FR2863706A1 - Mechanical load measuring device for e.g. dryer`s antifriction bearing, has insulator disposed in contact with external ring of antifriction bearing, where ring acts as electrode and thickness of insulator varies according to applied load - Google Patents

Abstract

The device has a capacitor comprising an insulator (23) disposed in contact with an external ring (2) of an antifriction bearing, where the ring acts as an electrode and thickness of insulator varies according to applied load. An electrode (22) is disposed between the insulator and a bore (19b) of a sleeve (19). A measuring unit arranged on a support measures capacitance between electrodes, where capacitance represents the load. An independent claim is also included for a machine with revolving drum comprising antifriction bearing that has a load measuring device.

Description

Device for measuring load on a bearing, rolling bearing and

rotary drum machine.

  The present invention relates to the field of devices for measuring mechanical load on a bearing, in particular a rolling bearing.

  DE-A-101 36 438 discloses a bearing provided with piezoelectric sensors mounted between the outer ring and the housing of said outer ring.

  Piezoelectric sensors have the major disadvantage of providing the information sought only when the bearing rotates. However, many applications require knowledge of the loads applied to the bearing regardless of the rotation of said bearing. Moreover, existing devices require changes to the bearing structure for the integration of sensors, which is expensive. The sensors can be arranged in a notch machined by chip removal in the outer ring. The manufacture of such rings is longer and generates waste.

  The invention aims to remedy these drawbacks.

  The invention proposes a load measurement on a standard bearing, whether the bearing is rotating or not.

  The load measuring device on a bearing provided with two rings, one of which is rotatable relative to the other according to one aspect of the invention, comprises at least one capacitor provided with electrodes and an insulator arranged between the electrodes, one of the electrodes being formed by one of the rings of the bearing. The thickness of the insulation may vary depending on the load. The device further comprises means for measuring the capacity of the capacitor, said capacitance being representative of the load applied perpendicularly to the electrodes. It is thus possible to measure the load of a standard rolling bearing manufactured in large series, during the rotation of the bearing or during a stationary phase.

  It is understood that, before mounting the measuring device on the bearing, the measuring device is in the form of a subassembly comprising the other electrode, the insulator and the capacitance measuring means.

  In one embodiment of the invention, the insulation comprises a layer of synthetic material. Alternatively, the insulation may comprise a fluid layer. Advantageously, the insulator disposed between the electrodes is subjected to a pre-charge. It is thus possible to control the deformation of the insulator as a function of the load.

  In one embodiment of the invention, the device comprises a plurality of capacitors having a common electrode. In other words, a plurality of electrodes arranged around the insulator can be provided when the insulator is mounted around the outer ring or in the bore of the insulator when the insulator is mounted in the bore. of the inner ring. The determination of the load is then more precise. One can also detect a possible imbalance during the rotation.

  In another embodiment of the invention, the device comprises a single capacitor.

  The invention also proposes a rolling bearing comprising two rings, one of which can rotate relative to the other, at least one row of rolling elements and a device for detecting the load applied to the bearing. The detection device comprises at least one capacitor provided with electrodes and an insulator. One of the electrodes is formed by one of the rings of the bearing. The thickness of the insulation may vary depending on the applied load.

  The detection device further comprises means for detecting the capacity of the capacitor, the capacitance being representative of the load. The term "load" here refers to the mechanical load to which the rolling bearing is subjected. A standard bearing can thus be equipped by a simple operation of mounting a measuring device. The electrode ring then performs a dual function, a ring mechanical function and an electrode electrical function.

  In one embodiment of the invention, the bearing comprises means for measuring the capacity of the capacitor.

  Advantageously, the bearing comprises a sleeve in contact with the other electrode and a housing in contact with the sleeve, so that the sleeve exerts a permanent force on the other electrode.

  To facilitate assembly, it can be provided that the sleeve comprises a frustoconical surface in contact with the housing. The housing, of generally annular shape, may comprise a frustoconical portion delimited by an outwardly directed radial portion and an inwardly directed radial portion.

  In one embodiment of the invention, the bearing comprises an outer ring serving as an electrode and provided with a cylindrical outer surface in contact with the insulator, the other electrode being in contact with a cylindrical bore of the sleeve.

