Cable actuator with improved compactness

Abstract

The present invention relates to an actuator (1), comprising a frame (20), a screw (2) / nut (4) assembly including a nut (4) that engages with a screw (2) extending along a longitudinal axis (Ox), and a motor (3) configured to rotate the screw (2) to effect a linear movement of the nut (4). The actuator (1) further includes a single pair of return mechanisms (10, 11) connected to the output (80) of the actuator (1) and rotatably mounted to the frame (20) together, a first transmission member (6) for transmitting a tensile force, which is connected to the nut (4) at a first end (6.1) and a second end (6.2) and engages with the first return mechanism (10) and the second return mechanism (11), and a detent device (40) for preventing the nut (4) from rotating relative to the screw (2).

Description

Technical Field

[0001] The present invention relates to a cable actuator including a screw / nut assembly, the nut of which is capable of translational movement and is connected to an element moved by a cable.

Background Art

[0002] Cable actuators are known that include a motorised screw extending along a longitudinal axis and attached to a frame. The nut engages with the screw and has anti-rotation means such that relative rotation of the screw and nut causes linear movement of the nut. A first cable having an end connected to the nut forms a first loop between a first pulley and a second pulley of a first pulley pair. A second cable having an end connected to the nut forms a second loop between a third pulley and a fourth pulley of a second pulley pair. The first and third pulleys are generally constrained to rotate on the same shaft and are connected to the output of the actuator. Thus, such a system is a rotary output actuator. Conventionally, the first pulley pair and the second pulley pair are arranged on either side of the screw such that a strand of the first cable extending between the nut and the pulley pair and a strand of the second cable extending between the nut and the pulley pair are located in the same plane including the longitudinal axis. Such a configuration is necessary to balance the forces applied to the nut and limit the risk of friction of the nut and jamming of the nut on the screw. However, due to uncertainties in implementation, parasitic kinematic oscillations of the nut with respect to the screw, and misalignment of the strands, achieving this balance is not a trivial matter. An actuator is obtained that has an overall length close to the maximum travel distance of the nut but has a significant volume with respect to its width (considered in a direction parallel to the axis of rotation of the pulley pair) and height (considered in a direction orthogonal to the axis of rotation of the pulley and the longitudinal axis). This is because the maximum width of such a cable actuator corresponds to the maximum width of the nut and two pulleys when its minimum height corresponds to half the height of the nut and the height of the pulley is added thereto.

[0003] There are also cable actuators that include an electric nut attached to a frame and engaging a screw extending along a longitudinal axis. The screw has anti-rotation means such that rotation of the nut causes linear movement of the screw. A first cable has an end connected to an end of the screw and forms a loop between a first pulley and a second pulley of a first pulley pair. The first pulley and the second pulley are included in a plane perpendicular to the axis of rotation of the pulley and including the longitudinal axis. The pulley is arranged relative to the longitudinal axis such that the longitudinal axis contacts the pulley. Such an arrangement of the pulley and the screw does not cause bending in the screw and is thus necessary to limit the risk of friction and jamming of the screw against the nut. This type of cable actuator has a reduced width compared to the actuator of the type described above, but has an overall length substantially equal to twice the maximum travel distance of the actuator, to which is added approximately the length of the screw. The minimum height of the actuator is also substantially equal to a dimension corresponding to half the height of the nut, to which is added the height of the pulley.

[0004] Therefore, these cable actuators are still considered unsuitable for manufacturing very compact and miniaturized actuators, although they have particularly advantageous properties with respect to the force transmitted and linearity.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to reduce the size of a cable actuator.

Means for Solving the Problems

[0007] For this purpose, an actuator is provided that includes a frame and a screw / nut assembly that includes a nut that engages a screw extending along a longitudinal axis and is configured to rotate the screw to cause linear movement of the nut. According to the present invention, the actuator also includes a single pair of return mechanisms that are both rotatably attached to the frame, and the first return mechanism is connected to the output of the actuator. A first member that transmits a tensile force is connected to the nut by its first end and second end and engages the first return mechanism and the second return mechanism.

