Drive device for a robot and robots with such a drive device

Abstract

The invention relates to a drive device (2) for a robot (1), comprising a worm drive (3) having a rotatable worm shaft (4) and a worm wheel (10) meshing therewith, wherein the worm shaft (4) is supported 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 configured to detect an axial force when a torque is transmitted to the worm shaft (4) via the worm wheel (5). The invention further relates to a robot (1) comprising such a drive device (2).

Description

The invention relates to a drive device for a robot. The invention further relates to a robot having such a drive device.DE 10 2017 215 941 A1 discloses a drive unit having a worm gear which has a worm which can be driven by an electric drive motor for a drive rotational movement about its longitudinal axis and a worm wheel which meshes with the worm and can be driven by the worm for a driven rotational movement about its longitudinal axis. The worm wheel is connectable or connected in a rotationally fixed manner to an output shaft. The worm is movable transversely to its longitudinal axis relative to the worm wheel and is self-adjustingly braced by a prestressing device having spring means with the toothing of the worm wheel rotatably mounted in a gear housing. The worm is mounted rotatably about its longitudinal axis in a worm carrier which is pivotable with respect to the gear housing about a worm carrier pivot axis spaced apart from and parallel to the longitudinal axis of the worm, so that a pivoting movement of the worm carrier about the worm carrier pivot axis is accompanied by a readjustment pivoting movement of the worm with a constant spatial orientation with respect to the worm wheel. The spring means exert a torque on the screw carrier with respect to the screw carrier pivot axis.The object of the invention is to provide a drive device for a robot that enables force-torque measurement in a simple manner. The object is achieved by the subject matter of claim 1 and by the subject matter of claim 10.A drive device according to the invention for a robot comprises a worm drive, having a worm shaft that can be driven in rotation and a worm wheel that is in meshing engagement therewith, wherein the worm shaft is mounted by a bearing element that transmits at least one axial force, characterized in that the bearing element that transmits 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.The drive device forms an actuator which, when it is used, for example, in a robot joint, generates a rotational movement or a torque between two robot arm segments which are articulated to one another. The worm drive is effectively arranged in the force flow between a drive unit and an output component of the drive device, in particular a shaft operatively connected to the worm wheel. The worm shaft can be designed to rise to the right and left and to be single- and multi-threaded and is in toothed engagement with an external toothing of the worm wheel.When a torque acts on the worm drive from the output side, i.e. via the worm wheel, the worm wheel presses the worm in the axial direction. In other words, the worm wheel generates an axial force acting on the worm shaft due to the torque acting. The at least one axial force-transmitting bearing element, whether it be a pure axial bearing or a bearing which 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 here much simpler in construction compared to conventional torque measuring devices, in particular torque sensors, and can therefore be produced particularly cost-effectively.In collaborative robots (also called robots), in addition to low production costs, high precision, high rigidity, light and compact construction due to the high torque and power density, long service life, low maintenance effort, good controllability, accurate torque detection, and good acoustic and vibration properties are realized due to the simple design of the drive device. The worm drive can be designed as a reduction stage much simpler than wave drives likewise used in robots. Robots are industrial robots that work together with humans and do not have to be separated from them by protective devices in the production process.The advantages of a worm gear are, among other things, the high gear ratios that can be realized, in particular of up to 80. In addition, the components of the drive device on the drive side and the output side can be produced cost-effectively, in particular by rolling and other methods. In addition, a high efficiency of more than 90% can be realized. Moreover, the worm gear can be manufactured with little play, i.e. with a higher kinematic accuracy, for example by more accurately manufacturing conical, spiral-shaped surfaces of the engaged worm drive components. It has been found that in worm gears with a locally axially conformable worm shaft and with a worm wheel with a deformable edge, a significant reduction in the play can be achieved.The worm drive is preferably designed to be self-locking, so that a brake device for holding a specific relative position of connected robot arm segments is not absolutely necessary. A gear is self-locking if the torque transmission