Drive device for a robot, and robot having such a drive device

Abstract

The invention relates to a drive device (2) for a robot (1), comprising a worm drive (3), having a rotatably drivable worm shaft (4) and a worm wheel (10) in toothed engagement therewith, wherein the worm shaft (4) is supported by a bearing element (5) which transfers at least one axial force, characterised in that the at least one bearing element (5) which transfers at least one axial force is axially supported at least indirectly on an axial-force measuring apparatus (6), wherein the axial-force measuring apparatus (6) is designed to detect an axial force when a torque is transferred to the worm shaft (4) via the worm wheel (5). The invention also relates to a robot (1) comprising such a drive device (2).

Description

[0001] Drive device for a robot and robot with such a drive device

[0002] The invention relates to a drive device for a robot. Furthermore, the invention relates to a robot with such a drive device.

[0003] DE 10 2017 215 941 A1 discloses a drive unit with a worm gear comprising a worm driven by an electric drive motor for a rotary drive movement around its longitudinal axis, and a worm gear meshing with the worm and driven by the worm for an output rotary movement around its longitudinal axis. The worm gear is connected or can be connected in a rotationally fixed manner to an output shaft. The worm is movable transversely to its longitudinal axis relative to the worm gear and is self-adjustingly clamped to the teeth of the worm gear, which is rotatably mounted in a gear housing, by a preloading device comprising spring means.The worm is mounted in a worm carrier, which can be rotated about its longitudinal axis and pivoted relative to the gear housing about a worm carrier pivot axis spaced apart from and parallel to the worm's longitudinal axis. A pivoting movement of the worm carrier about the worm carrier pivot axis is accompanied by an adjustment pivoting movement of the worm with a constant spatial orientation relative to the worm gear. The spring means exert a torque on the worm carrier relative to the worm carrier pivot axis.

[0004] The object of the invention is to provide a drive device for a robot that enables force-torque measurement in a simple manner. This object is achieved by the subject matter of patent claim 1 and by the subject matter of patent claim 10. Preferred embodiments can be found in the dependent claims, the description, and the figures.

[0005] A drive device according to the invention for a robot comprises a worm drive having a rotatably drivable worm shaft and a worm wheel meshing therewith, wherein the worm shaft is mounted by a bearing element transmitting at least one axial force, characterized in that the bearing element transmitting at least one axial force is axially supported at least indirectly on an axial force measuring device, wherein the axial force measuring device is configured to detect an axial force when a torque is transmitted to the worm shaft via the worm wheel.

[0006] The drive device forms an actuator which, when used, for example, in a robot joint, generates a rotary movement or torque between two articulated robot arm segments. The worm drive is operatively arranged in the power flow between a drive unit and an output component of the drive device, in particular a shaft operatively connected to the worm gear. The worm shaft can be right- or left-hand threaded, single- or multi-threaded, and meshes with the external teeth of the worm gear.

[0007] When a torque acts on the worm drive from the output side, i.e., via the worm gear, the worm gear pushes the worm in the axial direction. In other words, the worm gear generates an axial force acting on the worm shaft as a result of the acting torque. The at least one bearing element transmitting axial force, be it a pure axial bearing or a bearing that absorbs or transmits radial and axial forces, transmits this axial force at least indirectly to the axial force measuring device, which is designed in particular as an axial force sensor. The detected axial force can be converted into a torque acting on the robot arm joint. This is to be understood as a force-torque measurement. The axial force measuring device is significantly simpler in design than conventional torque measuring devices, in particular torque sensors, and is therefore particularly cost-effective to manufacture.

[0008] In collaborative robots (also called "cobots"), in addition to low manufacturing costs due to the simple design of the drive mechanism, they offer high precision, high rigidity, a lightweight and compact construction due to the high torque and power density, a long service life, low maintenance requirements, good controllability, precise torque measurement, and good acoustic and vibration characteristics. The worm drive can be designed as a reduction stage much more simply than the wave gears also used in cobots. Cobots are industrial robots or industrial robots that work alongside humans and do not need to be separated from them by protective devices during the production process.

