GB2639200A

GB2639200A - Force sensor and method for operation

Info

Publication number: GB2639200A
Application number: GB2403442.3A
Authority: GB
Inventors: Colby Edward
Original assignee: Cyclops Marine
Current assignee: Cyclops Marine
Priority date: 2024-03-11
Filing date: 2024-03-11
Publication date: 2025-09-17
Also published as: GB202403442D0; WO2025191465A1

Abstract

A force sensor for measuring a force applied through the device which has a substantially flat body provided with two openings 10 allowing attachment of shackles, belts, carabiners, ropes, wires, cables, bolts, etc. The force sensor also includes two additional openings 11 lying between the attachment openings, wherein the additional openings are configured to be separated by a measurement element 12, wherein the measurement element is configured with its elongate axis A1 arranged substantially orthogonally to a direction of action of the applied force, along axis AO. The measurement element 11 has a thinned section 13 to allow enough deformation for a strain gauge to generate an electrical signal which is substantially linear in relation to the force applied via the openings 10. A measurement body 30 in is formed by two clam shell halves (31 in figure 3) to form an enclosure around the stain gauge circuit electronic and battery. An alternative arrangement is in the form of a carabiner with a sprung gate (50 in figure 5). A method of using the sensor is also claimed.

Description

FORCE SENSOR AND METHOD FOR OPERATION

TECHNICAL FIELD

The present disclosure relates to force sensors, and more particularly to a force sensor including a thin force sensor suitable for measuring a force arising between two attachment points. Moreover, the present disclosure relates to a method operating the aforesaid force sensor. The force sensor is beneficially optimised for cost-effective manufacture, whilst also providing improved sensitivity and improved overload capability. Features of the force sensor permit its sensitivity to be tuned to suit various use applications, wherein the force sensor is designed so that it is simpler to provide a watertight enclosure therearound, for example around an incorporated power source and measurement electronics. The force sensor has particular application in recreational activities, such as in sailing and gym exercise and in personal safety equipment; however, the force sensor may be used is other situations.

BACKGROUND

There exist many known designs for force sensors which use an elastic measurement body coupled between two attachment points, wherein an extension of the elastic measurement body caused by applying a force to the attachment points is measured by strain gauge transducers that generate electrical signals that provide an indication of the applied force.

These known sensors are used in many applications including weighing loads, measuring human effort generated using gym equipment, and measuring tension in at least one of: wires, cables and rigging.

A consequence of the measurement body being in a load path between the attachment points is that a strength of the force sensor is related to a sensitivity of the force sensor. In practice, a technical problem that is encountered is that it is difficult to maximise the sensitivity and strength in the same design of force sensor where all the load carried is passed through a section whereat the measurement is made.

In a published US patent application US5589646A, there is disclosed a force sensor that uses a thinned measurement section to optimise sensitivity; however, the thinned measurement -2 -section comes at a cost of limiting an overall strength of the force sensor because all of the load to be carried passes through the thinned measurement section at which the measurement is made. This approach as described in the US patent application US5589646A is contemporarily commonly used.

In a published patent application having a search report BE1008198A3, there is described a tension sensor comprising a ring that is deformed into an ellipse under an effect of an applied load generating a force, which causes two lateral sides of the ring to be brought together, thereby causing activation of a simple limit switch. Such a ring-type configuration is a beneficial arrangement because the strength of the ring may be much made greater than the force to be measured.

A German published patent application DE102007044225A1 discloses a force sensor including a ring-type body with apertures arranged to receive bolts that transfer a force to be measured to a body. The force applied between the bolts is inferred by measuring at least one of a strain developed in lateral sides of the ring-type body, a displacement of the lateral sides. This design exhibits a beneficial feature to ensure that apertures that receive the bolts carry slots that prevent them from encircling the bolts. These are noted to be important because closed apertures potential serve to prevent the ring from being distorted under the influence of the force and thereby compromising the sensitivity of the force sensor.

SUMMARY

In order to be cost effective, it is desirable to manufacture a body of a force sensor from a planar element of material, wherein the planar element is manufactured by using forming operations in a single plane and with a strain gauge arrangement applied to the surfaces of the planar element. Using forming operation in a single plane simplifies manufacturing tooling required and significantly simplifies the bonding of the strain gauge arrangement to the planar element and making connections from the strain gauge arrangement to corresponding measurement electronics. Force sensors formed in this way are contemporarily available to the public; however, for the reasons given above, the measurement sensitivity of such sensors for a given strength is limited.

