Method for unloading at least one clamped part, associated clamping system and loading method

Abstract

This unloading method is carried out with a magnetic clamping system that comprises a detecting device with a transmitter of an electromagnetic signal (SI), controlled depending on a force (F), and a receiver of the electromagnetic signal configured to deliver an output signal (S104) including a first value (V1) when the receiver receives the electromagnetic signal and a second value in the contrary case. The method comprises steps consisting in determining (2078) the force (F) between a carriage and a hook and in comparing (2080) the force (F) with a threshold value (F0). If the force is higher than the threshold value, the transmitter is made to operate (2084). During this time, the output signal (S104) of the receiver is collected (2062) and the value included in this signal is determined (2086). If it is the first value (V1), input of an order to demagnetize magnetic pads is permitted (1012). Otherwise, input of the order to demagnetize the pads is prevented (2088).

Description

[0001] Method for unloading at least one clamped part, associated clamping system and loading method

[0002] The present invention relates to a method for unloading, using a hoist, at least one part clamped onto a magnetic clamping system of an industrial installation. The invention also relates to a magnetic clamping system configured to implement such a method. The invention finally relates to a method for loading, using a hoist, at least one part to be clamped onto such a magnetic clamping system.

[0003] The present invention relates to magnetic clamping systems and their operating methods, dedicated for example to plastics processing operations. It aims in particular to improve rapid mold change procedures on injection molding machines and, in particular, to limit the risk of mold falling when unloading a mold with a hoist-type lifting device.

[0004] In the field of rapid mold change on injection molding press installations, it is known to use mechanical clamping systems to secure each mold part to a fixed part and a moving part of the press. Since the securing can be tedious, it was desired to make these operations less restrictive for operators, in the presence of heavy and dangerous loads, and in an industrial environment of difficult space, heat and chemical vapors. The design of magnetic clamping systems has led the profession to evolve towards the automation of procedures in order to reduce operating times and secure maneuvers with the two parts of the mold between the plastic injection phases.

[0005] The operator uses a lifting device, generally of the hoist type, installed above the presses to convey the molds, according to the cycles necessary for the production of various plastic parts.

[0006] In the handling phase, it is necessary to consider the states of two different environments, namely, on the one hand, the press installation and, on the other hand, the lifting device, which do not usually communicate with each other. In particular, during mold unloading maneuvers in the injection press, there is a risk of initiating the demagnetization of the mold from the clamping plate, while the lifting device is not capable, or not yet capable, of retaining the mold and its fall from the installation.

[0007] The activation and deactivation of the electromagnets of a magnetic clamping system have so far been conditioned by the state of the injection molding machine but not by the state of the lifting device, the hoist not being designed to transmit information on its state to the magnetic clamping system or to communicate any loading data. In addition, the lifting device has a movement reference, and the press has its own movement reference, the distance between the lifting means and the press can be significant, of the order of 5, 10 or 20 meters. However, the mold unloading operation between the press and the lifting means requires relatively precise positioning of the hoist above the mold to be unloaded, to avoid swinging of the mold in the installation.

[0008] It should be noted that hoist-type lifting devices have their own computer language and comply with specific communication standards, so that plastics processing installations are difficult to communicate with them via a network, nor are they able to control their operation. For the safety of installations and personnel, it is even preferable that the lifting device is controlled in position, speed, or other, by the operator who is qualified for this operation and familiar with the workshop environment, without the press installation sending information to the hoist that contradicts the desired operation, which could be a source of breakdown or incident.

[0009] It is known from EP1867437A to add to the magnetic pads of a magnetic clamping system additional coils connected in series to a measuring circuit linked to a control unit, to measure the magnetic fluxes in the pad installation, and to monitor the mold movements to prevent them from falling. This solution is generally satisfactory. However, it does not address the problem of safely demagnetizing a mold, when it is taken over by the lifting device.

[0010] On the other hand, WO2008 / 142716A discloses a lifting device, with a test unit. This lifting device carries a load sensor to verify that the magnetic lifting force developed corresponds to the weight of the lifted part. This technology does not address the problem of demagnetizing a mold that needs to be unclamped for its extraction from a press.

[0011] Thus, with known equipment, the following incident situations cannot be excluded: the hoist has been positioned above the installation, but the hook has not been attached to the mold due to an operating error, with a risk of the mold falling upon demagnetization. the mold can be attached to the hoist, but it is incorrectly positioned due to an operating error, with a risk of the mold tipping over or the mold being unlocked from the hoist upon demagnetization. Similar problems arise in other types of installation that include machines, some parts of which must be changed during the lifetime of these machines, such as machining centers.

[0012] It is these drawbacks that the invention more particularly intends to remedy by proposing a new method of unloading, using a hoist, at least one part clamped on a magnetic clamping system, this method being more reliable than those of the prior art and making it possible to avoid, to a large extent, dangerous situations.

[0013] To this end, the invention relates to a method for unloading, using a hoist, at least one part clamped on a magnetic clamping system of an industrial installation, the hoist comprising: a trolley movable in a horizontal plane,

[0014] - a hook suspended from the trolley and movable vertically,

[0015] - a hook load sensing device, configured to determine a force between the trolley and the hook and

[0016] - a hoist control unit.

[0017] The magnetic clamping system includes:

[0018] - a magnetic clamping control unit,

[0019] - at least one magnetic clamping plate comprising several magnetic pads that are selectively magnetizable and controlled by the magnetic clamping control unit, a human-machine interface connected to the magnetic clamping control unit and making it possible to enter an order to demagnetize the magnetic pads

[0020] According to the invention, the magnetic clamping system includes a device for detecting a position of the carriage relative to the clamping plate, the detection device comprising: o a transmitter of an electromagnetic signal, secured to the carriage and controlled as a function of the force determined by the load detection device on the hook, o a receiver of the electromagnetic signal emitted by the transmitter, fixed relative to the clamping plate and configured to deliver an output signal including a first value when the receiver receives the electromagnetic signal and a second value when the receiver does not receive the electromagnetic signal, and

[0021] - the unloading method comprises at least steps consisting of a) determining the force between the carriage and the hook by means of the hook load detection device, b) comparing the force determined in step a) with a threshold value, c) in the case where the comparison carried out in step b) shows that the force determined in step a) is greater than the threshold value, operating the transmitter, d) during step c), collecting the output signal of the receiver, e) determining which value is included in the output signal of the receiver, among the first value and the second value, f) in the case where the determination of step e) shows that the output signal collected in step d) includes the first value, authorizing the input of an order for demagnetizing the magnetic pads by means of the human-machine interface, g) in the case where the determination of step e) shows that the output signal collected in step d) includes the second value,prevent the entry of the order to demagnetize the magnetic pads using the human-machine interface.,

[0022] Thanks to the invention, the unloading method can only induce effective demagnetization of the magnetic pads of the clamping system when the output signal from the receiver confirms that the hoist hook is actually under load and that the hoist trolley is correctly positioned relative to the clamping plate. The risks of untimely demagnetization of the magnetic pads of the clamping plate are thus minimized.

