WO1999008293A1 - Lifter with electropermanent magnets provided with a safety device - Google Patents

Lifter with electropermanent magnets provided with a safety device Download PDF

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Publication number
WO1999008293A1
WO1999008293A1 PCT/IB1997/000960 IB9700960W WO9908293A1 WO 1999008293 A1 WO1999008293 A1 WO 1999008293A1 IB 9700960 W IB9700960 W IB 9700960W WO 9908293 A1 WO9908293 A1 WO 9908293A1
Authority
WO
WIPO (PCT)
Prior art keywords
lifter
reversible
magnets
magnet
magnetic
Prior art date
Application number
PCT/IB1997/000960
Other languages
French (fr)
Inventor
Gregory E. Elias
Original Assignee
Railfix N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Railfix N.V. filed Critical Railfix N.V.
Priority to PL97332004A priority Critical patent/PL332004A1/en
Priority to JP10548961A priority patent/JP2001502852A/en
Priority to US09/194,392 priority patent/US6104270A/en
Priority to CA002261272A priority patent/CA2261272A1/en
Priority to DE69703746T priority patent/DE69703746T2/en
Priority to AU35554/97A priority patent/AU3555497A/en
Priority to KR10-1998-0709542A priority patent/KR100471505B1/en
Priority to EP97931980A priority patent/EP0929904B1/en
Priority to ES97931980T priority patent/ES2154467T3/en
Priority to DK97931980T priority patent/DK0929904T3/en
Priority to AT97931980T priority patent/ATE198243T1/en
Priority to PCT/IB1997/000960 priority patent/WO1999008293A1/en
Priority to RU98121314/09A priority patent/RU98121314A/en
Priority to NO985400A priority patent/NO985400D0/en
Publication of WO1999008293A1 publication Critical patent/WO1999008293A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/04—Means for releasing the attractive force
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66C—CRANES; LOAD-ENGAGING ELEMENTS OR DEVICES FOR CRANES, CAPSTANS, WINCHES, OR TACKLES
    • B66C1/00—Load-engaging elements or devices attached to lifting or lowering gear of cranes or adapted for connection therewith for transmitting lifting forces to articles or groups of articles
    • B66C1/04—Load-engaging elements or devices attached to lifting or lowering gear of cranes or adapted for connection therewith for transmitting lifting forces to articles or groups of articles by magnetic means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66C—CRANES; LOAD-ENGAGING ELEMENTS OR DEVICES FOR CRANES, CAPSTANS, WINCHES, OR TACKLES
    • B66C1/00—Load-engaging elements or devices attached to lifting or lowering gear of cranes or adapted for connection therewith for transmitting lifting forces to articles or groups of articles
    • B66C1/04—Load-engaging elements or devices attached to lifting or lowering gear of cranes or adapted for connection therewith for transmitting lifting forces to articles or groups of articles by magnetic means
    • B66C1/06—Load-engaging elements or devices attached to lifting or lowering gear of cranes or adapted for connection therewith for transmitting lifting forces to articles or groups of articles by magnetic means electromagnetic
    • B66C1/08—Circuits therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
    • G01R33/07—Hall effect devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/0231—Magnetic circuits with PM for power or force generation
    • H01F7/0252—PM holding devices
    • H01F7/0257—Lifting, pick-up magnetic objects
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/06—Electromagnets; Actuators including electromagnets
    • H01F7/20—Electromagnets; Actuators including electromagnets without armatures
    • H01F7/206—Electromagnets for lifting, handling or transporting of magnetic pieces or material
    • H01F2007/208—Electromagnets for lifting, handling or transporting of magnetic pieces or material combined with permanent magnets

