MXPA98010019A - Lifter with electropermanent magnets provided with a safety device - Google Patents

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

MONTACARGAS WITH ELECTROPEEMANENT MAGNETS PROVIDED WITH OT SECURITY DEVICE DESCRIPTIVE MEMORY The present invention relates to magnet hoists, and particularly to a forklift with electro-permanent magnets provided with a safety device to control its point of application. As it is known, forklifts are divided into three classes depending on the type of magnets used, that is, permanent magnets, electro-permanent magnets and electromagnets. Each type of forklift has its own advantages and disadvantages. Forklifts with permanent magnets have the advantage of an almost negligible energy consumption and a magnetic force produced that is reliably constant and independent of external sources of supply. On the other hand, it is not possible to increase the magnetic force if necessary, and the magnets are extremely bulky - for lifting heavy loads. In addition, the charge separation requires the application of a considerable amount of mechanical energy to reduce the magnetic force to a value less than the weight of the load. Alternatively, the magnets will be made movable to be removed from the load, thus decreasing the magnetic attraction. On the contrary, in the 'forklifts with , electromagnets, it is possible to freely vary the magnetic force by simply adjusting the sorne flowing in the windings that generate the magnetic field. However, any interruption of the power supply, even if it is very short, immediately cancels the magnetic force and thus causes the separation of the load. Therefore, it is evident that security systems are essential to ensure the ! continuity of supply. Forklifts with electro-permanent magnets | They substantially combine the advantages of the two types of hoists mentioned above. This is due to the use of a permanent magnet of the reversible type, that is, a magnet in which the polarity is easily reversible by the application of an electrical impulse. The reversible magnet thus generates an adjustable flow which can also direct the flow of a conventional permanent magnet combined therewith. Thus, it is possible to shorten the two magnets when the forklift is to be deactivated-, or arrange them in parallel to activate the forklift. Since only an electrical impulse is needed but not a continuous supply to reverse the reversible magnet, the safety problems affecting the electromagnets are overcome. At the same time, even when using permanent magnets, it is possible to vary the magnetic force within certain limits, and the load separation is easy to carry out with minimal energy consumption and without complex structures to move the magnets.

However, the electro-permanent magnets, with respect to the other two types of magnets, have the drawback of functional instability due to the particular magnetization curve of the reversible magnet. In fact, the reversible magnets are usually made of an aluminum-nickel alloy -cobalt (alnico) that has a hysteresis characterized because a high induction corresponds to a reduced coercive force. This feature makes it possible to direct the magnetic flux in the permanent magnet that forms the electro-permanent magnet. However, the magnetization curve has an "elbow" beyond which the behavior of the reversible magnet is still linear, but much more inclined than in the first region. This implies large induction variations that correspond to small variations of the coercive force. Practically, this means that forklifts with electro-permanent magnets are affected to a large extent by the dynamics of the lifted material. It is known in fact that the oscillations of the plates raised by said unit imply a variation of the air space and, consequently, a variation of the total magnetic resistance of the magnetic circuit, which can change the point of application of the magnetic masses of the magnetic circuit. forklift below said "elbow". This dynamic is affected even by small changes of the lifted material and, thus, light bends or hardly detectable curves are sufficient to cause a considerable variation of the force magnetomotive, thus making the lifting system very unstable. In known forklifts, there is a system to measure the magnetic force that is the same for all types of magnets. -This measurement system is only used to calculate the operational safety factor by comparing the magnetic force generated with the weight of the load to be lifted. This is carried out by arranging a measuring coil near the pole pieces that come in contact with the load, in order to measure the total flow linked to the load. ^ load. Obviously, said measure does not give an indication about the point of application, so that it is not capable of indicating the risk that "results from the instability, if any, of the reversible magnet." One object of the present invention is to provide a forklifts with electro-permanent magnets provided with a safety device that allows to control the ^^ instability, if any - of the lifting unit, depending on the actual working conditions. Said objective is achieved by means of a forklift equipped with a sensor capable of measuring the unique contribution of the reversible magnet and, consequently, its point of application. The main advantage of the present forklift is thus to ensure the highest operational safety, indicating not only the total safety factor, but also the focus of the condition of instability. Another advantage of the forklift in accordance with the present