DE102014105322B3 - Drive device in a joint of a robot with motor-gear unit - Google Patents

Abstract

The invention relates to a drive device having an electric motor (2) with a stator fixed in a motor housing and a rotor rotatably mounted radially to the stator for generating a torque on a drive shaft (10) which is connected to the input stage of a transmission (3). which is attached to the output end of the motor housing to form a motor-gear unit. According to the invention, a torsion bar unit (11) is indicated, via which the engine-transmission unit is coupled to a consumer. The torsion bar unit is associated with position sensors (9, 10) for detecting the torque transmitted via the torsion bar unit to detect the driving force to the load and in particular to control by controlling the engine power. The engine-gear unit is attached directly to a base (1).

Description

The invention relates to a drive device in a joint of a robot with an electric motor and a transmission according to the preamble of claim 1.

If the speed of a motor is too high for the intended use, the output or drive shaft is often coupled to a transmission in which the engine speed is downgraded to the desired speed. Another possibility is to control the engine speed electrically or electronically.

For high gear ratios in a motor-gearbox unit multistage gearboxes are required. Another way to achieve a high gear ratio is the use of a shaft gear, as z. B. by the company Harmonic Drive AG in D-65555 Limburg is sold, which consists essentially of three elements, namely a connected to the motor shaft elliptical wave generator, which rotates in a flexspline designed as a flexible sleeve and deforms them during rotation. The outer side of the Flexsplines contains an outer toothing, which engages in the deflection of the Flexsplines migratory in the internal toothing of a circular spline, wherein the number of teeth of the external toothing is different from the number of teeth of the internal toothing by a few teeth. This enables gear ratios of over 200: 1. Accordingly, such transmissions are often found in engine-gearbox units in which rotational movements are required only in small angular degrees, such as in servo drives and robots with strong speed and torque changes.

In many cases, it is necessary to detect both rotational speed and torque of a drive unit in order to be able to adjust or regulate these variables as required. This is necessary above all for robots in order to be able to use the generated forces in a targeted manner. While the detection of the speed causes no problems, the detection of torque designed as consuming. Known means consist in the use of strain gauges or position sensors, which are used at appropriate points in the power chain between the engine and the consumer and the drive shaft are assigned.

With robots and other automation equipment, it is often necessary to absorb shocks when a tool contacts an obstacle. For this purpose, it is known to use spring systems that absorb short-term energy overload of the drive or power surges. Such spring systems can also be used for torque detection.

From the EP 2239479 A1 a robot drive is known with such a spring system, in which the output shaft of a motor is in communication with a clutch in the circumferentially housed in a housing springs are deflected via arms which are connected to the drive shaft of the motor, wherein the housing with the Motor output shaft is in communication. A torque occurring in the clutch leads to the deflection of the springs according to the spring characteristic used. With this system, a coupling results with elasticity properties, in which the torsional force is absorbed by springs. Springs are in long-term operation but susceptible to failure design elements.

It is also known to absorb torsional forces on motors via torsion bars. From the DE 11 2010 001 389 T5 For example, an engine with torsional isolation means is known in which a torsion bar axially guided by the motor is fixed on one side to the motor armature and connected to the consumer on the other side of the motor. In this way, power surges in the drive system can be compensated by torsion of the torsion bar.

The above elasticity systems are located in the motor itself or are directly connected to the motor shaft, i. H. they operate at the respective engine speed, so that their effect is very limited when using a subsequent high transmission ratio transmission.

The invention is therefore based on the object to provide a drive device in a joint of a robot with an electric motor and a transmission that has a wide range of flexibility, even at low speeds and high stiffness, is spatially compact and störunanfälig.

This object is achieved by the invention defined in claim 1. Advantageous developments of the invention are specified in subclaims.

The invention relates to a drive device according to the preamble of claim 1 with an electric motor with a stator fixed in a motor housing and a rotor rotatably mounted radially to the stator for generating a torque to a drive shaft which is connected to the input stage of a transmission is attached to the output end of the motor housing to form a motor-gear unit.

According to the invention, a torsion bar unit is provided as part of the drive train following the transmission. The motor-gear unit is attached directly to the base. The output stage of the transmission is coupled to a consumer.

Consumer is any type of load cell, such as real energy consumers, but also energy storage, such. As spring systems and centrifugal masses understood.

The torsion bar unit is associated with two position sensors for detecting the torque to detect the driving force to the consumer and in particular to control by controlling the engine power.

Unlike in the cited prior art, in which the Torsionsstabeinheit is arranged as a motor shaft directly in the engine or in front of the transmission, it is in the invention behind the transmission between the transmission and the consumer.

The arrangement of the Torsionsstabeinheit behind the transmission allows easier detection of torque at higher torsional forces, and in particular when only small angular rotations of the torsion bar are required. Furthermore, with the use of standard motors and flanged shaft gearbox high compactness of the motor-gear unit can be achieved.

The output shaft of the engine is coupled with the elliptical wave generator and the flexspline of the transmission with the consumer. The preferred shaft gearbox is characterized by simple construction, no slippage and a high gear ratio.

For determining the torque occurring at the torsion bar unit, two position sensors spaced apart from each other in the longitudinal direction of the torsion bar unit are used to detect the torsion between the position sensors. In addition, for enhanced safety, strain gauges or other additional torque or position sensors may be associated with the torsion bar to provide redundancy of the measurement.

The detected signal may be used in a known manner to control the motor or other elements of a device to be driven.

