Drive unit with additionally driven planetary gearbox

Abstract

Drive unit with a planetary gear unit comprising a first (1) and a second central gear (2), one or more planetary gears (3), a drive shaft and an output shaft, and at least one first electric motor (7) connected to the drive shaft for driving the drive shaft, characterized by that one or more additional electric motors (4) are integrated into one or more of the planetary gear wheels (3) of the planetary gear set, via which the planetary gear wheels (3) can be driven, wherein the first (7) and the subsequent electric motors (4) are connected to a control device which, depending on the operating mode, controls the subsequent electric motors (4) at least temporarily to smooth the torque of the output shaft or to generate a braking effect on the output shaft.

Description

Technical application area

[0001] The present invention relates to a drive unit with a planetary gear having a first and a second central gear, one or more planetary gears, a drive axle and an output axle, and at least one first electric motor driving the drive axle.

[0002] Numerous machine drives require high torque in a small installation space. Examples include robotic drives, e.g., drives for lightweight robots, industrial robots, or wearable robots, as well as medically assistive devices such as exoskeletons or active prostheses. If an electric drive is used, it must usually be integrated into the robot axis using a high reduction ratio to achieve the required torque. Such reduction ratios are often more than 100:1 and can be implemented using gearboxes. However, due to their design, these have disadvantages in terms of efficiency and torque-speed transmission behavior. Furthermore, this drivetrain design requires numerous sensors and complex models, e.g., for the aforementioned torque-speed transmission behavior, to enable efficient operation. State of the art

[0003] The high torque densities required in robotics and medical technology, for example, have so far been achieved by using very high gear reductions. For these high gear reductions, often exceeding 100:1, special gears, particularly so-called harmonic drive gears (stress wave gears) or similar gear types, are used in these applications. Extensive sensor technology allows the required torques to be generated along controlled, adjustable paths.

[0004] The high reduction ratio limits the dynamics of the drive unit, as higher motor speeds are present and the moment of inertia in the gearbox is multiplied. This requires a functional principle or design of these gearboxes with partially deformable gear components. This, among other things, results in a lower efficiency of the gearbox (only up to 85% with Harmonic Drive) than with differently designed and less strongly reduced gearboxes. The Harmonic Drive gearboxes used also exhibit a strong nonlinear behavior with hysteresis effects, which must be compensated for with complex gearbox models and complicated control algorithms in order to achieve high absolute accuracy of the driven robot. In addition to these mechanical disadvantages, these gearboxes are also expensive and therefore not ideal from an economic perspective.

[0005] DE 10 2015 220 712 A1 and DE 10 2009 016 854 A1 describe drive units with a planetary gear according to the preamble of patent claim 1.

[0006] DE 198 38 400 A1 discloses a drive unit with a planetary gear, in which the planetary gear wheels are additionally constructed like a motor according to the information in this document.

[0007] A planetary gear with a planet carrier fixed to the frame is known from DE 10 2010 029 784 B3.

[0008] US Patent No. 4,761,588 A deals with a direct drive, i.e., a drive without an intermediate gearbox. Two motors are connected in series to compensate for nonlinearities of the first motor in the power transmission by the second motor.

[0009] The object of the present invention is to provide a drive unit for a machine, in particular for robots or medically assistive devices, which has a high torque density with high efficiency and high dynamics as well as good transmission behavior. Description of the invention

[0010] The object is achieved with the drive unit according to patent claim 1. Advantageous embodiments of the drive unit are the subject of the dependent patent claims or can be derived from the following description and the exemplary embodiment.

