LOAD-SENSING DEVICE

Abstract: The invention concerns a load-sensing device of the kind comprising a resiliently flexible member (2) and an arm (13), an end portion of which is rigidly connected to the flexible member whereas its opposite end portion is free. The distance between the free end portion of the arm and the flexible member is changeable in response to load exerting on the flexible member and to the resulting flexible deformation thereof. The flexible member (2) has a tubular cross-sectional shape with an interior cavity (12) in which the arm (13) is disposed. In the area of the free end portion of the arm a transducer (17) is located to sense the distance from the arm to the flexible member and/or a switch (15) which, in response to the mutual relative movement between the flexible member and the free end of the arm, may be shifted between an open and a closed position and which is arranged to close or open a signalling circuit upon attainment of a load of a predetermined value.

Description: LOAD-SENSING DEVICE The present invention relates to a load-sensing device of the kind comprising a resiliently flexible mem¬ ber having a tubular cross-sectional shape with an inte¬ rior cavity, and an arm disposed in said cavity and hav- ing a longitudinal axis extending essentially in parallel with or along a longitudinal axis of said flexible mem¬ ber, one end portion of said arm being rigidly connected to the flexible member whereas an opposite end portion of said arm is free, in consequence whereof the distance between the free end portion of the arm and the flexible member is changeable in response to load exerted on the flexible member and to the resulting flexural deformation of said member. Background of the Invention In many situations there is a need for limit load circuit breakers capable of opening or closing an elec¬ tric circuit when the load exceeds or is lower than a predetermined value. Such limit load circuit breakers may be used as load-limiting devices, for instance in storage bins or pockets, for alerting purposes or to interrupt the supply of material upon attainment of a critical weight load. It is already known to use electrical switches, for instance so-called microswitches in combination with resilient means, such as springs. One problem connect¬ ed with means of this kind is that the switches have a travel length which in situations of relevance to the present invention is comparatively long, and in the case of microswitches may amount to approximately 0.1-0.4 mm. One consequence thereof is that when the load is consi¬ derable and the requirements on measurement accuracy are strict the total travel length of the limit load circuit breaker becomes considerable, which in turn causes the breaker to be not only voluminous and cumbersome but also expensive to manufacture. In situations when the requirements on accuracy and small dimensions in the limit load circuit breaker are strict strain gauge devices have been used hitherto as a rule, such devices being characterised by their property to change their electrical conductivity when exposed to mechanical strain. A strain gauge device may be mounted for instance on the surface of a metal rod to sense the elongation or compression to which the rod is subjected when exposed to tensile, pressure or flexural load. An advantage found in strain gauge devices are that they may be used not only as limit load circuit breakers but also as a weighing device allowing the actual size of the load to be shown on a display. The signals emitted by a strain gauge of this kind are, however, very weak and must be amplified in order to be useful, and in order to be able to serve as limit load circuit breakers some type of relay must be provided. All this ancillary equip¬ ment makes such limit load circuit breakers comparatively expensive to manufacture. Other disadvantages inherent in strain gauge devices are that they are sensitive to tem¬ perature changes and that the electronics associated therewith are sensitive to electric disturbances. From SE 9200721-0 is previously known a load-limit¬ ing device intended for wires and designed as a limit load circuit breaker of the kind defined in the preamble of claim 1. In this limit load circuit breaker, a flex¬ ible element is provided at its end portions with pul¬ leys, and a drawing bar with through-holes therein is arranged at the centre of the flexible member. The cir- cuit breaker is adapted for application on a wire to be put under strain in that the wire is carried through the hole formed in the drawing bar and abuts against the two pulleys from the external face thereof. The relative positions of the drawing bar hole and the pulleys are such that the wire is given an initial curvature confi¬ guration when the limit load circuit breaker is mount¬ ed. Upon strain on the wire the latter will tend to straighten, causing in a bending deformation of the flex¬ ible member. A circuit breaker arm in the shape of a rod of approximately the same length as the flexible member is provided on the flexible member side facing away from the wire and an end portion thereof is securely connected