Title: Device for measuring displacement or strain
Description
The present invention relates to a device for measuring displacement or strain, in particular for measuring extremely small phenomena, such as displacement or deformation of relatively rigid measurement objects.
PRIOR ART
Such devices for measuring displacement or strain are known from the prior art.
In case of the use of electrically based sensors for e.g. deformation measurement, like electrical strain gauges, electronic amplification of the sensor’s signal does not improve the signal to noise ratio. Electronic amplification sets a fundamental limit to the use of electrical sensors for measurement of ultra-small phenomena, like e.g. the deformation or displacement of an object. Therefore, optical sensing is often employed to measure such ultra-small phenomena.
US 3.438.251 A, for instance, discloses a transducer which can be used either to measure displacement or to measure force, the former if the transducer resists motion with a negligible force, and the latter if the transducer produces a significant resisting force. Readout is by optics, for example by a beam of collimated light from an autocollimator entering the transducer, traversing a prescribed path within the transducer, and being returned to the autocollimator for sensing. As a force transducer, it may be made in combination with external or internal springs to provide greater resisting force than can be generated by full-scale deflection of the motion transducer alone. “Full-scale” is determined by the maximum angle the accessory autocollimator can accommodate, or alternately, by the maximum nonlinearity per mitted between the true motion or force input and the displayed reading. In a preferred form, the transducer is in the form of a hollow square with rigid sides hinged at the corners and reflecting means on the sides are optically aligned to transmit an incident beam successively to adjacent reflecting means.
WO 2016/149819 A1 discloses a sensor assembly that can measure axial and lateral forces and/or axial and lateral torques acting on an instrument independent of steady state temperature variations. The sensor assembly has a sensor body for coupling to the instrument such that a shaft and tip of the instrument extend from opposing ends of the sensor body. The sensor body has first and second strain sensing regions. The sensor assembly further includes first and second strain sensors coupled to and configured to measure axial strain of the first and second regions. When the sensor body is coupled to the instrument each of the first and second regions experience an opposite one of a tensile axial strain and a compressive axial strain in response to an axial force or an axial torque acting on the tip of the instrument.
EP 3.312.556 A1 discloses a transducer for assisting in measuring displacement or strain in an object of interest is described. The transducer comprises a plate having at least two end sections for mounting the transducer to the object of interest. The transducer furthermore comprises a flexible connection between the two end sections. The flexible connection comprises a plurality of rigid portions and flexible interconnections between the rigid portions for allowing relative movement of the rigid portions with respect to each other. The flexible connection has a central section comprising two rigid portions spaced from each other over a distance and adapted for positioning a strain sensing element at the spacing in between said two rigid portions. The rigid portions and flexible interconnections are arranged so that a displacement applied to the end sections results in a relative displacement at the spacing in the central section that is larger than the relative displacement applied to the end sections.
However, a problem with the abovementioned devices for measuring displacement or strain, in particular the device disclosed by EP 3.312.556 A1 , is that the aforementioned devices may be sensitive to differences in temperature, leading to inaccurate measurement results.
Another problem with the abovementioned devices, in particular the device disclosed in EP 3.312.556 A1 , is that the devices may not be energy-neutral, i.e. the energy required for “stretching” the device may be different from the energy needed to “relax” the device.
Yet another problem with the abovementioned devices, in particular the device disclosed in EP 3.312.556 A1 , is that out-of-plane strain may not be properly dealt with. Yet another problem with the abovementioned devices, in particular the device disclosed in EP 3.312.556 A1 , is that wavelength noise superimposed on the sensing signal may further decrease the accuracy of measurement results.
OBJECT OF THE INVENTION
An object of the present invention is thus to provide an abovementioned device for measuring displacement or strain, wherein sensitivity to differences in temperature is decreased.
Another object of the present invention is thus to provide an abovementioned device for measuring displacement or strain that is more “energyneutral”.
Yet another object of the present invention is thus to provide an abovementioned device for measuring displacement or strain, wherein out-of-plane strain is more properly dealt with.
Yet another object of the present invention is thus to provide an abovementioned device for measuring displacement or strain, wherein the influence of wavelength noise on the measurement results is decreased.
SUMMARY OF THE INVENTION
According to the present invention, a device for measuring displacement or strain is provided, comprising: a first portion having a first connection region for connection to a first measurement part, a second portion, spaced-apart from the first portion in an axial direction along a main axis, having a second connection region for connection to a second measurement part, wherein the first portion and the second portion are configured to be displaceable relative to each other in the axial direction and/or in a lateral direction transversal to the axial direction, when, respectively, an axial force and/or a lateral force is applied to the first connection region by the first measurement part and/or the second connection region by the second measurement part, a connection portion, connecting the first portion and the second portion to each other, wherein the axial force and/or the lateral force is transferred between the first portion and the second portion by the connection portion, wherein the axial stiffness and/or the lateral stiffness of the connection portion in the axial direction and/or lateral direction is lower than an axial stiffness and/or lateral stiffness of the first portion and/or second portion adjacent to the connection portion, wherein, when no axial force and/or lateral force is applied, the connection portion is symmetric with respect to the main axis, a displacement member connected to the first and/or second portion, being displaceable along with the first and/or second portion, wherein the displacement member does not transfer any axial force and/or lateral force between the first portion and the second portion, and one or more sensors, preferably optical sensors, for sensing the displacement of the displacement member in the axial direction and/or the lateral direction.
Thus, when for example the deformation of an object is too low to be measured accurately by attaching e.g. electrical or optical sensors to the object, or by contactless measurement techniques, the abovementioned device is capable of achieving accurate measurement of the deformation of the object by “amplification” of the effects resulting from deformation of the object and subsequent sensing of the amplified effects.
