element 50 to detect relative displacement, the sole main body 31 may or may not be in contact with the ground G when the sole protrusions 33A-33C are in contact with the ground G.

[0044] The detection element 50 according to this embodiment may include a plurality of displacement electrodes 51A-51C provided on the flexible portions 32A-32C and a plurality of fixed electrodes 52A-52C provided on the foot main body 20. Each of the displacement electrodes 51A-51C may face a corresponding fixed electrode 52A-52C. The detection element 50 may be configured as a capacitance element that detects a change in capacitance between the displacement electrodes 51A-51C and the corresponding fixed electrode 52A-52C. As shown in FIG. 4, when the sole protrusions 33A-33C come into contact with the ground G, the fixed electrodes 52A-52C are displaced relative to the displacement electrodes 51A-51C so as to approach the displacement electrodes 51A-51C. However, when the foot main body 20 is used as a reference, the displacement electrodes 51A-51C are displaced relative to the fixed electrodes 52A-52C so as to approach the fixed electrodes 52A-52C. For this reason, in this specification, the electrodes provided on the flexible portions 32A to 32C are referred to as displacement electrodes 51A to 51C, and the electrodes provided on the foot body portion 20 are referred to as fixed electrodes 52A to 52C.

[0045] 2, the detection element 50 according to this embodiment may include a first capacitance element CA, a second capacitance element CB, and a third capacitance element CC. Each of the capacitance elements CA to CC may include a corresponding fixed electrode 52A to 52C and a corresponding displacement electrode 51A to 51C.

[0046] The first capacitance element CA may include a first displacement electrode 51A and a first fixed electrode 52A. The first displacement electrode 51A may be attached to the first flexible portion 32A. The first displacement electrode 51A may be disposed in a body-side recess 35 formed by the first flexible portion 32A. The first fixed electrode 52A may be disposed in a corresponding body recess 21. The first fixed electrode 52A may be attached to the foot body portion 20. In this case, the first capacitance element CA is configured to detect relative displacement between the foot body portion 20 and the first plantar protrusion 33A.

[0047] The second capacitance element CB may include a second displacement electrode 51B and a second fixed electrode 52B. The second displacement electrode 51B may be attached to the second flexible portion 32B. The second displacement electrode 51B may be disposed in a main body recess 35 formed by the second flexible portion 32B. The second fixed electrode 52B may be disposed in a corresponding main body recess 21. The second fixed electrode 52B may be attached to the foot main body portion 20. In this case, the second capacitance element CB is configured to detect relative displacement between the foot main body portion 20 and the second plantar protrusion 33B.

[0048] The third capacitance element CC may include a third displacement electrode 51C and a third fixed electrode 52C. The third displacement electrode 51C may be attached to the third flexible portion 32C. The third displacement electrode 51C may be disposed in a main body recess 35 formed by the third flexible portion 32C. The third fixed electrode 52C may be disposed in a corresponding main body recess 21. The third fixed electrode 52C may be attached to the foot main body portion 20. In this case, the third capacitance element CC is configured to detect a relative displacement between the foot main body portion 20 and the third plantar protrusion 33C.

[0049] Each of the displacement electrodes 51A to 51C may be attached to the corresponding flexible portion 32A to 32C via an insulator (not shown). The insulator may be bonded to the corresponding flexible portion 32A to 32C with an adhesive or the like. Wiring (not shown) for connecting the displacement electrodes 51A to 51C to the detection circuit 60 may be connected to the displacement electrodes 51A to 51C. The displacement electrodes 51A to 51C and the insulator may be configured as an FPC board (flexible printed circuit board). Parts of a metal thin film formed on a polyimide film of the FPC board may be configured as the displacement electrodes 51A to 51C. In this case, the displacement electrodes 51A to 51C may be connected to wiring that forms part of the metal thin film.