[0023] According to advantageous but not mandatory aspects of the invention, such an unloading method may incorporate one or more of the following features taken in any technically admissible combinations:

[0024] Step g) is maintained as long as the signal collected in step d) has the second value.

[0025] The receiver outputs the output signal with the first value when the transmitter is activated and when the transmitter is in a predetermined position relative to the receiver and the receiver outputs the output signal with the second value when the transmitter is not operating and / or when the transmitter is not in the predetermined position relative to the second element.

[0026] - The predetermined position of the transmitter is opposite the receiver.

[0027] The predetermined position of the transmitter corresponds to a vertical alignment of the carriage with the part clamped on the magnetic clamping system. The electromagnetic signal emitted by the transmitter includes an identification frame intended to be collected by the receiver, while the method comprises an additional step h) of comparing the identification frame collected by the receiver with a reference identification frame and that, in the case where the result of the comparison of step h) is negative, the input of the instruction for demagnetizing the magnetic pads is prevented regardless of the value determined in step e).

[0028] The unloading method comprises additional steps consisting of i) prior to step c), determining whether the receiver is operational, j) in the case where the receiver is determined to be operational in step i), proceeding to step e) k) in the case where the receiver is determined to be non-operational in step i), proceeding to a manual mode where the operator must validate at least one step by answering a question, by means of a control terminal connected to the magnetic clamping control unit.

[0029] According to another aspect, the invention relates to a magnetic clamping system comprising a magnetic clamping control unit and at least one magnetic clamping plate comprising several magnetic pads that are selectively magnetizable and controlled by the magnetic clamping control unit, characterized in that: the magnetic clamping system includes a device for detecting a position of a carriage of a lifting device relative to the magnetic clamping plate, the detection device comprising: o a transmitter of an electromagnetic signal, secured to the carriage, o a receiver of the electromagnetic signal emitted by the transmitter, fixed relative to the clamping plate, configured to deliver an output signal including a first value when the receiver receives the electromagnetic signal and a second value when the receiver does not receive the electromagnetic signal,the clamping system is configured to implement at least steps c) to g) of a method as described previously.,

[0030] The system of the invention makes it possible to efficiently implement the method of the invention. According to advantageous but not mandatory aspects of the invention, such a system may incorporate one or more of the following features taken in any technically admissible combinations:

[0031] - The electromagnetic signal is an infrared signal and the receiver is configured to detect an infrared signal.

[0032] - The electromagnetic signal is emitted by a laser diode or a light-emitting diode and the receiver is configured to detect a laser or light-emitting signal.

[0033] - The receiver is directed along a vertical axis, while a receiving area of ​​the receiver is cone-shaped or truncated cone-shaped centered on the vertical axis.

[0034] - The receiver is directed along a horizontal axis while a reception area of ​​the receiver is in the shape of a cone or truncated cone centered on the horizontal axis.

[0035] - The receiver comprises a microcontroller capable of communicating the first value or the second value included in the output signal to the magnetic clamping control unit.

[0036] - The receiver is configured to deliver presence information to the magnetic clamping control unit.

[0037] According to a third aspect, the invention relates to a method of loading, using a hoist, at least one part to be clamped onto a magnetic clamping system of an industrial installation, the hoist comprising: a carriage movable in a horizontal plane,

[0038] - a hook suspended from the trolley and movable vertically,

[0039] - a hook load sensing device, configured to determine a force between the trolley and the hook and

[0040] - a hoist control unit.

[0041] According to the invention, the magnetic clamping system is as described above, the hook load detection device is configured to determine, on the basis of the force between the carriage and the hook, the mass of the part to be clamped, the electromagnetic signal emitted by the transmitter includes information relating to the mass of the part to be clamped, determined by the hook load detection device, the receiver is configured to extract the information relating to the mass of the part to be clamped from the electromagnetic signal received from the transmitter and to communicate it to the magnetic clamping control unit of the magnetic clamping system, - the loading method comprises at least steps carried out by the magnetic clamping system and consisting of l) comparing the information relating to the mass of the part to be clamped, extracted from the electromagnetic signal, with a predetermined threshold value,m) in the event that the comparison carried out in step I) shows that the mass of the part to be clamped is greater than the threshold value, prevent loading or issue an alarm, and n) in the event that the comparison carried out in step I) shows that the mass of the part to be clamped is less than the threshold value, authorize loading.,

[0042] The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of three embodiments of an unloading method, a clamping system and a loading method in accordance with its principle, given solely by way of example and with reference to the appended drawings in which:

[0043] [Fig.1] Figure 1 is a schematic representation of the principle of an injection press installation incorporating a clamping system according to the invention and configured to implement a method according to the invention;

[0044] - [Fig.2] Figure 2 shows, on two inserts A) and B), certain parts of the installation of figure 1 during two stages of an unloading process according to the invention;

[0045] - [Fig.3] Figure 3 shows, on two inserts C) and D), the same parts of the installation as figure 2, during two other possible stages of the unloading process;

[0046] - [Fig.4] Figure 4 shows, on two inserts E) and F), the same parts of the installation as figures 2 and 3, during two other stages of the unloading process;

[0047] - [Fig.5] Figure 5 is a block diagram of the unloading method according to the invention and implemented with the installation of Figures 1 to 4;

[0048] - [Fig.6] Figure 6 is a view similar to Figure 1, for an installation incorporating a clamping system according to a second embodiment and configured to implement a method according to the invention; and

[0049] - [Fig.7] Figure 7 is a view similar to Figure 1, for an installation comprising a clamping system according to a third embodiment of the invention and configured to implement a method according to the invention. The plastics processing installation 2 shown in Figure 1 is part of a factory for transforming synthetic material into molded parts. This installation comprises one or more manufacturing lines each formed of one or more injection presses, only one of which is shown in the figures with the reference 4. The injection press 4 comprises a fixed frame 6 and a movable platen 8 which can move parallel to an axis X of a fixed orthogonal reference XYZ, being guided by rails 10 parallel to this axis. The X axis is horizontal, the Y axis is also horizontal and perpendicular to the X axis and the Z axis is vertical, therefore perpendicular to the X and Y axes.

[0050] A mold 12, mounted on the injection press 4, comprises two parts 12A and 12B which are made of a ferromagnetic material and which are respectively secured to the fixed frame 6 and to the movable plate 8.

[0051] Thus, the movements of the movable plate 8 parallel to the X axis make it possible to ensure the function of opening and closing the mold 12, during the manufacture of molded parts.

[0052] The injection press 4 also comprises a control unit 14 which notably includes a computer 16 making it possible to control the injection press 4 according to a predetermined sequence stored in a memory 18.

[0053] The two parts 12A and 12B of the mold 12 are immobilized, respectively on the fixed frame 6 and on the movable platen 8, by means of a magnetic clamping system 20 which comprises several magnetic pads 24, which are selectively magnetizable in the sense that they can be magnetized or not selectively, that is to say that they can be controlled to switch between a configuration where they are magnetized and a configuration where they are not magnetized, and vice versa. These magnetic pads 24 are distributed on a first clamping plate 26 immobilized by mechanical means on the fixed frame 6 and a second clamping plate 28 immobilized by other mechanical means on the movable platen 8.