Definitions

  • the present invention relates to magnet lifters, and particularly to a lifter with electropermanent magnets provided with a safety device for controlling their working point.
  • lifters are divided into three classes depending on the type of used magnets, i.e. permanent magnets, electropermanent magnets and electromagnets.
  • Each lifter type has its own advantages and drawbacks.
  • the lifters with permanent magnets have the advantage of an almost negligible power consumption and of a produced magnetic force which is reliably constant and independent of outer supply sources.
  • the load detachment requires the apphcation of a considerable mechanical power amount in order to reduce the magnetic force to a value smaller than the load weight.
  • the magnets are to be made movable so as to be moved away from the load, thus decreasing the magnetic attraction.
  • the lifters with electropermanent magnets substantially combine the advantages of the two aforementioned lifter types. This is due to the use of a permanent magnet of the reversible type, i.e. a magnet wherein the polarity is easily reversible through the apphcation of an electric impulse. The reversible magnet thus generates an adjustable flux which also can direct the flux of a conventional permanent magnet combined therewith.
  • the electropermanent magnets with respect to the other two types of magnets, have a drawback in the working instability due to the particular magnetization curve of the reversible magnet.
  • the reversible magnets are usually made of an aluminum-nickel-cobalt (alnico) alloy having an hysteresis characterized in that a high induction corresponds to a reduced coercive force. This characteristic allows to direct the magnetic flux in the permanent magnet forming the electropermanent magnet.
  • the magnetization curve has a "knee” beyond which the behavior of the reversible magnet is still linear, but much more sloped than in the first region.
  • the lifters with electropermanent magnets are greatly affected by the dynamics of the lifted material. It is in fact known that the oscillations of the plates lifted by such a unit involve a variation of the ah gap, and accordingly a variation of the total reluctance of the magnetic circuit, which may shift the working point of the magnetic masses of the lifter below said "knee". This dynamics is affected even by little shifts of the lifted material and thus slight bendings or hardly detectable curvings are enough to cause a considerable variation of the magnetomotive force thereby making the lifting system very unstable.
  • Such an object is achieved by means of a lifter provided with a sensor capable of measuring the only contribution of the reversible magnet and accordingly its working point.
  • the main advantage of the present lifter is thus to ensure the highest operating safety by indicating not only the total safety factor but also the approach of the instability condition.
  • Another advantage of the lifter according to the present invention is that, by suitably combining the data supphed by the sensor measuring the reversible magnet flux with the data supphed by the sensor measuring the total magnetic flux, it is possible to compensate the reading error of the latter due to the magnetic dispersions caused by the air gap between the active polarities and the load, said error being proportional to the air gap size.
  • - Fig. 1 is a front diagrammatic view, with the left half in section, of a lifter according to the invention in the non- working phase;
  • - Fig. 2 is a partial view in horizontal section of a symmetrical half of the lifter of Fig. 1;
  • - Fig. 3 is a diagram comprising the magnetization curves of the reversible magnet and of the permanent magnet; and - Fig. 4 is a view of the lifter of Fig. 1, in the load conveying phase.
  • the lifter with electropermanent magnets in a known way comprises an outer supporting structure, a plurality of magnets and an adjustment and control unit.
  • the supporting structure consists in an upper block 1, provided with joints 2 for the fastening to lifting means, e.g. a crane, four sides 3 and a closing base plate
  • Each electropermanent magnet is formed by a reversible magnet 5 and a permanent magnet 6 arranged one above the other respectively.
  • the polarities of reversible magnet 5 are arranged on the horizontal sides of a core 5 a, made of alnico, around which a commuting coil 5b is arranged for controlling the pole reversal. While the lifter is not working, as shown in Fig. 1, the north pole (N) is on the upper side and the south pole (S) in on the lower side.
  • Permanent magnet 6 comprises a plurality of ferrite blocks 6a arranged along the lateral sides of an iron core 6b. This core 6b is fastened to block 1 through a plurality of bars 7 passing through the alnico core 5a and constrained by nuts 8 into suitable seats 9. Thus, also permanent magnet 5 is fastened under block 1. Core 6b extends downwards in a pole piece 6c, protruding from plate 4 and intended to contact the load to be lifted.
  • Fig. 2 The arrangement of the polarities of ferrite blocks 6a is clearly shown in Fig. 2, wherein on all sides the north pole is facing core 6b and the south pole is facing outwards.
  • another electropermanent magnet is suitably arranged with the reversed polarities in the right half of the lifter.
  • second reversible magnet 6' having its south pole on the upper side and its north pole on the lower side.