  In one embodiment of the invention, the bearing comprises a rotation parameter sensor mounted on one side of the rings.

  In one embodiment of the invention, the bearing comprises a temperature sensor of said bearing mounted on one side of the rings.

  The present invention also relates to a rotary drum machine comprising a non-rotating frame, a rotating drum and at least one bearing comprising a part integral with the frame and a part integral with said rotary drum, the bearing comprising a load sensor device making it possible to determine , in association with a signal processing device, the load exerted on said bearing.

  The present invention also relates to a rotary drum machine, for example a washing machine, comprising a non-rotating chassis, a rotating drum and at least one bearing comprising a part integral with the chassis, a part integral with the rotary drum and a measuring device. bearing load. The measuring device comprises a capacitor provided with at least two electrodes and an insulator. One of the electrodes is formed by one of the rings of the bearing. The insulation is of variable thickness depending on the load. The measuring device further comprises means for measuring capacitor capacitance, said capacitance being representative of the load.

  In other words, one of the two rings of the bearing is used as the electrode of the capacitor, and the other electrode is disposed facing said ring and separated therefrom by an insulator whose thickness may vary with the charge.

  The invention thus makes it possible to produce an instrumented rolling bearing capable of providing a great deal of information useful for controlling a machine, in a reliable and economical manner.

  The present invention will be better understood on studying the detailed description of some embodiments illustrated by the appended drawings, in which: FIG. 1 is a view in axial section of a rolling bearing according to one aspect of the invention; invention; FIG. 2 is a cross-sectional detail view of the capacitor; FIG. 3 is a diagrammatic and partial elevational side view of a variant of a rolling bearing close to that of FIG. 1, supplemented by an electric diagram; and FIG. 4 is a diagram showing the evolution of the charge as a function of capacitance of the capacitor.

  As can be seen in FIG. 1, a rolling bearing 1 comprises an outer race 2 provided with a raceway 3, an inner race 4 provided with a raceway 5, a row of rolling elements 6, here balls, arranged between the raceways 3 and 5, a cage 7 for maintaining the circumferential space of the rolling elements 6, and a sealing flange 8 mounted on the outer ring 2 and forming a narrow passage with a cylindrical bearing surface 4b of the inner ring 4, while being arranged radially between the two rings 2 and 4 and axially between the rolling elements 6 and one of the lateral surfaces 2a, 4a of the rings 2, 4. The sealing flange 8 is mounted in an annular groove 9 formed in the outer ring 2, near its radial lateral surface 2a. On the opposite side, the outer ring 2 is also provided with a groove 10, symmetrical with the groove 9, with respect to a plane passing through the center of the rolling elements 6.

  A sensor block, referenced 11 as a whole, is integral with the outer ring 2 and comprises a support 12, for example a printed circuit board, a metal cap 13 having an annular cup shape with an L-shaped cross section, one end of which forms a narrow passage with a front surface 4b of the inner ring 4, a sensor element 14, for example a Hall effect cell, fixed on the support 12, and a magnet 15 also fixed on the support 12. A coder element 16 , of annular shape, of L-shaped section, comprises an axial branch 16a fitted on an outer cylindrical surface of the inner ring 4 on the opposite side to the flange 8 and a radial branch 16b extending outwards from the axial branch 16a. The radial branch 16b is provided with windows or notches, not shown, and is arranged with a small gap with respect to the sensor 14. The encoder 16, made of magnetic material, disturbs the magnetic field generated by the magnet 15 during the rotation of the inner ring 4 with respect to the outer ring 2. The generated perturbation is detected by the sensor 14, which makes it possible to generate an electrical signal representative of the rotation of the encoder 16.

  A housing 17, of generally annular shape, comprises an annular radial portion 17a in contact near its bore with the radial face 2a of the outer ring 2, a slightly frustoconical portion 17b having a slope of the order of 9 to 13 % with respect to the axis of the bearing, extending from the large diameter end of the radial portion 17a surrounding the rolling bearing 1, and a radial flange 17c directed outwardly from the end of the frustoconical portion 17b opposite to the radial portion 17a.

