DESCRIPTION

The present invention refers to a bistable magnetic proximity sensor, which is particularly suitable for integration in systems provided to control the movement of a moving platform in general.

As is largely known in the art, a bistable magnetic proximity sensor is a device that detects the presence of a magnetic field generated by an external magnetic body, wherein it switches over into two distinct stable states in accordance with, i.e. depending on the polarity offered by the external magnetic body, while supplying a corresponding electric signal as an output.

A bistable magnetic proximity sensor of this kind is currently used in connection with a wide variety of applications in different fields of industrial automation; anyway, it is certainly - and above all - largely used in connection with equipment and apparatus falling within the general domain of moving platforms, wherein these moving platforms may be understood as including all kinds of lifting equipment, such as for instance elevators, gods lifts, hoists, chair lifts, escalators, stair lifts and elevators, aerial or overhead platforms, and the like, but also crane jibs and booms, moving staircases, passenger conveyors, and the like.

In particular, in a lift or elevator installation the bistable magnetic proximity sensor is used to detect and indicate an end-of-travel condition of an elevator car, or lift cage, moving inside a lift shaft, i.e. when the lift cage reaches either one of an uppermost and a lowermost floor.

As attached to the lift cage, the bistable magnetic proximity sensor keeps in an activation state when the cage is travelling along the lift shaft, whereas it keeps in a de-activation state when the cage is at an end-of-travel level. The state of the sensor changes when the sensor moves along in proximity of an external magnetic body provided in the lift shaft just slightly in advance of the uppermost floor or just slightly in advance of the lowermost floor. The sensor is arranged to deliver an indication of the state condition thereof to a control unit, such as for instance a microcontroller, a DSP, a computer, a PLC, or the like, via a respective electric output signal.

In an end-of-travel condition, the de-activation state signal delivered by the sensor to the control unit will indicate that there are no further floors beyond the one being reached, and that a subsequent operation of the lift cage can only occur in a reverse travelling direction as opposed to the one being completed.

From a construction point of view, known in the art there are bistable magnetic proximity sensors of a variety of kinds and types. Among these ones, widely used is in particular a bistable magnetic proximity sensor, the operation of which is based on thin reed-like plates or strips that are actuated magnetically. A sensor of this kind substantially comprises a casing, inside which there is enclosed a reed contact. This contact is formed of two thin strips of ferromagnetic material, which are kept at a pre-determined distance from each other in the contact zone, and which are submerged in an inert gas to ensure electrical insulation. The contact zone and the inert gas are contained inside a glass phial. The operation of the contact as a bistable one, i.e. in a bistable mode, is brought about through the use of one or more polarization magnets placed in contact with or close to the glass phial in view of inducing a magnetic field that is not by itself sufficient to cause the contact to close, but is certainly capable of keeping it in the closed state thereof after the action of an external magnet caused it to switch into such state. The reed-like strips can be actuated when a magnetic field generated by an external magnetic body combines with the magnetic field of the internal magnetic means. Such strips can therefore reach an operative position to perform a respective opening, closing or switching over of an electric contact. The operative or working condition reached by said actuation strips is maintained even when the sensor moves out of the action range, or sphere of activity, of the magnetic field generated by the external magnetic body, and the strips are able to switch over into a different operative position when the sensor eventually comes across an external magnetic body having an opposite polarity. Bistable magnetic proximity sensors made in accordance with this kind of construction have a major drawback in that they are rather brittle owing to the glass phial that is used to contain the inert gas and keep the reed-like strips in the due operative position thereof.

In the case that the sensor happens to suffer a shock, e.g. as due to its falling down from even quite modest a height, of say half a metre or so, the working ability thereof may be seriously impaired.

A further drawback is brought about by the possibility for the contact to switch over from a stable state thereof to the other one owing to vibrations or shocks of even a modest extent or magnitude that may not be such as to necessarily damage the internal reed contact. This circumstance gives in fact rise to certain reluctance in using these sensors in all such cases and applications in which the apparatus, which such sensors are intended for, is likely to undergo vibrations.

Still another drawback derives from the particular manufacturing difficulty found and the high production costs encountered in making a bistable magnetic proximity sensor that is further provided with an exchange-contact feature. In this case, in fact, the problems due to brittleness, vibration-induced malfunction or damage, and the like, are aggravated to a further extent.

