Bolt sensor assembly

A bolt sensor assembly provides a body adapted for insertion into a hole in a component, the body having a first end and a second end, and a longitudinal axis extending therebetween. The first end includes an attachment means for attachment of the bolt sensor assembly to the component, and the second end mounts a sensor element, such as a strain gauge element. The sensor element is movable with respect to the body in the direction of the longitudinal axis of the body and the sensor element is constrained against rotation about the longitudinal axis with respect to the body.

This application is the U.S. National Stage of International Application No. PCT/EP2014/074737 filed on Nov. 17, 2014, which claims the benefit of priority from Great Britain Patent Application No. 1320282.5 filed on Nov. 18, 2013, the contents of which are both herein incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to mounting of sensor elements, and in particular to sensor elements mountable in a threaded hole.

BACKGROUND OF THE INVENTION

In certain machines it is desirable to be able to measure the load on internal components of the machine. For example, in a wind turbine it is desirable to be able to measure the load on certain bearings.

Many different load measurement devices are available, but often at least a certain amount of disassembly of the wind turbine is required in order to gain access to the bearing.

One possibility for mounting a sensor to measure a load on a bearing is to drill a hole through a part of the component in which the bearing is housed and mount a sensor in that hole. Alternatively, a hole that is present in the component may provide a suitable location to mount a sensor, for example a hole that receives a bolt which is used to remove the bearing from the component may be used.

Strain gauge sensors which can be mounted in holes are well known.

One such strain gauge is described in U.S. Pat. No. 2,873,341. This strain gauge comprises a bolt having a central bore in which is mounted an epoxy core with a resistance wire is embedded therein.

The bolt strain gauge described in U.S. Pat. No. 2,873,341 has the strain measuring element in the centre of the bolt, which is not ideal for measuring strain in a component situated at the end of the bolt.

A more suitable form of strain sensor is a friction strain sensor. Such strain sensors are used in many applications. Such friction strain gauges must be pre-loaded to a certain extent in order to function. Furthermore, friction strain gauges are very sensitive to damage, for example when subject to shear forces. Friction strain gauges are described in general terms in GB 2,367,628.

There seems to be room for improvement.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a bolt sensor assembly comprising a body adapted for insertion into a hole in a component. The body has a first end and a second end, and a longitudinal axis extending therebetween, wherein the first end includes an attachment means for attachment of the bolt sensor assembly to the component. The second end mounts a sensor element and the sensor element is movable with respect to the body in the direction of the longitudinal axis of the body. The sensor element is further constrained against rotation about the longitudinal axis with respect to the body.

The body is preferably rotatable about the longitudinal axis to engage and disengage the body from the hole. The body may include a threaded portion for engagement with a correspondingly threaded portion of the hole.

Suitably at least a part of the body comprises the second end and the hole are provided with cooperating elements which prevent relative rotation therebetween, and wherein the sensor element is biased to project from said second end of the body. The attachment means then may comprise a collar that is slidably mounted on the body or the attachment means may be mounted on the body for relative rotation therebetween. Suitably a biasing element may be comprised located between the body and the attachment means, the biasing element configured to urge the body and the attachment means in opposite directions along the longitudinal axis. The sensor element may also be comprised in a sensor assembly, which assembly is mounted at the second end of the body, the assembly comprising a base including an opening in which the sensor element is slidably mounted, a reaction member and a biasing means situated between the sensor element and the reaction member. The sensor assembly may further include a mount to which the sensor element is attached and wherein the biasing mean is situated between the mount and the reaction member.

The sensor element may be movable between a first position and a second position. In the first position the sensor element lying behind the second end of the body and in the second position at least a part of the sensor element lying proud of the second end of the body. The bolt sensor assembly may further comprise an actuator adapted to move the sensor element between the first and second positions. The body may include a bore and the actuator then acts on the sensor element through the bore. The sensor element may be mounted on a shaft, and the actuator then engages the shaft. The bolt sensor assembly may further comprise biasing means arranged to exert a force on the sensor element biasing it into the second position. The end of the body in which the sensor element mounted may be configured such that the sensor element is constrained against rotation with respect to the body about the longitudinal axis. The second end of the body may comprise a cap removably attachable to the remainder of the body, the sensor element is then mounted in the cap.

Suitably the sensor element is one or more of an acoustic emission sensor, a vibration sensor, a strain gauge sensor, a friction strain gauge sensor, and a temperature sensor.

