Flexible 6-axis force sensor and its calculation method

Abstract

To provide a flexible 6-axial force sensor and a computation method thereof that can detect three-dimensional force applied to a detection part and torque on its three-dimensional axis without breaking an object of detection by deforming the detection part in conformity with an external shape of the object of detection.SOLUTION: A flexible 6-axial force sensor has: a first 6-axial force sensor and a second 6-axial force sensor which detect force and torque applied in a three-dimensional direction respectively; a curved flexible elastic body which has one end fixed to the first 6-axial force sensor and the other end fixed to the second 6-axial force sensor respectively, and extends in a belt-like or linear shape; and a computation part which computes coordinates of a point of action applied with the force and torque and magnitudes of the force and torque at the point of action when the force and torque are applied to the flexible elastic body from outside based upon information on the force and information on the torque output from the first 6-axial force sensor and the second 6-axial force sensor respectively.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a flexible 6-axis force sensor using an existing 6-axis force sensor, and a method for calculating the same. [Background technology]

[0002] The advancement of sophisticated robotics technology requires the evolution of sensor technology to detect the posture and forces of moving objects. Among the sensors used in such robots, the 6-axis force sensor is well-known.

[0003] A 6-axis force sensor can detect forces applied in three dimensions, i.e., along the X, Y, and Z directions, as well as torques around these three axes. This allows for actions such as grasping and moving an arbitrary object by detecting the force applied to a robot arm in three dimensions and the torque around the axes in these three dimensions (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-100702 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, conventional 6-axis force sensors are made of rigid materials that do not deform when detecting objects. For example, when detecting low-strength objects that are easily damaged by even a small force, there was a concern that the sensor might damage the object being detected. There was also a concern that the 6-axis force sensor itself might be damaged by impact forces generated by contact with the environment.

[0006] This invention has been proposed in view of the above problems, and aims to provide a flexible 6-axis force sensor and a calculation method thereof that can detect the force applied to the detection part in a three-dimensional direction, the torque around the axis in this three-dimensional direction, and the contact position without damaging the object to be detected or the device itself, by allowing the detection part to deform in accordance with the external shape of the object to be detected. [Means for solving the problem]

[0007] To solve the above problems, the flexible 6-axis force sensor of one embodiment of the present invention proposes the following means. (1) One aspect of the present invention includes a first 6-axis force sensor and a second 6-axis force sensor that detect forces and torques applied in three dimensions, respectively; a curved flexible elastic body that extends in a strip or linear shape and is fixed at one end to the first 6-axis force sensor and at the other end to the second 6-axis force sensor, respectively; and when a force and torque are applied to the flexible elastic body from the outside, based on the force information and torque information output from the first 6-axis force sensor and the second 6-axis force sensor, respectively, the system reacts to the applied force and torque. , the contact position of the object to be detected with respect to the flexible elastic body. Point of application three-dimensional It is characterized by having a calculation unit that calculates coordinates and the magnitude of force and torque at the point of application.

[0008] (2) Aspect 2 of the present invention is a flexible 6-axis force sensor of aspect 1, characterized in that the flexible elastic body is a strip or linear body having a known cross-sectional shape and a known elastic modulus along its entire length in the longitudinal direction. The flexible elastic body is allowed to deform significantly when subjected to external forces and torques.

[0009] (3) A third aspect of the present invention is a flexible 6-axis force sensor according to aspect 1 or 2, characterized in that the flexible elastic body is bent 180° with its longitudinal center as the apex.