[0054] The mechanical means for immobilizing the clamping plates 26 and 28 on the fixed frame 6 and on the movable plate 8 are advantageously screws.

[0055] In Figure 1, only the magnetic pads 24 of the clamping plate 26 which are not covered by the part 12B of the mold are visible.

[0056] Advantageously, the magnetic pads are of the type described in EP1867437A. The invention is also suitable for a technology clamping plate where the magnetic pads are each identified by a North or South polarity, and associated on a magnetic plate for clamping the mold. The invention is also suitable for a magnetic clamping plate of monolithic technology as described in EP2280803A. The magnetic pads 24 are controlled by a magnetic clamping control unit 34 which also belongs to the magnetic clamping system 20 and which comprises a computer 36 and a memory 38 associated with the computer 36. The computer 36 controls each of the magnetic pads 24 through control and power cables, which connect the magnetic clamping control unit 34 to the clamping plates 26 and 28 and only one of which is visible in FIG. 1, with the reference C20.

[0057] By convention, it is considered that a part 12A or 12B of the mold 12 is mounted against the front face of a clamping plate 26 or 28. The front face of a clamping plate therefore constitutes a clamping face of this plate onto which the magnetic pads 24 carried by this plate open. Each clamping plate 26 or 28 comprises, at its rear face opposite its front clamping face, housings (not shown) for receiving connection means 262 and 282 intended to electrically connect the different magnetic pads 24 to each other and to a terminal block, not shown, for connection to the magnetic clamping control unit 34 via the control cables C20 and equivalent. Grooves provided on the rear faces of each clamping plate 26 or 28 allow the routing of electrical wires and the installation of certain connection means 262 and 282.

[0058] The magnetic clamping system 20 also comprises a control terminal 40 intended to be handled by an operator and which interacts with the magnetic clamping control unit 34 through a wired connection represented by the cable C40 in FIG. 1 or, alternatively, through a wireless connection.

[0059] The magnetic clamping control unit 34 has the particular function of switching the poles of the magnetic pads 24 fixed on the clamping plates 26 and 28 according to the instructions of a program stored in the memory 38 and executed by the computer 36 or instructions received from the control terminal 40 which allows the operator to intervene to initiate, cancel or validate commands of the magnetic pads 24.

[0060] The control terminal 40 makes it possible in particular to keep the parts 12A and 12B fixed on the clamping plates 26 and 28, or to release the parts 12A and 12B relative to the clamping plates 26 and 28, by giving an operator the possibility of remotely magnetizing or demagnetizing the magnetic pads 24 of the clamping plates 26 and 28 by means of the control terminal. The control terminal 40 forms a human-machine interface. Alternatively, the entry of the demagnetization instruction can be carried out by means of a physical button connected to the control unit, which in this case forms a human-machine interface, or another form of human-machine interface. When the magnetic pads 24 are magnetized, due to an order received from the computer 36 or the terminal 40, the clamping control unit 34 controls a magnetic clamping force exerted by each clamping plate 26 or 28 on the corresponding mold part 12A or 12B.

[0061] Furthermore, the magnetic clamping control unit 34 is connected to various sensors, not shown, which are integrated with the magnetic clamping system 20 and which may include temperature sensors, mold presence sensors, etc.

[0062] The magnetic clamping system 20 is supplied with current through the injection molding machine 4.

[0063] Furthermore, the mold 12 comprises a locking mechanism 42 which is formed of a first part 42A mounted on the part 12A of the mold 12 and a second part 42B mounted on the part 12B of this same mold. The parts 42A and 42B are provided to cooperate, when the locking mechanism 42 is activated, in order to secure the two parts 12A and 12B of the mold together.

[0064] As can be seen in Figure 1 with the two parts 42B arranged on either side of the part 12B of the mold 12, a locking mechanism 42 is advantageously provided on each of the two vertical sides of the two parts of the mold.

[0065] When it is not placed in the injection press 4, the mold 12 is in a configuration where its locking mechanisms 42 are activated, that is to say in a position where the two parts 12A and 12B of the mold are pressed and immobilized against each other by this or these mechanisms.

[0066] The mold 12 is also equipped with a lifting ring 44 which, in the example, is mounted on an upper face of the part 12B of the mold. Thus, when the locking mechanism(s) 42 are activated, the lifting ring 44 makes it possible to lift the entire mold 12.

[0067] The installation 2 also includes a lifting device 50 which makes it possible to move the mold 12 in space, according to the three directions of the orthogonal reference XYZ.

[0068] The lifting device 50 comprises a carriage 52 mounted to slide on two rails 54 parallel to the X axis. Thus the carriage 52 is movable in a horizontal plane parallel to the X and Y axes.

[0069] Preferably, when several injection presses 4 are part of the plastics processing installation 2, they are aligned parallel to the X axis, with their injection planes parallel or perpendicular to this axis, so that these different injection presses are accessible to the same lifting device 50. According to a variant of the invention, the rails 54 can be slidably mounted on beams (not shown) which extend parallel to the Y axis and which are fixed to the structure of a building which contains the plastics processing installation 2, as shown for the third embodiment only.

[0070] The lifting device 50 also comprises a hoist 56, mounted on the carriage 52 and which includes a cable 58, which supports a pulley block 60 and the winding of which onto a drum 62 is controlled by an electric motor 64. A hook 66 is suspended from the pulley block 60 and is also part of the hoist 56. This hook is movable vertically under the carriage 52, due to the winding of the cable 58 onto the drum 62. The hook 66 is provided to interact with the lifting ring 44, when it is necessary to lift the mold 12 relative to the parts 6 and 8 of the injection press 4.

[0071] The lifting device 50 also comprises a hook load detection device which comprises a hoist load sensor 68. Advantageously, the hook load detection device also comprises the means (not shown) for processing the output signal from the hoist load sensor 68. This hoist load corresponds to the tension of the cable 58. The sensor 68 is capable of detecting this tension and of sending via a wired connection 72 a corresponding signal to a control unit 74 which includes in particular a computer 76 for controlling the lifting device 50, as well as a memory 78. The wired connection 72 also makes it possible to supply electrical power to the motor 64.

[0072] Alternatively, the output signal from the sensor 68 is provided to the control unit 74 via a wireless link.

[0073] The control unit 74 is provided to control the movement of the carriage 52 along the rails 54 and the rotational drive of the cable 58 on the drum 62 and to monitor a force F which is exerted between the carriage 52 and the hook 66 and which depends on the weight of the elements suspended from the carriage 52, in particular the weight of the block 60, the hook 66 and the weight of the mold 12 when the mold 12 is suspended from the hoist 56 by the lifting ring 44.

[0074] In practice, the force F monitored by the control unit 74 is the force detected by the sensor 68, which corresponds to a tension force on the strands of the cable 68 which extend between the pulley block 60 and the drum 62. This tension force opposes the magnetic force retaining the mold 12 on the clamping plate 26.

