The present invention relates to load-indicating devices and particularly to improved load-indicating washers and nuts for providing an indication of a predetermined tension or load between fastening components.

It is commonly known that if fastening components, such as nuts and bolts etc. are not correctly tensioned or secured together with the correct compressive force or load, then those components are likely to eventually fail or come apart or otherwise experience some form of mechanical fatigue. Accordingly, there are therefore numerous mechanical problems that may potentially result if a structural assembly comprising such fastening components is either under-loaded or over-loaded (i.e. under tensioned or over tensioned respectively).

Typically, an under-loaded condition will usually result in fatigue and failure of the structural components as external oscillating forces will generally be present. For example, if the oscillating forces act through a nut and bolt, with the tensioning of the nut and bolt being insufficient, the bolt will generally fail by either fracturing (due to fatigue) or otherwise will eventually become loose due to the oscillating forces.

In an over-loaded condition, the nut and bolt usually experience stresses that again may lead to failure of the fastening components. Therefore, if the tightening tension is too high, the bolt and/or nut, or their threads, will typically exceed their design load usually resulting in fracture or breakage of the components.

Accordingly it is very important to impart the correct tension, load or tightening force to fastening components to ensure the structural integrity of a mechanical assembly, which thereby increases longevity and/or safety of machines and assemblies. It is also extremely useful to know if, and when, fastening components begin to become loose or un-tensioned when in use, so that corrective measures can be taken to retighten the fastening components to the correct tension as soon as possible.

A common technique for tensioning fastening components, of the likes of nuts and bolts, is to use a device such as a torque wrench to apply a tightening load. However, such devices usually have the inherent drawback of using up to approximately 90% of the effort (depending on lubrication) to overcome frictional resistance in the different fastening components. Therefore, it may prove to be very difficult to overcome the unpredictable frictional resistances with only approximately 10% of the remaining effort being available to thereby to ensure the correct tensioning load is applied to the fastening components. Consequently, this technique of tightening can be inaccurate for some tightening applications, leading to possible under loading or over-loading of fastening components, without the operator being aware of such a condition being present.

Load-indicating devices which address many of the problems encountered in the prior art, are described in the published PCT application WO2014/106752, the contents of which are incorporated herein by reference.

The present invention provides improvements and enhancements to load- indicating devices, as well as describing further advantageous solutions to allow reliable and consistent tensioning of fastening components. In particular, the present invention also addresses the issue of remote, periodic and/or continuous monitoring of fastening components with a view to ensuring the long term structural integrity of mechanical assemblies.

In addition, the present invention also addresses the issues of temperature compensation, vibration compensation and speed of tightening compensation, either separately of any in combination. Such compensation functionality permits the device to mitigate against the effects of temperature variations, oscillations in the joint or environment of the device, and prevents possible damage due to rapid tightening of the fastening components.

According to an aspect of the present invention there is provided a load indicating device, comprising: a body portion defining a bore extending therethrough; at least one electrical conductor extending around at least a portion of the body portion and being secured thereto; and a processing module coupled to the conductor, wherein the processing module is configured to detect one or more changes in an electrical characteristic of the conductor when the body portion is compressed.

The provision of a load indicating device comprising at least one electrical conductor extending around at least part of the body portion of the device with a processor module configured to detect one or more changes in an electrical characteristic of the conductor as the body is compressed, is found to be particularly advantageous as the device is able to provide a reliable and accurate indication of the tension or load between two fastening components disposed either side of the body portion of the device.

In particular, due to the inherently configurable nature of the electrical conductor and its corresponding geometry, the load indicating device may consequently be ‘fine-tuned’ via appropriate calibration to suit the particular tension or loading requirement. Therefore, as the body portion is compressed, the electrical conductor undergoes a predetermined deformation that brings about a corresponding change in an electrical characteristic of the conductor which can then be detected as described in the following embodiments. In exemplary embodiments the body portion of the device may be in the form of a washer or a nut. The washer may be of any size and may be scaled to suit the particular application, with the bore of the body portion being unthreaded or threaded, as required. For embodiments in which the body portion takes the form of a washer, a nut or other conventional securing component will typically be used to secure the joint or mechanical assemblies, with the washer being ‘sandwiched’ between two nuts or the nut and the joint etc.

