Push rod and roller screw drives with damping system

Abstract

The present invention relates to a push rod (8) for a roller screw drive (1) with a damping system (14) and roller screw drives (1) with a damping system (14). The push rod (8) comprises: i) a first rod section (10) for attachment to an axially translating component (4) of the roller screw drive (1); ii) a second rod section (12) for attachment to a load to be moved; and iii) a damping system (14). The damping system (14) is formed by a piston element (16) arranged at a first end (12a) of the second rod section (12) and a cavity (18) filled with a damping fluid at a first end (10a) of the first rod section (10). The piston element (16) is arranged in the cavity (18) and is axially movable.

Description

[0001] The present invention relates to a push rod for a roller screw drive with a damping system and roller screw drives with a damping system.

[0002] Linear actuators are often used to move objects or machine parts, especially to position them as desired. These linear actuators typically have a motor whose rotational motion can be converted into translational motion by means of a linear unit. If these linear actuators have to operate under heavy loads, for example in robotics applications, the use of linear units designed as roller screw drives has proven advantageous. In such roller screw drives (RSDs), which are sometimes also called planetary roller screw drives, a spindle nut interacts with a threaded spindle via a plurality of planetary rollers. This allows the force to be transmitted over a relatively large area compared to, for example, ball screw drives, resulting in increased robustness with regard to axial force application.

[0003] In practice, roller screw drives are not only subjected to a predetermined, application-specific load, but also to unintended, yet unavoidable, load peaks. Such load peaks can occur, for example, in the joints of robots, due to malfunctions in the surrounding mechanics and / or external influences, such as unintentional collisions. The roller screw drives used to actuate the joints, in particular the gear teeth between the spindle nut and / or the threaded spindle with the planetary rollers, can be plastically deformed or even damaged by such impacts. This leads to inaccuracies in positioning or even a failure of the system in question. For similar reasons, a spring-based system is provided, for example, in DE 10 2021 119 937 A1, with which load peaks in a ball screw drive can be cushioned.

[0004] Against this background, it is an object of the present invention to enable the damping of load peaks on a roller screw drive, in particular to avoid impairments caused by such load peaks.

[0005] This task is solved by a push rod and a roller screw drive according to the independent claims.

[0006] Preferred embodiments of the invention are the subject of the dependent claims and the following description.

[0007] According to a first aspect of the invention, the push rod for a roller screw drive comprises: i) a first rod section for attachment to an axially translating component of the roller screw drive; ii) a second rod section, in particular a separate one, for attachment to a load to be moved; and iii) a damping system. The damping system is formed by a piston element arranged at a first end of the second rod section and a cavity filled with a damping fluid at a first end of the first rod section. The piston element is arranged in the cavity and is axially movable.

[0008] One aspect of the invention is based on the approach of providing a roller screw drive or a push rod for such a roller screw drive with a damping system. The damping system can be integrated at various positions within the drive train formed by the roller screw drive. In particular, the damping system can be located on the spindle side or the nut side. The damping system is preferably formed by a piston element and a cavity filled with a damping fluid, in which the piston element is arranged and axially movable. The cavity and / or the piston element is / are preferably formed in or by a component of the roller screw drive. The damping fluid can influence the movement of the piston element within the cavity. In particular, it can dampen applied load peaks or shocks.

[0009] For example, the damping system can be integrated into the push rod of the roller screw drive. For this purpose, the push rod is preferably designed in two parts: a first rod section for attachment to an axially translating component of the roller screw drive, e.g., the threaded spindle, and a second rod section for attachment to a load to be moved. The piston element is arranged at a first end of the second rod section, while the cavity filled with the damping fluid is located at a first end of the first rod section. This means that a free end of the push rod, i.e., the end of the second rod section opposite the first end of the second rod section, is axially movable relative to the translating component. The damping medium in the cavity can thus dampen any movement of the piston element within the cavity.Peak loads, such as impacts acting on the free end of the push rod, can be absorbed or at least mitigated because the second part of the rod can yield to some degree under the load. The gearing of the roller screw drive, i.e., the meshing between the threaded spindle and the planetary rollers and / or between the spindle nut and the planetary rollers, is thus protected from excessive force.