[0009] The advantages of a worm gear include the high achievable gear ratios, particularly up to 80. Furthermore, the input and output components of the drive device can be manufactured cost-effectively, particularly through rolling and other processes. Furthermore, a high efficiency of more than 90% is achievable. Furthermore, the worm gear can be manufactured with low backlash, i.e., with greater kinematic accuracy, for example, through more precise manufacturing of conical, spiral-shaped surfaces of the meshing worm drive components. It has been shown that a significant reduction in backlash can be achieved in worm gears with a locally axially adaptable worm shaft and a worm wheel with a deformable rim.

[0010] The worm drive is preferably self-locking, so that a braking device is not necessarily required to maintain a specific relative position of connected robot arm segments. A gearbox is self-locking if torque can only be transmitted in one direction. The worm drive can preferably only be set in motion via the gearbox input, i.e., the worm shaft. The worm drive can preferably not be moved via the gearbox output, i.e., the worm gear. This means that the input and output are fixed.

[0011] The worm shaft is rotatably driven on the input side by a drive unit. The worm shaft can be connected in one piece to a drive shaft of the drive unit. Additional components or stages in the power flow can be arranged between the worm shaft and the drive shaft. Alternatively, the worm shaft and the drive shaft can be separate components that are at least indirectly connected to one another in a rotationally fixed manner during assembly of the drive device. The drive unit with the drive shaft are arranged coaxially to the worm shaft. The drive unit is preferably an electric motor, in particular a brushless DC motor. In this sense, the worm shaft is driven by a brushless

[0012] DC motor can be driven in rotation.

[0013] A brushless DC motor is powered by direct current from an energy storage device, particularly a battery, which, using appropriate control electronics, converts the direct current into a suitable three-phase current for operation as a three-phase synchronous motor with the excitation of permanent magnets. The DC motor's typically three-phase winding is controlled by a suitable circuit to generate a moving magnetic field, which essentially "pulls" the permanently excited rotor.

[0014] Because the driving element, i.e., the worm shaft, and the driven element, i.e., the worm gear, are not arranged coaxially, there is no need for a hollow shaft running through the drive unit and / or rapidly rotating parts. Thus, the axial offset between the driving and driven elements enables easier cabling and routing of cables and lines.

[0015] The joint torque is detected or measured using the axial force measuring device on the worm shaft, which forms the drive element of the worm gear. An axial force measuring device within the meaning of the invention is generally more cost-effective than conventional torque sensors and can be easily arranged or supported on a non-rotating part in the power flow. An axial force acting on the axial force measuring device can be converted into an acting torque, in particular a joint torque, by suitable means.

[0016] The at least one axial force-transmitting bearing is designed to transmit an axial force, i.e., a force acting in the actuation direction or opposite to the actuation direction, from the worm shaft at least indirectly to the axial force measuring device. "At least indirectly" means that two components, here, for example, the worm shaft and the axial force measuring device, can be (operatively) connected to one another via at least one additional component arranged between the two components, or can be directly and thus immediately connected to one another.

[0017] The bearing element transmitting at least one axial force is preferably designed as a rolling bearing, in particular a ball bearing, or as a plain bearing. These bearing types ensure, on the one hand, the transmission of the axial force from the worm shaft to the axial force measuring device and, on the other hand, enable rotation of the worm shaft about its axis of rotation, in particular relative to the axial force measuring device. A rolling bearing is understood to be a bearing element that has rolling elements to reduce frictional resistance. If the bearing element is designed as a rolling bearing, this has the advantage that the rotation of the worm shaft is possible with particularly low friction. The rolling elements are particularly preferably balls, so that the rolling bearing is designed as a ball bearing. As an alternative to the design as a rolling bearing, the bearing element is designed as a plain bearing.A plain bearing is defined as a bearing in which frictional resistance is at least substantially reduced by lubrication. Designed as a plain bearing, this offers the advantage that particularly high axial forces can be transmitted through the bearing without damaging it.