Therefore, the device of the present invention may be deployed in any arrangement in which two or more mechanical assemblies are to be connected together. In this way, the present device makes it possible to tighten fastening components to a desired or predetermined tension without the need for a torque wrench or other mechanical (tension) measuring means. Hence, an operator, such as an engineer or mechanic, can be assured that in using the device of the present invention the required tension can be achieved without concern that the fastening components have been under- or over-loaded.

In exemplary embodiments, the electrical characteristic of the conductor is the resistance of the conductor. The electrical conductor is secured to the body portion via any suitable means, such as a screw, bolt or a solder tack etc. Indeed, any technique of securing the conductor to the body portion may be used, provided deformation of the conductor occurs when the body portion is compressed. The deformation of the conductor results in the electrical resistance of the conductor changing due to the physical change in the dimensions of the conductor (e.g. length or width etc.). Therefore, in particularly preferred embodiments in which the conductor is an electrical wire, the wire may be compressed (e.g. squashed) and/or stretched in length in response to the body portion being compressed. As such, a corresponding measurable change in resistance will occur in the wire, thereby enabling the load on the device to be calculated. Although the present device may comprise only a single electrical conductor, it is preferred that there are at least two electrical conductors in the device to ensure an accurate determination of the load. As mentioned above, the electrical conductor is most preferably a wire, but may alternatively be a metal band or strip or other suitable configuration of conductor.

The electrical conductor extends around at least a portion of the body portion of the device, and most preferably, extends completely around the circumference of the body portion. The body portion is preferably cylindrical in shape and most preferably resembles a flattened disk with a bore extending therethrough. The outer edge of the disk preferably comprises a circumferential recess into which the electrical conductor is disposed and secured. In exemplary embodiments, there are two electrical conductors in the recess.

Preferably, the electrical conductor is wrapped around the circumference of the body portion as a single loop of wire. However, any suitable geometry may be used in conjunction with the present device. Therefore, the electrical conductor may be wrapped around the body portion in a helical manner (e.g. multiple loops), sinusoidal (e.g. wave like) or in a zig-zag (e.g. saw tooth fashion) depending on the particular implementation or loading requirements. All that is required is that the conductor geometry deform in a predictable and repeatable manner. In all embodiments in which there are two or more electrical conductors, the conductors are arranged to be electrically isolated from each other. The two or more conductors may also be different in form to each other, with one having a thickness or other dimension that is larger of smaller than a neighbouring conductor. Indeed, each conductor may have a different configuration to all of the other conductors, which can enable a more accurate determination of any resistance change to be detected, since different conductor geometries may be more or less susceptible to deformation as the body portion is compressed.

The processing module is coupled to the at least one conductor in order to be able to determine when changes in the resistance of the conductor occur. The processing module may comprise at least one sensor in electrical communication with the conductor, with the sensor being configured to detect changes in resistance.

In exemplary embodiments, the processing module comprises at least one processor in communication with the at least one sensor. The processor is preferably in the form of a microprocessing unit comprising a bespoke semiconductor chip configured to determine the strain on the electrical conductor (in response to compression of the body portion). The strain can be determined by measuring the resistance of the electrical conductor (via appropriate calibration), which in turn can be converted into a corresponding load (again via calculation from calibration results). Therefore, the processing module, electrical conductor and sensor effectively act as an integral “strain gauge” from which the load on the device can be calculated. The electrical resistance is preferably measured multiple times each second, and is most preferably measured at a frequency of 8 times a second (i.e., 8 Hz), enabling the tension in the device to be calculated at a corresponding frequency with an average tension value being preferably calculated. Of course, other statistical measures (e.g. median) may additionally or alternatively also be calculated, as required.