[0008] Next, by using a pair of return mechanisms, a cable actuator having a small width and an overall length close to the maximum movement distance of the nut can be obtained.

[0009] Advantageously, the first member that transmits the tensile force is a cable or a notched belt.

[0010] When the anti-rotation device includes a carriage that is first connected to the nut and second connected to the first member that transmits the tensile force, the compactness of the actuator is improved.

[0011] By providing the anti-rotation device with a mechanism that guides the carriage in a direction parallel to the longitudinal axis of the carriage with respect to the frame, the compactness of the actuator can be further improved.

[0012] Advantageously, the guide mechanism is a prism-shaped linear guide mechanism and / or includes two translational guide points.

[0013] According to a preferred embodiment, the carriage is connected to the nut by a first cable pair including a second cable and a third cable extending on both sides of the screw, and a second cable pair including a fourth cable and a fifth cable extending on both sides of the screw.

[0014] When the second cable and the third cable are connected to the nut by a first intermediate support connected to the nut by a seventh cable and an eighth cable, and / or the fourth cable and the fifth cable are connected to the nut by a second intermediate support connected to the nut by a ninth cable and a tenth cable, the operation of the actuator is further improved. This is because this design allows tolerances in guidance and screw positioning and parallelism, as well as parasitic motion vibrations of the nut with respect to the screw, which is particularly favorable for reducing friction and uniformity.

[0015] Most preferably, the actuator comprises a device for tensioning the second and / or third cables. Since these cables are very short, they can be selected for strength rather than rigidity, which helps to reduce the diameter size of the nut.

[0016] If the first pulley and the second pulley have a plurality of grooves for accommodating an additional actuation cable, it is possible to increase the rigidity of the system or the force that can be transmitted.

[0017] Similarly, by using a notched belt instead of an actuation cable, it is possible to increase the articular movement, for example, instead of relying on a pulley with a more expensive helical cable.

[0018] Other features and advantages of the present invention will become apparent by reading the following description of specific non-limiting embodiments of the present invention.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0020] Referring to FIG. 1, an actuator 1 of the present invention, indicated as a whole by 1, includes a frame 20 to which a bearing 21 adapted to a screw 2 rotating about a longitudinal axis Ox is attached. The screw 2 is a ball screw and is rotated by an electric motor 3. A nut 4 engages with the screw 2 and includes a ring 5 protruding radially from the nut 4.

[0021] The actuator 1 is attached so as to rotate about a first shaft 22 fixed to the frame 20 by a first bearing 30 and a first pulley 10, and about a second shaft 23 connected to the frame 20 by a second bearing 31 and a second pulley 11. A pair of pulleys is provided. A first operating cable 6 engages with the first pulley 10 and the second pulley 11. The cable 6 is connected to the nut 4 at its first end 6.1 and second end 6.2 according to a method described later.

[0022] The actuator 1 is provided with an anti-rotation device 40 for preventing the nut 4 from rotating relative to the screw 2. The anti-rotation device 40 includes a carriage 41 that is attached by a guide mechanism 50 so as to be movable in a direction D1 parallel to the axis Ox. The mechanism 50 is, here, a prism-shaped linear guide mechanism including a rail 51 on which a first shoe 52 and a second shoe 53, both fixed to the carriage 41, slide.

[0023] The carriage 41 includes a base 42 that extends substantially parallel to the longitudinal axis Ox, and at the end of the base 42, a first arm 43 and a second arm 44 project. The carriage 41 is connected to the nut 4 by a first cable pair 60 consisting of a second cable 61 and a third cable 62 that extend on both sides of the screw 2, and a second cable pair 70 consisting of a fourth cable 71 and a fifth cable 72 that extend on both sides of the screw 2. As can be seen from FIG. 2, the first cable pair 60 and the second cable pair 70 extend in a direction substantially parallel to the longitudinal axis, and the first cable pair 60 and the second cable pair 70 are arranged on both sides of a first plane P1 that passes through the nut 4 and is perpendicular to the screw 2. More precisely, the third end 61.1 of the cable 61 and the fourth end 62.1 of the cable 62 are crimped to the arm 43. Symmetrically, the fifth end 71.1 of the cable 71 and the sixth end 72.1 of the cable 72 are crimped onto the arm 44.