[0011] The proposed drive unit comprises a planetary gear and a first electric motor connected to the drive axle of the planetary gear, which drives the drive axle of the planetary gear. This first electric motor represents the main drive of the drive unit. The planetary gear has, in a known manner, two central gears, one or more epicyclic or planetary gears, the drive axle, and an output axle. One of the two central gears represents the so-called sun gear. The other central gear is designed either as a ring gear or as a spur gear. The ring gear design leads to a particularly compact design of the planetary gear. The proposed drive unit is characterized in that a further electric motor is integrated into one or more of the epicyclic gears of the planetary gear, via which the respective epicyclic gear can be driven. Preferably, an electric motor is integrated into each of the epicyclic gears.In other embodiments, it is also possible to integrate an electric motor into only one or some of the planetary gears. In the proposed drive unit, the first and the additional electric motors are connected to a control device that, depending on the operating mode, at least temporarily controls the additional electric motors to smooth the torque of the output axle or to generate a braking effect on the output axle.

[0012] By using a planetary gear in the proposed drive unit, which has a significantly lower reduction ratio of, for example, only approximately 10:1 compared to harmonic drive gears, a higher mechanical efficiency is achieved due to the design. Planetary gears have efficiencies of up to 97%. At the same time, however, the electric main drive must deliver a higher torque than when using harmonic drive gears in order to achieve the same or higher output torque of the drive unit. By integrating additional electric drives or electric motors into the planetary gears, the main drive is supported in torque generation and the torque behavior of the drive unit is improved without increasing the installation space for the drive unit.By appropriately controlling the additional electric motors, the linearity of the transmission of speeds and torques can be improved compared to harmonic drive transmissions. The integration and interaction of multiple electric drives can thus improve the overall transmission behavior with regard to torque ripple and increase the total torque. The additional electric motors can also partially assume the function of a brake, for example, for providing resistance when manually guiding a robot. The safety brake, which is often required, can thus also be smaller.

[0013] The control system for controlling the individual electric motors, i.e., the main drive motor and the additional electric motors in the planetary gears, is designed to generate the required torques and the desired linearity of the transmission of speeds and torques to the output axle. Suitable control strategies enable variable drive behavior that can be adapted to the specific application.

[0014] By integrating the additional drives into several of the planetary gears, these additional electric motors can also be used for sensor technology. For this purpose, additional sensors are integrated into the individual electric motors, which can measure, for example, induced voltages, current, position, speeds, or torques and transmit the measured values ​​to the control unit. By combining sensors from all electric motors in the drive unit, an even better database for the operation and behavior of the drive unit can be achieved. By preloading the individual planetary drives / gears against each other, the position accuracy of the output can be increased or guaranteed.

[0015] In the preferred embodiment, the sun gear of the planetary gear is connected to the drive axle, and the other central gear, preferably designed as a ring gear, is connected to the output axle. The axes of the planetary gears are preferably connected via a planet carrier, also known as a carrier, fixed to the frame. Depending on the application of the drive unit, however, the second central gear can also be connected to the drive axle and the sun gear to the output axle. A design with a rotating planet carrier is also possible, which can then also be connected to the drive or output axle for certain applications of the drive unit.

[0016] The proposed drive unit is particularly suitable for machines that require high torque, low torque ripple, and high dynamics within a small drive unit installation space. This particularly applies to robotic drives for all types of robots or medically assistive devices, such as exoskeletons, active prostheses, etc. However, the application of the proposed drive unit is not limited to these applications. By integrating more than one electric motor, increasing the torque density with the additional electric motors, and replacing high-reduction gears such as the Harmonic Drive, the proposed drive unit can achieve significant advantages in the transmission behavior of the drive axes compared to currently used solutions. Short description of the drawings

[0017] The proposed drive unit is explained in more detail below using an exemplary embodiment in conjunction with the drawings. Herein: Fig. 1 a representation of an exemplary schematic structure of the drive unit according to the invention from the side and in cross section; and Fig. 2 an isometric view of the drive unit, partially cut away; Fig. 3 a detailed view of a planetary gear with integrated electric motor, partially cut away; Fig. 4 a representation of another exemplary structure of the drive unit according to the invention in cross section; and Fig. 5 a representation of another exemplary structure of the drive unit according to the invention in cross section. Ways to implement the invention

