FIELD OF THE INVENTION

The invention relates to an apparatus with a preload sensor for sensing a preload experienced by a component of the apparatus. The invention also relates to a preload sensor, and a method of generating a signal representative of a preload experienced by a component of the apparatus.

BACKGROUND ART

The performance and service life of a mechanical apparatus often depends on having the components of the apparatus mounted together under a pre-specified preload. That is, a first one of the components and a second one of the components are mounted so that they press against one another, either directly or indirectly via one or more intermediate other components. For example, bolts and nuts are to be set to a specific torque when mounting a cylinder head of an internal combustion engine to the engine block in order to prevent warping of the cylinder head and leakage. As another example, angular contact ball bearings, taper roller bearings and thrust bearings are mounted under a preload for best performance. JP02-164241 discloses a part of an apparatus having a first angular contact ball bearing and a second angular contact ball bearing coaxially mounted for supporting a rotating shaft. A spacer ring is mounted between the outer ring of the first angular contact ball bearing and an outer ring of the second angular contact ball bearing. A ring nut is used to axially preload the first and second angular contact ball bearings. The outer surface of the spacer ring has an axial groove accommodating a strain gauge for detecting the amount of preload. The pre-load causes a strain in the spacer ring, which is subjected to the same amount of preload. The strain corresponds to the elastic modulus and dimension of the spacer ring. The strain is detected by the strain gauge. SUMMARY OF THE INVENTION

The invention relates an apparatus comprising a first component and a second component that are mounted together under a first preload. For example, the first and second components are mounted directly on top of each other and bolted together. Alternatively, one or more intermediate components are mounted between the first component and the second component. The apparatus has a preload sensor, operative to generate a signal representative of the first preload. The preload sensor is mounted between the first component and the second component under a second preload. The second preload is exerted on the preload sensor via the first component and second component. The preload sensor comprises a main body and an ancillary portion that together form an elastically telescoping arrangement between the first component and the second component. The main body has a first stiffness, and the ancillary portion has a second stiffness lower than the first stiffness. The preload sensor is operative to generate the signal due to an elastic deformation of the main body.

The physical quantity "stiffness", as used herein, indicates a resistance of an elastic physical object to deformation as a result of an applied force or load. The stiffness is typically quantified by the ratio of the force representative of the load and the amount of deformation, e.g., a change of length or of width, as a result of the force applied. The stiffness of a physical object depends on the physical properties of the material (or: materials) of which the physical object is made, on the spatial configuration of the physical object, and generally also on the direction of the forces applied to the physical object.

The term "telescoping" refers to the configuration of the preload sensor, wherein the main body and the ancillary portion slide inward or outward of each other in overlapping sections. In the apparatus of the invention, the preload sensor has dual functionality. Before operational use of the apparatus, in a first phase, the preload sensor is mounted under a second preload in such a manner, that the main body of the telescoping arrangement coaxially fully overlaps the ancillary portion of the telescoping arrangement. In an unloaded condition, the ancillary portion extends beyond the main body by a predetermined amount. Under compression, the ancillary portion deforms elastically and becomes shorter until there is no longer any extension beyond the main body.

The preload sensor is initially mounted such that the ancillary portion is in contact with the first component and the main body is in contact with the second component. The ancillary portion is then compressed until the main body of the sensor makes contact with the first component. In other words, the main body is in contact with both the first and the second components and is mounted so as to experience a compressive force (second preload) between these components. The second preload, as sensed by the preload sensor, is indicative of the first preload with which the first and second components are mounted. If the first preload decreases or increases, the second preload decreases or increases as well. Monitoring the second preload by means of sensing deformation of the main body provides information about the first preload in this phase. The stiffness of the main body is relatively high, as a result of which a unit change in the deformation of the main body requires a large change in the second preload. The preload sensor then acts as a force sensor.

A second phase is reached when the first preload and, therefore, the second preload have decreased so far, that the main body does not fully axially overlap the ancillary portion anymore. In other words, only the ancillary portion is in contact with the first component. If the preload sensor were not equipped with the ancillary portion, the main body would no longer register any load when it ceases to be directly compressed between the first and second components. It would then be unclear to the operator whether the preload sensor was still operable or had become defective. What is more, the ancillary portion enables the main body in this second phase to still register a second preload, albeit a diminished one. The ancillary portion functions as a spring, which exerts a reaction force on the main body in the second phase. The reaction force is sufficient to maintain a compressive strain on the main body that is measurable, for example, by instrumenting the main body with one or more strain sensors.