[0075] The control unit 74 may also comprise one or more power circuits, not shown, which make it possible to power the electric motor 64 via the wired connection 72. The lifting device 50 also comprises a control terminal 80 intended to be handled by an operator and which interacts with the control unit 74 via a wired connection represented by the cable C80 in FIG. 1 or, alternatively, via a wireless connection.

[0076] The magnetic clamping system 20 also comprises a device 100 for detecting a position of the carriage relative to the clamping plate 26. This position detection device 100 comprises, on the one hand, an infrared transmitter 102 secured to the carriage 52 and, on the other hand, an infrared receiver 104 secured to the frame 6, therefore fixed relative to the clamping plate 26 which is immobilized on this frame.

[0077] In the example of the figures, the transmitter 102 is suspended from the carriage 52 by means of a rod 106. On the other hand, the receiver 104 is mounted on a mast 108 immobilized on the fixed frame 6.

[0078] Alternatively, and as shown in Figures 2 to 4, the transmitter 102 can be integrated into the carriage 52, while the receiver 104 is integrated into the fixed frame 6.

[0079] Here, the transmitter 102 is fixed in the reference frame of the carriage 52, while the receiver 104 is fixed in the reference frame of the clamping plate 26, that is to say in the fixed orthogonal reference frame XYZ.

[0080] The receiver 104 is directed along a vertical axis, parallel to the Z axis, and configured to detect an infrared signal SI emitted by the transmitter 102 when the transmitter 102 is actuated and arranged above the receiver 104, inside a reception cone truncated K104 defined by the receiver 104 and centered on the vertical axis. The receiver 104 has a detection zone configured to detect the infrared signal SL

[0081] The receiving truncated cone K104 provides a certain tolerance to the position detection device 100 because the receiver 104 can detect the infrared signal SI emitted by the transmitter 102 over an admissible disc-shaped range, which extends in the XY plane of the XYZ reference frame, in the upper part of the truncated cone K104.

[0082] To allow efficient and smooth lifting of the mold 12 relative to the injection press 4, the hook 66 should be correctly positioned relative to the lifting ring 44 before unclamping the mold 12 and lifting it by an upwardly directed tensile force, using the hoist 56. However, the position of the lifting ring 44 in the orthogonal reference frame XYZ varies according to the thickness E of the mold 12 which corresponds to the distance between the front faces of the clamping plates 26 and 28 measured parallel to the axis X. The transmitter 102 is secured to the carriage 52 and the receiver 104 is secured to the fixed frame 6 in positions such that the vertical alignment of the hook 66 on the lifting ring 44 corresponds to a predetermined position of the transmitter 102 relative to the receiver 104.Advantageously, in this embodiment, this predetermined position is a position where the transmitter 102 is opposite the receiver, in this example aligned vertically with the receiver 104.

[0083] When the transmitter 102 is in the predetermined position, the carriage 52 is vertically aligned with the mold 12 clamped in the injection press 4.

[0084] In the first embodiment shown in Figures 2 to 4, the direction of the infrared signal SI emitted by the transmitter 102 is parallel to the Z axis and directed downwards.

[0085] Advantageously, the direction of emission of the infrared signal SI is chosen such that this signal is concurrent with the receiver 104 only in a position of the carriage 52 which corresponds to the predetermined position of the transmitter relative to the receiver 104.

[0086] We note d102 a distance, measured parallel to the X axis, between the geometric center of the pulley 60 and the emission point of the infrared signal SI by the transmitter 102. We note d104 a distance measured parallel to the X axis between the geometric center of the reception zone of the receiver 104 and the geometric center of the lifting ring 44. These distances d102 and d104 are chosen as a function of the geometry of the injection press 4 and the carriage 52. These distances d102 and d104 correspond to each other so that the hook 66 is aligned vertically on the lifting ring 44, in the predetermined position of the transmitter 102 relative to the receiver 104.

[0087] The receiver 104 comprises a microcontroller, not shown, configured to communicate its state to the magnetic clamping control unit 34 in the form of an electronic signal S104 transmitted via an electrical cable C104 or, alternatively, via a wireless link. The signal S104 comprises state information of the receiver 104 which takes a first value V1 when the receiver 104 receives the infrared signal SI emitted by the transmitter 102 and a second value V2 when the receiver 104 does not receive this infrared signal.

[0088] For example, the first value V1 can be positive and the second value V2 can be negative.

[0089] If the transmitter 102 is in the predetermined position relative to the receiver 104 without operating, i.e. without emitting the infrared signal SI, the receiver does not detect this signal and its output signal includes the second value V2.

[0090] Advantageously, the receiver 104 is configured to send presence information to the magnetic clamping control unit 34, which allows it to be tested by this control unit, regularly or on demand. For example, it may be provided that the receiver 104 periodically sends to the clamping control unit 34 the output signal S104 with the second value V2, which makes it possible to ensure that the receiver is in place, connected and operational, independently of the position and activation of the transmitter 102. The reception of a first value V1 or a second value V2 of the signal S104 by the receiver 104 is assimilated to the reception of presence information from the receiver 104.Furthermore, if the receiver 104 is detected as being in place, connected and operational, the analysis of the state of the receiver, based on the two possible values ​​of the output signal 104 can be used to authorize or prohibit the demagnetization of the magnetic pads 24, in a secure manner, as explained below.

[0091] A method of unloading the mold 12 using the hoist 56 will now be described with reference to FIGS. 2 to 5.

[0092] At the end of an injection cycle, it may be necessary to change the mold 12 to produce a new type of part or for maintenance reasons of the mold 12 or the injection press 4. The challenge is to unload the mold 12, which is a steel assembly of significant mass, compared to the injection press 4, in a safe manner.

[0093] Securing the unloading is based in particular on synchronizing the operation of lifting the mold 12 by means of the hoist 56 with the demagnetization of the magnetic pads 24, and in particular the tensioning of the cable 58 vertically above the mold 12 before the demagnetization of the magnetic pads 24.

[0094] The unloading process begins with a step 1000 when the mold 12 is held in place in the injection molding machine 4 by the magnetic pads 24 which are in a magnetized state. During this step 1000, the hoist 56 is not loaded, that is to say available, and the cable 58 is, for the most part, wound around the drum 62, so that the hook 66 is in the high position. This step is shown in insert A) of Figure 2.

[0095] In a step 1002, the magnetic clamping control unit 34 checks whether the receiver 104 is operational.

[0096] If this is not the case, the method switches to a manual mode and implements a step 1004 during which the operator is questioned, by means of a human-machine interface which may be that formed by the control terminal 40, to find out whether the locking mechanism 42 is indeed in the locked configuration in which the parts 12A and 12B of the mold are secured to each other. The operator can respond to this question on this interface after having visually checked the locking mechanism(s) 42. If the operator responds in the negative or does not respond for a predetermined period of time At, for example equal to 5 seconds, the method returns to step 1000.If the operator confirms in step 1004 that the locking mechanism 42 is operational, the method proceeds to a step 1006 in which the operator is asked to manually confirm that the hoist 56 has been positioned correctly and that the hook 66 is engaged in the lifting ring 44. The operator can respond to this query, via the human-machine interface potentially formed by the control terminal 40, after having visually checked the lifting device 50. If the operator responds in the negative or after the expiration of a predetermined period of time At, for example equal to 5 seconds, the method returns to step 1000. If the operator confirms that the hoist is correctly attached, then the method proceeds to a step 1008 through a logic gate 1010 of the “OR” type.

