Torque Sensor Device

Abstract

To provide a torque sensor device which enables accurate torque measurement and can be produced in a compact, light-weight configuration.SOLUTION: A torque sensor device 100 is provided, having a circular body comprising an annular inner flange 10, an annular outer flange 20, and a circular intermediate portion 30 between the annular inner flange and the annular outer flange, the annular inner flange being closer to a center of the circular body than the annular outer flange. The circular intermediate portion is continuously solid.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a torque sensor device configured to determine the torque of some object, for example a driven shaft or a robot joint. [Background technology]

[0002] Accurate detection of torque on an object, such as any driven shaft or joint, is a problem relevant to several applications. A particular application concerns torque measurement during the motion of a robot joint. In robot joints, which are subject to loads in various directions, in order to accurately detect the rotational torque acting on the joint, some cancellation mechanism must usually be provided to exclude loads in directions other than the rotational direction from the measurement process. However, it is very difficult to reliably exclude such loads.

[0003] It is known in the art to compensate for loads in directions other than the rotational direction by means of a Wheatstone bridge circuit with radially elastic torque transmitting parts and a torque sensor (see, for example, WO2018 / 041948A1).

[0004] However, the known torque sensor devices still suffer from a lack of precision in torque measurement, a relatively large construction, and furthermore require additional members connected to the sensor body for the purpose of sealing the gearbox with the sensor device. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO2018 / 041948A1 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, there is a need for a torque sensor device that provides accurate torque measurements and that can be formed in a compact, lightweight configuration. [Means for solving the problem]

[0007] To address the above-mentioned needs, the present invention provides a torque sensor device comprising a circular body with an annular inner flange and an annular outer flange and a circular intermediate portion located between the annular inner flange and the annular outer flange, the circular inner flange being located closer to the center of the circular body than the annular outer flange. The circular intermediate portion may be a continuous solid portion (without openings / cutouts) and may have at least partially a smaller axial thickness than the inner and / or outer flanges. In principle, the circular body may be of one piece or may comprise portions attached to each other.

[0008] This compact configuration with an intermediate portion extending continuously from the inner flange to the outer flange in the radial direction allows the torque sensor device to be used, for example, to seal a gear box without the need for additional sealing means such as a sealing membrane as is necessary in the art, for example the torque sensor device is suitable for sealing a gear box of a robot joint.

[0009] According to one embodiment, an inner force aperture is formed in the inner flange and an outer force aperture is formed in the outer flange. The torque to be measured is transmitted via a connecting member connected to the inner and outer force apertures, for example by the rotating shaft under consideration and any stationary member. Thereby, the torque applied between the inner and outer flanges can be measured.

[0010] A plurality of measuring transducers may be formed in the circular intermediate portion, in particular in pairs. The measuring transducers may include or consist of at least one of the following: silicon gauges, foil strain gauges, and thin-layer strain gauges. In particular, the pairs of measuring transducers can be arranged symmetrically with respect to the axial direction of the torque sensor device (axis running through the center of the circular body in a direction perpendicular to the main surfaces of the circular body). The strain gauges can sense shear strains, in particular with an orientation tilted at 45° with respect to a radial axis running through the center of the circular body in a direction parallel to the main surfaces of the circular body on which the pair of strain gauges are symmetrically arranged. The pairs of measuring transducers located opposite each other define a measurement channel. This arrangement makes it possible to eliminate or significantly reduce the effect of tilt and radial and axial loads on the measurement of torque, thus making it possible to increase the accuracy of the measurement results obtained by the torque sensor device of the invention (see also the detailed description below).

[0011] According to a particular embodiment, the plurality of measuring transducers comprises at least four pairs of measuring transducers, the two measuring transducers of each pair being symmetrically positioned with respect to an axis (radial axis) running through the center of the circular body in a direction parallel to the main surface of the circular body. Such an arrangement can be advantageous with respect to the measurement accuracy by ensuring suppression of radial and axial loads as well as tilt effects.

[0012] Four pairs of measuring transducers (e.g. exactly four pairs of measuring transducers) may be provided, including that for each of the four pairs of measuring transducers, an axis extending through the center of the circular body in a direction parallel to a main surface of the circular body on which the two measuring transducers of the pair are symmetrically located is spaced circumferentially by 90° from an axis extending through the center of the circular body in a direction parallel to a main surface of the circular body on which the two measuring transducers of an adjacent pair are symmetrically located. This arrangement may improve the measurement accuracy, since it ensures that the effects of radial and axial loads and tilt are suppressed.