[0018] The worm shaft is further rotatably supported by at least one further bearing element, which provides radial support for the worm shaft. In a first embodiment, the worm shaft is rotatably supported in a housing by two radial bearings and a separate axial bearing, wherein the axial bearing is at least indirectly axially supported on the axial force measuring device. Accordingly, in one embodiment, the worm drive has three separate bearing elements, two of which are designed to support exclusively radial forces and one to support exclusively axial forces, in particular to absorb bidirectional forces in the direction of the shaft axis. According to an alternative embodiment, the at least one bearing element transmitting axial force is a four-point contact ball bearing.

[0019] Alternatively, the bearing element transmitting at least one axial force is also designed to transmit radial forces. Accordingly, in comparison to the previously described embodiment, only two bearing elements can be provided to support the worm shaft, with one of the bearing elements absorbing exclusively radial forces and the other bearing element absorbing both radial and axial forces. The latter bearing element is to be understood as a bearing element transmitting at least one axial force within the meaning of the invention. More precisely, this bearing element is a bearing element transmitting both an axial force and a radial force.

[0020] To prevent damage to the axial force measuring device, which is preferably designed as a load cell, in particular as a pressure cell, it is advantageous if a rotationally fixed ring of the bearing element transmitting at least one axial force is axially supported at least indirectly on the axial force measuring device. In one embodiment, the outer ring of the bearing element transmitting at least one axial force is rotationally fixed, while the inner ring of the same bearing element is rotatable relative thereto. Thus, the inner ring is rotationally fixedly connected to the worm shaft, and the outer ring is axially supported at least indirectly on the axial force measuring device.Depending on the design of the device, the inner ring of the bearing element can also be arranged in a rotationally fixed manner and at least indirectly supported on the axial force measuring device, so that the inner ring of the same bearing element can be rotated relative thereto and the outer ring is arranged accordingly on the rotatable worm shaft.

[0021] Preferably, a force transmission part is operatively arranged between the bearing element transmitting at least one axial force and the axial force measuring device. The force transmission part is arranged as a connecting piece or coupling element between the bearing element transmitting at least one axial force and the axial force measuring device and transmits the axial forces acting on the worm shaft from the bearing element to the axial force measuring device. The force transmission part is supported axially on the one hand by the bearing element transmitting at least one axial force and on the other hand by the axial force measuring device. The force transmission part can be made of a sheet metal or the like produced by stamping and forming. Alternatively, since the force transmission part must essentially transmit axial forces, it can be formed from a plastic material.The axial force measuring device can be connected to a data processing unit for signal transmission, which receives, retrieves, or requests the measurement data acquired by the axial force measuring device in order to determine an acting axial force from the measurement data and thereby draw conclusions about an acting torque. The data processing unit can be a control unit of the robot. The drive unit for rotating the worm shaft can be connected to the same or a separate data processing unit or a separate control unit for signal transmission, for example, analog, via a digital signal, or via a bus line.

[0022] The worm shaft is preferably designed as a globoid worm. Therefore, in this case, the worm drive is to be understood as a globoid worm drive. The external shape of the globoid worm describes an arc that partially "envelops" the worm wheel. In comparison to a cylindrical worm, the "wrapping" of the worm wheel in globoid worms ensures that multiple thread sections are involved in the power transmission. Globoid worms can therefore transmit higher power, especially greater torque, than conventional cylindrical worms. The external gearing of the worm wheel can be straight-toothed or helical-toothed, and the gearing of the worm shaft can be adapted accordingly.

[0023] According to an alternative embodiment, an intermediate housing is provided, which is axially supported on the axial force measuring device, wherein the at least one bearing element transmitting axial force is spatially arranged and supported within the intermediate housing. The worm shaft is thus also spatially arranged within the intermediate housing, wherein the worm shaft is supported and rotatably mounted both radially and axially in the intermediate housing.

