WO2018025121A1

WO2018025121A1 - Linear position sensor.

Info

Publication number: WO2018025121A1
Application number: PCT/IB2017/054502
Authority: WO
Inventors: Davide ALGHISI; Damiano Crescini
Original assignee: Tpi Snc Di Paolo Crescini E C.
Priority date: 2016-08-02
Filing date: 2017-07-25
Publication date: 2018-02-08
Also published as: IT201600081373A1

Abstract

There is described a linear position sensor comprising: - a nut (2) configured to move in a linear manner and adapted to be fixed to an element the position of which is desired to be detected, - a multi-flighted screw (1) adapted to rotate in response to the linear movement of the nut, - at least one magnet (5) integral with an end of the multi-flighted screw with polarization orthogonal to the axis of the screw and adapted to rotate synchronously with the screw, - means (6) not in contact with said magnet, adapted to detect the rotation of the magnet and output (OUT) the linear position of the nut. Said means comprise detection means (7, 15) configured to detect the angular position of the magnet on a single turn and to detect the number of turns of the magnet, said linear position sensor comprising an auxiliary power supply source (11, 12) for said detection means, and managing means (10) adapted to switch the power supply of said detection means on said auxiliary source in the absence of supply voltage (Vin) deriving from an external power supply network.

Description

"Linear position sensor"

* * *

The present invention relates to a linear position sensor. More in particular, the invention relates to a linear position sensor integrated inside hydraulic or pneumatic cylinders and linear guides.

Systems with position controlling sensors arranged in the main movable members of mechanical systems of numerically controlled machine tools and robotized production lines, industrial and farming vehicles and earth-moving machines are known from the prior art. Electric linear actuators and hydraulic cylinders are some of the most widespread linear actuators in the industrial field and in mobile hydraulics.

Generally, in the industrial field, the movable part of the electric actuators is connected to the slider of the linear position sensor, which resides outside the actuator. With regards to mobile hydraulic applications, the sensors arranged outside the actuator may be inconvenient because the mobile members of the machinery may have multiple degrees of freedom. Furthermore, considering the levels of dirt and fouling which characterize the typical working environment of farming and earth-moving machines, the sensor fitted on the outside of the drive risks being damaged if it is not duly protected. For this reason, all the linear position sensors which may be mounted directly inside the hydraulic or pneumatic cylinder, or more in general inside the drive, are particularly attractive.

Currently, there are linear position sensors based on various operating principles.

Resistive sensors are known, such as that described in Patent US

4,386,552, which uses a potentiometric resistive sensor as a primary element of a linear position sensor inside a cylinder. This type of sensor consists of a slider, which includes a sliding electric contact and a circular resistive track on which the slider runs. The slider moves in circular motion and, by sliding, modifies the electric path of the track, thus determining a variation of the equivalent resistance between the two terminals of the resistive track.

The potentiometric sensor is housed in the fixed end of the hydraulic cylinder and, together with the mechanical system which couples it to the movement of the piston rod by means of a threaded screw, forms the linear position sensor. The mechanical system consists of a twisted square section bar, which is supported inside the fixed end of the hydraulic cylinder and is free to turn about its axis. The piston rod is perforated and accommodated inside the bar, to which is it coupled by means of a control bushing. The bar rotates in response to the linear motion of the control bushing included in the piston rod and controls the slider of the potentiometric sensor by means of a series of reduction gears.

The main limitations of this measuring technique relate to the wear of the resistive track by the sliding contact. Furthermore, in order to transduce the position of the cylinder rod, the resistive potentiometric sensor must be housed together with the piston coupling mechanism in the oil compartment, thus exposing the resistive track to the corrosive effects of the oil and of the impurities it contains. Finally, following a malfunction, the potentiometric sensor cannot be easily extracted to be replaced except by removing the fixed end of the cylinder in which it is housed.

Capacitive sensors are known, such as that described in Patent FR 2539868, which use a capacitive sensor as a primary element of an inner cylinder linear position sensor. This type of sensor consists of two armatures, one consisting of the piston rod itself, which is perforated and which allows the second armature, consisting of a rod integral with the fixed end of the hydraulic cylinder, to slide therein. The two armatures are electrically insulated from each other. The equivalent electric capacitance which can be measured between the two armatures varies as a function of the length of the stretch in which the two armatures are side-by-side.

This contactless measuring technique preserves the primary elements which form the sensor from mechanical wear. However, the capacitive sensor must be housed inside the oil compartment in order to transduce the position of the piston rod. So, the entire sensitive part of the sensor is constantly immersed in oil, which, in addition to possible corrective effects, displays considerable variations of dielectric constant according to the variation of the level of impurities, such as dirt and water, working temperature and pressure. Such an undesired variation of the dielectric constant reflects on the equivalent capacitance between the two armatures and, if it is not compensated, may be incorrectly interpreted as the variation of the cylinder rod position.

Furthermore, following a malfunction, the capacitive sensor cannot be easily extracted to be replaced: an armature is an integral part of the piston, while the other armature may be removed only after having removed the fixed end of the hydraulic cylinder.

Inductive sensors are known, such as that described in Patent US 6,943,543 which consists of a guide on which two conductive tracks are arranged, one for energizing and one for measuring respectively rectangular and V-shaped, which develop over the entire length of the guide. A U- shaped slider runs on the guide which includes a passive oscillating circuit. The circuit is powered by means of a specific electric pulse transmitted along the energizing track. The free reply of the oscillating circuit couples to the measuring track by inductive coupling. The coupling surface between oscillating passive circuit and the measuring track varies according to the position of the slider. The amplitude of the voltage at the terminals of the measuring track can therefore be correlated with the linear position of the slider. Having electric tracks arranged over the entire length of the measuring range, a sensor of this type is particularly susceptible to phenomena such as electromagnetic interference and thermal drift.

Patents US 6,234,061 and US 7,290,476 use a Linear Variable Displacement Sensor - LVDT as a primary element to determine the position of the piston rod which runs inside a hydraulic cylinder. The sensor consists of a pipe consisting of three windings arranged with parallel axes and with a movable ferromagnetic cylindrical core inside, which is mechanically connected to the piston rod. The central winding is to be considered as the primary of a transformer, which couples differently to the two secondary windings as a function of the position of the ferromagnetic core. The variation of reluctance between the windings of the transformer is proportional to the displacement of the core.