[0010] The damping system thus formed advantageously connects the first rod section to the second rod section. This damping system is particularly space-saving. In particular, it can be integrated into the push rod without adding radial bulk to the push rod or the roller screw drive. The described push rod is therefore especially suitable for applications where available installation space is limited, but high demands are placed on the roller screw drive in terms of robustness and precision. Such push rods can be particularly advantageous in robotics, for example, for actuating a knee joint of a humanoid robot.

[0011] Preferred embodiments of the invention and their further developments are described below. These embodiments can be combined with each other and with the aspects of the invention described below, unless expressly excluded.

[0012] In a preferred embodiment, the piston element divides the cavity into two damping chambers. These damping chambers are advantageously connected to each other via a fluid-conducting system, so that when a force is applied to the second rod section or the axially translating component of the roller screw drive, damping fluid can flow from one damping chamber to the other. The applied force allows the piston element to displace the damping fluid in one damping chamber and force it into the other. The volumes separated within the cavity by the piston element are therefore variable in size, with the respective size depending on the (axial) position of the piston element within the cavity. The total volume of the cavity and the damping fluid remains constant.

[0013] The fluid-conducting connection between the two damping chambers allows the piston element to preferably move from one end of the cavity to the opposite end. In particular, the piston element can abut either of the two (axial) ends of the cavity, thereby directly transmitting an applied force. For example, the axial movement of the translating component of the roller screw drive can be directly transferred to the free end of the push rod when the piston element abuts the corresponding axial end of the cavity. Thus, because the piston element can abut either of the two opposite ends of the cavity, the necessary positive and force-fit connection of the push rod for transmitting a translational movement is ensured.

[0014] In a further preferred embodiment, the piston element has an axial end face and an axial rear face facing away from it. Preferably, the piston element has at least one channel for guiding the damping fluid, which opens into the respective damping chamber on both the end face and the rear face. The fluid flow between the damping chambers can be confined to the piston element by means of at least one such channel. This solution for the fluid flow between the damping chambers is particularly advantageous because such a channel in the piston element does not extend radially. The fluid flow can therefore be implemented in a particularly space-saving manner.

[0015] Alternatively or additionally, the fluid-conducting connection can also be located outside the cavity, e.g., in a wall of the cavity. For example, at least one channel connecting the two damping chambers via a fluid flow can run within the wall of the cavity. A fluid-conducting connection via an external reservoir is also possible. The fluid-conducting connection can therefore even run – at least partially – outside the first rod section.

[0016] Alternatively or additionally, a surface of the piston element can have a groove for fluid flow between the two damping chambers, thus forming a channel between the piston element and the cavity wall. More generally, the piston element can be designed, and in particular dimensioned, such that, when positioned in the cavity, fluid flow between its surface and a cavity wall is possible. In these cases, the piston element is therefore expediently not sealing with respect to fluid flow between the two damping chambers.

[0017] In a further preferred embodiment, at least one spring-elastic return element is provided, which couples the first rod section to the second rod section. The return element is advantageously arranged within the cavity. The return element can, for example, connect the end face of the piston element to an (axial) end of the cavity. Optionally, two return elements can also be provided, arranged on either side of the piston element. A damping system with such a spring-elastic return element allows not only the damping of applied load peaks, but also a (damped) spring action of the second rod section. The damping fluid prevents oscillation. Applied load peaks can be reduced even more smoothly by means of the spring-elastic element.

[0018] In an unloaded state, the piston element can also be held in a neutral position, for example, centered within the cavity, by such a spring-elastic return element. This allows the return element to serve as an energy storage device and support a movement executed by the roller screw drive, provided the force exerted by elongation or compression of the return element coincides with the direction of movement of the axially translating component of the roller screw drive.