to an end portion of the flexible member in such a manner that the circuit breaker arm and the flexible member become spaced apart, their longitudinal axes being essen¬ tially parallel in the unstrained condition. The outer free end of the circuit breaker arm supports an electri¬ cal switch. When the wire is under strain and when as a consequence thereof the flexible member bends, the switch will be displaced towards the flexible member as a result of the angular alteration of the cross-section of the flexible member where the circuit breaker arm is secured. Upon attainment of a critical limit load the switch is caused to abut against an adjustable screw provided in the flexible member and in response thereto the switch will close or open an electrical circuit, which in the conventional manner may be adapted to alert the user or to prevent further operation of the wire. One advantage of limit load circuit breakers of this nature is that the bending of the flexible member is amplified because of the construction as shown, whereby even very insignifi- cant bends cause a comparatively large relative movement of the adjustment screw and the contacting means. Conse¬ quently, the limit load circuit breaker may be made very small and compact in relation to the loads for which it is intended and the desired accuracy. The breaker con- struction is simple, making the breaker cheap to manu¬ facture. However, the field of application for this type of limit load circuit breakers is restricted to strain gauges for wires or lines. A further disadvantage is that if one wishes to make the limit load circuit breaker resistant to moisture and dust it must be enclosed in a separate cover, which makes the construction more expen¬ sive. Summary of the Invention The subject invention has for its purpose to create a load-sensing device which may be used as a separate limit load circuit breaker or as a combined limit load circuit breaker and weighing device. More precisely, the invention has for its immediate object to eliminate the limitations and drawbacks inherent in prior-art limit load circuit breakers and to create a circuit breaker which may be applied to any arbitrary object or support- ing face and which is adapted to sense when a tensile, pressure or bending load is in excess of or falls below a predetermined value. A further object is to create a limit load circuit breaker which is sturdy, cheap to manufacture and resistant to electrical disturbances and the dimensions of which are small in relation to the intended load and the desirable accuracy. A further object is to create a limit load circuit breaker which may have universal usefulness and which may be easily adjusted to sense loads of various kinds and in a large number of various applications. When the load-sensing device is used as a combined limit load circuit breaker and a weighing device the object of the invention essen¬ tially is the same as that indicated above, in addition to which it is intended to allow the actual magnitude of the load to be visualised and be read with great accu¬ racy. These objects and more are obtained by means of a load-sensing device as defined in claim 1. A further object is to create a load-sensing device which is resis¬ tant to the effects of dust and moisture. This object is achieved by means of a load-sensing device in accordance with claim 3. In accordance with the invention, the flexible mem¬ ber thus is given a tubular cross-sectional configuration and the arm is disposed in the hollow interior of the flexible member, preferably so as to be coaxial with the centre axis of the flexible member in the unloaded condi¬ tion thereof. Owing to this arrangement, it becomes pos- sible to make the load-sensing device very small and com¬ pact and by forming the flexible member with closed ends in conformity with a preferred embodiment, essential com¬ ponents of the load-sensing device, such as the switch, may be protected from dust and moisture in a very simple manner without the need of providing a separate cover. A load-sensing device in accordance with the inven¬ tion is universally useful in many different kinds of applications and according to need it may be provided with various types of attachments and mounting points to allow it to be suspended from or disposed on a support. In accordance with one embodiment the load-sensing device is intended to be placed freely on two supports and to be exposed to a load acting essentially midway between the supports. However, it is entirely possible to fix the load-sensing device by means of welding, for instance to weld an end face, in order to fixedly secure it to an object, and to arrange the point of attack of the force at a considerable distance therefrom, towards the end opposite to that of the fixed point of attachment. In some cases, this arrangement may be advantageous since it increases the sensitivity of the load-sensing device. The cross-sectional configuration of the flexible member may be varied optionally and need not be circular as in accordance with the embodiments disclosed herein. The same is true as regards the arm. In accordance with one preferred