[0097] During step 1008, the operator is questioned, via an input interface of the magnetic clamping control unit 34, which can be integrated into the terminal 40, to find out whether he confirms the demagnetization of the magnetic pads 24 in order to release the mold 12. If the operator does not respond within a time period corresponding to a time period At, for example equal to 5 seconds, the method automatically returns to step 1000.

[0098] If the operator confirms the demagnetization order via the input interface, this demagnetization of the magnetic pads 24 takes place during a step 1012. This is signaled to the operator by a corresponding message displayed on the human-machine interface of the control terminal 40 during a step 1014. The magnetic pads of the two clamping plates of the clamping system are demagnetized simultaneously during step 1012.

[0099] After this demagnetization, the injection press is opened during a step 1016, by moving the movable plate 8 away from the fixed frame 6, according to a translation movement parallel to the X axis.

[0100] The mold is then released during a step 1018 and the operator proceeds to lift and convey the mold 12 by means of the hoist 56, by controlling the lifting device 50 by means of the terminal 80, this during a step 1020 which constitutes the end of the unloading method of the invention.

[0101] After the implementation of step 1020, the operations for changing the mold 12 continue according to known conveying procedures.

[0102] Steps 1004 and 1006 correspond to a manual implementation of the unloading method, during which the operator commands the demagnetization of the magnetic pads 24 after having himself checked the state of the installation 2 and confirmed, by means of the terminal 40 and within a given time, that certain conditions are fulfilled by the locking mechanism(s) 42 and by the hoist 56.

[0103] Except when operator action is required, as explained with reference to steps 1004, 1006 and 1008, the above-mentioned steps 1000, 1002 and 1012 to 1018 are performed automatically by the clamping control unit 34 and by the control units 14 and 74 and the terminal 80. On the other hand, the unloading process takes place after a prior conveying operation has been performed in a step 2000 and the end of the previous conveying operation has taken place in a step 2010, which makes it possible to bring the hoist 56 into a configuration where it is available, i.e. unloaded, which occurs in a step 2020.

[0104] Following step 2020, the operator communicates, to the control unit 74 and via the terminal 80, instructions for positioning the carriage 52 along the X axis, this during a step 2030. This induces a movement of the hoist 56 which takes place during a step 2040 and normally brings the carriage into the position shown in insert B) of FIG. 2, where the transmitter 102 is vertically aligned with, and located above, the receiver 104. In particular, the transmitter 102 is then located in the receiving cone truncated K104 of the receiver 104. During a step 2050, the operator visually checks whether the carriage 52 is positioned along the X axis such that the hoist 56 is above the mold 12, in particular that the hook 56 is generally vertically aligned with the lifting ring 44.

[0105] If this is not the case, the movement of the hoist is restarted by the operator, by means of a return to step 2040. If this is the case, the method automatically goes to a step 2062 through a logic gate 2060 of the “ET” or “AND” type in English.

[0106] In parallel, at step 2030 and following step 2020, the operator communicates, to the control unit 74 and via the terminal 80, instructions for lowering the hook 66, this during a step 2070. This induces a lowering of the hook 66 which takes place during a step 2072 and a locking of the hook on the lifting ring 44 which takes place during a step 2074, with the help of the operator if necessary. We are then in the configuration shown in insert C) of figure 3 where the cable 58 is stretched.

[0107] In this position, the transmitter 102 is arranged inside the reception cone truncated K104 defined by the receiver 104.

[0108] In a following step 2076, the motor 64 is actuated to wind a portion of the cable 58 onto the drum 62, which is represented by the arrow A1 in the insert E) of FIG. 4. This has the effect of putting the hook 66 under load, that is to say of putting the cable 58 under tension, by exerting the tension force F of the cable 58, between the carriage 52 and the hook 66 and which corresponds to the load on the hook.

[0109] In a following step 2078, the hook load resulting from step 2076 is determined from the load information from the sensor 68 and by means of the hook load detection device which determines the force F. This force F determined in step 2078 is compared, in a following step 2080, to a reference value F o which constitutes a threshold value. This step 2078 is preferably carried out by means of the control unit 74 of the lifting device 50.

[0110] Alternatively, step 2078 is carried out at the level of a computer of the hook load detection device, on board the hoist 56, and connected to the processing means of the hook load detection device.

[0111] If the force F detected in step 2078 is strictly lower than this threshold value, then a step 2082 is implemented in which the transmitter 102 is deactivated, i.e. it stops emitting the infrared signal SI. In this case, the control unit 74 transmits an instruction to the transmitter 102 causing the transmitter to switch off, i.e. the emission of the infrared signal SI to stop. This case corresponds to the fact that step 2078 takes place cyclically, including after the transmitter 102 has started to operate following a step 2084 mentioned below, so that it makes it possible to react to a drop in the value of the force F during the unloading process. After step 2082, the method automatically returns to steps 2072, 2074 and 2076.

[0112] If the force F detected in step 2078 is greater than or equal to the threshold value Fo, then the method proceeds to a step 2084 of activating the transmitter 102, i.e. the transmission of an instruction to the power supply transmitter causing the operation of the transmitter, in other words the emission of the infrared signal SI. The operation of the transmitter 102 is carried out by the electrical power supply of the transmitter. The emission of the infrared signal SI is thus controlled by the load detection device as a function of the force F determined in step 2078. If this emission of the infrared signal SI does not take place within a time less than a predetermined period, which may be equal to 500 milliseconds, the method returns to step 2080. If the emission of the infrared signal takes place during step 2084, the method proceeds by itself to step 2062 through the logic gate 2060.

[0113] Thus, the logic gate 2060 of the “AND” type makes it possible to check whether, at the same time, the carriage 52 is in the determined position and the transmitter 102 emits the signal SI.

[0114] In step 2078, the sensor 68, which is a load sensor of the hoist 56, detects the increase in load on the hook.

[0115] The load detection device 68 on the hook comprises a calculator, not shown, which implements step 2080 as well as a memory, also not shown, which contains the threshold value F o, which is for example equal to 500 daN. This threshold value Fo was previously entered during the calibration of the installation 2. During step 2080, if the detected force F exceeds the threshold value Fo, the computer considers that there is an effective load on the hook, that is to say a loading state of the hoist 56, and transmits a power supply instruction to the transmitter causing the emission of the infrared signal which takes place during step 2084. Corresponding information can be transmitted to the terminal 80 to inform the operator of the loading state of the hoist.

[0116] Alternatively, the load detection device 68 of the hoist 56 transmits effective load information to the position detection device 100 of the trolley 52, the position detection device 100 comprising a computer and a memory containing the threshold value Fo. The detection device 100 then implements the step 2080 of comparing the detected force F with the threshold value F o and activates the infrared transmitter 102, if the force value F exceeds the threshold value Fo, or does not activate the infrared transmitter if the force value F does not exceed the threshold value F o .