  A plurality of fixing holes 18 are formed in the radial flange 17c to allow attachment of the housing 17 and the rolling bearing 1 which is located there by means of screws on another element, not shown, such as a frame or a washing machine frame.

  There is further provided a clamping sleeve 19, made of synthetic material, having a frustoconical outer surface conforming in shape with the inner surface of the frustoconical portion 17b of the housing 17 and being in the form of a ring split by a slot 20 occupying a small angular sector, in order to confer on said ring a certain radial elasticity.

  In addition, the cover 17 is provided with hooks 17d formed on its inner surface at the connection between the radial flange 17c and the frustoconical portion 17b. The hooks 17d project inwards and interfere diametrically with the free end of large diameter of the cover 13 by forming a means for retaining said cover 13. The cover 13 is further provided with an annular rib 13a projecting from direction of the rolling bearing 1 and bearing on the support 12, itself bearing axially on a shoulder of the sleeve 19.

  A unitary assembly is thus formed, comprising the rolling bearing 1 itself, the housing 17, the sleeve 19, the sensor unit 11 and the cover 13. Said unitary assembly can be handled without particular precautions and is well protected against the risk accidental disassembly through the cooperation of the hooks 17d of the housing 17 with the cover 13 and against the intrusion of undesirable external elements by the sealing flange 8 and the narrow passage formed between one end of the cover 13 and the inner ring 4, the other end of the cover 13 being in contact with the housing 17.

  The split sleeve 19 has, on its inner surface, a rib 21 directed inwards and providing a bearing surface to the radial surface 2c of the outer ring 2 opposite to the radial surface 2a. The split sleeve 19 further comprises a radial surface 19a disposed at a small distance from the radial portion 17a of the housing 17. Said short distance may be of the order of a few millimeters or tenths of a millimeter, but in normal operation, will remain strictly greater to zero. It is understood that, because of the conicity of the frustoconical portion 17b whose diameter is reduced as one approaches the radial portion 17a and that one moves away from the radial flange 17c, the sleeve 19 can slide in the inner surface of said frustoconical portion 17b while tightening slightly, which results in a tightening of the slot 20.

  Between the rib 21 and the radial end surface 19a, the sleeve 19 comprises a bore 19b in which is disposed an electrode 22 and an insulator 23 visible in Figure 2. The insulator 23 is disposed in contact with the surface 2b outside the outer ring 2, the electrode 22 being disposed between the outer surface of the insulator 23 and the bore 19b of the sleeve 19. A contact finger 24 connected to the support 12 comes into contact with the outer surface 2b of the outer ring 2. On the support 12 is also disposed a measuring member 25 of the capacitance between the electrode 22 and the outer ring 2 which also forms an electrode. The measurement sensor 25 is electrically connected to the contact finger 24 and to the electrode 22.

  In addition, the support 12 may be equipped with a processing and calculation module 26 electrically connected to the measurement sensor 25 and to deduce the load applied to the bearing from the measured capacity. The relationship between charge and capacitance is illustrated in Figure 4 and is hysteresis. To avoid the effects of hysteresis, we try to place ourselves on a relatively linear part of the curve so that we can easily interpret the load as a function of capacity, the chosen part of the curve has been represented in thick lines in the figure 4.

  The rolling bearing 1 is held radially with respect to the housing 17 by means of the radially deformable insulation 23, the electrode 22 and the split sleeve 19 which can be depressed axially with a predetermined force in the frustoconical portion 17b of the housing 17 to ensure sufficient pre-stressing of the insulator 23 to lie in a favorable part of the curve shown in Figure 4 and linking the load of the bearing and the capacity of the capacitor formed by the electrode 22 and the ring- electrode 2. The slope of the cone is chosen such that the tightening obtained also ensures sufficient mutual axial restraint of the split sleeve 19 on the housing 17.

  The electrode 22 may be in the form of a conductive metal foil disposed over a certain angular sector.