[0019] In another preferred embodiment, the damping fluid is compressible. For this purpose, the damping fluid can, for example, be gaseous. This also makes it possible for the damping system to act not only as a damper but also as a spring. This allows for even smoother reduction of applied load peaks. Advantageously, even with a compressible damping fluid, the damping effect is achieved by a fluid-conducting connection between the damping chambers.

[0020] In a further preferred embodiment, the cavity at the first end of the first rod section is closed by a cap. The cap can, for example, be screwed onto or into the first rod section, particularly into the cavity formed by an axial bore in the first rod section. The cap advantageously has a through-hole, preferably a central one, which is penetrated by the second rod section, for example, by a tapered section of the second rod section, such as a rod-like extension. Closing the cavity with such a cap simplifies the manufacture of the push rod, especially the first rod section. Furthermore, the cavity can be easily reopened if necessary.

[0021] In a further preferred embodiment, the second rod section has a rod-like extension at its first end. Preferably, the piston element is arranged at the end of this rod-like extension. Particularly preferably, the rod-like extension is screwed into the piston element. This significantly simplifies the assembly of the push rod. For example, the piston element can first be positioned in the cavity, and the cavity can then be closed by screwing the end cap onto or into the first rod section. The rod-like extension can then be guided through the through-hole in the end cap and screwed into the piston element to connect the second rod section to the first rod section.

[0022] According to a second aspect of the invention, the roller screw drive comprises: i) a rotatably mounted spindle nut; ii) a threaded spindle arranged within the spindle nut, which translates axially relative to the spindle nut and is operatively connected to the spindle nut via a plurality of planetary rollers arranged circumferentially around the threaded spindle and which translate together with the threaded spindle; iii) a push rod comprising a first rod section attached to the axially translating spindle nut and a second rod section, preferably a separate one, for attachment to a load to be moved; and iv) a damping system. The damping system is formed by a piston element arranged at a first end of the second rod section and a cavity filled with a damping fluid at a first end of the first rod section. The piston element is arranged in the cavity and is axially movable.

[0023] In such a roller screw drive, the damping system is located on the spindle side. This allows the free end of the push rod, i.e., the end of the second rod section opposite the first end, to move axially relative to the translating threaded spindle, at least to a limited extent. The damping medium in the cavity dampens this movement. In this way, shocks can be absorbed or at least mitigated. The roller screw drive can thus be protected from load peaks; in particular, the gear teeth between the threaded spindle and the planetary rollers and / or between the planetary rollers and the spindle nut can be protected from excessive force.

[0024] In a preferred embodiment, the first rod section is formed integrally with the axially translating threaded spindle. The first rod section can therefore be formed integrally with the threaded spindle. Preferably, the first rod section is formed integrally with the threaded spindle, i.e., manufactured from a single piece. The threaded spindle can, in particular, transition into the first rod section. In this respect, the cavity can also be formed within the threaded spindle. This simplifies the manufacture of the roller screw drive, since only one push rod with the punch element and one threaded spindle with the cavity need to be manufactured.

[0025] According to a third aspect of the invention, the roller screw drive comprises: i) a rotatably mounted spindle nut; ii) a threaded spindle arranged within the spindle nut, which translates axially relative to the spindle nut and is operatively connected to the spindle nut via a plurality of planetary rollers arranged circumferentially around the threaded spindle and which translate together with the threaded spindle; and iii) a damping system. The damping system advantageously consists of a piston element arranged on a cylindrical surface of the spindle nut and a cavity of a further component, which surrounds the spindle nut at least partially in the circumferential direction and is filled with a damping medium. The piston element is arranged in the cavity and is axially movable.

[0026] In such a roller screw drive, the damping system is arranged on the nut side. The entire spindle nut can thus move axially relative to the other component, for example, a housing of the roller screw drive, with the help of the plunger element. The principle of damping the roller screw drive according to the third aspect of the invention is the same as the damping principle of the roller screw drive according to the second aspect of the invention and of the push rod according to the first aspect of the invention. In other words, the push rod according to the first aspect of the invention, the roller screw drive according to the second aspect of the invention, and the roller screw drive according to the third aspect of the invention all share a single general inventive idea. In each of these aspects of the invention, load peaks can be absorbed or at least reduced by the axially movable plunger element in the cavity filled with damping medium directly at or within the roller screw drive.

