Articulation with controllable stiffness and force-measuring device

Abstract

The subject matter of the invention is an articulation (1) with controllable stiffness and a force-measuring system, comprising a first device (20) that comprises a frame (4) having a curved face and connected to a first motor element (2), the first device (20) regulating the position of the articulation (1), and a second device (22) that regulates the stiffness of the articulation (1) and comprises a thrust element (15), the movement (D) of which determines the pre-compression of a resistive element (11) and thus the stiffness of the articulation (1); the first motor element (2) causes the frame (4) to rotate such that a wheel (8) of the second device (22) rolls on the curved face of the frame (4), causing the resistive element (11) to be compressed (C) via a transmission rod (7) associated with the wheel (8) and with the resistive element (11).

Claims

1. An articulation (1) with controllable stiffness, comprising: a first device (20) comprising a frame (4) connected to a first motor element (2), this first device (20) being configured to regulate a position of the articulation (1), a second device (22) configured to regulate a stiffness of the articulation (1) and which anchors the first device (20) to the articulation (1), the second device (22) comprising: a resistive element (11), a transmission rod (7) having one end attached to the resistive element (11) and an opposite end comprising a wheel (8), a thrust element (15) with a threaded spindle (16) through it, on which the resistive element (11) rests, a second motor (12) attached to the spindle (16), which provides a displacement (D) to the thrust element (15) by a rotation of said spindle (16), and a coupling body (13) on which the resistive element (11), the transmission rod (7), the thrust element (16), and the second motor (12) are arranged, wherein the displacement D of the thrust element (15) determines a pre-compression of the resistive element (11), thus determining the articulation (1) stiffness, and the first motor element (2) provides a rotation to the frame (4) of the first device, wherein the frame (4) has a curved face, such that, with the rotation of the frame (4), the wheel (8) of the second device (22) rolls on the curved face of the frame (4), and the transmission rod (7) associated with said wheel (8) causes a compression (C) of the resistive element (11) of the second device (22), thus the compression (C) and the velocity at which it occurs determines a force F.sub.thrust developed by the resistive element (11).

2. The articulation (1) with controllable stiffness, according to claim 1, wherein the resistive element (11) comprises an elastic element with a characteristic constant K, and/or a shock absorber element with a characteristic constant A, or a combination thereof.

3. The articulation (1) with controllable stiffness, according to claim 1, wherein the second device (21) comprises a rotational measuring element (17) connected to the second motor (12), said rotational measuring element (17) counting the revolutions of a shaft of the second motor (12) such that the displacement (D) of the thrust element (15) can be determined by performing a conversion of the revolutions of the second motor (12) and of the pitch of the spindle (16), where a revolution of the second motor (12) is equivalent to the pitch of the spindle (16) in the linear displacement of the thrust element (15) associated with the spindle (16), so that the displacement (D) of the thrust element (15) can be determined by the relation D=Revolutions.Math.Pitch.

4. The articulation (1) with controllable stiffness, according to claim 3, wherein the second device (22) comprises a linear measurement element (9) and a graduated scale (10) attached to the transmission rod (7), such that compression experienced by the resistive element (11), and the velocity at which it occurs, associated to the rotation of the frame (4) can be determined through the linear measurement element (9), which measures the displacement of the transmission rod (7) on the graduated scale (7).

