EP0207923B1 - Displacement detector - Google Patents

Description

The invention relates to an apparatus for detecting a physical deviation of a part, for example movements or deformations of a part or variations in the thickness of a part.

Such an apparatus is known from document US-A-2,058,518. This document describes an apparatus for detecting variations in the thickness of a part comprising four electromagnets, a slurry electromagnet having its magnetic circuit open, and a movable frame linked to the part to be checked.

An exemplary application of the device according to the invention is that of load limiter for a lifting machine and it is in this exemplary application that the invention will be considered more particularly in the following.

The function of a load limiter on a hoist is to stop the movement of the hoist when the lifted load reaches a determined nominal value. The existing devices include a strain gauge detector which generates a signal proportional to the force which arises in the suspension cable and a measuring device possibly equipped with a means of protection against false alarms. A strain gauge must be closely linked to the part to be checked and is inseparable from it. In addition, the existing devices have performances which do not meet the conditions required to ensure perfect operational safety. In particular, it is not sufficient that a load limiter is capable of interrupting the rise of a load when a given admissible limit overload is reached, it must also be capable of limiting in any circumstance the dynamic forces to bridge supporting the lifting machine.

Finally, existing devices are sensitive to overloads, temperature variations and oscillations, which causes untimely tripping, performance degradation, or even mechanical degradation which renders the safety means themselves ineffective.

The subject of the invention is an electronic detection device which is of flexible adjustment and of universal application and which is relatively insensitive to oscillations and temperature variations.

Another object of the invention is a deviation detection device provided with a self-control which guarantees perfect operating and use safety.

According to another aspect, the invention relates to a safety device for a lifting machine, which is of great mechanical strength and which satisfies all the conditions required to ensure perfect safety and in particular to limit efforts at all times. dynamic at the bridge and which allows the admissible overload to be adjusted with great precision.

These objectives are achieved according to the invention by a deviation detection device comprising four electromagnets mounted on a Wheatstone bridge, at least one electromagnet having its magnetic circuit open and the other electromagnets having their magnetic circuit closed, a movable armature disposed at a certain distance from the ends of the aforementioned open magnetic circuit and linked to the part to be checked so as to gradually approach said open magnetic circuit as a function of the value of the physical difference of the part to be checked.

A threshold conditioner circuit is connected to receive the detection signal from the Wheatstone bridge and at least one threshold signal, preferably adjustable, to produce at least one alarm signal when the detection signal each time exceeds the value of a threshold signal.

The deviation detector can be combined with a deformation sensor comprising, according to the invention, a body having at least one elastic deformation zone capable of responding elastically to an external mechanical stress applied to said body so as to modify the length of this body, one end of the body being made integral with the housing of the detection bridge and the other end of the body being linked to the movable armature of the detector, so that the movable armature is displaced relative to the housing of the detector in operation of the external mechanical stress applied to the aforementioned body.

The detection device according to the invention has the advantages of being able to be used in any environment (vibrations, temperature) and of allowing great flexibility of adjustment. In addition, the detection signal produced is considerably (50 to 100 times) greater than that produced by the strain gauges so that this detection signal can be transmitted over a long distance to an electronic monitor without requiring any special precautions.

In addition, combined with the deformation sensor according to the invention, the detection device constitutes a very secure control device because the sensor does not undergo any degradation even if the stress applied to the sensor is five or six times greater. at the expected nominal value.

The deviation detector according to the invention makes it possible to detect and control any physical deviation, any displacement or any deformation, even micrometric, of a part. It is thus susceptible of numerous applications. For example, controlling the deformation of a beam, a frame, a machine frame, a truck chassis; continuous control of the thickness of a coating; the control of the flatness of a part, without counting its use in a load limiter as already mentioned above.

• - la figure est un schéma simplifié de l'appareil de détection d'écarts selon l'invention;
• - les figures 2 à 4 représentent trois modes d'exécution exemplaires d'un capteur à déformation selon l'invention destiné à être combiné à l'appareil de détection d'écarts selon l'invention.

The invention is described in more detail in the following, based on the attached drawings. wherein:

• - The figure is a simplified diagram of the deviation detection apparatus according to the invention;
• - Figures 2 to 4 show three exemplary embodiments of a deformation sensor according to the invention intended to be combined with the deviation detection device according to the invention.

Referring to Figure 1, we see four electromagnets 11 - 14 mounted in Wheatstone bridge. Two electromagnets 11, 13 have their magnetic circuit open and two electromagnets 12, 14 have their magnetic circuit closed. A single electromagnet could have an open magnetic circuit, but the inventor has found that the detection sensitivity is better when at least two electromagnets with open magnetic circuit are provided, connected in two non-contiguous branches of the bridge. The electromagnets are arranged in a metal case 16 and embedded in an epoxy resin used to freeze the electromagnets in the case and to insulate them in order to prevent their heating while keeping them all at exactly the same temperature.