embodiment the flexible member is manufac¬ tured to standard dimensions from a high-durability mate¬ rial, such as nickel-chromium steel. In order to adapt the flexible member and its deflection properties to the intended application the cross-section may be weakened to varying degrees, for instance by means of a groove pro¬ duced in a turning lathe to the desired depth in the middle portion of the flexible member. The signals derived from the load-sensing device may be utilised in different ways. For instance, they may be used to turn on and off lights or light emitting diodes, when an admissible limit load is exceeded or not reached. The output from the load-sensing device could also be used to produce acoustic signals or to operate a relay interrupting the energisation of for instance an electric motor in a lifting device. As will appear from the subse¬ quent exemplary embodiments the load-sensing device may optionally serve as a weighing device in combination with a limit load circuit breaker in order to allow reading of the actual magnitude of the load. Preferably, this is achieved by providing the load-sensing device with an indicating instrument, such as a so-called distance or angle gauge which is weight scale graduated. However, the invention is not limited to this type of indicating instruments but any kind of transducer capable of sensing the distance from the flexible member to the arm and to visualise the value thereof in some way, for instance by a pointer or a display, may be used for this purpose. Decisive characteristics in such transducers are primari¬ ly the accuracy by which they are able to measure the distance. An indicating instrument of the above-mentioned kind is able to sense distance deviations down to a thou¬ sandth of a millimetre. The energisation of the load-sensing device, for instance for the indicating lamps, may be effected optionally from the mains or through batteries. For instance, it is possible in accordance with an alter¬ native embodiment to provide a load-sensing device with built-in signalling means, such as lamps, and with a likewise built-in battery. Preferably, the lamps and the battery are disposed in the coupling housing. Brief Description of the Accompanying Drawings In the drawings Fig. 1 illustrates one embodiment of the load-sensing device in accordance with the invention in a perspective view, Fig. 2 is a sectional view through a load-sensing device in an unloaded condition, said device being somewhat modified compared to the one illustrated in Fig. 1. Fig. 3 illustrates the load-sensing device in accor¬ dance with Fig. 2 in a loaded condition, and Figs 4-8 show examples of various applications of a load- sensing device in accordance with the invention. Detailed Description of Preferred Embodiments of the Invention Reference is initially made to Fig. 1 illustrating a first embodiment of a load-sensing device in accordance with the invention in a perspective view. The load-sens¬ ing device comprises a flexible member 2, the lower face of which has two bearing supports 3 and the upper face of which has a load-receiving block 4. On one end of the flexible member a coupling housing 5 is provided, com¬ prising an indicating instrument 6 in the form of a so- called angle gauge which is connected to and is affected by a follower pin 7. An indicating device 8 in the shape of a box provided with in total four lamps 9, is electri- cally connected to the load-sensing device via a cable and a contacting means 10. In the following reference is also made to Figs 2 and 3 which are lateral sectional views as seen along the centre axis of a load-sensing device, Fig. 2 illustrating the load-sensing device in an unloaded condition whereas Fig. 3 illustrates the same device in a loaded condition thereof, an arrow illustrating the force applied on the load-receiving block 4. As appears from the drawing figures the flexible member has a tubular cross-sectional shape the tube walls 11 of which delimit an interior cavity 12. An arm 13 is disposed inside the cavity 12, out of contact with the inner face of the tube wall 11, and one of its end portions is secured to an end wall 14 of the flexible member. The length of the arm exceeds the length of the flexible member and the opposite, unattach¬ ed and free end of the arm extends in a free space in the coupling housing 5. Said free end of the arm supports a switch 15, preferably a so-called microswitch, which is adapted to cooperate with a set screw 16 arranged in the bottom wall of the coupling housing and adjustable by screwing upwards or downwards. In the unloaded position of the load-sensing device illustrated in Fig. 2 the arm assumes a neutral centred position, wherein it is essen¬ tially concentric with the centre axis of the flexible member. The switch 15 is also free with respect to the surrounding coupling housing walls. In the loaded condi- tion shown in Fig. 3 the flexible member has been some¬ what deflected at its centre in response to the load acting thereon. The deflection causes a certain change of the angle of the end wall 14, resulting in displacement of the free arm end towards the coupling