JP5683826B2 - Magnetic clamp device - Google Patents

Description

  The present invention relates to a magnetic clamping device that magnetically attracts and fixes a ferromagnetic object to be fixed to a fixed surface, and particularly relates to a device that detects a change in a magnetic adsorption state.

  The magnetic clamp device may be used for fixing a mold in, for example, an injection molding machine or a press molding machine. An example thereof is disclosed in Patent Document 1. In the technique of Patent Document 1, a plurality of magnetic generation units are provided on the clamp plate. The magnetism generating unit uses an alnico magnet as a magnet whose polarity can be switched, and includes a polarity switching coil for switching the polarity of the alnico magnet. When clamping, the polarity of the alnico magnet is switched by passing a direct current in a predetermined direction through the polarity switching coil for a predetermined time. In the case of unclamping, a current in a direction opposite to the predetermined direction is passed through the polarity switching coil for a certain period of time to restore the polarity of the alnico magnet. If an impact force larger than the magnetizing force is applied to the mold for some reason, the mold may come off. In order to detect this, a detection coil is provided outside the polarity switching coil, and a voltage is induced in the detection coil based on a change in magnetic flux generated when the mold is about to be removed. The voltage induced in the detection coil is compared with the reference voltage in the comparator, and when the voltage is larger than the reference voltage, a signal for stopping the injection molding machine or press molding machine or generating an alarm is generated. .

JP 2005-515080 A

In the technique of Patent Document 1, a detection coil is disposed around a polarity switching coil. This is presumed to avoid an increase in the size of the magnetic clamp device because the magnetic clamp device becomes large if the installation space for the detection coil is secured separately from the polarity switching coil. However, with this arrangement of the detection coil, in addition to the magnetic flux change caused by the mold coming off the clamp plate, the magnetic flux change generated in the polarity switching coil may be detected and erroneously detected. For example, a change in the magnetic flux applied to the polarity switching coil may cause a change in magnetic flux in the detection coil, and the voltage may be induced in the detection coil, or a voltage based on noise may be generated in the detection coil. There is.

  It is an object of the present invention to provide a magnetic clamp device that can prevent erroneous detection even when a detection coil is arranged around a polarity switching coil.

In the magnetic clamp device according to one aspect of the present invention, at least one magnetism generating unit is disposed on a fixed surface, for example, a clamp surface, to which a ferromagnetic fixed object, for example, a mold is fixed. At least one magnetism generating unit has a magnet whose polarity can be switched and a polarity switching coil which is arranged around the magnet whose polarity can be switched and which switches the polarity of the magnet whose polarity can be switched. When the polarity of the magnet whose polarity can be switched is switched by passing a current through the coil for switching polarity, in the magnetic clamping device, the fixed object is magnetically attracted to the fixed surface. A detection coil for detecting a change in magnetic flux is provided around the polarity switching coil of the at least one magnetism generating unit. A plurality of magnetism generating units may be provided, and a detection coil may be provided for each of these predetermined units. The induced voltage of the detection coil is zero or gradually increases depending on the state of the fixed object with respect to the fixed surface, or the maximum value is larger than the maximum value of the gradually increasing value, and the generation period is the gradually increasing value. It has a pulse shape shorter than the period of the maximum value. Each detection coil is preferably connected in series. The first comparison means compares the induced voltage induced in the detection coil with a predetermined first threshold voltage. When the induced voltage is equal to or higher than the first threshold voltage, the first output is output as an output signal. Occur. The first threshold voltage is set such that when the induced voltage of the detection coil is gradually increased, the gradually increased voltage is exceeded. When the first output continues for a predetermined first time longer than the generation period of the pulse-like induced voltage, the abnormality determination means outputs an abnormality determination signal.

  In the magnetic clamp device configured as described above, when the voltage applied to the polarity switching coil fluctuates, a magnetic flux change occurs in the detection coil due to the fluctuation, and an induced voltage equal to or higher than the first threshold voltage is generated in the detection coil. Occurs and the first comparing means generates a first output. However, this voltage variation hardly continues, does not continue over the first set time, the induced voltage generated in the detection coil disappears, and the first output also disappears. Therefore, the voltage fluctuation is not erroneously detected. On the other hand, when the fixed object magnetically clamped on the fixed surface is about to come off or shift, the change in magnetic flux in the detection coil continuously occurs, so that the induced voltage of the detection coil is the first threshold value. The state of being equal to or higher than the voltage continues for the first set time. Therefore, when the first output continues for the first set time, the abnormality determination means can determine that the fixed object is about to be detached and outputs an abnormality determination signal. Thereby, erroneous detection can be prevented.