can take place only in one direction. Preferably, the worm drive can be set in motion only via the transmission input, i.e. via the worm shaft. Via the gear output, i.e. via the worm wheel, the worm drive can preferably not be moved. As a result, the drive and output are fixedly predefined.The worm shaft is rotationally drivable 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. Further components or stages can be arranged in the power flow between the worm shaft and the drive shaft. Alternatively, the worm shaft and the drive shaft can be separate components which are connected to one another at least indirectly in a rotationally fixed manner at the latest during the assembly of the drive device. The drive unit with the drive shaft are arranged coaxially with the worm shaft. The drive unit is preferably an electric motor, in particular a brushless direct current motor. In this sense, the worm shaft is rotatably drivable by a brushless DC motor.A brushless direct current motor ("Brushless DC Motor") is supplied with direct current from an energy store, in particular a battery or a rechargeable battery, which converts the direct current into a matching three-phase current by means of corresponding control electronics in order to be operated as a three-phase synchronous machine with excitation of permanent magnets. The normally three-strand three-phase winding of the DC motor is controlled by a suitable circuit in such a way that it generates a travelling magnetic field which, as it were, "pulls" along the permanently excited rotor.Because the driving element, i.e. the worm shaft, and the driven element, i.e. the worm wheel, are not arranged coaxially with respect to one another, no hollow shaft is required which runs through the drive unit and / or rapidly rotating parts. Consequently, the axial offset between the driving and driven elements enables simpler cabling and guidance of cables and lines.The joint torque is detected or measured with the axial force measuring device on the worm shaft, which forms the drive element of the worm drive. An axial force measuring device in the sense of the invention is generally more cost-effective than conventional torque sensors and can be arranged on a non-rotating part in the power flow or supported thereon in a simple manner, wherein an axial force acting on the axial force measuring device can be converted by suitable means into an acting torque, in particular a joint torque.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 counter 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 or directly and thus directly connected to one another via at least one further component which is arranged between the two components.The at least one bearing element transmitting axial force is preferably designed as a rolling bearing, in particular a ball bearing, or as a sliding 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, make it possible for the worm shaft to rotate about its rotational axis, in particular relative to the axial force measuring device. A rolling bearing is understood to mean a bearing element which has rolling bodies for reducing a frictional resistance. In the case that the bearing element is designed as a rolling bearing, the advantage results that the rotation of the worm shaft is made possible with particularly low friction. Particularly preferably, the rolling bodies are balls, so that the rolling bearing is designed as a ball bearing. As an alternative to the embodiment as a rolling bearing, the bearing element is designed as a sliding bearing. A sliding bearing is understood to mean a bearing in which the frictional resistance is at least substantially reduced by lubricating the bearing. In the case that the bearing is designed as a slide bearing, the advantage results that particularly high axial forces can be transmitted through the bearing without damage to the bearing.The worm shaft is furthermore rotatably mounted by at least one further bearing element which realizes a radial support of the worm shaft. In a first embodiment, the worm shaft is rotatably mounted in a housing by two radial bearings and a separate axial bearing, wherein the axial bearing is axially supported at least indirectly 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 exemplary embodiment, the at least one axial force-transmitting bearing element is a four-point ball bearing.Alternatively, the at least one axial force-transmitting bearing element is additionally designed for transmitting radial forces. Accordingly, in comparison with the exemplary embodiment described above, only two bearing elements can be provided for supporting the worm shaft, wherein one of the bearing elements takes up exclusively radial forces and the respective other bearing element takes over both radial and axial forces. The last-mentioned bearing element is to be understood as at least one bearing element transmitting axial force in the sense of the invention. More specifically, this bearing element is a bearing element transmitting an axial force and a radial force.In order to avoid damage to the axial force measuring device, which is preferably designed as a load cell, in particular as a pressure load cell, it