Patent Publication Number: US-2022227025-A1

Title: Adhesion force confirmation method and adhesion force confirmation device

Description:
FIELD OF THE INVENTION 
     The present invention relates to an adhesion force confirmation method and an adhesion force confirmation device capable of confirming that a mold is magnetically adhered to a magnetic clamping device with a sufficient adhesion force. 
     In a mold handling equipment such as an injection molding machine, a magnetic clamping device using a magnetic adhesion force is known as a device for fixing a mold. The magnetic clamping device is a technique for magnetically fixing a mold by attaching a magnetic plate to a platen. The plate has magnets with non-reversible polarity and magnets with reversible polarity (alnico magnet) to switch between a magnetic circuit that closes inside a plate and a magnetic circuit that passes through a mold by controlling the magnetic polarity of the alnico magnet with a coil. 
     The mold is magnetically adhered to the magnetic clamping device while maintaining its precise position. The mold is a heavy object, and if the mold is detached from the magnetic clamping device, it may lead to a serious accident. Therefore, the magnetic clamping device is provided with a means for detecting that the mold is displaced or floated. 
     For example, according to Patent Document 1, a plurality of magnetic adhesion units for fixing molds and detection means for detecting an operating state of the magnetic clamping device are provided. An exploring coil of this detection means is mounted outside a main coil of the magnetic adhesion unit. According to this, when the mold moves slightly with respect to the magnetic clamping device, a voltage is induced in the exploring coil to detect an abnormality in the magnetization state. 
     The induced voltage is function of product of the number of windings and a change rate of a magnetic flux, and a small change in the magnetic flux in a short time interval produces a large voltage. According to Patent Document 2, a technique is known in which a coil for switching the polarity of an alnico magnet is effectively used as a detection coil for detecting misaligning or floating of a mold. By increasing the number of coil windings, weak magnetic flux changes are detected to generate a higher induced electromotive force compared to noise. 
     Further, Patent Document 3 discloses what determines an abnormality when the voltage waveform induced in the coil continues for a predetermined time from the first threshold value, or when a voltage exceeding a second threshold value over the first threshold value is generated even for a short period of time. 
     PRIOR ART 
     Patent Documents 
     Patent Document 1: Japanese Patent Laid Open Publication No. 2005-515080 
     Patent Document 2: Japanese Patent No. 5385544 
     Patent Document 3: Japanese Patent No. 5683826 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     In patent documents 1, 2 and 3, when the induced voltage generated in the coil is measured and exceeds a threshold value set in a comparison circuit, an emergency situation is generated as the mold is misaligned or floated. In these technologies, the mold can be detected only when misalignment or float from the magnetic clamping device occurs, and it is not possible to confirm whether the mold is magnetically adhered with enough or just barely enough adhesion force. 
     On the other hand, there are various molds owned by users of mold handling device, such as area of contact surface with magnetic clamping device side, mold size, mold weight, and type of mold material. In addition, the magnetic adhesion force varies depending on a change in surface roughness caused by scratches or rust on the contact surface of the mold, and by adhesion of dust. Therefore, on the magnetic clamping device side, it is not possible to confirm whether the magnetically adhered mold is in a magnetic adhesion state with a margin or not. 
     The object of the present invention is to provide an adhesion force confirmation method and an adhesion force confirmation device, which can confirm that the mold magnetically adhered to the magnetic clamping device is magnetically adhered with sufficient adhesion force not to be pulled off the magnetic clamping device by a mold opening force of the mold handling device. 
     Means to Solve the Problem 
     The adhesion force confirmation method of the present invention, in an adhesion force confirmation method of a mold handling device including a magnetic clamping device that has a magnetizing coil, a reversible magnet whose magnetic poles are reversed according to a direction of an electric current flowing in the magnetizing coil, and a non-reversible magnet on opposite plates proximate to or separated from each other, and the mold is adhered and fixed to the plates by the magnetic force of the reversible magnet and the magnetic force of the non-reversible magnet, is characterized in that the electric current of the magnetizing coil is applied so that the magnetic clamping device exerts a weaker magnetic adhesion force than normal magnetization, and the mold handling device is operated, and then opposing platens are separated to test if the mold detaches from the plates, and if peeling is detected, a warning that the adhesion force cannot be guaranteed is issued to an operator, and if peeling is not detected, the electric current of the magnetizing coil is applied so that the magnetic clamping device exerts the magnetic adhesion force by the normal magnetization. 
