Magnetic Clamping Device

Abstract

To provide a magnetic clamp device capable of detecting a position where a magnetic flux change has occurred on a magnetic plate.SOLUTION: A plurality of magnetic units (11) are provided in a magnetic plate (8) of a magnetic clamp. Each magnetic unit (11) has an Alnico magnet (14), and a search coil (20) through which an induced voltage is generated when a magnetic flux passing through the Alnico magnet (14) changes. The magnetic plate (8) is divided into a first area (22a) and a second area (22b). The search coils (20) of the magnetic units (11) arranged in the first area (22a) are serially connected. The search coils (20) of the magnetic units (11) arranged in the second area (22b) are serially connected.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a magnetic clamping device that magnetically attracts a mold, workpiece, or tool to a substrate, and in particular to a magnetic clamping device that measures an induced voltage generated in a search coil of the magnetic clamping device and calculates the amount of change in magnetic flux from the induced voltage. [Background technology]

[0002] A conventional magnetic clamping device of this type is described in Patent Document 1 (JP Patent Publication No. 2011-206860). This conventional technology is configured as follows. The magnetic plate has an attraction surface that magnetically attracts the mold. A plurality of mounting holes are opened in the attraction surface. A magnetic unit is provided for each mounting hole. The magnetic unit has a magnetic pole reversal coil, an alnico magnet, and a search coil. The magnetic poles of the alnico magnet are reversed by a current flowing in one direction through the magnetic pole reversal coil. The alnico magnet is returned to its state before the magnetic poles were reversed by a current flowing in the other direction opposite to the one direction. A search coil is wound around the outer circumferential wall of the alnico magnet. When the magnetic flux passing through the alnico magnet changes, an induced voltage is generated in the search coil. The amount of change in magnetic flux is calculated from the induced voltage. All magnetic pole reversal coils in the magnetic unit are connected in series. All search coils in the magnetic unit are also connected in series. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-206860 A Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned conventional techniques have the following problems. Since all the above search coils are connected in series, the search coils cannot detect at which position on the magnetic plate the magnetic flux is changing. SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a magnetic clamping device capable of detecting the position where the magnetic flux changes on the magnetic plate. [Means for solving the problem]

[0005] In order to achieve the above object, the present invention provides a magnetic clamping device configured as follows, for example, as shown in FIGS. 1 to 4. The magnetic plate 8 has an attraction surface 9 that magnetically attracts the magnetic attraction target 7. A plurality of mounting holes 10 are opened in the attraction surface 9. A magnetic unit 11 is provided for each of the mounting holes 10. The magnetic unit 11 has a magnetic pole reversal coil 12, a reversible magnet 14, and a search coil 20. The reversible magnet 14 has its magnetic pole reversed by a current flowing in one direction through the magnetic pole reversal coil 12, and is returned to its state before the magnetic pole was reversed by a current flowing in the other direction opposite to the one direction. A voltage is induced in the search coil 20 by a change in the magnetic flux passing through the reversible magnet 14. The magnetic plate 8 is divided into a plurality of areas, and a plurality of magnetic units 11 are disposed in a first area 22a, which is one of the plurality of areas. The search coils 20 of the magnetic units 11 arranged in the first area 22a are connected in series, and a first detection circuit 23a is formed by the search coils 20 in the first area 22a. The search coils 20 of the magnetic units 11 arranged in the second area 22b, which is an area different from the first area 22a, are connected in series, and a second detection circuit 23b is formed by the search coils 20 in the second area 22b.

[0006] The present invention provides the following advantageous effects. The magnetic plate is divided into a number of areas, and a search coil is connected in series to each area, so that the induced voltage generated in the search coil can be detected for each area. This makes it possible to detect the state of the mold, for example, whether or not there is a mold, and whether peeling or shifting of the magnetically attracted position occurs when an external force is applied to the magnetically attracted mold, for each area.