  By way of example illustrated in FIG. 3, the insulator 23 is disposed on the whole of the outer surface of the outer ring 2 and three electrodes 22 are each disposed on an angular sector, of the order of 20 to 50 , with two diametrically opposed electrodes and the third perpendicular to the two previous ones. The insulator 23 may be made of high density polyethylene, polypropylene or polyamide-12. As the measurement is based on the variation of the thickness of the insulator 23 under the effect of the variation of the load, the choice of the thickness of the insulator 23 will depend on the mechanical properties of the material used and in particular on its elasticity module.

  For example, polyethylene insulation sheets having a thickness of about 0.02 mm may be used. The insulator 23 is prestressed radially between the two electrodes by virtue of the split clamping sleeve 19 and thus remains in constant contact with the electrodes 2 and 22.

  Alternatively to the embodiment illustrated in FIG. 3, an insulator 23 can be provided occupying the angular sectors that are substantially equal to or only slightly greater than those occupied by the electrodes 22.

  It is known that there is a linear relationship between the variation of the distance between two electrodes of a capacitor and the capacitance of said capacitor. The relation is given by the following formula: C = (Eo + Er) S / e, in which: Eo is the permittivity in the vacuum, Er is the permittivity of the insulator, S is the surface opposite the gap , and e is the gap.

  If the electrodes are arranged in such a way that the radial load on the bearing passes through the electrodes, perpendicular to them, it is possible to measure the variations of the radial load on the bearing by measuring the variation of capacitance of the electrodes, said capacitance variation resulting from the approximation under the effect of the charge of the moving electrode and the fixed electrode 22.

  The radial prestressing of the insulation between the electrodes by the conical sleeve makes it possible to ensure a permanent close contact between the insulator and the electrodes, which guarantees an immediate reactivity of the charge sensor. The pre-charge also makes it possible to overcome possible hysteresis problems that could affect the reliability of the measurement. If the radial load to be measured is always oriented in the same direction, a judiciously placed electrode 22 will suffice to measure a force F applied at the electrodes 2, 22 in a direction perpendicular to said electrodes (FIG. 2).

  If it is desired to know, by means of an instrumented bearing, the static load of laundry in a drum of a washing machine, it suffices to equip said bearing with an electrode in its lower part, in addition to the ring. electrode. The determination of the drum load will be made by measuring the variation in the thickness of the insulation separating the electrode ring and the only other associated electrode between the empty state and the loaded state of the drum. On the other hand, if it is also desired to obtain information on the dynamic rotational loads due for example to the unbalance of the drum, it will suffice to have, for example, two complementary associated electrodes at 90, on either side of the first other electrode. to obtain the said information, see Figure 3.

  In addition to obtaining information on charges in different directions, the arrangement with three electrodes 90 also makes it possible to proceed by differential measurement with respect to a reference electrode which may be for example one of the lateral electrodes.

  Indeed, in the case of a washing machine, the side electrodes undergo substantially no air gap variation during the loading of the drum since the lateral electrodes of a capacitive sensor move parallel to one with respect to the other. By measuring the differences in capacitance of the different electrodes with respect to a reference electrode, it is thus possible to eliminate measurement anomalies that might result from variations in airgaps due, for example, to variations in temperature.

  Of course, this type of bearing can also be equipped with a temperature sensor 27, which can be particularly advantageous in the case of use in a washing machine or dryer.

  In order to mount the device, the rolling bearing 1 provided with the encoder 16 and the electrode or electrodes 22 in the sleeve 19 is first arranged. The sensor unit 11 is then disposed on the sleeve 19 and is closed and secured. the subassembly with the cover 13. The subassembly thus formed is introduced into the casing 17 until the rolling bearing 1 comes into axial abutment between the radial bottom 17a of the casing 17. The tightening of the sleeve 19 in the casing 17 and on the bearing then ensures cohesion to the assembly in the form of a cartridge easy to handle and transport, with a very low risk of inadvertent assembly of the elements.

  Such a cartridge offers many advantages, among which a reduced cost thanks to the absence of modification of the geometry of the bearing, in other words to the possible use of a standard bearing manufactured in very large series, compactness , the thickness of the insulator and the electrode 22 being negligible, and the thickness of the sensor block being extremely low, the ease of implementation by the user and the possibility of combining in the same bearing with instrumented bearing a system for detecting the loads applied to the bearing and a system for measuring rotation parameters of the bearing and / or a temperature measuring system.