Widely known is on the other hand also the use of electronic bistable magnetic proximity sensors based on the so-called Hall effect. As largely known in the art, the Hall effect is the formation of a difference in potential between two mutually opposite sides of a conductor carrying a current of electrons, when such conductor is immersed in a magnetic field that is orthogonal to the direction of said current of electrons. As is also largely known in the art, the operation of a sensor of this kind is substantially an electric one. Such sensor comprises a phnted-circuit board supporting a Hall-effect chip, which is assigned the task of detecting the presence of the magnetic field generated by the external magnetic body, which may in turn present either one of the two opposite polarities. Electronics is then used to maintain either one of the two stable states corresponding to the detected polarity of the external magnetic body encountered.

However, although the use of the Hall-effect bistable magnetic sensor is independent of the speed of displacement of the moving platform under regular operating conditions, the Hall-effect chip still requires being energized, i.e. a constant power supply, and this represents a kind of often insurmountable hindrance to its use in applications of the considered kind.

Moreover, sensors of this kind are not able to maintain the activation or de- activation state thereof in all operating contexts, i.e. under all operating conditions thereof, owing to them working in a basically electric mode. In case of a temporary power failure or a similar circumstance, the Hall-effect bistable magnetic proximity sensor would in fact give off, i.e. lose the state it had in a moment preceding the power-supply failure event and, when the power supply is then restored, i.e. it is switched on again, it always and in all cases re-initializes in the activation state thereof. Now, as all those skilled in the art are fully aware of, this is a shortcoming that gives rise to a number of rather serious, undesired drawbacks.

With reference to an elevator installation, for instance, if the power-supply is interrupted, i.e. fails, to be then immediately restored while the elevator cage is in an extra-run condition, the bistable Hall-effect magnetic proximity sensor, which was in the de-activation state thereof, re-initializes by assuming the activation state, instead of the de-activation one, to thereby deliver the enable signal to the control unit that would allow the elevator cage to resume extra-run travelling, i.e. a condition that had on the contrary to be prevented from occurring.

A drawback is furthermore encountered also when the bistable Hall-effect magnetic proximity sensor moves in front of and passes by an external magnetic body placed in a travelling shaft of the elevator cage just slightly in advance of the uppermost or top floor or just slightly in advance of the lowermost or bottom floor under a power-supply failure condition. In this case, in fact, the sensor is not able to switch over from the activation state to the de-activation state thereof, due to its being de-energized or turned off, actually, and, when the power supply is then restored, the sensor will therefore incorrectly take the activation state thereof. It therefore is a main object of the present invention to do away with the drawbacks encountered in the prior art by providing an improved kind of bistable magnetic proximity sensor that is not inherently brittle and has a good resistance to shocks and vibrations, while doing away with the need for it to be electrically energized, so as to definitely extend the limits of the applicability range thereof.

Another purpose of the present invention within the above-stated main object thereof is to provide a bistable magnetic proximity sensor that, by solely using a three-wire cable instead of a two-wire one, turns into a bistable with exchange contact.

Still another purpose of the present invention is to provide a bistable magnetic proximity sensor that is particularly robust and reliable.

An equally important purpose of the present invention is finally to provide a bistable magnetic proximity sensor, which is capable of being produced with production means and methods as they are readily available and largely used in the art.

According to the present invention, as recited and defined in the claims appended hereto, some advantageous improvements are set forth; in particular a simplification of both construction and assembly of the inventive bistable magnetic proximity sensor should be stressed in this connection.

A further advantage lies in a possibility given for a rated detection range (or sensitiveness field) of the bistable magnetic proximity sensor, i.e. a distance of the external magnetic body from the bistable magnetic proximity sensor at which the former can be detected by the latter, to be increased.

The object and the features of the present invention, as well as the purposes and advantages thereof as set forth above, along with further ones that shall become apparent from the following disclosure, are reached in a bistable magnetic proximity sensor as defined in the independent claims and sub-claims appended hereto.