invention is that, by properly combining the data ^^ supplied by the sensor that measures the magnet flow reversible with the data supplied by the sensor that measures 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 size of space 0 of air. Other advantages and characteristics of the forklift in accordance with the present invention will be apparent to those skilled in the art from the following detailed description of one embodiment thereof in relation to the accompanying drawings, in which: Figure 1 is a schematic front view, with the left half in section, of a forklift according to the invention in the inactive phase; Figure 2 is a partial view in horizontal section 0 of a symmetrical half of the montasargas of Figure 1; Figure 3 is a diagram comprising the magnetization curves of the reversible magnet and the permanent magnet; and Figure 4 is a view of the hoist of Figure 1, 5 in the cargo transportation phase. In relation to figure 1, the forklift with magnets Electropermanents according to the present invention in a conesida embodiment, comprise an external support shell, a plurality of magnets and a control unit and ^^ adjustment. The supporting structure consists of an upper block 1, provided with hinges 2 for securing to lifting means, for example, a crane, four sides 3 and a closing base plate 4. Obviously, said structure is made of materials Highly magnetically conductive to minimize the magnetic resistance of the magnetic circuit. Each permanent magnet is formed by a reversible magnet 5 and a permanent magnet 6 disposed one above the other, respec- tively. The polarities of the reversible magnet 5 are arranged on the horizontal sides of a nickel 5a, made of alnico, around which a switching coil 5b is arranged to control the reversal of the pole. While the forklift is not running, as shown in Figure 1, the north pole (N) is on the top side, and the south pole (S) is on the bottom side. The permanent magnet 6 comprises a plurality of ferrite blocks Sa disposed along the lateral sides of an iron core 6b- This core 6b is fastened to the block 1 through a plurality of bars 7 which pass through the core of the core. alnico 5a, and is constrained by nuts 8 in suitable seats 3. Thus, also the permanent magnet 5 is fastened under the block 1. The core 6b extends downwards in a piece of pole 6c, projecting from the plate 4 and ^^ ready to come in contact with the load that is going to be lifted. The arrangement of the polarities of the ferrite blocks 6a is clearly shown in Figure 2, where on all sides the north pole is facing the core 6b, and the south pole is facing outwards. refers to the magnets 5, 6, 0 arranged on the left side of the hoist shown in ^ figure 1, is to say, refers to those magnets visible in the middle session. To close the magnetic circuits indicated by the arrows, another electro-permanent magnet is conveniently arranged with the polarities inverted in the right half of the hoist. In other words, there is a second reversible magnet 6 'having its south pole on the upper side, and ^^ its north pole on the bottom side. Similarly, the second permanent magnet 6 'comprises a plurality of ferrite blocks 6a' arranged its south poles facing the core 6b1 and its poles north facing outwards (see Figure 2). This magnet arrangement induces a magnetic field comprising three bundles of flow lines oriented substantially in the direction indicated by the arrows of Figure 1. The intermediate beam of these flow lines passes through the two reversible magnets 5, 5. ', the two cores 6b, 6b ', and the ferrite blocks 6a, 6a' disposed therebetween, in addition to some portions of the external support structure. The two lateral beams of flow lines pass more ^^ well through only one of the reversible magnets 5, 5 ', one of the cores 6b, 6b1 and the ferrite blocks 6a, 6a', arranged between one of these cores and the sides 3. Said flow lines, being joined together, flow within the hoist, so that a ferromagnetic charge, disposed close to the pole pieces 6c, 6c ', would not be attracted by the hoist. "The adjustment and control circuits comprise at least one switching coil control circuit 5b, a first magnetic sensor 11 and a second magnetic sensor 12 arranged, respectively, up and down the ferrite blocks 6a, as well as at least one security device 13 to prosecute the signals that come from dishos ^^ sensors 11 and 12. The lower magnetic sensor 11 was, for example, a coil having its turns around the base of the core 6b to measure the vinsulated flow to the twill. The upper magnetic sensor 12, consisting, for example, of an additional coil having its turns around the upper portion of the core 6b, is the innovative aspect of the present forklift, since it allows to measure the unique contribution of the reversible magnet 5, as shown in FIG. will explain later. Although a single pair of sensors 11 and 12 is sufficient to control the operation of a pair of poles of an electro-permanent magnet, each electro-permanent magnet is preferably provided with its own pair of sensors to achieve greater measurement accuracy. Thus, a lower coil ^^ and an upper coil (not shown in the figure) 5 are also arranged around the core 6b 'of the magnet, both connected to a safety device 13, to reduce the measurement error by averaging the readings of the sensors. two pairs of coils. Referring to Figure 3, the magnetization curve 0 showing the relationship between the residual induction Br and the ^ Coercive field strength He has two different characteristics that depend on the type of forklift magnet.