[0007] The magnetic pole reversal coils 12 of the magnetic units 11 arranged in the first area 22a are connected in series to form a first magnetic pole reversal circuit 24a, and the magnetic pole reversal coils 12 of the magnetic units 11 arranged in the second area 22b form a second magnetic pole reversal circuit 24b. In this case, the magnetic pole reversal coil in the first area and the magnetic pole reversal coil in the second area can be operated separately or simultaneously depending on the induced voltage generated in each area in the search coil. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 shows a first embodiment of the present invention and is a schematic diagram showing a molding machine. [Diagram 2] FIG. 2 is a front view showing the magnetic clamp device mounted on the molding machine. [Diagram 3] FIG. 3 is a view taken along line AA in FIG. 2, showing the magnetic clamp device in a demagnetized state. [Figure 4] FIG. 4 is a cross-sectional view showing the magnetized state of the magnetic clamping device, and is similar to FIG. [Diagram 5] FIG. 5 is a front view similar to FIG. 2, showing a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A first embodiment of the present invention will be described with reference to FIGS. A molding machine 1 shown in Fig. 1 includes a fixed platen 2 and a support wall 3. Four guide rods 4 are provided in parallel across the fixed platen 2 and the support wall 3, and a movable platen 5 is provided on the guide rods 4 so as to be movable along the guide rods 4. Magnetic clamp devices 6 are attached to the side walls of the fixed platen 2 and the movable platen 5, respectively. A mold (magnetically attracted object) 7 is magnetically attracted by the magnetic force of the magnetic clamp device 6. The magnetic clamp device 6 is configured as follows, as shown in Figs. 1 to 4.

[0010] The magnetic clamp device 6 includes a magnetic plate 8, which is made of a ferromagnetic material, for example, an iron material. An attraction surface 9 is provided on the magnetic plate 8, and the mold 7 is magnetically attracted to the attraction surface 9. A plurality of mounting holes 10 are opened in a circular shape on the attraction surface 9 of the magnetic plate 8. One magnetic unit 11 is provided in each mounting hole 10. The magnetic unit 11 is configured as follows, as shown in Figs. 3 and 4.

[0011] A ring-shaped bobbin 13 around which a coil 12 for magnetic pole reversal is wound multiple times is inserted into the mounting hole 10. A reversible magnet 14 is inserted into the inner peripheral hole of the bobbin 13, and the reversible magnet 14 is abutted against the bottom wall 10a of the mounting hole 10. The reversible magnet 14 is made of, for example, an alnico magnet. A magnetic pole member 15 made of a ferromagnetic material similar to the magnetic plate 8 is inserted on the right (attraction surface 9) side of the reversible magnet 14 so as to abut against the reversible magnet 14. A ring-shaped non-magnetic member 16 is attached to the end of the outer peripheral wall of the magnetic pole member 15 on the attraction surface side. The non-magnetic member 16 is made of, for example, a brass or stainless steel member. An O-ring 17 as a sealing member is attached to a housing groove formed in the circumferential direction of the outer peripheral wall of the non-magnetic member 16. A permanent magnet 19, for example a neodymium magnet, is attached in an annular space 18 defined by the non-magnetic member 16, the outer peripheral wall of the magnetic pole member 15, the bobbin 13, the inner peripheral wall of the mounting hole 10, etc.

[0012] In the above embodiment, as shown in Figures 3 and 4, in one magnetic unit (hereinafter referred to as the first magnetic unit 11a) among the multiple magnetic units 11, one end on the right side (the side closer to the attraction surface 9) of the reversible magnet (hereinafter referred to as the first Alnico magnet 14a) is magnetized to be the S pole. Also, the other end opposite to the one end is magnetized to be the N pole.

[0013] Another magnetic unit (hereinafter referred to as the second magnetic unit 11b) adjacent to the first magnetic unit 11a is configured in the same manner as the first magnetic unit 11a, but differs from the first magnetic unit 14a in that the reversible magnet (hereinafter referred to as the second alnico magnet 14b) is magnetized so that one end of the right side (the side closer to the attracting surface 9) of the second alnico magnet 14b is the N pole. The other end of the second alnico magnet 14b is magnetized to the S pole. The coil (second coil) 12b of the second magnetic unit 11b is wound around the second bobbin 13b in the opposite direction to the coil (first coil) 12a of the first magnetic unit 11a, and the second coil 12b and the first coil 12a are connected in series. By passing a predetermined current through the coils 12a and 12b in one direction for a predetermined time, the magnetic poles of the first alnico magnet 14a and the second alnico magnet 14b are switched at once.