In order to obtain a predictable and stable response of the preload sensor, the predetermined amount by which the ancillary portion extends beyond the main body is suitably limited to a maximum elastic deformation of the ancillary portion. This enables the main body to become directly compressed between the first and second components before plastic deformation of the ancillary portion occurs. Such plastic deformation would adversely affect the predictability of the reaction force exerted on the main body.

The reaction force, or diminished second preload, can further be associated with a displacement of the main body relative to the first component or the second component in the second phase. In effect, the preload sensor according to the invention acts as a displacement sensor in the second phase. This is due to the lower stiffness of the ancillary body, as a result of which a unit change in the deformation of the ancillary body is brought about by a relatively small change in the second preload. The workpoint of the preload sensor of the invention is set as follows. Consider a first parameter region, wherein the second preload is low. In the first parameter region, a change in the overall length of the telescopic arrangement is largely due to a deformation of the ancillary portion. Increasing the second preload causes an increased deformation of the ancillary portion, determined by the second stiffness. The operation of the telescopic arrangement enters a second parameter region, when the deformation of the telescopic arrangement has reached the stage, wherein the main body axially fully overlaps the deformed ancillary portion. In this second parameter region, a change in the overall length of the telescopic arrangement is due to a deformation of the main body. Accordingly, the deformation of the telescopic arrangement depends on the second preload, and this dependence changes dramatically in the transition from the first parameter region to the second parameter and vice versa. The workpoint is set in the second parameter region, and more or less close to the transition from the second parameter region to the first parameter region, depending on the desired accuracy required from the preload sensor. In an embodiment of the apparatus of the invention, the main body of the preload sensor has a screw thread at an external surface of the main body, and the main body is screwed into a correspondingly threaded hole in the second component until the ancillary portion makes contact with the first component. The main body is then screwed in further until the ancillary portion has been compressed to an extent at which the main body is directly compressed between the first and second components. The screw connection between the main body and the second component enables to continuously vary the relative position of the main body with respect to the first component at installation of the preload sensor and, therefore, to accurately set the magnitude of the second preload for operational use of the preload sensor. During installation of the preload sensor, the installer varies the relative position of the main body with respect to the first component while monitoring the magnitude of the second preload. Thus, the installer can determine the proper workpoint of the preload sensor. After that, the position of the preload sensor can be fixed relative to the first component, using an adhesive or a lock nut, etc.

In an embodiment of the apparatus, the first stiffness of the main body is determined by a spatial configuration of the main body, wherein a first area of a first cross-section of the main body in a first plane, perpendicular to a direction of a telescoping action of the telescoping arrangement in operational use of the preload sensor, differs from a second area of a second cross-section of the main body in a second plane different from, and parallel to, the first plane. For example, the main body has a webbed configuration. A varying area of the cross-section implies that the local strain, e.g., pressure, in the material of the main body, as a result of the second preload, depends on the location in or at the main body. Different local pressures give rise to different local deformations of the main body, which can be measured by means of, e.g., strain gauges at those locations on the main body where significant deformation occur. The precise spatial configuration of the main body can be adapted to the magnitudes of the second preloads expected, the materials used in the main body, and the sensitivity of the strain gauges, etc.

In an embodiment of the apparatus, the main body is configured for telescoping into the ancillary portion. The ancillary portion may comprise one or more spring washers that determine the second stiffness. For example, in operational use of the preload sensor, the ancillary portion comprises a set of spring washers stacked coaxially around a nose piece of the main body. The ancillary portion is then an effective, but a very low-cost element, of the preload sensor. As another example, the ancillary portion comprises a helical spring positioned coaxially with, and around, the nose piece of the main body. Suitably, the second stiffness of the ancillary portion is selected so as to exert a measurable reaction force on the main body of the preload sensor.

In an embodiment of the apparatus, the ancillary portion is configured for telescoping into the main body. For example, the main body comprises a recess that accommodates the ancillary portion. The ancillary portion includes, for example, a helical spring or a piece of resilient material.