[0024] The other ends of the second cable 61, the third cable 62, the fourth cable 71, and the fifth cable 72 are crimped to the ring 5.

[0025] As can be seen from FIGS. 1 and 2, the first end 6.1 of the first cable 6 is crimped to the arm 43 and extends parallel to the longitudinal axis Ox up to the first pulley 10, engages in the first groove 10.1 and rotates the first pulley 10 by half a turn. The first cable 6 extends parallel to the longitudinal axis Ox so as to engage in the second groove 11.1 of the second pulley 11 and rotate by half a turn at the outlet of the first pulley 10. Next, the first cable 6 extends up to the ring 5 to which the second end 6.2 of the first cable 6 is crimped. To limit the friction between the cable 6 and the pulleys 10 and 11, the cable 6 is also preferentially connected to the pulley 10 or the pulley 11 by crimping.

[0026] The first pulley 10 is constrained to rotate by the finger 80 that constitutes the output of the actuator 1. Here, the finger 80 corresponds to the phalanx of a mechanized hand, although not shown.

[0027] During operation, under the influence of the command sent to the motor 3, the rotation of the screw 2 causes the same rotation of the nut 4 due to the contact friction between the screw 2 and the nut 4. By this movement, tension is applied to the first cable pair 60 and the second cable pair 70. The cable pairs 60, 70 are connected to the carriage 41 and can only move along the axis Ox of the carriage 41, so the cable pairs 60, 70 exert a force counteracting the rotational drive of the nut 4 by the screw 2. Therefore, when the screw 2 rotates under the action of the motor 3, the nut 4 moves linearly along the longitudinal axis Ox. This movement is transmitted to the carriage 41 by the cable pairs 60, 70, and the cable 6 is connected to the carriage 41. The linear movement of the carriage 41 drives the cable 6, rotates the pulley 10, and activates the finger 80.

[0028] As a result, a cable actuator 1 with a small width and an overall length close to the maximum movement distance of the nut 4 is obtained.

[0029] As can be seen in FIG. 1, the connections of the ends 6.1 and 6.2 of the first cable 6 to the carriage 41 are orthogonal to the first plane P1 and are located (according to the view in FIG. 1) below the second plane P2 that includes the longitudinal axis Ox.

[0030] In addition, components that are the same as or similar to the above-described components will be described with the same reference numerals as those in the second embodiment of the present invention described below.

[0031] According to the second embodiment of the present invention shown in FIGS. 3 and 4, the second end 61.2 of the second cable 61 and the eighth end 62.2 of the third cable 62 are connected to the nut 4 by a first intermediate support 90 connected to the nut 4 by the seventh cable 91 and the eighth cable 92. The first intermediate support 90 is in the form of a ring here and includes a first through-hole 90.1 to which the seventh end 61.2 of the cable 61 is crimped. The first intermediate support 90 also includes a second through-hole 90.2 that is diametrically opposed to the first through-hole 90.1 and to which the eighth end 62.2 of the cable 62 is crimped.

[0032] The first intermediate support 90 also includes a third through-hole 90.3 to which the ninth end 91.1 of the seventh cable 91 is crimped and a sixth through-hole 90.4 to which the tenth end 92.1 of the cable 92 is crimped. The eleventh end 91.2 of the cable 91 is crimped at the seventh through-hole 5.1 of the ring 5, and the twelfth end 92.2 of the cable 92 is crimped at the eighth through-hole 5.2 of the ring 5.

[0033] Similarly, the thirteenth end 71.2 of the fourth cable 71 and the fourteenth end 72.2 of the fifth cable 72 are connected to the nut 4 by a second intermediate support 95 connected to the nut 4 by the ninth cable 96 and the tenth cable 97. The second intermediate support 95 is in the form of a ring here and has a seventh through-hole 95.1 where the thirteenth end 71.2 of the cable 71 is crimped. The second intermediate support 95 also has an eighth through-hole 95.2 diametrically opposed to the seventh through-hole 95.1, and the fourteenth end 72.2 of the cable 72 is crimped there.