[0050] Each of the fixed electrodes 52A-52C may be attached to the foot body 20 via an insulator (not shown). The insulator may be bonded to the foot body 20 with an adhesive or the like. Wiring (not shown) for connecting the fixed electrodes 52A-52C to the detection circuit 60 may be connected to the fixed electrodes 52A-52C. The fixed electrodes 52A-52C and the insulator may be formed on an FPC board. Parts of a metal thin film formed on a polyimide film of the FPC board may be formed as the fixed electrodes 52A-52C. In this case, the fixed electrodes 52A-52C may be connected to wiring that forms part of the metal thin film.

[0051] 2, the planar shape of each of the displacement electrodes 51A-51C may be smaller than the planar shape of the corresponding fixed electrodes 52A-52C in a planar view. For example, the diameter of each of the displacement electrodes 51A-51C may be smaller than the diameter of the corresponding fixed electrodes 52A-52C. In a planar view, the center of each of the displacement electrodes 51A-51C may coincide with the center of the corresponding fixed electrode 52A-52C. The sizes of the displacement electrodes 51A-51C and the fixed electrodes 52A-52C may be set so that each of the displacement electrodes 51A-51C entirely overlaps the corresponding fixed electrode 52A-52C, even when the foot main body 20 receives a force or moment and the fixed electrodes 52A-52C and the displacement electrodes 51A-51C are displaced relative to each other. This prevents changes in the facing area between each of the displacement electrodes 51A-51C and the corresponding fixed electrodes 52A-52C, and prevents changes in the facing area from affecting changes in the capacitance value. Therefore, the capacitance value can be changed according to changes in the distance between the displacement electrodes 51A-51C and the corresponding fixed electrodes 52A-52C. Here, the facing area refers to the area where each of the displacement electrodes 51A-51C overlaps with the corresponding fixed electrode 52A-52C in a plan view.

[0052] As shown in FIG. 1, the detection circuit 60 may be configured to output an electrical signal indicating the force or moment acting on the foot main body 20 based on the detection result of the detection element 50. The detection circuit 60 may have a calculation function implemented, for example, by a microprocessor. The detection circuit 60 may also have a C / V conversion circuit that converts the capacitance value into a voltage value. The detection circuit 60 may also have an A / D conversion function that converts the analog signal (voltage) received from the detection element 50 into a digital signal, a signal amplification function, and a communication interface. Examples of communication interface standards include RS422, RS485, EtherCAT (registered trademark), and Ethernet. The detection circuit 60 may include a terminal that outputs an electrical signal, and the electrical signal is transmitted from this terminal to a robot controller (not shown) via an electric cable (not shown). The detection circuit 60 may be configured to be capable of wired and / or wireless communication with the robot controller or the like. The detection circuit 60 may also be disposed outside the foot main body 20 as shown in FIG. 1. However, the detection circuit 60 may be built into the foot body 20, although this is not shown.

[0053] The detection circuit 60 may be configured to calculate a force Fz in the Z-axis direction, a moment Mx about the X-axis, and a moment My about the Y-axis. More specifically, the detection circuit 60 may output an electrical signal indicative of the force Fz in the Z-axis direction based on the relative displacement between the foot main body 20 and the first plantar protrusion 33A, the relative displacement between the foot main body 20 and the second plantar protrusion 33B, and the relative displacement between the foot main body 20 and the third plantar protrusion 33C. The detection circuit 60 may output an electrical signal indicative of the moment Mx about the X-axis based on the relative displacement between the foot main body 20 and the first plantar protrusion 33A, the relative displacement between the foot main body 20 and the second plantar protrusion 33B, and the relative displacement between the foot main body 20 and the third plantar protrusion 33C. The detection circuit 60 may output an electrical signal indicating the moment My around the Y-axis based on the relative displacement between the foot main body portion 20 and the first plantar protrusion 33A, the relative displacement between the foot main body portion 20 and the second plantar protrusion 33B, and the relative displacement between the foot main body portion 20 and the third plantar protrusion 33C.

[0054] The force or moment calculated by the detection circuit 60 is transmitted as an electric signal to the controller of the robot. The controller controls the force of the robot based on the electric signal output from the detection circuit 60.