The sensor may be a standalone component or may form part of the bespoke semiconductor chip. In some preferred embodiments, the sensor may be an electronic sensor that is operable to detect changes in resistance due to variations in a voltage applied to the conductors. In such arrangements, the processing module provides a voltage to the conductors whereupon deformation of the conductors changes the resistance and hence the voltage drop across the conductors. In this way, the sensor can detect the change in resistance due to the variation in measured voltage. In other embodiments, the sensor may form part of a resistive bridge arrangement (e.g. a Wheatstone bridge) in which the resistances of the conductors are determined by balancing the resistances in the bridge, whereupon the sensor can detect the change in resistance.

In other embodiments, the electrical conductor itself may serve as the sensor with the changes in its resistance being determined by mechanical means, e.g. a closable switch that is actuated by the variation in the dimensions (e.g. length) of the conductors. The switch may comprise a potentiometer or similar device, and/or provide a measurable change in voltage whereby corresponding changes in resistance can be accurately determined. Of course, it is to be appreciated, that any suitable sensor or sensor means for determining changes in resistance may be used in conjunction with the present device, including electrical, electronic, mechanical and electro-mechanical components.

In preferred embodiments, the processing module further comprises at least one of temperature compensation means, vibration compensation means and speed of tightening compensation means. The electrical characteristics of the conductor may be affected by external ambient conditions, which may give rise to an inaccurate determination of changes in the load. Therefore, variations in temperature and/or vibrations in the vicinity of the device (e.g. from operating machinery etc.) may cause the resistance of the conductor to change unexpectedly. This effect may be mitigated to a certain degree by appropriate calibration of the device, but in preferred embodiments variations in temperature and/or vibration may be counteracted by using corresponding compensation means.

Therefore, the processing module comprises circuitry and program code to determine the temperature of the device and apply an appropriate correction factor based on pre-calibrated temperature data. Preferably, the circuitry comprises at least a temperature gauge or thermometer (e.g. a thermister etc.) to determine the temperature. Likewise, vibration is preferably sensed via one or more vibration sensors, which most preferably are in the form of integral accelerometers, which determine any oscillations in the vicinity of the device and apply an appropriate correction factor based on pre calibrated vibration data. Any form of suitable temperature measuring component or circuit and/or vibration sensor may be used in conjunction with the present device, without limitation. The vibration sensors are preferably multi-axis, in that vibration along all 3 Cartesian axes can be separately detected. In this way, a true 3-dimensional model of the vibration environment in and around the device can be established to apply accurate compensation. The temperature measurements are preferably sampled every second in order to quickly determine any variations in temperature. Preferably, no averaging is applied to the temperature samples, although any suitable statistical measure can be applied if required. The vibration measurements are preferably sampled 400 times per second (i.e. at 400 Hz), with a RMS velocity being calculated at the end of each second. Each of the 3 axes (x, y and z) may be calculated separately with a vibration result being available in mm/sec for each axis. According to preferred embodiments, the z axis is taken to be perpendicular to the body portion of the device and is mutually orthogonal to each of the other x and y axes.

During installation of the present device it is important to ensure that the device is correctly positioned within the mechanical joint and that damage does not occur due to rapid and/or excessive over-tightening. An over- tightened joint can suffer mechanical fatigue, leading to failure (such as fractures or warping) which is potentially hazardous for many applications. Moreover, over-tightening can also lead to stripping of threads on a bolt or stud, which again can seriously weaken a fastened component. Therefore, to mitigate any installation errors a speed of tightening compensation means determines if the device is being subjected to anomalous or undesirable forces. The speed of tightening compensation means also preferably comprises an accelerometer, which enables the tightening speed of the nut or bolt etc. to be compared to pre-calibrated tightening data to ascertain if corrective measures are required. The accelerometer may preferably detect and determine a speed of rotation associated with the tightening of the nut, such that excessive tightening speeds can be detected to enable a warning to be provided to an operator of the tightening means. In addition, the speed of tightening compensation means may also use the measured resistance data to determine whether the mechanical joint has been excessively tightened or over-loaded, which may or may not also be linked to rapid tightening of the nut. In this way, the operator can be notified during (or after) the tightening procedure in order to apply a corrective measure.