Due to the connection portion being symmetric with respect to the main axis, the device can be operated in “differential mode”, which enables compensation of the effect of temperature on thermal expansion of the transducer. Furthermore, the device is thus more “energy-neutral”, out-of-plane strain is optimally dealt with and wavelength noise on the measurement results is decreased.
As mentioned above, the device is suitable for measuring displacement or strain. Displacement or strain may be caused by a plurality of chemical and/or physical phenomena, which causes “actuation” of the device and thus, in turn, some form of displacement or strain exerted on the device. Such displacement or strain (directly) translates into displacement of the displacement member, for instance proportional displacement, such as “1-on-1” or equal displacement, which may be measured with appropriate measurement means, such as optical sensors.
Moreover, the device may also be used for measuring displacement or strain as a result of torque applied around the main (X-)axis or a bending moment applied around a Z-axis, i.e. an axis perpendicular to the main (X-)axis and a Y-axis aligned with the lateral direction, or a bending moment applied around the Y-axis aligned with the lateral direction.
In the context of this description “stiffness” is generally to be interpreted as resistance to deformation or strain due to an applied force (or torque/bending moment). The expression “lateral” furthermore generally relates to a direction perpendicular to the axial direction. In this respect, “lateral stiffness” thus generally relates to “shear stiffness”.
US 8.186.232 B2 discloses a displacement sensor which seeks to detect displacements along a linear axis (X). Measurement errors due to unwanted displacement (and rotation) on other axes are minimized by employing a structure with "anisotropic stiffness". It should be noted that the displacement member disclosed by US 8.186.232 B2 does not extend freely from the connection region, because the displacement member is connected to the rest of the sensor by intermediate structures. The displacement member is thus involved in force transfer, in contrast to the present disclosure. Furthermore, because the displacement member is connected to the rest of the sensor by intermediate structures, tuning of the (amplification of the) sensor according to US 8.186.232 B2 is difficult, due to “interference” of the intermediate structures.
US 5.510.581 A discloses a flat load cell for weighing an object with two beams that, upon lateral force exertion, bend in an “S-shaped manner” in order to negate the effects of such lateral forces, so that the weighing of the object is not affected. The load-receiving tongue disclosed by US 5.510.581 A again appears to be involved in force transfer, in contrast with the present disclosure. Also, US 5.510.581 A is furthermore (thus) not suitable for measuring lateral forces.
US 2009/100941 A1 discloses a device for measuring all kinds of “mechanical quantities”, for example by measuring a distance between two displacement members, wherein the distance varies in a non-linear manner in response to a force applied in a direction perpendicular to the displacement members. Because the distance is not proportional to the force applied, predictable and tunable “amplification” is hard to achieve with such a device.
An embodiment relates to an aforementioned device, wherein the displacement member extends freely from the first portion, such as from the first connection region, i.e. the displacement member is not connected to surrounding structures of the device, except for the position where the displacement member connects to the first portion, such as the first connection region. The displacement member thus does not “interfere” with force transfer.
An embodiment relates to an aforementioned device, wherein the connection portion transfers the axial and/or lateral force between the first portion and the second portion without involving the displacement member, i.e. the connection portion essentially transfers 100% of the axial and/or lateral force between the first portion and the second portion.
An embodiment relates to an aforementioned device, wherein the displacement member extends along the main axis. Thus, any displacement of the first portion along the main axis (with respect to the second portion) is directly translated into a displacement of the displacement member along the (same) main axis.
An embodiment relates to an aforementioned device, wherein the displacement member does not transfer any axial force and/or lateral force between the first connection region and the second connection region, i.e. the displacement member does not transfer any axial and/or lateral force between the first connection region and the second connection region.
An embodiment relates to an aforementioned device, wherein the axial stiffness and/or lateral stiffness of the connection portion comprises the lowest axial stiffness and/or lateral stiffness present between the first connection region and the second connection region. Thus, the amplification effects are most pronounced and very accurate measurements can be obtained. Of course, the axial stiffness and/or lateral stiffness should not be so low that the connection portion itself gets damaged, as the skilled person will understand.
An embodiment relates to an aforementioned device, wherein the connection portion has a total force transferring cross-sectional area lower than a total force transferring cross-sectional area of the first portion and/or second portion adjacent to the connection portion. Again, the connection portion will then maximally deform (provided a material is chosen for the connection portion that has an appropriate modulus of elasticity) and the device sensitivity is then most optimal.
An embodiment relates to an aforementioned device, wherein the total force transferring cross-sectional area of the connection portion constitutes the lowest total force transferring cross-sectional area between the first connection region and the second connection region. Analogous to the above, optimal sensitivity of the connection portion can then be obtained. An embodiment relates to an aforementioned device, wherein the total force transferring cross-sectional area of the connection portion is 10 - 30%, such as 15 - 25% of the total force transferring cross-sectional area of the first portion and/or second portion adjacent to the connection portion. In practice, such a total force transferring cross-sectional area leads to sufficient deformation of the connection portion, i.e. sufficient sensitivity of the transducer, whereas the connection portion is still able to transfer significant force between the first connection region and the second connection region.
An embodiment relates to an aforementioned device, wherein the first and/or second portion comprises a space into which a free end of the displacement member extends, wherein one or more sensors, such as optical or electrical sensors, are arranged in the space and/or in the first and/or second portion adjacent to the space for sensing the displacement of the free end of the displacement member in the axial direction and/or the lateral direction. The space can thus be conveniently used for measuring the axial and/or lateral displacements of the free end of the displacement member, by arranging the one or more sensors - in all sorts of configurations - in the area surrounding/enclosing the space.