  • Second permanent magnet 6' likewise comprises a plurality of ferrite blocks 6a' arranged with their south poles facing core 6b' and their north poles facing outwards (see Fig. 2).
  • This magnet arrangement induces a magnetic field comprising three sheaves of flux lines substantially oriented in the direction indicated by the arrows of Fig. 1.
  • the middle sheaf of these flux lines passes through the two reversible magnets 5, 5', the two cores 6b, 6b' and ferrite blocks 6a, 6a' arranged therebetween, besides some portions of the outer supporting structure.
  • the two side sheaves of flux lines pass instead through only one of reversible magnets 5, 5', one of cores 6b, 6b' and ferrite blocks 6a, 6a' arranged between one of these cores and sides 3.
  • Such flux lines being linked together, flow inside the lifter, so that a ferromagnetic load, arranged close to pole pieces 6c, 6c', would not be attracted by the lifter.
  • the adjustment and control circuits comprise at least a control circuit 10 of commuting coil 5b, a first magnetic sensor 11 and a second magnetic sensor 12 respectively arranged above and under ferrite blocks 6a, as well as at least a safety device 13 for processing the signals coming from said sensors 11 and 12.
  • Lower magnetic sensor 11 consists for instance of a coil having its loops surrounding the base of core 6b in order to measure the flux linked with the load.
  • Upper magnetic sensor 12, consisting for instance of a further coil having its loops surrounding the upper portion of core 6b, is the innovative aspect of the present lifter as it allows to measure the only contribution of reversible magnet 5, as it will be hereinafter explained.
  • each electropermanent magnet is preferably provided with its own pair of sensors in order to achieve a greater measure accuracy.
  • a lower coil and an upper coil are also arranged around core 6b' of the magnet, both connected to safety device 13. so as to reduce the measure error by averaging the readings of the two pairs of coils.
  • the magnetization curve showing the ratio between residual induction Br and coercive field intensity He has two different characteristics depending on the magnet type of the lifter.
  • magnetization curve 14 of reversible magnets 5, 5' unlike curve 15 of permanent magnets 6, 6', has a quite short linear segment 16 between "knee" 17 and the axis of residual induction Br corresponding to a zero level of coercive field intensity He.
  • magnetization curve 14 is highly sloped and shows hysteresis phenomena, whereby, if the working point of the lifter accidentally comes in that region, its lifting force is unstable, since residual induction Br swiftly varies upon slight variations of intensity He and moreover there is no bijection between these two quantities owing to the magnetic hysteresis.
  • a ferromagnetic load 18 may be attracted by the lifter according to the present invention by placing it close to pole pieces 6c, 6c' and by reversing the polarities of reversible magnets 5, 5' through the respective commuting coils.
  • sensors 12 detect the intensity of the magnetic flux generated only by the reversible magnets, whereas sensors 1 1 also detect the contribution given by ferrite blocks 6a, 6a'.
  • Safety device 13 in the present embodiment comprises an electronic circuit controlled by a microprocessor receiving as input the signals transmitted by sensors 11 and 12 and subsequently amplified and converted in digital form.
  • Device 13 processes the signals of sensors 11 and 12 in order to respectively obtain the total magnetic force of the electropermanent magnets and the working point of reversible magnets 5, 5' on curve 14. By comparing such values with each other, device 13 compensates the difference between the magnetic flux measured by sensors 1 1 and the magnetic flux actually passing through load 18. Such a difference results from the dispersions of the magnetic flux due to the air gap ⁇ , i.e. to the variations of the distance between load 18 and pole pieces 6c, 6c'.
  • Figure 4 on the left the flux lines are shown through the air gap ⁇ (enlarged) under real conditions, i.e. with the dispersion effects, and on the right the same flux lines under ideal conditions, i.e. without the dispersion effects.
  • device 13 determines the working point of reversible magnets 5, 5' on curve 14 of Figure 3, and accordingly calculates in sequence the size of air gap ⁇ , the value of induction Br, the magnetic linkage with load 18 and finally the effective magnetic force acting on the latter.
  • the software of safety device 13 thus comprises a specific algorithm capable of automatically correct the readings of sensors 11 so as to eliminate the errors due to the dispersed magnetic fluxes owing to the air gap ⁇ .
  • device 13 would provide for immediately signaling the risk situation to the operators by means of acoustic or optical alarm signals or the like.
  • the material the magnets are made of may vary depending on the lifter requirements.
  • the permanent magnets may be made of neodymium or other rare earths.
  • magnetic sensors 11 and 12 may not comprise coils, but other type of sensors, e.g. Hall effect sensors.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Power Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Load-Engaging Elements For Cranes (AREA)
  • Forklifts And Lifting Vehicles (AREA)
  • Valve-Gear Or Valve Arrangements (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
  • Push-Button Switches (AREA)
  • Measuring Magnetic Variables (AREA)
  • Escalators And Moving Walkways (AREA)