  An instrumented rolling bearing 1, used in a washing machine, thus makes it possible, in addition to its basic mechanical function, to provide useful information for a complete control of the machine and in particular of the electric drive motor.

  Of course, it would be possible, as an alternative, to provide a rolling bearing with a rotating outer ring and a fixed inner ring. It is also conceivable to make the insulation by a single layer of air. It is no longer necessary to provide a layer of synthetic material to separate the outer ring of the bearing and the electrode 22.

Claims (16)

  1-load measuring device on a bearing (1) provided with two rings (2, 4), one of which is rotatable relative to the other, of at least one capacitor provided with electrodes and a insulator (23) disposed between said electrodes, the thickness of the insulator (23) being variable depending on the load, the device further comprising means (25) for measuring the capacity of the capacitor, said capacitor being representative of the load applied perpendicularly to the electrodes, characterized in that one of the electrodes (2) is formed by one of the rings of the bearing (1).   2-Device according to claim 1, characterized in that the insulator (23) comprises a layer of synthetic material.   3-Device according to claim 1 or 2, characterized in that the insulator comprises a fluid layer.   4-Device according to any one of the preceding claims, characterized in that the insulator (23) is pre-charged between the electrodes (2, 22).   5-Device according to any one of the preceding claims, characterized in that it comprises a plurality of capacitors comprising a common electrode.   6-Device according to any one of claims 1 to 4, characterized in that it comprises a single capacitor.   7-Roller bearing (1) comprising two rings (2, 4), one of which is rotatable relative to the other, at least one row of rolling elements (6), and a device for detecting the applied load at the bearing, the detection device comprising at least one capacitor provided with electrodes (2, 22) and an insulator (23), the thickness of the insulator (23) being variable depending on the applied load, the detection device further comprising capacitor capacitor detecting means (25), said capacitance being representative of the charge, characterized in that one of the electrodes (2) is formed by one of the bearing rings (1).   8-rolling bearing (1) according to claim 7, characterized in that it comprises means (25) for measuring the capacity of the capacitor, said capacity being representative of the load applied to the bearing.   9-bearing according to claim 8, characterized in that it comprises a sleeve (19) in contact with the other electrode (22) and a housing (17) in contact with the sleeve (19) so that the sleeve exerts a permanent force on the other electrode (22).   10-Bearing according to claim 9, characterized in that the sleeve (19) comprises a frustoconical surface of contact with the housing (17).   11-Bearing according to claim 9 or 10, characterized in that the housing (17), of generally annular shape, comprises a frustoconical portion (17b) delimited by a radial portion (17c) directed outwards and by a portion radially (17a) directed inwards.   12-Bearing according to any one of claims 9 to 11, characterized in that it comprises an outer ring (2) also serving as an electrode and provided with a cylindrical outer surface in contact with the insulator (23) the other electrode (22) being in contact with a cylindrical bore of the sleeve (19).   13-bearing according to any one of claims 7 to 12, characterized in that it comprises a sensor (14) of rotation parameters mounted on one side of the rings (2, 22).   14-Bearing according to any one of claims 7 to 13, characterized in that it comprises a temperature sensor (27) of said bearing, mounted on one side of the rings (2, 22).   15-rotary drum machine comprising a non-rotating chassis, a rotary drum and at least one bearing (1) comprising a part integral with the frame and a part integral with said rotary drum, characterized in that the bearing comprises a device for detecting charge, comprising at least one capacitor provided with electrodes and an insulator (23) disposed between said electrodes, one of the electrodes (2) being formed by one of the bearing rings (1), the thickness of the load-varying insulation (23) for determining, in association with a signal processing device, the load exerted on said bearing.   Rotary drum machine according to Claim 15, characterized in that the measuring device comprises at least one capacitor provided with electrodes (2, 22) and an insulator (23), one of the electrodes ( 2) being formed by one of the rings of the bearing (1), the thickness of the insulator (23) being variable depending on the load applied, the measuring device further comprising a measuring means (25) of the capacity of the capacitor, said capacitance being representative of the load.