[0024] The intermediate housing is axially displaceable, in particular sliding within a robot arm, a robot arm segment, or a robot arm joint, specifically such that, when the worm shaft is subjected to axial load, the intermediate housing transmits the axial force to the axial force measuring device. The intermediate housing is thus configured to axially displace together with the worm shaft when a torque is applied to the worm gear in order to apply axial force to the axial force measuring device. For this purpose, the intermediate housing can be arranged, for example, so as to slide axially and be radially supported within a housing of the robot, in particular within the robot arm, the robot arm segment, or the robot arm joint.

[0025] The worm gear is preferably hollow on the inside. The hollow worm gear can be connected in a rotationally fixed manner to a coaxially arranged hollow shaft. The worm gear can accommodate the hollow shaft radially or be connected laterally to the hollow shaft in a rotationally fixed manner. Since the output is via the worm gear, the hollow shaft serves as the output part of the worm drive. The hollow shaft can be operatively connected at least indirectly to a robot arm segment on the output side. The hollow worm gear's hollow design allows electronics to be fed through the worm gear. In other words, this type of drive device design enables internal wiring within the robot arm, robot arm segment, or robot arm joint.

[0026] The invention also relates to a robot comprising a drive device according to the invention. In particular, the drive device according to the invention is arranged in a robot arm of the robot, in particular in a robot arm segment and / or a robot arm joint, and acts at least indirectly on at least one of the robot arm segments while being supported on the respective other robot arm segment.

[0027] The drive device is to be understood as the actuator of the robot, the robot arm, or the robot arm joint. In addition to the worm drive, the drive device further comprises a drive unit, preferably in the form of an electric motor, in particular a brushless DC motor, which is drivingly connected to the worm drive, in particular the worm shaft. The worm drive reduces the input rotational speed of a drive shaft of the drive unit, in particular the worm shaft connected thereto in a rotationally fixed manner, and thus acts as a reduction gear. In addition to the axial force measuring device, the drive device can comprise further sensors, such as torque sensors, angle encoders, and other devices. The drive device can be used in particular in service robots that have lower precision requirements. Such robots can thus be manufactured cost-effectively.Of course, such a drive device can also be used in other devices where it is necessary to determine a torque on a component of the drive device using the simplest possible means.

[0028] The above definitions as well as explanations of technical effects, advantages and advantageous embodiments of the drive device according to the first aspect of the invention also apply mutatis mutandis to the robot according to the second aspect of the invention, and vice versa.

[0029] Further measures improving the invention are described in more detail below together with the description of two preferred embodiments of the invention with reference to the figures.

[0030] Figure 1 is a schematic representation of a partially illustrated robot according to the invention in the form of an arm robot,

[0031] Figure 2 is a schematic longitudinal sectional view of a drive device according to the invention of the robot according to Figure 1 according to a first embodiment, and

[0032] Figure 3 is a schematic longitudinal sectional view of the drive device according to the invention according to a second embodiment.

[0033] According to Figure 1, a robot arm 11 of a robot 1—only partially shown here—is shown in a highly schematic and simplified manner. In this example, the robot arm 11 has a first robot arm segment 12 and a second robot arm segment 13, which are pivotably connected to one another via a joint 14.

[0034] According to Figures 2 and 3, a drive device 2 is arranged in the joint 14, which is to be understood as a robot arm joint. The drive device 2 has a drive side and an output side, wherein the drive side is operatively connected to or supported by the first robot arm segment 12, and wherein the output side is operatively connected to or supported by the second robot arm segment 13. The drive device 2 is to be understood as a drive train that functions as an actuator of the robot arm 11 in order to adjust a rotational position of the robot arm segments 12, 13.

[0035] In the present case, on the drive side there is a drive unit 15 in the form of a brushless DC motor, a control unit 20 including power electronics or angle encoder (not shown in detail here), and a worm shaft 4 of a worm drive 3. The worm drive 3 is a reduction gear in which the worm shaft 4 meshes with a worm wheel 10 of the worm drive 3, via which the output is provided, so that the worm wheel 10 is assigned to the output side of the drive device 2. The worm wheel 10 is hollow inside and connected to a hollow shaft (not shown here). The output is provided via the hollow shaft, wherein the worm wheel 10 is operatively connected, in particular rotationally fixed, to the second robot arm segment 13 via the hollow shaft.