An embodiment relates to an aforementioned device, wherein the displacement member has an intermediate portion connecting the free end of the displacement member to the connection portion, wherein the free end has a width in the lateral direction larger than a width of the intermediate portion. Thus, the displacement member has a sort of “head” (the free end of the displacement member) suitable for measurements and a “stem” (the intermediate portion) to displace the head in the axial and lateral directions. The “stem” may have a smaller width than the “head” in order to not unduly weaken the first and/or second portion through which the stem extends (and freely moves). Furthermore, one or more sensors can thus be specifically arranged to measure the axial displacement of the head, such as on the “front side” or the “back side” of the head (when seen in the axial direction) which would otherwise be more difficult to achieve.
An embodiment relates to an aforementioned device, wherein the width of the free end of the displacement member is 2 - 5 times, such as 2 - 4 times, larger than the width of the intermediate portion. In practice, at least one sensor can thus be arranged on one or both lateral sides of the displacement member to measure the axial displacement of the free end of the displacement member, i.e. the head without weakening the structure of the first and/or second portion.
An embodiment thus relates to an aforementioned device, wherein one of the sensors is arranged for sensing the displacement of the free end of the displacement member in the axial direction.
An embodiment relates to an aforementioned device, wherein one of the sensors is arranged for sensing the displacement of the portion of the displacement member in the lateral direction. Alternatively, the optical sensor can also be arranged to measure the displacement of the free end of the displacement.
An embodiment relates to an aforementioned device, wherein the connection portion comprises one or more, such as two, three or four, connection members extending in the axial direction, wherein the one or more connection members are arranged in a symmetric manner with respect to the main axis. Thus, the deformability of the connection portion can be designed and tuned in a relatively easy manner by adding or removing one or more connection members depending on the application. Furthermore, the deformability of the connection portion is also relatively well-predictable.
An embodiment relates to an aforementioned device, wherein the first portion, the second portion, the connection portion, the displacement member and the one or more sensors are arranged in such a way, that the device has a plate-like shape. Such a plate-like shape is relatively easy to connect to an object to be measured.
An embodiment relates to an aforementioned device, wherein the plate-like-shaped device is curved around a curvature axis parallel to the main axis. Thus, the plate-like-shaped device can be attached to curved surfaces. “Plate-like” in this respect is thus not to be exclusively interpreted as being “planar” (i.e. extending along a certain geometrical plane).
An embodiment relates to an aforementioned device, wherein the plate-like-shaped device is curved around a curvature axis parallel to the main axis, in such a way, that the plate-like-shaped device fully encloses the curvature axis, creating a ring-shaped device. Thus, the plate-like-shaped device can be installed onto a tube or shaft or can even be designed to be an integral part of such a tube or shaft.
An embodiment relates to an aforementioned device, wherein the one or more sensors for sensing the displacement of the displacement member in the axial direction and/or the lateral direction comprise one or more optical sensors and/or one or more electrical sensors.
Another aspect of the invention relates to a measurement assembly, comprising: a first measurement part, a second measurement part, an aforementioned device, wherein the first portion of the device is connected to the first measurement part with the first connection region, and wherein the second portion of the device, spaced-apart from the first portion in the axial direction along the main axis, is connected to the second measurement part with the second connection region.
It is noted that US 4.079.624 A discloses a cylindrical body with opposite sensors placed to measure axial and/or torsional forces in the cylindrical body. To this end, the sensors are equipped with piezo-resistive elements that can be arranged in various ways and orientations. However, US 4.079.624 A does not in any way relate to the “strain amplification” concept underlying the present disclosure.
An embodiment relates to an aforementioned measurement assembly, wherein the first measurement part and the second measurement part belong to a single measurement object. The single measurement object could for instance be a tube or shaft.
An embodiment thus relates to an aforementioned measurement assembly, wherein the first measurement part and the second measurement part have a tubular shape.
An embodiment relates to an aforementioned measurement assembly, wherein, in the axial direction, the first connection region is integrated with or transitions into the first measurement part and/or wherein the second connection region is integrated with or transitions into the second measurement part. Thus, the device can be conveniently integrated “by design” in between the first and second measurement parts and/or in the measurement object.
An embodiment relates to an aforementioned measurement assembly, wherein the first measurement part and the second measurement part comprise a first wall segment and a second wall segment, respectively, of a tubular wall of a single, tubular measurement object, having a centerline, wherein the second portion, the connection portion, the displacement member and the one or more sensors are arranged in such a way, that the device has a plate-like shape, wherein the plate-like-shaped device is curved around the centerline of the tubular measurement object, wherein the first connection region is connected to an outer surface of the first wall segment and the second connection region is connected to an outer surface of the second wall segment. Thus, the device can be attached conveniently to an outer surface of a curved measurement part of measurement object.
An embodiment relates to an aforementioned measurement assembly, wherein the first measurement part and the second measurement part comprise a first wall segment and a second wall segment, respectively, of a tubular wall of a single, tubular measurement object, having a centerline, wherein the second portion, the connection portion, the displacement member and the one or more sensors are arranged in such a way, that the device has a plate-like shape, wherein the plate-like-shaped device is curved around the centerline of the tubular measurement object, wherein, in the axial direction, the first connection region is integrated with or transitions into the first wall segment and wherein the second connection region is integrated with or transitions into the second wall segment. Thus, the device can be integrated with a tubular measurement object or between first and second measurement parts.