  In addition, when the voltage induced in the detection coil is integrated and the integrated value becomes equal to or higher than a predetermined value, it can be determined that the fixed object is about to be detached or shifted. However, in this case, as a result of integrating the noise induced in the detection coil over a long period of time, it may become equal to or more than the predetermined value. In this case, erroneous detection occurs. On the other hand, according to the method for determining whether the state where the induced voltage is equal to or higher than the first threshold voltage continues for the first set time, no erroneous detection due to noise occurs.

Second comparing means is provided for comparing the induced voltage with a second threshold voltage and generating a second output as an output signal when the induced voltage is equal to or higher than the second threshold voltage . The second threshold voltage is set to a value that exceeds the pulsed induced voltage when the induced voltage is pulsed and is larger than the first threshold voltage. The abnormality determination means immediately outputs the abnormality determination signal when the second output occurs.

  The fixed object may rapidly come off the fixed surface. In such a case, the change in magnetic flux generated in the detection coil is larger than the case where the fixed object continues to be detached from the fixed surface, and instantaneously exceeds the second threshold voltage. Even in such a case, if the abnormality determination signal is output after the first output has continued for the first set time, it takes time to detect that the fixed object has been removed. Therefore, the abnormality determination unit immediately outputs an abnormality determination signal when the second output occurs. As a result, it is found that the fixed object is detached from the fixed surface instantly.

  It should be noted that the abnormality determination means may output an abnormality determination signal when the second output continues for a predetermined second set time. The second set time is preferably shorter than the first set time.

  With this configuration, even if an induced voltage that is equal to or higher than the second threshold voltage is temporarily generated due to, for example, noise with large pulse characteristics, erroneous detection based on the induced voltage can be prevented.

  Even when the first output is occurring and the first set time has not elapsed, the abnormality determination means may be configured to output the abnormality determination signal when the second output is generated. If comprised in this way, even if it remove | deviates rapidly from the state which the fixed target object has come off from the fixed surface, it can detect that the fixed target object came off from the fixed surface instantly.

  Further, the abnormality determination signal can be output as a display signal to the display means, or the abnormality determination signal can be output as an emergency stop signal to the device provided with the clamp device.

  Third comparing means for comparing the induced voltage with a third threshold voltage that is a value between the first and second threshold voltages is provided, and the third comparing means has the induced voltage that is a third threshold voltage. A third output is generated at the above time, and the abnormality determination means can output an abnormality determination signal when the third output is supplied. If comprised in this way, the magnetic flux change larger than the case where the metal mold | die is about to remove | deviate or slip | deviates, but it can also detect that the magnetic flux change which is completely removed has not arisen. Note that when the third output is also continuously output over a predetermined time, an abnormality determination signal may be output.

  The abnormality determination signal can be used as a signal for operating the alarm device, can be used as a signal for stopping the device provided with the magnetic clamp device, or is again supplied to the polarity switching coil for a certain period of time. It can also be used as a command signal for passing a current in a predetermined direction.

  As described above, according to the present invention, the detection coil can be disposed in the vicinity of the polarity switching coil 8 to save space and prevent erroneous detection.

It is a front view of the magnetic clamp device of one embodiment of the present invention. FIG. 2 is a partially omitted enlarged longitudinal sectional view of the magnetic clamp device of FIG. 1. It is a block diagram of the magnetic clamp apparatus of FIG. It is a wave form diagram which shows the relationship between the induced voltage of a detection coil and the 1st threshold voltage in the magnetic clamp apparatus of FIG. It is a wave form diagram which shows the relationship between the induced voltage of a detection coil and the 2nd threshold voltage in the magnetic clamp apparatus of FIG. It is a flowchart which shows the process which the abnormality determination circuit shown in FIG. 3 performs.

  A magnetic clamping device according to an embodiment of the present invention is a ferromagnetic fixed object, for example, a fixed-side ferromagnetic mold or a movable-side ferromagnetic mold in a machine such as an injection molding machine. As shown in FIG. 1, these are magnetically attracted to a fixed surface forming member, for example, a fixed surface 2 a of a clamp plate 2. The clamp plate 2 is a ferromagnetic body, for example, a substantially rectangular plate made of steel, and is fixed to a platen (not shown) by bolts 3.

