Method for determining an angle of rotation of a first shaft

Abstract

The invention relates to a method for determining a torsion angle of a first shaft, wherein the angular position of the first shaft is detected at a first axial position of the first shaft, wherein the angular position of the first shaft is detected at a second axial position of the first shaft, wherein, in a first method step, the shaft is rotated without load and, for each angular position detected at the first position, the difference between the angular position detected at the first position and the angular position detected at the second position is determined and stored as an offset value, wherein in a second method step, the shaft is rotated under load and, for each angular position detected at the first position, the torsion angle is determined as the difference between the angular position detected at the first position and the angular position detected at the second position, reduced by the stored value corresponding to the angular position detected at the first position.

Description

[0001] Method for determining a twist angle of a first shaft

[0002] Description:

[0003] The invention relates to a method for determining a twist angle, in particular the torsion, of a first shaft.

[0004] It is generally known that the torsion of a shaft can be detected using strain gauges.

[0005] From DE 10 2019 200 530 A1, a device for measuring torque on a shaft is known as the closest prior art.

[0006] From DE 198 34 322 A1 a device for determining the torque acting on a shaft is known.

[0007] From DE 10 2016 205 781 A1 a device for determining a relative angular position of rotating components is known.

[0008] A rotary angle and torque measuring device is known from DE 603 ​​12 767 T2.

[0009] A method for measuring a torsion angle is known from DE 102010 062 776 A1.

[0010] A device for determining an angle of rotation is known from DE 102019 107 416 A1.

[0011] A joint connection for a robot is known from DE 102014 110 413 A1.

[0012] The invention is therefore based on the objective of capturing the torsion of a shaft very precisely and in a manner robust against disturbances.

[0013] According to the invention, the problem is solved by the method according to the features specified in claim 1. Important features of the invention in the method are that the method is provided for determining a twist angle, in particular the torsion, of a first shaft or for determining a torque transmitted through a first shaft, in particular a torsional torque, wherein the angular position of the first shaft is detected at a first axial position of the first shaft, wherein the angular position of the first shaft is detected at a second axial position of the first shaft, or wherein the angular position of the second shaft is detected at a second axial position of a second shaft, which is in operative connection with the first shaft via mutually meshing gear elements, wherein in a first method step the shaft is rotated without load, in particular no torque is transmitted through the shaft.and for each angular position recorded at the first position, the difference between the angular position recorded at the first position and the angular position recorded at the second position is determined and stored as an offset value, in particular a correction value, and wherein in a second process step carried out after the first process step, the shaft is rotated and twisted under load, in particular a torque is transmitted through the shaft, and for each angular position recorded at the first position, the difference between the angular position recorded at the first position and the angular position recorded at the second position, reduced by the offset value stored or extrapolated from the stored offset values ​​corresponding to the angular position recorded at the first position, is determined as the twist angle, in particular wherein a measure for the transmitted torque, in particular torsional torque,is determined as the product of a parameter representing the torsional stiffness and the specific twist angle, in particular the quotient of the twist angle and the axial distance between the two positions.

[0014] A key advantage is the robust, non-contact measurement of torsion by determining the relative rotation of the first shaft. High precision is achieved by first performing a reference measurement on an unloaded shaft and then determining the measured values ​​relative to this reference. Inaccuracies in the manufacturing of the shaft or the gears mounted on it, whose tooth geometry is used to determine the angular position, do not lead to a deterioration in accuracy. Even with transverse force-induced deflection of the shaft, the angular position can be determined with high precision if the angular position is measured axially on both sides at two diametrically opposed circumferential points. Similarly, inaccuracies in the tooth geometry of the gears during the reference measurement result in a corresponding offset, which is recorded and taken into account during the measurement.

[0015] In an advantageous embodiment, a first externally toothed gear, serving as a dimensioning element, is non-rotatably connected to the shaft at the first position, and the angle of rotation of the gear is detected at at least two circumferential points spaced apart from each other in the circumferential direction, in particular by 180°, especially by means of GMR sensors, which in particular each generate two voltage signals offset from each other by 90°, in particular phase-shifted according to the tooth pitch, wherein the angular position of the first shaft detected at the first position is determined as the average of the angles of rotation detected at the circumferential points. It is advantageous that, when transverse forces act upon the first shaft, it is indeed displaced transversely at the first position, and thus the phase of the voltage signals from the GMR sensors is shifted as the shaft rotates.However, the phase shifts during the measurement at both circumferential points cancel each other out, and the measurement of the angular position remains precise despite transverse forces.

