Magnetostrictive elongation sensor

A magnetostrictive position or elongation sensor of the type in which an elongated magnetorestrictive waveguide is influenced by a magnetic field from a moving magnet has a Villary type transformer at one end and a hermetically sealed housing containing the signal processing circuitry on a plurality of circuit boards. The signal processor can switch the sensor into a programmable mode in which a diagnostic output is obtained recognizing the magnet, the presence of the sensor in the programming mode and voltage values.

FIELD OF THE INVENTION

My present invention relates to a magnetostrictive elongation sensor, i.e. a sensor capable of determining the degree of relative movement of two parts in a longitudinal direction, the elongation of a member or the stretch in a member or structure. More particularly this invention relates to an elongation sensor of the type which can output elongation dependent signals from a magnetic field sensitive sensor element and which has a signal processor and optionally a diagnostics output which can be provided in a housing and which can cooperate with a shiftable magnet or magnets which act upon the sensor element.

BACKGROUND OF THE INVENTION

Elongation sensors of that type are known in the art in a variety of configurations and reference may be had, in that connection to German patent document DE 102 01 880 A1 and US patent application publication US 2005/0017710 A1.

Such a magnetostrictive elongation sensor has as a rule a wire-like or tubular waveguide extending in a measurement direction and provided from a magnetostrictive material. By means of a position magnet which is displaceable relative to the waveguide and along the waveguide, the contactless application of a magnetic field to the waveguide can result in a mechanical elastic wave therein. That mechanical elastic wave spreads in both directions along the waveguide and can be detected by the signal processing circuit as an end of the waveguide. From the propagation time of the wave along the waveguide, the exact spacing of the position magnet from the end of the waveguide can be determined and thus the position of the movable component, element or point to which the position magnet is affixed.

The waveguide is usually received in a support body, for example a tube, in order to provide a mechanically stable mounting of the sensing element and to permit it to be affixed to a component with respect to which the movable point is displaceable. The electronic parts forming the signal processor, for example, are usually arranged at one end of the waveguide. These can include a detector coil, a Villary-effect strip, the signal processing circuitry and optionally a diagnostic output. All of these elements can be provided in a housing and thereby protected against environmental effects.

On a machine to be monitored, it is not uncommon to provide a number of such elongation or longitudinal displacement sensors. At standstill of the machine it is important to be able to identify possibly defective parts of the apparatus as quickly as possible to thereby keep production losses to a minimum. Since both maintenance and restoring the apparatus to full production can result in operational interruptions or lags, it is essential to be able to diagnose a possible failure of the sensor as quickly as possible.

There are in the art sensors having BUS type interfaces which have been described as having optical diagnostic outputs. However, these optical diagnostic outputs themselves are exclusively provided by the BUS communication.

OBJECTS OF THE INVENTION

It is the principal object of the present invention to provide an elongation sensor of the aforedescribed type which enables a rapid and exact identification of a deflective part.

Another object of this invention is to provide an improved elongation or longitudinal position sensor of the magnetostrictive type with more effective protection against environmental effects, which is more easily monitored with respect to diagnostics and which has improved shielding by comparison with earlier systems.

It is another object of this invention to provide a sensor of the magnetostrictive type which is free from drawbacks of the prior art systems.

SUMMARY OF THE INVENTION

These objects and others which will become apparent are attained with magnetostrictive elongation sensor outputting an elongation or longitudinal position signal which comprises:

a magnetic-field-sensitive sensor element in the form of a waveguide and forming a signal generator;

a signal processor connected to the signal generator and having a diagnostic output;

a housing receiving the signal processor and at least an end of the sensor element; and

a shiftable magnet generating a magnetic field affecting the sensor element,the signal processor being constructed and arranged to switch the elongation sensor into a programmable mode in which the diagnostic output encompasses at least one of the following detection elements:a sensor unit for a function of the sensor element capable of recognizing a magnet,a sensor unit for a function of the elongation sensor finding itself in the programming mode, anda sensor unit for monitoring voltage with at least two voltage values different from zero.

Preferably the diagnostic output includes an infrared interface.