is advantageous if a ring, which is arranged in a rotationally fixed manner, of the at least one bearing element transmitting axial force is axially supported at least indirectly on the axial force measuring device. In one exemplary embodiment, the outer ring of the at least one bearing element transmitting axial force is arranged in a rotationally fixed manner, while the inner ring of the same bearing element is rotatable relative thereto. The inner ring is therefore connected to the worm shaft in a rotationally fixed manner and the outer ring is axially supported at least indirectly on the axial force measuring device. Depending on the configuration of the device, the inner ring of the bearing element can also be arranged in a rotationally fixed manner and supported at least indirectly on the axial force measuring device, such 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.Preferably, a force transmission part is effectively arranged between the at least one axial force transmitting bearing element and the axial force measuring device. The force transmission part is arranged as a connecting piece or coupling element between the at least one axial force transmitting bearing element 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 on the at least one axial force transmitting bearing element and on the other hand on the axial force measuring device. The power transmission member may be made of a sheet or the like which is formed by punching and forming. Alternatively, the force transmission part, since it must essentially transmit axial forces, can be made of a plastic.The axial force measuring device can be connected in a signal-transmitting manner to a data processing unit which receives or 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 to obtain conclusions from this about an acting torque. The data processing unit can be a control device 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 device in a signal-transmitting manner, for example in an analog manner, by means of a digital signal or via a bus line.The worm shaft is preferably designed as a globoid worm. The worm drive is therefore to be understood in this case as a globoid worm drive. The outer shape of the globoid worm describes an arc which partially "envelopes" the worm wheel. In comparison with the cylindrical worm, in the case of globoid worm, the "winding around" of the worm wheel achieves the effect that a plurality of threaded sections are involved in the force transmission. Globoid worms can thus transmit higher powers, in particular greater torques, than conventional cylindrical worms. The external toothing of the worm wheel can be a straight-toothed or helical-toothed external toothing, wherein the toothing of the worm shaft can be adapted thereto.According to an alternative exemplary 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 arranged and supported spatially within the intermediate housing. The worm shaft is thus likewise arranged spatially within the intermediate housing, wherein the worm shaft is supported and rotatably mounted both radially and axially in the intermediate housing.The intermediate housing is arranged axially displaceable, in particular slidingly within a robot arm, a robot arm segment or a robot arm joint, namely in such a way that the intermediate housing transmits the axial force to the axial force measuring device when the worm shaft is axially loaded. The intermediate housing is thus configured, when a torque is applied to the worm wheel, to axially displace it together with the worm shaft 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 in the axial direction and radially be supported within a housing of the robot, in particular within the robot arm, the robot arm segment or the robot arm joint.Preferably, the worm wheel is hollow on the inside. The internally hollow worm wheel can be connected in a rotationally fixed manner to a hollow shaft arranged coaxially thereto. The worm wheel can receive the hollow shaft radially or be connected laterally to the hollow shaft in a rotationally fixed manner. Since the output takes place via the worm wheel, 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. By making the worm wheel hollow on the inside, a passage of electronics through the worm wheel is made possible. In other words, such a configuration of the drive device enables internal wiring within the robot arm or the robot arm segment or the robot arm joint.