actuator unit

Abstract

Actuator unit, especially for operating a robot, with a motor (10) having a rotor (14) and a stator (12) and a harmonic drive transmission (16), wherein the harmonic drive transmission (16) is an elliptical disk element (20) driven by the motor (10), a flexible sleeve (24) surrounding the elliptical disc element (20) with external teeth and an outer ring (26) surrounding the flexible sleeve (24), with an internal toothing engaging in the external toothing of the flexible sleeve (24), wherein the disk element (20) has a bearing (22), wherein the disk element (20) is directly connected to the rotor (14), wherein the stator (12) and the outer ring (26) are fixed immovably relative to each other, characterized by the fact that the rotor (14) is directly supported by a bearing (28, 30) and that exactly one bearing (28, 30) is located essentially in the center of the motor or at the center of mass of the rotor.

Description

[0001] The invention relates to an actuator unit with a harmonic gear, in particular for the operation of a robot.

[0002] Geared motors play a crucial role in today's automation technology. Lorentz force actuators are often offered or required together with gearboxes as compact units. Brushless DC motors are increasingly being used in high-performance drives, although brushed actuators are still in use. In general, an actuator unit consists of an energy converter, in this case an electromagnetic energy converter, electronics, a rotor bearing, and, through the use of gearboxes or gear stages, at least one output bearing.

[0003] A harmonic gear is commonly used as a transmission or gear stage, particularly in robotics. Common harmonic gears feature an elliptical disk element driven by a motor. The elliptical disk element is surrounded by a flexible sleeve. The flexible sleeve has external gearing. Furthermore, the harmonic gear has an outer ring surrounding the flexible sleeve, with internal gearing that meshes with the external gearing of the flexible sleeve. The external gearing of the flexible sleeve has fewer teeth than the internal gearing of the outer ring.

[0004] The harmonic gear is also known as a sliding wedge gear, stress wave gear or wave gear. The term Harmonic Drive gear has also been adopted. ®This name is a trademark of Harmonic Drive AG. All of these terms are used synonymously below and refer to the harmonic gear described below.

[0005] The harmonic gear is a positive-locking gear with very little backlash, a relatively high reduction ratio (1:30 to 1:160), and high torque transmission capacity while maintaining a comparatively low weight and installation space. For this reason, actuator units, especially in robotics, are often equipped with these gears.

[0006] A harmonic transmission places special demands on the precision of the concentricity and axial runout of the shaft, which is connected to the elliptical disk element at the input of the transmission. In one well-known design of a harmonic transmission, a coupling is even provided here to compensate for possible radial misalignment. The coupling can, for example, be a so-called Oldham coupling.

[0007] In known actuator units with a harmonic gear, the rotor is provided with a separate bearing (fixed-loose bearing), which fixes the rotor and, in turn, firmly connects it to the elliptical disc element of the harmonic gear. This inevitably leads to stresses, as the elliptical disc element of the gear undergoes a rolling motion to implement tooth progression in the reduction gear. In this case, it is also typically necessary to provide a separate bearing for the elliptical disc element.

[0008] DE 10 2010 037 183 A1 discloses a harmonic transmission for a vehicle steering system. The transmission comprises an output shaft rotatably mounted by an output bearing and provided with internal gearing, as well as a deformable tube having external gearing in a gear plane that meshes with the internal gearing. The output bearing is also arranged in the gear plane.

[0009] JP 2010 - 130 830A relates to a drive device using a harmonic gear consisting of an electric motor and a rotation detection device. The electric motor is arranged coaxially with the gear and has a rotation detection device on the side opposite the gear.

[0010] US 2004 / 256 930 A1 discloses an improved flat vibration motor for installation in a mobile communication device.

[0011] EP 2 602 504 A1 relates to an integrated protective clutch for a planetary gear, e.g. for an electronic hedge trimmer.

[0012] EP 2 220 400 B1 relates to a harmonic motor comprising a stationary circular stator with internal teeth, a deformable cylindrical sleeve arranged coaxially within the stator, said sleeve comprising both external and internal toothings, and a transmission output shaft arranged coaxially within the deformable sleeve. The motor further comprises a device for sequentially deforming the cylindrical sleeve into an elliptical shape that engages the output shaft. The number of teeth on the stator corresponds to the number of external teeth on the sleeve, so that the sleeve engages at two points of the elliptical shape, each tooth on the sleeve engaging the same mating tooth on the stator.