At a certain distance E from the ends of the open magnetic circuit (s) of the bridge 10 is disposed a movable armature 15 linked to the part to be checked so as to progressively approach the abovementioned open magnetic circuit (s) as a function of the distance between the part to be checked, for example as this part deforms under the effect of a stress. The electric current flowing in the windings of the electromagnets 11 and 13 varies regularly as a function of the movement of the armature 15 with respect to the open magnetic circuits, that is to say as a function of the variation of the air gap E The detection current D is applied to a threshold conditioner circuit 20 in which it is compared with a predetermined adjustable threshold value S in order to produce an alarm signal A when the detection signal D exceeds the predetermined threshold. In the embodiment shown in FIG. 1, the detector comprises two threshold circuits each arranged for a distinct threshold value S1 and S2. The thresholds can be adjusted using potentiometers 21A and 21 B respectively. The alarm signals A produced at the output of the detector actuate control relays in a relay block 27 and these transmit the control signals necessary to the drive members of the machine on which the detection device is installed. Each threshold circuit 20 controls an output relay 26. The activation of these relays is advantageously timed by a timing device 23 adjustable using a potentiometer 24. Each crossing of threshold is indicated on an indicator light 25. The adjustment of each threshold S makes it possible to balance the bridge 10 to the desired value, regardless of the width of the air gap E. It is therefore possible to electronically balance the detection bridge in a range of variation of the air gap E ranging for example from 0 to 3 mm. This gives the detector according to the invention not only great sensitivity, but also great flexibility. It is even possible to provide four electromagnets with an open magnetic circuit, each arranged in a branch of the bridge in order to each control a separate gap or a separate load.

The movable frame 15 is linked to the part to be checked. In the application example considered here, that is to say that of a load limiter for a lifting machine, the aforementioned armature is integrated into a deformation sensor intended to sense the level of stress applied to the suspension cable by a suspended load. Exemplary embodiments of a deformation sensor according to the invention will be described later on, based on FIGS. 2 to 4.

For the moment, let us consider for example a sensor dimensioned for a nominal load of 1000 kg and equipped with the detection device described above, the assembly being installed on an overhead crane. The first detection threshold S1 is adjusted using the potentiometer 21A only with the weight of the hook used to suspend the load. The potentiometer 21A is precisely adjusted so as to pass, with the smallest possible overshoot, the point of ignition of the indicator 22A; the time delay T1 is then adjusted using the potentiometer 24A by displaying on an indicator light 25A. At this point, if the hook descends to the ground, the threshold detector automatically cuts the downward movement when the hook touches the ground.

After having suspended the load of 1000 kg, the second detection threshold S2 is adjusted using the potentiometer 21 B. This potentiometer is adjusted so as to pass with the smallest possible overstepping, the point of ignition of the indicator 22B then the potentiometer 21 B is adjusted very slowly in the opposite direction until the indicator 22B goes out. Simultaneously, after having started the lifting movement, the time delay T2 is adjusted using the potentiometer 24B so that the dynamic effects generated at the time of starting have no influence, which is displayed on the indicator 25B. At the time of start-up, the 25B warning light cannot light up. When these adjustments are made, the load limiter is set to stop the movement of the hoist as soon as the rated load of 1000 kg is exceeded. The design and adjustment of the detector thus have the effect of neutralizing the dynamic effects and the resonance effects in the structures on which the detection device is installed.

Returning now to FIGS. 2 to 4, it can be seen that the sensor consists of a parallelepipedal metallic part in the body of which is created at least one deformation zone capable of varying the length of the part. when it is subjected either to traction or to compression. In the example illustrated in Figure 2, the sensor is arranged to detect deformations caused by a tensile force. This sensor 30 has two deformation zones 31A and 31 B. The number of deformation zones can be arbitrary and vary according to the available surface of the part used and according to the value of the desired deformation. The deformation zones 31A and 31B are created by the formation of the cutouts 32 and 33 respectively, which leaves the part 30 with two branches 34 and 35. When a traction is exerted on the two branches 34 and 35, these branches serve as lever arm to produce the desired deformation in zones 31A and 31B, the deformation produced being automatically amplified mechanically at the end of the branches 34 and 35. A branch, in this case branch 34, carries a support piece 36 on which is fixed the housing of the detector 10. The end 37 of the other branch, namely the branch 35, carries the movable frame 15 of the detector.

The deformation sections are calculated as a function of the load to be checked and above all so that the working rate, under the effect of the nominal load for which the sensor is designed, is significantly lower than the buckling rate.