In particular, the magnetization curve 14 of the reversible magnets 5, 5 ', unlike the curve 15 of the permanent magnets 6, 6', has a fairly long linear segment 16 between the "sode" 17 and the axis of indussidn -residual Br that ^^ sorresponde to a sero level of coercive field intensity He. Beyond the "elbow" 17, the magnetization curve 14 is highly inclined and shows hysteresis phenomena, depending on which, if the point of application of the forklift enters this region, its lifting force is unstable, given that the residual induction Br varies rapidly on slight variations of intensity Hs and, furthermore, there is no bieyection between these two quantities due to the magnetic 5 hysteresis. In relation now also to figure 4, a load ferromagnetic 18 can be attracted by the hoist in accordance with the present invention, collating them near ^^ the pole pieces 6c, 6c ', and reversing the polarities of the reversible magnets 5, 5' through the coils of respectable commutations. Thus, the magnetic flux lines stop being vinsted to those of the permanent magnets 6a, 6a1, as shown in Figure 1. Rather, all the flow lines pass through the load 18 since, thanks to the particular magnet arrangement, the magnetic circuit is forced to leave the pole piece. 6c and enter back into the ^^ piece of polo £ s'. In the same way, in this case, there is a sampo magnetism comprising three hases of flow lines, which nevertheless are oriented substantially in the direction indicated by the arrows in figure 4, thus being concentric. In particular, it should be noted that the flow lines passing through the reversible magnets 5, 5 ', do not pass through the ferrite blocks 6a, 6a1, thus not being affected by the magnetic field generated from them. same. Therefore, sensors 12 detect the intensity of the magnetic flux generated only by the reversible magnets, while sensors 11 also detect the contribution made by the ferrite blocks 6a, 6a '. The security device 13 in the present embodiment comprises an electronic service controlled by a processor that receives the signals as input transmitted by sensors 11 and 12 and amplified _ and subsequently converted into digital form. The device 13 processes the signals of the sensors 11 and 12 to respectively obtain the total magnetic force of the electro-permanent magnets 5 and the point of application of the reversible magnets 5, 5 'on the curve 14. Comparing said values with each other, the device 13 compensates for the difference between the magnetic flux measured by the sensors 11 and the magnetic flux actually passing through the twill 18. This difference 0 results from the dispersions of the magnetic flux due to the delta air gap, ie to the variations of the distance between the load 18 and the pole pieces 6c, 6C. On the left of figure 4 flow lines are shown through the delta air space (increased) under real conditions, 5 is desir, are the dispersion effects, and on the right the same flow lines under ideal conditions, ie , without ^^ the effects of dispersion. Thanks to sensors 12 arranged on the permanent magnets, the device 13 determines the working point of 0 the reversible magnets 5, 5 'on the curve 14 of figure 3 and, consequently, calculates in sequence the size of the delta air space , the induction value Br, the magnetic bond with the load 18 and, finally, the magnetic force acting on the latter. The security device programs 13 thus comprise a specific algorithm capable of automatically correcting the readings of the sensors 11 for eliminate errors due to scattered magnetic fluxes due to the delta air gap. If the effective magnetic force that operates on the ^^ load 18 is insufficient for your lift, or if the point of the reversible magnets 5, 5 'is not on the linear segment 16, the device 13 would immediately indicate the risk situation to the operators by means of acoustic or optical alarm signals, or the like. Obviously, the hoistway modality described above illustrated in accordance with the invention is ^ L? only one example susceptible to undergo several modifications. In particular, the material from which the magnets are made may vary, depending on the requirements of the forklift. For example, permanent magnets can be made of neodymium 5 or other rare earths. Obviously, in the same way in another embodiment of the ^^ elevator of conformity are the present invention, the magnetic sensors 11 and 12 may not comprise coils, but another type of sensors, for example, Hall sensors or Hall.