Abstract

A lifter comprising at least a reversible magnet (5, 5") arranged with its polarities oriented along a vertical axis above at least a magnet (6, 6") provided with a least a pair of permanent magnets (6a, 6a") arranged with the polarities oriented along an horizontal axis on the sides of at least a ferromagnetic core (6b, 6b") suitable to contact the load (18) to be lifted, at least a magnetic sensor (11) arranged close to the base (6c, 6c") of said ferromagnetic core, and a further magnetic sensor (12) arranged over said permanent magnets (6a, 6a") so as to measure substantially only the magnetic flux passing through the reversible magnet (5, 5"), as well as a safety device (13) for processing the signals transmitted by said magnetic sensors (11, 12) and obtaining the working point of the lifter on the magnetization curve (14) of the reversible magnet (5, 5").

Description

"LIFTER WITH EI ECTROPERMAMENT MAGNETS PROVIDED WITH A
SAFETY DEVICE"
The present invention relates to magnet lifters, and particularly to a lifter with electropermanent magnets provided with a safety device for controlling their working point.
As it is known, lifters are divided into three classes depending on the type of used magnets, i.e. permanent magnets, electropermanent magnets and electromagnets. Each lifter type has its own advantages and drawbacks. The lifters with permanent magnets have the advantage of an almost negligible power consumption and of a produced magnetic force which is reliably constant and independent of outer supply sources. On the other hand, it is not possible to increase the magnetic force if necessary and the magnets are exceedingly bulky for lifting heavy loads. Furthermore, the load detachment requires the apphcation of a considerable mechanical power amount in order to reduce the magnetic force to a value smaller than the load weight. Alternatively, the magnets are to be made movable so as to be moved away from the load, thus decreasing the magnetic attraction.
On the contrary, in the lifters with electromagnets it is possible to freely vary the magnetic force by simply adjusting the current flowing in the windings which generate the magnetic field. However, any breakdown, even if very short, of the power supply immediately cancels the magnetic force and thus causes the load detachment. It is therefore evident that safety systems ensuring the supply continuity are essential. The lifters with electropermanent magnets substantially combine the advantages of the two aforementioned lifter types. This is due to the use of a permanent magnet of the reversible type, i.e. a magnet wherein the polarity is easily reversible through the apphcation of an electric impulse. The reversible magnet thus generates an adjustable flux which also can direct the flux of a conventional permanent magnet combined therewith. It is thus possible to short-circuit the two magnets when the lifter is to be deactivated, or arrange them in parallel for activating the lifter. Since just an electric impulse but not a continuous supply is needed for reversing the reversible magnet, the safety problems affecting electromagnets are overcome. At the same time, even though permanent magnets are used, it is possible to vary the magnetic force within some limits, and the load detachment is easy to carry out with a minimum power consumption and without complex structures for moving the magnets.
However, the electropermanent magnets, with respect to the other two types of magnets, have a drawback in the working instability due to the particular magnetization curve of the reversible magnet. In fact the reversible magnets are usually made of an aluminum-nickel-cobalt (alnico) alloy having an hysteresis characterized in that a high induction corresponds to a reduced coercive force. This characteristic allows to direct the magnetic flux in the permanent magnet forming the electropermanent magnet.
However, the magnetization curve has a "knee" beyond which the behavior of the reversible magnet is still linear, but much more sloped than in the first region. This involves great induction variations corresponding to small coercive force variations. Practically this means that the lifters with electropermanent magnets are greatly affected by the dynamics of the lifted material. It is in fact known that the oscillations of the plates lifted by such a unit involve a variation of the ah gap, and accordingly a variation of the total reluctance of the magnetic circuit, which may shift the working point of the magnetic masses of the lifter below said "knee". This dynamics is affected even by little shifts of the lifted material and thus slight bendings or hardly detectable curvings are enough to cause a considerable variation of the magnetomotive force thereby making the lifting system very unstable.
In the known lifters there is a system for measuring the magnetic force which is the same for any type of magnets. This measuring system only serves to calculate the safety operative factor by comparing the generated magnetic force with the weight of the load to be lifted. This is carried out by arranging a measuring coil close to the pole pieces contacting the load, so as to quite accurately measure the total flux linked with the load. Such a measure obviously gives no indication about the working point, so it is not capable of signaling the risk resulting from the instability, if any, of the reversible magnet.
It is an object of the present invention to provide a lifter with electropermanent magnets provided with a safety device which allows to control the instability, if any, of the lifting unit depending on the actual working conditions.
Such an object is achieved by means of a lifter provided with a sensor capable of measuring the only contribution of the reversible magnet and accordingly its working point.
The main advantage of the present lifter is thus to ensure the highest operating safety by indicating not only the total safety factor but also the approach of the instability condition.
Another advantage of the lifter according to the present invention is that, by suitably combining the data supphed by the sensor measuring the reversible magnet flux with the data supphed by the sensor measuring the total magnetic flux, it is possible to compensate the reading error of the latter due to the magnetic dispersions caused by the air gap between the active polarities and the load, said error being proportional to the air gap size. Further advantages and features of the lifter according to the present invention will be evident to those skilled in the art from the following detailed description of an embodiment thereof with reference to the attached drawings, wherein:
- Fig. 1 is a front diagrammatic view, with the left half in section, of a lifter according to the invention in the non- working phase;
- Fig. 2 is a partial view in horizontal section of a symmetrical half of the lifter of Fig. 1;
- Fig. 3 is a diagram comprising the magnetization curves of the reversible magnet and of the permanent magnet; and - Fig. 4 is a view of the lifter of Fig. 1, in the load conveying phase.
Referring to Fig. 1, the lifter with electropermanent magnets according to the present invention in a known way comprises an outer supporting structure, a plurality of magnets and an adjustment and control unit.
The supporting structure consists in an upper block 1, provided with joints 2 for the fastening to lifting means, e.g. a crane, four sides 3 and a closing base plate
4. Obviously such a structure is made of highly magnetically conductive materials in order to minimize the reluctance of the magnetic circuit.
