Device for determining the torque and/or rotational angle between a first shaft and a second shaft

A device for determines the torque and/or the rotary angle between a first shaft and a second shaft, which are coupled via a gear mechanism to rotate relative to one another about an axis of rotation. The first shaft has a first end region, a second end region, and a first direction vector pointing in parallel with the axis of rotation from the first end region to the second end region, and the second shaft has a first end region, a second end region, and a second direction vector pointing in parallel with the axis of rotation from the first end region to the second end region. The first shaft is designed as a hollow shaft and the second shaft is arranged coaxially in the first shaft in such a way that the first direction vector and the second direction vector have the same orientation.

This is a National Phase Application filed under 35 U.S.C. 371 as a national stage of PCT/EP2020/083728, filed Nov. 27, 2020, an application claiming the benefit of German Application No. 10 2019 134 392.5 filed Dec. 13, 2019, the content of each of which is hereby incorporated by reference in its entirety.

The invention relates to a device for determining the torque and/or the rotary angle between a first shaft and a second shaft, which are coupled via a gear mechanism so that they can rotate relative to one another about an axis of rotation, according to the preamble of claim1.

It is known to use a rotary angle measuring system to control a motor, for example a servomotor, on a moving axle such as the arm of a robot, which determines the information required for control, such as speed and rotary angle position. The motor usually has a drive shaft, which transmits the force applied by the motor to an output shaft via a gear mechanism. Gear mechanisms are known to be elastic and non-linear, which means that the speed of the motor does not behave linearly either after the transmission ratio has been increased or reduced by the gear mechanism. Therefore, the elasticity of the gear mechanism under load causes an rotary angle displacement between the expected rotary angle position of the output shaft and the actual rotary angle position of the output shaft. In known systems, in order to avoid such a rotary angle offset, a second rotary angle measuring system is arranged on the output shaft, which system directly detects the movement of the output shaft. Additional sensors such as strain gauges are used to determine the torque that acts between the two shafts. Overall, a large number of sensors is required, and therefore such systems are complicated and expensive.

The object of the invention is therefore to provide a device for determining the torque and/or the rotary angle between a first shaft and a second shaft which has a simpler structure and can be produced more cost-effectively.

The object is achieved according to the invention by a device for determining the torque and/or the rotary angle between a first shaft and a second shaft with the features of claim1.

Advantageous embodiments and developments of the invention are specified in the dependent claims.

The device according to the invention for determining the torque and/or the rotary angle between a first shaft and a second shaft, which are coupled via a gear mechanism to rotate relative to one another about an axis of rotation, wherein the first shaft has a first end region, a second end region, and an end region parallel to the axis of rotation has a first direction vector pointing from the first end region to the second end region, and the second shaft has a first end region, a second end region, and a second direction vector pointing parallel to the axis of rotation from the first end region to the second end region, is characterized in that the first shaft is designed as a hollow shaft and the second shaft is arranged coaxially in the first shaft in such a way that the first direction vector and the second direction vector have the same orientation, and that the first end region of the first shaft has a first measurement standard and the first end region of the second shaft has a second measurement standard, wherein the first measurement standard is scanned by a first sensor and the second measurement standard by a second sensor.

The basic idea of the invention is to insert one shaft into the other shaft, which is designed as a hollow shaft, and to arrange the measurement standards at the same end of the two shafts in close proximity to one another, which can be scanned by two sensors that are also located in close proximity to each other. Instead of two spatially separate rotary angle measuring systems, two measurement standards arranged in close proximity to each other can be scanned, whereby the rotary angle position of each of the two shafts can be determined. At the same time, this arrangement also enables the torque to be determined in a simple manner, which results from a rotary angle offset between the expected rotary angle position of the second shaft, for example the output shaft, and the actual rotary angle position of the second shaft, for example the output shaft, for example at a predetermined torque of a motor connected to the first shaft or by fixing the first shaft and measuring the resulting rotary angle on the second shaft under load.