     In addition, an adhesion force confirmation device of the present invention, in an adhesion force confirmation device of a mold handling device including a magnetic clamping device that has a magnetizing coil, a reversible magnet whose magnetic poles are reversed according to a direction of an electric current flowing in the magnetizing coil, and a non-reversible magnet on each of opposite plates proximate to or separated from each other, and the mold is adhered and fixed to the plates by the magnetic force of the reversible magnet and the magnetic force of the non-reversible magnet, is characterized in having an ignition circuit for controlling an amount of electric current of the magnetizing coil and a controller for controlling the magnetic clamping device or the mold handling device, and in that the controller controls the electric current of the magnetizing coil with the ignition circuit so that the magnetic clamping device exerts a magnetic adhesion force weaker than normal magnetization, and the mold handling device is operated, and then the opposing platens are separated to test if the mold detaches from the plates, and if peeling is detected, a warning is issued to the operator that the adhesion force cannot be guaranteed, and if peeling is not detected, the electric current of the magnetizing coil is controlled with the ignition circuit so that the magnetic clamping device exerts the magnetic adhesion force due to the normal magnetization. 
     Effects of Invention 
     According to the present invention, it is possible to guarantee adhesion in a state with a margin by once performing a test for whether or not peeling is performed by performing test magnetizing, and by then magnetizing with a normal magnetizing current Q 1  with an electric current larger than the test magnetizing current Q 2 . 
     The invention also has the effect of guaranteeing that the mold has sufficient adhesion force even when the magnetic adhesion force decreases due to a change in surface roughness caused by scratches or rust on the contact surface of the mold, and by adhesion of dust. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1E  show an injection molding machine and a magnetic clamping device.  FIG. 1A  is an overall view, and  FIGS. 1B to 1E  show configuration and action of the magnetic clamping device. 
         FIGS. 2A to 2C  show circuit and operation of a magnetic clamping device.  FIG. 2A  is a circuit diagram of the magnetic clamping device,  FIG. 2B  is a circuit diagram of a power supply, and  FIG. 2C  is a waveform diagram. 
         FIGS. 3A to 3B  show a processing flow of an adhesion force confirmation device.  FIG. 3A  is a processing flow corresponding to each mold, and  FIG. 3B  is a processing flow of a case where the first corresponding mold is continuously used. 
         FIGS. 4A to 4C  are explanatory diagrams showing a state where an injection molding machine, a magnetic clamping device, and a mold are installed, respectively. 
     
    
    
     PREFERRED EMBODIMENT OF THE INVENTION 
     Hereinafter, the adhesion force confirmation device according to this example of the present invention will be described. An example of an injection molding machine  1  is shown as a mold handling device. The adhesion force confirmation device is in a form of a processing program utilizing hardware assets of the injection molding machine  1  or magnetic clamping devices  10 ,  20  and executed on a controller  7  of the injection molding machine  1  or the magnetic clamping devices  10 ,  20 . 
     In  FIG. 1A , the injection molding machine  1  is provided with left and right facing platens  2 ,  3  on which molds M 1 , M 2  (see  FIG. 4 ) are mounted respectively, and a guide rod  9  for guiding and supporting the left side platen  2  to move forward and backward freely in a left-right direction. On the platens  2 ,  3 , the magnetic clamping devices  10 ,  20  for magnetically adhering the mold are mounted, respectively. Numeral  6  is a nozzle for injecting resin, numeral  7  is a controller with an input section and LCD display screen, and numeral  8  is an ejector rod for pushing the injection molded material out of the mold M 1 . Numerals  4 ,  5  are mold auxiliary fittings, respectively. The controller  7  controls operation of the injection molding machine  1  and the magnetic clamping devices  10 ,  20 . Since manufacturers that make the injection molding machine  1  and the magnetic clamping devices  10 ,  20  are usually different, the controllers  7  for the injection molding machine  1  and the magnetic clamping devices  10 ,  20  are often different, but in this example, they are shown as one unit to simplify the explanation. 