[0027] The invention will now be explained in more detail with reference to the figures. Where expedient, elements with equivalent effects are designated with the same reference numerals. The invention is not limited to the embodiments shown in the figures – not even with regard to functional features. The preceding description, as well as the subsequent description of the figures, contains numerous features, some of which are summarized in the dependent claims. However, those skilled in the art will also be able to consider these features, as well as all other features disclosed above and in the subsequent description of the figures, individually and combine them into meaningful further combinations.In particular, all of the aforementioned features can be combined individually and in any suitable combination with the push rod according to the first aspect of the invention, the roller screw drive according to the second aspect of the invention and the roller screw drive according to the third aspect of the invention.

[0028] They show, at least partially schematically: Fig. 1 an example of a roller screw drive with a spindle-side damping system; Fig. 2 an example of a roller screw drive with a damping system comprising a spring-elastic return element; and Fig. 3 an example of a roller screw drive with a nut-side damping system.

[0029] Fig. Figure 1 shows an example of a roller screw drive 1 with a rotatably mounted spindle nut 2, a threaded spindle 4 arranged inside the spindle nut 2 and axially translating relative to the spindle nut 2, a plurality of planetary rollers 6 arranged radially in the circumferential direction between the spindle nut 2 and the threaded spindle 4, a two-part push rod 8 and a damping system 14.

[0030] The push rod 8 comprises a first rod section 10, which is attached to the spindle nut 2, e.g., screwed on, and a separate second rod section 12 for attachment to a load to be moved. The first rod section 10 has a cavity 18 at a first end 10a, which faces the second rod section 12 and away from the threaded spindle 4. The cavity 18 can be formed, for example, by an axial bore or a blind hole in the first rod section 10, which is closed by a cap 24.

[0031] A punch element 16 of the second rod section 12 is arranged and axially movable within the cavity 18. The punch element 16 is located at a first end 12a of the second rod section 12, which faces the first rod section 10. The punch element 16 can, in particular, be positioned at the free end of a rod-like extension 28 of the second rod section 12. For easier assembly, the punch element 16 in the example shown has an internal thread with which it is screwed onto a corresponding external thread at the free end of the rod-like extension 28: thus, the punch element 16 can first be positioned in the cavity 18, and the cavity 18 can then be closed, for example, by screwing the end cap 24 onto the first end 10a of the first rod section 10. Subsequently, the rod-like extension 28 can be inserted through a through-hole 24a in the closure cap 24 into the cavity 18 and screwed into the stamp element 16.

[0032] The cavity 18 is advantageously filled with a damping fluid, e.g., a substantially incompressible liquid. The piston element 16, together with the cavity 18, thus forms the damping system 14. The piston element 16 divides the cavity 18 into two damping chambers 20, 22. Via channels 26, which fluidly connect the two damping chambers 20, 22, the damping fluid can be forced from one of the damping chambers 20, 22 to the other when the piston element 16 moves within the cavity 18. In the present example, these channels 26 extend from an axial end face 16a of the piston element 16 through the piston element 16 to an axial rear face 16b of the piston element 16. The damping system 14 forms a connection between the first rod section 10 and the second rod section 12. Consequently, the damping system 14 consists of Fig. 1 arranged on the spindle side.

[0033] The damping system 14 operates as follows: For example, the piston element 16 can be moved axially within the cavity 18 by applying a force F to a free end 8a of the push rod 8, i.e., to a second end 12b of the second rod section 12 opposite the first end 10a. This changes the size of the two damping chambers 20, 22, and damping fluid is forced from the decreasing damping chamber 22 through the channels 26 into the increasing damping chamber 20. Due to the fluid-dynamic properties of the damping fluid, such as viscosity, compressibility, density, and / or the like, the movement of the piston element 16 is not force-free, but rather delayed.The energy associated with the applied force F is therefore not completely transferred via the first rod section 10 to the threaded spindle 4, where it could damage the gearing between the planetary rollers 6 on the one hand and the threaded spindle 4 and / or the spindle nut 2 on the other. Instead, some of this energy can be transferred to the damping fluid or dissipated by its movement. In this way, the force F can be at least partially reduced, and the roller screw drive 1 can, in extreme cases, be protected from damage. In any case, the service life of the roller screw drive 1 can thus be increased with the help of the damping system 14.