[0055] Next, a method for detecting a force or moment acting on the foot main body 20 of the robot foot force sensor 10 according to this embodiment configured as described above will be described with reference to Figs. 4 to 6. Fig. 4 is a cross-sectional view of the first capacitance element CA in a state where the foot main body 20 of Fig. 1 is in contact with the ground and a force Fz in the Z-axis direction is acting thereon. Fig. 5 is a cross-sectional view for explaining the force acting on the capacitance element when a moment about the X-axis acts on the foot main body of Fig. 1. Fig. 6 is a cross-sectional view for explaining the force acting on the capacitance element when a moment about the Y-axis acts on the foot main body of Fig. 1.

[0056] When the foot main body 20 is subjected to a force or moment while the plantar protrusions 33A-33C of the sole 30 are in contact with the ground G, the force or moment is transmitted to the flexible portions 32A-32C of the sole 30. This causes elastic deformation in the flexible portions 32A-32C, displacing them relative to the displacement electrodes 51A-51C and the fixed electrodes 52A-52C. This changes the distance between the displacement electrodes 51A-51C and the fixed electrodes 52A-52C, changing the capacitance values ​​of the capacitance elements CA-CC. This change in capacitance value is detected by the detection element 50 as the relative displacement between the foot main body 20 and the plantar protrusions 33A-33C. In response to the change in capacitance value of each of the capacitance elements CA-CC, an output value is output from each of the capacitance elements CA-CC to the detection circuit 60, and the detection circuit 60 can output an electrical signal indicating the direction and magnitude of the force or moment acting on the foot main body 20.

[0057] Here, the change in the capacitance value of the first capacitance element CA when a force Fz in the Z-axis direction is applied will be described, taking the first capacitance element CA as an example.

[0058] As shown in Figure 3, when the first sole protrusion 33A of the sole 30 is not in contact with the ground G, no force Fz in the negative Z-axis direction is acting on the foot body 20. In this case, the first flexible portion 32A is not elastically deformed. In this state, the inter-electrode distance (distance in the Z-axis direction) between the fixed electrodes 52A-52C and the displacement electrodes 51A-51C of the first capacitance element CA is defined as the reference distance. The capacitance value of the first capacitance element CA at this time is defined as the reference capacitance value.

[0059] As shown in FIG. 4, when the first sole protrusion 33A of the sole 30 comes into contact with the ground G, a force Fz acts on the foot main body 20 in the negative Z-axis direction. In this case, the first sole protrusion 33A is pressed against the ground G. This causes the first flexible portion 32A to elastically deform, and the foot main body 20 is displaced in the negative Z-axis direction relative to the first sole protrusion 33A. The fixed electrodes 52A-52C of the first capacitance element CA approach the displacement electrodes 51A-51C, and the inter-electrode distance between the fixed electrodes 52A-52C and the displacement electrodes 51A-51C decreases from the reference distance described above. As a result, the capacitance value of the first capacitance element CA increases from the reference capacitance value described above.

[0060] Although not shown, when the second sole protrusion 33B of the sole 30 comes into contact with the ground G, the capacitance value of the second capacitance element CB increases in the same manner as the first capacitance element CA described above, and when the third sole protrusion 33C of the sole 30 comes into contact with the ground G, the capacitance value of the third capacitance element CC increases in the same manner as the first capacitance element CA described above.

[0061] The detection circuit 60 calculates the force or moment acting on the foot main body 20 based on the output values ​​of each of the capacitance elements CA to CC. For example, the detection circuit 60 may include a capacitance-to-voltage conversion circuit (C / V conversion circuit). When the output value of the first capacitance element CA is V1, the output value of the second capacitance element CB is V2, and the output value of the third capacitance element CC is V3, the detection circuit 60 may calculate the force Fz in the Z-axis direction acting on the foot main body 20 using the following equation (1). This makes it possible to detect not only whether or not the force Fz has acted on the foot main body 20, but also the magnitude of the force Fz. The output values ​​V1 to V3 are positive when the force Fz acts on the negative side in the Z-axis direction. The output values ​​V1 to V3 of each of the capacitance elements CA to CC correspond to voltage values.

number

[0062] In equation (1), for convenience, the force or moment and the output value are connected with "=". However, since the force or moment and the output value are different physical quantities, in reality, the force or moment is found by converting the output value. This is also true for the other equations described below.