[0013] WO 2011 / 029 472 A1 describes a drive assembly consisting of a motor with a motor housing, a rotor, a rotor shaft, and a harmonic gear. The rotor shaft is mounted in the motor housing with a rear bearing on the rear side of the rotor. The harmonic gear comprises a circular spline attached to the motor housing, a flexible spline that engages the circular spline, and a shaft generator. The shaft generator engages the flexible spline and is attached to a drive end of the rotor shaft. Between the circular spline and the shaft generator is a shaft generator bearing, which serves as the exclusive drive bearing for supporting the rotor shaft in the motor housing on one end of the rotor.

[0014] DE 11 2009 000 487 T5 relates to a reduction gear comprising a rotary transmission shaft and a motor. The front end of the rotary transmission shaft is firmly attached to a rotary output element of the reduction gear by means of an adhesive that exhibits flexibility or elasticity after curing. The rear end of the rotary transmission shaft is rotatably supported by a sensor cover via a bearing in a position adjacent to the output shaft sensor. The rotary transmission shaft can be supported without runout by deformation of the adhesive and the bearing.

[0015] The object of the present invention is to provide an actuator unit with a harmonic gear in which the structure is simplified.

[0016] The problem is solved by the actuator unit according to claim 1.

[0017] The actuator unit according to the invention, in particular for operating a robot, has a motor with a rotor and a stator. The motor is in particular a brushless motor. Furthermore, according to the invention, the actuator unit has a harmonic gear with an elliptical disk element driven by the motor. The elliptical disk element is surrounded by a flexible sleeve which has external teeth. An internal toothing of an outer ring surrounding the flexible sleeve engages with the external teeth of the flexible sleeve. The rotation of the elliptical disk element results in a translation movement of the flexible sleeve, which can be used as a drive. For this purpose, the disk element has a bearing, which is arranged in particular on the outer circumference of the disk element.

[0018] According to the invention, the disk element is directly connected to the rotor. Thus, no additional coupling is provided between the rotor of the motor and the disk element. This simplifies the structure. The connection of the disk element to the rotor is particularly strong, so that power can be transmitted from the motor to the disk element. Preferably, the connection between the disk element and the rotor is also free of play, so that power can be transmitted from the motor to the disk element, in particular without slippage, even during load changes. The connection between the disk element and the rotor can be designed in several parts, e.g. as a backlash-free plug-in connection that can be released in the axial direction.Preferably, however, the disc element is formed integrally with the rotor, and particularly preferably, the rotor and disc element are manufactured in a single setup to enable the most precise design of the rotor and disc elements. This design further simplifies the construction of the actuator unit without compromising the advantages of the harmonic drive, such as low backlash and high torque transmission capacity.

[0019] According to the invention, the rotor is directly supported by exactly one bearing, so that the bearing is directly connected to the rotor. Thus, the actuator unit has exactly one bearing in the area of ​​the motor. Preferably, the entire actuator unit has exactly two bearings, namely one bearing for the disk element and exactly one bearing for the rotor. Thus, a second bearing for the rotor can be avoided, since the bearing of the disk element is also used to support the rotor. This is made possible by the direct connection of the disk element to the rotor and, in particular, because this connection is firm and free of play. In this case, the bearing that is already located on the disk element of the harmonic gear system is used to form the loose bearing of the rotor bearing. The exact one bearing of the rotor is, in particular, designed as a fixed bearing.This is necessary because the disc element exerts axial forces that depend on the direction of rotation. With this bearing, the rotor is fixedly mounted on one side and loosely supported by the disc element on the other.

[0020] Preferably, the exact one bearing is arranged or mounted essentially in the center of the rotor. The loose bearing of the disk element performs a slight elliptical movement, which, however, does not negatively influence the motor, provided that care is taken to ensure that the wobbling movement of the rotor is not great. This is achieved by positioning the rotor bearing in the center of the motor, if possible, or by having only a slight offset. This means that the exact center or exact central arrangement of the bearing on the rotor can be deviated from in order to reduce the wobbling movement of the rotor, if necessary. In particular, the bearing can be arranged at the center of mass of the rotor, which does not necessarily coincide with the geometric center if the rotor is shaped accordingly.

[0021] Preferably, the rotor has no bearing at its end facing the harmonic gear. This bearing is replaced by the bearing of the disc element as described above, so that a separate bearing at the end facing the harmonic gear is no longer required, thus eliminating the need for a bearing.

[0022] The bearings are preferably ball bearings. These are widely used and have a simple design, which can further simplify the design of the actuator unit. In particular, they can be double bearings.