[0014] The permanent magnet of the first magnetic unit 11a (hereinafter referred to as the first neodymium magnet 19a) is magnetized so that its inner circumferential side is the N pole and its outer circumferential side is the S pole. The permanent magnet of the second magnetic unit 11b (the second neodymium magnet 19b) is magnetized so that its inner circumferential side is the S pole and its outer circumferential side is the N pole. Therefore, in a demagnetized state of the magnetic clamp device in which one end of the first alnico magnet 14a is an S pole and one end of the second alnico magnet 14b is an N pole, the magnetic flux starts from the first alnico magnet 14a, passes through the magnetic pole member (first magnetic pole member 15a) of the first magnetic unit 11a, the first neodymium magnet 19a, the magnetic plate 8, the second neodymium magnet 19b, the magnetic pole member (second magnetic pole member 15b) of the second magnetic unit 11b, the second alnico magnet 14b, and the magnetic plate 8 in this order, and returns to the first alnico magnet 14a, as shown by the two-dot chain line in Fig. 3. At this time, since a magnetic field is generated only inside the magnetic plate 8, the mold 7 is not magnetically attracted even if it is brought close to the magnetic plate 8.

[0015] In addition, in a magnetized state of the magnetic clamp device in which one end of the first Alnico magnet 14a is switched from S pole to N pole and one end of the second Alnico magnet 14b is switched from N pole to S pole, part of the magnetic flux originates from the first Alnico magnet 14a, passes through the first magnetic pole member 15a, the die 7, the second magnetic pole member 15b, the second Alnico magnet 14b, and the magnetic plate 8 in this order, and returns to the first Alnico magnet 14a, as shown by the two-dot chain line in Fig. 4. At this time, a magnetic field is generated across the magnetic plate 8 and the die 7 in contact with the magnetic plate 8, so that the die 7 is magnetically attracted to the magnetic plate 8.

[0016] In the magnetic clamp device 6 of this embodiment, a search coil 20 is disposed in an annular space 18 formed between a neodymium magnet 19 and a non-magnetic member 16 so as to be wound along the outer circumferential surface of the non-magnetic member 16. The search coil 20 detects magnetic flux passing through the magnetic pole member 15 and the alnico magnet 14. The search coil (first search coil) 20a of the first magnetic unit 11a is connected in series to the search coil (second search coil) 20b of the second magnetic unit. The second search coil 20b is disposed so as to be wound along the outer circumferential surface of the non-magnetic member 16 of the first magnetic unit 11b in the opposite direction to the first search coil 20a. A communication hole 21 that communicates the mounting hole 10 of the first magnetic unit 11a with the mounting hole 10 of the second magnetic unit 11b is opened on the back surface of the magnetic plate 8, and one end of the first search coil 20a and one end of the first search coil 20b are inserted into the communication hole 21. The search coils 20a and 20b are connected in the communication hole 21. In this way, the search coils 20a and 20b of the adjacent magnetic units 11a and 11b are connected in series. The voltmeter of the control device measures the induced voltage generated in the search coils 20a and 20b at predetermined time intervals (about 1 msec). The measurement results are sent to the memory unit of the control device and recorded. The amount of change in magnetic flux dφ is calculated by the calculation unit of the control device using the following formula from the induced voltage e recorded in the memory unit and the number of turns N of the coil. e = -Ndφ / dt In the above formula, the magnetic flux change amount φ is calculated by integrating the output voltage e with respect to time and dividing the result by the number of turns N of the coil.

[0017] In the magnetic clamp device 6 of the above embodiment, the magnetic flux changes when the magnetic clamp device 6 is switched from a demagnetized state to a magnetized state, and the amount of change in the magnetic flux is called the initial magnetic flux. Also, when the die 7 magnetically attracted to the magnetic plate 8 is about to peel off due to an external force or the die's own weight, or when the magnetic attraction position shifts, the magnetic flux changes to decrease from the initial magnetic flux, and this magnetic flux is called magnetic flux disappearance.