[0063] When a force Fz in the Z-axis direction is acting on the foot main body 20 without any other force or moment components acting on it, the entire foot main body 20 is pressed evenly against the ground G. In this case, the first plantar protrusion 33A, the second plantar protrusion 33B, and the third plantar protrusion 33C of the sole 30 are pressed evenly against the ground G, and the capacitance values ​​of the capacitance elements CA to CC are equal. However, when the robot's leg 1 (see FIG. 1) tilts, force components or moment components other than the force Fz in the Z-axis direction may act on the foot main body 20. Below, we will explain the cases where a moment Mx about the X-axis and a moment My about the Y-axis act on the foot main body 20 when a force Fz in the Z-axis direction is acting on the foot main body 20.

[0064] Next, a case where a moment Mx about the X-axis acts on the foot main body 20 will be described. As shown in Fig. 5, the moment Mx about the X-axis is a clockwise moment toward the negative side of the X-axis direction around the first central axis CL1 along the X-axis direction. For example, if the leg 1 of the robot is tilted to the right when viewed from behind, the moment Mx may act on the foot main body 20.

[0065] When the moment Mx acts on the foot main body 20, the capacitance value of the first capacitance element CA can be considered to remain unchanged because the first capacitance element CA is located on the first central axis CL1 in a plan view. More specifically, the portion of the first fixed electrode 52A of the first capacitance element CA that is located on the positive side of the Y axis direction from the first central axis CL1 moves closer to the first displacement electrode 51A, and the capacitance value of that portion increases. However, the portion of the first fixed electrode 52A that is located on the negative side of the Y axis direction from the first central axis CL1 moves farther away from the first displacement electrode 51A, and the capacitance value of that portion decreases. Therefore, when the moment Mx acts on the foot main body 20, the changes in the capacitance values ​​of the above two portions of the first capacitance element CA cancel each other out, and the capacitance value of the first capacitance element CA as a whole can be considered to remain unchanged.

[0066] The second capacitance element CB is disposed on the positive side in the Y-axis direction relative to the first central axis CL1. As a result, as shown in FIG. 5, when a moment Mx acts on the foot body portion 20, a force Fz acts on the negative side in the Z-axis direction on the second capacitance element CB. As a result, the second fixed electrode 52B of the second capacitance element CB moves closer to the second displacement electrode 51B as a whole. In this case, the capacitance value of the second capacitance element CB increases compared to the capacitance value when no moment Mx is acting.

[0067] The third capacitance element CC is disposed on the negative side of the first central axis CL1 in the Y-axis direction. Therefore, as shown in FIG. 5, when a moment Mx acts on the foot body 20, a force Fz acts on the positive side of the Z-axis direction on the third capacitance element CC. Therefore, the third fixed electrode 52C of the third capacitance element CC moves away from the third displacement electrode 51C as a whole. In this case, the capacitance value of the third capacitance element CC decreases compared to the capacitance value when no moment Mx is acting.

[0068] The detection circuit 60 may calculate the moment Mx about the X-axis acting on the foot body 20 using the following equation (2). This makes it possible to detect not only whether or not the moment Mx has acted on the foot body 20, but also the magnitude of the moment Mx. The output values ​​V2 and V3 are set to positive values ​​when a force Fz on the negative side in the Z-axis direction acts. As a prerequisite for detecting the moment Mx, the force Fz on the negative side in the Z-axis direction acts on the fixed electrodes 52A-52C, and the plantar protrusions 33A-33C are in contact with the ground G. Therefore, as described above, the capacitance value of the third capacitance element CC is smaller than the capacitance value of the second capacitance element CB, but is maintained at a value greater than the reference capacitance value described above.

number

[0069] Next, a case where a moment My about the Y-axis acts on the foot main body 20 will be described. As shown in FIG. 6, the moment My about the Y-axis is a clockwise moment toward the positive side of the Y-axis direction around the second central axis CL2 along the Y-axis direction. For example, when the leg 1 of the robot leans backward, the moment My may act on the foot main body 20. When the leg 1 of the robot leans forward, a moment My in the opposite direction may act on the foot main body 20.

