Patent Description:
Accurately detecting the torque of an object, for example, some driven shaft or joint, represents a problem that is of relevance in a plurality of applications. A particular application relates to 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 bridge circuitries and torques sensors comprising radially elastic torque transfer portions (see, for example, <CIT>). Another torque sensor is known from <CIT>.

Recently, a torque sensor device that allows for reliable accurate torque measurements and that can be formed in a compact light-weighted configuration that, in particular, allows for some manufacturing tolerance with respect to the positioning of the measurement transducers has been provided (<CIT>). <FIG> illustrate an example of such a torque sensor device <NUM>.

The torque sensor device <NUM> comprises an inner portion <NUM> and an outer portion <NUM>. An intermediate portion <NUM> continuously extends radially from the inner portion <NUM> to the outer portion <NUM>. The inner portion <NUM>, the outer portion <NUM> and the intermediate portion <NUM> form a circular body/diaphragm, for example, a monolithic circular body.

The intermediate portion <NUM> may comprise sub-portions 30a and 30b that might be separated from each other by a separator 30c. The separator 30c may be a rim or it may be a circumferential groove 30c as illustrated in <FIG>. Such a circumferential groove 30c may serve to orientate/direct the applied stress and strain with respect to the positions of measurement transducers.

A plurality of pairwise measurement transducers <NUM> is formed over or 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 portion <NUM> inner force application openings <NUM> and <NUM> of different sizes are formed and in the outer portion <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.

A torque sensor device like the torque sensor device <NUM> shown in <FIG> provides for accurate torque measurements. However, the overall configuration is relatively complex and expensive, in particular, since the circular body/diaphragm is made of stainless steel which exhibit a high material price.

In view of the above, it is an object of the present invention to provide a system for sensing torque of an object that is relatively easily to be manufacture at relatively low prices.

In order to address the above-mentioned need the claimed invention provides a system for sensing torque as defined in claim <NUM>. The flange is configured to receive torque to be measured by the torque sensor device and can be connected, for example, to a rotating shaft and a static member. For example, the flange may comprise inner force application openings formed in an inner portion of the flange and outer force application openings formed in an outer portion of the flange. Torque to be measured by the torque sensor device can be 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 portions of the flange can be measured. Particularly, the flange can be connected to a gear box and it can be configured to be connected to and sealing a gear box of a robot joint.

The at least one torque sensor device comprises a sensing portion and a plurality of measurement transducers formed over or on the sensing portion. The sensing portion may be a sensing membrane. The measurement transducers may comprise or consist of at least one of silicon gages, foil strain gages, and thin layer strain gages. The measurement transducers may, alternatively, be configured for sensing torque based on other measurement methods as, for example, magnetic or optical measurement methods.

The at least one torque sensor device has a second length parallel to the main surface of the flange (in a length direction of the torque sensor device) and a third length different from the second length parallel to the main surface of the flange (in a width direction of the torque sensor device). The second and third lengths of the at least one torque sensor device are smaller than half of the first length of the flange. Thus, a plurality of, particularly, miniaturized, torque sensor devices can be provided on the flange. For example, the flange may have a diameter of <NUM> to <NUM>, particularly, <NUM> to <NUM> and, more particularly, <NUM> to <NUM>.

Expensive materials, as stainless steel, may be used for manufacturing the sensing portion of the at least one torque sensor device but the (relatively large as compared to the torque sensor device) flange can be made without stainless steel. For example, the flange comprises or is made of an isotropic material such as aluminum or an aluminum alloy. As compared to stainless steel aluminum is a relatively cheap material that, nevertheless, provides a sufficiently high stiffness (for example, against tilting moments that otherwise would negatively affect accuracy of torque measurements). Thereby, overall costs can be reduced. Moreover, the one or more torque sensor devices can be manufactured separately from the flange and the flange can, advantageously, be designed separately in accordance with actual applications, particularly, with respect to attachment to and sealing of the object the torque of which is it be measured.

According to an embodiment, the flange has a circular shape parallel to the main surface, in particular, the flange comprises a circular main surface, and the first axis defines a diameter of the flange. By such a flange a circular gear box of a robot joint can be sealed without the need for additional sealing means, for example. Alternatively, the flange has a different geometric shape symmetric about an axis extending perpendicular to the main surface of the flange through the center of the main surface, for example, an elliptical, or square, hexagonal or octagonal shape.