       FIG. 1B  is a front view of the magnetic clamping device  10 . A plurality of magnet blocks  11  are arranged on a front side of the magnetic clamping device  10 . In addition, a proximity sensor  12  and a magnetic flux coil (not shown) for detecting changes in magnetic flux are arranged. The ejector rod  8  is inserted into a through hole  13 . The magnetic clamping device  20  is almost the same as the magnetic clamping device  10  and the description thereof will be omitted, but the magnetic clamping device  20  is different in that the through hole  13  provided in the magnetic clamping device  10  does not exist. 
     The main body of the magnetic clamping device  10  is a plate (steel) PL made of magnetic material, and a large number of circular groove portions  14  are provided on the front side (the drawing, left side). A portion surrounded by each groove portion  14  corresponds to a magnet block  11 . 
       FIG. 1C  is an exploded sectional view taken along X-X line in  FIG. 1B . In the figure, the plate PL is integrally provided with a portion D 1  having a reduced steel thickness on an inner peripheral side of the groove portion  14  and a disk-shaped inner pole D 2  having a thicker steel inside the portion D 1 . A ring-shaped non-reversible magnet  15  is fitted into the portion D 1  from a back side of the plate PL. The non-reversible magnet  15  has magnetic poles on the inner peripheral side and outer peripheral side of the ring, which is its outer shape. For example, the inner peripheral side has an S pole and the outer peripheral side has an N pole. As the non-reversible magnet  15 , for example, a neodymium magnet can be used. Behind the non-reversible magnet  15 , a reversible magnet  18  composed of a disc-shaped alnico magnet  16  and a magnetizing coil  17  wound around the outside of the alnico magnet  16  are arranged. A disc-shaped joint iron  19  is fitted behind the reversible magnet  18 . The inner peripheral side of the non-reversible magnet  15  is magnetically coupled to the inner pole D 2 , and is magnetically coupled to the outer peripheral side (outer pole D 3 ) of the portion D 1  where the thickness on the outer peripheral side is thinned. Further, the alnico magnet  16  is magnetically coupled to the inner pole D 2  and the joint iron  19 , and the joint iron  19  is magnetically coupled to the outer pole D 3 . Further, the portion D 4  of the groove portion  14  is further thinned as compared with the other portions, so that it is easily magnetically saturated. Since the front side of the plate PL is entirely covered with the steel of the plate PL, the non-reversible magnet  15  and the reversible magnet  18  can be sealed from a work area where the mold M 1  is mounted. 
       FIG. 1D  shows a state when the magnetic clamping device  10  is in a demagnetized state. The alnico magnet  16  is a permanent magnet having an N pole on the front side of the plate PL (in the drawing, left side) and an S pole on the back side. As a result, the magnetic flux passes through the magnetic circuit composed of the non-reversible magnet  15 , the outer pole D 3 , the joint iron  19 , the alnico magnet  16 , and the inner pole D 2 . In this state, the magnetic flux does not leak to the front side of the plate PL, and the mold M 1  is not adhered. 
       FIG. 1E  shows a state when the magnetic clamping device  10  is in a magnetized state. By passing DC current through the magnetizing coil  17  from the outside, the magnetic poles of the alnico magnet  16  are inverted. The alnico magnet  16  is a permanent magnet having an S pole on the front side of the plate PL and an N pole on the back side. The polarity of the alnico magnet  16  is reversed, and the DC current may be passed for the time to magnetize the required magnetic flux. On the front side of the plate PL, both the non-reversible magnet  15  and the reversible magnet  18  are coupled to the inner pole D 2  as S poles. When the mold M 1  is pressed against the front side of the plate PL, these magnetic fluxes pass through the mold M 1 . As a result, a magnetic circuit composed of the non-reversible magnet  15 , the outer pole D 3 , the mold M 1  and the inner pole D 2 , and a magnetic circuit composed of the alnico magnet  16 , the outer pole D 3 , the mold M 1  and the inner pole D 2 , are formed. Since the alnico magnet  16  does not have a relatively high coercive force as a permanent magnet, when the mold M 1  is lost, the magnetic force from the front side of the plate PL toward the outside is immediately lost by the magnetic force of the non-reversible magnet  15 . 