[0070] The first capacitance element CA is disposed on the positive side in the X-axis direction of the second central axis CL2. As a result, as shown in Fig. 6, when a moment My acts on the foot body portion 20, a force Fz acts on the negative side in the Z-axis direction on the first capacitance element CA. As a result, the fixed electrodes 52A to 52C of the first capacitance element CA move closer to the first displacement electrode 51A of the first capacitance element CA as a whole. In this case, the capacitance value of the first capacitance element CA increases compared to the capacitance value when no moment My is acting.

[0071] The second capacitance element CB is disposed on the negative side of the second central axis CL2 in the X-axis direction. Therefore, as shown in FIG. 6, when a moment My acts on the foot body 20, a force Fz acts on the positive side of the Z-axis direction on the second capacitance element CB. Therefore, the second fixed electrode 52B of the second capacitance element CB moves away from the second displacement electrode 51B as a whole. In this case, the capacitance value of the second capacitance element CB decreases compared to the capacitance value when no moment My is acting.

[0072] Similar to the second capacitance element CB, the third capacitance element CC is disposed on the negative side of the second central axis CL2 in the X-axis direction, which reduces the capacitance value of the third capacitance element CC compared to the capacitance value when no moment My is acting.

[0073] The detection circuit 60 may calculate the moment My about the Y-axis acting on the foot body 20 using the following equation (3). This makes it possible to detect not only whether or not the moment My has acted on the foot body 20, but also the magnitude of the moment My. The output values ​​V1 to V3 are set to positive values ​​when a force Fz on the negative side in the Z-axis direction is acting. To detect the moment My, the fixed electrodes 52A to 52C are subjected to a force Fz on the negative side in the Z-axis direction, and the plantar protrusions 33A to 33C are in contact with the ground G. Therefore, as described above, the capacitance values ​​of the second capacitance element CB and the third capacitance element CC are each reduced from the capacitance value of the first capacitance element CA, but are maintained at a value greater than the reference capacitance value.

number

[0074] In this way, the robot foot force sensor 10 according to this embodiment can calculate the force Fz in the Z-axis direction, the moment Mx about the X-axis, and the moment My about the Y-axis, and can detect the three-axis components of force. The detected moment Mx or moment My is output as an electrical signal from the detection circuit 60 to the robot's controller. Based on this electrical signal, the controller controls the robot's force and corrects the robot's posture. This makes it possible to prevent the robot from falling over.

[0075] As described above, according to this embodiment, the sole portion 30 provided on the plantar side of the foot main portion 20 includes a plurality of flexible portions 32A-32C and a plurality of plantar protrusions 33A-33C provided on the plantar side of each of the flexible portions 32A-32C. The detection element 50 detects relative displacement between the foot main portion 20 and the plantar protrusions 33A-33C due to a force or moment acting on the foot main portion 20. The detection circuit 60 outputs an electrical signal indicating the force or moment acting on the foot main portion 20 based on the detection result of the detection element 50. As a result, when a force or moment acts on the foot main portion 20 while the plantar protrusions 33A-33C of the sole portion 30 are in contact with the ground G, the flexible portions 32A-32C can elastically deform. Therefore, the detection element 50 can detect the relative displacement between the foot main body 20 and each of the sole protrusions 33A to 33C, and the detection circuit 60 can output an electrical signal indicating the force or moment acting on the foot main body 20. As a result, it is possible to provide a robot foot force sensor 10 that can be used in the foot of a robot.