housing bottom. In situations when the force is sufficient and results in deflection, the switch 15 will be pressed against the set screw 16 as illustrated in Fig. 3. Consequently, the switch will be actuated so as to shift from an open to a closed position or vice versa, with the result that an electric circuit is closed or opened. The load-sensing device illustrated in Figs 2 and 3 is distinguished from the one illustrated in Fig. 1 in that instead of having an indicating instrument in the form of an angle gauge which is affected by a follower pin 7 the indicating instrument in accordance with the embodiment of Figs 2 and 3 consists of a distance meter which is applied on the upper face of the coupling hous¬ ing and which, via a sensing arm 17 extending through the coupling housing wall, abuts against the upper face of the arm in the area of the free end thereof. In this manner the distance meter senses the relative spacing between the coupling housing and the arm. On the other hand, in accordance with embodiment of Fig. 1 the fol¬ lower pin 7 is connected to the arm and is carried through the flexible member wall 11, and the relative spacing between the arm and the coupling housing is sensed from the angular deflection of the corresponding sensing arm 18 of the angle gauge which arm engages the follower pin 7. As regards measurement accuracy and reliability it is insignificant which type of indicating instrument, angle meter or distance meter, that is used in practice. However, the position of the indicating instrument may be varied according to need, and either it may be positioned horizontally as illustrated in Fig. 1, in parallel with the longitudinal axis of the load-sens¬ ing device, or be directed outwardly relatively to the longitudinal axis, as illustrated in Figs 2 and 3. The two positions may not be equally well suited for all applications. Reference is now made to Figs 4-8 showing a number of possible applications of the present invention. In Fig. 4, the inventive object thus is used to sense the load on a wire and it is mounted on the wire in such a manner that the latter assumes an initially curved confi¬ guration. When loaded, the wire will tend to straighten and in doing so will expose the load-sensing device to a bending moment which may be read on the indicating instrument. Upon attainment of a critical load the micro¬ switch will break or close an electric circuit, thereby affecting an indicating device or a relay, which serves to actuate an external electric circuit, e.g. the one charged with energising an electric motor. In accordance with the embodiment of Fig. 5 an upper portion of the load-sensing device is provided with a projecting lug 19, applied by welding, and at its lower end it supports a lifting hook 20. The lug 19 is attached to a chain and when a load is exerted on the lifting hook the flexible member will be exposed to a bending moment which may be read on the indicating instrument. This embodiment of the load-sensing device is designed to be used purely as a weighing device, having no switch, and for this reason the cable and contacting means have been omitted. In Fig. 6 the load-sensing device in accordance with the invention consists of a horizontal shaft or pin mounted in a shackle. When the shackle is exposed to load in connection with lifts or pulls, the load-sens- ing device is exposed to a bending moment, allowing the size of the load to be determined. Fig. 7 illustrates the legs on which for instance a storage bin or pocket is supported. Two possible posi¬ tions of the load-sensing device are illustrated, a first position underneath the left-hand support leg in which case the load-sensing device is exposed to load in the same manner as a freely deposited beam, and a second position in which the device by means of its bearing sup¬ ports is welded to the right-hand support leg, whereby that load exerted on the support leg and the compression of said leg resulting from said load will affect the load-sensing device as a bending moment. In Fig. 8, finally, is shown an embodiment, accord¬ ing to which the load-sensing device is used as a vehicle axle mounted load guard. Also in this case, the load- sensing device is intended to be welded with the aid of the bearing supports and will be affected by a bending moment resulting from the load on the vehicle axle. Pre¬ ferably, the indicating device may be positioned in the driver's cabin of the vehicle in order to alert the driver when a critical load level is attained. The dis¬ play instrument, on the other hand, has been omitted, since the load-sensing device position as a rule makes reading of the instrument impossible. Possible Modifications of the Invention It should be obvious that the present invention may be modified in various ways within the scope of the appended claims. For example, the flexible member and the arm need not have a circular cross-sectional configura- tion but varieties of other cross-sectional configura¬ tions are possible. In addition, it is possible to use more than one switch in each load-sensing device. In this case, the various switches may be adjusted to open or