An embodiment relates to an aforementioned measurement assembly, comprising a plurality of laterally connected plate-like-shaped devices, wherein the plate-like-shaped devices are curved around the centerline in such a way, that the plate-like-shaped devices fully enclose the centerline, creating a ring-shaped device forming an intermediate wall segment between the first wall segment and the second wall segment. Again, the device can between tubular first and second measurement parts. The device can thus even be retrofitted between existing tubular parts.
Another aspect of the invention concerns a motor assembly, comprising a motor and an aforementioned measurement assembly, wherein the motor is configured for driving the tubular measurement object around the centerline of the tubular measurement object. The device can thus be advantageously used for measuring torque, thrust, et cetera, produced by the motor and exerted on the tubular measurement object (and any reaction forces or torque exerted on the tubular measurement object, for instance by a fluid, bearings, et cetera). Another aspect of the invention concerns a mixing device, comprising an aforementioned motor assembly, wherein the motor is configured for driving the tubular measurement object around the centerline of the tubular measurement object for mixing a substance, wherein the tubular measurement object is arranged for transferring driving forces from the motor to the substance to be mixed. A particular embodiment foreseen by the Applicant concerns a mixing device for mixing substances, such as fluids, wherein the tubular measurement object preferably comprises a shaft, preferably provided with stirring or mixing means, such as a propeller, helix, or the like, for transferring driving/mixing forces produced by the motor assembly to the substance(s) to be mixed.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in more detail below, with reference to illustrative embodiments shown in the drawings. Therein:
Figure 1 shows an example embodiment of a device according to the invention;
Figure 2 shows a close-up of the axially arranged optical sensors of Figure 1 , wherein the optical sensors are embodied by a set of reflecting mirrors;
Figures 3A and 3B show an example embodiment of a device according to the invention in an axially undeformed and a deformed condition, respectively;
Figure 4 shows a perspective view of an example embodiment of a device according to the invention, wherein the device has a plate-like shape;
Figure 5 shows an example embodiment of a device according to the invention, serving to illustrate the effects of thermal expansion;
Figure 6 shows an example embodiment of a device according to the invention, wherein the device is shown in a laterally deformed condition, with the optical sensors being laterally arranged;
Figures 7A and 7B show cross-sensitivity of laterally and axially responsive optical sensors, respectively;
Figures 8A and 8B show an example embodiment of a mechanical transducer for transferring forces to an optical sensor enclosed by the mechanical transducer; Figure 8C shows the change in gap distance for the mechanical transducer shown in Figures 8A and 8B;
Figure 9 shows a graph with the mechanical amplification factor (relative displacement amplification factor) for the mechanical transducer of Figures 8A and 8B;
Figure 10 shows an example embodiment of a device according to the invention, comprising three abovementioned mechanical transducers (as depicted in Figures 8A and 8B);
Figures 11A and 11 B show an example embodiment of a measurement assembly according to the invention, comprising a first measurement part, a second measurement part, and an example embodiment of one, respectively two, devices according to the invention connecting the first measurement part and the second measurement part in the axial direction;
Figure 12 shows an example embodiment of a measurement assembly according to the invention, comprising a tubular measurement object and an example embodiment of a device according to the invention, having a curved, platelike shape, wherein the device is attached to an outer wall surface of the tubular measurement object;
Figure 13 shows an example embodiment of a measurement assembly according to the invention, comprising a tubular measurement object and example embodiments of a plurality of laterally connected plate-like-shaped devices according to the invention, forming a ring-shape, with the device being curved around the centerline of the tubular measurement object, wherein the ring-shaped device is integrated with or transitions into wall segments of the tubular measurement object in the axial direction;
Figure 14 shows an example embodiment of a mixing device according to the invention; and
Figures 15a-15c show example embodiments of a connection member according to the invention.
DETAILED DESCRIPTION
Figure 1 shows an example embodiment of a device 1 according to the invention. A device 1 for measuring displacement, deformation or strain is shown. The device 1 as shown comprises a first portion 2 having a first connection region 3 for connection to a first measurement part 4. The device 1 also comprises a second portion 5, spaced-apart from the first portion 2 in an axial direction (X) along a main axis X, having a second connection region 6 for connection to a second measurement part 7. The first connection region 3 and the second connection region 6 may provide connection or attachment to the first measurement part 4 and the second measurement part 7, respectively, by means of bolting, screwing, clamping, welding, gluing or any other suitable connection means. E.g. ball bearings could also be used. The first portion 2 and the second portion 5 are configured to be displaceable or deformable relative to each other in the axial direction X and/or in a lateral direction Y transversal to the axial direction X, when, respectively, an axial force and/or a lateral force is applied to the first connection region 3 by the first measurement part 4 and/or the second connection region 6 by the second measurement part 7.
In a broader sense, Figure 1 shows a measurement assembly 17, comprising a first measurement part 4, a second measurement part 7 and the aforementioned device 1 , wherein the first portion 2 of the device 1 is connected to the first measurement part 4 with the first connection region 3, and wherein the second portion 5 of the device 1 , spaced-apart from the first portion 2 in the axial direction along the main axis X, is connected to the second measurement part 7 with the second connection region 6. The device 1 may be embodied by a monolithic body or element.
The device 1 also comprises a connection portion 8, connecting the first portion 2 and the second portion 5 to each other. The axial force and/or the lateral force is transferred between the first portion 2 and the second portion 5 by the connection portion 8. The axial stiffness and/or the lateral stiffness of the connection portion 8 in the axial direction X and/or lateral direction Y is lower than an axial stiffness and/or lateral stiffness of the first portion 2 and/or second portion 5 adjacent to the connection portion 8. When no axial force and/or lateral force is applied, the connection portion 8 is symmetric with respect to the main axis X.