[0010] (4) Aspect 4 of the present invention is a calculation method for a flexible 6-axis force sensor using any one of the flexible 6-axis force sensors of aspects 1 to 3, characterized in that the calculation unit compares first deformation information obtained from the signal output from the first 6-axis force sensor, which is numerically calculated from one end to the other of the flexible elastic body, with second deformation information obtained from the signal output from the second 6-axis force sensor, which is numerically calculated from the other end to the one end of the flexible elastic body, and determines a point of application where the coordinate values ​​and orientation values ​​are similar to each other, outputs the coordinate value of the point of application and the applied force value, and displays the overall deformation shape of the flexible elastic body. [Effects of the Invention]

[0011] According to the present invention, by allowing deformation of the detection portion to conform to the external shape of the object to be detected, it becomes possible to provide a flexible 6-axis force sensor and a calculation method thereof that can detect the force applied to the detection portion in a three-dimensional direction and the torque around the axis in this three-dimensional direction without damaging the object to be detected. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram showing the external appearance of the flexible 6-axis force sensor of this embodiment. [Figure 2] This is an explanatory diagram showing the force and torque applied to each part of the flexible 6-axis force sensor. [Figure 3] This is an explanatory diagram showing the calculation method of a flexible 6-axis force sensor. [Figure 4] This is an explanatory diagram showing the calculation method of a flexible 6-axis force sensor. [Figure 5] This is an explanatory diagram showing the calculation method of a flexible 6-axis force sensor. [Figure 6] This is an explanatory diagram showing the calculation method of a flexible 6-axis force sensor. [Figure 7] This is an explanatory diagram showing the calculation method of a flexible 6-axis force sensor. [Figure 8] This is an explanatory diagram showing the measurement results using the flexible 6-axis force sensor of this embodiment. [Figure 9]This is an explanatory diagram showing the measurement results using the flexible 6-axis force sensor of this embodiment. [Figure 10] This is an explanatory diagram showing the measurement results using the flexible 6-axis force sensor of this embodiment. [Figure 11] This is an explanatory diagram showing the measurement results using the flexible 6-axis force sensor of this embodiment. [Modes for carrying out the invention]

[0013] The following describes a flexible 6-axis force sensor and its calculation method according to one embodiment of the present invention, with reference to the drawings. The embodiments described below are provided specifically to better illustrate the spirit of the invention and do not limit the present invention unless otherwise specified. In addition, the drawings used in the following description may be enlarged for convenience to make the features of the present invention easier to understand, and the dimensional ratios of each component may not be the same as in reality.

[0014] (Flexible 6-axis force sensor) This document describes a flexible 6-axis force sensor according to one embodiment of the present invention. Figure 1 is a schematic diagram showing the flexible 6-axis force sensor of this embodiment. The flexible 6-axis force sensor 10 of this embodiment comprises at least a first 6-axis force sensor (hereinafter sometimes simply referred to as the first sensor) 11, a second 6-axis force sensor (hereinafter sometimes simply referred to as the second sensor) 12, a flexible elastic body 13, and a calculation unit 14.

[0015] The first sensor 11 and the second sensor 12 detect forces along the three-dimensional directions (X, Y, and Z axes perpendicular to each other) and torque (rotational force) around the X, Y, and Z axes, respectively, and output them to the calculation unit 14. Known 6-axis force sensors can be used for these first and second sensors 11 and 12. In this embodiment, the first sensor 11 and the second sensor 12 are formed on the same plane, with a certain distance between them.

[0016] The flexible elastic body 13 is composed of flexible elastic materials processed into strips or lines. The constituent material of the flexible elastic body 13 is not particularly limited as long as it is a flexible elastic material, but examples include synthetic resins such as polyethylene terephthalate (PET resin) and polyimide resin, and metals such as steel plates. In this embodiment, hardened ribbon steel is used as the flexible elastic body 13, having a uniform cross-sectional shape and a uniform elastic modulus over its entire length in the longitudinal direction.

[0017] The flexible elastic body 13 is fixed at one end 13a to the first sensor 11 and at the other end 13b to the second sensor 12, forming a restraining portion. In this embodiment, the flexible elastic body 13 is positioned between the first sensor 11 and the second sensor 12, which are spaced apart, in an uncontacted state, so as to bend 180° against an elastic force with its longitudinal center as the apex.