The accelerometer data used to determine the speed of rotation of the nut, may also be associated with the environmental vibration data, which is used to determine any oscillations in the vicinity of the device, and again can be used to apply an appropriate compensation if the nut is being tightened while also experiencing other oscillations within the mechanical joint or structure that is being fastened together.

The pre-calibrated temperature data, vibration data and tightening data may all be stored locally in the device, and are preferably stored in the processing module. The data may be in the form of a look-up table (LUT), a calibration curve or other mathematical relationship, or may comprise any combination thereof. The sensor data can then be directly compared to the calibration data to determine temperature, vibration and speed of tightening compensation, with appropriate thresholds also preferably being defined as part of the calibration data. The pre-calibrated data can be periodically updated or replaced by a different calibration data if the present device is removed and/or reused for other applications or if any mechanical change occurs in the structure or fastening components. A firmware update or a software upload etc. may be used to modify the pre-calibrated data as appropriate. Indeed, any suitable method may be used to update or modify the calibration data according to the present invention.

In exemplary embodiments, the processing module further comprises an output port. The output port is configured to provide data to an external device that can be inserted into or otherwise connected to the port. Therefore, data concerning the detected changes in resistance, and correspondingly the strain, may be obtained directly from the processing module of the device. The external device may be an external monitoring device and is preferably, a hand-held unit that can be plugged into, or otherwise coupled, to the output port via a wire or cable.

The hand-held unit preferably comprises a processor, memory, a power source and a display means. The processor is configured to receive and process the data from the processing module of the device, and to convert the strain data into a corresponding load measurement via pre-calibration data stored in the memory of the hand-held unit. The load measurements are preferably displayed on a LCD or TFT screen or similar visual display means. In this way, the loading of the device can be conveyed to an operator either as a numerical value (e.g. the exact load in newtons or a % load etc.) or via some form of graphical display, e.g. graph or bar chart or coloured sequence etc. Indeed, any suitable form of data presentation may be used to indicate the loading of the device.

The hand-held unit preferably contains all of the necessary software for interrogating the data processing module and for receiving the resistance/strain data. Depending on the implementation, the hand-held unit may also comprise a capacitor amplifier and signal conditioner to ensure clear and reliable (i.e. error free) communications between the hand-held device and the data processing unit. In other exemplary embodiments, the external device may be a transceiver that is preferably plugged directly into, or otherwise coupled, to the output port of the device. In this way, data concerning the detected changes in resistance, and correspondingly the strain, may be obtained from the processing module of the device via wireless communications, such as WiFi, Bluetooth or a cellular telecommunications network. Moreover, the transceiver may also be configured to provide a text based message, such as a SMS type message providing information relating to the current degree of loading of the device. It is to be appreciated that any suitable transceiver may be used in conjunction with the present invention.

The wireless communications embodiments are particularly advantageous in environments where direct inspection of the device is difficult or hazardous to an operator. Therefore, the transceiver permits the load to be determined while remaining remote from the device. Indeed, the transceiver may be configured to send information to an operator’s personal computer or laptop, which is physically isolated from the location of the device and/or installation site.

In some embodiments, the transceiver may be permanently connected to the device, while in other arrangements, the transceiver may be connected to the device only while data is being downloaded. Therefore, as will be appreciated, the device may not only be configured to provide information regarding the loading of the device during initial tightening of the joint or mechanical assemblies, by may also serve as a long-term monitoring system by being able to provide periodic updates or warnings to a personal computer, central server or smart phone etc. to thereby notify an operator that attention is required for a particular mechanical assembly or group of assemblies that may require re-tightening of the fasteners.