       FIG. 2A  shows an electric circuit of the magnet blocks  11  of the magnetic clamping device  10 . Each magnet block  11  is provided with a magnetizing coil  17  for inverting the magnetic polarity of an alnico magnet (not shown) and a sensor coil  44  for measuring the adhesion force. The sensor coil  44  is a coil that detects changes in magnetic flux passing through the alnico magnet. The sensor coil  44  is wound around, for example, the alnico magnet. The sensor coils  44  of the magnet blocks  11  are connected in series, and detect changes in magnetic flux with respect to the entire magnetic clamping device  10 . 
       FIG. 2B  shows a power supply for driving the magnetizing coil  17  of all of the magnet blocks  11  of the magnetic clamping device  10 . The power supply is rectified by thyristor  46 ,  47  with respect to an external AC power supply  49 . The thyristor  46  is turned on when magnetizing, and the thyristor  47  is turned on when demagnetizing. Each of the thyristor  46 ,  47  is controlled by an ignition circuit  48  for an ignition angle θ. The ignition circuit  48  can change the ignition angle θ of the thyristor  46  according to the instruction of the controller  7 . The ignition circuit  48  can generate a trigger pulse TC for the thyristor  46  in a phase t 1  at a rising time of the AC power supply  49  or in a phase t 2  shifted by the ignition angle θ (see  FIG. 2C ). Hereinafter, the electric current flowing through the magnetizing coil  17  when the trigger pulse TC is generated at the time of the phase t 1  is referred to as “normal magnetizing current” Q 1 . Further, the electric current flowing when the trigger pulse TC is generated at the time of the phase t 2  is referred to as “test magnetizing current” Q 2 . When these electric currents flow through the magnetizing coil  17 , the magnetic clamping device  10  is in a magnetized state (as the polarity of the alnico magnet is determined). Here, an adhesion force exerted by the magnetic clamping device  10  when the “normal magnetizing current” Q 1  flows through the magnetizing coil  17  is defined as an adhesion force MF 1  (which can be measured by the sensor coil  44 ), and an adhesion force exerted by the magnetic clamping device  10  when the “test magnetizing current” Q 2  flows is defined as an adhesion force MF 2 . Further, mold opening force F is the force of an injection molding machine that opens the molds M 1 , M 2  shown in  FIG. 4 , and the adhesion force MF 2  is set to be equal to or larger than a value obtained by multiplying the mold opening force F by a safety factor SF. In this example, the safety factor SF was set to 110%, and the adhesion force ratio MF 2 /MF 1  was set to 80% in order to secure this. In the figure, reference code V is a power supply voltage and reference code I is an electric current. 
       FIG. 3  shows an adhesion force confirmation device mounted as a processing flow of the controller  7 . The adhesion force confirmation device of  FIG. 3A  is mounted on the controller  7  as a program corresponding to each mold. The processing flow of  FIG. 3A  of this program will be described with reference to  FIG. 4 . 