Anyway, features and advantages of the present invention will be more readily understood from the detailed description of an exemplary embodiment that is given below by way of non-limiting example with reference to the accompanying drawings, in which:

- Figure 1 is a schematical, perspective view of a bistable magnetic proximity sensor according to an embodiment of the present invention, as viewed with the cover thereof removed;

- Figure 2 is a schematical, perspective view of a detail of the bistable magnetic proximity sensor illustrated in Figure 1 ;

- Figures 3A and 3B are schematical views of an actuation reed-like strip in a first and a second operating position thereof, respectively; and

- Figure 4 is a schematical perspective, exploded view of a rotating magnetic element of the sensor shown in Figure 1.

With reference to Figures 1 and 2, the bistable magnetic proximity sensor according to an embodiment of the present invention comprises a casing 10, a cover (not shown), a switching unit 24, a phnted-circuit board 22, an actuation strip 26, a bipolar actuation magnet 70, and at least a first bipolar magnetic rotating element 28 and a second bipolar magnetic rotating element 30.

The casing 10 has a structure that develops, i.e. extends substantially longitudinally, i.e. in a lengthwise direction along an axis X contained in a reference plane, and is open on one side thereof that can be closed by joining a cover thereupon, in an inherently known manner. To such purpose, in the casing 10 there are provided a plurality of coupling means 32 that are adapted to couple with a corresponding plurality of complementary coupling means provided in the cover, in a manner that is largely known as such in the art. The casing 10 is comprised of a first housing portion 20, e.g. in the shape of a parallelepiped, and a second threaded terminal portion 80, e.g. in the shape of a cylinder, which can be joined by means of a collar 82 in the form of a nut. The second threaded terminal portion 80 is provided to enable the sensor to be mounted and secured either via a support that has already been patented by this same Applicant, or by means of a nut and locknut in any support whatsoever provided with a through-bore.

The first housing portion 20 provides internally a compartment that is so shaped and sized as to be adapted to accommodate the phnted-circuit board 22, the switching unit 24, the actuation strip 26, the bipolar actuation magnet 70, as well as the first bipolar magnetic rotating element 28 and the second bipolar magnetic rotating element 30 therein. Such inner compartment is delimited at the base thereof by a bottom wall 36 lying in front of and extending parallel to the side due to be closed with the cover, whereas on the sides thereof it is delimited by a first wall 38 and a second wall 40, which extend substantially parallel to each other, and which, jointly with a longitudinal boundary wall 58 of the sensor, join the respective sides of the bottom wall 36 with the sides of the cover.

On the bottom wall there are provided pegs 34, preferably more than just a single one, e.g. in the number of two, in a position adjacent to the connection region, at which the first housing portion 20 joins with the second cylindrically shaped threaded terminal portion 80. The way in which such pegs 34 are arranged may be selected as desired, e.g. they can be provided in a longitudinal arrangement.

The side walls 38, 40 are both formed so as to feature - at least in a respective terminal section 74, 76 thereof close to the boundary wall 58 - a thickening extending transversally, i.e. in the direction of a width extending in the direction of an axis Y contained in the reference plane and substantially orthogonal to the axis X. Such transversal thickening enables a first pocket-like recess 42 and a second pocket-like recess 44 - spaced from each other and arranged longitudinally - to be provided in the terminal portion 74 of the side wall 38. These pocket-like recesses 42, 44 are open on the fitting side of the cover and, in a continuous manner, also laterally so as to let such aperture look towards, i.e. face the interior of the compartment. Similarly, a third pocket-like recess 46 and a fourth pocket- like recess 48 are provided - spaced from each other and arranged longitudinally - in the terminal portion 76 of the side wall 40 so as to be open on the fitting side of the cover and, in a continuous manner, also laterally so as to face the interior of the compartment. The pocket-like recess 42 is substantially symmetrical to the pocket-like recess 46 relative to the axis X. Similarly, the pocket-like recess 44 is substantially symmetrical to the pocket-like recess 48 relative to the axis X.

Optionally, one of the two side walls 38, 40, such as for example the side wall 38, may be provided with a support 60 for securing an optional bipolar magnetic element 62 thereto.

The switching unit 24 is any type of device or structure adapted to open, close or switching over the connections of an electric or electronic circuit by the actuation of, say, a push-button or any other similar control device. The switching unit 24 may for instance be comprised of, say, a miniaturized switch (i.e. a so- called microswitch), a DIP-type switch, a jumper, a pure or bare contact such as the one of a closed switch, and the like.