It will be appreciated from the aforesaid application BE1008198A3 that the degree to which the lateral sides are brought together is a measure of force generated by the applied load. Such -3 -a principle of operation is used in hardware described in a European patent application EP0003685A2 to yield a crane overload indicator which uses an electrical transducer to measure a displacement and to trigger an alarm when a pre-set threshold displacement is reached. This arrangement is problematic because there is used a separate displacement transducer that must be extremely sensitive to detect small displacements that occur for anything but permanent damage to the ring, wherein the separate transducer does not lend itself to cost effective manufacture.

An alternative approach to measure the displacement is to place an elastic element between the two sides of the ring so that the elastic element is compressed and deformed in proportion to the applied load that generates the force. The compression of the elastic element may be measured by using an attached strain gauges. Such an arrangement is potentially easily incorporated into a sensor body made from a planar material.

Such arrangements are advantageous because the ring may be optimised for strength, permitting such a sensor to carry large forces without breaking, whilst the elastic member may be simultaneously optimised for sensitivity, giving accurate measurement of comparatively small forces.

However, it will be appreciated that force sensor described in DE102007044225A1 is not well suited to manufacture from planar material because the body so formed is unstable to buckling under load as its structure becomes progressively less stiff as it deforms out the plane when the force is applied thereto. Including the aforesaid slots contributes significantly to the instability. Moreover, it will be appreciated that an arrangement which is similar to that disclosed in DE102007044225A1, but which does not use the slots in the apertures, may be optimised so that the effect of bridges where the slots would otherwise may be to increase the compression of the elastic measurement element lying across the ring.

In such an arrangement, the bridge pieces may serve to increase the stability of the arrangement, thereby maximising its ultimate strength, whilst also providing useful surfaces against which an enclosure may be sealed without significant impact on the accuracy of the sensor. This enclosure may accommodate a power supply, measurement electronics, display, controls and means to wirelessly transmit measurements from the sensor. -4 -

Furthermore, the use of a compressed elastic element to measure the displacement allows the sensitivity of the sensor to be tuned to the application. If a portion of the element is thinned relative to the rest of the element, then the compressive strain may be concentrated in this thinned section. This concentration acts as a mechanical amplifier which may be used to maximise the output from strain gauges bonded to this section.

It is the aim of the present invention to provide a simple reliable force sensor with large overload capacity which can be manufactured cost effectively. The combination of selected features of published applications BE1008198A3 and DE102007044225A1 along with a compressed elastic measurement element enables a force sensor to be manufactured that achieves an improved overload capability whilst also being more cost-effective when being manufactured. Further aspects of the invention make its incorporation into a sealed enclosure simple and enable the sensitivity of the sensor to be simply tuned to a given use case.

In a first aspect, there is provided a force sensor as defined in appended claim 1 There is provided a force sensor for measuring a force applied between two attachment openings, wherein the force sensor includes two additional openings lying between the attachment openings, wherein the additional openings are configured to be separated by a measurement element, wherein the measurement element is configured with its elongate axis arranged substantially orthogonally to a direction of action of the applied force.

In a second aspect, there is provided a force sensor as define in appended claim 2.

There is provided a force sensor for measuring a force applied between two attachment openings, wherein the force is measured by measuring a compressive strain developed in a measurement element by at least a portion of the force being coupled to the measurement element.

In a third aspect, there is provided a force sensor as defined in appended claim 3.

There is provided a force sensor for measuring a force applied between two attachment openings, wherein the force sensor is configured to couple the force to generate a compressive strain in a measurement element that is measured by using a strain gauge arrangement.

Optionally, for the force sensor of the first, second or third aspect, the measurement element us couple to at least two strain gauges that are arranged above and below the measurement -5 -element so that their combined output is substantially null to bending of the measurement element.

More optionally, for the force sensor of the first, second or third aspect, a portion of the measurement element is thinned, wherein the thinned portion is configured to function as a region of concentrated compressive strain in response to the force being applied to the force sensor. Yet more optionally, the measurement element is symmetrically thinned around a mid-plane of the force sensor.

According to a fourth aspect, there is provided a method as claim in appended claim 7.

There is provided a method of using a force sensor for measuring a force applied between two attachment openings, wherein the method includes: (i) configuring the force sensor to includes two additional openings lying between the attachment openings, wherein the additional openings are configured to be separated by a measurement element; and (ii) configuring the measurement element with its elongate axis arranged substantially orthogonally to a direction of action of the applied force.