     The left and right molds M 1 , M 2  are suspended and transported between the magnetic clamping devices  10 ,  20  in a state of being fitted to each other ( FIG. 4A ). At this time, the magnetic clamping devices  10 ,  20  are in a state in which the molds M 1 , M 2  are demagnetized (a magnetized release state in which magnetic adhesion is not performed). Next, the left platen  2  is moved to the right to sandwich the molds M 1 , M 2  between the magnetic clamping devices  10 ,  20 . In this state, the magnetic clamping devices  10 ,  20  switch the molds M 1 , M 2  from the demagnetized state to the magnetized state ( FIG. 4B ). At this time, the ignition circuit  48  is controlled so that the magnetic clamping device  10  is in a state of weak adhesion force MF 2  (80% magnetization) (step  21 ,  FIG. 3A ). At this time, the magnetizing of the magnetic clamping device  10  by passing the “test magnetizing current” Q 2  is referred to as “test magnetizing”. Wires W that suspend the molds M 1 , M 2  are attached to the mold auxiliary metal fittings  4 ,  5  provided on the platens  2 ,  3 , respectively. The mold auxiliary metal fittings  4 ,  5  are used to prevent the molds M 1 , M 2  from falling to the floor. In the test magnetizing, the mold handling device is operated under the same conditions as the normal magnetizing state except for the adhesion force. That is, in the case of the injection molding machine  1 , resin is ejected from the nozzle  6  into the molds M 1 , M 2  to manufacture a molding material (molded product). This is the same condition as the normal magnetizing state, because even when the same mold is used, depending on the conditions such as the material and temperature of the base material molded by the mold and a surface area of the molded product, the degree of adhesive strength (or viscosity) between the molding material and the mold differs, and a force necessary and sufficient to open the molds M 1 , M 2  (referred to as “mold opening force F”) also changes. When the mold handling device is a press machine, the test magnetizing is performed in a state where the product is actually pressed. Further, even when the mold handling device is a die casting device, the test magnetizing is performed in a state where the product is actually cast. 
     In this state, the injection molding machine  1  separates the platens  2 ,  3  (step  22  in  FIG. 3A ). The injection molding machine  1  separates the platens  2 ,  3  with a force much larger than the mold opening force F, the adhesion force MF 1  and the adhesion force MF 2 , and pushes out the molded product with the ejector rod  8 . At this time, if the molds M 1 , M 2  are misaligned or float, a change in the magnetic flux flowing through the molds M 1 , M 2  causes an electric current to flow in the sensor coil  44 , thereby detecting peeling of the molds M 1 , M 2  (step  23 ). The peeling of the molds M 1 , M 2  can be detected by the proximity sensor  12 . If no peeling is detected, it can be confirmed that the adhesion force MF 2  exceeds the mold opening force F. The controller  7  controls the ignition circuit  48  so that the magnetic clamping device  10  exerts the adhesion force MF 1  (100% magnetizing) stronger than the adhesion force MF 2  by flowing the “normal magnetizing current” Q 1  (step  24 ). The magnetizing of the magnetic clamping device  10  at this time is referred to as “normal magnetizing”. After that, the injection work is performed in a state where it is guaranteed that the molds M 1 , M 2  are clamped by the adhesion force, which is sufficiently larger than the mold opening force F (the adhesion force MF 1  is 110% or more with respect to the mold opening force F), thereby enabling mass-production of molded products. 
     On the other hand, when peeling is detected in step  23 , even if the adhesion force is increased from the adhesion force MF 2  to the adhesion force MF 1 , it is not possible to guarantee adhesion with a margin of only 10% over the mold opening force F. The liquid crystal display screen of the controller  7  notifies the operator of a warning that the adhesion cannot be guaranteed. 
     According to a processing flow of the adhesion force confirmation device shown in  FIG. 3A  of this example, once test magnetization is performed to test whether or not peeling will occur, and then normal magnetization with a current higher than the test magnetization current Q 2  is performed, thereby enabling to guarantee the adhesion force MF 1  to adsorb with a margin of 10% or more of the mold opening force F. 