The device may further comprise a cover portion that at least partially encloses the body portion, and most preferably completely encloses the body portion. The cover portion serves to prevent the ingress of dust or other undesirable contaminants into the device. In exemplary embodiments, the cover portion is configured to hermetically seal the device for full environmental protection.

In the above embodiments, the device may advantageously be reused many times for different mechanical assemblies. Therefore, the present device can be recycled and/or retro-fit as required.

The device may preferably be heat treated during fabrication to improve the performance of the device. Moreover, the sealed device may also be covered with a plastic or plastics material coating, such as nylon, to prevent or inhibit corrosion over time. Of course, any suitable coating or material may be used in conjunction with the device of the present invention depending on the particular application.

It is to be appreciated in the present invention that the dimensions of the device can be fabricated according to any desired shape or size, and that by carefully selecting the type of material and resilience of the material the device can be optimised to deform by any amount according to any required compression. Therefore, the load-indicating device of the present invention can be used in numerous mechanical applications and can be scaled to whatever size the particular application requires.

The present invention also provides a system for load determination, the system comprising: a load indicating device according to any of the preceding embodiments; and an external monitoring device in the form of a hand-held unit, wherein the external monitoring device is removably connectable to the load indicating device. The present invention further provides a system for load determination, the system comprising: a load indicating device according to any of the preceding embodiments; and a transceiver, wherein the transceiver is removably connectable to the load indicating device and is operable to remotely communicate data relating to the load on the device. It is to be appreciated that none of the aspects or embodiments described in relation to the present invention are mutually exclusive, and therefore the features and functionality of one aspect and/or embodiment may be used interchangeably or additionally with the features and functionality of any other aspect and/or embodiment without limitation.

Embodiments of the present invention will now be described in detail by way of example and with reference to the accompanying drawings in which: Figure 1 - shows a side cross-sectional view of a load indicating device according to a preferred embodiment;

Figure 2 - shows a top perspective view of an exemplary load indicating device, without its cover, according to the present invention;

Figure 3 - shows a top perspective view of the exemplary load indicating device of Figure 2, with its cover; Figure 4 - shows a side cross-sectional view of a load indicating device according to a preferred embodiment of the present invention; Figure 5 - shows a side cross-sectional view of a load indicating device and example hand-held unit according to another embodiment of the present invention;

Figure 6 - shows a side cross-sectional view of a load indicating device according to another embodiment of the present invention;

Figure 7a - shows a top perspective view of an exemplary load indicating device, with its cover, according to the present invention;

Figure 7b - shows a schematic of an example load indicating device, illustrating a preferred orientation of the respective axes of the device;

Figure 8 (Table 1) - shows a table of specification data together with Tension, Vibration and Temperature data for a preferred example of the load indicating device of the present invention;

Figure 9 (Table 2) - shows a table of example size data for a range of load indicating devices of the present invention;

Figure 10 (Table 3) - shows a table of specification data for another preferred example of the load indicating device of the present invention;

Figure 11 (Table 4) - shows a table of specification data for example transmitter types for use with the load indicating device of the present invention;

Figure 12 - shows a schematic of an example pin configuration for the output port of the load indicating device, together with a specification data for the pins; Figure 13 (Table 5) - shows a table of ModBus Protocols-Register description for use with the load indicating device of the present invention;

Figure 14 (Table 6) - shows a table of ASCII Protocol-Command description for use with the load indicating device of the present invention. Referring to Figure 1, there is a shown a preferred embodiment of a load indicating device 10 according to the present invention. The device 10 is shown in use in a typical situation, namely ‘sandwiched’ between a mechanical support la and an overlying conventional nut 2a on threaded stud 3a. In this embodiment, the device 10 undergoes tensioning by tightening the nut 2a, which thereby causes compression of the device.

It is to be understood that the device 10 as shown in Figure 1 is not drawn to any particular scale and therefore the figure is intended for illustrative purposes only.

Referring to Figure 2, there is shown an exemplary embodiment of a device 10 according to the present invention. The device 10 comprises a body portion 12 in the form of a washer, which defines a bore 12a extending therethrough. The bore 12a is configured to receive a stud or bolt etc. In this embodiment, the body portion 12 is cylindrical in shape and resembles a flattened circular disk with an outer edge of the disk comprising a circumferential recess 12b.