[0016] In an advantageous embodiment, a second externally toothed gear, serving as a dimensioning element, is non-rotatably connected to the shaft at the second position, and the rotation angle of the second gear is detected at at least two circumferentially spaced points, in particular by means of GMR sensors, which each generate two voltage signals offset by 90° from each other, and in particular phase-shifted according to the tooth pitch. The angular position detected at the second position is determined as the average of the rotation angles detected at the circumferential points. An advantage of this is that, when transverse forces are applied, the second shaft is indeed displaced laterally at the second position, and thus the phase of the voltage signals from the GMR sensors located there is shifted as the shaft rotates.However, the phase shifts during the measurement at both circumferential points cancel each other out, and the measurement of the angular position remains precise despite transverse forces.

[0017] In an advantageous embodiment, the angle of rotation is determined by calculating an arctangent function from the two voltage signals measured at the respective circumferential points during angular position detection. A key advantage is that the angle determination is quick and easy. In particular, commercially available GMR sensors can be used, as they provide two voltage signals offset by 90°, and especially phase-shifted to match the tooth pitch.

[0018] In an advantageous embodiment, the first gear has a marking on its outer circumference, particularly one that serves as a zero position. A range of rotation angles detected at a first circumferential point of the first gear, which includes the marking, is replaced by a corresponding range of rotation angles detected at a second circumferential point of the first gear, which does not include the marking. The first and second circumferential points are diametrically opposed to each other. An advantage of this is that the disturbances caused by the marking can be eliminated by using the signal from the diametrically opposite sensor instead of the original signal. Thus, a sufficiently precise determination of the angular position is possible.

[0019] In an advantageous embodiment, the second gear has a second marking on its outer circumference, which in particular serves as a zero position. A range of rotation angles measured at a first circumferential point of the second gear, which includes the second marking, is replaced by a corresponding range of rotation angles measured at a second circumferential point of the second gear, which does not include the second marking. In particular, the first and second circumferential points are diametrically opposed to each other. An advantage of this is that an absolute position determination is possible at each circumferential point, and not only a relative determination of the shaft's circumferential angular position. By defining a separate zero position for each gear, even though only one would be necessary, redundancy is created, thus increasing the reliability of the determination.Because the values ​​determined with the first of the zero positions can be redundantly determined using the second of the zero positions and the calculation adapted accordingly, and can thus be verified.

[0020] In an advantageous embodiment, between the first and second process steps, specifically after the first and before the second, an upper and a lower envelope are applied to the profile of the stored offset values, which is determined by the angular position recorded at the first position. The respective mean values ​​calculated from the upper and lower envelope values ​​are then stored as new offset values, thus replacing and / or overwriting the offset values ​​resulting from the first process step. An advantage of this approach is that high-frequency changes and noise can be suppressed by using the mean value from the upper and lower envelope values.

[0021] In a preferred embodiment, the new offset values ​​are additionally averaged over several revolutions of the shaft. The advantage here is that measurement inaccuracies and noise can be suppressed.

[0022] In an advantageous embodiment, a gear ratio effective between the first gear and the second gear, particularly via meshing gear teeth, is taken into account. It is advantageous that the transmitted torque can be determined even in a gearbox where the two gears are located on different shafts of the gearbox.

[0023] Key features of the arrangement for carrying out the aforementioned method are that a sensor, in particular a pair of GMR sensors, is arranged radially outside the respective gear at the respective circumferential point. An advantage of this arrangement is that it enables simple, cost-effective, and robust measurement. In an advantageous embodiment, the first measuring point is arranged on the first shaft, while the second measuring point is arranged on a second shaft, which is rotationally connected to a gear tooth that is in mesh with another gear tooth that is rotationally connected to the first shaft, or with another shaft driven by the first shaft via gear teeth. An advantage of this arrangement is that the transmitted torque in a gearbox can be determined.

[0024] Further advantages arise from the dependent claims. The invention is not limited to the combination of features in the claims. For those skilled in the art, further meaningful combinations of claims and / or individual features will be apparent.

[0025] Claim features and / or features of the description and / or the figures, in particular from the problem statement and / or the problem arising from comparison with the prior art.

[0026] The invention will now be explained in more detail with reference to schematic illustrations:

[0027] Figure 1 shows an arrangement for carrying out a method according to the invention for determining torque.

[0028] As shown in the figures, the arrangement includes a wave whose angular position is recorded repeatedly at a first measuring point 1 and whose angular position is recorded repeatedly at a second measuring point 2.

[0029] The first measuring point 1 is axially, in particular in the direction of the axis of rotation of the shaft, spaced away from the second measuring point 2.

[0030] The torque is determined from the difference between the recorded values ​​for angular position and multiplication by a parameter corresponding to the torsional stiffness.

[0031] For this purpose, a first gear is connected to the first shaft in a rotationally fixed manner at the first measuring point 1, and a first sensor 3 is arranged in a stationary position, which preferably has a GMR sensor for detecting the toothing of the first gear.