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 it is supported on the respective other robot arm segment.The drive device is to be understood as an actuator of the robot or of the robot arm or of 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 direct current motor, which is connected to the worm drive, in particular the worm shaft, in a drive-effective manner. The worm drive reduces an input-side rotational speed of a drive shaft of the drive unit, in particular of the worm shaft connected thereto in a rotationally fixed manner, and thus acts as a reduction gear. Besides 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, which require lower requirements for precision. Robots of this type can thus be produced cost-effectively. Of course, such a drive device can also be used in other devices in which it is necessary to determine a torque on a component of the drive device with the simplest possible means.The above definitions and statements regarding technical effects, advantages and advantageous embodiments relating to the drive device according to the first aspect of the invention also apply analogously to the robot according to the second aspect of the invention, and vice versa.Further measures which improve the invention are described in more detail below together with the description of two preferred exemplary embodiments of the invention on the basis of the figures. This shows FIG. 1 shows a schematic illustration of a robot according to the invention, which is only partially illustrated, in the form of an arm robot, FIG. 2 shows a schematic longitudinal sectional illustration of a drive device according to the invention of the robot according to FIG. 1 according to a first embodiment, and FIG. 3 shows a schematic longitudinal sectional illustration of the drive device according to the invention according to a second embodiment.According to FIG. 1, a robot arm 11 of a robot 1, which is only partially shown here, is shown in a highly schematic and simplified manner. In the present case, the robot arm 11 has, by way of example, a first robot arm segment 12 and a second robot arm segment 13, which are connected to one another in an articulated, i.e. pivotable, manner via a joint 14.In the joint 14, which is to be understood as a robot arm joint, a drive device 2 is arranged according to FIGS. 2 and 3. The drive device 2 has a drive side and an output side, wherein the drive side is operatively connected to or supported on the first robot arm segment 12, and wherein the output side is operatively connected to or supported on the second robot arm segment 13. The drive device 2 is understood as a drive train which functions as an actuator of the robot arm 11 in order to set a rotational position of the robot arm segments 12, 13.In the present case, on the drive side, a drive unit 15 in the form of a brushless DC motor, a control unit 20 including power electronics or angle encoders-not shown or shown here-and a worm shaft 4 of a worm drive 3 are provided. The worm drive 3 is a reduction gear in which the worm shaft 4 is in toothed engagement with a worm wheel 10 of the worm drive 3, via which the output takes place, so that the worm wheel 10 is assigned to the output side of the drive device 2. The worm wheel 10 is formed hollow on the inside and is connected to a hollow shaft-not shown here. The output takes place via the hollow shaft, wherein the worm wheel 10 is operatively connected, in particular connected in a rotationally fixed manner, to the second robot arm segment 13 via the hollow shaft.The internally hollow design of the worm wheel 10 is advantageous for wire guidance, as is to be indicated here by the two cables 18, 19, which, coming from the first robot arm segment 12, are introduced into the worm wheel 10 from the front and are guided to the rear into the second robot arm segment 13. The worm wheel 10 is rotatably mounted by corresponding bearing elements-not shown here. Moreover, bearings may be provided to assist the rotation of the two robot arm segments 12, 13 connected by the joint 14. These may be cross roller bearings or other suitable types of bearings.The worm shaft 4 is a globoid worm in the present case in order to be able to transmit high torques. According to the first exemplary embodiment according to FIG. 2, the worm shaft 4 is mounted with respect to the first robot arm segment 12 via three bearing elements, namely on the one hand by a first radial bearing 16 and a second radial bearing 17, which radially support the worm shaft 4 with respect to the first robot arm segment 12, and on the other hand by a bearing element 5, which exclusively transmits an axial force and is axially supported via a force transmission component 8 on an axial force measurement device 6, which is in turn received on the first robot arm segment 12. The drive device 2 is therefore arranged directly or directly in the first robot arm segment 12. The axial force measuring device 6 is configured to detect an axial force when a torque is transmitted to the worm shaft 4 via the worm wheel 10. If a torque is present on the worm wheel 10, this generates an axial force on the worm shaft 4, which axial force can be detected by the axial force measuring device 6. The axial force measuring device 6 is designed as a pressure measuring cell, wherein the force transmission component 8 exclusively transmits 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 axial force transmitting bearing element 5 absorbs bidirectional forces in the direction of the shaft axis of the worm shaft 4. Here, the bearing element 5 is a four-point ball bearing.When a torque is applied from the drive side, the worm wheel 10 presses the worm shaft 4 in an axial direction, here in the direction of 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 the force transmission, it being possible to obtain conclusions about the acting torque on the basis of the measurement data about the axial force. The