The device 10 further comprises two electrical conductors in the form of deformable wires 14a, 14b that are disposed within the recess 12b. The wires 14a, 14b extend completely around the circumference of the body portion 12 and are secured to the body portion 12, such that compression of the body portion 12 causes the wires 14a, 14b to deform. As a result, when the wires 14a 14b are deformed, their electrical resistances vary due to the physical change in the dimensions of the wires. Therefore, as the body portion 12 is compressed, the wires 14a, 14b are consequently (reversibly) squashed and/or stretched in length, leading to corresponding measurable changes in the resistances of the wires.

As shown in Figure 2, the wires 14a, 14b are wrapped around the body portion 12 as single loops of wire, insulated from each other. The device 10 further comprises a processing module 16 coupled to the wires 14a, 14b, which is operable to determine changes in the resistances of the wires 14a, 14b. The processing module 16 comprises a sensor 16a in electrical communication with the wires 14a, 14b, with the sensor 16a being configured to detect changes in resistance.

The processing module 16 comprises a processor in communication with the sensor 16a. The processor is in the form of a microprocessing unit 16b comprising a bespoke semiconductor chip configured to determine the strain on the wires 14a, 14b (in response to compression of the body portion 12). The strain can be determined by measuring the changes in the resistances of the wires 14a, 14b (via appropriate calibration), which in turn can be converted into a corresponding load (again via calculation from calibration results). Therefore, the processing module 16, wires 14a, 14b and sensor 16a effectively act as an integral “strain gauge” from which the load on the device 10 can be calculated.

In practice, the device 10 is calibrated using standardised load cells during manufacture (e.g. certified to British or other national standards). The measured changes in resistances of the wires are calibrated against the corresponding strain using established mathematical relations (e.g. Hooke’s Law and Poisson’s Ratio) in order to establish a resistance/strain relationship for the device. The load may then be readily calculated from the determined strain in order to accurately ascertain the load on the device. Therefore, the device of the present invention electronically measures the strain on the wires and converts the measurements into corresponding load information.

Referring to Figure 2 again, the processing module 16 further comprises an output port 16c. The output port 16c is configured to provide data to an external device that can be inserted into or otherwise connected to the port 16c. Therefore, data concerning the detected changes in resistance, and correspondingly the strain, may be obtained directly from the processing module 16 of the device 10 (as described in more detail below).

As shown in Figure 3, the device 10 further comprises a cover portion 18 into which the body portion 12 can be inserted. The cover portion 18 completely encloses the body portion 12 to prevent the ingress of dust or other undesirable contaminants into the device 12. The cover portion 18 can be configured to hermetically seal the device 10 for full environmental protection.

Referring to Figure 4, there is shown another example of a typical use of the device 10, in which the device 10 is sandwiched between a bolt head 20a and a mechanical structure 20b. The arrangement of Figure 4 is placed under compression by tightening nut 20c. In this example, an external device in the form of a transceiver 22 is plugged directly into the output port 16c of the device 10. In this way, data concerning the detected changes in the resistances of the wires 14a, 14b, and correspondingly the strain, may be obtained from the processing module 16 of the device 10 via wireless communications, such as WiFi, Bluetooth or a cellular telecommunications network.

The wireless communication embodiment of Figure 4 is particularly advantageous in environments where direct inspection of the device 10 is difficult or hazardous to an operator. Therefore, the transceiver 22 permits the load to be determined while remaining remote from the device 10. Indeed, the transceiver 22 may be configured to send information to an operator’s personal computer or laptop, which is physically isolated from the location of the device and/or installation site (not shown).

