Patent Description:
Accurately detecting the torque of an object, as some driven shaft or joint, represents a problem that is of relevance in a plurality of applications. A particular application relates to the torque measurement during the movement of joints of robots. In a joint of a robot on which loads in various directions act, in order to accurately detect a torque in the rotation direction acting on the joint, usually some cancellation mechanism have to be provided in order to exclude loads in directions other than the rotation direction from the measurement process. However, reliable exclusion of such loads is very difficult.

In the art it is known to compensate for loads in directions other than the rotation direction by means of Wheatstone circuitries and torques sensors comprising radially elastic torque transfer portions (see, for example, <CIT>).

<CIT> discloses a torque sensor device comprising an inner flange and an outer flange and an intermediate portion between the inner and outer flanges, wherein the intermediate portion comprises thinned receptacles for accommodating strain gages. Pairs of strain gages are arranged symmetrically to measurement channels to reduce the effects of tilt moments.

<CIT> discloses a torque sensor, which consists of two disc-shaped fastening flanges that lie parallel opposite one another, and that are connected with one another by a radially inner moment or torque transmission element. One fastening flange is embodied as a measuring flange, which comprises several recesses on a coaxial encircling area between its outer fastening ring surface and the torque transmission element, and shear force transducers are applied on the outer or base surfaces of the recesses. The recesses are formed by at least three measuring pockets, which are separated from one another by at least three radial stiffening webs. The measuring flange, on its radially inwardly lying area relative to the radially outer fastening ring surface is embodied as an encircling closed or continuous surface, on which the measuring electronics is fastened, which is hermetically closed with a cover.

<CIT> discloses a sensor for measuring axial or radial forces comprising a rotationally symmetric body comprising an inner force introducing portion and an outer force outputting portion separated from each other by a deforming portion. Transducers are formed over the deforming portion and arranged in tapered out portions formed in the inner force introducing portion and an outer force outputting portion.

However, known torque sensor devices still suffer from a lack of accuracy of the torque measurements and relatively bulky configurations that, moreover, require additional members connected to the sensor bodies when it comes to sealing purposes of gear boxes by means of the sensor devices.

Consequently, there is a need for a torque sensor device that allows for accurate torque measurements and that can be formed in a compact light-weighted configuration.

In order to address the above-mentioned need the invention provides a torque sensor device, as defined in claim <NUM>, the.

The circular intermediate portion is a continuously solid portion (comprising no openings/cutouts) that at least partially may have a smaller thickness in an axial direction as the inner and/or outer flange. In principle, the circular body may be a monolithic body or may comprise parts attached to each other.

This compact configuration with an intermediate portion extending continuously from the inner flange to the outer flange in a radial direction allows for using the torque sensor device for sealing, for example, of a gear box without the need for an additional sealing means, like a sealing membrane, as it is necessary in the art. For example, the torque sensor device is suitable for sealing a gear box of a robot joint.

Torque to be measured is transferred, for example, by a rotating shaft under consideration and some static member, via connection members connected to the inner and outer force application openings. Thereby, the torque applied between the inner and outer flanges can be measured.

The measurement transducers may comprise or consist of at least one of silicon gages, foil strain gages, and thin layer strain gages. Particularly, the pairs of measurement transducers may be arranged symmetrically about an axial direction (axis extending through the center of the circular body in a direction perpendicular to the main surface of the circular body) of the torque sensor device. The strain gages may sense shear strain, particularly, oriented <NUM>° inclined to the radial axis running through the center of the circular body in a direction parallel to the main surface of the circular body to which the strain gages of a pair of strain gages are symmetrically arranged. Pairs of measurement transducers that are located opposite to each other define a measurement channel. The arrangement allows for eliminating or largely reducing the effects of tilts and radial and axial loads on the measurement of the torque and, thus, allows for an increased accuracy of the measurement results obtained by means of the torque sensor device of the invention (see also detailed description below).

According to a particular embodiment, the plurality of measurement transducers comprises at least four pairs of measurement transducers wherein the two measurement transducers of each of the pairs of measurement transducers are located symmetrically to an axis extending through the center of the circular body in a direction parallel to the main surface of the circular body (radial axis). Such an arrangement may be advantageous with respect to the measurement accuracy by reliably suppressing influences of radial and axial loads as well as tilts.