axial force measuring device 6 can be connected to the control unit 20 in a signal-transmitting manner, wherein the control unit 20 further processes the measurement data of the axial force measuring device 6 for conversion into a torque or forwards them to a further device for determining the acting torque.FIG. 3 shows an alternative, second exemplary embodiment of the drive device 2. accordingly, the worm shaft 4 is mounted with respect 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 contact surfaces with the intermediate housing 9. The worm shaft 4 is supported by a radial bearing 16 and a bearing element 5 that additionally transmits radial forces in addition to an axial force, relative to the intermediate housing 9, and is accordingly supported. Consequently, the bearings and the worm shaft 4, i.e. the drive-side components of the drive device 2, are arranged spatially within the intermediate housing 9. In addition, the at least one axial force-transmitting bearing element 5 is additionally designed for transmitting radial forces.The intermediate housing 9 is in turn mounted slidingly with respect to the first robot arm segment 12, which is to be illustrated by the double arrows 21 at 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 pre-assembled unit during assembly.If a torque is applied to the worm wheel 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 and is detected there. In this exemplary embodiment, the intermediate housing 9 is connected in an axially fixed manner to the outer ring of the bearing element 5 transmitting an axial force, so that the required axial force transmission can take place 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 the radial movement is prevented, but an 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 repetitions, reference is also made to the explanations relating to the first exemplary embodiment according to FIGS. 1 and 2.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 this. In addition, the angle encoder can be arranged at another location, for example on the hollow shaft connected to the worm wheel 10. In addition, two or more angle encoders may also be provided. Furthermore, starting from the exemplary embodiment according to FIG. 2, it is conceivable to combine the second radial bearing 17 and the bearing element 5 transmitting an axial force to form a bearing element, for example analogous to FIG. 3. In this case, this bearing element can be arranged radially and axially slidingly on the force transmission component 8.List of reference characters1 Robot 2 Drive device 3 Worm drive 4 Worm shaft 5 Axial force transmitting bearing element 6 Axial force measuring device 7 Ring of axial force transmitting bearing element 8 Force transmission part 9 Intermediate housing 10 Worm wheel 11 Robot arm 12 First robot arm segment 13 Second robot arm segment 14 Joint 15 Drive unit 16 First radial bearing 17 Second radial bearing 18 First cable 19 Second cable 20 Control unit 21 Double arrowReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2017 215 941 A1

[0002]

Claims

Drive device (2) for a robot (1), comprising a worm drive (3), having a worm shaft (4) which can be driven in rotation and a worm wheel (10) which is in toothed engagement therewith, wherein the worm shaft (4) is mounted by a bearing element (5) which transmits at least one axial force, characterized in that the bearing element (5) which transmits at least one axial force is axially supported at least indirectly on an axial force measurement device (6), wherein the axial force measurement device (6) is configured to detect an axial force if a torque is transmitted to the worm shaft (4) via the worm wheel (10).Drive device (2) according to Claim 1, characterized in that the at least one bearing element (5) transmitting axial force is additionally designed for transmitting radial forces.Drive device (2) according to Claim 1 or Claim 2, characterized in that a ring (7) of the at least one bearing element (5) which is arranged in a rotationally fixed manner is axially supported at least indirectly on the axial force measurement device (6).Drive device (2) according to one of the preceding claims, characterized in that a force transmission part (8) is effectively arranged between the at least one bearing element (5) transmitting axial force and the axial force measuring device (6).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.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 direct current motor.Drive device (2) according to one of the preceding claims, characterized in that the worm shaft (4) is designed as a globoid worm.Drive device (2) according to one of the preceding claims, characterized byan intermediate housing (9) which is axially supported on the axial force measuring device (6), wherein the at least one bearing element (5) transmitting axial force is arranged and supported spatially within the intermediate housing (9).Drive device (2) according to one of the preceding claims, characterized in that the worm wheel (10) is formed hollow on the inside.Robot (1) comprising a drive device (2) according to any of the preceding claims.

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