[0117] Regardless of the method of obtaining the information on the load on the hook and the way in which the comparison of step 2080 is implemented, the transmitter receives binary information which corresponds to the result of the comparison of step 2080 and which allows or does not allow its operation.

[0118] The unloading method therefore comprises prior steps 2000 to 2080 which condition the operation of the transmitter 102 and which consist in particular in determining, during step 2078, the force F between the carriage 52 and the hook 66, by means of the hook load detection device 68, and in comparing, during step 2080, the force F determined in the previous step with a threshold value Fo. These steps are carried out by the hook load detection device or by the detection device 100.

[0119] Steps 2000 to 2080 are implemented by means of the control unit 74 and the terminal 80 of the lifting device 50, while steps 2082 and 2084 are implemented within the detection device 100, therefore by the magnetic clamping system 20.

[0120] During step 2062, which is implemented within the magnetic clamping device 20, as long as the transmitter 102 emits the infrared signal S1, this signal is assumed to be picked up by the receiver 104 and the output signal of the receiver 104 is transmitted to the clamping control unit 34, in a step 2062. In other words, step 2062 consists of collecting the state of the output signal S104 of the receiver, which allows the clamping control unit 34 to determine whether it includes the first value V1 or the second value V2.

[0121] In a step 2086 which takes place after step 1002, if the result of this step is positive, as well as after step 2062, it is checked whether the receiver 104 actually receives the infrared signal S1, by determining whether the signal S104 includes the first value V1. If this is not the case, the method automatically proceeds to a step 2088 inviting the operator to attach the hoist 56 and the unloading procedure is suspended, so that the magnetic pads 24 are maintained in the magnetized configuration and the mold 12 is held by the magnetic clamping device 20, securely within the injection molding machine 4, without the operator being able to progress in the mold demagnetization procedure. In other words, in step 2088, the demagnetization of the magnetic pads 24 is prevented. A fall of the mold is thus avoided.

[0122] If the result of the verification of step 2086 is positive, that is to say if the output signal S104 includes the first value V1, and if the receiver 104 is present at step 1002, then the magnetic clamping control unit 34 considers that the transmitter 102 is, relative to the receiver 104, in the predetermined position. The magnetic clamping control unit 34 can then authorize demagnetization of the magnetic pads 24, during a subsequent step.

[0123] The method then automatically proceeds to a step 2090 comparable to step 1004 and in which the operator is questioned, by means of the control terminal 40, to know whether the locking mechanism 42 is in the locked configuration. The operator can respond to this question after having visually checked the locking mechanism(s) 42. If the operator responds negatively or does not respond for a predetermined period of time At, for example equal to 5 seconds, the method automatically proceeds to a step 2092 in which the operator is invited, by means of a message displayed on the terminal 80, to lock the locking mechanism(s) 42. If the operator confirms in step 2090 that the locking mechanism 42 is operational, the method automatically proceeds to step 1008, through the logic gate 1010.This verification of the locking mechanism limits the risk of retaining the mold part 12B with the lifting ring 44 without retaining the mold part 12A. Alternatively, this verification is carried out by an automatic process using additional sensors not shown.

[0124] During step 1008, the operator validates the instruction to demagnetize the magnetic pads of the clamping system by means of the terminal 40, which is not prevented since the verification steps have been completed.

[0125] It is then possible to implement steps 1012 to 1020, which is represented by insert F) of figure 4 with arrows A2, A3 and A4.

[0126] Thus, the authorization to demagnetize the magnetic pads which results from the verification of step 2086, when it is positive, is conditioned on the result of the comparison of step 2090. Except when an action by the operator is necessary, steps 2086 to 2092 and 1012 to 1020 mentioned above are carried out automatically by the clamping control unit 34.

[0127] In summary, the steps of the unloading method of the invention involve several components of the installation 2. Indeed, steps 1002 to 1006, 1008 to 1014, 2062 and 2082 to 2092 are implemented within the magnetic clamping system 20, in particular thanks to the magnetic clamping control unit 34, the terminal 40 and the position detection device 100. Steps 1016 and 1018 are implemented, in particular, by means of the control unit 14 of the injection molding machine. Steps 1020 and 2000 to 2080 are implemented, in particular, by means of the control unit 74, the terminal 80, the motor 64 and the sensor 68 of the lifting device 50.

[0128] In particular, according to one aspect of the invention, the magnetic clamping system 20 is configured to implement at least steps 1012, 2062, 2084, 2086 and 2088 and, preferably, all of steps 1002 to 1006, 1008 to 1014, 2062 and 2082 to 2092.

[0129] Insert D) of Figure 3 represents the case where the transmitter 102 transmits the infrared signal SI without being in the predetermined position relative to the receiver 104, to the point that the infrared signal SI transmitted by the transmitter 102 is offset from the sensor 104 along the X axis. This is detected during step 2086 because the output signal S104 of the receiver 104 contains the value V2, which leads to the implementation of step 2088.

[0130] Thus, the method of the invention allows the magnetic clamping control unit 34 to ensure that the receiver 104 is identified as present and operational during step 1002, to continue the unloading method in manual mode if the receiver 104 is not identified as present and operational, with steps 1004 to 1020 and conveying steps carried out by the operator elsewhere, or to continue the unloading method in secure and semi-automatic mode if the receiver 104 is identified as present and operational, with steps 2000 to 2092, then 1008 to 1020.

[0131] The secure nature of the unloading method of the invention comes in particular from the fact that the output signal S104 of the receiver 104 retains the second value V2, which is detected during step 2086, as long as the lifting device 50 has not been correctly positioned relative to the injection press 4 during step 2040 or if the hoist 56 is not capable of retaining the mold 12 because the load detection device, which comprises the sensor 68, has not detected a load on the hook during step 2078.

[0132] In the second and third embodiments of the installation 2 shown in Figures 6 and 7, the elements similar to those of the first embodiment bear the same reference. If a part of the installation 2 of these second and third embodiments is mentioned in the description without being shown in these figures, it is the same part as that mentioned for the first embodiment. Conversely, if a part is referenced in one of Figures 6 or 7 without being mentioned in the description, it is the same part as that bearing the same reference in the first embodiment. In the following, we mainly describe what differentiates the second and third embodiments from the first embodiment.

[0133] In the second embodiment shown in Figure 6, the transmitter 102 and the sensor 104 are arranged such that the infrared signal SI is emitted in a direction parallel to the Y axis of the orthogonal reference frame XYZ. The sensor 104 output signal S104 includes the first value V1 when the transmitter 102 emits the infrared signal SI and the transmitter 102 and the sensor 104 are facing each other and aligned on the same straight line Dsi parallel to this Y axis, which corresponds to a predetermined position of the transmitter 102 relative to the receiver 104. The sensor 104 output signal S104 includes the second value V2 when the transmitter 102 does not emit the infrared signal SI and / or when the transmitter 102 and the sensor 104 are not facing each other and aligned on the straight line DFI.