According to a second aspect of the invention there is provided a friction strain gauge sensor comprising a body adapted for insertion into a hole in a component, the body having a first end and a second end, and a longitudinal axis extending therebetween, wherein the first end includes an attachment means for attachment of the sensor to the component, wherein the second end mounts a friction strain gauge element and wherein the friction strain gauge element is movable with respect to the body in the direction of the longitudinal axis of the body and wherein the friction strain gauge element is constrained against rotation about the longitudinal axis with respect to the body.

Preferably, at least a part of the body is rotatable about the longitudinal axis to engage and disengage the body from the hole.

The body may include a threaded portion for engagement with a correspondingly threaded portion of the hole.

The body may include a hollow portion, preferably extending from one of the first and second ends.

Advantageously, at least a part of the body comprising the second end and the hole are provided with cooperating elements which prevent relative rotation therebetween, such as a recess and a protrusion engaging the recess. Part of the body may include a rib and the hole may include a recess for receiving the rib.

Preferably the friction strain sensor element is biased to project from said second end of the body.

The attachment means may be slidably mounted on the body and may comprise a collar that is slidably mounted on the body.

The attachment means may be mounted on the body for relative rotation therebetween. The attachment means may comprise a threaded portion for engaging a correspondingly threaded portion of the hole, and the threaded portion may be part of the collar.

The friction strain gauge sensor may further comprise a biasing element located between the body and the attachment means, the biasing element configured to urge the body and the attachment means in opposite directions along the longitudinal axis. The biasing element may be a spring, such as a coil spring.

The body may include a shaft portion of reduced diameter, the biasing element and the attachment means being mounted on the shaft portion.

The body may include an attachment means retaining portion, the retaining portion limiting movement of the attachment means relative to the body.

The friction strain sensor element may be comprised in a friction strain sensor assembly, which assembly is mounted at the second end of the body, the assembly comprising a base including an opening in which the friction strain sensor element is slidably mounted, a reaction member and a biasing means situated between the friction strain sensor element and the reaction member.

The friction strain sensor assembly may further include arms configured for engagement with recesses formed in an inner wall of the body. The arms may be printed circuit boards. The arms may be attached to the base, for example by brackets.

Preferably, the friction strain sensor assembly further includes a mount to which the friction strain sensor element is attached and wherein the biasing means is situated between the mount and the reaction member.

Advantageously, the base is mounted on pins which are slidingly engaged with holes in reaction member. Biasing elements may be provided between the reaction member and the base to urge the base in the longitudinal direction of the body and away from the reaction member. The biasing means may be springs mounted on the pins.

The reaction member is preferably a bridge extending across a hollow portion of the body.

Advantageously, the friction strain sensor element is movable between a first position and a second position, in the first position the friction strain sensor element lying behind the second end of the body and in the second position at least a part of the friction strain sensor element lying proud of the second end of the body, the sensor further comprising an actuator adapted to move the friction strain sensor element between the first and second positions.

The body may include a bore and the actuator may act on the friction strain sensor element through the bore.

Preferably, the friction strain sensor element is mounted on a shaft, and the actuator engages the shaft. The shaft may comprise a collar, the collar configured to constrain the shaft against rotation.

The friction strain gauge may further comprise biasing means arranged to exert a force on the friction strain sensor element biasing it into the second position.

The end of the body in which the friction strain sensor element is mounted may be configured such that the friction strain sensor element is constrained against rotation with respect to the body about the longitudinal axis.

The second end of the body may comprise a cap removably attachable to the remainder of the body, the friction strain sensor element mounted in the cap.

The second end of the body is provided with a seal. The seal may be an O-ring seal. The purpose of the seal is to prevent ingress of contaminants to the area of the friction strain sensor element.

The friction strain gauge sensor may mount other sensors such as, but not limited to, acoustic emission sensors, vibration sensors, temperature sensors.

A second aspect of the invention provides a friction strain gauge sensor according to the first aspect of the invention mounted in a hole in a first component, and the friction strain gauge sensor element engaging a second component.

Other preferred features of the invention can be found in the detailed description of the preferred embodiments.

DETAILED DESCRIPTION

Referring now toFIGS. 1 to 4, there is shown a bolt sensor1comprising a bolt member2, and a sensor housing10.

The bolt member2includes a hexagonal head3and a threaded collar4. Referring in particular toFIG. 4, it can be seen that a bore5extends axially through the bolt member2, the bore5providing two bore sections5aand5b, each of a different diameter.