[0013] With regard to reducing the effect of radial loads on the measurement of torque of the object under consideration, it may be advantageous to form a tapered / thinned portion in the circular intermediate portion that does not extend completely through the thickness of the intermediate portion, i.e. in a direction along an axis extending through the center of the circular body in a direction perpendicular to the main surfaces of the circular body. The tapered / thinned portion may, for example, be located closer to the outer flange than the inner flange and extend further in the circular direction than in the radial direction.

[0014] In particular, the centre of each of the circumferentially tapered portions may be circumferentially spaced 22.5° from an axis extending through the centre of the circular body in a direction parallel to the main surface of the circular body on which the two measurement transducers of the pair of measurement transducers are symmetrically located (this axis defines a measurement channel).

[0015] Alternatively or in addition to the tapered portion, the intermediate portion may be provided with some radially elastic zone, for example located closer to the inner flange than the outer flange, or located substantially halfway (radially) between the inner and outer flanges. The radially elastic zone may comprise or consist of a groove formed in the intermediate portion of the body.

[0016] The measurement of torque by the torque sensor device of the present invention can be based on strain gauges representing measurement transducers. These strain gauges can be connected to a Wheatstone bridge circuit, which becomes unbalanced when a torque is applied and outputs a voltage (caused by the resistance change of the strain gauges) proportional to the applied torque. Thus, according to one embodiment, the torque sensor device of the present invention comprises a first printed circuit board arranged on the intermediate part, the first printed circuit board comprising a Wheatstone bridge circuit electrically connected to the measurement transducers. The first printed circuit board can also comprise a DC or AC excitation source for the Wheatstone bridge circuit.

[0017] Furthermore, the torque sensor device may comprise a second printed circuit board arranged on the first printed circuit board, the second printed circuit board comprising circuitry for signal conditioning, in particular means for analog-to-digital conversion and / or amplification of the signal provided by the Wheatstone bridge circuit of the first printed circuit board. The second printed circuit board may cover the first printed circuit board to protect the first printed circuit board and sensitive circuits formed on the first printed circuit board and on the bottom side of the second printed circuit board facing the first printed circuit board.

[0018] Furthermore, a robot, in particular a collaborative robot, is provided that comprises a joint, the joint comprising a gearbox, the robot further comprising a torque sensor device according to one of the above mentioned embodiments. In particular, the torque sensor device can be positioned to seal the gearbox of the joint of the robot.

[0019] Additionally, there is provided a method for measuring the torque of a shaft positioned in a gearbox, in particular a gearbox of a joint of a robot, comprising mounting a torque sensor device according to one of the above described embodiments on the gearbox such that the gearbox is sealed, and measuring the torque by means of the torque sensor device sealing the gearbox.

[0020] Further features and exemplary embodiments and advantages of the present disclosure will be described in detail with reference to the drawings. It will be understood that the present disclosure should not be construed as being limited by the following description of the embodiments. It will also be understood that some or all of the features described below can be combined in alternative ways. [Brief description of the drawings]

[0021] [Figure 1A]1A and 1B show torque sensor devices each including an inner flange, an outer flange, and a solid intermediate portion extending radially and continuously from the inner flange to the outer flange according to an embodiment of the present invention. [Figure 1B] 1A and 1B show torque sensor devices each including an inner flange, an outer flange, and a solid intermediate portion extending radially and continuously from the inner flange to the outer flange according to an embodiment of the present invention. [Diagram 2] FIG. 1C shows the torque sensor device of FIG. 1A or FIG. 1B with a first printed circuit board. [Diagram 3] FIG. 3 shows the torque sensor device of FIG. 2 with a second printed circuit board. [Figure 4A] FIG. 1 illustrates torque measurement with compensation for tilt, axial load, and radial load. [Figure 4B] FIG. 13 illustrates torque measurement with compensation for tilt. [Figure 4C] FIG. 1 illustrates torque measurement with compensation for axial load. [Figure 4D] FIG. 13 illustrates torque measurement with compensation for radial load. [Diagram 5] FIG. 13 illustrates another embodiment of a torque sensor device comprising a tapered region in an intermediate portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The invention provides a torque sensor device that allows to accurately measure the torque of an object, e.g. a rotating shaft or a robot joint, the measurement being less affected by axial or radial loads or tilting moments. In particular, the torque sensor device can be used for sealing purposes, e.g. for sealing gearboxes. The torque sensor device is suitable for measuring the torque of joints, e.g. of (collaborative) robots. Torque control based on measurements made by the torque sensor device can be advantageously implemented in robots, e.g. to facilitate robot-human interaction.