The mechanical coupling between the ferromagnetic core and the piston rod is achieved by means of a system included inside the cylinder and consisting of a wire, fixed by one end to the tip of the rod and by the other end to a drum provided with return spring. By means of a worm screw mechanism, the rotation of the drum is converted into the translation of a pin which, with a cam system, insists on the ferromagnetic core of the inductive displacement sensor.

This contactless measuring technique preserves the primary elements which form the sensor from mechanical wear. However, in order to detect the position of the piston rod, the inductive sensor must be housed inside the oil compartment, thus being subjected to its corrosive effects. Furthermore, although this transduction technique is relatively robust to the variations of the working temperature of the oil, it may suffer from the influence of the impurities present therein, such as dirt and water, which may generate an undesired variation of the reluctance, such as, if not compensated for, may be erroneously interpreted as the variation of the position of the cylinder rod.

The replacement of the primary inductive element following a malfunction necessarily implies the removal of the fixed end of the hydraulic cylinder in which it is housed.

Magnetoresistance sensors are known, such as those described in Patent JP 62229003A, in which a magnetic displacement sensor based on magnetoresistors (Giant Magnetoresistance - GMR) is used as a primary element in order to determine the position of the piston rod which runs inside a hydraulic cylinder. The sensor consists of one or more pairs of magnets placed inside the hydraulic cylinder and of a magnetic field intensity sensor, consisting of four magnetoresistors arranged as a Wheatstone bridge and positioned inside the cylinder, fixed to the piston rod. The magnets of each pair are positioned in a diagrammatically opposite manner with respect to the cylinder axis, thus generating a magnetic field orthogonal to the direction of displacement of the piston axis. By appropriately coating the cylinder with high magnetic permeability material, the field generated by the magnet pairs extends for its entire length. The magnetoresistors can thus move within a magnetic field with intensity which is as a function of the position of the piston rod.

This sensor technique is contactless, so the sensitive element is not subject to mechanical wear. Furthermore, although the magnetic field intensity sensor is arranged in the oil compartment, it may be duly coated with non-ferromagnetic passivating material to be immune from possible corrosive effects of the oil.

On the other hand, the magnetoresistors are particularly sensitive to working temperature variations. Furthermore, being positioned on the movable part of the hydraulic cylinder, they require a specific anti-twisting wiring system to be able to return the electrical signal into the mechanical apparatus by means of the appropriate connector.

Such a complexity is also apparent in the operation of replacing the sensor following a failure: while the magnets which generate the reference magnetic field may be housed outside the cylinder, and so in a place which can more easily accessed by the maintenance operator, the end of the cylinder must be removed and the piston rod must be pulled out in order to reach the sensitive magnetoresistive element.

Magnetostrictive sensors, to the family of which the sensor presented in Patent EP 1571425 belongs, are a typical solution for obtaining an accurate measurement of the linear position of a movable member of a mechanical system. The magnetostrictive technique is based on measuring the flight time of an acoustic wave transmitted along a magnetostrictive material wire, which is reflected back near the choke induced by a magnetic ring which runs along the wave guide. This contactless technique allows to obtain high measurement resolutions, but to the detriment of high costs, high susceptibility to variations of temperature, vibrations and external magnetic fields. Mechanical knocks accidentally applied to the rod containing the wave guide must compromise sensor calibration, even damaging it beyond repair.

Patent CN 104,595,282 shows one of the more traditional configurations for magnetostrictive sensors used inside a hydraulic cylinder to measure the position of the piston rod. In such configurations, the magnetostrictive sensor is housed in the fixed end of the hydraulic cylinder with the magnetic ring connected to the piston rod, made hollow so that the rod containing the wave guide may run inside. Although they do not suffer from particular sensor wiring problems, such configurations expose the sensor rod containing the wave guide to the sudden pressure changes which are generated in the oil compartment during the normal operation of the hydraulic cylinder, thus subjecting the sensor to continuous stress which could damage it.

For this reason, in Patent CN 104,895,862 it is suggested to insert the magnetostrictive sensor directly inside the piston rod, made hollow for this purpose and hermetically closed, while the magnetic ring is fixed at the end of the stator part of the cylinder. The sensor is therefore installed in an environment which is not subject to the high pressure of the oil, protected from water hammers which may be generated during the step of starting of the hydraulic system. On the other hand, supplying power and taking the measuring data from a sensor arranged on the movable part of the cylinder implies various wiring difficulties, the twisting of the power and signal wires being the most obvious. Because of the high consumption of the magneto strictive technique, such limitations cannot be completely overcome by powering the sensor by battery and transmitting the data via radio frequency.

Replacing the magneto strictive sensor after a malfunction is not at all easy: it indeed implies removing the either fixed or movable end of the hydraulic cylinder in which it is housed.

Magnetic sensors are known, like those described in Patents US 8,829,893 and US 9,062,694; in said patents, an array of magnetic sensors arranged over the entire length of the fixed part of a hydraulic cylinder, coupled to one or more magnets housed in the piston rod, is used. Both in the case of magnetoresistive elements or Hall effect elements arranged in a bridge, the measuring principle is contactless, and so the primary sensitive element is free from mechanical wear and its degree of protection may be increased by means of traditional passivating techniques, such as resin coating.

Magnetic sensors detect the intensity of the magnetic field. The rod position can be determined by querying each sensor and combining the respective outputs. The merit of this solution is that the array of magnetic sensors may be positioned outside the hydraulic cylinder, thus being easily accessible for maintenance and protected from the typical mechanical and thermal stresses of the oil compartment. On the other hand, the structure of the cylinder itself may attenuate the magnetic field produced by the movable magnets therein, forcing the sensor array to work in conditions of poor sensitivity. Furthermore, the sensor array is exposed to possible interferences generated by metallic or magnetic components which move near the cylinder. For these reasons, Patent US 9,062,694 suggests to house the sensor array on a magnetic polarized support, which on one hand screens from interferences and on the other makes the magnetic field intensity measurement more robust. Finally, the complexity and the cost of such a sensor are directly proportional to the maximum measurable travel: the greater is the length of the piston rod, the greater is the number of magnetic sensors to be arranged and the more complex become the wiring, the routing and the management of each sensitive element.