Optionally, the method further includes configuring the force sensor to couple the force to generate a compressive strain in a measurement element that is measured by using a strain gauge arrangement. More optionally, the method includes configuring the force sensor so that the measurement element is coupled to at least two strain gauges that are arranged above and below the measurement element so that their combined output is substantially null to bending of the measurement element. More optionally, the method includes configuring the force sensor so that a portion of the measurement element is thinned, wherein the thinned portion is configured to function as a region of concentrated compressive strain in response to the force being applied to the force sensor.

DESCRIPTION OF DIAGRAMS

Embodiments of the invention will be described with reference to the following drawings, wherein: FIG. 1 is an illustration of a force sensor of the present disclosure; -6 -FIG. 2 is an illustration of a mechanism for applying a force to an attachment opening of the force sensor of FIG. 1; FIG. 3 is an exploded view of a sensor assembly of the force sensor of FIG. 1; FIG. 4 is an illustration of an alternative form of a sensor body in which attachment openings are slots through which canvas straps are attachable for applying force to the sensor body; and FIG. 5 is an illustration of an alternative form of the sensor assembly which incorporates a sprung gate in one of its attachment openings for allowing the force sensor of FIG. I to be conveniently attached and detached from a load point.

DETAILED DESCRIPTION OF EMBODIMENTS

In overview, the present disclosure provides a force sensor including a substantially flat body, wherein the flat body is provided with two openings to which are attachable one or more of shackles, carabiners, ropes, wires, bolts or other fittings. There is thereby applied a tension force to the flat body. A line of symmetry includes centres of the two attachment openings and in-line, wherein, when the force sensor is in use, the line of symmetry is aligned with a direction of a pull of the applied tension force applied to the force sensor. This line of symmetry is a pull axis for the force sensor. Along the pull axis and between the two attachment openings are included two more additional openings which serve to separate the attachment openings from a measurement element lying along a second line of symmetry substantially orthogonal to the first line of symmetry. This orthogonal axis is the measurement axis of the force sensor. The portions of the flat body lying between each attachment opening and its adjacent additional opening form bridges of material that are resistant to compression.

Under the influence of an applied tension force to the force sensor, each of the bridge elements is placed in compression such that the applied force also results in bending moments in the body around the end of the bridges. These bending moments transfer a compressive stress to the measurement element resulting in a strain which may be measured by using strain gauges. Optionally, beneficially, a portion of the measurement element is made thinner than a remainder of the measurement element, so that this thinner portion is subject to increased strain in response to the compressive stress, thereby maximising the output of strain gauges attached thereto. -7 -

Optimally, the thinner section is made by removing material from both sides of the measurement element so that the thinner section lies in a mid-plane of the sensor, wherein the mid-plane is a plane of symmetry. This symmetry serves to reduce the sensitivity of the sensor to forces other than the direct in-line pull along the pull axis. Thinning may be implemented by machining, laser ablating, water-jet cutting or stamping the planar material.

Optimally, the strain gauges attached for measuring the strain in the thinner section are configured in a bridge arrangement, with strain gauge elements above and below the thinner section. Such a configuration for the strain gauges serves to minimise sensitivity of the bridge arrangement to bending moments in the measurement element due to externally applied forces.

Optionally, beneficially, the force sensor is protected within an enclosure comprising two half-clam shells that are arranged on respective both side of the substantially flat body to protect the strain gauges, their measurement electronics, their power supply, and their wireless transmission arrangement. A boundary of the body and the bridge arrangement forms substantially flat surfaces against which the half-clam shells maybe sealed such that the sealing forces are substantially orthogonal to the in-plane measurement forces and strains, thereby minimising the influence of these forces on the measurement function of the force sensor. In such an arrangement, the strain gauges generate, when in use, a sensor signal that is substantially linear in response to the magnitude of the applied force to the force sensor.

Next, further additional optional features of embodiments of the present disclosure will be described.

For the force sensor to function as intended, it is only necessary that the additional openings cross the pull axis.

The force sensor as described above has two axes of symmetry. However, optionally, such two axes of symmetry are not essential, wherein embodiments of the present disclosure may be configured to have asymmetry. Thus, an asymmetry between the attachment openings, the additional openings or non-orthogonality between the pull axis and measurement axis result in changes in an effective measuring sensitivity (namely "gain") of the force system and may be accommodated though any calibration processes to the force sensor. -8 -

Optionally, the attachment openings need not be of mutually same shape and size; the attachment openings may be individually matched to a use case of the force sensor, and may accommodate belts, strops, ropes, wires or incorporate a gate to so that they may be used as a quick release fitting.

The force sensor may optionally include a power supply and also measurement electronics; more optionally, the force sensor may also include a display to display at least one of: a pulling force being experienced in use by the force sensor, a status indication of the force sensor (namely, to determine whether or not the force sensor is functioning correctly to calibration).