  At least one, for example, a plurality of magnetism generating units 4 are provided on the fixed surface of the clamp plate 2. In this embodiment, four magnetism generating units 4 are arranged adjacent to each other in the vertical and horizontal directions, two of these four units are adjacent to each other in the vertical direction, and two are horizontally adjacent to each other, for a total of eight magnetism generating units. 4 constitutes one group. Four groups are arranged symmetrically about the center of the fixed surface 2a. In FIG. 1, reference numeral 5 denotes a hole for an eject pin of an injection molding machine.

  As shown in FIG. 2, the magnetism generating unit 4 is disposed in a recess 7 opened to the fixed surface 2 a side of the clamp plate 2, and has a polarity switching magnet, for example, an alnico magnet 6. The alnico magnet 6 is formed in a rectangular flat plate shape, and a polarity switching coil 8 is arranged on the outer periphery so as to surround the alnico magnet 6. The polarity of the alnico magnet 6 can be switched by passing a current through the polarity switching coil 8 in a predetermined direction for a predetermined time. This state of switching the polarity is maintained until a current is passed through the polarity switching coil 8 in a direction opposite to the above for a predetermined time. A ferromagnetic block, for example, a steel block 10 is disposed on the upper surface side of the alnico magnet 6. The steel block 10 is also a rectangular flat plate. A permanent magnet, for example, a neodymium magnet block 12 is disposed along each side of the steel block 10 so as to surround the outer periphery of the steel block 10. The neodymium magnet block 12 is shared by the adjacent magnetism generating units 4. Reference numeral 14 denotes a bolt for fixing the steel block 10 and the alnico magnet 6 to the clamp plate 2.

  In this magnetic clamping device, the polarity of the alnico magnet 6 can be switched by passing a current through the polarity switching coil 8 of each magnetism generating unit 4 while the mold is in contact with the fixed surface 2a. As a result, the mold is magnetically attracted and clamped. In addition, the mold can be unclamped by flowing a current in the opposite direction to the polarity switching coil 8 for a certain period of time. Since the principle of clamping and unclamping by this magnetic clamping device is known, further explanation is omitted.

  A detection coil 16 is arranged on the outer peripheral surface of the plurality of pre-selected polarity switching coils 8 among the magnetic generation units 4 so as to surround them. The reason why the detection coil 16 is arranged in this way is to save space.

  When the mold is displaced on the fixed surface 2a or the mold is detached from the fixed surface 2a, the magnetic flux of the alnico magnet 6 changes. Based on this magnetic flux change, a voltage is induced in each detection coil 16. As shown in FIG. 3, each detection coil 16 is connected in series. As a result, the induced voltages of the detection coils 16 are added and supplied to the control device 18. In the control device 18, the added induced voltage of each detection coil 16 is supplied to first to third comparison means, for example, comparators 22, 24, and 26, via the relay 20. The relay 20 is opened when the mold is unclamped so that the induced voltage of each detection coil 16 is not supplied to the comparators 22, 24, and 26. After the mold is clamped, the relay 20 is closed, and the added value of the induced voltage of each detection coil 16 is supplied to the comparators 22, 24 and 26.

  The comparator 22 is supplied with the first threshold voltage from the first threshold voltage source 28. The comparator 22 compares the added value of the induced voltage of each detection coil 16 with the first threshold voltage, and outputs the output when the added value of the induced voltage of each detection coil 16 is smaller than the first threshold voltage. In the first state, for example, the L level, and when the sum of the induced voltages of the detection coils 16 is equal to or higher than the first threshold voltage, the output is in the second state, for example, the H level. For example, the first threshold voltage is set to a value that is assumed to exceed the added value of the induced voltage generated in each detection coil 16 when the mold is displaced from the fixed surface 2a. In addition, the first threshold voltage is set to a value larger than the noise that is normally predicted to be generated in a state where no induced voltage is generated, but is smaller than the noise that is predicted to be suddenly generated. It is.