In an embodiment of the apparatus, at least the first component or the second component comprises at least part of a rolling element bearing. As known, an angular contact ball bearing, a taper rolling bearing, or a thrust bearing is typically installed under an axial preload exerted on the bearing's inner or outer ring. A loss of preload in operational use of the rolling element bearing can have disastrous consequences. The preload sensor in the invention is therefore a suitable, low- cost tool for a monitoring system that monitors changes in the preload of the rolling element bearing in operational use. Above embodiments of the invention are relevant to commercially exploiting the invention as an apparatus including the first and second components as well as the preload sensor. Commercial exploitation of the invention can also be based on manufacturing, using or providing a preload sensor suitable for use in the apparatus discussed above. The invention therefore also relates to a preload sensor configured for generating a signal in response to sensing a preload. The preload sensor comprises a main body and an ancillary portion. The main body and the ancillary portion together form an elastically telescoping arrangement. The main body has a first stiffness. The ancillary portion has a second stiffness lower than the first stiffness. The preload sensor is operative to generate the signal due to an elastic deformation of the main body. In an embodiment of the preload sensor, the first stiffness of the main body is determined by a spatial configuration of the main body. A first area of a first cross- section of the main body in a first plane, perpendicular to a direction of a telescoping action of the telescoping arrangement in operational use of the preload sensor, differs from a second area of a second cross-section of the main body in a second plane different from, and parallel to, the first plane.

In an embodiment of the preload sensor, the main body has an external surface with a screw thread. In an embodiment of the preload sensor, the main body is configured for telescoping into the ancillary portion. The main body then has, for example, a nose piece, and the ancillary portion comprises at least one of a spring washer positioned around the nose piece; a plurality of spring washers stacked coaxially around the nose piece; and a helical spring positioned coaxially with, and around, the nose piece. In an embodiment of the preload sensor the ancillary portion is configured for telescoping into the main body. The main body may then have a recess for accommodating the ancillary portion. The ancillary portion includes, e.g., a helical spring, or a piece of resilient material.

The invention can also be commercially exploited as a method. The invention therefore also relates to a method of generating a signal representative of a first preload experienced by a first component and a second component that are mounted together in an apparatus. The method comprises using an elastically telescoping arrangement of a main body and an ancillary portion. The telescopic arrangement is mounted between the first component and the second component. The telescopic arrangement experiences a second preload exerted via the first component and the second component. The main body has a first stiffness, and the ancillary portion has a second stiffness lower than the first stiffness. The method further comprises generating the signal due to an elastic deformation of the main body.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in further detail, by way of example and with reference to the accompanying drawings, wherein:

Figs.1 , 2 and 3 are diagrams of a first embodiment of an apparatus in the invention;

Fig.4 is a graph explaining operation of a preload sensor in the invention;

Fig.5 is a diagram of an embodiment of a preload sensor n the invention;

Figs 6 and 7 are diagrams of a second embodiment of an apparatus in the invention; and

Fig.8 is a diagram of an example of an apparatus of the invention.

Throughout the drawings, similar or corresponding features are indicated by same reference numerals. DETAILED EMBODIMENTS

Figs.1 and 2 are diagrams of a first embodiment 100 of an apparatus in the invention, shown in cross-section. The first embodiment 100 comprises a first component 102 and a second component 104 that are mounted together under a first preload caused by external means, not shown here. The first embodiment 100 also comprises a preload sensor 130 operative to generate a signal representative of a first magnitude of the first preload. The preload sensor 130 is mounted between the first component 102 and the second component 104 under a second preload. The second preload is exerted on the preload sensor 130 via the first component 102 and the second component 104. The preload sensor 130 comprises a main body 132 and an ancillary portion 134. The main body 132 and the ancillary portion 134 are, at least partly, spatially coaxially overlapping so as to form a coaxially and elastically telescoping arrangement. The telescoping of the telescoping arrangement occurs in a direction as indicated by an arrow 131. The second preload is assumed to be a compressive preload as a result of the first component 102 and the second component 104 being pressed towards each other. The main body 132 has a first stiffness, and the ancillary portion 134 has a second stiffness lower than the first stiffness. That is, in order to achieve a unit of deformation, e.g., a unit of length, of the main body 132, a larger load is required than for obtaining a unit of deformation of the ancillary portion 134.