[0018] The calculation unit 14 includes an A / D converter 21 and an information processing device 22 which is a personal computer. The A / D converter 21 converts the analog signals output from the first sensor 11 and the second sensor 12, respectively, into digital signals and inputs them to the information processing device 22. The A / D converter 21 is not particularly limited and can be mounted on the PCI bus of the information processing device 22, or it can use various interfaces such as USB or LAN cables.

[0019] The information processing device 22 can use a general-purpose personal computer and is equipped with, for example, a CPU 23, ROM 24, RAM 25, display unit 26, operation unit (keyboard, mouse) 27, non-volatile storage (hard disk drive) 28, etc.

[0020] The information processing device 22 performs calculations based on various pre-inputted settings and the output signals of the first sensor 11 and the second sensor 12. Based on the contact position (coordinates) of the object to be detected with respect to the flexible elastic body 13 provided between the first sensor 11 and the second sensor 12, the static characteristics of the force and torque received from the object, and the deformation theory of the flexible elastic body 13, it calculates the deformed shape of the flexible elastic body 13, the coordinates of the point of application of the force, and the magnitude of the force and torque at this point of application. These calculation results are then displayed on the display unit 106. Specific examples of such calculations (calculation methods of the calculation unit) will be described later.

[0021] With the flexible 6-axis force sensor 10 configured as described above, by providing a curved flexible elastic body 13 between the two 6-axis force sensors, the first sensor 11 and the second sensor 12, it is possible to detect the coordinates of the contact position of the object to be detected with respect to the flexible elastic body 13, and the contact force of the object to be detected with respect to the flexible elastic body 13, without deforming or damaging the object to be detected, even if the object to be detected is a low-strength item.

[0022] For example, if such a flexible 6-axis force sensor 10 is used as a force sensor on a robot arm, it can be used to detect soft foods or paper cups containing liquids and to grasp them with appropriate gripping force.

[0023] In this embodiment, the flexible elastic body 13 is provided so as to bend 180° between the first sensor 11 and the second sensor 12 with its longitudinal center as the apex when it is not in contact with the object to be detected. However, the degree of bending of the flexible elastic body 13 is not limited to 180°. The bending angle of the flexible elastic body 13 can be any angle other than 0° (planar state), and for example, it can be bent to 45° or 60°.

[0024] (Calculation method for flexible 6-axis force sensor) Next, the calculation method of the flexible 6-axis force sensor 10 described above will be explained. First, the operating principle of the flexible six-axis force sensor 10 will be described. FIG. 2 is an explanatory diagram showing the forces and torques applied to each part of the flexible six-axis force sensor 10. The reference signs in FIG. 2 are as follows. t: Point of action applied to the flexible elastic body 13 m: Load torque at the point of action f: External force O: Focus of the first sensor 11 and the origin p <><: Position vector of the point of action with respect to the first sensor 11 p g : Position vector of the focus of the second sensor 12 with respect to the first sensor 11 f S1 : Force measured by the first sensor 11 f S2 : Force measured by the second sensor 12 m S1 : Torque measured by the first sensor 11 m S2 : Torque measured by the second sensor 12 f b1 : Reaction force received by the first sensor 11 from the installation surface f b2 : Reaction force received by the second sensor​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Furthermore, the relationship between the sensor in the second sensor 12 and the flexible elastic body 13 is given by the following equations (3) and (4). f S2 +f b2 =0···(3) m S2 +m b2 =0···(4) Furthermore, the quasi-static force equilibrium of the flexible elastic body 13 is given by equation (5). f+f b1 +f b2 =0···(5) Furthermore, the balance of moments around the origin O of the flexible elastic body 13 is given by equation (6). m b1 +m b2 +m+(p t ×f)+(p g ×f b2 )=0···(6) When equations (1) to (6) are rearranged and summarized, we get equations (7) and (8). f=f S1 +f S2 ...(7) p t × (f S1 +f S2 )=m s1 +m s1 +p g ×f s2 -m···(8) From equation (7), it can be seen that the external force f can be immediately determined from the sensor value. On the other hand, equation (8) is p t This shows the relationship between and m, but this alone is not enough to find the solution, so by examining the shape of the flexible elastic body 13, p t We find the result and obtain m from it.