[0034] The second intermediate support 95 also has a ninth through-hole 95.3 where the fifteenth end 96.1 of the ninth cable 96 is crimped and a tenth through-hole 95.4 where the sixteenth end 97.1 of the tenth cable 97 is crimped.

[0035] The seventeenth end 96.2 of the cable 96 is crimped at the seventh through-hole 5.1, and the eighteenth end 97.2 of the tenth cable 97 is crimped at the eighth through-hole 5.2.

[0036] Optionally, the third end 61.1 of the cable 61 is not crimped to the arm 43 here, but is fixed to a threaded end piece passing through the ninth through-hole 43.1 of the arm 43. A knurled nut is engaged with the threaded end piece, and one of its faces abuts against the arm 43. By the action of the nut, tension can be applied to the cables 61, 62, 71, 72, 91, 92, 96, 97.

[0037] According to the third embodiment shown in FIGS. 5 and 6, the connection of the ends 6.1 and 6.2 of the first cable 6 to the carriage 41 is located on a second plane P2 orthogonal to the first plane P1 and including the longitudinal axis Ox. With this configuration, the installation area of the actuator 1 can be made smaller without generating a parasitic force on the screw 2 / nut 4 assembly.

[0038] In all of the described embodiments, the cables 6, 61, 62, 71, 72, 91, 92, 96 and 97 are advantageously pre-loaded.

[0039] Of course, the present invention is not limited to the described embodiments and encompasses any variations included in the field of the present invention as defined by the claims.

[0040] - Here, the actuator includes a ball screw, but the present invention is also applicable to other types of screws, such as a simple screw or a screw with rollers; - The first cable is connected to the nut by crimping mounted on a ring fixed to the nut, but the present invention is also applicable to other means of connecting the cable to the nut, such as crimping, adhering, or welding to a through-hole made in the nut; - Here, the cable extends parallel to the longitudinal axis, but the present invention is also applicable to other configurations of the cable where no part of the cable extends parallel to the longitudinal axis and the remaining part of the cable can take any orientation with respect to the longitudinal axis; - Here, all the cables of the actuator are pre-loaded, but the present invention is also applicable to a single pre-loaded cable or only a part of the pre-loaded cable; - Here, the first pulley and the second pulley are pulleys with cylindrical grooves, but the present invention is also applicable to the second pulley and the fourth pulley with different types of grooves, such as spiral grooves; - Here, only one cable is engaged with the first pulley pair, but the present invention is also applicable to pulley pairs with a plurality of grooves for accommodating additional operating cables; - Here, although the first cable is engaged with two pulleys, the present invention also applies to a first cable having a first strand connecting a nut (via a frame) and the first pulley, and a second strand different from the first strand, one end of which is crimped to the first pulley and the other end of which is crimped to the second pulley. Finally, the first cable can include a third strand with one end crimped to the second pulley and the other end connected to the nut (via the frame). All separate strands cooperate with the first and second pulleys to form a first cable for effecting transmission between two connection points to the nut; - Here, the anti-rotation device includes a cable connecting the nut to a carriage linearly guided, but the present invention also applies to other types of anti-rotation, such as one or more rollers fixed to the nut and engaging one or more grooves or a connecting shaft of the nut linearly guided; - Here, the actuator includes a guiding mechanism having two translational guidance points, but the present invention also applies to guiding mechanisms having different numbers of guiding points, such as one guiding point or two or more guiding points; - Here, the guiding mechanism is a prism-shaped linear guiding mechanism, but the present invention also applies to other types of translational guidance, such as one or more sliding pivots; - Here, the linear guiding mechanism includes two shoes engaging with a rail, but the present invention also applies to other types of linear guiding mechanisms, such as a prism-shaped linear guiding mechanism using one or more shoes having a ball circulation function, or a linear guiding mechanism including a socket having ball recirculation attached to a grooved shaft, etc.; - Here, the first cable is connected by crimping to the pulley, but the present invention also applies to other methods for the cooperation between the first cable and the pulley, such as connection by friction, for example, connection by one or more dead turns of the cable around the pulley; - Here, the output of the actuator is a finger constrained to rotate with the first pulley, but the present invention is also applicable to other types of outputs of the actuator, such as an output that is fixed to a first cable and translates to obtain a linear actuator; - Here, the third end of the second cable comprises a threaded end piece that engages a knurled nut, but the present invention is also applicable to other types of devices for tensioning the second and / or third cables, such as a fir tooth type catch assembly or an eccentric roller; - Here, the actuator includes a cable connected to the nut and engaging a smooth pulley, but the present invention is also applicable to other types of members for transmitting tensile force, such as a chain, a belt, a hybrid member including links connected by a cable with or without notches; - Here, the cable engages a pulley, but the present invention is also applicable to other types of direction return mechanisms adapted to other types of members for transmitting force, such as a pinion for a chain, a wheel with or without notches, a guide roller for a notched belt, or for a strap or tape.