5. The articulation (1) with controllable stiffness, according claim 1, wherein the resistive element (11) associated with its stiffness may be used to obtain the measure of a torque generated at the articulation (1) by the relation:
Torque={right arrow over (b)}{right arrow over (F)}.sub.n, which is converted into Torque=b.Math.F.sub.n.Math.sin(*) where b is a vector that represents a distance between an articulation rotation axis (O) and a point of contact of the frame (4) with the wheel (8), and F.sub.n is the contact force between the surfaces of the frame (4) and of the wheel (8) in the radial direction of the wheel (8); * is an angle between the vector {right arrow over (b)} and the vector F.sub.n, where b is obtained from the relation: {circumflex over (b)}={square root over (OB.sup.2+R.sup.22.Math.OB.Math.R.Math.cos())} where is the complementary angle which defines the inclination of the vector of the contact force {right arrow over (F)}.sub.n, and is obtained by the relation $=\stackrel{\_}{\mathrm{OA}}.Math.\frac{\sin }{\stackrel{\_}{\mathrm{BA}}},$ where is the deflection angle obtained from $=\mathrm{acos}\left[\frac{\stackrel{\_}{{\mathrm{OB}}^2}+{\stackrel{\_}{\mathrm{OA}}}^2-{\stackrel{\_}{\mathrm{BA}}}^2}{2\stackrel{\_}{\mathrm{OB}}.Math.\stackrel{\_}{\mathrm{OA}}}\right],$ where: OB: distance from the rotation axis of the articulation (1) to the centre of curvature of the frame (B); OA: distance from the articulation rotation axis (O) to the centre of the wheel (A); BA: distance from the centre of the curvature of the frame (B) to the centre of the wheel (A), * is obtained from the expression *=++, where $=\mathrm{arc}\cos \left[\frac{{\stackrel{\_}{b}}^2+{\stackrel{\_}{\mathrm{OA}}}^{2-r^2}}{2.Math.\stackrel{\_}{b}.Math.\stackrel{\_}{\mathrm{OA}}}\right]$ $\mathrm{Fn}=F_{\mathrm{thrust}}\cos \left(\right)$ where:
F.sub.thrust=K.Math.C+A.Math.Vel where K and A are the constant characteristic of the resistive element (11), C is the compression of the resistive element (11) and Vel is the velocity at which such compression occurs in the resistive element (11).

6. The articulation (1) with controllable stiffness according to claim 1, wherein the first device (20) comprises, in addition to the frame (4) and the first motor element (2): a reducer (3) having an stationary part and an outlet part, the frame (4) being connected to the stationary part of the reducer (3), a first disc (6) connected to the reducer output (3), and a second disk (5), connected to the frame (4), into which the first disc (6) is inserted.

7. The articulation (1) with controllable stiffness, according to claim 1, wherein the coupling body (13) of the second device (22) comprises guide channels (14) that guide the movement of the thrust element (15) and through-holes (21), with the transmission rod (7) passing through the through-holes (21).

8. The articulation (1) with controllable stiffness, according to claim 1, wherein the thrust element (15) is a flat piece, whose movement is limited by the guide channels (14) of the coupling body (13) of the second device (22).

Description

DESCRIPTION OF THE FIGURES

(1) In order to complete the description and to help achieve a better understanding of the features of the invention, this patent specification is accompanied by a set of drawings as an integral part, wherein the following has been represented merely for illustrative and non-limiting purpose:

(2) FIG. 1 shows an elevation view of an embodiment of the articulation object of the invention.

(3) FIG. 2 shows an exploded view of an embodiment of the articulation object of the invention.

(4) FIG. 3 shows a front view of the articulation in neutral position and with deflection.

(5) FIG. 4 shows a front view of the articulation with different pre-compression.

(6) FIG. 5 shows the articulation by evidencing the influence of the deflection and compression of the resistive element in the contact angles, where the geometric relations that allow to obtain the reaction force Fn as a function of the vertical component F.sub.thrust can be seen.

(7) FIG. 6 shows an elevation view of the elements of the position variation.

(8) FIG. 7 shows an elevation view of the elements for the fixation and control of the stiffness.

(9) FIG. 8 shows four configurations of the element resistive, i.e., elastic cushioned stationary, elastic cushioned variable, only elastic or only cushioned and adjustable configuration.