The sensor housing10comprises a hollow portion11, a shaft portion12and a head13. The shaft portion12is of smaller diameter than the hollow portion11providing a radially extending rim where the hollow portion11meets the shaft portion12. The head13is attached to the end of the shaft portion12after the bolt member2has been mounted on the shaft portion12.

A spring15is also mounted on the shaft portion12, between the bolt member2and the hollow portion11. One end of the spring15abuts the rim14. The other end of the spring15is engaged by the end face4aof the threaded collar4.

The shaft portion12passes through and is slidably mounted in the bore section5b, with the head13being located in the bore section5a. The spring15therefore urges the sensor housing away from the bolt member2, the extent of relative movement between the two components being limited by the head13situated in the first bore section5a.

By mounting the bolt member2and the spring15on the shaft portion12, as the bolt member is tightened the spring exerts a force on the housing10. The head13retains the housing10in the bolt member2.

FIGS. 2 and 3illustrate a sensor assembly20, such as a friction strain gauge assembly, comprising a base21, which is circular in the example, and extending from the base21a pair of arms22connected together at their ends distal from the base by a connector element23. The arms22are printed circuit boards are connected to the base plate by brackets40each including a tab41which attaches to one of the arms. One of the brackets40may suitably mount a vibration and temperature sensor43and the other may mount an AE sensor44.

The base21includes an aperture24, which is rectangular in the illustrated example, and which is configured to receive the sensor element30, such as a friction strain gauge, strain gauge, vibration or other type of sensor, as will be described in greater detail below. Two small holes25are situated to either side of the aperture24. The holes25each receive a pin26. The pins26each comprise a pin head26aand a pin shaft26b. The end of the pin shaft26bdistal from the pin head26asits in one of the holes25. In the present example, the holes25and the ends of the pin shafts26bare provided with corresponding threads to secure the pins26to the base21.

A spring27is mounted on the pin shaft26b. The function of the spring will be described in greater detail below with reference toFIGS. 4, 5, 9 and 9a.

The friction strain sensor element30forms part of the friction strain sensor assembly20. The friction strain sensor assembly includes a plate31which mounts a pin32, the pin32fixed to the plate31, a spring33and a bridge35extending from one side of the hollow portion11to the other. The bridge35includes holes38through which the pin shafts26bpass. The pin shafts26bmay slide in the holes38, the pin heads26aproviding an end stop to movement of the pins26and hence the base21.

The underside of the bridge35comprises a central spigot36, with recesses37to either side. One end of the spring33sits in the recesses37. The other end of the spring33engages with the plate31, sitting in an annular recess31aand receiving the pin32. The end32aof the pin32is attached to the friction strain sensor element30.

The friction strain sensor assembly20is inserted into the hollow portion11of the sensor housing10without the cross-member23in place. The arms22engage in slots39in the inner wall of hollow portion11and may slide therein. The cross-member23is attached to the arms22, by soldering from example, post insertion of the friction strain sensor assembly20into the hollow portion. Cross-member23in some embodiments may be omitted. The mounting of arms22in slots39assists in resisting rotational forces experienced by the base plate21.

The base21is slidable into and out of the hollow portion11, this securing the friction strain sensor assembly20in the hollow portion11, sliding of the base21out of the hollow portion11being constrained by the pin heads26acoming into engagement with the surface of the bridge35.

The lower edge of the hollow portion11is provided with a rebate11ain which a seal50sits. The hollow portion also includes on its outer surface a protrusion, which in the present example is a rib11b.

Referring toFIGS. 3 and 6in particular, it can be seen that the plate31includes curved recesses31binto which the springs27extend.

FIGS. 7 and 8illustrates a component60having a bolt sensor1mounted therein. The component60includes a bore61which has a recess62in the wall thereof. The bolt sensor1is aligned with the bore61such that the rib11bis aligned with the recess62.

The friction strain sensor assembly functions as follows:

The springs27exert a force urging the base plate21out of the hollow portion11, this movement limited by abutment of the underside of pin heads26awith the top surface of the bridge35. The spring33pushes the plate31away from the bridge35, which acts as a reaction member, and hence urges the friction strain sensor element30out of the aperture24. The rectangular shape of the aperture24and the friction strain sensor element30constrain the friction strain sensor element to reciprocal movement in the axial direction of the hollow portion11.

The spring33is specified such that the friction strain sensor element30is urged against a surface engaged by the lower surface of the base plate21with a pre-determined force on the friction strain sensor element30when the bolt sensor1is in place.

Hence, when a bolt sensor1is introduced into a bore61, as the bolt head3is rotated base plate21comes into abutment with a surface of a component adjacent the end of the bore61, and further rotation of the bolt head causes the base plate21to slide into the hollow portion11, compressing the springs27and the seal50.