[0023] Preferably, the actuator unit has a common housing that at least partially surrounds the harmonic gear and the motor. This ensures optimal power transmission by jointly securing the stator of the motor and the outer ring of the harmonic gear. The common housing is preferably manufactured in a single clamping operation to minimize the axial offset between the outer ring of the harmonic gear and the motor stator.

[0024] Preferably, the outer ring has recesses that engage positively with elevations in the housing. Alternatively, the outer ring has elevations that engage positively with corresponding recesses in the housing. Thus, co-rotation of the outer ring in the housing is prevented by the corresponding recesses and elevations, whereby vulnerable gluing or screwing, which would significantly increase the weight of the actuator unit, can be dispensed with. In particular, the actuator unit is further developed as described in the application by the same applicant with the same filing date, which is titled "harmonic gear" (DE 10 2015 201 146.1). Alternatively or additionally, the actuator unit is further developed according to the application by the same applicant with the same filing date, which is titled "brushless DC motor" (DE 10 2015 201 160.7).

[0025] The invention is explained in more detail below using a preferred embodiment with reference to the attached figures.

[0026] They show: Fig. 1 a sectional side view of a first embodiment of the invention and Fig. 2 a sectional side view of an alternative embodiment of the invention.

[0027] According to the invention, the actuator unit comprises a motor 10 with a stator 12 and a rotor 14. A harmonic gear 16 is directly connected to the rotor 14. The harmonic gear 16 and the motor 10 are combined in a common housing 18 as an actuator unit.

[0028] The harmonic gear 16 has an elliptical disc element 20 with a double bearing 22, which are designed as ball bearings. The elliptical disc element 20 is surrounded by a flexible sleeve 24. The flexible sleeve 24 has external teeth (not shown) and is surrounded by an outer ring 26. The outer ring 26 has internal teeth (not shown) that engage with the external teeth of the flexible sleeve 24. The elliptical disc element 20 is rotated by the motor 10, thus generating a transmission movement on the flexible sleeve 24.

[0029] The rotor is directly supported by a bearing 28. No additional bearing is provided at the end of the rotor 14 facing the harmonic gear. Here, the rotor 14 is supported by the bearings 22 of the elliptical disk element 20. Thus, the actuator unit has only one bearing 28 for the rotor 14 and the bearings 22 for the disk element 20. No additional bearings are required for the operation of the actuator unit.

[0030] In the second embodiment shown in Fig.2, identical or identical components are identified by the same reference numerals. In the second embodiment, the rotor and the disk element of the harmonic gear are also directly connected to one another and, as shown, are formed in particular as a single piece. The motor 10 has precisely one bearing 30, which is arranged centrally on the rotor. For this purpose, it is assumed that the rotor 14 extends to the disk element 20. Due to the essentially central arrangement of the bearing 30 with respect to the rotor 14, wobbling movements of the rotor 14 are reduced. The bearing 30 is arranged at the center of mass of the rotor.

Claims

[1] Actuator unit, in particular for operating a robot, with a motor (10) having a rotor (14) and a stator (12) and a harmonic drive gear (16), wherein the harmonic drive gear (16) comprises an elliptical disc element (20) driven by the motor (10), a flexible sleeve (24) surrounding the elliptical disc element (20) with an external toothing and an outer ring (26) surrounding the flexible sleeve (24) with an internal toothing engaging in the external toothing of the flexible sleeve (24), wherein the disc element (20) has a bearing (22), wherein the disc element (20) is directly connected to the rotor (14), wherein the stator (12) and the outer ring (26) are fixed immovably relative to each other, characterized by , that the rotor (14) is directly supported by a bearing (28, 30) and that exactly one bearing (28, 30) is arranged substantially in the center of the motor or at the center of mass of the rotor. [2] Actuator unit according to claim 1, characterized by that the rotor (14) has no bearing at its end facing the harmonic drive gear (16). [3] Actuator unit according to claim 1 or 2, characterized by that the bearings (22, 28, 30) are ball bearings. [4] Actuator unit according to one of claims 1 to 3, characterized by that the motor (10) is in particular a brushless electric motor. [5] Actuator unit according to one of claims 1 to 4, characterized by a common housing (18) at least partially surrounding the harmonic drive gear (16) and the motor (10). [6] Actuator unit according to claim 5, characterized bythat the outer ring (26) has recesses into which corresponding elevations of the housing (18) engage in a form-fitting manner or the outer ring (26) has elevations which engage in a form-fitting manner in corresponding recesses in the housing (18).

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