Claims

1. An actuator (1), comprising: - a frame (20); - a screw (2) / nut (4) assembly including a nut (4) engaged with a screw (2) extending along a longitudinal axis (Ox); - a motor (3) configured to rotate the screw (2) to cause linear movement of the nut (4). The actuator (1) further comprises: - a pair of return mechanisms (10, 11) including a first return mechanism (10) and a second return mechanism (11) connected to an output (80) of the actuator (1) and rotatably attached to the frame (20) together; - a first member (6) for transmitting a tensile force, connected to the nut (4) at a first end (6.1) and a second end (6.2), and engaged with the first return mechanism (10) and the second return mechanism (11); - a detent device (40) for preventing the nut (4) from rotating relative to the screw (2). The carriage (41) is connected to the nut (4) by a first cable pair (60) including a second cable (61) and a third cable (62) extending on both sides of the screw (2), and a second cable pair (70) including a fourth cable (71) and a fifth cable (72) extending on both sides of the screw (2). The first cable pair (60) and the second cable pair (70) extend in a direction substantially parallel to the longitudinal axis (Ox), and the first cable pair (60) and the second cable pair (70) penetrate the nut (4) and are disposed on both sides of a first plane (P1) perpendicular to the screw (2). Actuator (1).

2. The actuator (1) according to claim 1, wherein the first member (6) for transmitting a tensile force is a cable (6) or a notched belt.

3. The actuator (1) according to claim 1 or 2, wherein the detent device (40) comprises a carriage (41) connected first to the nut (4) and second to the first member (6) for transmitting a tensile force.

4. The actuator (1) according to claim 3, wherein the detent device (40) comprises a mechanism (50) for guiding translation of the carriage (41) in a direction (D1) parallel to the longitudinal axis (Ox) of the carriage (41) relative to the frame (20).

5. The actuator (1) according to claim 4, wherein the guiding mechanism (50) is a prism-shaped linear guiding mechanism.

6. The actuator (1) according to any one of claims 3 to 5, wherein the guiding mechanism (50) has two translational guiding points.

7. The second cable (61) and the third cable (62) are connected to the nut (4) by a first intermediate support (90), and the first intermediate support (90) is connected to the nut (4) by a seventh cable (91) and an eighth cable (92). The actuator (1) according to any one of claims 1 to 6.

8. The fourth cable (71) and the fifth cable (72) are connected to the nut (4) by a second intermediate support (95), and the second intermediate support (95) is connected to the nut (4) by a ninth cable (96) and a tenth cable (97). The actuator (1) according to any one of claims 1 to 7.

9. The actuator (1) according to any one of claims 1 to 8, further comprising devices (7, 8) for tensioning the second cable (61) and / or the third cable (62).

10. The first pulley (10) and the second pulley (11) according to any one of claims 1 to 9, have a plurality of grooves for accommodating additional members for transmitting tensile force.

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