[0027] To investigate the shape of the flexible elastic body 13, the present inventors used the method described in Japanese Patent No. 6558727, and modeled a virtual cross-section of the flexible elastic body 13 divided into two by point, as shown in Figure 3. Of the divided flexible elastic body 13, the side facing the first sensor 11 is designated as rod 1, and the side facing the second sensor 12 is designated as rod 2.

[0028] Then, the internal force f acts on the virtual cross-sectional end of rod 1. t1 , internal force vector m t1 Let f be the internal force acting on the virtual cross-sectional end of rod 2. t2 , internal force vector m t2 Therefore, Figure 3 only considers a virtual cross-section of the flexible elastic body 13 divided into two parts, and there is no essential change in the internal state. Thus, the internal forces and internal force vectors acting on the end of rod 1 on the first sensor 11 side (one end) and the end of rod 2 on the second sensor 12 side (the other end) are the same as in Figure 2.

[0029] First, let's consider the shape of rod 1. Figure 4 is a schematic diagram showing the state of rod 1. Using the endpoint of rod 1 fixed to the jig as a reference, let s be the length (arc length) of rod 1 along the deflection curve. Let l1 be the total length of rod 1, which is an unknown variable. On rod 1, s ∈ [0, l1]. Next, let's consider the position vector p(s) on the deflection curve, parameterized by s, and the Freinet mark F(s) = [t(s)n(s)b(s)].

[0030] Here, t(s), n(s), and b(s) represent the unit tangent vector, unit principal normal vector, and unit binormal vector of the deflection curve parameterized by the arc length s, respectively. Similarly, m(s) is the bending moment parameterized by the arc length. However, the positive direction of the bending moment is defined as the direction in which bending is performed such that a positive rotation is applied around each axis of the Freinet guide structure when viewed from the fixed end side (s=0 in this case), which is the sensor side.

[0031] Next, we consider a virtual cross-section at an arbitrary arc length point s∈[0,l1]. In this case, the moments acting on the ends of the virtual cross-section of the flexible elastic body 13 coincide with m(s) and -m(s), as shown in Figure 3. For the rod on the side where m(s) is acting, the balance of moments around the ends of the virtual cross-section is given by equation (9). m(s)+m b1 +(-p(s))×f b1 =0···(9) By rearranging equation (9) using equations (1) and (2), we obtain equation (10) for any s ∈ [0, l1]. m(s) = m s1 -p(s) × f s1 ...(10)

[0032] Here, there is a small line element d at any point s∈[0,l1]. s We consider the mechanics of deformation by focusing on this. The Kirchhoff elastic rod model describes the deformation of a beam whose length is sufficiently large relative to its cross-sectional area when in equilibrium. This model assumes that at a certain arc length s, the rotation axis vector ω(s), which represents the rotation of the Freinet rod per unit length, is approximately proportional to the bending moment vector and is hardly affected by shear force, and can be expressed by equation (11). F(s)K·ω(s)=m(s)···(11)

[0033] However, K in equation (11) is the stiffness matrix of the flexible elastic body 13 in the F(s) system and is a constant throughout the entire flexible elastic body 13. Also, F(s) on the left side of equation (11) transforms the force moment into the same system as the external torque. By rearranging equation (11) taking into account that F(s) is an orthogonal matrix, we obtain equation (12). ω(s)=K -1 F T (s)m(s)···(12) However, F T (s) is the transpose of F(s).