It has been found to be advantageous, further, when the diagnostic output includes an optical output element which can encompass a visible light or light in the visible wavelength range so that at least some aspect of the diagnostic can be recognized by the eye of the viewer.

Furthermore, it is preferred for the diagnostic output to encompass at least two of the sensor elements or units previously described.

Because of the optically differentiable diagnoses which can be carried out in accordance with the invention, defects at a corresponding apparatus or component can be relatively rapidly and simply identified which, in turn, enables replacement of the exact magnetostrictive elongation sensor of the machine which is found to be defective. Superfluous replacement of sensors which in the past may have falsely indicated a defect is no longer required.

According to the invention, the voltage is monitored to determine whether the requisite voltage is applied or not and whether the voltage which may be applied is in the permissible voltage range or not. The invention also allows determination as to whether, following the programming of the sensor, the programming for the desired function of the sensor has been. concluded or whether the sensor may still be in a programming mode which must be concluded before the sensor is placed in operation.

The invention can also establish whether the magnet on the monitored component is positioned too far away from the waveguide or even possibly positioned outside the measurement range. The corresponding data can be read out for example via the infrared interface with a palm or like electronic reader which not only can indicate the occurrence of a defect but the significance or value of the defect.

According to a further feature of the invention, the signal processing can be such that an elongation value outputted by the signal generator is converted by an output signal generator of the sensor into a digital or analog output signal. The circuitry within the housing can include an interconnection circuit or network which is located between the output signal generator and an output to which the elongation dependant signal is applied. To reduce shock and vibration sensitivity and to limit or prevent the coupling into the system of stray signals or noise, at least one of the electrical connections between the signal generator and signal processor and between the output signal generator and the interconnection circuit should be formed as a cable-free or wireless connection between separate circuit boards.

The sensors of this general type known in the art generally have a single circuit board of which substantially all of the electronics are mounted, thereby leading to magnetostrictive elongation sensors with large volumes and high sensitivity to shock and vibration. When, in accordance with the invention, the electronic circuitry of the sensor is divided and provided on a multiplicity of circuit boards, this problem can be eliminated as will be described below.

When, in the past a multiplicity of circuit boards were provided and were wired to each other there was always the danger that wiring errors could arise. Furthermore, the wiring could function as antennae and pick up noise or otherwise make the sensors sensitive to external electromagnetic fields. Shock-produced cable breakage could occur.

With the system of the invention in which at least two of the boards are connected by a wireless connection and advantageously all of the boards can be interconnected by wireless or cableless connections, a highly compact construction can be provided with a minimal volume and maximal shock and vibration resistance which is less sensitive to noise and more convenient to fabricate. At least the signal conversion parts of the circuitry should have a cableless connection thereto.

According to a feature of the invention at least one of the connections mentioned above is provided as a plug connection. When we refer here to a plug connection, we mean a connection in which a plug can engage a jack. In an especially preferred embodiment the signal generator is connected in a cable-free or wireless connection with a first circuit board, the latter is connected with a second circuit board with signal processing elements by a plug connector and the latter with a third circuit board with output signal generator elements also by a plug connection. The three circuit boards can all be interconnected by plug connectors in a preferred embodiment.

To provide an especially compact construction and to minimize noise pickup, the three circuit boards can be arranged parallel to one another with the first printed circuit board between the second and third printed circuit board and the electronic elements mounted on the sides of the second and third boards which face the first board.

The first board can be provided with a bandpass filter. The first board can be directly connected with the waveguide of the signal generator.

According to a further feature of the invention, the third board is connected with a fourth board carrying the interconnection circuitry by a plug connector. The fourth board can be mounted on the stack of the first three boards at a side thereof turned away from the waveguide or the signal generator formed thereby and at a right angle to the first three boards so that edges of the first three boards are located adjacent the surface of the fourth board turned toward the waveguide.

The individual boards can be assembled into a compact stack and interconnected by plug connectors so that the volume of the board assembly is especially small.