[0018] The drive unit illustrated below as an example comprises a planetary gear set with a sun gear 1 and a ring gear 2 as central gears, as well as three planetary gears 3, hereinafter also referred to as planetary gears. The gear set shown in the figures was implemented with straight gears, but could also be designed with helical gears in the same way. Fig. Figure 1 shows a side view in the left part and a cross-section in the right part of the schematic structure of this exemplary drive unit. The side view shows the electric main drive 7 and the ring gear 2. The cross-sectional view shows the sun gear 1, the planet gears 3 and the ring gear 2, which each mesh with each other via their gear rings. The main drive 7 of the drive unit is connected to the sun gear 1 of the planetary gear via a shaft. The torque is transmitted via the planet gears 3 to the ring gear 2, which serves as the power output and is connected to the robot axis as the output axis. In addition to the transmitted torque of the main drive, additional torque is generated in the planet gears 3 by the electric motors 4 integrated therein and is also transmitted to the ring gear 2. The planet gears 3 are connected by the Fig. 1 planet carrier not visible and are, in this example, stationary, just like the planet carrier itself.

[0019] The electric motors 4 integrated in the planetary gears 3 each have, in a known manner, a stator 5 and a rotor 6 which is connected to the ring gear of the planetary gears. Fig. 3 shows a partially cutaway view of a planetary gear 3 with integrated electric motor. In this view, as in Fig. 2 shows a circuit board on the front side of the stator 5, where the windings 9 of the respective electric motors can be connected. The exact topologies of the electric motors for the main and auxiliary drives can be selected depending on the application. Both separately controlled and electrically coupled drives are possible as integrated drives for the concept. The design of the main drive can also be adapted to the respective requirements.

[0020] Fig. 2 shows a partially cutaway isometric view of the drive unit of the Fig. 1, in which the main drive 7 and the planetary carrier 8 can be seen. Both the drives and the drive train or drive unit as a whole are scalable and adaptable to specific requirements.

[0021] The planetary gear can also have a different number of planetary gears, as shown for example in the Fig. 4 and Fig. 5 with 6 or 15 planet gears 3 is shown in cross section. List of reference symbols 1 sun gear 2 ring gear 3 planetary gears 4 additional electric motors 5 Stator 6 Rotor 7 Main drive 8 planet carriers 9 windings

Claims

[1] Drive unit with a planetary gear having a first (1) and a second central wheel (2), one or more planetary gears (3), a drive axle and an output axle, and at least one first electric motor (7) connected to the drive axle for driving the drive axle, characterized by , that one or more further electric motors (4) are integrated into one or more of the planetary gears (3) of the planetary gear, via which the planetary gears (3) can be driven, wherein the first (7) and the further electric motors (4) are connected to a control device which, depending on the operating mode, controls the further electric motors (4) at least temporarily to smooth the torque of the output axle or to generate a braking effect on the output axle. [2] Drive unit according to claim 1, characterized by that the second central gear (2) is a ring gear. [3] Drive unit according to claim 2, characterized by that the first central wheel (1) is connected to the drive axle. [4] Drive unit according to claim 2, characterized by that the second central wheel (2) is connected to the drive axle. [5] Drive unit according to one of claims 1 to 4, characterized by that the axes of the planetary gears (3) are connected via a planet carrier (8) fixed to the frame. [6] Drive unit according to one of claims 1 to 5, characterized by that the control device is designed such that, by controlling the further electric motors (4), it increases a linearity of the transmission of speeds and torques from the drive axle to the output axle compared to an operating mode without the further electric motors (4). [7] Drive unit according to one of claims 1 to 6, characterized bythat sensors for measuring induced voltages and / or speeds and / or torques are integrated into the further electric motors (4) and connected to the control device. [8] Drive unit according to claim 7, characterized by that the control device is designed such that it uses measurement data obtained from the sensors to control the further electric motors (4).

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