Claims (1)

1. NOVELTY PE I ?. INVENTION CLAIMS 5. A lift truck comprising at least one reversible magnet (5, 5 ') arranged with its polarities oriented along a vertical axis on at least one magnet (6, 6') provided with at least one pair of permanent magnets (6a, 6a ') arranged with their polarities oriented along a horizontal axis on the sides of at least one core ^ ferromagnetic (6b, 6b ') suitable for coming into contact with the charge (18) to be lifted, and at least one magnetic sensor (11) disposed near the base (6c, 6c') of said ferromagnetic core , characterized in that at least one additional magnetic sensor (12) arranged on said permanent magnets (6a, 6a ') is provided to measure substantially the ^ _ Unique 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 or Cll, 12) and obtaining the working point of the hoist on the magnetization curve (14) of the reversible magnet (5, 5'). 2. - A forklift according to the preceding claim, further comprising a pair of reversible magnets (5, 5 '), each being arranged with their polarities oriented mutually inverted along a vertical axis on a magnet (6, 6 ') provided with a plurality of permanent magnets (6a, 6a') arranged with their polarities oriented along a horizontal axis on the sides of a ferromagnetic core (6b, 6 '), where 5 the magnetic fluxes induced by the reversible magnets (5, 5 ') are linked together. 3. - A forklift according to the preceding claim, further characterized in that it comprises a magnetic sensor (11) arranged on the base of each of two ferromagnetic cores (6b, 6b '), and an additional magnetic sensor ^^ (12) ) arranged between each of the two reversible magnets (5, 5 ') and the permanent magnets (6a, 6a') associated thereto. 4. - A forklift according to its alley-of the preceding claims, further characterized in that at least one of the reversible magnets (5, 5 ') is made ^ f. of a metallised aleasión that produces aluminum, nickel and cobalt. 5. - A forklift according to any of the preceding claims, further characterized in that at least one of the magnetic sensors (11, 12) comprises a coil having its turns around a portion of said ferromagnetic cores (6b, 6b) '). 6. - A forklift according to any of claims 1 to 4, further characterized in that at least one of the magnetic sensors (11, 12) comprises üh Hall effect sensor. 7. - A forklift according to any of the preceding claims, further characterized by the reversible magnets. { 5, 5 ') and the permanent magnets (6a, 5 6a') are housed within a highly magnetically conductive structure (1, 3, 4) having the ferromagnetic cores (6b, 6b ') projecting partially from their base. 8. - A montasargas according to any of the preceding claims, further characterized in that the ^^ security device (13) comprises an electronic circuit controlled by a microprocessor that receives as input the signals transmitted by the magnetic sensors (11, 12) and converted into digital form. 9. - A forklift in accordance with the preceding claim, characterized in that the ^^ safety device (13) calculates the magnetic flux that passes through the lifted load (18), depending on the difference of the values detected through the magnetic sensors (11, 12). 10. A forklift in accordance with the preceding claim, further characterized in that the safety device (13) comprises alarm means that are activated automatically if the work point of the forklift on the magnetization surva (14J of the reversible magnets (5). , 5 ') is not in the linear segment- (16) between the elbow (17) and the axis of the residual induction (Br) that corresponds to a zero level of the coercive sampo intensity (He).