Magnetic clamping device

Abstract

To provide a magnetic clamping device capable of easily separating even when an object to be clamped itself is magnetized by residual magnetism in an open state.SOLUTION: A magnetic pad 3 disposed in an accommodation hole 2a of a plate body 2 has: a magnetic core 4 having a pad surface PS; a reversible magnet 8 having magnetic polarity capable of being reversed; and an irreversible magnet 7 having magnetic polarity incapable of being reversed, provided surrounding the magnetic core 4 between the magnetic core 4 and a side wall 2b of the accommodation hole 2a. The magnetic core 4 is provided with a main body core 5 having a space 5a open toward the reversible magnet 8 side, with the back side of a ceiling surface 5d of the space 5a being the pad surface PS, and a movable core 6 movable in the space 5a. When a magnetic clamping device 1 is in a clamped state, a top surface 6d of the movable core 6 comes into contact with the ceiling surface 5d, and when the magnetic clamping device 1 is in an open state, a gap is generated between the top surface 6d and the ceiling surface 5d.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a magnetic clamping device.

[0002] A magnetic clamping device for an injection molding machine that utilizes magnetic attraction is known as a fixing device for an object to be clamped, such as a mold. The magnetic clamping device is a device that magnetically fixes a mold to a plate body made of a magnetic material attached to a platen of an injection molding machine. The plate body is provided with a plurality of magnetic pads, and each magnetic pad has a non-reversible magnet (e.g., a neodymium magnet) whose magnetic polarity is non-reversible provided around a magnetic pole and a reversible magnet (e.g., an alnico magnet) whose magnetic polarity is reversible provided on the back side of the magnetic pole. By controlling the magnetic polarity of the alnico magnet with a coil, it is possible to switch between an open state in which the magnetic flux of the non-reversible magnet passes through the reversible magnet and a clamped state in which the magnetic flux of the non-reversible magnet passes through the mold.

[0003] For example, according to Patent Document 1, a magnet unit for a magnetic clamping device has a magnetic body having a pair of flat surfaces, one of which serves as an attraction surface for attracting an object to be clamped, an RTB-based permanent magnet (e.g., a neodymium magnet) arranged around the side surface of the magnetic body, an Fe-Cr-Co-based permanent magnet arranged opposite the other flat surface of the magnetic body, and a coil arranged around the side surface of the Fe-Cr-Co-based permanent magnet.

[0004] By using an Fe-Cr-Co permanent magnet, which has an easier-to-adjust magnetic flux amount, instead of an alnico magnet, the magnetic flux amounts of the RTB permanent magnet and the alnico magnet can be precisely matched, making it easier to remove the clamped object when unclamping.

[0005] According to Patent Document 2, a magnet unit having a structure in which a coil is wound around a hard magnetic body is installed on the mold mounting surface of a platen, and the hard magnetic body is magnetized to become a permanent magnet by passing current through the coil, thereby attracting the mold, and the hard magnetic body is demagnetized by passing current through the coil to lose its magnetic force, and the mold is removed from the platen. During demagnetization, multiple pulse currents whose polarity alternates and whose amplitude gradually decreases are applied to the coil. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2021-153179 A [Patent Document 2] Japanese Patent Application Publication No. 9-174559 DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0007] The clamped object is a magnetic material and has a certain coercive force. When the magnetic flux of the non-reversible magnet passes through the clamped object, the clamped object itself remains magnetized due to residual magnetism even when the clamped object transitions from the clamped state to the released state. Therefore, in order to remove the clamped object from the magnetic clamping device, a removal force that is strong enough to overcome this residual magnetism is required.

[0008] The technology of Patent Document 1 does not take into consideration the magnetism remaining in the object to be clamped. In addition, the technology of Patent Document 2 makes it possible to demagnetize the die itself as well as the hard magnetic material by demagnetizing the hard magnetic material. However, this technology cannot be applied to a magnetic clamping device that uses a non-reversible magnet.