[0018] As described above, when the die 7 begins to peel off, the magnetic flux decreases from the initial magnetic flux by the amount of magnetic flux loss. When the value obtained by subtracting the magnetic flux loss value from the initial magnetic flux falls below a preset threshold, the determination unit of the control device determines that there is a possibility that the die 7 will fall from the magnetic plate 8. At this time, the determination unit transmits a signal according to the determination result to the alarm. The alarm displays a warning or the like that the die 7 may fall from the magnetic plate 8.

[0019] As described above, when the warning is displayed, if an operator or the like confirms that the mold 7 has hardly moved from the position on the magnetic plate 8 where it was initially magnetically fixed and that there is no problem with driving the molding machine 1, a re-magnetization operation is performed as follows. In the re-magnetization operation, first, the movable platen 5 is moved toward the fixed platen 2, and the mold 7 is sandwiched between the movable platen 5 and the fixed platen 2. Next, the magnetic clamp device 6 is switched from a magnetized state to a demagnetized state, and then switched from the demagnetized state to a magnetized state again. This allows the magnetic flux of the magnetic clamp device 6 to return to the initial state before it disappeared.

[0020] In this embodiment, as shown in FIG. 2, 24 magnetic units 11 are arranged on the magnetic plate 8. The magnetic plate 8 is divided into four areas, vertically and horizontally. When the magnetic plate 8 is viewed from the front, the upper right area is called the first area 22a, the lower right area is called the second area 22b, the lower left area is called the third area 22c, and the upper left area is called the fourth area 22d. Six magnetic units 11 are arranged in the first area 22a. The search coils 20 of the six magnetic units 11 are connected in series as shown by dotted lines in FIG. 2 to form a detection circuit 23 (first detection circuit 23a), and an end of the detection circuit is connected to a control device (not shown). The electric wiring as the detection circuit 23 (including not only the first detection circuit 23a but also the second detection circuit 23b to the fourth detection circuit 23d described later) is arranged in a groove or hole formed in the back wall of the magnetic plate 8. Similarly, electrical wiring as inversion circuits 24 (first inversion circuit 24a to fourth inversion circuit 24d) described later is also disposed in grooves or holes formed in the rear wall or the like of the magnetic plate 8. For this reason, although the detection circuit 23 and the inversion circuit 24 are shown together by dotted lines in Fig. 2, the detection circuit 23 and the inversion circuit 24 in this embodiment are configured by separate wiring.

[0021] Six magnetic units 11 are also arranged in each of the second area 22b to fourth area 22d other than the first area 22a, and six search coils 20 of the six magnetic units 11 are connected in series (second detection circuit 23b to fourth detection circuit 23d). By measuring the induced voltages generated in the six search coils 20 for each area, the control device can calculate the amount of magnetic flux change when the magnetic flux disappears for each area. This allows the control device to detect for each area that the mold 7 magnetically attracted to the magnetic plate 8 has moved or peeled off from the magnetic plate 8. In addition, when the total amount of magnetic flux change in each area exceeds a predetermined value, the control device determines that there is a risk of the mold 7 falling off the magnetic plate 8.

[0022] In addition, in the six magnetic units 11 arranged in each of the areas 22, the coils 12 for reversing the magnetic poles of the alnico magnets 14 are connected in series to form a magnetic pole reversal circuit 25 (first magnetic pole reversal circuit 25a), and the end of the magnetic pole reversal circuit 25a is connected to a power supply (not shown). The magnetic units 11 in the other areas are also connected in series for each area (second magnetic pole reversal circuit 25b to fourth magnetic pole reversal circuit 25d). Therefore, when the control device determines that there is a risk of the mold 7 falling off the magnetic plate 8, the magnetic clamp device 6 is once demagnetized and then switched to a magnetized state in order to return the magnetic force with which the magnetic clamp device magnetically attracts the mold to the initial state. The procedure is as follows. First, the magnetic flux when the magnetic units in three of the four areas can magnetically attract the mold without dropping it is measured or calculated in advance for each mold, and the measured or calculated value (hereinafter referred to as the measured value, etc.) is stored in the memory unit of the control device as a reference value. When the sum of the magnetic fluxes in three of the four areas reaches a reference value, the operation of the molding machine 1 is stopped (if the operation of the molding machine 1 is not affected, the molding machine 1 may be left in operation), and the magnetic unit 11 in one of the four areas 22 is switched from the magnetized state to the demagnetized state, and then switched back to the magnetized state (hereinafter referred to as the re-magnetization operation). This re-magnetization operation is also performed in sequence on the magnetic units in the other three areas. Therefore, unlike the above-mentioned conventional magnetic clamp device that requires the mold to be sandwiched between a fixed platen and a movable platen, the magnetic clamp device 6 of this embodiment does not require the mold 7 to be sandwiched. Therefore, the re-magnetization operation can be simplified in the magnetic clamp device of this embodiment.