In order to reduce the number of Hall sensors to be included in the magnetic sensor array the measuring range being equal, Patent WO 2016046537 suggests the use of a sensor array, connected to the fixed end of the cylinder, which may run inside the piston rod, which is hollow. A magnet, also hollow, specifically worked to generate a magnetic field in its cavity with intensity which varies in linear fashion according to its position, is included in the piston rod. Also in this case, the position of the rod can be determined by combining the measurement of the magnetic field intensity of each sensor of the array. The particular geometry of the magnet ensures an increase of the intensity of the magnetic field along the movement axis of the piston rod with respect to the preceding solutions, allowing a more dispersed positioning of the sensors which form the array. Furthermore, by positioning the sensor array in the cylinder, the effects deriving from electromagnetic interference sources are reduced, despite being obliged to immerse the sensor electronics in the oil compartment, with all the problems of difficult accessibility in case of maintenance which derive from this.

Patents US 7,956,606 and US 9,341,266 use a single magnetic rotary sensor as a primary element to determine the position of a rod which runs inside a hydraulic cylinder. The sensitive element faces and is aligned with the center of a magnet, which rotates according to the movement of the piston rod. The angular position of the polarization vector of the magnet is thus transduced by the sensitive element into an electric signal. The electronic board and the magnetic system, which couples the linear movement of the piston rod to the rotary movement of the magnet, reside in two separate housings. This solution allows to screen the magnetic sensor with respect to the interferences coming from the environment outside the cylinder. Replacing the primary sensitive element following a malfunction is instead more complicated than in the system suggested in Patent US 8,829,893, because the fixed end of the hydraulic cylinder in which the electronics are housed must be removed.

In Patent US 7,956,606, the heart of the mechanical coupling system is a bar twisted as a helix and an appropriate roller slider. The piston rod is perforated and allows the bar to slide therein, which bar is fixed to the end of the hydraulic cylinder and is free to turn about its axis. The bar, closed between the slider rollers, rotates in response to the linear movement of the slider, fixed to the inside of the piston rod, and its rotation is directly transmitted to the magnet, housed in its end.

Similarly, in Patent US 9,341,266 the mechanical coupling movement between piston rod and magnet consists of a helical screw and a slider or a nut. The helical screw rotates in response to the linear movement of the control nut engaged in its threading and included in the piston rod. In single configuration, the magnet, facing its magnetic sensor, is arranged at the end of the helical screw. In the perspective of obtaining a redundant measurement of the angular position, the rotation of the helical screw is transmitted to two gears, each of which includes its own magnet facing the respective magnetic sensor. If the helical screw, in response to the linear movement of the nut, rotates by more than one turn, the gear system allows to count the number of turns on the slow gear and to obtain the angular position on the single turn by means of the fast speed instead. This strategy constrains the maximum number of multiple turns which can be counted by the resolution of the magnetic sensor, which is typically of the order of 12 bits. Operative conditions with high speeds and accelerations, possibly in combination with shock effects due to hard braking and restarting, may limit the working life of the gears of the multi-turn to single turn reduction system. Furthermore, having a high reduction ratio considerably penalizes the overall dimensions of the sensor.

In view of the prior art, it is the object of the present invention to provide a linear position sensor which is more simple, more robust, less costly and more effective than those known. The suggested sensor is configured as a solution for measuring the linear position which implements the magnetic measuring technique, i.e. contactless, by means of magnetoresistors (GMR) or Hall effect devices. The sensitive element is concentrated in a single portion of the sensor, screened from external magnetic interferences, protected from mechanical shocks and corrosive actions of fluids, compact, extractable from the outside for possible replacement or maintenance, the size and cost of which are independent from the length of the measuring range of the sensor. The suggested solution may be included inside industrial linear guides or hydraulic cylinders.

According to the present invention, such an object is achieved by means of a linear position sensor comprising:

- a nut configured to move in a linear manner and adapted to be fixed to an element the position of which is desired to be detected,

- a screw adapted to rotate in response to the linear movement of the nut,

- at least one magnet integral with an end of the screw and adapted to rotate synchronously with the screw,

- means not in contact with said magnet, adapted to detect the rotation of the magnet and to output the linear position of the nut, characterized in that said screw is a multi-flighted screw and the polarization of said magnet is orthogonal to the screw axis, said means comprising detection means comprising a sensitive magnet device configured to detect the angular position of the magnet on a single turn and to detect the turns of the magnet, said linear position sensor comprising an auxiliary power supply source for said detection means and managing means adapted to switch the power supply of said detection means to said auxiliary source in the absence of supply voltage coming from an external power supply network.

The features and advantages of the present invention will become apparent from the following detailed description of practical embodiments thereof, shown by way of non-limitative example in the accompanying drawings, in which:

figure 1 shows a linear position sensor according to the first embodiment of the invention;

figure 2 shows part of the sensor in figure 1 greater in detail;

figure 3 shows the electronic board of the linear position sensor in figure 1;

figures 4 and 5 show magnetic band rings to be used instead of the magnet in figure 1 ;

figure 6 shows a linear position sensor according to a variant of the first embodiment of the invention;

figures 7-9 show a linear position sensor according to the second embodiment of the invention;

figures 10-11 show a linear position sensor according to the third embodiment of the invention;

figure 12 shows a linear position sensor according to the fourth embodiment of the invention;

figure 13 shows a linear position sensor according to the fifth embodiment of the invention;

figure 14 shows a linear position sensor according to the sixth embodiment of the invention;

figures 15-16 show part of the linear position sensor in figure 14; figure 17 is an exploded view of the linear position sensor in figure 14.