[0076] Furthermore, according to this embodiment, the flexible portions 32A-32C of the sole portion 30 include thin portions 34 that are thinner than the sole main body portion 31. This allows the flexible portions 32A-32C to easily elastically deform when a force or moment acts on the foot main body portion 20. This allows for a large relative displacement between the foot main body portion 20 and the sole protrusions 33A-33C, improving the detection accuracy of the force or moment acting on the foot main body portion 20. Furthermore, when the thin portions 34 are formed along the X-axis and Y-axis directions, the thin portions 34 can easily elastically deform in the Z-axis direction.

[0077] Furthermore, according to this embodiment, the thin-walled portion 34 has a circular planar shape, which allows the elastic deformation of the thin-walled portion 34 to be uniform in the XY plane including the X-axis and Y-axis, thereby improving the detection accuracy of the force or moment acting on the foot body 20.

[0078] Furthermore, according to this embodiment, the detection element 50 includes a plurality of displacement electrodes 51A-51C provided on the corresponding flexible portions 32A-32C, and a plurality of fixed electrodes 52A-52C provided on the sole main body 31, facing the corresponding displacement electrodes 51A-51C. The detection element 50 detects changes in the capacitance between each of the displacement electrodes 51A-51C and the corresponding fixed electrode 52A-52C. This makes it possible to detect not only whether a force or moment has acted on the foot main body 20, but also the magnitude of the force or moment. This allows the robot controller to control the robot's force according to the magnitude of the force or moment, thereby optimizing the control of the robot.

[0079] Furthermore, according to this embodiment, the foot main body portion 20 includes a plurality of main body recesses 21 that open toward the corresponding flexible portions 32A to 32C, and the fixed electrodes 52A to 52C of the detection element 50 are disposed within the corresponding main body recesses 21. This allows the Z-axis dimension (thickness) of the robot foot force sensor 10 to be reduced, thereby enabling the robot foot force sensor 10 to be made more compact.

[0080] Furthermore, according to this embodiment, the flexible portions 32A to 32C include a thin portion 34 that is thinner than the sole main body portion 31, and a main body recess 35 is formed on the foot main body 20 side of the thin portion 34. The displacement electrodes 51A to 51C of the detection element 50 are arranged in the main body recess 35. This allows the Z-axis dimension (thickness) of the robot foot force sensor 10 to be reduced. This allows the robot foot force sensor 10 to be made more compact.

[0081] Furthermore, according to this embodiment, the detection circuit 60 outputs an electrical signal indicating the moment My about the Y-axis acting on the foot main body 20, based on the relative displacement between the foot main body 20 and the first sole protrusion 33A, the relative displacement between the foot main body 20 and the second sole protrusion 33B, and the relative displacement between the foot main body 20 and the third sole protrusion 33C. This allows the robot controller to control the force of the robot according to the moment My about the Y-axis, thereby preventing the robot from falling over.

[0082] Furthermore, according to this embodiment, the detection element 50 detects relative displacement when the sole protrusions 33A to 33C are in contact with the ground G. This prevents the detection element 50 from detecting relative displacement when the sole protrusions 33A to 33C are not in contact with the ground G. This prevents the detection circuit 60 from erroneously outputting an electrical signal indicating the force or moment acting on the foot main body 20, improving quality.

[0083] In the above-described embodiment, the flexible portions 32A to 32C include thin portions 34 having a circular planar shape and are configured as diaphragms. However, the embodiment is not limited to this. For example, the flexible portions 32A to 32C may include thin portions 34 having a cross-beam-like planar shape. The flexible portions 32A to 32C may also have a cross-shaped planar shape. Even in this case, the flexible portions 32A to 32C can be elastically deformed by a force or moment acting on the foot body 20.

[0084] In the above-described embodiment, an example has been described in which the foot main body portion 20 includes the main body recess 21, and the fixed electrodes 52A to 52C are arranged in the main body recess 21. However, the embodiment is not limited to this. For example, the foot main body portion 20 does not need to include the main body recess 21 as long as the fixed electrodes 52A to 52C can form capacitance elements together with the corresponding displacement electrodes 51A to 51C.