[0023] Fig. 5 shows a second embodiment of the present invention. In this second embodiment, the same components (or similar components) as those in the first embodiment are generally designated by the same reference numerals. The second embodiment differs from the first embodiment in the following respects.

[0024] The magnetic plate 8 shown in FIG. 5 is divided into five areas. The central area of ​​the five areas is referred to as the first area 22a, the two areas arranged to the right and left of the first area 22a are collectively referred to as the second area 22b, and the two areas on the left and right outer sides of the second area 22b are collectively referred to as the third area 22c. The first area 22a is provided with 16 magnetic units 11, and the coils 12 for magnetic pole reversal of the 16 magnetic units 11 are connected in series, and the search coils 20 are also connected in series. In the eight magnetic units 11 of the second area 22b and the eight magnetic units of the third area 11, the coils 12 for magnetic pole reversal and the search coils 20 are also connected in series for each area, as in the first area 22a.

[0025] In the magnetic clamping device 6, molds 7 of different sizes may be magnetically attracted to the magnetic plate 8. For example, when the molds 7 are a large mold 7A large enough to cover all areas, a medium mold 7B large enough to cover the first area 22a and the second area 22b, and a small mold 7C large enough to cover only the first area 22a, the magnetic clamping device 6 magnetically attracts each mold 7 to the magnetic plate 8 in the following procedure. First, when the large mold 7A sandwiched between the fixed platen 2 and the movable platen 3 is magnetically attracted, the magnetic units 11 in the first area 22a and the second area 22b are activated to switch from a demagnetized state to a magnetized state. At this time, a magnetic flux is calculated from an induced voltage generated in the search coil 20 in the second area 22b. When the calculated magnetic flux value is equal to or greater than a predetermined value, the magnetic unit 11 in the third area 22c is activated. As a result, the large mold 7A is attracted and fixed by the magnetic units 11 in the three areas.

[0026] The procedure by which the magnetic clamp device 6 magnetically attracts the medium-sized mold 7B to the magnetic plate 8 is the same as that for the large-sized mold 7A. At this time, since almost no induced voltage is generated in the search coil 20 in the third area 22c, the control device detects that the size of the mold 7 is medium.

[0027] When the magnetic clamp device 6 magnetically attracts the small mold 7C to the magnetic plate 8, first, the magnetic units 11 in the first area 22a and the second area 22b are activated to switch from a demagnetized state to a magnetized state. At this time, since almost no induced voltage is generated in the search coil 20 in the second area 22b, the control device detects that the size of the mold 7 is small. In addition, since the magnetic units 11 in the first area 22a and the second area 22b can sufficiently magnetically attract the small mold 7 to the magnetic plate 8, no current is supplied to the coil 12 of the magnetic unit 11 in the third area 22c. Therefore, the magnetic unit 11 in the third area 22c is not activated, so that power consumption can be kept low.