According to the claimed invention, the plurality of measurement transducers of the at least one torque sensor device is arranged over a (for example, symmetric as circular, elliptical, square etc., shaped) transducers area of the flange that has a smaller thickness in a direction perpendicular to the main surface of the flange than a thickness of at least a portion of the flange in the direction perpendicular to the main surface of the flange outside the (for example, symmetric as circular, elliptical, square etc., shaped) transducers area. The smaller thickness facilitates the transfer of externally applied torque to be measured to the measurement site(s), i.e., the location(s) of the torque sensor device(s).

According to the claimed invention, a stiffening region is provided within the transducers area of the flange that has a thickness in the direction perpendicular to the main surface of the flange larger than the thickness of the transducers area in the direction perpendicular to the main surface of the flange. The stiffening region of the flange provides for a higher stiffness (insensitivity) against tilting moments at the measurement site(s). Particularly, the stiffening region may be continuously or discontinuously formed along a circular region within the circular transducers area. In principle, the thickness of the stiffening region may be chosen depending on the thickness of the transducers area (for example, <NUM> times to <NUM> times the thickness of the transducers area).

The stiffening region may comprise a first portion radially extending (fully or partially) over the circular transducers area and a second portion radially extending (fully or partially) over the transducers area wherein the first and second portions define an angular range between about <NUM>° to <NUM>°, for example, <NUM>° to <NUM>°. The plurality of measurement transducers of the at least one torque sensor device is arranged over the thus defined angular range. This arrangement may be particular advantageous with respect to providing for a higher stiffness (insensitivity) against tilting moments and, consequently, may result in very accurate torque measurements.

In principle, the geometrical shape of the stiffening region is not limited. The stiffening region may be or comprise one or more u-shaped or v-shaped step portions comprising sidewalls extending perpendicular or at some inclination angle from the circular transducers area of the flange.

According to an embodiment, the plurality of measurement transducers of the at least one torque sensor device comprises or consists of two pairs of measurement transducers. Each of the two pairs of measurement transducers may consist of two measurement transducers arranged at an angle to each other that lies in the range of <NUM>° to <NUM>°. This angle may be <NUM>°.

Torque sensor devices of at least one pair of torque sensor devices may be formed over or on the main surface of the flange opposite to each other with respect to an axis extending through the center of the main surface of the flange perpendicular to the main surface of the flange. Provision of more than one torque sensor device, in principle, can provide redundancy for accurate torque measurements. In particular, pairs of torque sensor devices (and their respective measurement transducers) that are located opposite to each other may define one or more common measurement channels that may allow for torque measurements with higher accuracies as compared to measurements achieved by a single torques sensor device only.

The measurement of a torque by means of one or more torque sensor devices of the provided system according to the above-described embodiments 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, the at least one torque sensor device of the system may comprise a bridge circuitry, for example, a Wheatstone bridge circuitry, electrically connected to the measurement transducers. The system or at least one torque sensor device of the system may also comprise a DC or AC excitation source for the (for example, Wheatstone) bridge circuitry. Moreover, the system or the torque sensor device of the system may comprise a printed circuit board arranged above the (for example, Wheatstone) bridge circuitry and comprising a circuitry for signal conditioning, in particular, means for analogue-to-digital conversion and/or amplification of signals provided by the (for example, Wheatstone) bridge circuitry.

According to an embodiment, at least one pair of torque sensor devices is comprised by the system wherein one torque sensor device of the at least one pair of torque sensor devices comprises a half of a Wheatstone bridge circuitry and the other torque sensor device of the at least one pair of torque sensor devices comprises another half of the Wheatstone bridge circuitry. By the distributed Wheatstone bridge circuitry one or more measurement channels defined by the torque sensor device of the at least one pair of torque sensor devices can reliably be sensed.

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 the system according to one of the above-described embodiments. Particularly, the flange may be attached to the joint and positioned to seal the gear box of the joint of the robot. The robot may not comprise any cross roller bearing, when the stiffening region described above reliably provides for sufficient stiffness against axial loads and tilting moments applied by the joint of the robot. Thus, costs can be reduced since no cross roller bearing might be necessary.

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 for a system comprising at least one torque sensor device formed over or on a flange. The system allows for reliably 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 and, nevertheless, the manufacturing process of the system can be performed relatively easily and at relatively low costs. Torque control based on torque measurements achieved by the at least one torque sensor device of the system can advantageously be implemented in robots, for example, collaborative robots, to facilitate robot-human interactions.

<FIG> shows a system <NUM> for sensing torque of an object according to an embodiment of the present invention. The system <NUM> comprises a pair of relatively tiny torque sensor devices <NUM> and <NUM> that are formed over or on a main surface of a circular shaped flange <NUM>. The flange <NUM> may not comprise stainless steel which is a relatively expensive material and it may be advantageous in terms of the overall costs that there is no need for making the relatively large flange component <NUM> of the system <NUM> of stainless steel. For example, the flange <NUM> may be made of or comprise aluminum or an aluminum alloy.