The device 1 furthermore comprises a displacement member 9 connected to the first portion 2 and/or second portion 5. The displacement member 9 is displaceable along with the first portion 2 and/or second portion 5. The displacement member 9 as shown in Figure 1 is connected to the first portion 2. The displacement member 9 does not transfer any axial force and/or lateral force between the first portion 2 and the second portion 5. In the exemplary embodiment as shown, the device 1 moreover comprises one or more optical sensors 10, 10A, 10B, 10C, 10D for sensing the displacement of the displacement member 9 in the axial direction X and/or the lateral direction Y. However, electrical sensors may also be used, provided the device 1 is carefully designed.
Preferably, the axial stiffness and/or lateral stiffness of the connection portion 8 comprises the lowest axial stiffness and/or lateral stiffness present between the first connection region 3 and the second connection region 6.
As shown in Figure 1 , the first portion 2 and/or second portion 5 comprises a space 11 into which a free end 12 of the displacement member 9 extends. The one or more optical sensors 10, 10A, 10B, 10C, 10D are arranged in the space
11 and/or in the first portion 2 and/or second portion 5 adjacent to the space 11 for sensing the displacement of the free end 12 of the displacement member 9 in the axial direction X and/or the lateral direction Y. The one or more optical sensors 10 to detect the parameter(s) of interest, like deformation of the device 1 , may be arranged or attached at various locations in or around the space 11 , as depicted in Figure 1 .
The displacement member 9 as shown in Figure 1 has an intermediate portion 13 connecting the free end 12 of the displacement member 9 to the connection portion 8. The free end has a width W12 in the lateral direction Y larger than a width W13 of the intermediate portion 13.
The width W12 of the free end 12 of the displacement member 9 may be 2 - 5 times, such as 2 - 4 times, larger than the width W13 of the intermediate portion 13.
The optical sensors 10A and 10B of the example embodiment of the device as shown in Figure 1 are arranged for sensing the displacement of the free end
12 of the displacement member 9 in the axial direction X. Other optical sensors 10, i.e. 10C and 10D, are arranged for sensing the displacement of the intermediate portion 13 of the displacement member 9 in the lateral direction Y. The one or more optical sensors 10 may comprise an optical fiber 32, for instance routed along locations of interest as shown in Figure 1 , as well as fiber fixation (points) 33 for fixing the optical fiber 32 in or around the space 11 , and furthermore one or more (optical) sensing elements 31 , such as Fiber Bragg Gratings (FBG’s).
The connection portion 8 preferably comprises one or more, such as two (as shown in Figure 1), three or four, connection members 14 extending in the axial direction X. The one or more connection members 14 are arranged in a symmetric manner with respect to the main axis X.
The device 1 can be from metal or non-metal, like ceramics, as to construct an all “dielectric” device 1.
Figure 2 shows a close-up of the axially arranged optical sensors 10 of Figure 1 , although the optical sensors 10 are now embodied by a set of reflecting mirrors 34 (connected to an optical fiber 32) to measure the deformation of the device 1 , like e.g. with an interferometric- or wavelength-modulated technique. The set of reflecting mirrors 34 are plan-parallel and may operate in e.g. interferometry mode.
Figures 3A and 3B show an example embodiment of a device 1 according to the invention, such as the embodiment of Figure 1 , in an axially undeformed and a deformed condition, respectively. In case of responding to a change in axial distance between the first portion 2 and the second portion 5, Figure 3B shows the (planar) device 1 in deformed condition, resulting from e.g. an external force or displacement of the first and/or second connection regions (see e.g. Figure 1). As the connection portion 8 and the connection members 14 may be designed to have much smaller lateral dimensions than any other part of the device 1 , the deformation as shown will result from deformation of the connection members 14. Note the equivalence of the variation AL at various locations of the device 1 (by design). In case the device 1 is attached to a measurement object (as shown in Figure 1) via the first connection region 3 and second connection region 6 (or, for that matter, to a first measurement part 4 and second measurement part 7, as shown in Figure 1), and the measurement object is exposed to a force in such a way that the measurement object is deformed, the relative displacement of the first connection region 3 and second connection region 6 (representing e.g. the strain, e1 , of the object to which the device 1 is rigidly attached) of the object (E1) is defined as: ei = AL / Li
Characteristic for the invention is that, given a rigid coupling between the object and the first connection region 3 and second connection region 6 of the device 1 and a (designed-in) low stiffness of the connection portion 8, the change in distance Li between the first and second connection regions of the device 1 , denoted by AL, is transferred via the displacement member 9 - with the displacement member 9 by design not being deformed by the deformation of the measurement object - to a change in distance L2. Given this conservation AL, the relative displacement over a gap denoted by £2, is given by:
£2 — AL I L2
And hence:
£2/£I = LI / L2 or
£2 = (Li I L2) . £1
Thus, the relative displacement (‘strain’), £1, of the measurement object is converted into a relative displacement denoted by £2 with an amplification factor given by Li I L2. By proper design of Li and L2, the mechanical amplification factor can be adjusted to the desired sensitivity of the device 1.
The displacement in the axial direction X, AL, can be measured using a suitable optical sensor 10, which can be of various constructions and based on a multitude of operating principles. One type of a fiber-optic based sensor is the Fiber Bragg Grating (FBG), but other sensing mechanisms can be applied as well. Also contactless sensing techniques like interferometry using a set of plan parallel mirrors as depicted in Figure 2 can be used. Careful design of the device 1 allows the use of electrical sensors, such as capacitive transducers or alike.