[0028] The above embodiments can be modified as follows. In the above embodiment, the search coil 20 is provided for all the magnetic units 11, but the search coil 20 may be selectively provided for one of the magnetic units 11 arranged in the area 22. Also, instead of inserting only one turn of the search coil 20 into the annular space 18, the search coil 20 may be wound more than one turn or may be wound less than one turn. In the above embodiment, the magnetic plate 8 is divided into three or four areas, but this is not limiting, and the magnetic plate 8 may be divided into two areas or five or more areas. In the above embodiment, the search coil 20 and the magnetic pole reversal coil 12 are separate coils, but the magnetic pole reversal coil 12 may be switched and used as the search coil 20. When the magnetic pole reversal coil 12 is used as the search coil 20, a switching circuit is provided. The magnetic pole reversal coil 12 is wound multiple times around the bobbin 13, which has the advantage of improving sensitivity compared to a case where the number of turns is smaller. The search coil 20 may be arranged so as to be wound around the outer periphery of the magnetic pole member 15 or the outer periphery of the Alnico magnet, instead of being wound around the outer periphery of the non-magnetic member 16. The warning device is not limited to the LED display device exemplified above, and may be a speaker, a warning lamp, or any other device that allows the type of warning to be recognized. In the above embodiment, one end of the first alnico magnet 14a of the first magnetic unit 11a is magnetized to the S pole and the other end to the N pole, and one end of the second alnico magnet 14b of the second magnetic unit 11b is magnetized to the N pole and the other end to the S pole. Alternatively, one end of the alnico magnets 14 of all the magnetic units 11 may be made to have the same magnetic pole. In this way, when both the end of the alnico magnet 14 facing the magnetic pole member and the end of the neodymium magnet 19 have the same magnetic pole, the magnetic flux starts from the alnico magnet 14 and returns to the magnetic pole member 15, the mold 7, the magnetic plate 8, and the alnico magnet 14. At this time, the mold 7 is magnetically attracted to the attraction surface 9 of the magnetic clamp device 6. When the end of the alnico magnet 14 facing the magnetic pole member 15 and the end of the neodymium magnet 19 are of different magnetic poles, the magnetic flux starts from the alnico magnet 14 and returns to the magnetic pole member 15, the neodymium magnet 19, the magnetic plate 8, and the alnico magnet 14. At this time, even if the mold 7 is brought close to the magnetic clamp device 6, it is not magnetically attracted to the magnetic clamp device 6. Instead of arranging a plurality of magnetic units 11 in each of the areas 22, one magnetic unit 11 may be arranged in one area. In this case, the detection circuit is composed of one search coil and wiring connecting the search coil and the control device. [Explanation of symbols]

[0029] 7: mold (object to be magnetically attracted), 9: attraction surface, 8: magnetic plate, 10: mounting hole, 11: magnetic unit, 12: coil for magnetic pole reversal, 14: Alnico magnet (reversible magnet), 20: search coil, 22: area, 22a: first area, 22b: second area, 23a: first detection circuit, 23b: second detection circuit, 24a: first magnetic pole reversal circuit, 24b: second magnetic pole reversal circuit.

Claims

[Claim 1] a magnetic plate (8) having an attraction surface (9) for magnetically attracting an object (7) to be magnetically attracted; A plurality of mounting holes (10) opened in the suction surface (9); a magnetic unit (11) provided for each of the mounting holes (10); The magnetic unit (11) comprises: A magnetic pole reversal coil (12); a reversible magnet (14) whose magnetic poles are reversed by a current flowing in one direction through the magnetic pole reversal coil (12) and whose magnetic poles are returned to the state before the reversal by a current flowing in the other direction opposite to the one direction; a search coil (20) in which an induced voltage is generated by a change in magnetic flux passing through the reversible magnet (14); The magnetic plate (8) is divided into a plurality of areas (22), and a plurality of the magnetic units (11) are arranged in a first area (22a) that is one of the plurality of areas (22); the search coils (20) of the plurality of magnetic units (11) arranged in the first area (22a) are connected in series, and a first detection circuit (23a) is formed by the plurality of search coils (20) in the first area (22a); the search coils (20) of the magnetic units (11) arranged in a second area (22b) different from the first area (22a) are connected in series, and a second detection circuit (23b) is formed by the search coils (20) in the second area (22b); the magnetic pole reversal coils (12) of the plurality of magnetic units (11) arranged in the first area (22a) are connected in series, and a first magnetic pole reversal circuit (24a) is formed by the plurality of magnetic pole reversal coils (12) in the first area (22a); a second magnetic pole reversal circuit (24b) is formed by the magnetic pole reversal coils (12) of the plurality of magnetic units (11) arranged in the second area (22b); A magnetic clamp device characterized in that the size of the magnetically attracted object (7) attracted to the magnetic plate (8) is detected by a control device connected to the first detection circuit (23a) and the second detection circuit (23b) from the magnetic flux detected by the first detection circuit (23a) and the second detection circuit (23b).

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