According to an advantageous embodiment of the invention, the two sensors are arranged on the face side in front of the first end region of the two shafts, which enables a compact structure.

The two sensors are particularly preferably arranged on a single printed circuit board, as a result of which the number of components required can be reduced.

In a particularly advantageous development of the invention, the sensors are designed as optical scanning elements and the measurement standards as reflective measurement standards. Such angle measuring systems are particularly robust and enable a high resolution of the rotary angle to be detected.

The two measurement standards are preferably designed to be circumferential in order to be able to detect the rotary angle in a simple manner.

Particularly preferably, the first measurement standard is arranged on a first element in the shape of a disk ring, which element is arranged on the first end region of the first shaft, and the second measurement standard is arranged on a second element in the shape of a disk ring, which element is arranged on the first end region of the second shaft. This allows for a compact structure.

The two measurement standards are advantageously arranged concentrically to one another, which can simplify the evaluation of the detected angles of rotation.

According to a particularly preferred embodiment of the invention, the two measurement standards are arranged in the same plane, which can further simplify the evaluation of the detected angles of rotation.

The first shaft is preferably a drive shaft of the gear mechanism and the second shaft is an output shaft of the gear mechanism. Since the first shaft, which is designed as a hollow shaft, forms the drive shaft of the gear mechanism, the drive can be arranged on the first shaft in a space-saving manner.

In particular, the first shaft can advantageously be non-rotatably connected to the rotor of an electric motor.

Preferably, the gear mechanism is a tension shaft gear mechanism, which makes high transmission increase or reduction ratios possible in a small space.

The device according to the invention as described above is particularly preferably used in a robot, since it is particularly necessary in the case of robots to control their movement precisely. A robot according to the invention therefore comprises a device according to the invention.

FIGS.1and2show two views of a device1for determining the torque and/or the rotary angle between a first shaft10and a second shaft20, which are rotatably coupled via a gear mechanism30relative to each other about an axis of rotation A. The first shaft10has a first end region10a, a second end region10b, and a first direction vector R1, which runs in parallel with the axis of rotation A and points from the first end region10ato the second end region10b. The second shaft20has a first end region20a, a second end region20b, and a second direction vector R2, which runs in parallel with the axis of rotation A and points from the first end region20ato the second end region20b. The first shaft10is designed as a hollow shaft in which the second shaft20is arranged coaxially. The arrangement is such that the first direction vector R1and the second direction vector R2have the same orientation, or in other words that the first end region10aof the first shaft and the first end region20aof the second shaft point to the same side. The first end region20aof the second shaft20can lie within the first end region10aof the first shaft10, in particular end so as to be flush with it, or protrude slightly beyond it.

The first end region10aof the first shaft10has a first measurement standard11, while the first end region20aof the second shaft20has a second measurement standard21. The measurement standards11,21can be formed circumferentially. For this purpose, the measurement standards11,21can be arranged, for example, on the outer surface of the shafts10,20. In the exemplary embodiment shown, a first element12in the shape of a disk ring is arranged on the first end region10aof the first shaft10, at or on which the first measurement standard11is arranged, in particular circumferentially, while a second element22in the shape of a disk ring is arranged on the first end region20aof the second shaft20, at or on which the second measurement standard21is arranged, in particular circumferentially. The measurement standards11,21are in particular arranged concentrically to one another. The disk ring-shaped elements12,22each have a plane which is arranged in particular perpendicularly to the axis of rotation A, with the two disk ring-shaped elements12,22and/or the two measurement standards11,21in particular being arranged in the same plane. For this purpose, the first element21in the shape of a disk ring can be of a stepped design so that an outer region12aof the first element12in the shape of a disk ring is arranged radially outside the second element22in the shape of a disk ring and in the same plane with it, while an inner region12bof the first element12in the shape of a disk ring is arranged axially behind the disk-shaped second element22.

The measurement standards11,21permit at least one relative angle determination over one revolution. The measurement standards11,21are preferably absolute measuring standards, which enable an angle to be determined over a large number of revolutions.