[0085] In the above-described embodiment, the body-side recess 35 is formed on the foot body 20 side of the thin-walled portion 34, and the displacement electrodes 51A to 51C are arranged in the body-side recess 35. However, the embodiment is not limited to this. For example, as long as the displacement electrodes 51A to 51C can form capacitance elements with the corresponding fixed electrodes 52A to 52C, the body-side recess 35 does not have to be formed on the foot body 20 side of the thin-walled portion 34.

[0086] In the above-described embodiment, the detection element 50 is configured as a capacitance element. However, the present embodiment is not limited to this. For example, the detection element 50 may be configured as a strain gauge, an optical sensor, or a magnetic sensor. When the detection element 50 is configured as a strain gauge, as shown in FIG. 7, multiple strain gauges 53 may be attached to the thin-walled portion 34 at positions that do not overlap with the plantar protrusions 33A to 33C. FIG. 7 is a plan view showing strain gauges attached to a diaphragm as a modification of the present embodiment. While FIG. 7 shows a representative example in which the strain gauge 53 is attached to the thin-walled portion 34 of the first flexible portion 32A, strain gauges 53 may also be attached to the second flexible portion 32B and the third flexible portion 32C.

[0087] In the above-described embodiment, a buffer member 70 may be provided on the sole side of the sole portion 30, as shown in FIG. 8. FIG. 8 is a cross-sectional view showing a robot foot force sensor as a variation of the embodiment. The buffer member 70 may be made of a flexible material, such as rubber or synthetic resin. This can reduce noise generated when the robot walks, even when the sole portion 30, including the sole protrusions 33A-33C, is made of a metal material. The buffer member 70 can also prevent the robot's foot from slipping on the ground G, enabling efficient walking. The buffer member 70 may be detachably attached to the sole portion 30. In the example shown in FIG. 8, the peripheral edge 31a of the sole body 31 protrudes outward beyond the foot body 20. The buffer member 70 may be fastened to this peripheral edge 31a. When the buffer member 70 is made of a flexible material, such as rubber or synthetic resin, the buffer member 70 can be easily attached to and detached from the peripheral edge 31a. Alternatively, the cushioning member 70 may be detachably attached to the sole 30 using bolts or the like. The cushioning member 70 may be fixed to the sole 30 using an adhesive.

[0088] In the example shown in FIG. 8, the cushioning member 70 may include a cushioning main body 71, a plurality of cushioning accommodation portions 72, and a plurality of cushioning protrusions 73. The cushioning main body 71 may include a portion that abuts against the sole main body 31 and a portion that engages with the peripheral edge portion 31a. Each cushioning accommodation portion 72 may be formed on the surface of the cushioning main body 71 facing the sole 30, and configured to accommodate the corresponding sole protrusions 33A to 33C. Each cushioning protrusion 73 may protrude further toward the sole of the foot than the cushioning main body 71. Each cushioning protrusion 73 may have a corresponding cushioning accommodation portion 72 formed on the inside.

[0089] However, as shown in Fig. 9, the cushioning member 70 does not have to include the cushioning protrusion 73. Fig. 9 is a cross-sectional view showing a robot foot force sensor as a modification of the sensor shown in Fig. 8. In the example shown in Fig. 9, the portion of the cushioning main body 71 on the plantar side of the sole main body 31 may be made thicker. The lower surface of the cushioning member 70 shown in Fig. 9 may be made flat.

[0090] In the present embodiment described above, a stopper 74 may be provided on the plantar side of the sole portion 30, as shown in Fig. 10. Fig. 10 is a cross-sectional view showing a robot foot force sensor as a modified example of the present embodiment. The stopper 74 is configured to restrict relative displacement between the foot main body portion 20 and the sole protrusions 33A-33C, and functions to prevent the sole protrusions 33A-33C from coming too close to the foot main body portion 20.

[0091] More specifically, the stopper 74 is formed on the underside of the sole body 31. The stopper 74 may be adjacent to the plantar recess 36. The stopper 74 may be formed in a ring shape around the plantar recess 36. As shown in FIG. 10 , the thickness t of the stopper 74 may be set to a thickness that prevents the displacement electrodes 51A-51C from contacting the fixed electrodes 52A-52C even when the plantar protrusions 33A-33C contact the ground G due to a negative Z-axis force Fz. In this case, contact and damage to the displacement electrodes 51A-51C and the fixed electrodes 52A-52C can be prevented. Although not shown, a buffer member may be provided on the sole side of the stopper 74. In this case, the buffer member may be formed to cover the stopper 74 but not the sole body 31. Alternatively, the buffer member may cover the entire sole body 31.