In a further embodiment of the invention can be provided that the motor shaft is formed as a hollow shaft. The output shaft of the transmission, which also forms the torsion bar, can then be fed back through the gearbox and the engine to the back of the engine and there coupled to a consumer. This measure increases the compactness of the drive device and shortens their overall length considerably. This has significant advantages in a robotic arm with the prevailing tight space.

The device according to the invention is particularly suitable for use in robot joints.

The invention will be explained in more detail by exemplary embodiments.

1 shows an overall schematic view of a motor-gear unit with a Torsionsstabeinheit at the output of the transmission

2 shows a view according to 1 in which the torsion bar unit is returned to the rear of the engine.

In the 1 shown view shows an electric motor 2 , z. B. a brushless DC motor with a motor shaft 6 that in the Wave Generator 5 a known wave transmission 3 intervenes. The gear 3 is firmly on the housing of the engine 2 attached to form a motor-gear unit. In the radial direction, the gear is larger than the diameter of the motor.

The Wave Generator 5 The gear deflects during circulation due to its elliptical shape formed as a sleeve Flexspline 4 of the gearbox. The one on the radial outside of the flexspline 4 arranged ring gear engages punctiform in each case in the internal toothing of the Flexspline 4 surrounding Circular Splines 8th one. Due to a different number of teeth from Flexspline 4 and Circular Spline 8th results in a strong speed downgrade on the Flexspline 4 opposite the motor shaft 6 of the motor 2 ,

The engine-gear unit can be fitted with appropriate fasteners at the base 1 be attached. Preferably, the attachment to the base via the circular spline 8th of the transmission.

The Flexspline 4 of the transmission 3 has a flange for an output shaft 7 on, which leads to a consumer, not shown.

In the invention, the shaft 7 as Torsionsstabeinheit in the form of a torsion bar 11 attached to the output of the shaft gear and connects the gearbox with the consumer. Here, the engine-gear unit is fixed to a base 1 attached. The torsion takes place in the torsion bar 11 instead of. Due to the lack of reference base two position sensors are used, which detect the torsion of the torsion bar relative to each other. The sensor signals may be applied to a computing, evaluation and control circuit to control the motor or to detect, adjust or regulate further parameters dependent on the generated torque.

The torsion bar 11 can be made of solid metal or a tube. A bundling of a plurality of parallel individual bars may also be used, which are accommodated in end pieces, such as retaining rings. The bundle rods can also be received in a circular manner and parallel to each other in lateral retaining rings or retaining washers. This results in a basket-like structure of the torsion bar, wherein the bundle bars themselves are essentially stressed only on bending. Therefore, the bending bars in this case may also be rectangular or sheet-shaped. Polymeric materials can also be used between the bundle bars, or individual bundle bars can be made of polymers, thereby additionally achieving damping properties of the torsion bar unit.

In one example, the torsion bar had a length of 82 mm. Its diameter was 8.5 mm. At a torque of 60 Nm there was a deflection, d. H. a twist of the ends of the torsion bar, of 5 degrees.

An advantage of the use of the invention lies in the fact that by the elastic properties of the torsion bar increased protection against shock from the outside can be achieved on the motor-gear unit. If the torsion bar is designed as a cantilever, multi-dimensional measurements, such. B. make 6-dimensional measurements of the applied forces and moments, by appropriately used position or torque sensors.

2 shows an arrangement of the drive device according to the invention, in which the motor shaft as a hollow shaft 12 is trained. This hollow shaft also intervenes in the wave generator of the shaft gear. With a suitable flange formation on the Flexspline, the output shaft can 13 , which also forms the torsion bar, are guided through the motor shaft to the back of the motor and connected there to a consumer. This significantly shortens the overall length of the drive device.

LIST OF REFERENCE NUMBERS

1

Base

2

engine

3

transmission

4

flexpline

5

Wave generator

6

motor shaft

7

output shaft

8th

Circular spline

9

position sensor

10

position sensor

11

torsion bar

12

hollow shaft

13

output shaft

Claims (6)

Drive device in a joint of a robot with an electric motor ( 2 ) with a stator fixed in a motor housing and a rotor rotatably mounted radially to the stator for generating a torque on a drive shaft ( 6 ) connected to the input stage of a transmission ( 3 ), which is attached to the output end of the motor housing to form a motor-gear unit, characterized in that - the motor-gear unit ( 11 ) is attached to a base which forms a first structural element of the robot, against which a second structural element is rotatably mounted and driven by means of the motor-gear unit, - that the output stage ( 4 ) of the transmission via a torsion bar unit ( 11 ) is coupled to the second construction element, and - that the torsion bar unit ( 11 ) two position sensors ( 9 . 10 ) for detecting the over the torsion bar unit ( 11 ) are assigned to detect and regulate the drive torque to the second structural element. Drive device according to claim 1, characterized in that the transmission ( 3 ) is a shaft gear whose elliptical wave generator ( 7 ) with the motor shaft ( 6 ) and its flexspline ( 4 ) is coupled to the second construction element. Drive device according to claim 3, characterized in that the circular spline ( 8th ) of the shaft gear ( 3 ) is attached to the motor housing. Drive device according to claim 1, characterized in that a first position sensor ( 9 ) at the end of the torsion bar unit facing the second construction element ( 11 ), and a second position sensor ( 10 ) is arranged at the end facing the transmission of the Torsionsstabeinheit. Drive device according to claim 1, characterized in that the Torsionsstabeinheit ( 11 ) is designed as a rod, as a tube or as a bundle of individual rods. Drive device according to one or more of the preceding claims, characterized in that the motor shaft as a hollow shaft ( 12 ) is formed, and that the output shaft of the transmission through the hollow shaft ( 12 ) to the back of the engine ( 2 ) and coupled there with the second construction element.

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