The waveguide can be provided with a signal generator in the form of a Villary-effect transformer which outputs the elongation-dependant value. With an elongation sensor thus equipped, vibrations can be mechanically coupled to the sensor and can be superimposed on the measurement signal and lead to errors in prior art devices. The output signal of a Villary transformer are applied to a comparator through amplifying stages for further processing. It is possible in such cases to amplify the raw signal excessively and prevent adequate separation between the signals and noise (low signal/noise ratio). Filters are then required to filter out the noise.

To avoid these drawbacks, according to the invention, between the signal processor and the sensor element, for example the waveguide, a passive bond pass filter is provided.

The use of an appropriate electrical filter to minimize the environmental effects like those of shock and vibration, utilizes the fact that the shock and vibration produce low frequency affects which are superimposed upon the measurement signal. With the band pass filter the frequency contributions of shock and vibration can be filtered out so that other effects upon the measured value can be eliminated. Preferably the band pass filter is a high pass filter.

According to another feature of the invention, the band pass filter is provided together with the Villary transformer on a common carrier, i.e. the same printed circuit board. In that case the band pass filter will be a shock and/or vibration filter in the sense described above.

The invention also relates to an elongation sensor in accordance with the principles of the invention previously described which has a signal processor receiving the output of the signal generator formed by the waveguide and produces an elongation-dependent value which, upon further processing, gives rise to the output signal of the unit.

In industrial applications, such sensors are subject to strong electromagnetic effects which introduce noise to the measured signal. These electromagnetic effects can be produced by electromagnetic machine drives (motors), frequency converters or welding apparatus in the vicinity. In some cases, the noise can exceed predetermined thresholds which can render the measured signal indiscernible or can mask the measured signal. The possible coupling of the noise to the sensor therefore requires steps to prevent or limit the incursion of such noise.

In the past individual components have generally been enclosed in a shield which, however, may not adequately shield the wiring to and from those components.

In accordance with the present invention, the sensor element is surrounded by a first shield, especially a housing of an electrically conductive material such as sheet metal and this first shield is surrounded by an insulating shell closely fitted to the first shield and a second shield, especially a housing of electrically conductive material such as sheet metal, surrounds the insulating layer. The shiftable magnet is disposed externally of that second shield. The system of the invention greatly reduces or completely eliminates noise from the electromagnetic effects mentioned previously.

Preferably the signal generator formed by the waveguide and the signal processor are provided on a common carrier within the first shield, i.e. on the same printed circuit board. If the common carrier is not a printed circuit board it can be a hybrid circuit.

It has been found to be advantageous in addition for the circuit boards and especially the first, second, third and fourth circuit boards to be received within the housing formed by the first shield and, therefore, within the second shield as. well, the latter surrounding the first shield.

The housing forming the first shield can be provided with guide grooves into which the boards can be slid and which serves to receive the boards, to guide them and to hold them in position. Alternatively, some or all of the boards can be fitted into a shape stable auxiliary housing which is received in and surrounded by the first shield. In this case electrical content between the boards and the first shield can be avoided and mechanical mounting can be achieved while insulation from the first shield is ensured.

In earlier sensor systems, it frequently has not been possible to obtain the protection required for an IP 67 rated protected product. An IP 67 rated protected product is one which has an ingress protection (IP) rating such that the system is totally protected from dust and is protected from the effect of immersion between 15 cm and 1 m. Such protection is particularly. desirable when the sensor is to be used on a machine like a drilling or boring machine which produces very fine particles and uses cutting fluids or coolants.

As a result of contamination from dust or other particulates and the penetration of oil or coolants through capillaries in the housing or other structures of such sensors, the sensor can fail.

According to the invention, however, the housing is formed as an open hollow profile and is closed at its ends by respective covers-and between each cover and the respective mouth of the housing a profiled seal is provided which, on the one hand, has a planar region sandwiched between and abutting planar regions of the cover in housing. In addition, each seal has a second region forming a lip seal against a wall of the housing just inwardly of the mouth. The seals are generally annular and projections on the cover extend through the seals into the housing.

The covers can be affixed by screws to the housing and the flat portion of the seal can have bores through which the screws pass and which are located inwardly of the periphery of the seals. Because of the multistage sealing between cover and housing, the housing is reliably and permanently sealed so that ingress protection of the IP 67 type is readily obtainable.