[0036] The internally hollow design of the worm gear 10 is advantageous for wire guidance, as indicated here by the two cables 18, 19, which originate from the first robot arm segment 12, are introduced from the front into the worm gear 10, and are guided rearward into the second robot arm segment 13. The worm gear 10 is rotatably supported by corresponding bearing elements (not shown here). Bearings can also be provided to support the rotation of the two robot arm segments 12, 13 connected by the joint 14. These can be crossed roller bearings or other suitable bearing types.

[0037] The worm shaft 4 is a globoid worm in this case in order to be able to transmit high torques. According to the first exemplary embodiment shown in Figure 2, the worm shaft 4 is mounted relative to the first robot arm segment 12 via three bearing elements: firstly, a first radial bearing 16 and a second radial bearing 17, which radially support the worm shaft 4 relative to the first robot arm segment 12, and secondly, a bearing element 5 which exclusively transmits an axial force and is axially supported via a force transmission component 8 on an axial force measuring device 6, which in turn is received on the first robot arm segment 12. Thus, the drive device 2 is arranged immediately or directly in the first robot arm segment 12. The axial force measuring device 6 is designed to detect an axial force when a torque is transmitted to the worm shaft 4 via the worm gear 10.If a torque is applied to the worm gear 10, this generates an axial force on the worm shaft 4, which can be measured by the axial force measuring device 6. The axial force measuring device 6 is designed as a pressure cell, with the force transmission component 8 transmitting exclusively axial forces to the axial force measuring device 6. For this purpose, the force transmission component 8 is arranged on a rotationally fixed ring 7, here the outer ring, of the bearing element 5 transmitting an axial force. The bearing element 5 transmitting the axial force absorbs bidirectional forces in the direction of the shaft axis of the worm shaft 4. Here, the bearing element 5 is a four-point contact ball bearing.

[0038] When a torque is applied from the drive side, the worm gear 10 pushes the worm shaft 4 in an axial direction, here toward the axial force measuring device 6. The axial bearing 5 transmits this axial force to the axial force measuring device 6 via its outer ring 7 and the force transmission component 8, which is an adapter part for force transmission. Conclusions about the acting torque can be drawn from the measured axial force data. The axial force measuring device 6 can be connected to the control unit 20 for signal transmission. The control unit 20 further processes the measured data from the axial force measuring device 6 for conversion into a torque or forwards it to another device for determining the acting torque.

[0039] Figure 3 shows an alternative, second embodiment of the drive device 2. Accordingly, the worm shaft 4 is mounted relative to an intermediate housing 9 via two bearing elements. In this example, the drive device 2 with the drive-side components is arranged within the intermediate housing 9, wherein the worm wheel 10 of the output side is free of contact points or surfaces with the intermediate housing 9. The worm shaft 4 is mounted and supported relative to the intermediate housing 9 by a radial bearing 16 and a bearing element 5 which transmits not only an axial force but also radial forces. Thus, the bearings and the worm shaft 4, i.e. the drive-side components of the drive device 2, are spatially arranged within the intermediate housing 9. Furthermore, the bearing element 5 which transmits at least one axial force is also designed to transmit radial forces.

[0040] The intermediate housing 9 is in turn mounted in a sliding manner relative to the first robot arm segment 12, as indicated by the double arrows 21 on the housing sections of the first robot arm segment 12. The intermediate housing 9 is axially supported on the axial force measuring device 6, which in turn is supported on the housing of the first robot arm segment 12. The provision of an intermediate housing 9 can be advantageous if the drive device 2, in particular its drive side, is to be inserted into the first robot arm segment 12 as a preassembled unit during assembly.