In the diagram of Fig.1 , the telescoping arrangement of the main body 132 and the ancillary portion 134 experiences a second preload of a magnitude, at which the main body 132 of the preload sensor 130 fully engages with the first component 102 and the second component 104. The ancillary portion 134 is compressed to such an extent that the main body 132 axially (i.e., in the direction of the arrow 131 ) overlaps the ancillary portion 134 fully. Deformation of the main body 132 as a result of changes in the second preload is registered by a suitable transducer 140, e.g. a strain gauge or a piezoelectric element, which converts the deformation registered for the main body 132 into an electric signal. The electric signal is supplied to a signal processing system 144, which may be external to the pre-load sensor 130, so as to be able to monitor the magnitude of the second preload as experienced by the telescopic arrangement of the main body 132 and the ancillary portion 134, and raise an alarm if needed.

In the diagram of Fig.2, the telescoping arrangement of the main body 132 and the ancillary portion 134 experiences a second preload of a magnitude, at which the main body 132 of the preload sensor 130 has disengaged from the second component 104. The ancillary portion 134 remains engaged with the second component 104, owing to the telescoping configuration of the preload sensor 130 and the elasticity of the ancillary portion 134, governed by the second stiffness. As a result, the telescoping arrangement of the main body 132 and the ancillary portion 134 as a whole stays engaged with the first and second components 102 and 104. The transducer 140 still registers the deformation of the main body 132, due to the reaction force exerted on the main body by the ancillary portion 134. The deformation of the main body 132 is representative of the magnitude of the second preload on the telescoping arrangement, as discussed above with reference to Fig.1. In addition, the deformation of the main body 132 is also representative of a displacement 146 of the main body 132 relative to the second component 104. Accordingly, if the magnitude of the second preload is such that the main body 132 does not fully axially overlap the ancillary portion 134, the preload sensor 130 can also be used to sense the displacement 146, owing to the telescoping configuration of the main body 132 and the ancillary portion 134.

The maximum displacement 146 that may be sensed corresponds to a predetermined amount by which the ancillary portion 134 extends beyond the main body 132 when the preload sensor 130 is in an unloaded condition. Suitably, this predetermined amount does not exceed a maximum elastic deformation of the ancillary portion 134. If this maximum is exceeded, the ancillary portion will be deformed plastically. Thereafter, when a loss of preload results in the main body 132 losing contact with the second component 104, the ancillary portion will no longer exert a predictable reaction force on the main body 132. If extreme plastic deformation occurs, a measurable reaction force may even be lost altogether. Fig. 3 is a more detailed diagram of a further example 300 of the first embodiment 100 of an apparatus of the invention. In Fig.3, the main body 132 is attached to the first component 102. For example, the main body 132 has a screw thread 136 cut on its surface. The main body 132 is screwed into a correspondingly threaded hole in the first component 102. Other means are feasible for attaching the main body 132 to the first component 102. For example, the main body 132 is formed as an integral part of the first component 102, or the main body 132 is glued to the first component 102. However, the screw connection illustrated in Fig.3 enables calibrating the preload sensor 130 by continuously varying the relative position of the main body 132 with respect to the first component 130, and therefore, with respect to the second component 134. In this example, the second component 104 has a recess 138, into which the preload sensor 130 extends. The preload sensor 130 is mounted so that the main body 132 presses against a bottom surface 139 of the recess 138, i.e. the main body 134 is fully engaged with the second component 104, and the ancillary portion 134 is elastically compressed. Suitably, the preload sensor is designed such that the ancillary portion experiences almost full elastic deformation before a nose part 148 of the main body 132 makes contact with the second component 104. This ensures that a strong reaction force is exerted on the main body. The ancillary portion 134 is implemented with, e.g. a helical spring, or a spring washer, or a stack of multiple spring washers, or a stiff air cushion that fits around the nose part 148 of the main body 132. As shown, the nose part 148 engages with the second component 104 at the bottom surface 139 of the recess. Fig.4 is a graph 400 illustrating the operation of the preload sensor 130 in the embodiment 300 of the apparatus in Fig.3. The numerical values of the deformation "5L" of the length "L" of the telescoping arrangement of the main body 132 and the ancillary portion 134 are represented by locations on the horizontal axis. The magnitude of the compressive second preload "CP", the compression force (or: strain) bringing about this deformation of the telescopic arrangement, is represented by locations on the vertical axis. The elastic deformation "5L" of the telescopic arrangement of the main body 132 and the ancillary portion 134 is a response to the second preload. The elastic deformation "δΙ_" is the combined effect of a first elastic deformation of the main body 132 as determined by the first stiffness, and a second elastic deformation of the ancillary body 134 as determined by the second stiffness. This follows from the fact that static mechanical equilibrium requires that the main body 132 experience the same compressive second preload as the ancillary portion 134.