According to yet another feature of the invention a portion of the housing has an optically transparent window through which an optical signal transmitter within the housing is accessible form the point of view of optical signal transmission. This window can be formed by a body of transparent material filled into an opening of corresponding shape in a wall of the housing or of the cover. In the past, windows for optical transmission have been pressed into the housing or cemented thereon and generally because of fabrication tolerances and differences in thermal expansion, it has been impossible to prevent the formation of cracks or gaps through which liquids could enter the housing.

With the invention this is avoided by providing the body with a circumferential groove in which an O-ring or like seal is received and is compressed against the wall of the opening. The body has a shoulder which can engage an inwardly extending ledge of the wall portion to fix the window in the housing with the outer wall surface of the window slush with that of the wall which it is received. The yieldable seal here can compensate for temperature dependent dimensional changes and prevent the penetration of liquids or the like into the interior.

According to the invention, the sensor has at least one plug fitting on a housing part, especially on a cover of the housing and which can receive a plug or jack and whose shield is connected with the shield formed by the housing or cover. While it is customary in earlier systems to provide plug connections on a housing, generally such connections are pass throughs traversing the cover. In that case, the plug can take up considerable space, especially if the electrical connector is of the screw type or bayonet type.

The invention can minimize the space required for the plug connector by having the outer shield formed by the outer member of the housing, in one piece with the shield of the plug or jack connector. The connector fitting can be provided with an external or internal thread to accommodate the plug or jack to be inserted therein. Where the cover is composed of metal it may be provided with two or more such fittings. With a one piece configuration of the fitting and the housing cover or other housing part, a screw assembly of a connector to the housing is not required and a more compact configuration is achieved. Furthermore, the one piece formation of te fitting as part of the housing measures freedom from cracks or the like which can allow contaminants into the housing.

According to another feature of the housing a signal output is provided from the housing.

In practice, high flexibility of installation of the sensor on a machine and avoidance of defective connections is important. The output on the housing enable a programmer to be connected to the unit to enable the sensor to be programmed, especially in the case of an analog signal output. The signal lines of the signal output should be protected against short circuiting and the application of stray voltages. It is also important to be able to detect when the sensor is in a programming mode and when, for example, an output signal fails in a measuring mode.

The sensor for the output connection can thus monitor an output signal and can provide an input in the programming mode which upon failure causes switchover to the measuring mode optionally with a time delay. The device connected to the output can be switched over to detect stray voltage, short circuit or modulated serial data. A time window can be provided for switchover.

According to a feature of the invention the signal output is monitored by a sensor for the output wiring. When input signals (data) are fed to the wiring, the sensor switches automatically to the programming mode. Analogously, the sensor can switch to the measuring mode for output signals to the extent no input signals are detected, optionally after a short time period which is given by the time window.

The signal lines for the measured value are monitored by the sensor as well. Should the sensor recognize that the signal lines have been connected to a programming device, the sensor can then switch itself into the programming mode. This operational status can detect in sequence strong voltage, short circuit or modulated serial data. For security or reliability it is then reasonable to carry out this sequence change within a predetermined time window after it has been initiated. This is not however compulsory.

The sensor can also detect the type of programming device, for example, a PC or a hand-held programmer and respond to a single wire bus with an analog output or via a four wire bus or two wire bus with a binary output to call up diagnostic data, generate parameters and adjust the system.

The type of data which can be drawn from the programming unit or delivered thereto can include diagnostic data interrogatories (software version, serial number, gradient measured cycling time, manufacturing data, nature of the output signal, memory failure signals, defective positioning signals, voltage for auxiliary energy, voltage of the sensor element).

Manufacturing Details

Excitation Currents Matched to the Sensor Length.

Details as to whether the sensor element responds automatically or based upon programming at fixed or variable values.

The nature of the triggering of the measurement, external free running synchronized.