[0092] The present invention is not limited to the above-described embodiments and modifications, and can be embodied by modifying the components within the scope of the gist of the present invention in the implementation stage. Furthermore, various inventions can be formed by appropriately combining multiple components disclosed in the above-described embodiments and modifications. Some components may be omitted from all the components shown in the embodiments and modifications. Furthermore, components from different embodiments and modifications may be appropriately combined. [Explanation of symbols]

[0093] 2 Ankle 10 Force sensor for robot feet 20 Foot body 21 Main body recess 30 Sole of the Foot 31 Sole body 32A 1st flexible part 32B 2nd flexible part 32C 3rd flexible part 33A First plantar protrusion 33B Second plantar protrusion 33C Third plantar protrusion 34 Thin-walled section 50 Detector element 51A First displacement electrode 51B Second displacement electrode 51C Third displacement electrode 52A 1st fixed electrode 52B 2nd fixed electrode 52C 3rd fixed electrode 60 Detection circuit 70 Cushioning material 74 Stopper CA: first capacitance element CB: second capacitance element CC: Third capacitance element G ground

Claims

1. A robot foot force sensor connected to an ankle of a robot, A foot body portion; a sole portion provided on the sole side of the foot body portion; A detection element; a detection circuit; Equipped with The sole portion includes a sole body portion, a plurality of flexible portions connected to the sole body portion and having greater flexibility than the sole body portion, and a plurality of sole protruding portions provided on the sole side of each of the flexible portions and protruding further toward the sole side than the sole body portion, the detection element detects a relative displacement between the foot main body portion and the plantar protrusion due to a force or moment acting on the foot main body portion when the plantar protrusion is in contact with the ground; The detection circuit outputs an electrical signal indicating the force or moment acting on the foot body portion based on the detection result of the detection element. Force sensor for robotic feet.

2. The flexible portion includes a thin portion that is thinner than the sole body portion. The force sensor for a robot foot according to claim 1 .

3. The thin-walled portion has a circular planar shape. The force sensor for a robot foot according to claim 2 .

4. the detection elements include a plurality of displacement electrodes provided on the corresponding flexible portions, and a plurality of fixed electrodes provided on the sole body portion and facing the corresponding displacement electrodes; the detection element detects a change in capacitance value between each of the fixed electrodes and the corresponding displacement electrode; 3. The force sensor for a robot foot according to claim 1.

5. the foot body portion includes a plurality of body recesses that open toward the corresponding flexible portions; the fixed electrodes are disposed within the corresponding body recesses; 5. The force sensor for a robot foot according to claim 4.

6. the flexible portion includes a thin portion that is thinner than the sole body portion; a main body side recess is formed on the foot main body side of the thin-walled portion; The displacement electrode is disposed in the main body recess.

5. The force sensor for a robot foot according to claim 4.

7. The front-rear direction of the robot is defined as an X-axis direction, and the direction perpendicular to the X-axis direction in a plan view is defined as a Y-axis direction, the plurality of sole protrusions include a first sole protrusion and a second sole protrusion disposed at a position different from that of the first sole protrusion in the X-axis direction; The detection circuit outputs an electrical signal indicating a moment about the Y-axis acting on the foot body portion based on the relative displacement between the foot body portion and the first plantar protrusion and the relative displacement between the foot body portion and the second plantar protrusion.

3. The force sensor for a robot foot according to claim 1.

8. Further provided with a cushioning member provided on the sole side of the sole portion, 3. The force sensor for a robot foot according to claim 1.

9. The sole portion includes a stopper that restricts relative displacement between the foot body portion and the sole protrusion.

3. The force sensor for a robot foot according to claim 1.

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