In the absence of any compressive preload "CP" on the preload sensor 130, the deformation "5L" is zero. If the compressive second preload "CP" increases, the deformation "5L" increases substantially under control of the value of the second stiffness of the ancillary portion 134. That is, the ancillary portion 134 gets compressed. An angle "a" in the graph 400 is a good representation of the second stiffness. The ancillary portion 134 is fully overlapped by the main body 132, when the deformation "δΙ_" has reached a magnitude indicated by a reference numeral 402 in response to a compressive second preload "CP" of a magnitude indicated by a reference numeral 404. At this point the nose part 148 of the main body 32 engages the bottom surface 139 of the recess 138.

Note that the magnitude of the deformation "6L" indicated by reference numeral 402 corresponds to the maximum of the displacement 146 discussed above.

Further increasing the compressive second preload "CP" beyond the magnitude indicated by the reference numeral 404 causes the main body 132 to assume a substantial deformation under control of the first stiffness. That is, a change in the deformation "5L" of the telescoping arrangement is, from here on, largely due to the change in the deformation of the main body 132. An angle "β" in the graph 400 is a good representation of the first stiffness. In order to change the deformation "δΙ_" by a certain amount, now effected in the main body 132, a much larger change in the compressive second preload ""CP" is needed than for the same amount of the deformation "δΙ_" effected in the ancillary portion 132 at magnitudes of the second preload "CP" lower than the level indicated by the reference numeral 404. If the second preload is further increased beyond a second magnitude indicated by a reference numeral 406, a parameter region is entered, wherein the first stiffness starts to behave dramatically differently from what has been discussed so far, or wherein plastic deformation of the main body 132 and/or the ancillary portion 134 begins to occur. This parameter region is not further discussed here.

Fig.5 is a diagram of an example implementation 500 of the main body 132 and the ancillary portion 134. In the implementation 500, the main body 132 can be made from a cylindrical, massive steel rod that has been subjected to electrical discharge machining (EDM), also referred to as "spark eroding", using a spark erosion wire cutting machine. An advantage of this type of machining is that the resulting main body 132 is stress-free, i.e., has no noticeable internal stresses. This is advantageous because in a preferred embodiment, the main body 132 is instrumented with one or more strain gauges. Internal material stresses can cause a non-linear response in strain gauges, which is undesirable.

The main body 132 thus created has a spatial configuration with a profiled surface and/or holes. Note that the area of different cross-sections of the machined steel rod varies in an axial direction, i.e., the direction wherein the telescoping arrangement of the main body 132 and the ancillary portion 134 are telescoping. Removal of material from the steel rod affects its stiffness with regard to axial compression. This can be envisaged as follows. The compression is brought about by two axial forces of the same magnitude but opposite polarity, applied at the two ends of the machined rod. The opposite forces give rise to a pressure on each slice of the machined rod, the slice having two faces perpendicular to the axis of the rod. As there is mechanical equilibrium, the forces on the opposite faces of the slice must cancel each other. The magnitude of the force on a particular face is the integral of the product of the local pressure and the area of the local surface element, the integral taken over the surface of the face. If material has been removed from the cylindrical rod at specific locations, a first face of the slice may have a smaller surface area than the second face. Under the condition of mechanical equilibrium, the integrals taken over the two faces of the slice must cancel. As the surface areas of the faces are different, the spatial distribution of the pressure values per individual face will be different, and the pressure will vary depending on the location of the surface element of the relevant face. A locally varying pressure gives rise to a locally varying elastic deformation. Removing more material from the rod, so that the surface area of an axial cross section decreases further, will therefore lead to increases in local pressure, which in turn leads to larger local deformations.