As the base plate21slides into the hollow portion21, the friction strain sensor element30moves closer to the surface of the component adjacent the end of the bore61and is urged against the said surface by the spring33.

When the bolt sensor is released from the bore61the reverse occurs.

The seal50prevents ingress of lubricant or contaminants to the region immediately surrounding the friction strain sensor element30.

The base21therefore protects the sensitive sensor element30, as the sensor element30sits behind the surface of the base plate21, until the base plate21engages a surface that is to be instrumented by the sensor element30.

An antenna52is mounted in a collar51that sits in the head3of the bolt member2. The antenna52is powered by a power connector53, which includes a cap54and a socket55. The friction strain sensor30, the AE sensor and the vibration and temperature sensors may communicate with the antenna wirelessly, or may be connected by wires. The antenna52may relay information wirelessly.

A second embodiment of the invention is illustrated inFIGS. 10 to 13. In this embodiment, shear forces on the friction strain sensor element are avoided by positioning the friction strain sensor element so that it may be moved to engage the component to be monitored by moving the friction strain sensor element along the axis of the bolt, after the bolt has been positioned in the hole, when the bolt is stationary, thereby avoiding shear forces acting on the friction strain sensor element30.

The bolt sensor100comprises a bolt member101including a threaded collar102and a hexagonal head103. A elongate portion104extends from and is attached to the end of the collar102. The elongate portion104includes a central bore105and two threaded holes106situated to either side of the central bore105and extending into the free end of the elongate portion104.

An end cap107attaches to the free end of the elongate portion104by means of screws108. The end cap107includes screw head seats111and holes112, which are aligned with the holes106, with a shank109of one of the screws108passing through a hole112and engaging with a hole106until the screw's head110is seated in the screw head seat111.

The end of the cap107that abuts the end of the elongate portion104includes a channel115and a bore116, which aligns with the central bore105.

A friction strain sensor element assembly130includes a mount131mounting a friction strain sensor element131a, and a shaft132. The shaft132includes a collar133extending around the shaft132and fast with respect to the shaft132, and a spring134. The shaft132is attached to the friction strain sensor element mount131such that the axial movement of the shaft132causes axial movement of the mount131.

The shaft132sits in the bore116, with the collar133situated in the channel115, the flat sides of the collar engaging the parallel walls of the channel115, thereby preventing rotation of the shaft132. The bore116is smaller in diameter than the spring134, the spring134engaging the wall immediately around the bore116, thereby urging the mount131axially out of end cap107.

An actuating thumb screw140is mounted in the central bore105. One end141of the thumb screw140is configured to attach releasably to the shaft132. The end141of the thumb screw includes an internally threaded bore, and the shaft132is threaded externally between the free end of the shaft proximate the thumb screw140and the collar133. By rotating the thumb screw140the corresponding threads of the shaft132and thumb screw140cause the shaft132and hence the friction strain sensor element assembly130to move in the axial direction of the thumb screw140. Rotating the thumb screw140in one direction causes the shaft132and hence the mount131and frictions sensor element131ato retract into the channel135compressing the spring134. The mount131is most retracted when the collar133engages the end141of the thumb screw140.

Rotating the thumb screw140in the other direction causes the mount131and friction sensor element131ato move axially in a direction out of the channel135so that the friction sensor element131aengages a component facing the end of the end cap107.

A hole150accommodates a cable that attaches to the friction strain sensor131a.

Before introducing the bolt sensor100into a hole, the thumb screw is rotated to draw the friction strain sensor mount131into the channel135such that the friction strain sensor element131alies behind the end face of the bolt cap107. The bolt sensor100is introduced into a hole and turned until the end of the end cap107is in abutment with the surface of a component to be monitored. The thumb screw140is then turned in the opposite direction which moves the mount131and friction sensor element131atoward the component to be monitored. The force of the spring134pushes the friction strain sensor element131ainto engagement with the surface of the component to be monitored.

Both illustrated embodiments of the invention provide a bolt sensor utilising a friction strain sensor element, which is desirable, and prevent the friction strain sensor element from being subjected to the kind of forces which are likely to damage it.

In both embodiments, the springs urging the friction strain sensor element against the component being monitored ensure that the friction strain sensor element is subjected to the required load for operation of the friction strain sensor element.

Individual technical features of the illustrated embodiments are not limited to use in those embodiments, and may where suitable, be used with any embodiment falling within the scope of the claims.