Parameters of the output signal (start stop) or pulsed with modulation, type of reflection of the start signal, the nature of average value formation, selection of the measurement direction, selection of the resolution of the measured value, selection of the signal stroke with an analog output)

Adjustment of the Displacement and Speed Adjustments (Start and End Values)

It is customary in earlier systems to provide digital sensors with BUS interfaces (PROFIBUS, CAN or the like) which can have their parameters set over the bus. With analog sensors the usual parameters (for example 0 to 20 mA or 4 to 20 mA) are established by the hardware and can be modified with open sensors by switches, jumpers, bridges or component replacements. The setting of the 0 point or the end point is carried out by pushbuttons or potentiometers which are accessible through a housing opening or potentiometers which are activated by means of magnets through a housing wall. With the start/stop interface it is possible to read out the serial number, the measurement length, the transit time gradient, manufacturing information and the date on which the device was made by means of a modified start pulse lying the signal wiring. It is already known in addition to replace corresponding buttons by read switches which can be actuated by magnets though the housing wall.

With the system of the of the invention, the adjustment can take place in the field. The removal of the sensor is not required. Parameter setting, sensor diagnosis can be carried out at any optional location of the wiring between the sensor and the control, even in a switching closet so that even sensors which are accessible only with difficulty can be adjusted in place.

According to another feature of the invention the adjustment of the sensor can be simplified in the manner described below. It is recognized in the art that for various purposes different hardware paths may be desired (start/stop or pulse width modulation). Small adjustments like the setting of the zero point can be carried out by mechanical or digital potentiometer settings, change of components like resistors, switches or bridges. However, the invention also enables adjustment in place or prior to mounting simple means and permitting a detail diagnosis to be obtained in the case of failure. In this case the displacement or elongation sensor of the invention has an optical interface enabling at least one of the following elements or devices to be connected:

Diagnosis output memory,

Measured value output memory,

Measured output device,

Signal type detection device (for example a reader or signal varying element, start/stop element, pulse width modulator,

analog signal detector)

Device or element for setting pulse width, for recognizing the type of reflection of the start signal or for determining an external or free running measurement.

A Device or Element for Averaging Over a Number of Measurements

With the optical interface at least one of the functions assigned to this group of devices or elements can be carried out. For instance, for example, the output can provide diagnostic information like version number, serial number, fabrication date, measurement rate transit time constants, memory errors, position detection failures, auxiliary energy voltage, sensor element voltage, etc. The measured value output can be delivered by the interface as well. Furthermore, the signal type of the output can be read and changed and a detection allowed as to whether the signal is a start/stop signal, a pulse width modulation signal, an analog signal, a 0 to 10 V, signal a −10V . . . +10 V signal, a 0 to 20 mA, signal or a 4 to 20 mA signal. The interface can match the output signal as may be required and allow both zero point and n value adjustments. For example pulse width settings, reflection type for the start signal and switchovers between external and free running measurements can be made there as well. The interface can also carry out the averaging over 1 to n measurements.

The adjustment in place can be carried out with simple means and can enable a detail diagnosis to be made without interfering with anything of the adjustment features described. The removal and opening of the sensor is not required.

SPECIFIC DESCRIPTION

FIGS. 1 and 2show in highly diagrammatic form a magnetostrictive elongation sensor for outputting an elongation or longitudinal displacement-dependent signal. In this device, a magnetic wave waveguide2is provided in a protective tube1, the protective tube1being enclosed in turn in a support body3.

The electronic components are combined substantially in a unit which has been illustrated inFIGS. 3 and 4. This unit encompasses the electronic components which can include a Villary strip and a detector coil. The Villary strip is, of course, a strip of metal which may use a magnetoelectric effect or Villary effect and is a change in the longitudinal magnetic properties, for example, the permeability of the ferromagnetic strip which can be caused by a distortion in the longitudinal direction. The effector coil can pick up such a permeability change in a magnetic field by the induction principle and transform it into an electrical signal which is thereby made available for electronic signal conditioning. As a result this system can also be referred to as a Villary transformer.

The components shown inFIGS. 3 and 4, therefore, can include a first circuit board4which can be directly connected to the signal changer1and on which, for example, a band pass filter can be provided, a second printed circuit board5carrying the signal processing elements or circuit6, a third printed circuit board7with the output signal generator elements, circuits or components and a fourth printed circuit board9with the elements of the interconnection circuit.