Four pairs of measurement transducers (for example, exactly four pairs of measurement transducers) may be provided wherein for each of the four pairs of measurement transducers it holds that an axis extending through the center of the circular body in a direction parallel to the main surface of the circular body to which the two measurement transducers of that pair of measurement transducers are located symmetrically is spaced apart by <NUM>° in a 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 to which two measurement transducers of a neighboring pair of measurement transducers are located symmetrically. The measurement accuracy may be enhanced by this arrangement due to reliably suppressing influences of radial and axial loads as well as tilts.

With respect to reducing the effects of radial loads on the measurement of the torque of an object under consideration it might be advantageous to form in the circular intermediate portion tapered/thinned out portions not extending completely through the thickness direction 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 surface of the circular body. The tapered/thinned out portions are, for example, located closer the outer flange than the inner flange and may have longer extensions in a circular direction than in a radial direction.

In particular, the center of each of the tapered out portions in a circumferential direction may be spaced apart from an axis extending through the center of the circular body in a direction parallel to the main surface of the circular body with respect to which two measurement transducers of a pair of measurement transducers are located symmetrically (this axis defining a measurement channel) by <NUM>° in a circumferential direction.

The measurement of a torque by means of the inventive torque sensor device may be based on strain gages representing the measurement transducers. The strain gages may be connected to a Wheatstone bridge circuitry that becomes unbalanced when a torque is applied and outputs a voltage (caused by the resistance change of the strain gages) proportional to the applied torque. Thus, according to an embodiment, the inventive torque sensor device comprises a first printed circuit board arranged over the intermediate portion and comprising a Wheatstone bridge circuitry electrically connected to the measurement transducers. The first printed circuit board may also comprise a DC or AC excitation source for the Wheatstone bridge circuitry.

Moreover, the torque sensor device may comprise a second printed circuit board arranged above the first printed circuit board and comprising a circuitry for signal conditioning, in particular, means for analogue-to-digital conversion and/or amplification of signals provided by the Wheatstone bridge circuitry of the first printed circuit board. The second printed circuit board may cover the first printed circuit board in order to protect it and the sensitive circuitry formed on the first printed circuit board and at the bottom of the second printed circuit board facing the first printed circuit board.

Furthermore, it is provided a robot, in particular, a collaborative robot, comprising a joint, wherein the joint comprises a gear box, and wherein the robot further comprises a torque sensor device according to one of the above-described embodiments. Particularly, the torque sensor device may be positioned to seal the gear box of the joint of the robot.

Additionally, it is provided a method of measuring a torque of a shaft positioned in a gear box, in particular, a gear box of a joint of a robot, the method comprising attaching the torque sensor device according to one of the above-described embodiments to the gear box such that the gear box is sealed and measuring the torque by means of that torque sensor device that is sealing the gear box.

Further features and exemplary embodiments as well as advantages of the present disclosure will be explained in detail with respect to the drawings. It is understood that the present disclosure should not be construed as being limited by the description of the following embodiments. It should furthermore be understood that some or all of the features described in the following may also be combined in alternative ways.

The present invention provides a torque sensor device that allows for accurately measuring the torque of an object, for example, a rotating shaft or a robot joint wherein the measurement is not significantly affected by axial or radial loads or tilting moments. In particular, the torque sensor device can be used for sealing purposes, for example, for sealing a gear box. The torque sensor device is suitable for measuring the torque of a joint of a (collaborative) robot, for example. Torque control based on measurements made by the torque sensor device can be advantageously implemented in robots to facilitate robot-human interactions, for example.

Exemplary embodiments of the inventive torque sensor device <NUM> are shown in <FIG>. The torque sensor device <NUM> comprises an inner flange <NUM> and an outer flange <NUM>. An intermediate portion <NUM> continuously extends radially from the inner flange <NUM> to the outer flange <NUM>. The inner flange <NUM>, the outer flange <NUM> and the intermediate portion <NUM> form a circular body, for example, a monolithic circular body. The circular body may consist of or comprise, for example, steel, aluminum or an aluminum alloy. Different parts of the circular body may be made of different materials when no monolithic circular body is provided. No openings extending through the entire material are formed in the intermediate portion <NUM>. Thus, the intermediate portion <NUM> can serve as a seal, for example, for sealing a gear box.

The intermediate portion <NUM> comprises sub-portions 30a and 30b that are separated from each other by a circumferential groove 30c as illustrated in <FIG>. Such a circumferential groove 30c serves as a radially elastic portion provided in order to suppress effects of radial loads (see also description below) in the process of measuring torque.