Figures 1-5 show a linear position sensor according to the first embodiment of the present invention. The linear position sensor comprises two subsystems, one mechanical and one electronic. The mechanical subsystem converts the linear movement of a slider or nut into the rotation of a magnet. The electronic subsystem detects the angular position of the magnet and encodes it at the output proportionally to the linear position of the slider or nut.

The mechanical subsystem consists of a multi-flighted screw or multifunction screw 1 which rotates in response to the linear movement of the control nut 2 engaged on its treading and which can be fixed to an element the position of which is desired to be detected. The multi-flighted screw 1 is preferably made of AISI 304 or 316 stainless steel, while the nut 2 is preferably made of abrasion resistant self-lubricating plastic, with minimum friction coefficient in dry operation. The multi-flighted screw allows a better resolution with respect to the traditional helical screws and the presence of self-lubricating plastic materials for achieving the nut 2 allow better linearity and better wear resistance of the multi-flighted screw- nut pair with respect to the prior art.

The nut 2 may have a fixing flange 3 with movable member of the machinery the position of which is desired to be monitored, as shown in figure 2. Either one or both ends of the screw may display a radial containment and axial locking element 4 of the screw 1 itself. Such a system may be provided by means of either ball or roller bearings combined with conical or thrust bearings or, preferably, self-centering bearings. The latter allows to compensate for the misalignments which generally occur during the installation of the sensor, thus further reducing the effects of frictions and ensuring a longer working life to the suggested sensor as a result.

A magnet 5 is fixed to one of the ends of the screw 1. The magnet 5, with polarization which is horizontal or in all cases orthogonal to the rotation axis of the multi-flighted screw, rotates synchronously with respect to the screw 1, without its speed being reduced by gears or mechanical reducers in general. As a function of the measuring length of the sensor, the magnet 5 can thus perform more than one turn about its rotation axis; thereby, the resolution of the linear position sensor is increased without gears or multi-turn to single turn reducers, the suggested mechanical subsystem is simpler, more compact, and thus more reliable and with a longer working life than that presented in Patents US 4,386,552 and US 9,341,266. Indeed, the linear position sensor according to the present invention exhibits the absence of gears because being mechanical accuracy components, they would limit the robustness, size, maximum speed of the movement between screw and nut and the overall life of the system from the mechanical point of view, but they would also limit the linearity and repeatability of the sensor from the metrological point of view because of backlash. Furthermore, there are no mechanical limits to the maximum number of turns that the magnet may perform in the linear position sensors according to the present invention, unlike that which occurs for the sensor suggested in Patent US 9,341,266. Indeed, in this case, the dimension, the cost and the gear backlash factors limit the maximum number of multiple turns of the helical screws which can be related to a single turn of the magnet to a few thousand. In the linear sensor according to the present invention, instead, since the turns are counted by detection means not in contact with the magnet, such a number may exceed the thousands of billions, without any mechanical or metrological penalty or technological difficulty. Furthermore, it is worth considering that replacing the functionality of a mechanical component with an electronic component determines an increase of the reliability of the sensor as a whole, with a substantial abatement of the failure rate and a consequent adaptation to the international standards in the matter of functional safety.

The suggested invention further provides for the magnet 5 performing several turns about its rotation axis in response to the displacement of the nut 2 over the entire length of the range. Indeed, the detection means of the present invention can identify and store the turn count also in the absence of external power supply. Thereby, it is possible to select an electronic device which counts the rotations at lower resolution, and therefore lower costs, without losing the overall resolution of the position measurement, which is thus determined from the number of turns performed by the magnet. Resuming the preceding example, an electronic device with a resolution starting from 3 bits will be sufficient for a measurement range of 1 m to which a 36000 degree rotation of the magnet corresponds (so the magnet has performed 100 turns), if obtaining a reading resolution of approximately 1 mm is desired.

The linear sensors suggested in Patents US 7,956,606 and US 9,341,266 with measurement interval of 1 m with which a single 360 degree rotation of the magnet may be associated, equipped with a single electronic device with a resolution of 12 bits = 4096 levels, may be considered, for example. They would thus display a position measuring resolution equal to 0.24 mm (1 m / 4096 levels), value, which for some applications could be limiting. Instead, the suggested sensor for a measuring range of 1 m to which a rotation of 36000 degrees of the magnet corresponds (so the magnet has performed 100 turns), also equipped with a single 12 bit electronic device, has a resolution of 2.4 μιη (1 m / 100 turns / 4096 levels), which is compatible with the typical resolution of magnetostrictive sensors. By combining high resolution with the better linearity value of the multi- flighted screw with respect to the helical screw of Patent US 7,956,606 and with the better repeatability value due to the absence of backlash of the mechanical reduction gears present in Patent US 9,341,266, the suggested sensor stands out for greater accuracy.

The electronic subsystem comprises the means 6, preferably an electronic board, facing the magnet 5 and not in contact with the magnet 5; the means 6 are adapted to convert the angular position of the magnet 5 into linear position, outputting it as an absolute or incremental datum.

Such a contactless measuring technique prevents the mechanical wear of the primary sensitive element, thus extending the operative life and has very contained thermal drifts. In particular, the sensitive magnetic device 7, e.g. a chip which exploits the Hall effect or comprises at least two or three magnetoresistor (GMR) bridges according to whether it includes a bidimensional or a tridimensional reference system, is responsible for identifying the angular position of the magnet 5 on a single turn and is adapted to detect the turns of the magnet; the sensitive device 7 is only operative in the presence of a power supply voltage, e.g. a supply voltage Vin of an external network applied between the terminal 8 and the ground Gnd. Indeed, the main feature of this type of chip is the high accuracy of the measurement of the angular position of the magnet, regardless of the necessary energy consumption. In redundant configuration, such a chip houses two or more identical DIEs inside, which are galvanically insulated from one another so as to produce multiple independent measurements of the same item to be measured, i.e. of the angular position of the magnet 5, at the same time.

The magnet 5 may be provided as a single magnet or as a magnetic band ring shown in figure 4 or even as the magnetic band ring shown in figure 5. A magnetic band ring allows to use simpler and more cost-effective sensitive elements 7 than those shown in Patents US 9,341,266 and US 7,956,606. Furthermore, the use of a magnetic band ring allows to position the sensitive ring 7 not only horizontally as already suggested in the prior art but also vertically on the side, outside or inside the ring.