[0009] An object of the present invention is to provide a magnetic clamping device that can easily separate objects to be clamped even when the objects are themselves magnetized due to residual magnetism in the open state. [Means for solving the problem]

[0010] The present invention provides a magnetic clamping device having a plate body made of a magnetic material with a number of magnetic pads arranged in receiving holes on the surface thereof, The magnetic pad includes a magnetic core having a pad surface on the front side that contacts the magnetic body to be fixed, a reversible magnet that is disposed on the rear side of the magnetic core and has a reversible magnetic polarity, and a non-reversible magnet that is disposed between the magnetic core and a side wall of the receiving hole and surrounds the magnetic core and has a non-reversible magnetic polarity, The magnetic core includes a main core having a space that is open toward the reversible magnet, and the top surface of the space is the pad surface on the back side of the main core, and a movable core that is movable within the space. The present invention is characterized in that when in a clamped state in which the magnetic flux of the non-reversible magnet passes through the object, the ceiling surface of the movable core abuts against the ceiling surface, and when in an open state in which the magnetic flux of the non-reversible magnet passes through the reversible magnet, a gap is generated between the top surface of the movable core and the ceiling surface. Effect of the Invention

[0011] According to the present invention, by dividing the magnetic core into a movable core and a main core, when the magnetic flux of the non-reversible magnet is in an open state passing through the reversible magnet, a gap is created between the top surface of the movable core and the ceiling surface, thereby reducing the residual adhesive force. [Brief description of the drawings]

[0012] [Figure 1] 1A is an enlarged cross-sectional view of a magnetic pad of a magnetic clamp device, and FIG. 1B is an exploded perspective view of a magnetic core of the magnetic pad. [Diagram 2] 13A and 13B are diagrams showing how a movable core moves within a main core. [Diagram 3] 3A and 3B are diagrams for explaining the evaluation environment, where FIG. 3A is a diagram for explaining the evaluation tool, and FIG. 3B is a diagram for explaining the range of the magnetic pads to be evaluated. [Figure 4] FIG. 13 is a diagram showing experimental results. [Diagram 5]FIG. 13 is a diagram for explaining another embodiment. [Figure 6] FIG. 13 is a diagram for explaining another embodiment. BEST MODE FOR CARRYING OUT THEINVENTION

[0013] The following describes an embodiment of the present invention. [Example 1] FIG. 1A is an enlarged cross-sectional view of a magnetic pad 3 of a magnetic clamping device, and FIG. 1B is an exploded perspective view of a magnetic core 4 of the magnetic pad 3. As shown in FIG.

[0014] In FIG. 1A, the magnetic clamp device 1 includes a plate body 2 made of a magnetic material, a housing hole 2a on the front side of the plate body 2, and a magnetic pad 3 disposed therein. The front surface (pad surface PS) of the magnetic pad 3 is an attraction surface that contacts and magnetically attracts an object to be clamped. The magnetic pad 3 includes a magnetic core 4, a non-reversible magnet 7 (e.g., a neodymium magnet) whose magnetic polarity is non-reversible and disposed between the side wall 2b of the housing hole 2a so as to surround the magnetic core 4, a reversible magnet 8 (e.g., an alnico magnet) whose magnetic polarity is reversible and disposed on the back side of the magnetic core 4, a bobbin 9 disposed around the reversible magnet 8, and a coil 10 wound around the bobbin 9. The back side of the reversible magnet 8 contacts the plate body 2. The front surface of the magnetic core 4 is the pad surface PS of the magnetic pad 3.

[0015] The magnetic core 4 and the reversible magnet 8 have through holes 4a and 8a, respectively, along the central axis c, and the through holes 4a and 8a communicate with each other. A deep countersink 13 is provided at the entrance of the through hole 4a to accommodate the head 12a of the bolt 12. The bolt 12 fixes the magnetic core 4 and the reversible magnet 8 to the plate body 2 via a seal material 12b (seal washer).

[0016] The magnetic core 4 is in contact with the non-reversible magnet 7 along the outer periphery 4b of its outer periphery. A seal material 11 (O-ring) is provided on the upper side of the non-reversible magnet 7 to enhance watertightness.

[0017] The adjustment recess 14 is a recess that is similar to the outer peripheral shape of the magnetic core 4 or the circular shape of the inner peripheral side of the non-reversible magnet 7, and is centered on the central axis c of the magnetic core 4. The adjustment recess 14 is provided around the deep countersink 13 and at the center of the pad surface PS. The reason why the adjustment recess 14 is not provided on the outer peripheral side of the magnetic core 4 is that if the adjustment recess 14 is provided on the outer peripheral side of the magnetic core 4, only a long path will remain from the non-reversible magnet 7 to the mold.