A plurality of pairwise measurement transducers <NUM> is formed on the intermediate portion <NUM>, for example sub-portion 30a, as it is shown in the top view of the main surface of the torque sensor device <NUM> of <FIG>. The measurement transducers <NUM> are arranged symmetrically about an axis running through the center of the circular body perpendicular to the main surface (axial axis). The measurement transducers <NUM> can, in principle, be strain-sensitive transducers, in particular, strain gages.

Moreover, in the inner flange <NUM> inner force application openings <NUM> and <NUM> of different sizes are formed and in the outer flange <NUM> outer force application openings <NUM> and <NUM> of different sizes are formed. The inner and outer force application openings <NUM>, <NUM>, <NUM> and <NUM> may be bores extending in an axial direction. The bores are open at least one side or the respective flange and may have any suitable geometrical shape, for example, a circular or polygonal shape cross-section.

<FIG> shows the torque sensor of <FIG> wherein a first printed circuit board <NUM> comprising some circuitry devices as, for example, resistors and capacitors, and a connector <NUM> for connection to another printed circuit board <NUM> (see below) is provided over the intermediate portion <NUM>. The measurement transducers <NUM> may be connected with an included measurement portion to the intermediate portion <NUM> and they may have free connecting portions for connection to the first printed circuit board <NUM> and, thus, the circuitry devices of the first printed circuit board <NUM>. Particularly, the first printed circuit board <NUM> may comprise Wheatstone bridge elements (resistors) for converting an applied torque to voltage output signals as it is known in the art. Depending on actual applications half or full Wheatstone bridge may be used.

The first printed circuit board <NUM> may be covered by a second printed circuit board <NUM> as it is illustrated in <FIG>. The second printed circuit board <NUM> protects the measurement transducers <NUM> and circuitry devices <NUM> against the environment. Particularly, the second printed circuit board <NUM> may have sensitive circuitry devices at the bottom (facing the first printed circuit boards <NUM>) and a connector <NUM> for connection to the first printed circuit board. The second printed circuit board <NUM> is configured for signal conditioning, for example, for analogue-to-digital conversion of voltage output signals supplied by the circuitry devices of the first printed circuit board <NUM>. Signal conditioning may also include amplification of voltage output signals supplied by the circuitry devices of the first printed circuit board <NUM>.

As already mentioned measurement transducers <NUM> can be arranged about an axial axis running 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 <NUM> may be arranged spaced apart from one or two neighboring pairs of measurement transducers <NUM> by <NUM>° in a circumferential direction. <FIG> illustrate an embodiment wherein strain gages <NUM> are arranged pairwise symmetrically about an axial axis running through the center of the circular body in a direction perpendicular to the main surface of the circular body and wherein two measuring channels C are defined by opposing pairs of strain gages <NUM> that are spaced apart from each other by <NUM>° (from one channel to the other channel) in a circumferential direction. Each measuring channel C runs through the center of particular pairs of strain gages <NUM> that are arranged opposite to each other.

A torque (indicated by the arrow in <FIG>) can be measured based on a differential strain +ε and -ε where +ε is experienced by one strain gage of a pair of strain gages <NUM> and -ε is experienced by the other strain gage of the pair of strain gages <NUM>. The strain gages <NUM> are connected to a Wheatstone bridge circuitry formed on a printed circuit board <NUM>. Due to the selected geometry of the arrangement of the strain gages <NUM> (and the corresponding architecture of the Wheatstone bridge circuitry) the voltage output signal supplied by the Wheatstone bridge circuitry caused by an applied torque (strain in the intermediate portion of the torque sensor device on which the strain gages <NUM> are provided for sensing the strain) is proportional to Σε = <NUM>ε + <NUM>ε = <NUM>ε, i.e., a sufficiently high wanted voltage output signal can be provided.

On the other hand, perturbations due to tilt and axial and radial loads can be largely suppressed as illustrated in <FIG>. The arrow in <FIG> indicates a tilt that might be applied to the torque sensor device. The tilt applied to the torque sensor device <NUM> results in differential strains +ε<NUM> and +ε<NUM>, +ε<NUM> and +ε<NUM>, -ε<NUM> and -ε<NUM>, and -ε<NUM> and -ε<NUM>, respectively, for the four pairs of strain gages <NUM> defining the measuring channels C. Accordingly, the strain caused by the tilt is compensated by the chosen geometry of the arrangement of the strain gages <NUM> (and the corresponding architecture of the Wheatstone bridge circuitry): Σε = ε<NUM> - ε<NUM> + ε<NUM> - ε<NUM> = <NUM> such that it does not contribute to a voltage output signal being proportional to the applied torque a shown in <FIG>.