The sensitive device 7 communicates with a supervisor device 15 dedicated to the counting of the turns of the magnet 5 and the registration of the state of the sensitive device 7. The turn counting values and the state of the device 7 may be stored either in the volatile memory (RAM) 151 included in the supervisor device 15, or in an external non-volatile memory, such as a magnetoresistive random-access memory (MRAM), a ferroelectric memory (FRAM) or an electrically erasable programmable memory (EEPROM). Thereby, the maximum number of multiple turns which can be counted is limited only by the type of associated numeric data type, which may be from at most 32 bits for 8-bit chips up to 128 bits for 64-bit chips. So the 12 bits which can be obtained by the multi-turn systems with mechanical reducer, such as that described in Patent US 9,341,266, are widely exceeded. In order to manufacture a sensor with absolute output, the power supply of the chip must be backed up to avoid losing the turn count in the absence of power supply Vin between the terminals 8 and ground Gnd. So, it is of primary importance for the sensitive device 7 to have pronounced low consumption features. Once the operative speed and the maximum angular acceleration conditions to which the magnet is subjected have been defined, the supervisor device 15 determines the time frequency with which to wake up the sensitive device 7 from the low-consumption inactivity condition to check whether one turn was actually performed and in which sense, either clockwise or anticlockwise.

The supervisor device 15 may be a separate device or a subsystem of the sensitive device 7, or a subsystem of a control device 18. Being backed up by battery 11, superconductor 12 or energy recovery system 14, the supervisor device 15 can monitor the state of the sensor and of the auxiliary energy sources also in the absence of power supply Vin between the terminals 8 and ground Gnd. Each significant variation of the state of the monitored variables is thus recorded either in the volatile memory (RAM) 151 included in the supervisor device 15 or in an external non-volatile memory, and is transmitted to the control device 18 once the sensor power supply is restored.

The specific management device 10 monitors and manages the power supply of the sensitive device 7 and supervisor device 15 according to the following logic: the preferred power supply source is the external power supply Vin but for lack of voltage between the terminals 8 and ground Gnd detected by the device 10, the device 10 itself allows the power supply of the sensitive device 7 and supervisor device 15 by means of the auxiliary energy source included aboard the board 6. Such an auxiliary energy source may be a non-rechargeable battery 11 or a rechargeable battery or a supercapacitor 12. The supercapacitor 12 is generally characterized by higher self-discharge currents that the rechargeable batteries, however it allows nearly infinite charging and discharging cycles, making it suited to back up the power supply of the sensor for periods of the order of tens of hours. On the other hand, non-rechargeable modern batteries exhibit self-discharge currents such as to ensure the nominal energy capacitance of the battery also after several years of non-use.

In lack of voltage between the terminals 8 and ground Gnd, the management device 10 allows to supply the sensitive device 7 and the supervisor device 15 preferably with the rechargeable energy source 12 first and if this also finishes with the non-rechargeable energy source 11. The rechargeable energy sources may be recharged by a specific recharging circuit 16 normally connected to the terminal 8. If the non-rechargeable back-up battery 11 is not present and in the absence of power supply Vin between the terminals 8 and ground Gnd, a switch 17 controlled by the management device 10, connects the recharging circuit 16 to an energy recovery system 14, consisting, for example, of a piezoelectric or magnetic converter 141, and an optimized circuit 142 for extracting energy from the converter. For example, the device 10 may consists of transistors driven by a comparator or diodes connected to a common cathode.

In the linear position sensor according to the invention, a turn-counting chip which exploits the Hall effect or which is of the magnetoresistive type was specifically chosen because it may be manufactured using thin-film solid-state technology, thus being more reliable than electromechanical devices, such as Reed contacts.

A control device 18, comprising at least one microcontroller 180 or multiple microcontrollers for redundancy logic and a memory 181, in which an application software, which supervises the operation of the entire electronic subsystem, is stored and operative. In particular, it communicates with the device 7, being responsible for its configuration, linearization, resetting, heat compensation, coherence control in redundancy logic, self- check test. Specific algorithms implemented in the microcontroller combine the number of turns and the angular position on the single turn provided by the two devices 7 and 15 to obtain the linear position value of the nut, if the device 7 includes a bidimensional reference system. Such a linear position value of the nut may be compared with two settable threshold values, related to the extreme positions of the maximum permitted travel of the sensor, to generate the ON/OFF control signal for a relay or transistor. The linear position data is transmitted to the output terminal OUT as an analog signal (e.g.: output voltage 0.5...4.5V or 0...10 V or current 0...20 niA or 4...20 mA) or digital (e.g.: CANOpen, SAE J1939, RS232, RS485, SPI, I²C,

PWM, squaring, PROFIBUS, Ethernet). In addition to the linear position data, specific diagnostic signals of the sensor, such as for example missing magnet, redundancy control failure, power supply overvoltage, power supply speed, excessive rotation speed, excessive acceleration, reaching of the travel stop, are preferably sent to the output terminal OUT. Other diagnostic information recorded during the period in which there was no power supply Vin between the terminals 8 and ground GND may be read by the control device 18 and transmitted on the output terminal OUT.

In order to further increase the measuring resolution, a further sensitive device is preferably provided which includes a bidimensional reference system; the data from the devices 15 and 7 are combined with those supplied by the further sensitive device.

Being backed up by a battery or energy recovery system, it may be necessary to reset the turn and angle count of the devices 7 and 15 by means of the input terminal IN at the end of the installation of the entire sensor.

Furthermore, the analogue output of the sensor may be re- scaled as a function of the real measuring interface required by the application. Such a functionality may be activated by setting the specific input IN to ground GND and to the value of the power supply voltage Vin, respectively, with the nut near the zero and the full-scale of the required measuring range. The two subsystems, i.e. the electronic board 6 and the mechanical system consisting of the multi-flighted screw 1, the nut 2 and the magnet 5, may reside in two separate housings made of paramagnetic or diamagnetic material. This allows, for example, to passivate the electronic board using resins, inserting it in a robust aluminum or stainless steel casing.