[0034] In the example shown, the threaded spindle 4 forms an axially translating component of the roller screw drive 1. Such a roller screw drive 1 is also referred to as an inverted roller screw drive 1. In a complementary embodiment of the roller screw drive 1, it is also possible to mount the (axially extended) threaded spindle 4 so that it can rotate, allowing the spindle nut 2 to translate axially along the threaded spindle 4. In this case, the push rod 8 can be attached to the spindle nut 2, in particular screwed onto it or into it.

[0035] Alternatively, the first rod section 10 can also be formed integrally with the threaded spindle 4 – or, in the complementary embodiment of the roller screw drive 1, with the spindle nut 2 – as is the case in connection with Fig. 2 is shown.

[0036] Fig. Figure 2 shows another example of a roller screw drive 1. The roller screw drive 1 essentially corresponds to the roller screw drive from Fig. 1, with the difference that the first rod section 10 is formed integrally with the threaded spindle 4, i.e., the threaded spindle 4 and the first rod section 10 are manufactured from a single piece. Consequently, the arrangement of the cavity 18 at the first end 10a of the first rod section 10 is equivalent to an end-end arrangement of the cavity 18 in the threaded spindle 4. In this sense, the push rod 8 can therefore be considered as being connected to the threaded spindle 4 by the damping system 14. In this case as well, the damping system 14 is arranged on the spindle side.

[0037] Another difference between the one in Fig. The damping system 14 shown in Figure 1 comprises a spring-loaded return element 30. Advantageously, the return element 30 couples the second rod section 12, in particular the piston element 16, to the first rod section 10 or, in this example, to the threaded spindle 4. The return element 30 is arranged within the cavity 18, for example, between the axial end face 16a and a base 18a of the cavity 18. The return element 30 enables spring mounting of the second rod section 12 or the free end 8a of the push rod 8. The damping fluid in the cavity 18 can prevent free oscillation or rebound of the second rod section 12.

[0038] Fig. Figure 3 shows another example of a roller screw drive 1. The roller screw drive 1 shown is essentially the same as the roller screw drives from the Fig. 1 and Fig. 2, with the difference that the damping system 14 is located on the nut side rather than the spindle side. Consequently, the push rod 8 is not formed in two parts or connected to the threaded spindle 4 via the damping system 14, but is screwed directly onto the threaded spindle 4. Instead, the spindle nut 2 has the punch element 16 on its cylindrical surface 2a. The punch element 16 thus forms a kind of step or plateau on the cylindrical surface 2a of the spindle nut 2. Together with the cavity 18 filled with damping fluid, which is formed in a further component 32 that surrounds the spindle nut 2 at least partially in the circumferential direction, the punch element 16 forms the damping system 14.

[0039] The mode of operation of the damping system 14 from Fig. 3 is analogous to the damping systems that are in Fig. 1 and Fig. 2 are shown. Here too, a force F acting on the free end 8a of the push rod 8, after being transmitted via the threaded spindle 4 and the planetary rollers 6 to the spindle nut 2, can move the punch element 16 axially in the cavity 18, whereby the energy associated with the acting force F is at least not completely transferred to the further component 32, but at least partially transferred to the damping fluid or dissipated by its movement. For this purpose as well, at least one channel 26 is provided for directing the damping fluid from one of the two damping chambers 22 to the other damping chamber 20. In contrast to the ones shown in Fig. 1 and Fig. In the two examples shown, the channel 26 does not run through the stamp element 16, but through the further component 32.