Given the design of the device 1 , the indicated deformation of the device 1 e.g. results in signals for the optical sensors 10 shown in the lower right part of the space 11 , i.e. optical sensors 10A and 10B, as shown in Figure 1 having an equal amplitude, but opposite sign. In case of the use of fiber-based sensors 10, pretensioning of the optical fibers 32 is required to achieve an operating range spanning a decrease in distance L2 as well. In that case, during assembly of the optical sensors 10, pre-tensioning of the optical fibers 32 of the optical sensors 10 will be at the same level. In case optical fiber-based sensors 10 are used as depicted in Figure 1 , conservation of symmetry in in-plane lateral forces acting on the displacement member 9 can be “balanced” even more by attachment of optical fibers 32 at the locations shown in Figure 1. These optical fibers 32 are to be stretched to the same amount as the optical fibers 32 actually involved in “sensing” in order to balance out pre-tensioning forces even further, or to increase the resonance frequency of the displacement member 9.
It is noted that the described device 1 geometry can be used as a “stand-alone” element, mounted to an object of which the effects are to measured, or the device 1 geometry can be directly machined into the material (like a wall) of an object of which properties of interest are to be monitored (see e.g. Figure 13).
Figure 4 shows a perspective view of an example embodiment of a device 1 according to the invention, such as the embodiment of Figure 1 , wherein the device 1 has a plate-like shape 15. More specifically, the first portion 2, the second portion 5, the connection portion 8, the displacement member 9 and the one or more optical sensors 10 (not shown for sake of clarity) are arranged in such a way, that the device 1 has a plate-like shape 15, i.e. having a relatively large length and width (in the X and Y directions) compared to a thickness of the device 1 (i.e. perpendicular to X and Y directions), for instance a thickness of 1 - 5% of a length in the X direction or 1 - 5% of a width in the Y directions.
The connection portion 8 as shown in Figure 4 has a total force transferring cross-sectional area As lower than a total force transferring cross- sectional area A2, As of the first portion 2 and/or second portion 5 adjacent to the connection portion 8.
Preferably, the total force transferring cross-sectional area As of the connection portion 8 constitutes the lowest total force transferring cross-sectional area between the first connection region 3 and the second connection region 6.
More preferably, the total force transferring cross-sectional area As of the connection portion 8 is 10 - 30%, such as 15 - 25% of the total force transferring cross-sectional area A2, As of the first portion 2 and/or second portion 5 adjacent to the connection portion 8.
Figure 5 shows an example embodiment of a device 1 according to the invention, serving to illustrate the effects of thermal expansion. For the optical sensors 10A and 10B, as depicted in the lower right part of the space 11 in Figure 1 , and (axial) reference points A, B, C and D as shown Figure 5, optical sensor 10A will respond to the difference in distance BA, while optical sensor 10B will respond to a change in distance DC. With R as a reference point, the temperature-induced displacement of point A (AA) amounts to:
AA = L3 . a . AT
In which: a = Thermal expansion of the transducer material [m/(m.°C)]
AT = Change in temperature [°C]
The temperature-induced displacement of point B (AB) amounts to:
AB = Li . a . AT - (L4 + W) . a . AT = Li . a . AT - (Li - L2 - L3) . a . AT = (L2 + L3) . a . AT
And hence:
ABA = AB - AA = L2 . a . AT
The temperature-induced displacement of point C (AC) amounts to:
AC = Li . a . AT - L4 . a . AT = (Li - L4) . a . AT
And the temperature-induced displacement of point D (AD) amounts:
AD = Li . a . AT - L4 . a . AT + L2 . a . AT = (Li - L4 + L2). a . AT
And hence:
ADC = L2 . a . AT Thermal expansion of the device 1 therefore results in an equal change of the distance L2 at the locations of optical sensor 10A and 10B. The difference between optical sensor 10A and 10B is therefore insensitive to temperature.
Figure 6 shows an example embodiment of a device 1 according to the invention, wherein the device 1 is shown in a laterally deformed condition, with the optical sensors 10 being laterally arranged (i.e. laterally extending). Sensing of lateral movements of the first portion 2 of the device 1 is depicted in Figure 6 and can be measured using the laterally arranged optical sensors 10. The optical sensors 10 again operate as a set of sensors with an identical response in amplitude but with opposite sign.
Figures 7A and 7B show cross-sensitivity of laterally (Ry) and axially responsive (Rx) optical sensors 10, respectively.
For the embodiment shown in Figure 1 , pure axial actuation of the device 1 will induce a response (Ry) of optical sensors 10A and 10B. Given the geometry of the device 1 , laterally responding optical sensors 10C and 10D are crosssensitive to pure axial actuation of the device 1 as illustrated in Figure 7A.
Given the geometry of the device 1 and the identical attachment of (the optical fibers belonging to) the optical sensors 10C and 10D to the device 1 , the cross-sensitivity response Rx will be the same for optical sensors 10C and 10D. Hence, by subtraction of the signals of optical sensors 10C and 10D, the cross-sensitivity S cancels out in the result, as illustrated by the following example:
Assume the following signals: S4 = a4 + AX4
S5= Las + Axs
Given the designed-in identical sensitivities of S4 and S5:
Ss = -La4 + AX4
Subtraction results in:
S4 - Ss - 2 . La4 — 2 . Las The same argumentation holds for the cross-sensitivity-induced response (Ry) of Si and S2 to pure lateral actuation of the device 1. Note that in case of using contactless sensing of the variation in deformation of the device 1 , using e.g. a plan-parallel mirror (such as shown in Figure 2), the cross-sensitivity response of the device 1 can be neglected.