Referring now also to Figures 3A and 3B, the switching unit 24 is provided with recesses adapted to allow the pegs 34 to be fitted thereinto, and comprises a button 129, e.g. a spring-type push-button, located on a side of the switching unit 24 for opening/closing the contact terminals thereof. Such contact terminals may be connected to respective conductive pathways of the printed-circuit board 22, e.g. by soldering. For the related connections to be properly safeguarded, the switching unit 24 may be joined to the printed-circuit board 22 in such manner as to form a single-piece unitary construction therewith, e.g. by means of soldering, adhesive bonding or similar techniques. The conductive pathways of the printed- circuit board 22 are provided so as to extend and reach up to lands 64, 66, 68 that remain uncovered even after the switching unit 24 has been attached to the printed-circuit board 22.

At an outermost point 122 along the side of the switching unit 24 on which there is located the button 120, there is hinged on a first end portion of the actuation strip 26 so that the latter is able to oscillate by forming an acute angle with the side of the switching unit 24. The actuation strip 26 then extends towards the site of the button 120, moves beyond it, and keeps extending for example in a zigzag or similar pattern, thereby spacing out, i.e. moving away longitudinally from the switching unit 24 to eventually terminate into a second end portion thereof, on which there is formed an anchoring support 72. This anchoring support 72 enables the bipolar actuation magnet 70 to be attached there with the polarities thereof oriented in a substantially orthogonal manner relative to the longitudinal extension of the actuation strip 26, using any of a variety of techniques as largely known in the art, such as for instance adhesive bonding or the like, to this purpose.

Or, in a modified embodiment of the present invention, at least one portion of the actuation strip 26 may be formed of a permanent magnet with the polarities thereof oriented in a substantially orthogonal manner relative to the longitudinal extension of the actuation strip 26.

The pushable portion of the button 120 comes therefore to be located by construction in the enclosed space between the side of the switching unit 24 and the actuation strip 26. As a result, following an oscillation of the actuation strip 26 towards the side of the switching unit 24, a portion of the actuation strip 26 will be able to press against the button 120 until it fully closes down, whereas an oscillation of the actuation strip 26 in the opposite direction, i.e. away from the side of the switching unit 24, will be able to release the button 120 until the latter is enabled to fully open.

An assembly made up by the connection of the elements 22, 24, 26, 70 as described hereinbefore is then introduced in the inner compartment of the first housing portion 20, wherein due care shall be used to ensure that the pegs 34 fit into the related accommodation recesses in the switching unit 24, and that the lands 64, 66, 68 are located close to, i.e. on the side facing the second cylindhcally shaped threaded terminal portion 80. Securing the assembly 22, 24, 26, 70 in the receiving compartment may be done in any of a variety of manners as largely known as such in the art, such as for example by strewing the pegs 34 with adhesive or similar glue masses or by applying a simple locking device on the cover.

The actuation strip 26 is thus arranged in the receiving compartment with the second end portion thereof looking towards the boundary wall 58 and, as a result, the bipolar actuating magnet 70 attached thereto has its NORTH and SOUTH polarities oriented substantially along the direction of the axis Y.

In addition, the actuation strip 26 can avail itself of a fully clear space, i.e. a space free of any encumbrance or hindrance, inside said compartment, so that it is capable of freely oscillating along the direction of the axis Y between two different operating positions. As this is best shown in Figure 3A, in a first operating position thereof, the actuation strip 26 keeps the button 120 in its pressed-down state, so that the contact terminals of the switching unit 24 are closed in this condition, whereas, as best illustrated in Figure 3B, in a second operating position thereof, the actuation strip 26 does not exert any pressure onto the button 120, which therefore remains in the released state thereof and the contact terminals of the switching unit 24 are open in this condition.

The lands 64, 66, 68 may be connected, for example by soldering, with a first lead wire (not shown) acting as the return or common wire, a second lead wire (not shown) acting as the normally open or N. O. contact wire, and a third lead wire (not shown) acting as the normally closed or N. C. contact wire, all of them coming out of the cylindhcally shaped threaded terminal portion 80.

When all above-cited lead wires are connected, the operation of the sensor can be the typical one of an exchange-mode bistable, whereas, if the connection of either one of the second N. O. lead wire and the third N. C. lead wire is excluded, the operation of the sensor is the typical one of a simple bistable.