close an associated electric circuit in response to dif¬ fering load values. In accordance with Fig. 1 including four indicating lamps, for example four switches are needed, said switches closing and opening one electric circuit each. The switch need not either be a separate switch affected by a set screw. Following certain minor modifications it is quite possible to arrange for the set screw and a contacting surface on the arm to form the switch proper. It is likewise possible to dispose the set screw on the arm and a switch on the flexible member or in the coupling housing, i.e. a reversed location compar¬ ed to the embodiments illustrated in the drawing figures. In order to obtain maximum amplification of the deflection of the flexible member at the outer free end of the arm it is advantageous to connect the arm with the flexible member as near as possible to one end por¬ tion thereof, and to position the switch as far as pos¬ sible towards the opposite end portion of the flexible member. However, the invention is not limited to such locations but instead the expression "end portion" should be regarded to comprise at least the outermost fourth of the length of the member concerned. In addition, the expression "parallel or alongside" should not be inter- preted to define a strictly parallel orientation but rather to indicate that the longitudinal axes extend in the same main direction at an angle with respect to one another that could, however, be comparatively large, per¬ haps up to approximately 10-20°. Although preferable it is not necessary that the arm is attached to the end wall of the flexible member as it could also be attached to the tube wall. Obviously, it is not either necessary that the load-sensing device is formed with a separate cou¬ pling housing as the flexible member could be of equal length as or even longer than the arm, and house the switch. In the above description and in accordance with the embodiment illustrated in the drawings several ways of exerting load of the load-sensing device are described. Further applications and load exertion ways are possible within the scope of the appended claims, and the inven¬ tion encompasses all arbitrary loading methods according to which the load-sensing device is exposed to a bending moment. However, it should be understood that a load- sensing device in accordance with the present invention is not limited to use only in connection with an electric circuit but that also other types of signalling circuits are possible, such as optic signalling circuits. Obvious¬ ly it is also possible to use the load-sensing device to indicate, to alert, or to interrupt the energisation when a low load level is sensed, for instance when a pocket comes close to being empty.

Claims: CLAIMS 1. A load-sensing device of the kind comprising a resiliently flexible member (2) having a tubular cross- sectional shape with an interior cavity (12), and an arm (13) disposed in said cavity (12) and having a longitudi- nal axis extending essentially in parallel with or along a longitudinal axis of said flexible member (2), one end portion of said arm being rigidly connected to the flex¬ ible member whereas an opposite end portion of said arm is free, in consequence whereof the distance between the free end portion of the arm and the flexible member is changeable in response to load exerted on the flexible member and to the resulting flexural deformation of said member, c h a r a c t e r i s e d in that in the area of the free end portion of the arm said device comprises a switch (15) which, owing to the relative movement between the flexible member and the free arm end, may be shifted between an open and a closed position, and which is arranged to close or open a signalling circuit upon attainment of a predetermined load the value of which may be set by means of a set screw (16) affecting said switch (15). 2. A load-sensing device as claimed in claim 1, c h a r a c t e r i s e d in that said arm (13) is rigid¬ ly connected to an end wall (14) of said flexible member (2). 3. A load-sensing device as claimed in claim 1 or 2, c h a r a c t e r i s e d in that the flexible member (2) is closed in order to serve as an essentially dust and moisture impervious housing. 4. A load-sensing device as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the flexible member (2) has a tubular shape with an end wall ( 14) at one end and a coupling housing (5) at the opposite end. 5. A load-sensing device as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that in the area of the free end portion of the arm said device comprises a transducer (17, 18) arranged to sense the distance between the arm (13) and the flexible member (2). 6. A load-sensing device as claimed in claim 5, c h a r a c t e r i s e d in that the transducer (17, 18) affects an indicating instrument (6) arranged to indicate the relative distance between the flexible member (2) and the arm (13).

Inventors: JOHANSSON EILERT, JOHANSSON, EILERT
Applicants: HALL FRANK, JOHANSSON EILERT, HALL, FRANK, JOHANSSON, EILERT
Application year: 1996
Main classification: G01L1
IPC codes: G01G3, G01G19, G01L1, G01L5