Figures 8A and 8B show an example embodiment of a mechanical transducer 36 for transferring forces to an optical sensor 10 enclosed by the mechanical transducer 36. If an amplification factor (say: A1) is not sufficient to achieve the required sensitivity or required signal to noise ratio, a concept of an alternative construction of a mechanical amplifier 36 is shown in Figures 8A and 8B, depicting a preferably monolithic planar object consisting of rigid elements 38 connected by elastic hinges 39. According to Figure 8C, the change in gap distance G of the “diamondshaped” transducer 36, denoted by AG, is given by:
AG = 2. Ax = (-y / x) . Ay
By mounting the “diamond-shaped” transducer to an object or to two objects having a relative displacement with respect to each other, being connected by the transducer 36, a change in distance between the fixation points 37, AL, results in:
Ax = (-y / x) . AL / 2,
And hence:
AG = 2. x = (-y/x). AL
In case object 31 is a Fibre Bragg Grating, the relative change in distance of gap G of the transducer (TRD) introduces a variation in strain of the FBG (EG) given by
EG =AG/G = (-y/x).AL/G.
Furthermore, AL can be expressed by:
AL = EO. L, In which £0 represents the variation in strain of the object to which the diamond structure is mounted to.
The strain amplification (A) is given by:
For the simplified condition of D = 0 (see Figure 8a), and hence G = 2x
A = £g/£o = (-y I x).(L.2.x) = (-y/x2) . (L/2)
In analogy, the relative displacement of the transducer-gap (TRD), Ax I x, can be related to the relative displacement of the object (ORD) by: (again, assuming D=0 and hence G=2x)
TRD = (-y / x2) . (L/ 2) . ORD
With L being the distance between the fixations 37 of the diamond-like transducer 36.
(Note: L can be greater than 2y.)
The mechanical amplification factor can be written as:
Am = TRD I ORD = (-y I x2) . (L/ 2)
Am represents the relative displacement of the transducer 36 with respect to the relative displacement of the object.
Figure 9 shows a graph with the mechanical amplification factor (relative displacement amplification factor) for the mechanical transducer 36 of Figures 8A and 8B. By means of illustration, the calculated amplification factor for y = 20 mm, Li = 100 mm and x ranging from 1 to 20 mm is depicted in Figure 9.
Figure 10 shows an example embodiment of a device 1 according to the invention, comprising three abovementioned mechanical transducers 32 (as depicted in Figures 8A and 8B), wherein one of the mechanical transducers 36 is axially arranged and two of the mechanical transducers 36 are laterally arranged.
Figures 11A and 11 B show an example embodiment of a measurement assembly 17 according to the invention, comprising a first measurement part 4, a second measurement part 7, and an example embodiment of one, respectively two, devices 1 according to the invention connecting the first measurement part 4 and the second measurement part 7 in the axial direction X. Figures 11 A and 11 B serve to illustrate that sensing can be done in multiple dimensions. The devices 1 are shown as a rectangular element mounted to the measurement parts 4, 7. However, the device 1 can have various (sensing) geometries to optimize the response to the parameters of interest (e.g. the design shown in Figure 1).
Figure 12 shows an example embodiment of a measurement assembly 17 according to the invention, comprising a tubular measurement object 23 and an example embodiment of a device 1 according to the invention, having a curved, plate-like shape 15. The device 1 is attached to an outer wall surface 24, 25 of the tubular measurement object 23. Figure 12 more in particular shows that the first measurement part 4 and the second measurement part 7 belong to a single measurement object 18. The first measurement part 4 and the second measurement part 7 have a tubular shape 19. The first measurement part 4 and the second measurement part 7 comprise a first wall segment 20 and a second wall segment 21 , respectively, of a tubular wall 22 of a single, tubular measurement object 23, having a centerline C. The second portion 5, the connection portion 8, the displacement member 9 and the one or more optical sensors 10 are arranged in such a way, that the device 1 has a plate-like shape 15, wherein the plate-like-shaped device 15 is curved around the centerline C of the tubular measurement object 23. The first connection region 3 is connected to an outer surface 24 of the first wall segment 20 and the second connection region 6 is connected to an outer surface 25 of the second wall segment 21. The device 1 can thus be advantageously used to measure torsional forces/deformations as well as axial forces/deformations. Instead of attaching the plate-like-shaped device 1 to the outer wall surfaces 24, 25 the device 1 could also be machined/milled into the tubular wall 22. Of course, it is furthermore conceivable to attach a plurality of devices 1 to/into the tubular wall 22, possibly at various angles with respect to the centerline C (and with respect to each other). An embodiment is moreover foreseen, wherein e.g. a fluid flows through the tubular measurement object 23 and the device 1 is used to measure the effects of the fluid on the tubular measurement object 23.