Through the connection of the above-cited lead wires, the bistable magnetic proximity sensor is thus able to deliver an output signal to a control unit, which is indicative of a respective one of the operating positions taken each time by the actuation strip 26. Optionally, a visual indication of the state of the output may be provided with the aid of a LED-based display (not shown).

To the purpose of facilitating, i.e. promoting the oscillation of the actuation strip 26 along the axis Y, the optional bipolar magnetic element 62 may be optionally secured to the support 60 of the wall 38, so that it turns out as being arranged in a manner in which it faces the bipolar actuating magnet 70.

Referring now also to Figure 4, each first and second rotating bipolar magnetic element 28, 30 may be made and provided to substantially include a pin 90, a bearing 92, a first magnetic piece 94, a second magnetic piece 96, a first bush 98 and a second bush 100.

In this embodiment of the present invention, for example, the bearing 92 is in a cylindrical shape and features two cavities separated by a partition, within which the pin 90 is co-moulded, in such manner as to enable the same pin 90 to extend from the bearing 92 on both sides thereof.

In a modified embodiment of the present invention, for example, the bearing 92 is in a hollow cylindrical shape and the pin 90 is able to be fitted into a pair of bores provided in a diametrically opposite arrangement in the bearing 92 so that the same pin 90 is again able to extend from the bearing 92 on both sides thereof.

The magnetic pieces 94, 96 are secured inside the respective ones of the two cavities lying diametrically opposite relative to the pin 90, so that the configuration is able to take a substantially cylindrical shape with the bases thereof formed by the surfaces of the same magnetic pieces. Each end of the pin 90 is coupled by fitting it into one of the bores 112, 114 provided in the bushes 98, 100, respectively, so that the pin 90 is allowed to freely rotate according to an axis of its own.

The first magnetic element 28 may be housed in the inner compartment of the first housing portion 20 by for instance fitting the bush 98 into the pocket-like recess 42 and the bush 100 into the pocket-like recess 46, or vice-versa. Similarly, the second magnetic element 30 may be housed in the inner compartment of the first housing portion 20 by fitting the respective bushes thereof into the pocket-like recesses 44, 48. The bushes 98, 100 are fitted so as to become firmly joined with the respective terminal sections 74, 76 of the respective side walls 38, 40.

This kind of coupling allows for free rotation of both the first magnetic element 20 and the second magnetic element 30 within the inner compartment of the first housing portion 20 about a respective axis Z1 , Z2 contained in the reference plane and substantially orthogonal to the axis X.

Advantageously, the pin 90 is made of a metal material, such as for instance stainless steel, which is different from the one used to make the bushes 98, 100, which may for instance be made of brass or bronze, so that each rotating bipolar magnetic element 28, 30 turns out as being self-lubricating, and this obviously allows each such magnetic element 28, 30 to rotate very smoothly under reduced friction and noise.

From an operational point of view, the bistable magnetic proximity sensor according to the present invention is capable of detecting the presence of a first external bipolar magnetic body. When the bistable magnetic proximity sensor happens to be immersed in a magnetic field of said first external magnetic body, the surface of the magnetic piece of the second rotating bipolar magnetic element 30 becomes the location of a magnetic flux. The second rotating bipolar magnetic element 30 is therefore able to rotate to thereby position itself so as to be facing said first external magnetic body with a polarity of an opposite sign.

When the first rotating bipolar magnetic element 28 happens to be immersed in a magnetic field generated by the second rotating bipolar magnetic element 30, or even said first external magnetic body, the surface of the magnetic piece of the first rotating bipolar magnetic element 28 becomes the location of a magnetic flux. Therefore, the first rotating bipolar magnetic element 28 is in turn able to rotate to thereby position itself so as to be facing said second rotating bipolar magnetic element 30 with a polarity of an opposite sign.

The first and second rotating bipolar magnetic elements 28, 30 can therefore move into a first configuration of mutual magnetic attraction that is a stable one, since said rotating bipolar magnetic elements 28, 30 are facing each other with the respective polarities of opposite sign. This first configuration of mutual magnetic attraction is therefore maintained even when the bistable magnetic proximity sensor moves out of the sphere of influence of, i.e. stops being affected by the magnetic field generated by the first external bipolar magnetic body.