[0023] In Fig. 1A and Fig. 1B an exemplary embodiment of a torque sensor device 100 of the invention is shown. The torque sensor device 100 comprises an inner flange 10 and an outer flange 20. From the inner flange 10 to the outer flange 20, an intermediate portion 30 extends in a radially continuous manner. The inner flange 10, the outer flange 20 and the intermediate portion 30 form a circular body, even a one-piece circular body. The circular body can consist of or be made of, for example, steel, aluminum or an aluminum alloy. When a one-piece circular body is not provided, different parts of the circular body can be made of different materials. The intermediate portion 30 is not formed with an opening extending through the entire material. The intermediate portion 30 can therefore act as a seal, for example to seal a gearbox.

[0024] The intermediate portion 30 may comprise sub-portions 30a and 30b, which may also be separated from each other by a separator 30c. The separator 30c may be a lip or may be a circumferential groove 30c as shown in FIG. 1B. Such a circumferential groove 30c may be a radially elastic portion provided to counteract the effect of radial loads (see also below) during the torque measuring process.

[0025] As shown in the top view of the main surface of the torque sensor device 100 in Fig. 1A, a plurality of pairs of measurement transducers 40 are formed in the intermediate portion 30, for example the lower portion 30a. The measurement transducers 40 are arranged symmetrically with respect to an axis (axial axis) extending through the center of the circular body perpendicular to the main surface. The measurement transducers 40 can in principle be strain-sensing transducers, in particular strain gauges.

[0026] Furthermore, the inner flange 10 is formed with inner force openings 11 and 12 of different sizes, and the outer flange 20 is formed with outer force openings 21 and 22 of different sizes. The inner force openings 11 and 12 and the outer force openings 21 and 22 may be axially extending holes that are open on at least one side or the respective flange and may have any suitable geometric shape, for example a circular or polygonal cross section.

[0027] FIG. 2 shows the torque sensor of FIG. 1A or 1B, on which a first printed circuit board 50 is provided on the intermediate part 30, which comprises some circuit devices, e.g. resistors and capacitors, and a connector 55 for connecting to another printed circuit board 60 (see below). The measurement transducer 40, together with the included measurement part, can be connected to the intermediate part 30 and can have free connection parts for connecting to the first printed circuit board 50 and thus to the circuit devices of the first printed circuit board 50. In particular, the first printed circuit board 50 can comprise Wheatstone bridge elements (resistors) for converting the applied torque into a voltage output signal, as known in the art. Depending on the actual application, a half or full Wheatstone bridge can be used.

[0028] As shown in FIG. 3, the first printed circuit board 50 can be covered by a second printed circuit board 60. The second printed circuit board 60 protects the measurement transducer 40 and the circuit device 55 from the environment. In particular, the second printed circuit board 60 can have a vulnerable circuit device located on the bottom side (facing the first printed circuit board 50) and a connector 65 that connects to the first printed circuit board. The second printed circuit board 60 is configured for signal conditioning, such as analog-to-digital conversion of the voltage output signal provided by the circuit device of the first printed circuit board 50. The signal conditioning can also include amplification of the voltage output signal provided by the circuit device of the first printed circuit board 50.

[0029] As mentioned above, the measurement transducers 40 can be arranged around an axial axis that extends through the center of the circular body in a direction perpendicular to the main surface of the circular body. For example, one or two pairs of measurement transducers 40 can be arranged 90° apart in the circumferential direction from one or two adjacent pairs of measurement transducers 40. Figures 4A-4D show an embodiment in which the strain gauges 40 are arranged in pairs symmetrically with respect to an axial axis that extends through the center of the circular body in a direction perpendicular to the main surface of the circular body, with the strain gauges 40 of opposite pairs defining two measurement channels C that are 90° apart from each other in the circumferential direction (from one channel to the other). Each measurement channel C extends through the center of a particular pair of strain gauges 40 arranged opposite each other.