[0018] The magnetic core 4 includes a main core 5 and a movable core 6. The main core 5 and the movable core 6 are integrally formed from a ferromagnetic material such as steel. FIG. 1B shows the main core 5. The main core 5 has a space 5a that opens toward the surface on the reversible magnet 8 side. The back side of the ceiling surface 5d of the space 5a is the pad surface PS. In this embodiment, the space 5a is donut-shaped and concentric with the central axis c, the first inner peripheral surface 5b and the second inner peripheral surface 5c are parallel to the central axis c, and the ceiling surface 5d is a surface perpendicular to the central axis c.

[0019] The movable core 6 has a shape that almost fills the space 5a, and slides in the space 5a in the direction of the central axis c. In this embodiment, the movable core 6 is in a doughnut shape that is concentric with the central axis c. The first outer peripheral surface 6b and the second outer peripheral surface 6c are parallel to the central axis c, and the top surface 6d and the bottom surface 6a are surfaces perpendicular to the central axis c. The bottom surface 6a is almost equal to the opening of the space 5a toward the surface on the side of the reversible magnet 8. On the other hand, the length t of the first outer peripheral surface 6b and the second outer peripheral surface 6c in the direction of the central axis c is shorter than the length d of the first inner peripheral surface 5b and the second inner peripheral surface 5c in the direction of the central axis c by a difference st (=dt). The movable core 6 can move in the space 5a in the direction of the central axis c by the difference st in the direction of the central axis c.

[0020] FIG. 2 shows how the movable core 6 moves in the main core 5. In FIG. 2A, the magnetic clamp device 1 is shown in a clamped state, and FIG. 2B shows an open state. In FIG. 2A, the magnetic clamp device 1 has a loop φ1 in which the magnetic flux returns to the non-reversible magnet 7 via the non-reversible magnet 7, the magnetic core 4, the mold M (shown by a two-dot chain line), and the plate body 2, and a loop φ2 in which the magnetic flux returns to the non-reversible magnet 8 via the reversible magnet 8, the magnetic core 4, the mold M, and the plate body 2. The magnetic force of the non-reversible magnet 7 moves the movable core 6 of the magnetic core 4 to the upper side of the drawing in the direction of the central axis c, so that the magnetic flux passing through the loop φ1 can pass most easily, and the top surface 6d of the movable core 6 abuts against the ceiling surface 5d of the space 5a.

[0021] In both loops, the magnetic flux is concentrated so as to pass through positions on the outer periphery of the magnetic core 4, and the magnetic flux that passes through the center of the magnetic core 4 is small. This is because magnetic flux tends to form short paths, and the center of the magnetic core 4 has a long path from the non-reversible magnet 7 to the mold, so the magnetic flux that passes through is small to begin with. This is also partly due to the adjustment recess 14 provided in the center of the magnetic core 4. And, in the places where a lot of magnetic flux passes through, the magnetic poles of the residual magnetic flux due to the holding force of the mold appear.

[0022] 2B, in the magnetic clamp device 1, the magnetic flux of the irreversible magnet 7 forms a loop φ3 that returns to the irreversible magnet 7 via the magnetic core 4, the reversible magnet 8, and the plate body 2. The movable core 6 of the magnetic core 4 moves downward in the drawing in the direction of the central axis c due to the magnetic forces of the irreversible magnet 7 and the reversible magnet 8, and the bottom surface 6a of the movable core 6 abuts against the reversible magnet 8, forming the loop φ3 so that the magnetic flux of the irreversible magnet 7 can pass most easily. A gap GP equivalent to the difference st is generated between the top surface 6d of the movable core 6 and the ceiling surface 5d of the space 5a.

[0023] 2B, this is indicated by a loop φ4 remaining due to the holding force of the mold M. Since a gap GP exists at the end of this path so as to interrupt the loop φ4, the force of attraction of the mold M to the magnetic clamping device 1 is weakened.

[0024] The evaluation of the size of the gap GP (difference st) will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a diagram for explaining the evaluation environment, Fig. 3A is a diagram for explaining the evaluation tool 20, and Fig. 3B is a diagram for explaining the range of the magnetic pad 3 to be evaluated. Moreover, Fig. 4 shows the evaluation results.