The flange may, for example, have a diameter of <NUM> to <NUM>, particularly, <NUM> to <NUM> and, more particularly, <NUM> to <NUM>. The system <NUM> may be configured for sensing torque in the range of <NUM> to <NUM>, particularly, <NUM> to <NUM> and, more particularly, <NUM> to <NUM>.

Each of the relatively tiny torque sensor devices <NUM> and <NUM> has a length parallel to the main surface of the flange <NUM> in a length direction of the respective torque sensor device and a length parallel to the main surface of the flange in a width direction of the torque sensor device. Both the length in the length direction and the length in the width direction are smaller than half of the diameter of the flange <NUM>, for example, smaller than <NUM>/<NUM> or <NUM>/<NUM> of the diameter of the flange <NUM>.

Outer force application openings <NUM>, possibly of different sizes, are formed in the flange <NUM> and supplemented by inner force application openings (not shown in <FIG>), also possibly of different sizes. The outer force application openings <NUM> and the inner force application openings may be bores extending in an axial direction. The bores may have any suitable geometrical shape, for example, a circular or polygonal shape cross-section. Torque to be measured by the torque sensor devices <NUM> and <NUM> can be transferred, for example, by a rotating shaft under consideration and some static member, via connection members connected to the inner force application openings and outer force application openings <NUM>. Thereby, the torque applied between inner and outer portions of the flange can be measured.

The torque sensor device <NUM> comprises a printed circuit board <NUM> comprising some circuitry <NUM> configured for signal conditioning, for example, for analogue-to-digital conversion of voltage output signals supplied by circuitry devices covered by the printed circuit board <NUM>. Signal conditioning may also include amplification of voltage output signals supplied by the circuitry devices covered by the printed circuit board <NUM>. The printed circuit board <NUM> may be made of or comprise ceramic, glass, or any other material carrying electronic components and connectors. The circuitry devices covered by the printed circuit board <NUM> are connected to measurement transducers of the torque sensor device <NUM>. Particularly, the circuitry devices 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 bridges may be used for the torque sensor device <NUM>.

Similarly, the torque sensor device <NUM> comprises a printed circuit board <NUM> comprising some circuitry <NUM> configured for signal conditioning, for example, for analogue-to-digital conversion of voltage output signals supplied by circuitry devices covered by the printed circuit board <NUM>. Signal conditioning may also include amplification of voltage output signals supplied by the circuitry devices covered by the printed circuit board <NUM>. The circuitry devices covered by the printed circuit board <NUM> are connected to measurement transducers of the torque sensor device <NUM>. Particularly, the circuitry devices may comprise Wheatstone bridge elements (resistors) for converting an applied torque to voltage output signals. Depending on actual applications half or full Wheatstone bridges may be used for the torque sensor device <NUM>.

The two torque sensor devices <NUM> and <NUM> are arranged opposite to each other about an axial axis running through the center of the circular flange <NUM> in a direction perpendicular to the main surface of the circular <NUM>. In principle, torque sensor devices as the torque sensor devices <NUM> and <NUM> shown in <FIG> may be arranged pairwise symmetrically or asymmetrical about the axial axis running through the center of the circular flange <NUM> in a direction perpendicular to the main surface of the circular flange and the torque sensor devices define one or more measurement channels. In some embodiments, <NUM> % redundancy of the torque measurement may be provided by providing two torque sensor devices <NUM>, <NUM> on the flange <NUM> rather than providing only one of the torque sensor devices <NUM>, <NUM> on the flange <NUM>.

<FIG> illustrate details of torque sensor devices of a system <NUM> for sensing torque, for example, the torque sensor devices <NUM> and <NUM> comprised by the system <NUM> shown in <FIG>. The system <NUM> comprises a flange <NUM>, for example, made of or comprising aluminum or an aluminum alloy. The flange <NUM> comprises outer force application openings <NUM> and inner force application openings <NUM>. A first sensing membrane <NUM> of a first torque sensor device and a second sensing membrane <NUM> of a second torque sensor device are attached to the flange <NUM> (see <FIG>). The first sensing membrane <NUM> and the second sensing membrane <NUM> may consist of or comprise stainless steel. On each of the sensing membranes measurement transducers <NUM>, <NUM>, for example, strain gages, are formed as it is illustrated in <FIG>. For example, two pairs of measurement transducers <NUM>, <NUM> are provided wherein the individual transducers of each pair of measurement transducers <NUM>, <NUM> define an angular range of about <NUM>°. Each of the pairs of measurement transducers <NUM>, <NUM> may define a measurement channel together with a respective other pair of measurement transducers (confer <FIG>) comprised in another torque sensor device arranged on a flange opposite to the one comprising the sensing membrane <NUM>, <NUM> shown in <FIG>.