Designs of the main body 132 can be simulated and tuned on a computer, e.g., using a finite element method (FEM), so as to determine a spatial configuration of the main body 132, suitable for use in the desired range of deformation and/or in the desired range of magnitudes of the second preload, given the properties used of the material from which to make the main body 132, e.g., steel, as discussed in the example above.

The transducer 140 comprises, for example, one or more strain gauges. Using the computer simulations, the proper locations can be determined for positioning the strain gauges, e.g., those locations where the main body 132 experiences the largest deformations under a given magnitude of the second preload. When resistive strain gauges are used to sense the deformation of the main body 132, the preload sensor is preferably also provided with at least one temperature sensor. This enables compensation of apparent strain due to temperature effects, so that a more accurate strain signal is obtained. In the implementation 500, the ancillary portion 134 is implemented by a set of first, second, third and fourth spring washers 502, 504, 506 and 508. In operational use of the preload sensor 130, the first, second third and fourth spring washers 502, 504, 506 and 508 are stacked coaxially on top of each other and positioned at the nose 148 of the main body 132. The combined elasticity of the first, second, third and fourth spring washers 502, 504, 506 and 508 determines the second stiffness of the ancillary portion 134. The first, second, third and fourth spring washers 502, 504, 506 and 508 are kept in place on the nose 148 with e.g. a flexible silicone glue.

As an example, the maximum elastic deformation of the first, second third and fourth spring washers 502, 504, 506 and 508 combined is, e.g., 0.4 mm. The maximum elastic deformation of the main body 132 is, e.g., 0.1 mm.

The main body 132 in the implementation 500 is equipped with the screw thread 136 to enable the main body 132 to be screwed into a correspondingly threaded hole made in the first component 102. At an extremity 512 of the main body 132, the main body 132 suitably has a head of a hexagonal cross-section, so as to be able to use a wrench in order to screw the main body 132 into the first component 102.

Now consider the main body 132 of the preload sensor 130 being screwed into the first component 102 after the first and second components have been mounted together under the first preload. Once the ancillary portion 134 touches the bottom 139 of the recess 138, the torque to be applied to the second extremity 512 of the preload sensor 130 in order to continue the screwing, increases with the linear distance over which the main body 132 travels in the axial direction towards the second component 104. The distance travelled indicates the elastic axial deformation "δΙ_" of the set of the first, second, third and fourth spring washers 502, 504, 506 and 508, used as the ancillary portion 134. The increase in magnitude of the torque needed is low, as indicated in the graph 400, owing to the low value of the stiffness of the ancillary portion 134. The magnitude of the compressive second preload "CP" on the telescopic arrangement of the main body 132 and the ancillary portion 134 can be monitored during the screwing, using the signals from the transducer 140. The point gets reached, at which the first, second, third and fourth spring washers 502, 504, 506 and 508 have been flattened under the increased second preload "CP" to such an extent, that the nose 148 of the main body 132 engages with the second component 104. Past this point, the magnitude of the torque, needed to screw the main body 132 further into the first component 102, rises dramatically. This stage is reached when the deformation "δΙ_" of the telescopic arrangement of the main body 132 and the ancillary portion 134 has reached the value indicated with the reference numeral 402 in the graph 400. This dramatic increase notifies the installer of the fact that the preload sensor 130 is starting to operate in the parameter region wherein the main body 132 starts to get deformed significantly. The workpoint of the preload sensor 130 is then chosen in this parameter region, corresponding to a magnitude of the second preload "CP" that is set somewhat higher than the value indicated with the reference numeral 404 in the graph 400. In this region, a small deformation "5L" of the telescopic arrangement of the main body 132 and the calibration portion 134 corresponds to a large change in the value of the second preload ""CP. Accordingly, the preload sensor 130 has been calibrated for operation in the most sensitive range in its parameter region.

Once the preload sensor 130 has been properly positioned with respect to the first component 102, the position of the preload sensor 130 may be secured, e.g., by means of using an adhesive resin between the preload sensor 130 and the first component 102.