[0025] In Fig. 3A, the evaluation tool 20 includes a leg 21 attached to the magnetic clamp device 1, a movable part 24 on which a dummy die 23 is attached by moving up and down the track of a guide rod 22, a drive part 25 for lifting the movable part 24, and a load sensor 27 for measuring the tensile force between an output shaft 26 of the drive part 25 and the movable part 24. The evaluation tool 20 is attached to the magnetic clamp device 1, and the dummy die 23 is attracted by the magnetic pad 3. In Fig. 3B, the dummy die 23 has a size indicated by a dotted line 28. The magnetic polarities of the many magnetic pads 3 arranged on the plate body 2 are arranged so that the magnetic polarities of adjacent magnetic pads are different from each other. In this example, a large number of N-pole magnetic pads 3 and S-pole magnetic pads 3 are arranged alternately, and the dummy die 23 is attracted to a total of four bipolar poles consisting of four N-pole magnetic pads 3 and four S-pole magnetic pads 3, the movable part 24 is raised by the driving part 25, and the tensile force when the dummy die 23 is peeled off from the magnetic pads 3 is measured by the load sensor 27. The dummy die 23 is made of SCM440H (chrome molybdenum steel).

[0026] In FIG. 4A, the tensile force was measured by changing the magnitude of the difference st. For the measurement, magnetic cores 4 with a difference st of 0 mm (a conventional one in which the magnetic core 4 is not divided into a movable core 6 and a main core 5), 0.2 mm, and 0.5 mm were prepared. In addition, a test was conducted on a case in which the magnetic cores 4 of the four N-pole magnetic pads 3 and the four S-pole magnetic pads 3 are all divided into a movable core 6 and a main core 5 (indicated as "ALL" in the figure). Then, a test was also conducted on a case in which the magnetic cores 4 of only the four N-pole magnetic pads 3 are divided into a movable core 6 and a main core 5, and the magnetic cores 4 of the four S-pole magnetic pads 3 are integrated (indicated as "N-pole only" in the figure). Note that the case in which the magnetic core 4 of only the S-pole magnetic pad 3 is divided into a movable core 6 and a main core 5 is the same as the case of "N-pole only", and will be omitted. The other configurations of the magnetic pads 3 are common.

[0027] The adhesive force did not decrease significantly when the magnetic core 4 of only the magnetic pad 3 having one magnetic pole was divided into the movable core 6 and the main core 5, and when the magnetic core 4 of the magnetic pad 3 having both magnetic poles was divided into the movable core 6 and the main core 5. In both cases, the adhesive force tends to decrease significantly as the difference st increases. As a result, it can be seen that in order to reduce the residual adhesive force, it is sufficient to at least divide the magnetic core 4 of only the magnetic pad 3 having one magnetic pole into the movable core 6 and the main core 5.

[0028] The holding force also differs depending on the material of the die. The residual adhesive force was measured for a dummy die 23 made of a different material. The measured dummy dies were made of SS400 (general structural rolled steel), S50C (carbon steel for mechanical construction), FC250 (gray cast iron), and SK3 (carbon tool steel). Figure 4B shows the measurement results for five types of materials, including the die material SCM440H that was measured earlier. There was not much difference in the die made of materials that have little residual magnetic flux to begin with, but when only the magnetic pole on the N pole side was used, the residual adhesive force could be reduced for both magnetic poles.