The transceiver 22 comprises its own integral power source, which in addition to providing power to the transceiver 22, also provides power to the processing module 16 via output port 16c. The power source can be a rechargeable cell or battery. The transceiver 22 can be configured to reside in a “sleep” mode and to periodically “wake” in order to transmit resistance/strain data to a remote operator etc. Alternatively, the transceiver 22 can remain permanently powered, so as to provide continuous monitoring of the load condition. The processing module 16 may also have its own separate power source depending on the implementation. Once powered, the processing module 16 is able to provide power to the sensor and may provide an applied voltage to the wires 14a, 14b depending on the type of sensor being used.

In an alternative example, as shown in Figure 5, the external device is a hand-held unit 24 that can be removably plugged into the output port 16c via a wire or cable 26. The hand-held unit 24 comprises a processor, memory, a power source and a display means. The processor is configured to receive and process the data from the processing module 16 of the device 10, and to convert the strain data into a corresponding load measurement via pre-calibration data stored in the memory of the hand-held unit 24. The load measurements are displayed on a LCD screen 24a. In this way, the loading of the device 10 can be conveyed to an operator either as a numerical value (e.g. the exact load in newtons or a % load etc.) or via some form of graphical display. The hand-held unit 24 contains all of the necessary software for interrogating the processing module 16 and for receiving the resistance/strain data. Depending on the implementation, the hand-held unit 24 may also comprise a capacitor amplifier and signal conditioner to ensure clear and reliable (i.e. error free) communications between the hand-held device 24 and the processing module 16.

The power source in the hand-held unit 24 is typically a cell or battery. The power source provides electrical power to the processing module 16 upon insertion of the wire or cable 26 into the output port 16c of the processing module 16. Therefore, the device 10 need not be permanently powered, but instead can be “wakened” when the hand-held unit 24 is connected to the device 10. Thereafter, the device 10 can be configured to enter a “sleep” mode after the hand-held unit (i.e. power source) is removed. Alternatively, in other examples, the device 10 itself may comprise an integral power source, which can be a rechargeable cell or battery, in order to provide power to the processing module 16.

In other preferred embodiments, the device 10 may actually be incorporated into a nut 30 as an integral component, as shown in Figure 6. Therefore, unlike the preceding examples in which the device 10 is implemented as a separate washer, the device 10 may form part of the nut 30 itself. The nut example of the device 10 operates in exactly the same fashion as in the above examples, therefore as the nut 30 is tightened on the bolt 32, the body portion of the device 10 is compressed thereby causing variations in the resistances of the wires. The changes in resistance can then be mapped to corresponding strain values, which in turn can be converted into an accurate determination of load.

Figure 7a shows another example of the device 10 with the output port 16c clearly shown. The cover portion 18 into which the body portion 12 is inserted is also shown in this figure. The cover portion 18 completely encloses the body portion 12 to prevent the ingress of dust or other undesirable contaminants into the device 12. As mentioned previously, the cover portion 18 can be configured to hermetically seal the device 10 for full environmental protection. As shown in Figure 7a, the output port 16c is threaded to enable the secure attachment of a connecting wire or an external device in the form of a transceiver 22 (not shown).

In Figure 7b, there is shown a schematic view of an example load indicating device according to the present invention. The schematic illustrates the preferred orientation of the respective Cartesian axes of the device, with the z-axis being perpendicular to the body of the device (e.g. to the body of the washer) and as such would extend upwardly out of the page in this example. The x- and y-axes all mutually orthogonal to each other and to the z-axis. These axes define the directions along which the vibrations may be sensed in and around the device in 3-dimensions to enable vibration compensation to be accurately applied.