The linear position sensor in its variant to the first embodiment, is simple and cost-effective and may exhibit an IP69k degree of protection, again comprises the nut 2 and the multi-flighted screw 1, and unlike the first embodiment, a container 19, which houses the radial containment and axial locking element 4 of the screw 1, the magnet 5 and the electronic board 6, possibly provided with outer seal 20, as shown in figure 6.

The nut 2 and the container 19 are preferably provided with fixing flange 3 integral with the movable part and with the stator part of the mechanical member the movement of which is desired to be measured, respectively.

The radial containment and axial locking element 4 of the screw 1 may be provided by means of a bronze bearing with a seal 20 to prevent the penetration of fluids into the chamber 22 which houses the magnet 5. The electronic board 6 passivated by means of resin and housed in the provided chamber 23, which is separated from the chamber 22 which houses the radial containment and axial locking element 4 of the screw 1 and magnet 5 by a layer of diamagnetic or paramagnetic material. The output terminal OUT, the input terminal IN and the power supply terminal 8 of the electronic board 6 are provided by means of the wire or integrated connector 24 of the container 19 of the sensor.

According to a second embodiment of the present invention shown in figures 7-9, the linear position sensor is used in this case inside the cylinder 27. The linear position sensor of the second embodiment of the invention comprises the elements of the first embodiment and/or of its variant, thus comprising again the nut 2, the multi-flighted screw 1, a container 19 which houses the radial containment and axial locking element 4 of the screw 1 and the magnet 5, and a specific housing 23 for the electronic board 6; the cylinder may be of the pneumatic or hydraulic type. The mechanical subsystem is in this case completely immersed in the fluid used for actuating the cylinder. In the case of hydraulic cylinder 27, the presence of oil is to be understood as favorable for this traducer because its lubricating properties promote the functionality of the mechanical subsystem. Furthermore, considering the forces which concern the components of the cylinder during its typical operation, any dirt deposited in the mobile parts of the mechanical subsystem, such as between the threading of the screw 1 and nut 2 or between the rings of the ball bearings 4, cannot cause gripping. The mechanical subsystem must be made of a material which is compatible with and resistant to fluid corrosion used inside the cylinder, such as for example AISI 304 or 316 stainless steel.

The chamber 22 which houses the magnet 5 and the housing 23 of the electronic board 6 are insulated by a layer of diamagnetic or paramagnetic material. The nut 2 and the container 19 are both provided with fixing flange 3 integral to the piston rod 25 and to the fixed end 26 of the hydraulic cylinder 27, respectively.

Since there are no passages for connectors or wires between the inside and the outside of the cylinder 27 which occurs instead when magneto strictive sensors are used, it is not necessary to equip the mechanical subsystem with a seal, which translates into more reliable and longer working life of the sensor and of the entire cylinder 27. It is worth noting that the seals are constantly subjected to wear caused by high pressure, thermal gradients and corrosiveness of the fluid used in the cylinder 27, so that their use negatively affects the overall calculation of the reliability and working life of the system.

In particular, in the second embodiment of the invention, the housing 23 of the electronic board 6 is arranged in the fixed end 26 of the hydraulic cylinder 27 and allows to insert the electronic board 6 without needing to remove the cylinder. This solution opens to two-step assembly strategies of the suggested sensor e.g. before and after sales. By virtue of the low cost of its components, the mechanical subsystem may be already included in the cylinder 27 during the production process. The cylinder 27 may thus exhibit an arrangement for the integrated measurement of the position of the piston rod 25, which is only enabled if the customer actually selects this function, by inserting the electronic subsystem in the appropriate compartment 23.

The electronic board 6 is passivated by resin and housed in a particular container 28 which includes output with integrated connector 24 or wire and which may be arranged in the various manners shown in figures 7-9. Such a container is provided with fixing flange 3 to ensure the locking once it is inserted in the specific housing 23.

According to a third embodiment of the present invention shown in figures 10-11, the linear position sensor is used in such a case for piston rod inclination and inside the cylinder. The linear position sensor of the third embodiment of the invention comprises the elements of the first embodiment and/or of its variant, thus comprising again the nut 2, the multi-flighted screw 1, a container 19 which houses the radial containment and axial locking element 4 of the screw 1, the magnet 5, but in such a third embodiment the traducer comprises a further magnet 35 (fig. 11) and the specific housing 23 for the electronic board 6. In this fourth embodiment, the radial containment and axial locking element 4 comprises a self-centering bearing 40 which allow the rotation of the screw 1 about its axis A and also a slight inclination thereof with respect to such an axis A, indicated by means of the angle β in figure 11. Such an inclination may be due to the tolerances of the mechanical components which form the cylinder, i.e. the misalignments which are found during the step of assembling of the sensor inside the cylinder. In particular cases, the inclination of the screw 1 may be associated with the inclination of the piston rod 25 itself, caused, for example, by peak loads which are forcing the hydraulic actuator in unsafe working conditions. In this sense, the data related to the inclination of the screw may be used to monitor the correct operating condition of the actuator and the wear of its mechanical parts.

In order to measure the inclination of the screw 1 , the magnet support 34 is connected to its end, which support comprises the magnet 5 with polarization which is horizontal or in all cases orthogonal to axis A, which by coupling to the sensitive device 7 allows measuring the angular position and by coupling to the device 15 allows counting the turns of the magnet 5, and the magnet 35 with polarization which is vertical or in all cases parallel to axis A, which couples to a further sensitive device 9, shown in figure 3, for measuring the inclination of the multi-flighted screw (fig. 11).

The further sensitive device 9, e.g. a chip which exploits the Hall effect or which comprises two or three magnetoresistor (GMR) bridges, according to whether it includes a bidimensional or a tridimensional reference system, is responsible for the inclination of the magnet 35 and is operative only in the presence of supply voltage Vin applied between the terminal 8 and the ground Gnd. Indeed, the main feature of this type of chip is the high accuracy of the measurement of the position of the magnet, regardless of the necessary energy consumption. In redundant configuration, such a chip houses two or more identical DIEs inside, which are galvanically insulated from one another so as to produce multiple independent measurements of the same item to be measured, i.e. the inclination of the magnet 35, at the same time.