[0029] [Example 2] In the second embodiment, a gap is provided between the center side of the movable core 6, i.e., the second outer peripheral surface 6c, and the second inner peripheral surface 5c of the main core 5, and the spring 15 is disposed in the gap. In the first embodiment, the movable core 6 is shaped to almost fill the space 5a, and the movable core 6 is smaller than the space 5a by the difference st (=dt). In this embodiment, the length of the movable core 6 in the direction of the central axis c is shorter by the difference st as in the previous embodiment, but the movable core 6 is further smaller at its center. As described above, the magnetic flux passing through the center position of the magnetic core 4 is small, so the position of the spring 15 is selected to be between the second outer peripheral surface 6c and the second inner peripheral surface of the main core 5. The spring 15 is a compression spring, and the lower end of the spring 15 is fixed to the main core 5, and the upper end of the spring 15 is fixed to the movable core 6. The spring 15 acts to bias the movable core 6 toward the ceiling surface 5d of the main core 5. When in an open state in which the magnetic flux of the non-reversible magnet 7 passes through the reversible magnet 8, the magnetic forces of the non-reversible magnet 7 and the reversible magnet 8 attract the movable core 6 to the reversible magnet 8, and the spring 15 is used to assist in peeling it off from the reversible magnet 8. On the other hand, the spring 15 may be a tension spring instead of a compression spring so as to act to attract the movable core 6 to the reversible magnet 8. When the magnetic flux remaining in the mold is stronger than expected, the spring 15 is used conversely to assist in returning the movable core 6 to the reversible magnet 8.

[0030] [Example 3] In the first embodiment, the movable core 6 is doughnut-shaped, but may have other shapes. For example, as shown in FIG. 6, it may be cylindrical. In FIG. 6, only the magnetic core 4 is shown, and other configurations are omitted since they are the same. A cylindrical space 5a is also provided on the main core 5 side. The length of the movable core 6 in the direction of the central axis c is shorter by the difference st as in the previous embodiment, and the outer peripheral surface 6e of the movable core 6 slides in contact with the inner peripheral surface 5e of the main core 5. In an open state in which the magnetic flux of the non-reversible magnet 7 passes through the reversible magnet 8, the bottom surface 6a of the movable core 6 and the reversible magnet come into contact, and in a clamped state in which the magnetic flux of the non-reversible magnet 7 passes through the mold M, the top surface 6d of the movable core 6 and the ceiling surface 5d of the space 5a come into contact. [Explanation of symbols]

[0031] 1 Magnetic clamping device 2 Plate body 2a Receiving hole 2b side wall 3 Magnetic Pads 4 Magnetic Core 4a, 8a through hole 4b Outer periphery 5 Main body core 5a Space 5b 1st inner surface 5c 2nd inner surface 5d Ceiling surface 5e Inner surface 6 Movable Core 6a Bottom 6b First outer surface 6c 2nd outer surface 6d top surface 6e Outer surface 7 Non-reversible magnets 8 Reversible Magnets 9. Bobbin 10 Coil 11 Sealing material 12 Volts 12a head 12b Sealing material 13 Deep countersinking 14 Adjustment recess 15 Spring 20 Evaluation Instruments 21 Legs 22 Guide Rod 23 Pseudo-mold 24 Moving parts 25 Drive unit 26 Output shaft 27 Load Sensor 28 Dotted Line

Claims

1. A magnetic clamping device having a plate body made of a magnetic material and a number of magnetic pads arranged in receiving holes on a surface thereof, The magnetic pad includes a magnetic core having a pad surface on the front side that contacts the magnetic body to be fixed, a reversible magnet that is disposed on the rear side of the magnetic core and has a reversible magnetic polarity, and a non-reversible magnet that is disposed between the magnetic core and a side wall of the receiving hole and surrounds the magnetic core and has a non-reversible magnetic polarity, The magnetic core includes a main core having a space that is open toward the reversible magnet, and the top surface of the space is the pad surface on the back side of the main core, and a movable core that is movable within the space. A magnetic clamping device characterized in that, when in a clamped state in which the magnetic flux of the non-reversible magnet passes through the object, the top surface of the movable core abuts against the ceiling surface, and when in an open state in which the magnetic flux of the non-reversible magnet passes through the reversible magnet, a gap is generated between the top surface of the movable core and the ceiling surface.

2. 2. The magnetic clamp device according to claim 1, further comprising a spring for attracting said movable core to said non-reversible magnet within said space.

3. 3. The magnetic clamp device according to claim 1, wherein the pad surface has an adjustment recess at the center of the pad surface, the adjustment recess being similar to the outer peripheral shape of the magnetic core or the inner peripheral shape of the non-reversible magnet.

4. 2. The magnetic clamp device of claim 1, wherein the magnetic polarities of the multiple magnetic pads arranged on the plate body are arranged so that the magnetic polarities of adjacent magnetic pads are different magnetic polarities, and the magnetic core of a magnetic pad having at least one magnetic pole is divided into the movable core and the main body core.

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