[0040] Similarly, it would also be possible to include at least one channel 26 in the Fig. 1 and Fig.The 2 examples shown provide the radially bounding wall of the first rod section or the spindle nut 4 for the cavity 18. Alternatively or additionally, the punch element 16 in all three examples shown could be designed, and in particular dimensioned, such that it does not act as a seal with regard to a fluid-conducting connection between the two damping chambers 20, 22, i.e., it does not seal the two damping chambers 20, 22 against each other. Reference symbol list 1 Roller screw drive 2 spindle nuts 2a Surface area 4 threaded spindles 6 planetary roles 8 Push rod 8a free end 10 first rod section 10a first end of the first rod section 12 second rod section 12a first end of the second rod section 12b second end of the second rod section 14 Damping system 16 stamp elements 16a Front 16b reverse 18 Cavity 18a Ground 20 damping chamber 22 damping chamber 24 Cap 24a Through hole 26 Channel 28 rod-like extension 30 spring-elastic return element 32 additional components F force QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 119 937 A1

[0003]

Claims

Push rod (8) for a roller screw drive (1), comprising a first rod part (10) for attachment to an axially translating component (4) of the roller screw drive (1), a second rod part (12) for attachment to a load to be moved and a damping system (14), characterized in that the damping system (14) is formed by a plunger element (16) arranged at a first end (12a) of the second rod part (12) and a cavity (18) filled with a damping fluid at a first end (10a) of the first rod part (10), in which the plunger element (16) is arranged and is axially movable. Push rod (8) according to claim 1, wherein the punch element (16) divides the cavity (18) into two damping chambers (20, 22) and the damping chambers (20, 22) are fluidly connected to each other, so that when a force (F) acts on the second rod part (12) or the axially translating component (4) of the roller screw drive (1), damping fluid can flow from one of the damping chambers (20, 22) into the other of the damping chambers (20, 22). Push rod (8) according to claim 2, wherein the punch element (16) has an axial end face (16a), an axial rear face (16b) facing away from it and at least one channel (26) for guiding the damping fluid, wherein the at least one channel (26) opens into the respective damping chamber (20, 22) on the end face (16a) and the rear face (16b). Push rod (8) according to one of the preceding claims, with at least one spring-elastic return element (30) which couples the first rod part (10) with the second rod part (12). Push rod (8) according to one of the preceding claims, wherein the damping fluid is compressible. Push rod (8) according to one of the preceding claims, wherein the cavity (18) at the first end (10a) of the first rod part (10) is closed by a closing cap (24) which has a through bore (24a) extending through the second rod part (12). Push rod (8) according to one of the preceding claims, wherein the second rod part (12) has a rod-like extension (28) at the first end (12a) which is screwed into the punch element (16). Roller screw drive (1) comprising: - a rotatably mounted spindle nut (2), - a threaded spindle (4) arranged within the spindle nut (2) and axially translating relative to the spindle nut (2), which is operatively connected to the spindle nut (2) via a plurality of planetary rollers (6) arranged circumferentially around the threaded spindle (4) and translating together with the threaded spindle (4), and - a push rod (8) which has a first rod section (10) attached to the axially translating spindle nut (4) and a second rod section (12) for attachment to a load to be moved, characterized by a damping system (14) which is formed by a piston element (16) arranged at a first end (12a) of the second rod section (12) and a cavity (18) filled with a damping fluid at a first end (10a) of the first rod section (10), in which the piston element (16) is received and axially movable is. Roller screw drive (1) according to claim 8, wherein the first rod part (10) is formed in one piece with the axially translating threaded spindle (4). Roller screw drive (1) with a rotatably mounted spindle nut (2) and a threaded spindle (4) arranged within the spindle nut (2) and axially translating relative to the spindle nut (2), which is operatively connected to the spindle nut (2) via a plurality of planetary rollers (6) arranged circumferentially around the threaded spindle (4) and translating together with the threaded spindle (4), characterized by a damping system (14) which is formed by a punch element (16) arranged on a cylindrical surface (2a) of the spindle nut (2) and a cavity (18) filled with a damping fluid of a further component (32) which surrounds the spindle nut (2) at least partially in the circumferential direction, in which the punch element (16) is arranged and axially movable.

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