The first measurement standard11is scanned by a first sensor41, while the second measurement standard21is scanned by a second sensor42. The scanning can in particular take place optically. For this purpose, the measurement standards11,21are designed to be reflective, while the sensors41,42are designed as optical scanning elements.

The sensors41,42are arranged, for example, on the face side in front of the first end regions10a,20aof the two shafts10,20so that the measurement standards11,21are scanned substantially in parallel with the axis of rotation A. Alternatively, scanning can also take place in the radial direction to the shafts10,20.

The sensors41,42are particularly preferably arranged on a single printed circuit board40. The scanning signals detected by the sensors41,42are forwarded to an evaluation unit to determine the rotary angle positions of the first and second shaft10,20and, if necessary, also to determine the torque acting between the shafts10,20as described below. The angular positions can be determined independently of one another, i.e. the angular position of the first shaft10by scanning the first measurement standard11using the first sensor41and the angular position of the second shaft20by scanning the second measuring standard21using the second sensor42. If the elasticity of the gear mechanism30is known, i.e. if it is known which angular difference is present between the two shafts10,20without load during operation at a predetermined speed of the motor50, the torque can be determined on the basis of the angular difference with load during operation between the two shafts10,20.

The device1can have a housing50which is closed by a cover52, for example. In this case, the printed circuit board40can be arranged in the cover52, as a result of which the sensor system is easily accessible.

The first shaft10may be the drive shaft of the gear mechanism30, while the second shaft20may be the output shaft of the transmission30. The first shaft10is in particular the motor shaft of a motor50which is preferably designed as an electric motor, in particular as a servomotor. The motor50has a rotor55aand a stator55b, the rotor55abeing coupled to the first shaft10in a torque-proof manner.

The gear mechanism30couples the second end region20aof the first shaft10to the second end region20bof the second shaft20. The gear mechanism can be designed, for example, as a tension shaft gear mechanism. For this purpose, a radial projection31, which has an elliptical cross section perpendicular to the axis of rotation A, can be arranged on the second end region10bof the first shaft10, on the outer circumference of which a ball bearing32, which is designed as a roller bearing, for example, is arranged. A flexible, thin-walled sleeve33is arranged on the outer circumference of the ball bearing32and is arranged in a fixed manner in the housing50via a circumferential collar33a. The outside of the sleeve33has external teeth34. A radial projection20cis arranged on the second end region20bof the second shaft, which as a circumferential projection20don its surface facing in the direction of the first end region20aso that a circumferential groove20eis formed, which is open in the direction of the first end region20a. Internal teeth35are arranged in the groove20e, in which the external teeth34of the sleeve33engage. There is a difference in the number of teeth between the external teeth34and the internal teeth35, for example by one or two teeth. When the first shaft10rotates about the axis of rotation A, the elliptical projection31deforms the sleeve33, and, due to the tooth difference, a rotation of the second shaft20relative to the first shaft10is achieved. With a large number of teeth, a high transmission ratio increase or reduction can be achieved.

The device1is used in particular in a robot, for example in a moving joint of a robot.

The device1enables the angular positions of the first shaft10and the second shaft20to be determined in a simple manner, since the angular positions of the shafts10,20, in particular the angular position of the motor50and the angular position of the output shaft20and thus the output of the gear mechanism30, can be determined independently using the sensors41,42, in each case. The device1enables, for example, the torque acting between the two shafts10,20to be determined in the manner described below, but also in particular without additional mechanical components. If the first shaft10is fixed in its position and a torque to be determined acts on the second shaft20, an angular difference occurs between the second shaft20and the first shaft10, since the gear mechanism30has elasticity and acts like a torsion bar when the torque is applied. If the elasticity of the gear mechanism is known, the torque can be determined from the size of the angle difference. The known elasticity of the gear mechanism can be determined, for example, by determining the angular difference between the first shaft10, i.e. the motor shaft or the drive shaft, and the second shaft20, i.e. the output shaft, over the entire travel range without an additionally acting torque.

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