(10) Below is a list of the elements represented in the figures that make up the invention:

(11) 1.articulation, 2.first motor element, 3.reducer, 4.frame, 5.second disc, 6.first disc, 7.transmission rod, 8.wheel, 9.linear measurement element, 10.graduated scale, 11.resistive element, 12.second motor element, 13.coupling body, 14.guide channels, 15.thrust element, 16.spindle, 17.rotational measurement element, 18.first body, 19.second body, 20.first device, 21.through-hole, 22.second device; O.rotation axis of the articulation; A.center of the wheel; B.centre of curvature of the frame; C.compression of the resistive element, D.Displacement of the thrust element. K.constant characteristic of the resistive element, A.shock absorption constant of the resistive element.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

(12) In view of the above mentioned and with reference to the numbering adopted in the figures, the object of the invention is an articulation (1) with controllable stiffness, which allows to control the automatic rotational motion of a first body (18) and a second body (19), which are attached to a pivot point and simultaneously allow to control the stiffness of said rotational motion.

(13) The articulation (1) object of the invention has the ability to regulate its position and stiffness independently, and for this regulation it uses two devices (20, 22) arranged in series along the said articulation (1) so that the presence of the two devices (20, 22) does not cause an increase in total volume with respect to an articulation (1) that does not have said devices (20, 22) for regulating the position and stiffness that the articulation (1), object of the invention, has. By these regulations the articulation (1) object of the invention allows the measurement of the force developed in the articulation (1) through the devices regulating the position and stiffness of the articulation (1).

(14) The articulation (1) object of the invention (which can be seen in FIGS. 1 and 2) comprises a first device (20) (which can be seen in FIG. 6) which performs the regulation of the position of the articulation (1), this first device (20) comprising the following elements: a frame (4) connected to a first motor element (2), which has a curved face; a reducer (3) having a stationary part and an output part (4), the frame being connected to the stationary part of the reducer (3); a first disc (6) connected to the reducer output (3); a second disk (5), connected to the frame (4), into which the first disc (6) is inserted.

(15) The joining of the pieces that make up this first device (20) is made by nuts and bolts.

(16) This first device (20) (which can be seen in FIG. 6) connects to the first body (18) at the point where the first body (18) is pivotally connected relative to the second body (19).

(17) The second device (22) is a device that regulates the stiffness of the articulation (1) (which can be seen in FIG. 7) and acts as anchorage for the first device (20). The second device (22) comprises the following elements: a coupling body (13) comprising guide channels (14) and through-holes (21), with the coupling body (13) embracing the first body (18); a resistive element (11) with different configurations (which can be seen in FIG. 8); a transmission rod (7) moving along the inside of the through-holes (21) of the coupling body (13), the transmission rod (7) being connected at one end to the resistive element (11) and comprising a wheel (8) at the opposite end, with the wheel (8) being in contact with the curved face of the frame (4) of the first device (20); a thrust element (15) which is moved guided by the guide channels (14) of the coupling body (13) and contacts the resistive element (11); a second motor (12) which changes the position of the thrust element (15) through a threaded spindle (16) on said thrust element (15); a linear measuring element (9) which is fixed in the coupling body (13); a graduated scale (10) connected to the transmission rod (7) moving inside the linear measurement element (9).

(18) The element (11) is formed by the combination of two elements: an elastic element (having a characteristic constant K) and a shock absorber element (with a shock absorption constant A) and possible combinations thereof. Furthermore, the shock absorber element has two options: being a stationary shock absorber or a variable shock absorber.

(19) In one embodiment of the invention, the thrust element (15) is a flat piece that is guided within the guide channels (14) of the coupling body (13). On this flat piece, the resistive element (11) rests, so that through the displacement of the thrust element (15) a pre-compression of the aforementioned resistive element (11) can be performed. Also the transmission rod (7) is attached to this resistive element (11).

(20) The second motor (12) modifies, through the spindle (16), the position of the thrust element (15) that is moved over the guide channels (14). By varying the position of the thrust element (15) the pre-compression of the resistive element (11) of the second device (22) is modified. Since this thrust element (15) is the element on which the resistive element (11) rests, the position in which the thrust element (15) is determines the pre-compression of the aforementioned resistive element (11).