The inclination measurement of the screw 1 may also be carried out with the magnet 5 with polarization which is orthogonal to axis A only and the sensitive device 7 with tridimensional reference system only (fig. 10). Specific algorithms implemented in the control device 18 combine the number of turns and the position along the three dimensions provided by the devices 15 and 7, respectively, to obtain the linear position value of the nut and the inclination value of the screw. The linear position value of the nut and the inclination position of the screw may be compared with two settable threshold values, related to the extreme positions of the maximum permitted travel/inclination of the sensor, to generate the ON/OFF control signal for a relay or transistor. The data related to the linear position of the nut and to the inclination of the screw are transmitted by means of the interface circuit 182 to the output terminals OUT as an analog signal (e.g.: output voltage

0.5...4.5V or 0...10 V or current 0...20 mA or 4...20 mA) or digital (e.g.: CANOpen, SAE J1939, RS232, RS485, SPI, I²C, PWM, squaring, PROFIBUS, Ethernet).

In order to further increase the measuring resolution, both sensitive devices 7 and 9 are included, and both include a tridimensional reference system; the data from the devices 15 and 7 are combined with those supplied by the sensitive device 9.

According to a fourth embodiment of the present invention shown in figures 12, the linear position sensor is used in this case for linear guide. The linear position sensor of the fourth embodiment of the invention comprises the elements of the first embodiment and/or of its variant, thus comprising the nut 2, the multi-flighted screw 1, a container 19 which houses the radial containment and axial locking element 4 of the screw 1, the magnet 5 and the electronic board 6, but in this fourth embodiment it is all hermetically closed by a cylinder 29 which guides in the tip the screw 1 with a second radial containment and axial locking element 4. In said fourth embodiment, the nut 2 is provided with magnets 31 and in the cylinder 29 a magnetic slider 30 runs provided with magnets 31 and magnetically coupled to the inner nut 2 exploiting a combination of magnets in Halbach configuration, as shown in figure 12, for example. One or more rods 32 parallel to the screw

1, passing inside the nut 2 and fixed at the two ends to the radial containment and axial locking element 4 of the screw 1, are included in the cylinder 29 containing the traducer to prevent the nut 2 from turning on itself, thus inducing a rotation on the screw 1 which is not associated with an actual linear displacement of the magnetic slider 30. Furthermore, the magnets 31 housed on the nut 2 may interface with it by means of a rotation uncoupling system 21, e.g. a roller or ball bearing, so that the rotation induced on the screw 1 is only associated with the liner motion of the magnetic slider 30 and not with its rotation.

This solution ensures an IP69k degree of protection to the entire sensor, making it particularly attractive as a position sensor for use in the food-processing, explosive risk sector or as a level sensor for cryogenic or corrosive fluids if provided with floating slider and duly coated. If needed, the mechanical subsystem may be immersed in fluid to reduce the mechanical frictions on its movable parts. Furthermore, since the movement of the screw 1 is only accessible by means of the linear displacement of the outer slider 30, the linear curve of the sensor can be univocally mapped, by associating the linear position of the slider 30 directly with the angular position combined with the number of turns of the magnet 5, thus obtaining performance in terms of accuracy higher than the open screw solutions.

The magnetic slider 30 and the container 19 are provided with fixing flange 3 integral with the movable part and the stator part of the mechanical member the movement of which is desired to be measured, respectively. The electronic board 6 is passivated by resin and housed in a particular container 33 which includes output with integrated connector or wire 8. Such a container 33 is inserted by means quick connector, e.g. screw or bayonet, into the chamber 23 provided to house the electronic board 6, which is separated from the chamber 22 which houses the radial containment and axial locking element 4 of the screw 1 and magnet 5 by a layer of diamagnetic or paramagnetic material.

According to a fifth embodiment of the present invention shown in figures 13, the linear position sensor is included in a commercial linear slide. The linear position sensor of the fifth embodiment of the invention comprises the elements of the first embodiment and/or its variant, thus comprises the nut 2 with fixing flange 3, the multi-flighted screw 1, but in said fifth embodiment, comprises two supports 36 which house the radial containment and axial locking element 4 which guide the screw 1. The linear position sensor of the fifth embodiment of the invention comprises one or more rods 32 parallel to the screw 1, passing in the nut 2 are fixed to the ends of the supports 36. The rods 32 prevent the nut 2 from turning on itself, inducing a rotation on the screw 1 which is not associated with an actual linear displacement of the nut 2. The linear position of the nut 2 can be measured with the only addition of the magnet 5 and of the electronic board 6 to the pre-existing mechanical structure. The electronic board 6 is passivated by means of resin and housed in the container 19 which includes output with integrated connector or wire 8 and fixing flange 3 to the support 36 of the linear guide.

This solution also opens to two-step assembly strategies of the suggested sensor, e.g. before and after sales. By virtue of the low cost of the magnet 5, it may be already included in the linear guide during the production process. The linear guide may thus exhibit an arrangement for the integrated measurement of the position of the nut 2, which is only enabled if the customer actually chooses such a function, applying the electronic subsystem by means of the appropriate fixing flanges 3 to the support 36 of the guide which houses the magnet 5.

A linear position sensor according to a sixth embodiment of the present invention is shown in figures 14-17. The linear position sensor of the sixth embodiment of the invention comprises the elements of the first embodiment and/or of its variant, thus comprising again the nut 2, the multi- flighted screw 1, a container 19 which houses the radial containment and axial locking element 4 of the screw 1 and the magnet 5, and a specific housing 23 for the electronic board 6.

The linear position sensor of the sixth embodiment is made in two parts, a first part 500 (shown in greater detail in figures 15 and 17) and a second part 600 (shown in greater detail in figures 16 and 17), which can be separated and joined to each other. The first part 500 comprises the multi- flighted screw 1, the nut 2, the radial containment and axial locking element 4 of the screw 1 represented by a bearing, the magnet 5 arranged on a specific support 501 and a locking element 502 arranged between the bearing 4 and the screw 1 and adapted to lock the first part 500 on the second part 600.