     Adding some steps to the processing flow of the adhesion force confirmation device of  FIG. 3A ,  FIG. 3B  shows an adhesion force confirmation device mounted on the controller  7  as a program for a case where the mold once attached to the injection molding machine  1  is once removed and then attached to the injection molding machine  1  again to be used.  FIG. 3B  is a processing flow of this program. Type ID for identifying the molds M 1 , M 2  is input (Step  31 ). The input of the type ID can be performed by affixing a barcode to the molds M 1 , M 2  and reading it with a barcode reader (not shown), or it can be typed directly by the operator from the input section of the controller  7 . Next, it is judged whether or not the type ID has been handled in the past (Step  32 ). If it has not been handled before, test magnetization is performed by the test magnetizing current Q 2  to bring the magnetic clamping device  10  into a magnetized state of 80% (Step  33 ). Then, in this state, the platens  2 ,  3  are separated to perform mold opening (Step  35 ). At that time, the sensor coil  44  measures the adhesion force by 80% magnetization. The measured adhesion force is stored as initial data P 0  in association with the type ID (Step  34 ). 
     Similar to  FIG. 3A , it is determined whether or not the molds M 1 , M 2  are peeled off (Step  36 ). If peeling cannot be detected, the magnetic clamp once releases the state in which the molds M 1 , M 2  are adhered, and then the normal magnetizing current Q 1  is passed to change the magnetized state of the magnetic clamping device  10  to the normal magnetized state, i.e., the adhesion force MF 1  (100% magnetization) (Step  37 ). 
     On the other hand, in Step  32 , if the mold of the relevant type ID has been handled in the past, the mold is magnetized with the adhesion force MF 1  (100% magnetization) by passing the “normal magnetizing current” Q 1  in the state where the molds M 1 , M 2  of  FIG. 4B  are put together (Step  38 ). Then, the current data P 1  is gotten by measuring the adhesion force by the sensor coil  44 . 
     The already stored initial data P 0  is compared with the current data P 1  (Step  40 ). As a result of comparison, if the current data P 1  is lower than the initial data P 0 , adhesion with a margin excessing 110% cannot be guaranteed. On the other hand, if the current data P 1  is the same or higher than the initial data P 0 , the adhesion in a state with a margin can be guaranteed, so that the following normal injection molding work is allowed to be performed. These results are displayed on the liquid crystal display screen of the controller  7  to notify the operator. The operator can continue the work after confirming the adhesion in a state with a margin. 
     According to the processing flow of the adhesion force confirmation device shown in  FIG. 3B  according to this example, it can be confirmed whether or not it can be guaranteed to have sufficient magnetic adhesion force even when the magnetic adhesion force decreases even after 100% magnetization due to changes in surface roughness caused by scratches or rust generated on the contact surface of the mold, or adhesion of dust. 
     In the above example, the magnetizing current was controlled in order to control the magnetizing state of the magnetic clamping device  10 . That is, although the magnitudes of the magnetizing currents Q 1 , Q 2  were controlled so that the test magnetizing current Q 2  was set to a value smaller than the normal magnetizing current Q 1  and the adhesion force MF 2  was 1.1 times or more the adhesion force MF 1 , other methods can be used. For example, it can be controlled by changing the voltage of the AC power supply  49 . 
     In the above example, although the sensor coil  44  was provided separately from the magnetizing coil  17 , as shown in Patent Document 2, a magnetic pole reversing coil (corresponding to the magnetizing coil  17 ) can be switched and used as a sensor coil. When the magnetic pole reversing coil is used as a sensor coil, a circuit for switching is required, but it has an advantage of improved sensitivity due to the large number of turns. 
     In the above example, although the measurement of the adhesion force of the magnetic clamping device  10  during magnetization and the measurement of changes in magnetic flux during so-called peeling when the mold shifts or floats were both performed with one of the sensor coils  44 , each event can be measured using separate sensor coils. 
     DESCRIPTION OF SYMBOLS 
       1  injection molding machine 
       2 ,  3  platen 
       4 ,  5  mold auxiliary metal fitting 
       6  nozzle 
       7  controller 
       8  ejector rod 
       9  guide rod 
       10 ,  20  magnetic clamping device 
       11  magnet block 
       12  proximity sensor 
       13  through hole 
       14  groove portion 
       15  non-reversible magnet 
       16  alnico magnet 
       17  magnetizing coil 
       18  reversible magnet 
       19  joint iron 
       44  sensor coil 
       46 ,  47  thyristor 
       48  ignition circuit 
       49  AC power supply 
     PL plate