The additional openings in the sensor body may be used to accommodate such components, for example the power supply and the measurement electronics and, optionally, the display.

The sensor may optionally incorporate a temperature sensor which may be configured to be included into into the measurement electronics and spatially placed close to the strain gauges so as to compensate for changes in the gauges and body material modulus due to changes in temperature of the force sensor.

Whereas strain gauges provide a convenient sensor arrangement to use to transduce the strain in the measurement element of the force sensor into an electrical signal, it will be appreciated that other strain sensing transducers may be used in the force sensor, for example at least one of piezo-electric transducers, optical transducers, magnetostrictive transducers and capacitive transducers.

Referring next to FIG. 1, there is shown an illustration of a force sensor of the present disclosure. The force sensor has a pull axis denoted by A0, and a measurement axis denoted by Al; the measurement axis Al is substantially orthogonal to the pull axis A0. Attachment openings 10 are included that are disposed on the pull axis A0; the openings 10 are provided for the attachment of fittings (not shown in FIG. 1) to the force sensor. Additional openings 11 are included that separate the attachment openings 10 from a measurement element 12 lying along the measurement axis Al. In the measurement element 12, strain gauges are attached to the surface of a thinned section 13 of the measurement element 12, so enable the strain gauges to generate, when in use, an electrical signal which is substantially linearly related to the force applied to the attachment openings 10. -9 -

Referring next to FIG. 2, there is shown is an illustration of a mechanism by which a force 20 applied to an attachment opening 21 is transferred through a substantially stiff lever around an effective pivot 23 at the end of a bridge element 24 into a compressive force 25 in the measurement element. Strain gauges bonded at a thinned section 26 are configured to detect compressive strain arising due to the compressive force 25 being applied to the thinned section 26.

In FIG. 3, there is shown an exploded view of the force sensor including its additional component parts namely a measurement body 30 surrounded by two (2) clam shell halves 31 10 which form an enclosure for measurement electronics 32 and a battery 33.

Referring next to FIG. 4, here is shown an illustration of an alternative form of the sensor body of the force sensor, wherein attachment openings 40 are implemented as slots through which canvas straps are attachable to apply force to the sensor body.

Finally, referring to FIG. 5, there is shown an illustration of an alternative form of the sensor assembly force sensor, wherein sensor assembly incorporates a sprung gate 50 in one of the attachment openings to allow the force sensor to be conveniently attached and detached from a load point, when in use.

Claims

CLAIMS 2. 3. 4. 7.A force sensor for measuring a force applied between two attachment openings, wherein the force sensor includes two additional openings lying between the attachment openings, wherein the additional openings are configured to be separated by a measurement element, wherein the measurement element is configured with its elongate axis arranged substantially orthogonally to a direction of action of the applied force.
A force sensor for measuring a force applied between two attachment openings, wherein the force is measured by measuring a compressive strain developed in a measurement element by at least a portion of the force being coupled to the measurement element.
A force sensor for measuring a force applied between two attachment openings, wherein the force sensor is configured to couple the force to generate a compressive strain in a measurement element that is measured by using a strain gauge arrangement.
A force sensor of claim 1, 2 or 3, wherein the measurement element is coupled to at least two strain gauges that are arranged above and below the measurement element so that their combined output is substantially null to bending of the measurement element.
A force sensor of claim t, 2, 3 or 4, wherein a portion of the measurement element is thinned, wherein the thinned portion is configured to function as a region of concentrated compressive strain in response to the force being applied to the force sensor.
A force sensor of claim 5, wherein the measurement element is symmetrically thinned around a mid-plane of the force sensor.
A method of using a force sensor for measuring a force applied between two attachment openings, wherein the method includes: (i) configuring the force sensor to includes two additional openings lying between the attachment openings, wherein the additional openings are configured to be separated by a measurement element; and (ii) configuring the measurement element with its elongate axis arranged substantially orthogonally to a direction of action of the applied force.
8. A method of claim 7, wherein the method further includes configuring the force sensor to couple the force to generate a compressive strain in a measurement element that is measured by using a strain gauge arrangement.
9. A method of claim 7, wherein the method includes configuring the force sensor so that the measurement element is coupled to at least two strain gauges that are arranged above and below the measurement element so that their combined output is substantially null to bending of the measurement element.
10. A method of claim 7, 8 or 9, wherein the method includes configuring the force sensor so that a portion of the measurement element is thinned, wherein the thinned portion is configured to function as a region of concentrated compressive strain in response to the force being applied to the force sensor.