[0034] Next, we consider the relationship between the axis of rotation ω(s) and the Freinet stylus F(s) that represents the attitude. For this purpose, we use the unit vector n=[n1n2n3] T Let us consider the rotation representation matrix Rn(θ) which represents a rotation by an angle θ around the axis. Here, the superscript T represents the transpose. This can be expressed as equation (13) from Rodrigues' rotation formula. R n (θ)=e θS(n) =I+sinθ·S(n)+(1-cosθ)·S 2 (n)···(13) However, I is the cubic identity matrix and S(n) is the cross product representation matrix, which is a skew-symmetric matrix as shown in equation (14).

[0035]

number

[0036] Here, the rotation axis vector whose magnitude is the rotation angle of the uniform rotation from the Freinet mark F(s) to F(s+ds) at the endpoint of the small interval is ds·ω(s). Using equation (13), we can express this and, taking into account that ds is small and the properties of the skew-symmetric matrix, we obtain equation (15).

[0037]

number

[0038] However, in equation (15), θ is the magnitude of ω(s) and n is a unit vector in the direction of ω(s), so ω(s) = θ·n. Thus, the relationship between the rotation axis vector ω(s) per unit length representing the deformation at arc length s and the Freinet standard F(s) representing the attitude is clarified. Furthermore, the position vector p(s) on the deflection curve of the flexible elastic body 13 is parameterized by the arc length, and since dp / ds is a unit tangent vector of magnitude 1, equation (16) is obtained. dp / ds = t(s) ... (16)

[0039] Based on equations (10), (12), (15), and (16) described above, the values ​​of p(s) and F(s) are determined by numerical integration. This can be done by discretizing these equations and successively determining the values ​​using recurrence relations. Since the values ​​of p(0) and F(0) are known, representing the position and orientation of the fixed end (sensor-side fixed part) of the flexible elastic body 13, these are used as initial values. For example, a 4-stage, 4th-order Runge-Kutta method can be used.

[0040] Here, the problem is that the value of s = l1, which is the end point of the recurrence formula for numerical integration, is unknown. The result of the numerical integration described above is only an approximate solution for the range of s ∈ [0, l1]. Although the value of numerical integration can be obtained without problems in the range of l1 < s, the result no longer approximates the shape of the flexible elastic body 13. However, first, regarding the total length of the flexible elastic body 13 as l, numerical integration is performed for the corresponding range of s ∈ [0, l] in this entire range, and all the obtained values of p(s) and F(s) are saved. An image of the result of the numerical integration of the rod 1 is shown in FIG. 5.

[0041] Next, considering the rod 2 in FIG. 3 in the same way, the following equations (17) to (20) are obtained. m σ (σ)=m s2 -(p σ (σ)-p g )×f s2 ···(17) ω σ (σ)=K -1 F σ T (σ)m σ (σ)···(18) (d / dσ)×p σ (σ)=F σ (σ)S(ω)···(19) (d / dσ)×p σ (σ)=t σ (σ) ···(20)

[0042] However, σ is an arc length parameter based on the end point of the flexible elastic body 13 (rod 2) on the side of the second sensor 12, and the above equations (17) to (20) hold for σ ∈ [0, l - l1]. Also, the subscript σ indicates that it is a function parameterized by the arc length σ, showing that it is different from the function parameterized by the arc length s without a subscript. Here, regarding p σ (0) and F σNumerical integration is performed with (0) as the initial value. However, as with rod 1, numerical product decomposition can be obtained in the range l-l1<σ, but this no longer approximates the shape of the flexible elastic body 13. However, for the time being, numerical integration is performed in the range σ∈[0,l] which corresponds to the entire range of the flexible elastic body 13, and p σ (σ) and F σ Save all the results of (σ). Figure 6 shows an image of the result of the numerical integration of rod 2.