  The comparator 24 is supplied with the second threshold voltage from the second threshold voltage source 30. The comparator 24 compares the added value of the induced voltage of each detection coil 16 with the second threshold voltage, and outputs the output when the added value of the induced voltage of each detection coil 16 is smaller than the second threshold voltage. In the first state, for example, the L level, and when the sum of the induced voltages of the detection coils 16 is equal to or higher than the second threshold voltage, the output is in the second state, for example, the H level. For example, the second threshold voltage is set to a value that is assumed to exceed the added value of the induced voltage generated in each detection coil 16 when the mold is detached from the fixed surface 2a. The second threshold voltage is set to a value larger than the first threshold voltage.

  The comparator 26 is supplied with the third threshold voltage from the third threshold voltage source 32. The comparator 26 compares the added value of the induced voltage of each detection coil 16 with the third threshold voltage, and outputs the output when the added value of the induced voltage of each detection coil 16 is smaller than the third threshold voltage. In the first state, for example, L level, when the added value of the induced voltage of each detection coil 16 is equal to or higher than the third threshold voltage, the output is in the second state, for example, H level. The third threshold voltage is set to a value larger than the first threshold voltage and smaller than the second threshold voltage.

  The outputs of the comparators 22, 24, and 26 are supplied to an abnormality determination unit, for example, an abnormality determination circuit 34. In the abnormality determination circuit 34, the comparator 22 generates an H level output. That is, as shown in FIG. 4A, the sum of the induced voltages of the detection coils 16 is equal to or higher than the first threshold voltage. When the state continues for a predetermined time T, for example, 10 milliseconds, an abnormality determination signal is output as shown in FIG. In addition, since the abnormality determination signal is output when the comparator 22 generates an H level output over a predetermined time T, noise exceeding the first threshold voltage suddenly occurs. However, it is possible to prevent erroneous detection based on this noise. In addition, a magnetic flux change caused by a change in the voltage applied to the polarity switching coil 8 is not erroneously detected.

  Further, the abnormality determination circuit 34, when the comparator 24 generates an H level output, that is, when the added value of the induced voltage of each detection coil 16 is equal to or higher than the second threshold as shown in FIG. As shown in FIG. 5B, an abnormality determination signal is immediately output. As a result, it is detected that a large magnetic flux change that causes the mold to come off occurs.

  Further, the abnormality determination circuit 34 is configured such that when the comparator 26 generates an H level output, that is, the sum of the induced voltages of the detection coils 16 is equal to or higher than the third threshold voltage, and the second threshold voltage is exceeded. Is also smaller, an abnormality determination signal is output. As a result, it is possible to detect that the magnetic flux change is larger than when the mold is about to come off or about to be displaced, but the magnetic flux change is not so great that it is completely removed.

  Any abnormality determination output can be used as a signal for displaying an abnormality on the abnormality output display unit 36 shown in FIG. 2, or can be used as an emergency stop signal for emergency stop of the injection molding machine. Alternatively, it can be used as a signal for instructing the magnetizing coil control circuit 38 to flow a current in a predetermined direction again for a predetermined time.

  The control unit 18 is actually constituted by a microcomputer, and the functions of the comparators 22, 24, and 26 are also realized by the microcomputer. Further, the processing executed by the abnormality determination circuit 34 is represented by a flowchart as shown in FIG. 6, for example. Note that a timer to be described later is reset when this process is executed.

  That is, the abnormality determination circuit 34 first determines whether there is a first output (H level output) from the comparator 22 (step S2). If the answer to this determination is no, the abnormality determination circuit 34 resets a timer for measuring a predetermined time T, which will be described later (step S4), and executes step S2 again.

  If the answer to the determination in step S2 is yes, the abnormality determination circuit 34 counts up a timer for measuring a predetermined time T (step S6). Next, the abnormality determination circuit 34 determines whether there is a second output (H level output) from the comparator 24 (step S8). If the answer to this determination is no, it is determined whether there is a third output (H level output) from the comparator 26 (step S10). If the answer to this determination is no, the abnormality determination circuit 34 determines whether the timer has timed up by measuring a predetermined time T (step S12). If the answer to this determination is no, the abnormality determination circuit 34 executes again from step S2.

  If the answer to the determination in step S12 is yes, since the first output has continued for a predetermined time, it is determined that the mold is displaced or disengaged, and the abnormality determination circuit 34 outputs the abnormality determination output. Is output (step S14). And the timer mentioned above is reset (step S16), and a process is complete | finished.