Each electropermanent magnet is formed by a reversible magnet 5 and a permanent magnet 6 arranged one above the other respectively. The polarities of reversible magnet 5 are arranged on the horizontal sides of a core 5 a, made of alnico, around which a commuting coil 5b is arranged for controlling the pole reversal. While the lifter is not working, as shown in Fig. 1, the north pole (N) is on the upper side and the south pole (S) in on the lower side.
Permanent magnet 6 comprises a plurality of ferrite blocks 6a arranged along the lateral sides of an iron core 6b. This core 6b is fastened to block 1 through a plurality of bars 7 passing through the alnico core 5a and constrained by nuts 8 into suitable seats 9. Thus, also permanent magnet 5 is fastened under block 1. Core 6b extends downwards in a pole piece 6c, protruding from plate 4 and intended to contact the load to be lifted.
The arrangement of the polarities of ferrite blocks 6a is clearly shown in Fig. 2, wherein on all sides the north pole is facing core 6b and the south pole is facing outwards.
The above description relates to magnets 5, 6, arranged on the left of the lifter shown in Fig. 1, i.e. to those visible in the half section. For closing of the magnetic circuits indicated by the arrows, another electropermanent magnet is suitably arranged with the reversed polarities in the right half of the lifter. In other words, there is a second reversible magnet 6' having its south pole on the upper side and its north pole on the lower side. Second permanent magnet 6' likewise comprises a plurality of ferrite blocks 6a' arranged with their south poles facing core 6b' and their north poles facing outwards (see Fig. 2). This magnet arrangement induces a magnetic field comprising three sheaves of flux lines substantially oriented in the direction indicated by the arrows of Fig. 1. The middle sheaf of these flux lines passes through the two reversible magnets 5, 5', the two cores 6b, 6b' and ferrite blocks 6a, 6a' arranged therebetween, besides some portions of the outer supporting structure. The two side sheaves of flux lines pass instead through only one of reversible magnets 5, 5', one of cores 6b, 6b' and ferrite blocks 6a, 6a' arranged between one of these cores and sides 3. Such flux lines, being linked together, flow inside the lifter, so that a ferromagnetic load, arranged close to pole pieces 6c, 6c', would not be attracted by the lifter.
The adjustment and control circuits comprise at least a control circuit 10 of commuting coil 5b, a first magnetic sensor 11 and a second magnetic sensor 12 respectively arranged above and under ferrite blocks 6a, as well as at least a safety device 13 for processing the signals coming from said sensors 11 and 12. Lower magnetic sensor 11 consists for instance of a coil having its loops surrounding the base of core 6b in order to measure the flux linked with the load. Upper magnetic sensor 12, consisting for instance of a further coil having its loops surrounding the upper portion of core 6b, is the innovative aspect of the present lifter as it allows to measure the only contribution of reversible magnet 5, as it will be hereinafter explained.
Although a single pair of sensors 11 and 12 is enough to control the working of a pole pair of an electropermanent magnet, each electropermanent magnet is preferably provided with its own pair of sensors in order to achieve a greater measure accuracy. Thus, a lower coil and an upper coil (not shown in figure) are also arranged around core 6b' of the magnet, both connected to safety device 13. so as to reduce the measure error by averaging the readings of the two pairs of coils.
Referring to Fig. 3, the magnetization curve showing the ratio between residual induction Br and coercive field intensity He has two different characteristics depending on the magnet type of the lifter. In particular, magnetization curve 14 of reversible magnets 5, 5', unlike curve 15 of permanent magnets 6, 6', has a quite short linear segment 16 between "knee" 17 and the axis of residual induction Br corresponding to a zero level of coercive field intensity He. Beyond "knee" 17, magnetization curve 14 is highly sloped and shows hysteresis phenomena, whereby, if the working point of the lifter accidentally comes in that region, its lifting force is unstable, since residual induction Br swiftly varies upon slight variations of intensity He and moreover there is no bijection between these two quantities owing to the magnetic hysteresis. Referring now also to Fig. 4, a ferromagnetic load 18 may be attracted by the lifter according to the present invention by placing it close to pole pieces 6c, 6c' and by reversing the polarities of reversible magnets 5, 5' through the respective commuting coils. Thus the magnetic flux lines are no longer linked with those of permanent magnets 6a, 6a', as shown in Fig. 1. Instead, all the flux lines pass through load 18, since, thanks to the particular magnet arrangement, the magnetic circuit is forced to come out of pole piece 6c and go back into pole piece 6c'. Also in this case a magnetic field is induced comprising three sheaves of flux lines, which are however substantially oriented in the direction indicated by the arrows in Fig. 4 and thus being concentric.
In particular, it should be noted that the flux lines passing through reversible magnets 5, 5' do not pass through ferrite blocks 6a, 6a', thus not being affected by the magnetic field generated therefrom. Therefore sensors 12 detect the intensity of the magnetic flux generated only by the reversible magnets, whereas sensors 1 1 also detect the contribution given by ferrite blocks 6a, 6a'.
Safety device 13 in the present embodiment comprises an electronic circuit controlled by a microprocessor receiving as input the signals transmitted by sensors 11 and 12 and subsequently amplified and converted in digital form. Device 13 processes the signals of sensors 11 and 12 in order to respectively obtain the total magnetic force of the electropermanent magnets and the working point of reversible magnets 5, 5' on curve 14. By comparing such values with each other, device 13 compensates the difference between the magnetic flux measured by sensors 1 1 and the magnetic flux actually passing through load 18. Such a difference results from the dispersions of the magnetic flux due to the air gap Δ, i.e. to the variations of the distance between load 18 and pole pieces 6c, 6c'. In Figure 4 on the left the flux lines are shown through the air gap Δ (enlarged) under real conditions, i.e. with the dispersion effects, and on the right the same flux lines under ideal conditions, i.e. without the dispersion effects.
Thanks to sensors 12 arranged over the permanent magnets, device 13 determines the working point of reversible magnets 5, 5' on curve 14 of Figure 3, and accordingly calculates in sequence the size of air gap Δ, the value of induction Br, the magnetic linkage with load 18 and finally the effective magnetic force acting on the latter. The software of safety device 13 thus comprises a specific algorithm capable of automatically correct the readings of sensors 11 so as to eliminate the errors due to the dispersed magnetic fluxes owing to the air gap Δ.
Should the effective magnetic force operating on load 18 be insufficient for its lifting, or should the working point of reversible magnets 5, 5' not be on linear segment 16, device 13 would provide for immediately signaling the risk situation to the operators by means of acoustic or optical alarm signals or the like.
Obviously the above described and illustrated embodiment of the lifter according to the invention is only an example susceptible of various modifications.
In particular, the material the magnets are made of may vary depending on the lifter requirements. For example, the permanent magnets may be made of neodymium or other rare earths.
Likewise obviously, in another embodiment of the lifter according to the present invention, magnetic sensors 11 and 12 may not comprise coils, but other type of sensors, e.g. Hall effect sensors.