The buckling of the mechanical part is made impossible by the addition of the stop parts 38 and 39 controlling the deformation of the part, in the desired parameters. These two stops 38 and 39 are high-strength steel screws, quality 12.9 for example, calculated as a function of the traction torque that they will have to undergo. They cross respectively and over the entire height, the branches 34 and 35 in a bore of diameter greater than their own diameter and each come to be screwed into the central body of the part 30. The screws 38 and 39 are adjusted according to the deformation desired, and permanently blocked to prevent any variation of the parameters.

By adjusting the length of the branches 34 and 35 or the distance between the axis of the measurement points 36 and 37 and the axis of application of the force, the deformation value which will be measured at the aforementioned measurement points is adjusted. Similarly, it suffices to act on the two screws 38 and 39 to limit the threshold of mechanical deformation of the part, making it impossible to exceed the elastic limit of the deformation sections 31. This sensor can withstand stresses five to six times greater than the nominal load for which it was designed, without any risk of deterioration. By varying the deformation section (s) or by simply increasing the thickness of the part 30, an unlimited range of traction sensors is obtained which are a function of the load to be checked.

For example, a sensor calculated for a nominal load of 1000 kg. When this load acts directly on the sensor and an elongation of 0.6 mm is obtained between the two combined measurement points, the deformation of 0.6 mm is the cumulative deformation value of the branches 34 and 35, namely , at equal value, 0.3 mm for branch 34 and 0.3 mm for branch 35. The two screws 38 and 39 are then adjusted for a maximum deformation of approximately 0.4 mm from rest, c that is to say without charge. Therefore, the range of deformation controlled and measured may vary under the effect of the load from 0 to 0.8 mm, maximum point to reach the mechanical blocking of the traction sensor. The tolerance of the air gap E is established so as to maintain a small clearance (for example 0.2 mm) when the maximum locking is achieved, mechanical deformation at the measurement points 36 and 37 then being impossible.

Figure 3 shows a sensor having the same body as the sensor of Figure 2 but arranged to measure deformations caused by compression forces. The difference in arrangement is observed, in particular when mounting the parts 36 and 37 coupling the branches 34 and 35 of the sensor to the detector. In this embodiment, the locking screws 38 and 39 work in compression and no longer in traction.

Figure 4 shows an embodiment of the sensor according to the invention arranged to be fixed on a suspension cable. This allows the device according to the invention to be installed on an existing lifting device without modifying the structure. The sensor here consists of a part 30 having an elastic deformation zone 31 and two branches 34 and 35 formed by a cutout 32. The branch 34 carries two arms 41 and 42 on which two pulleys 43 and 44 are mounted. The branch 35 carries an arm 45 at the end of which is mounted a cable clamp device 46. The apparatus is fixed to the suspension cable so that the cable C passes through the grooves of the two pulleys 43 and 44 and under the cable clamp 46. The ends of the arms 41 and 42 are provided with two stop screws 47 and 48 intended to hold the cable C in the grooves of the pulleys. The detector is mounted on the branch 35 of the sensor and the movable armature 15 is fixed on the arm 41. The armature 15 approaches the open magnetic circuit contained in the detector as the stress created in the suspension cable increases. by the suspended load. In this case, the mechanical resistance of the sensor has no influence on the safety factor of the installation since the sensor is not inserted in the traction chain; the safety factor only depends on the safety factor of the cable.

To extend the range of this sensor as a function of the load to be checked, it suffices to vary three parameters: the deformation section of the part, the thickness of the alloy steel part and the cable deflection angle by acting on the length of the arm 45 or on the diameter of the pulleys 43 and 44. The combination of these three factors gives an unlimited range of sensors traction.

To obtain the blocking of the deformation at the desired value, it is also sufficient to act on the blocking screw 49. The above characteristics are the only differences between the two sensors which, if necessary, can be used simultaneously to control a same charge.

• - signaler tout dérangement possible dans le lecteur, par exemple: interruption où défectuosité d'un enroulement d'électro-aimant, interruption dans le câble de raccordement, mauvais contact au bornier, écrasement du câble, etc.;
• - signaler toute défectuosité d'un élément dans l'alimentation stabilisée, par exemple: fusible sauté, transformateur brûlé, stabilisateur défectueux, etc.;
• - signaler toute coupure du courant réseau ou tout déséquilibre d'une phase;
• - signaler toute défectuosité dans le module électronique, par exemple: circuit intégré défectueux, diode défectueuse, mauvais contact au bornier, etc.
• - signaler toute défectuosité dans le circuit de relayage, par exemple: bobine de relais brûlée, contact perlé, fusible de protection sauté, mauvaise connexion, etc.;
• - signaler toute défectuosité du capteur, par exemple: affaiblissement d'un élément mécanique, mauvaise utilisation du capteur, déformation permanente, etc.