The second part 600 (shown in greater detail in figures 16 and 17) comprises the container 19, the board 6 with the sensitive devices and a closing cap 601. The upper part of the container 19 comprises the housing 22 for the bearing 4 which also houses the container 501, the magnet 5 and the locking element 502; the housing 22 is shaped so that the locking element 502, once inserted in the housing 22, is adapted to lock the first part 500 on the second part 600. Preferably, the locking element 502 is C-shaped and the housing 22 is of the ring type.

Therefore, the linear position traducer of the sixth embodiment consists of two parts 500, 600, which can be joined to each other by means of the action of the locking element 502 on the housing 22, and which can be separated from each other again by means of the unlocking action on the locking element 502. Thereby, the first part 500 or the second part 600 can be easily replaced.

The linear position sensors in the embodiments shown in figures 1-16 may also be mutually combined; for example, the linear position sensors of the third, fourth and fifth embodiments may be combined with elements of the linear position sensor of the second or sixth embodiment of the invention, and so forth.

Claims

1. A linear position sensor comprising:

- a nut (2) configured to move in a linear manner and adapted to be fixed to an element the position of which is desired to be detected,

- a screw (1) adapted to rotate in response to the linear movement of the nut,

- at least one magnet (5) integral with one end of the screw and adapted to rotate synchronously with the screw,

- means (6) not in contact with said magnet, adapted to detect the rotation of the magnet and to output (OUT) the linear position of the nut, characterized in that said screw is a multi-flighted screw and the polarization of said magnet is orthogonal to the screw axis, said means comprising detection means (7, 15) comprising a sensitive magnet device (7) configured to detect the angular position of the magnet on a single turn and to detect the turns of the magnet, said linear position sensor comprising an auxiliary power supply source (11, 12) for said detection means and managing means (10) adapted to switch the power supply of said detection means to said auxiliary source in the absence of supply voltage (Vin) coming from an external power supply network.

2. A sensor according to claim 1, characterized in that said magnet is made as a magnetic band ring.

3. A sensor according to claim 1 or 2, characterized in that said detection means comprise another device configured to count and store the detected number of the turns of the magnet, said another device being adapted to detect the state of the sensitive device.

4. A sensor according to claim 3, characterized in that said means comprise a control device (18) comprising at least one microcontroller (180) and a memory (181), where an operative software is installed and run, said control device being adapted to receive the data detected by said sensitive device and by said other device, and being configured to output the linear position of the nut at the output terminal (OUT) of said means.

5. A sensor according to any one of the preceding claims, characterized in that it comprises a first housing (22) adapted to house at least said magnet and a second housing adapted to house said means (23), said first housing being separated from said second housing by means of a diamagnetic or paramagnetic material.

6. A sensor according to claim 5, characterized in that it comprises a radial containment and axial locking element (4) of said multi-flighted screw arranged at one end of the screw, said first housing being adapted to house said radial containment and axial locking element of said multi-flighted screw.

7. A sensor according to claim 5, characterized in that it comprises a container (19) of said first housing and of said second housing.

8. A sensor according to claim 6, characterized in that said radial containment and axial locking element of said multi-flighted screw comprises a self-centering bearing (40) configured to allow an inclination of the multi-flighted screw with respect to its rotation axis (A).

9. A sensor according to claim 8, characterized in that it comprises a further magnet (35) with polarization parallel to the rotation axis (A) of the multi-flighted screw, and another sensitive device (9), magnetically coupled to said further magnet and being configured to detect the inclination of said multi-flighted screw with respect to its rotation axis (A).

10. A sensor according to claim 8, characterized in that said sensitive device (7) comprises a tridimensional reference system, said sensitive device (7) being magnetically coupled to said magnet and being configured to detect the inclination of the multi-flighted screw with respect to its rotation axis (A).

11. A sensor according to claim 1, characterized in that said multi- flighted screw is made of stainless steel and said nut is made of self- lubricating plastic material.

12. A sensor according to claim 7, characterized in that it comprises another radial containment and axial locking element (4) of said multi- flighted screw which is arranged at the other end of the multi-flighted screw and at least one rod (32) parallel to the multi-flighted screw and passing through said nut, said at least one rod being configured to prevent the rotation of the nut.

13. A sensor according to claim 7, characterized in that it comprises a cylinder (29) containing said multi-flighted screw and a further radial containment and axial locking element (4) of said multi-flighted screw which is arranged at the other end of the multi-flighted screw.

14. A sensor according to claim 13, characterized in that said nut comprises first magnetic means (31) and said cylinder comprises a slider (30) provided with second magnetic means (31) which are magnetically coupled to said first magnetic means of the nut.

15. A sensor according to claim 14, characterized in that said cylinder comprises at least one rod (32) parallel to the multi-flighted screw and passing through said nut, said at least one rod being configured to prevent the rotation of the nut.

16. A sensor according to claim 14, characterized in that said slider (30) comprises a flange (3) which is fixable to the movable part of the mechanical component the displacement of which is desired to be detected.

17. A sensor according to any one of the preceding claims, characterized in that it is made in two parts (500, 600) which can be separated from each other and joined to each other.

18. A sensor according to claims 5 and 17, characterized in that said first part comprises the multi-flighted screw (1), the magnet (5) and said radial containment and axial locking element (4) of said multi-flighted screw and said second part comprises said container (19), said first part comprising a locking element (502) which can be inserted in said first housing for locking the first part onto the second part.

19. A hydraulic or pneumatic cylinder (27) comprising a piston (25), characterized in that it comprises a linear position sensor as defined in any one of the preceding claims, said piston being integral with the nut of said linear position sensor.

20. A cylinder according to claim 19, characterized in that it comprises a further container (28) containing said means, a first housing adapted to house at least said magnet and a second housing adapted to house said means, said first housing being separated from said second housing by means of a diamagnetic or paramagnetic material, said further container being insertable in and removable from said second housing.