[0032] In particular, a second sensor 4 is also arranged in a stationary position, which also includes a GMR sensor for detecting the tooth engagement of the first gear. Preferably, the second sensor 4 is arranged diametrically opposite the first sensor 3. This enables a transverse force-compensated determination of the angular position of the first gear.

[0033] Furthermore, at the second measuring point 2 a second gear is non-rotatably connected to the first shaft and a third sensor 5 is arranged stationary, which also preferably has a GMR sensor for detecting the toothing of the second gear.

[0034] In particular, a fourth sensor 6 is also arranged in a stationary position, which also includes a GMR sensor for detecting the tooth engagement of the second gear. Preferably, the fourth sensor 6 is arranged diametrically opposite the third sensor 5. This enables a transverse force-compensated determination of the angular position of the second gear. Instead of the respective GMR sensor, other sine-cosine sensors can also be used.

[0035] Each of the gears preferably has more than two hundred teeth around its circumference.

[0036] Each of the sensors (3, 4, 5, 6) is designed as a sine-cosine encoder, i.e. it has two voltage signals that are 90° out of phase with each other, so that a relative angular position could be determined with each of the sensors (3, 4, 5, 6).

[0037] At least one, and in particular each, of the two gears has a marking on its circumference, so that the corresponding circumferential angle position can be used as the zero position and therefore each of the sensors (3, 4, 5, 6) can be used to determine the absolute angle of rotation. Preferably, the marking is provided on one of the teeth of the respective gear.

[0038] However, since the periodic course of the voltage signals is disrupted as the marker rotates past the respective sensor (3, 4, 5, 6), the course of the voltage signals of the respective sensor (3, 4, 5, 6) within a circumferential angle range around the marker is replaced by an evaluation unit, to which the voltage signals of all sensors (3, 4, 5, 6) are fed, with the corresponding course of the respective diametrically opposite sensor (3, 4, 5, 6). This is because, in an ideal design, the voltage signals of the two diametrically opposed sensors (3, 4, 5, 6) are identical. Alternatively, the calculated angle signal, in particular the calculated value of the arctangent function, is replaced in the disrupted area.

[0039] The mean value of the circumferential angle values ​​determined by the two diametrically opposed sensors (3, 4, 5, 6) is used to determine the angular position of the shaft. This is because transverse forces on the shaft or other disturbances can cause the first shaft to deflect, shifting the phase of the voltage signals from the respective sensor (3, 4, 5, 6) and thus resulting in an error in the angle determination.

[0040] By averaging the data, a robust determination of the shaft's angular position at each measuring point (1, 2) is enabled. Errors in determining the angular position caused by shaft eccentricity are thus avoided. During commissioning, the shaft is first set into rotation in a load-free state, i.e., without any load on the shaft, and the difference between the two average values—that is, the difference between the angular position of the first shaft at the first measuring point and the angular position of the first shaft at the second measuring point—is determined. However, this difference signal contains noise components whose frequency is higher than the shaft's rotational frequency.

[0041] In order to obtain a twist angle curve, in particular a torsion curve, that is at the same frequency as the rotational speed of the shaft, and in particular a low frequency, an upper and a lower envelope are applied to the curve of the difference signal, so that the twist angle curve is determined as the average value between the upper envelope value and the lower envelope value.

[0042] The twist angle profile determined in this way assigns a twist angle value to each angular position of the shaft at the first measuring point, which is caused by the design of the arrangement.

[0043] The twist angle profile is stored in a memory of the evaluation unit.

[0044] After commissioning, the shaft is subjected to a load, in particular to transmit a torque, so that a non-zero torsion is caused.

[0045] At regular intervals, the difference between the mean values ​​of the shaft's angular positions determined at the two measuring points (1, 2) is calculated, and the corresponding value of the twist angle profile stored in memory is subtracted as an offset. Thus, a specific offset value is taken into account at each angular position.

[0046] In this way, the existing twist angle of the shaft can be determined with high accuracy, and by multiplying it with the parameter describing the torsional stiffness, a value for torsion and thus also a value for torque can be determined easily and quickly with high accuracy.

[0047] The first shaft is enclosed by a gearbox. For example, the first shaft is the output shaft of the gearbox. According to the invention, the disruptive effects of lateral forces acting on the first shaft are eliminated by redundantly measuring the rotation angles of the respective gear. Manufacturing-related deviations can be compensated for by means of the reference measurement performed during commissioning. The markings on the gears enable absolute angle determination using the GMR sensors arranged on the circumference of the respective gear.By means of the series of mean values ​​formed from the upper and lower envelopes, noise and high-frequency variations can be suppressed, thus improving the signal-to-noise ratio of the measurement result. In further embodiments of the invention, the first measuring point 1 is indeed arranged on the first shaft; however, the second measuring point is arranged on a second shaft, which is rotationally fixed to a gear element that engages with another gear element that is rotationally fixed to the first shaft, or with another shaft that is driven by the first shaft via gear elements. When determining the twist angle, the gear ratio effective between the first and second shafts is taken into account. Furthermore, preferably only a single direction of rotation of the first shaft is provided in order to avoid disruptive effects of backlash in the transmission.