The relay block performs the following functions:

• - report any possible fault in the reader, for example: interruption or defect in an electromagnet winding, interruption in the connection cable, poor contact at the terminal block, crushing of the cable, etc .;
• - report any defect of an element in the stabilized supply, for example: blown fuse, burnt transformer, defective stabilizer, etc .;
• - report any mains power cut or any phase imbalance;
• - report any defect in the electronic module, for example: defective integrated circuit, defective diode, poor contact at the terminal block, etc.
• - report any defect in the relaying circuit, for example: burnt relay coil, pearl contact, blown protection fuse, poor connection, etc .;
• - report any defect in the sensor, for example: weakening of a mechanical element, improper use of the sensor, permanent deformation, etc.

In short, the relay block signals any variation in the parameters for which the electronic module has been set, that is to say that any misadjustment at the level of the fixing of the detector to the sensor or any pirate modification test automatically leads to neutralization. of the installation.

The device is thus provided with a permanent self-control which prevents any operation if a fault appears, the device being placed in safety instantaneously in the same way as if the nominal load for which the device has been set is exceeded In other words, the safety device according to the invention is not used simply to monitor a load securely, it also signals any external circumstance which hinders it in its operation.

The device can be completed by a light and / or acoustic signaling device, provided near or at a distance, to directly inform the user when the load for which the device has been set is exceeded or when its operation is hindered.

Claims (10)

1. Device for detecting a physical deviation of a component, comprising four electromagnets (11 - 14) connected in the form of a Wheatstone bridge (10), at least one electromagnet (11, 13) having its magnetic circuit open, the other electromagnets (12, 14) having their magnetic circuit closed, a moveable armature (15) located at a certain distance (E) from the ends of the abovementioned open magnetic circuit and connected to the component to be monitored, in such a way as to come progressively nearer to the said open magnetic circuit as a function of the value of the said physical deviation of the component to be monitored.

2. Device according to claim 1, characterized in that the Wheatstone bridge (10) comprises at least two electromagnets with an open magnetic circuit, which are connected in two non-contiguous branches.

3. Device according to claim 1 or 2, characterized in that it also possesses a threshold conditioning circuit (20) connected for receiving the detection signal (D) from the Wheatstone bridge (10) and at least one preferably adjustable threshold signal (S) and for generating at least one alarm signal (A) whenever the detection signal (D) exceeds the value of the threshold signal.

4. Device according to claim 3, characterized in that delay means (23, 24) are connected to the output of the threshold conditioning circuit, in order to delay the generation of the alarm signal or alarm signals (A).

5. Device according to any one of the preceding claims, characterized in that it comprises a deformation sensor consisting of a body (30) having at least one elastic deformation zone (31) capable of reacting elastically to an external mechanical stress exerted on the said body so as to change the length of the said body, one end of the body (30) being fixed to the housing of the detection bridge (10) and the other end of the body (30) being connected to the moveable armature (15) of the detector, in such a way that the moveable armature (15) is displaced relative to the housing of the detector as a function of the external mechanical stress exerted on the abovementioned body.

6. Device according to claim 5, characterized in that the sensor consists of a part (30) having at least one branch (34, 35) connected to the body of the part by means of an elastic deformation zone (31), so as to experience an angular movement relative to the body of the part under the effect of a mechanical stress exerted on the part.

7. Device according to claim 5 or 6, characterized in that the body (30) of the deformation sensor is equipped with at least one preferably adjustable stop (38, 39), to limit the deformation caused by a mechanical stress for the purpose of preventing buckling.

8. Device according to any one of the preceding claims, characterized in that it is associated with a deformation sensor comprising a body (30) having at least one elastic deformation zone (31) capable of reacting elastically to a mechanical stress caused by the said load or the said force, so as to change the length of the abovementioned body (30).

9. Device according to any one of claims 1 to 7, characterized in that it is associated with a deformation sensor consisting of a part (30) having at least one branch (34, 35) connected to the body of the part by means of an elastic deformation zone (31), so as to experience an angular movement relative to the body of the part under the effect of a mechanical stress exerted on the part.

10. Use of the device according to any one of claim 1 to 7 in a deformation sensor comprising a body (30) having at least one elastic deformation zone (31) capable of reacting elastically to a mechanical stress caused by the said load or the said force, so as to change the length of the abovementioned body (30), especially a body of a part comprising at least one branch (34, 35) connected to the said body by means of an elastic deformation zone (31), so as to experience an angular movement relative to the body of the part under the effect of a mechanical stress exerted on the part.

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