In order to achieve an accurate torque measurement it is also necessary to compensate for any axial loads. Such kind of compensation can also be achieved by the selected geometry of the arrangement of the strain gages <NUM> (and the corresponding architecture of the Wheatstone bridge circuitry) as it is illustrated in <FIG> (the arrow indicates the applied axial load). The axial load (due to the axially symmetrically arrangement of the strain gages <NUM>) results in strains +ε at each of the strain gages <NUM> and, therefore, in a zero net effect: Σε = <NUM>ε - <NUM>ε. With respect to compensating for tilt and axial loads it might be advantageous to locate the strain gages <NUM> at the same radial distance to the inner flange <NUM> and to the outer flange <NUM>.

Compensation for radial loads by the selected geometry of the arrangement of the strain gages <NUM> (and the corresponding architecture of the Wheatstone bridge circuitry) is illustrated in <FIG>. The applied radial load is indicated by the arrows. The radial load results in differential strains -ε<NUM> and +ε<NUM>, +ε<NUM> and -ε<NUM>, -ε<NUM> and +ε<NUM>, and +ε<NUM> and -ε<NUM>, respectively, for the four pairs of strain gages <NUM> defining the two measuring channels C. Accordingly, the contribution to the voltage output signal of the Wheatstone bridge circuitry of the printed circuit board <NUM> is proportional to Σε = -<NUM>ε<NUM> + <NUM>ε<NUM> + <NUM>ε<NUM> - <NUM>ε<NUM> = <NUM>.

However, it has to be noted that exact compensation for radial loads as illustrated in <FIG> might not be achieved, if some radial loads are applied in a radial direction shifted with respect to the measuring channels C in the circumferential direction by <NUM>°. In this case, some Σε ≠ <NUM> may occur and negatively affect the accuracy of the measurement of the torque. In order to alleviate this problem some radially elastic portion realized by some groove 30c as illustrated in <FIG> is provided in the intermediate portion <NUM> of the torque sensor device <NUM>. The radially elastic portion may be machined on the top or the bottom of the intermediate portion <NUM>.

According to another approach the problem of non-compensation of radial loads that are applied in a radial direction shifted with respect to the measuring channels C in the circumferential direction by <NUM>° tapered out portions <NUM> can be formed in the intermediate portion <NUM> of the torque sensor device <NUM>' as it is illustrated in <FIG>. The tapered out portions <NUM> may be machined on the top or the bottom of the intermediate portion <NUM>. In the example shown in <FIG> not being part of the invention the tapered out portions <NUM> are arranged closer to the outer flange <NUM> than the inner flange <NUM> at the <NUM>° positions. The tapered out portions <NUM> have larger dimensions in the circumferential direction than the radial direction.

Experiments have proven that such an arrangement of the tapered out portions <NUM> significantly reduces any contributions of the corresponding radial loads to Σε and, thus, the measurement result. It has to be noted that the tapered out portions <NUM> have not to be punched through the intermediate portion <NUM> in order not to drop the advantageous sealing property of the torque sensor device <NUM>'.

Claim 1:
Torque sensor device (<NUM>, <NUM>'), comprising
a circular body comprising an annular inner flange (<NUM>) and an annular outer flange (<NUM>) and a circular intermediate portion (<NUM>) located between the annular inner flange (<NUM>) and the annular outer flange (<NUM>), wherein the annular inner flange (<NUM>) is completely located closer to the center of the circular body than the annular outer flange (<NUM>) and comprises inner force application openings (<NUM>, <NUM>) formed therein exclusively closer to the center of the circular body than the circular intermediate portion (<NUM>), the annular outer flange (<NUM>) comprises outer force application openings (<NUM>, <NUM>) formed therein, and the circular intermediate portion (<NUM>) comprises an inner sub-portion (30a), an outer sub-portion (30b) and a circumferential groove (30c) for suppressing effects of radial loads and separating the inner sub-portion (30a) and the outer sub-portion (30b) from each other; and
a plurality of measurement transducers (<NUM>) formed in and/or on the inner sub-portion (30a) of the circular intermediate portion (<NUM>), in particular, in a pairwise manner; and
wherein the circular intermediate portion (<NUM>) is a continuously solid portion.