Figs. 6 and 7 are diagrams of a second embodiment 600 of an apparatus in the invention, shown in cross-section. The functionality, operation and features are similar to those discussed with regard to the first embodiment 100. The second embodiment 600 of an apparatus in the invention differs from the first embodiment 00 with regard to the telescoping configuration of the preload sensor 130. In the first embodiment 100, the main body 132 forms the male part of the telescoping arrangement, and the ancillary portion 134 forms the female part of the telescoping arrangement. In the second embodiment 600, the main body 132 forms the female part of the telescoping arrangement and the ancillary portion forms the male part of the telescoping arrangement. In the second embodiment 600, the ancillary portion 134 can be implemented by, e.g., a helical spring, an air cushion, a piece of rubber, etc. Suitably, the reaction force exerted on the main body 132 of the sensor by the ancillary portion 134 is sufficient to induce a measurable strain on the main body. Figs. 1 , 2, 6 and 7 illustrate only two variations on the theme of the telescoping arrangement of the main body 132 and the ancillary portion 134 for use in an apparatus according to the invention. A further variation (not shown) includes, for example, a telescoping arrangement of a single main body sandwiched between a first ancillary portion and a second ancillary portion, the whole being positioned between the first component 102 and the second component 104. Another variation comprises a series arrangement of telescoping units between the first component 102 and the second component 104, wherein each respective telescoping unit comprises a respective telescoping arrangement of a respective main body and a respective ancillary portion. Still another variation includes an arrangement of multiple telescoping units operating in parallel, each respective telescoping unit comprising a respective telescoping arrangement of a respective main body and a respective ancillary portion. Yet another variation comprises a telescoping arrangement of three or more telescoping sections, each respective one of the sections has a respective stiffness different from the stiffness of another section. In a further variation at least the main body 132 is physically integrated with the first component or the ancillary portion 134 is physically integrated with the second component 104.

Fig.8 is a diagram of an example of an apparatus according to the first embodiment of the invention. In the example, the apparatus is a bearing and shaft arrangement in which a preload sensor 130 is provided for monitoring the first preload with which a spherical roller bearing has been mounted on a shaft 810. The bearing comprises an outer ring 802 and first and second inner rings 804, 104. The second inner ring 104 also functions as the second component 104 as discussed above. The bearing further comprises a first set of rolling elements 805 and a second set of rolling elements 806, which are respectively disposed between a first inner raceway on the first inner ring 804 and a first outer raceway on the outer ring 802, and between a second inner raceway on the second inner ring 104 and a second outer raceway on the outer ring 802. In this example, the bearing is mounted on the shaft 810 such that the first inner ring 804 abuts against a shoulder 808. To remove any unwanted clearance and play, the bearing is then given a predefined preload by applying an axial load to the second inner ring 104. This can be done using a locknut that is tightened against the second inner ring 104 or, as shown, by means of a retaining ring 102 that is welded to the shaft 802 after the desired preload (first preload) has been achieved. The first and second inner rings 804, 104 are therefore axially located under the first preload between the shoulder 808 and the retaining ring 102. Over time, bearing preload can vary due to thermal expansion and contraction. To measure the variation in preload, loss of preload in particular, the arrangement 800 is provided with a preload sensor 130 according to the invention.

Suitably, the retaining ring 102 - which functions as the first component 102 as described previously - comprises an opening with a threaded portion. The preload sensor 130 is screwed into the opening until the nose part 148 makes contact with a side face of the second inner ring 104. The workpoint of the sensor is set as previously described. If a loss of preload occurs, which causes the nose part 148 of the sensor and the second inner ring 804 to lose contact with each other, the ancillary portion 134 of the sensor continues to exert a reaction force on the instrumented sensor body. In other words, the extent of the loss of preload is measurable. In some embodiments of an apparatus according to the invention comprising a bearing, the apparatus further comprises signalling means for indicating that the preload has fallen below a predetermined minimum value. Suitably, the apparatus may further comprise speed limiting means, to reduce or limit bearing speed to a "safe" level at which the vibrations caused by lack of preload do not damage the apparatus as a whole.

In mechanical equilibrium, the force exerted by the retaining ring 102 on the second inner ring 104 of the bearing equals the force that the second inner ring 104 exerts on the first inner ring 804, which in turn equals the force that the first inner ring 804 exerts on the shoulder 808. In a further example, the shoulder 808 is provided with a threaded opening for receiving the preload sensor 130 and the nose part 148 is mounted against a side face of the first bearing ring 804.

A number of aspects/embodiments of the invention have been described. It is to be understood that each aspect/embodiment may be combined with any other aspect/embodiment. The invention may thus be varied within the scope of the accompanying patent claims.