[0030] Torque (indicated by the arrows in FIG. 4A ) can be measured based on the differential strains +ε and −ε, where +ε is experienced by one strain gauge of the pair of strain gauges 40 and −ε is experienced by the other strain gauge of the pair. The strain gauges 40 are connected to a Wheatstone bridge circuit formed on a printed circuit board 50. Due to the selected geometry of the arrangement of the strain gauges 40 (and the corresponding structure of the Wheatstone bridge circuit), the voltage output signal provided by the Wheatstone bridge circuit induced by an applied torque (strain at an intermediate portion of the torque sensor device at which the strain gauges 40 are positioned to sense that strain) is Σ ε =4ε+4ε=8ε, i.e., a sufficiently high required voltage output signal can be provided.

[0031] On the other hand, as shown in Figures 4B-4D, disturbances due to tilt and axial and radial loads can be largely suppressed. The arrows in Figure 4B indicate tilts that can be applied to the torque sensor device. The application of a tilt to the torque sensor device 100 results in differential strains +ε1 and +ε2, +ε2 and +ε1, -ε2 and -ε1, and -ε1 and -ε2, respectively, for the four pairs of strain gauges 40 that define the measurement channel C. Accordingly, the strains induced by the tilt are compensated for by the selected geometry of the arrangement of the strain gauges 40 (and the corresponding structure of the Wheatstone bridge circuit), resulting in a strain of Σ ε =ε1-ε1+ε2-ε2=0 and therefore does not contribute to the voltage output signal proportional to the applied torque as shown in FIG. 4A.

[0032] To achieve accurate torque measurement, it is also necessary to compensate for the axial load. Such a type of compensation can also be achieved by a selected geometry of the arrangement of the strain gauges 40 (and the corresponding structure of the Wheatstone bridge circuit), as shown in FIG. 4C (the arrows indicate the applied axial load). The axial load (due to the axially symmetric arrangement of the strain gauges 40) results in a strain +ε in each of the strain gauges 40, thus resulting in a zero net effect and a Σ ε With regard to compensating for tilt and axial loads, it may be advantageous to position the strain gauges 40 at the same radial distance relative to the inner flange 10 and the outer flange 20.

[0033] The compensation for radial loads by the selected geometry of the arrangement of the strain gauges 40 (and the corresponding structure of the Wheatstone bridge circuit) is shown in FIG. 4D. The applied radial loads are indicated by arrows. The radial loads result in differential strains -ε1 and +ε2, +ε2 and -ε1, -ε1 and +ε2, and +ε2 and -ε1, respectively, for the four pairs of strain gauges 40 that define the two measurement channels C. Correspondingly, the contribution to the voltage output signal of the Wheatstone bridge circuit of the printed circuit board 50 is Σ ε=-2ε1+2ε2+2ε1-2ε2=0.

[0034] However, it should be noted that if any radial load is applied radially with a circumferential shift of 22.5° relative to measurement channel C, the exact compensation for the radial load shown in FIG. 4D may not be achieved. In this case, any Σ ε ≠0, which may adversely affect the accuracy of the torque measurement. To alleviate this problem, some radially elastic portion may be provided in the middle portion 30 of the torque sensor device 100. The radially elastic portion may be realized by some groove 30c as shown in FIG. 1B. The radially elastic portion may be machined into the top or bottom surface of the middle portion 30.

[0035] According to another approach to the problem of non-compensation of radial loads applied radially at a 22.5° circumferential shift with respect to the measurement channel C, a tapered portion 70 can be formed in the middle portion 30 of the torque sensor device 100′, as shown in Figure 5. The tapered portion 70 can be machined into the top or bottom surface of the middle portion 30. In the embodiment shown in Figure 5, the tapered portion 70 is located at 22.5°, closer to the outer flange 20 than to the inner flange 10. The tapered portion 70 has a larger dimension in the circumferential direction than in the radial direction.

[0036] Experiments have shown that such an arrangement of the tapered portion 70 reduces Σ ε , and thus it has been found that the contribution of the corresponding radial loads to the measurement results is significantly reduced. It is noted that the tapered portion 70 is not drilled through the intermediate portion 30 in order not to degrade the advantageous sealing properties of the torque sensor device 100'.

[0037] According to the above-mentioned embodiment, a torque sensor device can be provided that operates accurately with a compact design and low cost with reduced height compared to the prior art, that can seal the gearbox without the need for additional sealing means and that can provide at least two channel measurements. In particular, all the associated measurement transducers can be formed on one and the same surface of the intermediate part 30 of the above-mentioned torque sensor device 100, 100'.