[0043] As can be seen by comparing Figure 5 and Figure 6, the point of application p t Therefore, both numerical integration results are correct, and theoretically, the position and orientation match. On the correct deflection curve of the flexible elastic body 13, σ = ls, and since dσ = -ds, the directions are reversed, we get equations (21) and (22). p σ (l-l1)=p(l1)···(21) F σ (l-l1)=-F(l1)···(22)

[0044] If the step size of the numerical integration is sufficiently small, then among the results of the numerical integrations of rod 1 and rod 2 that were saved, s = l - σ that satisfies equations (21) and (22) gives s = l1. In actual calculations, there are errors in numerical calculations, modeling errors of the flexible elastic body 13, noise from the first sensor 11 and the second sensor 12, and the step size of the finite numerical integration. As a result, it is generally considered that there are no saved numerical integration results that satisfy equations (21) and (22). Therefore, the value of s that minimizes these errors is selected and set as l1. Equation (23) is an example of such an error function.

[0045]

number

[0046] However, in equation (23), tr is the trace of the matrix, c p c is the weighting value for the position error. Fis the weighted value of the posture error. The second term on the right side of Equation (23) expresses the magnitude of the posture matrix error in terms of the rotation angle around the rotation axis from the inverse of Rodrigues' rotation formula.

[0047] In the above procedure, l1 is obtained, and p t = p(l1) = p σ (l - l1) is obtained. By substituting this result into Equation (8), m is obtained. In the above procedure, from the values f S1 , f S2 , m S1 , m S2 of the first sensor 11 and the second sensor 12, the shape of the flexible elastic body 13 deformed by the externally applied force and torque, and the position vector p t of the acting point, the external force f, and the value of the load torque m at the acting point can be estimated.

[0048] Based on the above principle, the calculation method actually performed by the calculation unit 14 of the flexible six-axis force sensor 10 will be described. However, taking the x-axis in the direction of p g , the z-axis in the vertically upward direction, and the y-axis such that the x-axis, y-axis, and z-axis form a right-handed system. In the explanation of the above principle, a load torque was applied to the flexible elastic body 13. For this, it is necessary to apply a force to the lever fixed on the flexible elastic body 13 or pinch the flexible elastic body 13. When such an input is not conceivable, it can be assumed that m = 0 for the load torque. Also, since the flexible elastic body 13 hardly deforms in the width direction, p = [p x 0 p z T is assumed. At this time, it can also be assumed that the force acts within the x-z plane. For the same reason, the force detected by the first sensor 11 is f s1 = [f x1 0 f x1 T , and the force detected by the second sensor 12 is f s2 = [f x2 0 f x2 T is set. Also, regarding the moments detected by the first sensor 11 and the second sensor 12, it is considered that they occur only around the y-axis, so m s1+m s1 =[0m y 0] T Assume that. p g =[p g 00] T Then, the above-mentioned formula (8) can be simplified to the following formula (24).

[0049]

Number

[0050]

Number

[0051] From formula (25), the straight line passing through the point of action of the force is obtained, and the shape curve of the flexible elastic body 13 intersects this straight line at the point of action of the force. Therefore, by performing the rod integration until it intersects the straight line using this straight line as the discriminant, the magnitude and point of action of the force can be obtained by one rod integration for one sample of sensor information.

[0052] Based on the above principle, it is performed by the arithmetic unit 14 of the flexible six-axis force sensor 10. (Step 0) First, in a state where no load is applied to the flexible elastic body 13, the user makes a zero-point correction request via the operation unit 27.

[0053] (Step 1) Upon receiving the zero-point correction request, the operation program of the arithmetic unit 14 estimates the force and torque detected by the first sensor 11 and the second sensor 12 in a state where no force or moment is applied to the flexible elastic body 13. First, as shown in Figure 7, we use a model in which only one end of the flexible elastic body 13 is fixed to the sensor. In this case, the flexible elastic body 13 is in equilibrium in an upright position, pointing vertically upward from the fixed end. Now, we apply a force vertically downward to the end of the flexible elastic body 13 that is not fixed to the 6-axis force sensor, and focus on the state in which the end is facing horizontally when it reaches equilibrium, as shown in A in Figure 7. Since the dimensions and elastic modulus of the flexible elastic body 13 are known, the shape of the flexible elastic body 13 and the magnitude of the external force at this time are analytically known and can be determined using elliptic functions.