Claims

1. A lifter comprising at least a reversible magnet (5, 5') arranged with its polarities oriented along a vertical axis over at least a magnet (6, 6') provided with at least a pair of permanent magnets (6a, 6a') arranged with their polarities oriented along an horizontal axis on the sides of at least a ferromagnetic core (6b, 6b') suitable to contact the load (18) to be lifted, and at least a magnetic sensor (11) arranged close to the base (6c, 6c') of said ferromagnetic core, characterized in that it comprises at least a further magnetic sensor (12) arranged above said permanent magnets (6a, 6a') so as to measure substantially the only magnetic flux passing through the reversible magnet (5, 5'), as well as a safety device (13) for processing the signals transmitted by said magnetic sensors (11, 12) and obtaining the working point of the lifter on the magnetization curve (14) of the reversible magnet (5, 5').
2. A lifter according to the previous claim, characterized in that it comprises a pair of reversible magnets (5, 5'), each being arranged with its polarities oriented mutually reversed along a vertical axis over a magnet (6, 6') provided with a plurahty of permanent magnets (6a, 6a') arranged with their polarities oriented along a horizontal axis on the sides of a ferromagnetic core (6b, 6b'), wherein the magnetic fluxes induced by the reversible magnets (5.
5') are linked together.
3. A lifter according to the previous claim, characterized in that it comprises a magnetic sensor (11) arranged at the base of each of two ferromagnetic cores (6b, 6b') and a further magnetic sensor (12) arranged between each of the two reversible magnets (5, 5') and the permanent magnets (6a, 6a') thereto associated.
4. A lifter according to any of the previous claims, characterized in that at least one of the reversible magnets (5, 5') is made of a metallic alloy comprising aluminum, nickel and cobalt.
5. A lifter according to any of the previous claims, characterized in that at least one of the magnetic sensors (11, 12) comprises a coil having its loops surrounding a portion of said ferromagnetic cores (6b, 6b').
6. A lifter according to any of claims 1 to 4, characterized in that at least one of the magnetic sensors (11, 12) comprises an Hall effect sensor.
7. A lifter according to any of the previous claims, characterized in that the reversible magnets (5, 5') and the permanent magnets (6a, 6a') are housed inside a highly magnetically conductive structure (1, 3, 4), having the ferromagnetic cores (6b, 6b') partially protruding from its base.
8. A lifter according to any of the previous claims, characterized in that the safety device (13) comprises an electronic circuit controlled by a microprocessor receiving as input the signals transmitted by the magnetic sensors (11, 12) and converted in digital form.
9. A lifter according to the previous claim, characterized in that the safety device (13) calculates the magnetic flux passing through the lifted load ( 18) depending on the difference of values detected through the magnetic sensors (11, 12).
10. A lifter according to the previous claim, characterized in that the safety device (13) comprises alarm means being automatically activated if the working point of the lifter on the magnetization curve (14) of the reversible magnets (5, 5') is not in the linear segment (16) between the knee ( 17) and the axis of the residual induction (Br) corresponding to a zero level of the coercive field intensity (He).
PCT/IB1997/000960 1997-08-04 1997-08-04 Lifter with electropermanent magnets provided with a safety device WO1999008293A1 (en)

Priority Applications (14)

Application Number Priority Date Filing Date Title
PL97332004A PL332004A1 (en) 1997-08-04 1997-08-04 Hoisting apparatus with electromagnets provided with a protective device
JP10548961A JP2001502852A (en) 1997-08-04 1997-08-04 Electromagnetic permanent magnet system type hoist with safety device
US09/194,392 US6104270A (en) 1997-08-04 1997-08-04 Lifter with electropermanent magnets provided with a safety device
CA002261272A CA2261272A1 (en) 1997-08-04 1997-08-04 Lifter with electropermanent magnets provided with a safety device
DE69703746T DE69703746T2 (en) 1997-08-04 1997-08-04 LIFT WITH ELECTROPERMANENT MAGNETS WITH A SAFETY DEVICE
AU35554/97A AU3555497A (en) 1997-08-04 1997-08-04 Lifter with electropermanent magnets provided with a safety device
KR10-1998-0709542A KR100471505B1 (en) 1997-08-04 1997-08-04 Lifter with electropermanent magnets provided with a safety device
EP97931980A EP0929904B1 (en) 1997-08-04 1997-08-04 Lifter with electropermanent magnets provided with a safety device
ES97931980T ES2154467T3 (en) 1997-08-04 1997-08-04 SUSPENSOR WITH ELECTROPERMANENT MAGNETS PROVIDED WITH A SAFETY DEVICE.
DK97931980T DK0929904T3 (en) 1997-08-04 1997-08-04 Lifting device with electropermanent magnets fitted with a safety device
AT97931980T ATE198243T1 (en) 1997-08-04 1997-08-04 LIFTER WITH ELECTROPERMANENT MAGNETS WITH A SAFETY DEVICE
PCT/IB1997/000960 WO1999008293A1 (en) 1997-08-04 1997-08-04 Lifter with electropermanent magnets provided with a safety device
RU98121314/09A RU98121314A (en) 1997-08-04 1997-08-04 LIFT WITH POLARIZED MAGNETS, PROTECTED WITH SAFETY DEVICE
NO985400A NO985400D0 (en) 1997-08-04 1998-11-20 L ° fteanordning