  If the determination in step S8 is yes, the abnormality determination circuit 34 outputs an abnormality determination output (step S18), stops the machine, resets the timer described above (step S20), and ends the process. As described above, even when it is determined whether or not the mold is shifted, if the second output is generated, it can be determined that the mold is detached.

  If the answer to the determination in step S10 is yes, the abnormality determination circuit 34 outputs an abnormality determination output (step S22), resets the timer described above (step S24), and ends the process.

  In the above embodiment, an example has been shown in which the magnetic clamping device magnetically clamps the mold in the injection molding machine. However, the present invention is not limited to this. For example, the magnetic clamping device in the press molding machine magnetically molds on the fixed surface. It can be used to clamp, or it can be used to magnetically clamp a workpiece to a fixed surface in a machine tool. The magnetic clamping device can also be used to fix the door so that the door cannot be manually opened when the door is closed, for example, in an automatic door device. When used in this automatic door, only one magnetism generating unit can be used. In the above embodiment, when the second output occurs, the abnormality determination signal is output immediately. However, when the second output occurs over a predetermined second set time, the abnormality determination signal may be output. it can. In the above embodiment, the value obtained by adding the induced voltages of the plurality of detection coils 16 is compared with the first to third threshold voltages. However, at a minimum, the induced voltage of one detection coil 16 is the first to third threshold voltages. It can also be compared with a threshold voltage. In the above embodiment, the comparator 26 is provided and configured to output an abnormality determination signal when an induced voltage equal to or higher than the third threshold voltage is generated. However, in some cases, the comparator 26 may be removed. it can. Similarly, the comparator 24 can be eliminated. In the above-described embodiment, the voltage generated in the detection coil 16 is supplied to the comparators 22, 24, and 26. However, the voltage generated in the detection coil 16 is supplied to the comparators 22, 24, and 26 via, for example, a photocoupler. It can also be configured.

2a Fixed surface 4 Magnetic generation unit 22 Comparator (first comparison means)
24 comparator (second comparing means)
34 Abnormality determination circuit (abnormality determination means)

Claims (4)

At least one magnetic generation unit is arranged on a fixed surface to which a ferromagnetic fixed object is fixed, and the at least one magnetic generation unit is arranged around a magnet capable of switching polarity and around the magnet capable of switching polarity. And a polarity switching coil for switching the polarity of the polarity switchable magnet, and when the polarity of the polarity switchable magnet is switched by passing a current through the polarity switching coil, the fixed A magnet clamping device in which an object is magnetically attracted to the fixed surface,
Provided around the polarity switching coil of the at least one magnetism generating unit, and generates an induced voltage according to a change in magnetic flux, and the induced voltage is zero according to a state of the fixed object with respect to the fixed surface. A detection coil that is pulse-like or gradually increasing, or whose maximum value is larger than the maximum value of the gradually increasing and whose generation period is shorter than the period in which the increasing value is the maximum value of the gradually increasing value ;
When the induced voltage of the detection coil is gradually increased, the first threshold voltage set so that the gradually increased voltage exceeds the induced voltage is compared, and when the induced voltage is equal to or higher than the first threshold voltage, an output is obtained. First comparing means for generating a first output as a signal;
When the induced voltage is in the form of a pulse, the induced voltage is compared with a second threshold voltage that is set to a value that exceeds the pulsed induced voltage and is greater than the first threshold voltage, and the induced voltage Second comparing means for generating a second output as an output signal when is equal to or higher than a second threshold voltage;
When the second output occurs, the abnormality determination signal is immediately output, and when the first output continues for a predetermined first time longer than the generation period of the pulsed induced voltage, the abnormality determination An abnormality determination means for outputting a signal;
Magnetic clamp device having. 2. The magnetic clamp device according to claim 1 , wherein the abnormality determination means outputs the abnormality determination signal when the second output continues for a predetermined second set time. 3. The magnetic clamp device according to claim 1, wherein when the first output is being generated and the first set time has not elapsed, and the second output is generated, the abnormality determination signal is output. Magnetic clamping device. 4. The magnetic clamping device according to claim 1 , further comprising a third comparison unit that compares the induced voltage with a third threshold voltage that is a value between the first and second threshold voltages. 3 is a magnetic clamp device in which the abnormality determination means outputs the abnormality determination signal when the induced voltage is equal to or higher than a third threshold voltage.

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