The first circuit board4, as has been noted, directly connected with the waveguide system, all of the circuit boards are interconnected by plug connectors, i.e. plug-and-jack connectors, whereby the first, second and third boards4,5and7are spaced apart but parallel to one another, one above the other and interconnected by plug connectors10. These three circuit boards form an assembly which can be turned on edge to the signal generator or waveguide assembly. The board9is oriented at a right angle to the board stack4,5,7so that a highly compact assembly of the boards is provided.

The unit shown inFIGS. 3 and 4is surrounded by an insulating shell and this, in turn, is enclosed in a first shield11in the form of a housing. On this shield11(FIG. 2) an insulating sleeve12of the same general shape is provided. The sleeve12is so dimensioned that it can be slid onto the shield11.

Surrounding the insulating sleeve12is a second shield13in the form of a metal housing. The shields may all be grounded.

The thus-formed unit is closed at its ends by covers14and15and seals16can be provided between these covers and the ends of the shield13. The seals are best seen inFIGS. 9 and 10and the cover14has been shown in detail inFIGS. 7 and 8.

Thus the corresponding cover and seal arrangements for the unit shown inFIG. 2have been illustrated inFIG. 7 through 10.

The connection of the covers14and15with the housing formed by the shield13is effected by means of screws17. A further fastening element19cooperates with a sealing ring18to tie the sensing unit to the housing and screws20traversing the cover14, the housing13, the seals16, the plate15extend into the cover art21(FIG. 2) to join the sensing element to the housing.

The housing art11can have guide and insertion grooves, e.g. as formed by the corrugated portion11′ and11″, in which the edges of the circuit boards5-7can be inserted and fit snugly.

The seals16are formed as multistep profile seals (seeFIGS. 9 and 10in particular) and can comprise a flat or planar region27which can engage between the planar end faces of the housing and the cover. The planar portion27is provided with bores27′ through which the tie bolts20can pass. A second region of the seal16is shown at28and constitute a lip which is axially spaced from the planar portion27and sealingly engages the inner surface of the housing. InFIG. 8, the planar portion27is shown to lie against the flat or planar portion14′ of a cover14. The planar portion27is annular and has a window27″ in which an axial projection14″ of the cover14is snugly received. The seal lip28has indentations28′ at the bores27′ which engage around the screws20.

As can be seen especially fromFIGS. 7 and 8as well, a body22can be received in the cover14and can be transparent to form a window through which an optical signal transmitter shown through that window at22′ can output an optical signal. The body22is flush with the outer surface14aof the cover at its wall22aand can be provided with a circumferential groove22breceiving an O ring23which is compressed against the surrounding wall23aof an opening in the cover14accommodating the body22. On the interior of the cover14, the body22can have a shoulder22bengaged against an inwardly extending ledge14bof the cover14to hold the transparent body in place.

FIGS. 5 and 6show another construction for a cover114, which can be used as a substitute for the cover14and has two plug-shaped outputs24and25, one of which can receive a jack and the other a plug. The outer shielding24aand25aof these connectors are formed in one piece with the housing body114aso that no additional seal or shielding is required for the plug connectors. The one piece connector shield is a space-saving feature which allows direct connection of plugs or jacks to the sensor.

InFIGS. 11 and 12the sensor1has been shown very generally and can have an optical signal output which is detected as represented by the broken line and arrow26. The sensor waveguide is juxtaposed with a permanent magnet1aand the relative movement of the magnet and the sensor1results in a magnetic field propagation through the waveguide which is. detected by the circuitry on the circuit boards within the housing13. The sensor1also has a cable connection40with an SPS control29via a T-connector30and into which a hand-held programmer31can be plugged. As an alternative to the controller29, an interface32and a PC34can be connected by plug41to the T-connector30. In this manner the parameter assignments and data collection can be achieved in a simple way.

In the illustration inFIG. 12an optical output26is likewise provided but also is used for coupling (wireless connection) to a hand-held programmer33for the diagnostics, adjustment or setting of the sensor.

The invention is of course not limited to the embodiment described and can be modified within the bounds of the appended claims. All of the novel features described in the specification and/or shown in the drawing can be used individually or in combination with others and are considered within the scope of this invention.