(21) As the resistive element (11) is associated to the thrust force of the transmission (7) and the wheel (8) contacts the frame (4), it is the pre-compression of the resistive element (11), together with the values of the constants K and A of the resistive element (11) that determine the stiffness of the articulation (which can be seen in FIG. 5).

(22) The initial pre-compression of the resistive element (11) is known thanks to a rotational measurement element (17) connected to the second motor (12). Said rotational measurement element (17) is a rotational encoder that allows to know the revolutions of the second motor (12) when said second motor (12) is moving. In order to know the initial pre-compression, a conversion of the revolutions of the second motor (11) and of the pitch of the spindle (16) must be performed, a revolution of the second motor (12) being equivalent to the pitch of the spindle (16) in the linear displacement of the mentioned spindle (16).

(23) The conversion of the revolutions of the second motor (12) and the pitch of the spindle (16) to the linear displacement of the thrust element (15), is such that once the pitch of the spindle (16) and the number of revolutions made by the second motor (12) are known, the linear displacement of the thrust element (15) connected to the spindle (16) is known through the relation:
Displacement=N.Math.P
Where: D: Displacement of the thrust element (15), N: N.sup.o of revolutions of the second motor (12), P: Pitch of the spindle (16).

(24) The linear measurement element (9) in the preferred embodiment of the invention is a linear encoder, which in combination with the graduated scale (10) performs the measurement of the linear displacement of the transmission rod (7) in the graduated scale (10).

(25) With the thrust element (15) fixed at a position, i.e., with the stiffness of the articulation (1) already fixed, it is the shape of the frame (4) of the first device (20) that causes a compression of the resistive element (11) of the second device (22) in the presence of deflection at the articulation (1) (see FIG. 3).

(26) The geometric shape of the frame (4) contributes to the measurement of torque and to a mechanical locking that allows a maximum of deflection to be adjusted as a function of the geometry of the frame (4).

(27) The second device (22) acts as an anchorage of the first device (20), while through the contact of the wheel (8) on the curved face of the frame (4), the wheel (8) applies a pressure corresponding to the force transmitted by the transmission rod (7) attached to the resistive element (11), the transmission rod (7) moving inside the through-holes (21).

(28) The second device (22) can modify its geometry, thus allowing a greater or lesser deflection in the articulation (1) (as shown in FIG. 3). The torque of the articulation (1) can be measured by the trigonometric relations between the elements of the second device (22) for force control in the articulation (1).

(29) When the first motor element (2) of the first device (20) applies a torque and the frame (4) performs a rotational movement, the wheel (8) of the second device (22) rolls on the curved face of said frame (4), thus transmitting a reaction along the transmission rod (7), which is connected to the resistive element (11). The resistive element (11), as a function of its pre-compression, exerts more or less resistance to deformation, on which the deflection of the articulation depends (see FIGS. 3 and 4).

(30) Deflection means a rotation in the frame (4) and therefore in the first device (20), without the need of any variation occurring in the position of the articulation (1), or the opposite case, i.e. in which the articulation (1) allows a rotation even when the first motor element (2) has not caused the movement.

(31) The articulation (1) object of the present invention prevents the presence of additional torque measurement elements in the articulation (1) as it takes advantage of the various functionalities of the structural components that can simultaneously be used as sensors.

(32) The articulation (1) object of the invention performs a force measurement of one of the components of F.sub.n, this component being the one that is given by the resistive force of the resistive element (11) (F.sub.thrust). In FIG. 5, the geometric relations that allow obtaining the resistive force F.sub.n as a function of the vertical component, i.e. as a function of F.sub.thrust can be seen.

(33) The graduated scale (10) and the linear measurement element (9) allow knowing the compression (C) of the resistive element (11) and the velocity when knowing the time at which this compression occurs (velocity=change in the position/time).