[0041] If a torque is applied to the worm gear 10, this generates an axial force on the worm shaft 4, which is transmitted via the bearing element 5 and the intermediate housing 9 to the axial force measuring device 6, where it is measured. In this exemplary embodiment, the intermediate housing 9 is axially fixedly connected to the outer ring of the bearing element 5, which transmits an axial force, so that the required axial force can be transmitted to the intermediate housing 9 and from there to the axial force measuring device 6. In this sense, the drive elements are accommodated in a separate housing, which is mounted in the first robot arm segment 12 in such a way that radial movement is prevented, but axial movement between the first robot arm segment 12 or the joint 14 and the intermediate housing 9 is possible with little resistance. Instead of a sliding bearing, means for axially guiding the intermediate housing 9 can also be provided.To avoid repetition, reference is made to the explanations for the first embodiment according to Figures 1 and 2.

[0042] For all exemplary embodiments, power electronics on the control unit 20 can be dispensed with, for example, if the drive unit 15 does not require it. Furthermore, the angle encoder can be arranged at a different location, for example on the hollow shaft connected to the worm gear 10. Furthermore, two or more angle encoders can also be provided. Furthermore, starting from the exemplary embodiment according to Figure 2, it is conceivable to combine the second radial bearing 17 and the bearing element 5 transmitting an axial force into one bearing element, for example analogous to Figure 3. This bearing element can be arranged radially and axially sliding on the force transmission component 8.

[0043] List of reference symbols

[0044] 1 robot

[0045] 2 drive device

[0046] 3 worm gear

[0047] 4 Worm shaft

[0048] 5 Axial force transmitting bearing element

[0049] 6 Axial force measuring device

[0050] 7 Ring of the bearing element transmitting an axial force

[0051] 8 Power transmission part

[0052] 9 Intermediate housing

[0053] 10 Worm gear

[0054] 11 Robot arm

[0055] 12 first robot arm segment

[0056] 13 second robot arm segment

[0057] 14 joint

[0058] 15 Drive unit

[0059] 16 First radial bearing

[0060] 17 Second radial bearing

[0061] 18 First cable

[0062] 19 Second cable

[0063] 20 Control unit

[0064] 21 Double arrow

Claims

Patent claims 1. Drive device (2) for a robot (1), comprising a worm drive (3) having a rotatably drivable worm shaft (4) and a worm gear (10) meshing therewith, wherein the worm shaft (4) is mounted by a bearing element (5) transmitting at least one axial force, characterized in that the bearing element (5) transmitting at least one axial force is axially supported at least indirectly on an axial force measuring device (6), wherein the axial force measuring device (6) is designed to detect an axial force when a torque is transmitted to the worm shaft (4) via the worm gear (10).

2. Drive device (2) according to claim 1, characterized in that the at least one bearing element (5) transmitting axial force is additionally designed to transmit radial forces.

3. Drive device (2) according to claim 1 or claim 2, characterized in that a rotationally fixed ring (7) of the bearing element (5) transmitting at least one axial force is axially supported at least indirectly on the axial force measuring device (6).

4. Drive device (2) according to one of the preceding claims, characterized in that a force transmission part (8) is effectively arranged between the bearing element (5) transmitting at least one axial force and the axial force measuring device (6).

5. Drive device (2) according to one of the preceding claims, characterized in that the axial force measuring device (6) is designed as a load cell, in particular as a pressure cell.

6. Drive device (2) according to one of the preceding claims, characterized in that the worm shaft (4) can be driven in rotation by a brushless DC motor.

7. Drive device (2) according to one of the preceding claims, characterized in that the worm shaft (4) is designed as a globoid worm.

8. Drive device (2) according to one of the preceding claims, characterized by an intermediate housing (9) which is axially supported on the axial force measuring device (6), wherein the at least one axial force-transmitting bearing element (5) is spatially arranged and supported within the intermediate housing (9).

9. Drive device (2) according to one of the preceding claims, characterized in that the worm wheel (10) is hollow on the inside.

10. Robot (1) comprising a drive device (2) according to one of the preceding claims.

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