Claims

1. a circular body having an annular inner flange (10) and an annular outer flange (20) and a circular intermediate portion (30) located between said annular inner flange (10) and said annular outer flange (20); the inner annular flange (10) is located closer to the center of the body than the outer annular flange (20); The circular intermediate portion (30) is a continuous solid portion; the circular intermediate portion (30) comprises an inner subportion (30a), an outer subportion (30b) and a circumferential groove (30c) separating the inner subportion (30a) and the outer subportion (30b) from each other; A plurality of measurement transducers (40) are formed in the inner lower portion (30a) of the circular intermediate portion (30). A torque sensor device (100, 100').

2. 2. The torque sensor device (100, 100') of claim 1, wherein the inner flange (10) is formed with inner force application openings (11, 12) and the outer flange (20) is formed with outer force application openings (21, 22).

3. 2. The torque sensor device (100, 100') according to claim 1, wherein the measurement transducers (40) are formed in pairs in the inner lower portion (30a) of the circular intermediate portion (30).

4. 4. The torque sensor device (100, 100') of claim 3, wherein the plurality of measurement transducers (40) are positioned axially symmetrically with respect to an axis extending through the center of the circular body in a direction perpendicular to the main surfaces of the circular body.

5. 5. The torque sensor device (100, 100') of claim 4, wherein the plurality of measurement transducers (40) comprises at least four pairs of measurement transducers (40), two measurement transducers (40) of each of the at least four pairs of measurement transducers (40) being symmetrically positioned with respect to an axis extending through the center of the circular body in a direction parallel to the main surfaces of the circular body.

6. 6. The torque sensor device (100, 100') according to claim 5, wherein four pairs of measurement transducers (40) are provided, and for each of the four pairs of measurement transducers (40), an axis extending through the center of the circular body in a direction parallel to the main surface of the circular body about which the two measurement transducers (40) of the pair are symmetrically located is spaced circumferentially by 90° from an axis extending through the center of the circular body in a direction parallel to the main surface of the circular body about which the two measurement transducers (40) of an adjacent pair are symmetrically located.

7. 2. The torque sensor device of claim 1, wherein the circular intermediate portion (30) comprises a tapered portion (70) that does not extend completely through the intermediate portion (30) in a direction along an axis extending through a center of the circular body in a direction perpendicular to a main surface of the circular body, the tapered portion (70) being located closer to the outer flange (20) than to the inner flange (10) and extending further in a circular direction than in a radial direction.

8. 8. The torque sensor device (100, 100') according to claim 7, wherein the center of each of the tapered portions (70) in the circumferential direction is spaced 22.5° in the circumferential direction from an axis extending through the center of the circular body in a direction parallel to the main surface of the circular body about which the two measurement transducers (40) of the pair of measurement transducers (40) are symmetrically located.

9. 2. The torque sensor device (100, 100') of claim 1, further comprising a first printed circuit board (50) disposed on the intermediate portion (30), the first printed circuit board (50) comprising a Wheatstone bridge circuit electrically connected to the plurality of measurement transducers (40).

10. 10. The torque sensor device (100, 100') of claim 9, further comprising a second printed circuit board (60) arranged on the first printed circuit board (50), the second printed circuit board (60) comprising, as a circuit for signal conditioning, means for analog-to-digital conversion and / or amplification of a signal provided by the Wheatstone bridge circuit of the first printed circuit board.

11. The torque sensor device (100, 100') of claim 1, wherein the plurality of measurement transducers (40) include or consist of at least one of silicon gauges, foil strain gauges, and thin layer strain gauges.

12. A robot comprising a joint, said robot being a collaborative robot, said joint comprising a gearbox, and further comprising a torque sensor device (100, 100') according to any one of claims 1 to 11.

13. The robot of claim 12, wherein the torque sensor device (100, 100') is positioned to seal the gearbox.

14. A method for measuring the torque of a shaft positioned in a gearbox, comprising mounting a torque sensor device (100, 100') according to any one of claims 1 to 11 to the gearbox such that the gearbox is sealed, and measuring the torque by the torque sensor device (100, 100') sealing the gearbox.

15. The method described in claim 14, wherein the gearbox is a gearbox of a joint of a robot.

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