A typical example of the specification of a load-indicating device according to the present invention is disclosed in Figure 8 - Table 1. In Table 1, the typical operating parameters are shown, as well as information relating to the tension, vibration and temperature sensing functionalities of the device. Therefore, as indicated, the typical operating voltage of the device is in the range of 8-28V DC (for a wired connectivity device), while the device can operate over a temperature range -20°C to +85°C with an accuracy of ±0.5°C. In terms of communicating data, the device may use a communication interface according to RS485 (serial), ModBus or ASCII protocols. However, other communication protocols may also be used. For RS485 communication, the typical maximum cable length (for wired connectivity) is around 1000m (1 km). As shown in Table 1, the tension (or load) can be measured with an accuracy of ±2% FS over a temperature compensation range of -20°C to +65°C. Likewise, vibration measurements can be obtained with an accuracy of ±2% FS with a resolution of mm/sec. Table 2 of Figure 9 shows the typical loading of a device according to the present invention. In this case, the device is in the form of a compressible washer having a size range from M20 to M52 (NB: sizes of up to M64 can also be achieved, but are not shown in this table). Columns 4 and 7 respectively indicate the Stress Area (in mm ² ) and the Maximum Load Metric Tonne 70% Yield for the same washer thickness of 10 mm. Such data is used to form part of the pre-calibrated data for temperature, vibration and speed of tightening compensation, which have been discussed previously. Of course, this data can be adapted accordingly for different washer sizes and thicknesses.

Following on from Table 1 of Figure 8, Table 3 of Figure 10 also shows specification data for a load-indicating device according to the present invention. In this example, the load-indicating device has wireless connectivity with the Sensor Range being typically 0-120% of the Load and Sensor Resolution of 0.1% of the Load. Typical power consumption at a 3.6V is 2.5mA.

The operating voltages of the device are generally lower for the wireless connectivity variants, which as shown in Table 4 of Figure 11 are around 3.3V ± 10% for the NB-IoT and LoRa (wireless) devices. There are many options for the transceiver in the present invention, but preferred examples include the standard transmitters of 4-20mA, ModBus (over RS485), NB- IoT and LoRa, the latter two being wireless transmitter protocols. For the wired configurations, only a single wire or cable is required to communicate with and/or interrogate the device. An example specification data is shown in Table 4 of Figure 11 for each of the four example transmitter types.

An example pin configuration for the output port of the device is shown schematically in Figure 12. In this example, the pin is arranged for use with the ModBus communication protocols, which are employed to convey the load measurements to a remote computing device, e.g. the operator’s laptop etc. The device uses a RS485 serial link with typical settings of Baud Rate: 9600, Parity: None; and Data: 8 bits. The ModBus address of the device is fixed at 1 and the load measurements are obtained by reading an Input Register (command 0x04) at address 0x00 (ModBus address 0x01). The returned values are float with a length of 2 words. As shown in Figure 12, the output port is wired with PINs 1 and 3 providing power (Power Supply and GND, respectively) with data communication on PINs 2 and 4.

An example of the ModBus Protocol-Register description used with the load-indicating device is shown in Table 5 of Figure 13.

In other examples, an ASCII protocol may alternatively be used with the load-indicating device. In this case, commands are sent over the serial connection as a data string, which can be interpreted accordingly by the processor module in the device. An example of the ASCII Protocol- Command description used with the load-indicating device is shown in Table 6 of Figure 14.

It should be appreciated that Tables 1-6 relate to specific examples of the load-indicating device and thus are not intended to be exhaustive or otherwise limiting in their teaching. Instead, the present device is inherently scalable and can be adapted for any particular loading use and/or communication protocols depending on the required application.

Indeed, as will be appreciated from the foregoing embodiments, the present invention is able to provide an improved, easy to fit, and cost-effective means of indicating accurate loading of a mechanical assembly. No modification to existing fastening components is required for use with the present invention (except for the example of the device when integrated in a nut). In addition, the present device can be operated without specialist training or experience. Moreover, although the present device is ideally suited for ensuring a reliable and consistent tensioning of fastening components, it will be recognised that one or more of the principles of the invention may extend to other fastening or securing applications, whereby it is required to tension or load a mechanical connection to an accurate predetermined value or tolerance. In particular, the present device may also find use with domestic and/or commercial wheel studs in which incorrectly tightened wheel nuts may result in wheels becoming detached during motion thereby leading to vehicle damage and/or driver injury.

The above embodiments are described by way of example only. Many variations are possible without departing from the invention.