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IB1997/000960 WO1999008293A1 (en) 1997-08-04 1997-08-04 Lifter with electropermanent magnets provided with a safety device

Publications (1)

Publication Number Publication Date
WO1999008293A1 true WO1999008293A1 (en) 1999-02-18

Family

ID=11004595

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB1997/000960 WO1999008293A1 (en) 1997-08-04 1997-08-04 Lifter with electropermanent magnets provided with a safety device

Country Status (12)

Country Link
US (1) US6104270A (en)
EP (1) EP0929904B1 (en)
JP (1) JP2001502852A (en)
KR (1) KR100471505B1 (en)
AT (1) ATE198243T1 (en)
AU (1) AU3555497A (en)
CA (1) CA2261272A1 (en)
DE (1) DE69703746T2 (en)
DK (1) DK0929904T3 (en)
ES (1) ES2154467T3 (en)
RU (1) RU98121314A (en)
WO (1) WO1999008293A1 (en)

Cited By (8)

* Cited by examiner, † Cited by third party
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WO2014033757A1 (en) * 2012-08-31 2014-03-06 Uttam Sarda Electro permanent magnetic holding apparatus with magnetic flux sensor
CN104854015A (en) * 2012-11-30 2015-08-19 Sgm台架股份公司 Lifter with electropermanent magnets
WO2015193837A1 (en) * 2014-06-20 2015-12-23 Sgm Gantry S.P.A. Electromagnetic lifter for hot materials
WO2016038487A1 (en) * 2014-09-09 2016-03-17 Sgm Gantry S.P.A. Lifter with electropermanent magnets
WO2019209553A1 (en) 2017-04-27 2019-10-31 Magswitch Technology Worldwide Pty Ltd. Magnetic coupling device with at least one of a sensor arrangement and a degauss capability
US11651883B2 (en) 2017-06-08 2023-05-16 Magswitch Technology Worldwide Pty Ltd. Electromagnet-switchable permanent magnet device
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Families Citing this family (31)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NO985263D0 (en) * 1998-11-11 1998-11-11 Jarle Breivik System that can reversibly reproduce itself
KR20010010081A (en) * 1999-07-15 2001-02-05 이구택 A safty device for permanent magnetic lifter
US6489871B1 (en) * 1999-12-11 2002-12-03 Simon C. Barton Magnetic workholding device
US6636153B1 (en) * 2000-07-26 2003-10-21 Simon C. Barton Sensing system for magnetic clamping devices
NL1022885C2 (en) 2003-03-10 2004-09-13 Walker Europ Holding B V Electrically operated magnetic rail brake device, as well as device movable along one or more rails, provided with a rail brake device.
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DE102005046575A1 (en) 2005-09-29 2007-10-31 Deere & Company, Moline Clutch system for making a separable connection between a vehicle and a work implement
FR2902361B1 (en) * 2006-06-16 2008-08-08 Staubli Faverges Sca MAGNETIC CLAMPING DEVICE, INJECTION MOLDING MACHINE EQUIPPED WITH SUCH A DEVICE, AND METHOD FOR MANUFACTURING SUCH A DEVICE
WO2008105041A1 (en) * 2007-02-23 2008-09-04 Pascal Engineering Corporation Magnetic fixing device
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DE102010052396A1 (en) 2010-11-24 2012-05-24 Kuka Roboter Gmbh Method and device for controlling a peripheral component of a robot system
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US8907754B2 (en) * 2012-08-16 2014-12-09 DocMagnet, Inc. Variable field magnetic holding system
US10378652B2 (en) 2014-08-20 2019-08-13 Vacuworx Global, LLC Seal for a vacuum material lifter
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US11749438B2 (en) * 2018-06-19 2023-09-05 The Aerospace Corporation Thermo-mechanical magnetic coupler
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2043354A (en) * 1979-01-09 1980-10-01 Cardone Tecnomagnetica Lifting device with permanent magnet heads
US4965695A (en) * 1987-05-22 1990-10-23 Baumann Joseph D Permanent magnetic retaining device to move, affix or carry ferromagnetic parts or loads with electronic switching of the magnetic flux to release the carried load
JPH04345498A (en) * 1991-05-23 1992-12-01 Fuji Jikou Kk Permanent electromagnetic lifting device which can regulate its attraction force
WO1997003911A1 (en) * 1995-07-24 1997-02-06 Railfix N.V. Electrical permanent-magnet system for manoeuvring a magnetic, particularly a ferromagnetic, load