[0134] In the third embodiment shown in Figure 7, the transmitter 102 and the sensor 104 are oriented such that the infrared signal SI is parallel to the X axis of the orthogonal reference frame XYZ. The output signal S104 of the receiver 104 includes the first value V1 when the transmitter 102 emits the infrared signal SI and the transmitter 102 and the sensor 104 are facing each other and aligned on the same straight line D'si parallel to this X axis, which corresponds to a predetermined position of the transmitter 102 relative to the receiver 104. The output signal S104 of the receiver 104 includes the second value V2, when the transmitter 102 does not emit the infrared signal SI and / or when the transmitter 102 and the sensor 104 are not facing each other and aligned on the straight line D'FI-

[0135] This detection direction along the line D'si corresponds to the fact that the rails 154 of the lifting device 50 are supported by two carriages 57 mounted movably on two beams 55 which extend parallel to the Y axis. Thus, the hoist 56 is movable in a horizontal plane both along the directions of the X and Y axes, therefore in particular perpendicular to the Y axis.

[0136] In the second and third embodiments, when the transmitter 102 is in the predetermined position, the carriage 52 is vertically aligned with the mold 12 clamped in the injection press.

[0137] In the second and third embodiments, the receiver 104 has a reception zone in the shape of a truncated cone (not shown), according to an approach comparable to that of the first embodiment. Whatever the embodiment, the unloading method and the magnetic clamping system 20 of the invention allow satisfactory conditions for positioning the hoist 56 relative to the injection press 4 to be detected to allow the demagnetization of the magnetic pads 24. The solution of the invention has the advantage of being simple and inexpensive while being almost universal, that is to say adaptable to a large number of operating configurations. This solution is also unidirectional due to the communication directed from the transmitter to the receiver, without the reciprocal being necessary.This solution operates without a wired connection between the transmitter 102 and the receiver 104 of the position detection device 100. The solution of the invention also has the advantage of being secure and tamper-proof due to the fact that the detection of the electromagnetic signal can only be carried out under unique alignment conditions.

[0138] The invention is not limited to one type of lifting device. Alternatively, the lifting device may be a chain or sling lifting device, a robot, or a crane.

[0139] According to a variant of the invention not shown, the emission direction of the transmitter 102, the reception direction of the receiver 104 and the reception truncated cone K104 can be inclined relative to the XYZ axes in all directions.

[0140] According to another variant of the invention, not shown, the transmitter can emit an electromagnetic signal other than an infrared signal, in particular a laser signal or a unidirectional electroluminescent signal emitted by a light-emitting diode, in other words an LED. In this case, the receiver 104 is configured to detect a laser or electroluminescent signal.

[0141] The invention is not limited to use in a plastics processing installation but applies to other types of installation which include machines of which certain parts must be changed during the lifetime of these machines, such as machining centers. In particular, this invention can be applied to machining centers with a vertically arranged magnetic clamping plate where there is a risk of the workpiece falling during demagnetization.

[0142] According to a variant of the invention, not shown, applicable to all embodiments, the hook load detection device, which comprises the sensor 68 and the means (not shown) for processing its output signal, can be configured to determine, on the basis of the force between the carriage 52 and the hook 66, the mass of the part to be clamped, namely the mold 12 in the exemplary embodiments shown. In this case, the electromagnetic signal emitted by the transmitter 102 advantageously includes information relating to the mass of the part to be clamped, as determined by the hook load detection device. The receiver 104 is then configured to extract the information relating to the mass of the part to be clamped from the electromagnetic signal received from the transmitter 102 and to communicate it to the magnetic clamping control unit 34.In this case, when loading a mold 12 into an injection molding machine 4 or another part to be clamped onto another machine, the method for loading this part may comprise a step, carried out within the magnetic clamping control unit 34 and consisting of comparing the information relating to the mass of the part to be clamped, extracted from the electromagnetic signal emitted by the transmitter 102, with a predetermined threshold value. When the aforementioned comparison shows that the mass of the part to be clamped is greater than the threshold value, an additional step may be implemented, also within the magnetic clamping control unit 34, to prevent the loading of this part or to emit an alarm.On the contrary, in the case where the aforementioned comparison shows that the mass of the part to be clamped is less than the threshold value, a step can be carried out within the magnetic clamping control unit 34 to authorize the loading of this part into the machine.

[0143] Thus, in the example of a mold, if a mold 12 is brought by the hoist 56 to an injection press 4 whose magnetic clamping capabilities are limited to a threshold value, the clamping can be prevented or an alarm can be triggered before the actual clamping operations.

[0144] According to another variant, applicable to all embodiments of the invention, the electromagnetic signal emitted by the transmitter 102, for example the infrared signal SI, may comprise a Tiio2 identification frame of this transmitter, intended to be collected by the receiver 104. In this case, the method comprises an additional step not shown and for example implemented between steps 2060 and 2090, during which this identification frame Tiio2 is compared with a reference identification frame Trefios, assigned to the transmitter 102 assumed to belong to the same position detection device 100 as the receiver 104. If the result of this comparison is negative, that is to say if the frames Thoa and Tref a are different, the method returns to step 2088 regardless of the value V1 or V2 included in the signal S104. If the result of this comparison is positive, the method goes to step 2090.This ensures that the signal detected by a sensor 104 corresponds to the hoist 56 associated with a row of machines which includes the machine relative to the clamping plate of which this receiver is fixed and that it is not a parasitic electromagnetic signal coming from neighboring equipment. According to another variant applicable to all embodiments, the receiver 104 is mounted on a fixed part of the installation 2 but offset from the clamping plate 26, to reduce environmental constraints, particularly in terms of wiring.

[0145] Alternatively, the position of the receiver 104 may be adapted on the machine, for example by means of a slide and a clamping means which makes it possible to fix the receiver on the machine in one of several possible positions.

[0146] Alternatively, several transmitters 102 and / or several receivers 104 can be used for the same machine, in particular the same injection press 4, and the same hoist 56. This makes it possible to ensure that the positioning of the hook 66 is correct in two perpendicular directions, in particular when the hoist 56 can move along the X and Y axes as in the third embodiment. In this case, it is possible to combine the orientations of the parts of the position detection device 100 shown in FIGS. 6 and 7. The authorization of demagnetization is then conditioned by the combined reception of several signals.

[0147] According to another variant of the invention, not shown, each mold part 12A and 12B is equipped with a lifting ring 44 and handled independently during the operations of unloading and loading the mold into the injection molding machine. In this case, it is not necessary to provide a locking mechanism 42 and steps 1004 and 2090 of the method are not implemented. In this case, the demagnetization of the magnetic pads 24 is controlled independently for the two clamping plates 26 and 28.

[0148] Alternatively, the mold 12 may comprise more than two parts 12A and 12B, handled at once or independently.

[0149] According to another variant, the truncated cone K104 can be a cone, if the detection zone of the receiver 104 is point-like.

[0150] The embodiments and variants of the invention mentioned above can be combined with each other to generate new embodiments.