In this first configuration of mutual magnetic attraction, the first and second rotating bipolar magnetic elements 28, 30 have their NORTH and SOUTH polarities oriented along the direction of the axis X and a respective polarity of the same NORTH or SOUTH sign looking to the actuating bipolar magnet 70. Conversely, such actuating bipolar magnet 70 is arranged with its NORTH and SOUTH polarities oriented substantially along the direction of the axis Y. As a result, assuming a reference surface that is substantially orthogonal to the reference plane containing the axis Y, the flux generated by the first and second rotating bipolar magnetic elements 28, 30 on the reference surface is substantially orthogonal to the flux produced by the actuating bipolar magnet 70 on the same reference surface.

The magnetic interaction that establishes between the rotating bipolar magnetic elements 28, 30 and the actuating bipolar magnet 70 is therefore reduced to a minimum as necessary for the actuation strip 26 to be moved into the first operating position thereof, while ensuring at the same time a stable contact that holds, i.e. keeps as such even when the bistable magnetic proximity sensor moves out of, i.e. stops being affected by the magnetic field generated by the first external bipolar magnetic body.

In the first operating position of the actuation strip 26, a corresponding first signal is delivered to a control unit.

When the bistable magnetic proximity sensor happens to come across a second external magnetic body that presents an opposite polarity as compared with the one of the first external magnetic body, the rotating bipolar magnetic elements 28, 30 are able to rotate to thereby move into a second configuration of magnetic attraction in the same way as described afore. Therefore, the reference surface becomes the location of magnetic fluxes that are orthogonal relative to the rotating bipolar magnetic elements 28, 30 and the actuation strip 26, respectively. As a result, the actuation strip 26 reaches the second operating position thereof.

This second operating position of the actuation strip 26 is kept unaltered even when the sensor leaves, i.e. moves out of the magnetic field generated by the second external magnetic body, since the sensor remains in the second configuration of magnetic attraction thereof.

In the second operating position of the actuation strip 26, a corresponding second signal is delivered to the control unit.

When used in conjunction with a control system for controlling the movement of a moving platform, such as a lift or elevator installation, to indicate an end-of-travel condition of the elevator cage, the bistable magnetic proximity sensor according to the present invention can be positioned on a cage at rather long a working distance, since the magnetic interaction between the rotating bipolar magnetic elements 28, 30 and the actuation strip 26 is relatively weak.

In addition, the bistable magnetic proximity sensor according to the present invention is capable of correctly issuing a signal indicating an activation or deactivation state thereof under any operating circumstance and condition. In fact, correct operation in the case of a temporary power-supply failure is anyway ensured by the position of the rotating magnetic elements, which, as this has been described afore, rotate depending on or according to the polarity of an external magnetic body in a manner that is fully independent of a power supply being or not being delivered to the sensor, actually.

In particular, when the above-cited sensor installed in the elevator cage passes by or close to one of the external magnetic bodies, which are provided in the elevator shaft in a position located in advance of a topmost floor and/or a bottommost floor, under a power-supply failure condition of the same sensor, the state of activation can be switched over, i.e. change into the de-activation state owing to the magnetic interaction of the magnetic elements 28, 30 with said external magnetic body, and this configuration of the magnetic elements 28, 30 is then kept as such in the same manner as described afore. When the power supply is eventually restored, the above-mentioned sensor shows correctly up in the de- activation state thereof, thereby delivering the correct signal to a control unit of the above-noted control system.

Fully apparent from the above description is therefore the ability of the bistable magnetic proximity sensor according to the present invention to effectively reach the aims and advantages cited afore, by in fact providing a bistable magnetic proximity sensor, as particularly suitable for integration in a control system adapted to control the movement, i.e. displacement of a moving platform, which is robust and reliable, and which allows for a definitely wider field of application. Provided is furthermore a bistable magnetic proximity sensor that may take the form of an exchange-contact bistable device.

It shall be appreciated that the present invention shall certainly not be solely embodied in the manner that has been described and illustrated hereinbefore, but can rather be implemented in many other embodiments, as well as modifications and variants thereof, without departing from the scope of the present invention, and that all embodiments and related modifications thereof set forth hereinbefore may apply either individually or in combination with each other.