<FIG> shows details of a flange of a system for sensing torques, for example, the flange <NUM> shown in <FIG> or the flange <NUM> shown in <FIG> in a view from a direction opposite to the one shown in <FIG> and <FIG>, respectively. The flange <NUM> is made of or comprises aluminum or an aluminum alloy, for example. The flange <NUM> comprises outer force application openings <NUM> and inner force application openings <NUM>. In some embodiments, a flange comprised in a system for sensing torque has a uniform thickness. However, the flange <NUM> shown in <FIG> has a weakened/thinned circular transducers area <NUM> over which measurement transducers, for example, strain gages, are formed. Furthermore, a stiffening region comprising stiffening rips (step portions) <NUM>, <NUM> is provided in an area below the measurement transducers in order to enhance stiffness against cross loads. The stiffening rips <NUM> and <NUM> may, respectively, define an angular range from <NUM>° to <NUM>° over which the measurement transducers are formed. The stiffening region (stiffening rips <NUM>, <NUM>) may have a thickness in the range of <NUM> to <NUM> times the thickness of the circular transducers area <NUM>. The stiffening region (stiffening rips <NUM>, <NUM>) may be made of the same material as the flange <NUM> and may be made integrally with the same. For example, torque measurement of robot joints/arms might be negatively affected by cross loads, particularly, when cross roll bearings are not provided for cost reasons. Provision of the stiffening region provides a high stiffness against cross and axial loads but does not influence significantly sensitivity regarding torque. The stiffening rips <NUM>, <NUM> may be formed in a u-shape or v-shape with sidewalls extending perpendicular or at some inclination angle from the main surface of the flange <NUM> in a direction opposite to the provided measurement transducers that are hidden by the flange <NUM> in the perspective view shown in <FIG>.

Claim 1:
System (<NUM>, <NUM>, <NUM>, <NUM>) for sensing torque of an object, comprising
a flange (<NUM>, <NUM>, <NUM>, <NUM>) configured to be connected to the object and having a first length along a main axis of a main surface of the flange (<NUM>, <NUM>, <NUM>, <NUM>), wherein the main surface of the flange (<NUM>, <NUM>, <NUM>, <NUM>) is of a symmetric shape and the first length defines a diameter of the flange (<NUM>, <NUM>, <NUM>, <NUM>); and
at least one torque sensor device (<NUM>, <NUM>, <NUM>, <NUM>) formed over the main surface of the flange (<NUM>, <NUM>, <NUM>, <NUM>) and comprising
a) a sensing portion (<NUM>, <NUM>); and
b) a plurality of measurement transducers (<NUM>, <NUM>) formed over the sensing portion (<NUM>, <NUM>); and
having
c) a second length parallel to the main surface of the flange (<NUM>, <NUM>, <NUM>, <NUM>); and
d) a third length parallel to the main surface of the flange (<NUM>, <NUM>, <NUM>, <NUM>);
and wherein the second and third lengths of the at least one torque sensor device (<NUM>, <NUM>, <NUM>, <NUM>) are smaller than half of the first length of the flange (<NUM>, <NUM>, <NUM>, <NUM>);
and wherein
the plurality of measurement transducers (<NUM>, <NUM>) of the at least one torque sensor device (<NUM>, <NUM>, <NUM>, <NUM>) is arranged over a transducers area (<NUM>), in particular, a circular transducers area (<NUM>), of the flange (<NUM>, <NUM>, <NUM>, <NUM>); and wherein
the transducers area (<NUM>) has
i) a smaller thickness in a direction perpendicular to the main surface of the flange (<NUM>, <NUM>, <NUM>, <NUM>) than a thickness in the direction perpendicular to the main surface of the flange (<NUM>, <NUM>, <NUM>, <NUM>) of at least a portion of the flange (<NUM>, <NUM>, <NUM>, <NUM>) outside the transducers area (<NUM>); characterized in that the transducers area (<NUM>) further has
ii) a stiffening region having a thickness in the direction perpendicular to the main surface of the flange (<NUM>, <NUM>, <NUM>, <NUM>) larger than the thickness of the transducers area (<NUM>) in the direction perpendicular to the main surface of the flange (<NUM>, <NUM>, <NUM>, <NUM>).