[0048] Reference symbol list

[0049] 1. First measuring point, in particular axial position 2. Second measuring point, in particular axial position

[0050] 3 Sensor

[0051] 4 Sensor

[0052] 5 Sensor

[0053] 6 Sensor

Claims

Patent claims:

1. A method for determining a twist angle, in particular the torsion, of a first shaft or for determining a torque transmitted through a first shaft, in particular a torsional torque, wherein the angular position of the first shaft is detected at a first axial position of the first shaft, wherein the angular position of the first shaft is detected at a second axial position of the first shaft, or wherein the angular position of the second shaft is detected at a second axial position of a second shaft, which is or is in operative connection with the first shaft via meshing gear parts, characterized in that in a first method step the shaft is rotated without load, in particular no torque is transmitted through the shaft.and for each angular position recorded at the first position, the difference between the angular position recorded at the first position and the angular position recorded at the second position is determined and stored as an offset value, in particular a correction value, and that in a second process step carried out after the first process step, the shaft is rotated under load, in particular a torque is transmitted through the shaft, and for each angular position recorded at the first position, the difference between the angular position recorded at the first position and the angular position recorded at the second position, reduced by the offset value stored or extrapolated from the stored offset values ​​corresponding to the angular position recorded at the first position, is determined as the twist angle, in particular wherein a measure for the transmitted torque, in particular torsional torque,is determined as the product of a parameter representing the torsional stiffness and the specific twist angle, in particular the quotient of the twist angle and the axial distance between the two positions.

2. Method according to claim 1, characterized in that at the first position a first externally toothed gear, serving as a dimensioning element, is non-rotatably connected to the shaft and the angle of rotation of the gear is detected at at least two circumferential points spaced apart from each other in the circumferential direction, in particular by 180°, in particular by means of GMR sensors, in particular which each generate two voltage signals offset from each other by 90°, in particular phase-shifted according to the tooth pitch, wherein the angular position of the first shaft detected at the first position is determined as the mean value of the angles of rotation detected at the circumferential points, and / or that at the second position a second externally toothed gear, serving as a dimensioning element, is non-rotatably connected to the shaft and the angle of rotation of the second gear is detected at at least two circumferential points spaced apart from each other in the circumferential direction, in particular by means of sine / cosine sensors.in particular by means of GMR sensors, in particular which each generate two voltage signals offset by 90° to each other, in particular phase-shifted to match the tooth pitch, wherein the angular position detected at the second position is determined as the mean of the rotation angles detected at the circumferential points.

3. Method according to one of the preceding claims, characterized in that the angle of rotation is determined in each case by determining an arctangent function from the respective two voltage signals.

4. Method according to one of the preceding claims, characterized in that the first gear has a marking on its outer circumference, in particular functioning as a zero position, wherein a region of rotation angles detected at a first circumferential point of the first gear, which contains the marking, is replaced by a corresponding region of rotation angles detected at a second circumferential point of the first gear, which does not contain the marking, in particular wherein the first circumferential point and the second circumferential point are diametrically opposed to each other.

5. Method according to one of the preceding claims, characterized in that the second gear has a second marking on its outer circumference, in particular functioning as a zero position, wherein a region of rotation angles detected at a first circumferential point of the second gear, which contains the second marking, is replaced by a corresponding region of rotation angles detected at a second circumferential point of the second gear, which does not contain the second marking, in particular wherein the first circumferential point and the second circumferential point are diametrically opposed to each other.

6. Method according to one of the preceding claims, characterized in that between the first and the second method step, in particular after the first method step and before the second method step, an upper envelope and a lower envelope are applied to the course of the stored offset values, which depends on the angular position recorded at the first position, and the respective mean values ​​formed from the respective upper and lower envelope values ​​are stored as new offset values, in particular replacing and / or overwriting the offset values ​​resulting from the first method step.

7. Method according to claim 6, characterized in that the new offset values ​​are additionally averaged over several revolutions of the shaft.

8. Method according to one of the preceding claims, characterized in that a transmission ratio effective between the first gear and the second gear, in particular via meshing gear parts, is taken into account.

9. Arrangement for carrying out a method according to one of the preceding claims, characterized in that a respective sensor, in particular a Sin / Cos sensor, in particular a GMR sensor pair, is arranged radially outside the respective gear at the respective circumferential location.

10. Arrangement according to one of the preceding claims, characterized in that the first measuring point is arranged on the first shaft, wherein the second measuring point is arranged on a second shaft which is rotationally fixed to a toothed part which is in engagement with a further toothed part which is rotationally fixed to the first shaft or with another shaft which is driven by the first shaft via toothed parts.

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