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2346042B2 (en) * 1973-09-13 1978-09-21 Thyssen Edelstahlwerke Ag, 4000 Duesseldorf Permanent magnet system with adjustable adhesive force
US4237455A (en) * 1978-07-10 1980-12-02 British Steel Corporation Safety device for lifting magnets
IT1219706B (en) * 1988-06-10 1990-05-24 Cardone Tecnomagnetica MAGNETIC ANCHORAGE EQUIPMENT, WITH CIRCUIT FOR THE ELIMINATION OF THE RESIDUAL FLOW
US4910633A (en) * 1988-09-07 1990-03-20 Quinn Louis P Magnetic levitation apparatus and method
DE4322825C1 (en) * 1993-07-08 1994-10-20 Busch Dieter & Co Prueftech Holding device for an object picking up measured values

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2043354A (en) * 1979-01-09 1980-10-01 Cardone Tecnomagnetica Lifting device with permanent magnet heads
US4965695A (en) * 1987-05-22 1990-10-23 Baumann Joseph D Permanent magnetic retaining device to move, affix or carry ferromagnetic parts or loads with electronic switching of the magnetic flux to release the carried load
JPH04345498A (en) * 1991-05-23 1992-12-01 Fuji Jikou Kk Permanent electromagnetic lifting device which can regulate its attraction force
WO1997003911A1 (en) * 1995-07-24 1997-02-06 Railfix N.V. Electrical permanent-magnet system for manoeuvring a magnetic, particularly a ferromagnetic, load

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 017, no. 201 (M - 1399) 20 April 1993 (1993-04-20) *

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WO2008032333A1 (en) * 2006-09-13 2008-03-20 Uttam Sarda An electro permanent magnetic work holding system which clamps ferromagnetic work piece(s) and simultaneously senses displacement
WO2014033757A1 (en) * 2012-08-31 2014-03-06 Uttam Sarda Electro permanent magnetic holding apparatus with magnetic flux sensor
CN104854015A (en) * 2012-11-30 2015-08-19 Sgm台架股份公司 Lifter with electropermanent magnets
WO2015193837A1 (en) * 2014-06-20 2015-12-23 Sgm Gantry S.P.A. Electromagnetic lifter for hot materials
US10167174B2 (en) 2014-06-20 2019-01-01 Sgm Magnetics S.P.A. Electromagnetic lifter for hot materials
WO2016038487A1 (en) * 2014-09-09 2016-03-17 Sgm Gantry S.P.A. Lifter with electropermanent magnets
US10144618B2 (en) 2014-09-09 2018-12-04 Sgm Magnetics S.P.A. Lifter with electropermanent magnets
EP3810380A4 (en) * 2017-04-27 2022-01-26 Magswitch Technology Worldwide Pty Ltd. Magnetic coupling device with at least one of a sensor arrangement and a degauss capability
WO2019209553A1 (en) 2017-04-27 2019-10-31 Magswitch Technology Worldwide Pty Ltd. Magnetic coupling device with at least one of a sensor arrangement and a degauss capability
US11511396B2 (en) 2017-04-27 2022-11-29 Magswitch Technology Worldwide Pty Ltd. Magnetic coupling devices
US11839954B2 (en) 2017-04-27 2023-12-12 Magswitch Technology, Inc. Magnetic coupling device with at least one of a sensor arrangement and a degauss capability
US11850708B2 (en) 2017-04-27 2023-12-26 Magswitch Technology, Inc. Magnetic coupling device with at least one of a sensor arrangement and a degauss capability
US11901141B2 (en) 2017-04-27 2024-02-13 Magswitch Technology, Inc. Variable field magnetic couplers and methods for engaging a ferromagnetic workpiece
US11901142B2 (en) 2017-04-27 2024-02-13 Magswitch Technology, Inc. Variable field magnetic couplers and methods for engaging a ferromagnetic workpiece
US11651883B2 (en) 2017-06-08 2023-05-16 Magswitch Technology Worldwide Pty Ltd. Electromagnet-switchable permanent magnet device
US11837402B2 (en) 2017-06-08 2023-12-05 Magswitch Technology, Inc. Electromagnet-switchable permanent magnet device

Also Published As

Publication number Publication date
EP0929904B1 (en) 2000-12-20
KR20000065224A (en) 2000-11-06
ES2154467T3 (en) 2001-04-01
US6104270A (en) 2000-08-15
JP2001502852A (en) 2001-02-27
KR100471505B1 (en) 2005-07-21
ATE198243T1 (en) 2001-01-15
DE69703746T2 (en) 2001-05-10
DE69703746D1 (en) 2001-01-25
EP0929904A1 (en) 1999-07-21
CA2261272A1 (en) 1999-02-18
DK0929904T3 (en) 2001-04-02
RU98121314A (en) 2000-09-20
AU3555497A (en) 1999-03-01

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