(34) So, knowing the intrinsic characteristics of the resistive element (11) (mainly the constants K and A of the elements that make up this resistive element (11)) and the values measured by the measurement elements (9, 17), it is possible to know the reactive force on the second device (22).

(35) Once knowing the pre-compression of the resistive element (11), i.e. the displacement (D) that the thrust element (15) moved by the spindle (16) associated to the second motor (12) has experienced, the linear measurement element (9) gives the reading of the displacement experienced by the transmission rod (7) in the deflection of the articulation (1) (coincident with the compression (C) of the resistive element (11)), and the resistive force of the resistive element (F.sub.thrust) is obtained from:
F.sub.thrust=K.Math.C+A.Math.Vel

(36) To know the torque developed by the articulation, it is necessary to know the value of F.sub.n, where F.sub.n, is the force of contact between the surfaces of the frame (4) and of the wheel (8) in the radial direction of the wheel (8).
Torque={right arrow over (b)}{right arrow over (F)}.sub.n
Force {right arrow over (F)}.sub.n can be decomposed into: a perpendicular force supported by the structure (F.sub.structure) and the reaction force of the resistive element (11) (F.sub.thrust) in the compression direction.

(37) $\mathrm{Fn}=F_{\mathrm{thrust}}\cos \left(\right)$$=\mathrm{arc}\cos \left[\frac{{\stackrel{\_}{b}}^2+{\stackrel{\_}{\mathrm{OA}}}^{2-r^2}}{2.Math.\stackrel{\_}{b}.Math.\stackrel{\_}{\mathrm{OA}}}\right]$ b, the vector that represents an arm distance between the articulation rotation axis (O) and the point of contact of the frame (4) with the wheel (8) is known from the relation, (see FIG. 5)
b={square root over (OB.sup.2+R.sup.22.Math.OB.Math.R.Math.cos())}
where (see FIG. 4), OB, is the distance from the articulation rotation axis (O) to the centre of curvature of the frame (B); OA is the distance from the articulation rotation axis (O) to the centre of the wheel (A), which is a function of the compression of the resistive element (11); BA, is the distance from the centre of the curvature of the frame (B) to the centre of the wheel (A). is the complementary angle which defines the inclination of the contact force vector

(38) With equation 2, the expression of the complementary angle p that defines the inclination of the contact force vector is obtained (see FIG. 4):

(39) $=\stackrel{\_}{\mathrm{OA}}.Math.\frac{\sin }{\stackrel{\_}{\mathrm{BA}}}$ is the angle of deflection, which is calculated according to the formula;

(40) $=\mathrm{acos}\left[\frac{\stackrel{\_}{{\mathrm{OB}}^2}+{\stackrel{\_}{\mathrm{OA}}}^2-{\stackrel{\_}{\mathrm{BA}}}^2}{2\stackrel{\_}{\mathrm{OB}}.Math.\stackrel{\_}{\mathrm{OA}}}\right]$

(41) The measurement of the torque generated is obtained, as already mentioned, by the relation:
Torque={right arrow over (b)}{right arrow over (F)}.sub.n
Torque=b.Math.F.sub.n.Math.sin(*) where * is the angle between the vectors of arm and force, which is given by the expression:
*=++

(42) As already mentioned, using the linear measurement element (9) and the graduated scale (10) the compression (C) of the resistive element (11) is known. Furthermore, the movement of the thrust element (15) is also restricted by the transmission rod (7), which moves within the through-holes (21).

(43) The invention discloses an articulation (1), which is actuated with controllable stiffness, and a compact force measuring device, which has a compact arrangement of elements in order to reduce the volume of the articulation (1) and which takes advantage of the resistive element (11) associated to its stiffness to provide a measure of the torque generated.

(44) The invention should not be limited to the particular mode for carrying out the invention described in this document. Those skilled in the art can develop other modes for carrying out the invention in view of the description made herein. Accordingly, the scope of the invention is defined by the following claims.