[0054] A method for determining the constraint force and torque information at both ends of a rod that takes a specified tip position and orientation from an arbitrary rod shape as an initial value, using convergence calculations, is proposed, for example, in Japanese Patent No. 6558727, discovered by the present inventors. Using this method, it is possible to determine the constraint force and torque information at both ends of a rod that takes the shape shown in Figure 7, B, using a known shape like A in Figure 7 as the initial shape. From the action-reaction relationship, the force and torque information detected by the first sensor 11 and the second sensor 12 can also be determined using this constraint force and torque information. The values ​​of the two 6-axis forces and torques obtained in this way are stored in RAM 25. For convenience, it is assumed that these values ​​are stored in a variable called SigA.

[0055] (Step 2) Next, the program of the calculation unit 14 acquires the force and torque detected by the first sensor 11 and the second sensor 12 while no force or moment is actually applied to the flexible elastic body 13, and stores them in the RAM 25. For convenience, let's assume that it is stored in a variable called SigB. Ideally, SigB should match SigA, but in reality, they do not match due to the measurement principles of the first sensor 11 and the second sensor 12, and for some offset signal Offset, it is shown by the following equation (26). SigB = SigA + Offset (26) The preparations are now complete.

[0056] (Step 3) The program enters an infinite loop and reads the signals from the first sensor 11 and the second sensor 12. Let the read signal be SigC. Since SigC also has the same offset signal Offset as SigB, the actual force / torque signal Sig applied at the base of the rod is given by the following equation (27). Sig = SigC + Offset···(27) Therefore, to actually obtain Sig, we perform the operation in equation (28) based on equations (26) and (27). However, the operation is performed element by element. Sig = SigC - SigB + SigA...(28) SigA and SigB are retrieved from RAM25 for calculations, and the resulting Sig values ​​are stored in RAM25.

[0057] (Step 4) A subroutine for the discriminant expression is constructed using the value of Sig and equation (25). By substituting the position vector of the flexible elastic body 13 into this discriminant expression, it is possible to determine whether that point is on the flexible elastic body 13 on the side of the first sensor 11 or on the side of the second sensor 12 relative to the point of application.

[0058] (Step 5) Using the Sig signal, numerical integration is first performed with the first sensor 11 as the initial value. In this embodiment, a 4-stage, 4th-order Runge-Kutta method is used for numerical integration. Performing one step of numerical integration yields the position and orientation of the flexible elastic body 13 a certain length ahead. Since the length of the flexible elastic body 13 is fixed and the distance advanced in one step is also fixed, the number of rod integrations is finite. Let this number be N. The position and orientation information of step i is stored in the i-th element of an array Z of length N. The position vector is substituted into the discrimination subroutine created in step 4. If the result is "towards the second sensor 12" rather than the point of application, proceed to step 5; otherwise, continue the numerical integration steps. However, if step i exceeds N, terminate the rod integration and proceed to step 7.

[0059] (Step 6) Let I be the number of steps in the numerical integration performed in Step 5. Now, we perform numerical integration using the second sensor 12 as the initial value to determine the position and orientation of the flexible elastic body 13. The result of the j-th step of this rod integration is stored in the Nj-th element of array Z. After performing NI rod integrations, values ​​will be stored in exactly all elements of array Z.

[0060] (Step 7) The first element of array Z represents information about the point of application. Output regarding the point of application is performed here. In addition, the force and torque information is calculated and output from the point of application information, the Sig information, and equation (25).

[0061] (Step 8) Furthermore, if necessary, the shape of the deformed flexible elastic body 13 is displayed on the display unit (display) 26 based on array Z. If measurements are to be performed continuously, return to step 3 and continue the calculation.

[0062] The calculations performed by the calculation unit 14 as described above enable the calculations of the flexible 6-axis force sensor 10 of this embodiment.