Claims

DEMANDS 1. A method for unloading, using a hoist (56), at least one part (12) clamped on a magnetic clamping system (20) of an industrial installation (2), the hoist comprising - a trolley (52) that moves in a horizontal plane, - a hook (66) suspended from the trolley and movable vertically, - a load detection device (68) on the hook, configured to determine a force (F) between the trolley and the hook and - a hoist control unit (74), the magnetic clamping system (20) comprising - a magnetic clamping control unit (34), - at least one magnetic clamping plate (26) comprising several selectively magnetizable magnetic pads (24) controlled by the magnetic clamping control unit, a human-machine interface (40) connected to the magnetic clamping control unit (34) and allowing entry of a demagnetization command (1008) for the magnetic pads, characterized in that the magnetic clamping system (20) includes a detection device (100) for the position of the carriage (52) relative to the clamping plate (26), the detection device (100) comprising: o a transmitter (102) of an electromagnetic signal (SI), fixed to the carriage and controlled according to the force (F) determined by the hook load detection device (68), o a receiver (104) of the electromagnetic signal emitted by the transmitter,fixed relative to the clamping plate (26) and configured to deliver an output signal (S104) including a first value (V1) when the receiver receives the electromagnetic signal and a second value (V2) when the receiver does not receive the electromagnetic signal, and, - the unloading process includes at least steps consisting of a) determining (2078) the force (F) between the trolley (52) and the hook (66) by means of the hook load detection device (68), b) comparing (2080) the force (F) determined in step a) with a threshold value (F o ), c) if the comparison performed in step b) shows that the force determined in step a) is greater than the threshold value, operate (2084) the transmitter (102), d) during step c), collect (2062) the output signal (S104) from the receiver, e) determine (2086) which value is included in the output signal (S104) from the receiver (104), between the first value (V1) and the second value (V2), f) if the determination in step e) shows that the output signal collected in step d) includes the first value (V1), allow (1012) the entry of a command to demagnetize the magnetic pads using the human-machine interface (40), g) if the determination in step e) shows that the output signal collected in step d) includes the second value (V2), prevent (2088) the input of the demagnetization order of the magnetic pads by means of the human-machine interface (40).

2. Unloading method according to claim 1, characterized in that step g) (2088) is maintained as long as the signal collected in step d) (2062) has the second value.

3. Unloading method according to any one of the preceding claims, characterized in that the receiver (104) delivers the output signal (S104) with the first value (V1) when the transmitter (102) is activated and when the transmitter is in a predetermined position relative to the receiver and in that the receiver delivers the output signal with the second value (V2) when the transmitter is not operating and / or when the transmitter is not in the predetermined position relative to the second element.

4. Unloading method according to claim 3, characterized in that the predetermined position of the emitter (102) is opposite the receiver (104).

5. Unloading method according to any one of claims 3 and 4, characterized in that the predetermined position of the transmitter (102) corresponds to a vertical alignment of the carriage (52) with the part (12) clamped on the magnetic clamping system.

6. A discharge method according to any one of the preceding claims, characterized in that the electromagnetic signal (SI) emitted by the transmitter includes an identification frame (Ti s) intended to be collected by the receiver the process includes an additional step h) of comparing the identification frame collected by the receiver with a reference identification frame (Tref s) and in the case where the result of the comparison in step h) is negative, the input of the instruction to demagnetize the magnetic pads is prevented (2088) regardless of the value (V1 , V2) determined in step e) (2086).

7. Unloading method according to any one of the preceding claims, characterized in that it comprises additional steps consisting of i) prior to step c), determining (1004) whether the receiver (104) is operational, j) in the case where the receiver is determined to be operational in step i), proceeding to step e) k) in the case where the receiver is determined to be non-operational in step i), proceeding to a manual mode where the operator must validate at least one step (1004, 1006) by answering a question, by means of a control terminal (40) connected to the magnetic clamping control unit (34).

8. A magnetic clamping system (20) comprising a magnetic clamping control unit (34) and at least one magnetic clamping plate (26) comprising several selectively magnetizable magnetic pads (24) controlled by the magnetic clamping control unit, characterized in that the magnetic clamping system (20) includes a device (100) for detecting the position of a trolley (52) of a lifting device (50) relative to the magnetic clamping plate (26), the detection device comprising: o a transmitter (102) of an electromagnetic signal (11), fixed to the trolley (52), o a receiver (104) of the electromagnetic signal emitted by the transmitter, fixed relative to the clamping plate, configured to deliver an output signal (104) comprising a first value (V1) when the receiver receives the electromagnetic signal and a second value (V2) when the receiver does not receive the signal electromagnetic,The clamping system is configured to implement at least steps c) to g) of a method according to one of the preceding claims.

9. Magnetic clamping system according to claim 8, characterized in that the electromagnetic signal is an infrared (SI) signal and in that the receiver (104) is configured to detect an infrared signal.

10. Magnetic clamping system according to claim 8, characterized in that the electromagnetic signal is emitted by a laser diode or a light-emitting diode and in that the receiver is configured to detect a laser or light-emitting diode signal.

11. Magnetic clamping system according to any one of claims 8 to 10, characterized in that the receiver (104) is directed along a vertical axis and in that a receiving area of ​​the receiver is in the shape of a cone or truncated cone (K104) centered on the vertical axis.

12. Magnetic clamping system according to any one of claims 8 to 10, characterized in that the receiver (104) is directed along a horizontal axis (X, Y) and in that a receiving area of ​​the receiver is in the shape of a cone or truncated cone (K104) centered on the horizontal axis.

13. Magnetic clamping system according to any one of claims 8 to 12, characterized in that the receiver (104) comprises a microcontroller capable of communicating the first value (V1) or the second value (V2) included in the output signal (S104) to the magnetic clamping control unit (34).

14. Magnetic clamping system according to any one of claims 8 to 13, characterized in that the receiver (104) is configured to deliver a presence information (S104) to the magnetic clamping control unit (34).

15. Method for loading, using a hoist (56), at least one part (12) to be clamped onto a magnetic clamping system (20) of an industrial installation (2), the hoist comprising - a trolley (52) that moves in a horizontal plane, - a hook (66) suspended from the trolley and movable vertically, - a load detection device (68) on the hook, configured to determine a force (F) between the trolley and the hook and - a hoist control unit (74), characterized in that the magnetic clamping system (20) is, according to any one of claims 8 to 14, the load detection device (68) on the hook is configured to determine, on the basis of the force (F) between the trolley and the hook, the mass of the part (12) to be clamped, the electromagnetic signal (SI) emitted by the transmitter (102) includes information relating to the mass of the part to be clamped, determined by the load detection device (68) on the hook, The receiver (104) is configured to extract the mass information of the part to be clamped from the electromagnetic signal received from the transmitter and to communicate it to the magnetic clamping control unit (34) of the magnetic clamping system (20), - the loading process includes at least steps carried out by the magnetic clamping system (20) and consisting of l) comparing the mass information of the part to be clamped, extracted from the electromagnetic signal, to a predetermined threshold value, m) in the case where the comparison carried out in step I) shows that the mass of the part to be clamped is greater than the threshold value, preventing loading or issuing an alarm, and n) in the case where the comparison carried out in step I) shows that the mass of the part to be clamped is less than the threshold value, allowing loading.

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