Figure 13 shows an example embodiment of a measurement assembly 17 according to the invention, comprising a tubular measurement object 23 and example embodiments of a plurality of laterally connected plate-like-shaped devices 1 , 15 according to the invention, forming a ring-shape 16, with the devices 1 , 15 being curved around the centerline C of the tubular measurement object 23. The ring-shaped device 16 is integrated with or transitions into wall segments 20, 21 of the tubular measurement object 23 in the axial direction X, i.e. in the axial direction X, the first connection region 3 is integrated with or transitions into the first measurement part 4 and/or the second connection region 6 is integrated with or transitions into the second measurement part 7. More specifically, the first measurement part 4 and the second measurement part 7 comprise a first wall segment 20 and a second wall segment 21 , respectively, of a tubular wall 22 of a single, tubular measurement object 23, having a centerline C. Although not shown in Figure 13, the second portion 5, the connection portion 8, the displacement member 9 and the one or more optical sensors 10 are arranged in such a way, that the device 1 has a plate-like shape 15, wherein the plate-like-shaped device is curved around the centerline C of the tubular measurement object 23, wherein, in the axial direction X, the first connection region 3 is integrated with or transitions into the first wall segment 20 and wherein the second connection region 6 is integrated with or transitions into the second wall segment 21. As mentioned before, the measurement assembly 17 comprises a plurality of laterally connected plate-like-shaped devices 1 , 15, wherein the plate-like-shaped devices 15 are curved around the centerline C in such a way, that the plate-like-shaped devices 15 fully enclose the centerline C, creating a ring-shaped device 16 forming an intermediate wall segment 26 between the first wall segment 20 and the second wall segment 21. One of the optical sensors 10 (not shown in Figure 13) may be axially arranged to measure “thrust”, while another optical sensor 10 may be laterally arranged to measure “torque”.
Figure 14 shows an example embodiment of a mixing device 29 according to the invention. The mixing device 29 comprises a motor assembly 27, comprising a motor 28 and an aforementioned measurement assembly 17. The motor 28 is configured for driving the tubular measurement object 23 around the centerline C of the tubular measurement object 23 for mixing a substance 30. The tubular measurement object 23 is thus arranged for transferring driving forces from the motor 28 to the substance 30 to be mixed.
As a general remark, in case the optical sensors 10 of the device 1 comprise optical fibers 32 with integrated sensing elements, the optical fibers 32 are to be pre-stressed as to allow positive and negative variations in AL. Therefore, the optical fibers 32 act as a pre-tensioned ‘spring’. In general, the potential energy, Ep, stored in a spring, elongated over a length x is given by:
Ep = k . x2/ 2
In which: k = spring constant [N/m] x = length variation of the spring [m]
In case of the optical fibers 23, during assembly of the optical fibers 32 in/to the device 1 , the optical fibers 32 are pre-strained introducing a change of length equal to: x = £o . Lo
In which:
£o: Pre-strain of the optical fiber [-]
Lo: Length of fiber in unstrained condition [m]
Now, by design of the device 1 , in differential mode, i.e. using a set of optical fibers 10A, 10B and/or a set of optical fibers 10C, 10D as depicted in Figure 1 , the pre-strain, £0, and unstrained length, Lo, are equal.
On top of the pre-strain contribution to the potential energy are the variations in potential energy due to actuation of the device 1. Given the earlier variation in pre-strained length of the optical fibers 32 designated by AL (see Figures 3A and 3B), the change in potential energy due to actuation is:
AEP = k . (AL)2/ 2 And:
AEP / AL = k . (AL)
For a set of optical fibers 32 operated in differential mode, the length between the fixation points 33 is set equal for both optical fibers 32. Given an identical cross-section and material properties of the both (usually) glass wires, the spring constant, k, is equal for a set of differentially operated optical fibers 32.
Given the “by design” anti-symmetric (equal in amplitude but opposite in sign) variations in AL for the set of two in differential mode operating optical fibers 32, the increase in potential energy stored in one of the two optical fibers 32 is equal but opposite in sign to the variation in potential energy for the second fiber 32 of the set.
As a net result, the energy needed to activate a differential (antisymmetric-responding set of optical fibers 32, both being pre-strained to the same level and both fixed between two points 33 at identical length L apart, equals zero. This is of great importance for minimizing the energy required to activate the device 1.
Figures 15a - 15c show example embodiments of a connection member 14 according to the invention. Figure 15a shows a relatively straightforward embodiment of the connection member 14, i.e. a connection member 14 having a constant cross-section. Figure 15b shown a connection member 14 having a curved shape. Figure 15c shows a connection member 14 having a decreasing/increasing cross-section (like an hourglass). Of course, pairs of such connection members 14 are to be arranged in a symmetrical fashion with respect to the main (X-)axis. The skilled person will understand that many more shapes are conceivable for the connection member 14. The connection member 14 may even e.g. comprise one or more piezo elements - or such piezo elements may be arranged separately between the first portion 2 and the second portion 5. LIST OF REFERENCE NUMERALS
1. Device
2. First portion
3. First connection region
4. First measurement part
5. Second portion
6. Second connection region
7. Second measurement part
8. Connection portion
9. Displacement member
10. Optical sensor (10A, 10B, 10C, 10D)
11. Space
12. Free end of displacement member
13. Intermediate portion of displacement member
14. Connection member
15. Plate-like-shaped device
16. Ring-shaped device
17. Measurement assembly
18. Single measurement object
19. Tubular shape of first and second measurement part
20. First wall segment, of first measurement part
21. Second wall segment, of second measurement part
22. Tubular wall of a single tubular measurement object
23. Single tubular measurement object
24. Outer surface of the first wall segment
25. Outer surface of the second wall segment
26. Intermediate wall segment
27. Motor assembly
28. Motor
29. Mixing device
30. Substance
31. Sensing element
32. Optical fiber 33. Fiber fixation
34. Reflecting mirror
35. Interference- or wavelength-modulated detection
36. Mechanical transducer
37. Mechanical transducer fixation point
38. Rigid element
39. Elastic hinge
X. Main axis/axial direction
Y. Lateral direction
W12. Width of free end of displacement member
W13. Width of intermediate portion of displacement member
A2. Total force transferring cross-sectional area of first portion
A5. Total force transferring cross-sectional area of second portion
As. Total force transferring cross-sectional area of connection portion