[0063] Although embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Examples]

[0064] The effects of the present invention were verified. For the verification process, we prepared a flexible 6-axis force sensor as shown in Figure 1. (Flexible elastic material) Size: Length (effective length) 260mm x Width 20mm x Thickness 0.2mm Material: Hardened ribbon steel (SK85: manufactured by Nippon Polishing Belt Co., Ltd.): Calculated with Young's modulus of 206 GPa and Poisson's ratio of 0.3. (Flexible 6-axis force sensor (common to both sensor 1 and sensor 2)) Model number FFS080F500M5R0A6 (manufactured by Leptrino Inc.): Rated 50N / 5Nm, resolution ±1 / 4000, sampling rate 1.2kHz, depth to focus 8mm (the reference point for moment measurement of the flexible 6-axis force sensor is slightly deeper than the package surface). Distance between the first and second sensors (focal distance): 150 mm (Base (sensor mounting surface)) Acrylic sheet (5mm thick) (Jig (support member for flexible elastic body)) Made from PLA resin (polylactic acid), created using a 3D printer. Jig height: 22mm (designed so that the base of the flexible elastic body is 30mm from the sensor focus)

[0065] Using the flexible 6-axis force sensor configured as described above, a load was applied to an arbitrary point of application of a flexible elastic body, and the coordinates of the point of application, the magnitude of the force applied to the point of application, the direction of the force applied to the point of application (torque), and the deformation shape were output. The set values ​​and obtained measurements for each of the measurement examples 1 to 4 are summarized in Figures 8 to 11.

[0066] As shown in the measurement examples in Figures 8-11, when a load was applied to an arbitrary position (point of application) of a flexible elastic body using the flexible 6-axis force sensor of this embodiment, measured values ​​(coordinates, magnitude of force, direction of force (torque)) that approximated the set value were obtained. Furthermore, it was possible to display the shape of the flexible elastic body that approximated the actual deformed shape. Therefore, the effectiveness of the flexible 6-axis force sensor of this embodiment could be confirmed. [Industrial applicability]

[0067] According to the flexible 6-axis force sensor and its calculation method of the present invention, even flexible objects can be detected without damage or deformation, making them suitable for use in devices such as robot hands. Therefore, it has industrial applicability. [Explanation of symbols]

[0068] 10... Flexible 6-axis force sensor 11…First 6-axis force sensor (first sensor) 12…Second 6-axis force sensor (second sensor) 13…Flexible elastic body 14...Arithmetic section

Claims

1. A first six-axis force sensor and a second six-axis force sensor that detect forces and torques applied in each of the three dimensions, A curved, flexible elastic body extending in a strip or linear shape is fixed at one end to the first six-axis force sensor and at the other end to the second six-axis force sensor, A flexible six-axis force sensor, characterized by having a calculation unit that calculates the three-dimensional coordinates of the point of application, which is the contact position of the object to be detected with the flexible elastic body where the force and torque are applied, and the magnitude of the force and torque at the point of application, based on the force information and torque information output from the first six-axis force sensor and the second six-axis force sensor, respectively, when force and torque are applied to the flexible elastic body from an external source.

2. The flexible six-axis force sensor according to claim 1, characterized in that the flexible elastic body is a strip or linear body having a known cross-sectional shape and a known elastic modulus along its entire length.

3. The flexible 6-axis force sensor according to claim 1 or 2, characterized in that the flexible elastic body is bent 180° with its longitudinal center as the apex.

4. A method for calculating with a flexible six-axis force sensor using the flexible six-axis force sensor described in claim 1 or 2, The calculation unit compares first deformation information obtained from the signal output from the first six-axis force sensor, which is numerically calculated from one end of the flexible elastic body toward the other end, with second deformation information obtained from the signal output from the second six-axis force sensor, which is numerically calculated from the other end of the flexible elastic body toward the one end, and determines a point of application where the coordinate values ​​and orientation values ​​are similar to each other, outputs the coordinate values ​​of the point of application and the applied force value, and displays the overall deformation shape of the flexible elastic body.

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