Patent Publication Number: US-11642717-B2

Title: Punching device

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a punching device for shearing a workpiece such as metal using a mold, and more specifically, to a punching device capable of detecting the generation of foreign matter. 
     2. Description of the Related Art 
     In the related art, in punching for shearing a workpiece using a die and a punch, foreign matter mixed between the die and the punch or between the punch and the workpiece causes a processing abnormality, which is a problem. In particular, the phenomenon called “scrap floating” is a phenomenon in which the scrap of the workpiece generated during punching is mixed as foreign matter between the die and the punch or between the punch and the workpiece as the punch rises, and it is well known that this phenomenon causes product defects and mold damage. 
     The punching device according to Japanese Patent Unexamined Publication No. 7-164075 is provided with a plurality of distance sensors around a mold for detecting a distance between an upper mold including a punch and a lower mold including a die, and in a case where a relationship between the detected values does not satisfy a predetermined reference, it is determined that foreign matter is mixed between the punch and the workpiece, an abnormality is output and detected by the operator, and the operation of the punching device is automatically stopped. 
     SUMMARY 
     According to one aspect of the present disclosure, there is provided a punching device for punching a workpiece into a predetermined shape using a die including a mold with a hole having the predetermined shape and a punch including a mold having the predetermined shape, the device including: load sensors which are disposed respectively at positions where a force applied to the die is transmitted in the punching device, and measure a load in a punching direction at each of at least three predetermined points different from each other in the die; and a control device that calculates a first moment, which is a sum of moments of the measured load around a first axis, and a second moment, which is a sum of moments of the measured load around a second axis, with respect to the first and second axes on a plane perpendicular to the punching direction, and determines that foreign matter is generated in a case where a magnitude of at least one of the first and second moments is deviated from a range of predetermined values. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram illustrating a configuration example of a punching device according to a first exemplary embodiment; 
         FIG.  2 A  is a side view illustrating a detailed configuration example of a mold of the punching device of  FIG.  1   ; 
         FIG.  2 B  is a perspective view illustrating a detailed configuration example of the mold of the punching device of  FIG.  1   ; 
         FIG.  3    is a top view illustrating an arrangement example of a load sensor of the punching device of  FIG.  1   ; 
         FIG.  4 A  is a side view illustrating an operation example of a case where foreign matter is generated on a workpiece in the punching device of  FIG.  1   ; 
         FIG.  4 B  is a side view illustrating an operation example of a case where foreign matter is generated beside the workpiece in the punching device of  FIG.  1   ; 
         FIG.  5 A  is a perspective view illustrating an example of a force and a moment in a foreign matter detecting operation in the punching device of  FIG.  1   ; 
         FIG.  5 B  is a front view illustrating a display example of a display device in the foreign matter detecting operation in the punching device of  FIG.  1   ; 
         FIG.  6    is a view illustrating a display example of a setting screen of a foreign matter detection threshold value in the punching device of  FIG.  1   ; and 
         FIG.  7    is a view illustrating an example of a foreign matter detecting operation result table in the punching device of  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION 
     In the punching device according to Japanese Patent Unexamined Publication No. 7-164075, in a case where foreign matter represented by the above-described punching scrap does not overlap the workpiece and is generated beside the workpiece, the distance between the upper mold and the lower mold does not change, and thus, foreign matter cannot be detected. In the punching device according to Japanese Patent Unexamined Publication No. 7-164075, in a case where the upper mold further includes a stripper that presses the workpiece before punching, when the punching cycle is shortened (faster), due to the rebound of the stripper or the like, there is a case where a change in distance is detected even though there is no foreign matter. Such error detection is not preferable because continuous punching is hindered and work efficiency deteriorates. 
     The present disclosure solves the above-described problems and provides a punching device capable of detecting foreign matter with higher accuracy as compared with the related art. 
     According to a first aspect of the disclosure, there is provided a punching device for punching a workpiece into a predetermined shape using a die including a mold with a hole having the predetermined shape and a punch including a mold having the predetermined shape, the device including: load sensors which are disposed respectively at positions where a force applied to the die is transmitted in the punching device, and measure a load in a punching direction at at least three predetermined points different from each other in the die; and a control device that calculates a first moment, which is a sum of moments of the measured load around a first axis, and a second moment, which is a sum of moments of the measured load around a second axis, with respect to the first and second axes on a plane perpendicular to the punching direction, and determines that foreign matter is generated in a case where a magnitude of at least one of the first and second moments is deviated from a range of predetermined values. 
     According to a second aspect of the disclosure, in the punching device according to the above-described first aspect, the first and second axes may be orthogonal to each other at a center of the hole of the die. 
     According to a third aspect of the disclosure, in the punching device according to the above-described first or second aspect, the range of predetermined values may be a range of values having a width of predetermined values in positive and negative directions, based on values of first and second initial moments, which are the first and second moments measured in advance when no foreign matter is generated. 
     According to a fourth aspect of the disclosure, in the punching device according to any one of the above-described first to third aspects, the control device may estimate in which of four quadrants divided by the first and second axes the foreign matter is generated, based on a magnitude relationship between the magnitude of the first moment and the magnitude of the first initial moment, and a magnitude relationship between the magnitude of the second moment and the magnitude of the second initial moment, when it is determined that the foreign matter is generated, and provide an estimation result to the user via the output device. 
     According to a fifth aspect of the disclosure, in the punching device according to any one of the above-described first to fourth aspects, a stripper that presses and holds the workpiece before the punching may further be provided. 
     According to a sixth aspect of the disclosure, in the punching device according to any one of the above-described first to fifth aspects, the control device may stop the punching of the punching device when it is determined that the foreign matter is generated. 
     In the punching device according to the present disclosure, foreign matter can be detected with higher accuracy than in the related art. 
     Hereinafter, a punching device according to a first exemplary embodiment will be described with reference to the drawings. In the drawings, substantially the same members will be given the same reference numerals. Components unnecessary for the description of the exemplary embodiment may be omitted without notice. 
     First Exemplary Embodiment 
       FIG.  1    is a block diagram illustrating a configuration example of punching device  51  according to the first exemplary embodiment of the present disclosure. In  FIG.  1   , punching device  51  includes servomotor  52 , top plate  53 , slider plate  54 , base plate  55 , slide bar  56 , ball screw  57 , control device  58 , mold  31 , a plurality of load sensors  35 , load amplifier  36 , computer  37 , and display device  38 . 
     In  FIG.  1   , servomotor  52  is disposed on top plate  53  and is driven and controlled by control device  58  to rotate. Ball screw  57  converts the rotation of servomotor  52  into a linear movement, and moves slider plate  54  up and down along slide bar  56 . 
     Mold  31  includes upper mold  32  and lower mold  33 . Lower mold  33  is fixed to base plate  55 . Upper mold  32  is fixed to slider plate  54 , and moves up and down with the movement of slider plate  54  described above. Punching is performed by sandwiching workpiece  21  between lower mold  33  and upper mold  32  that moves downward. The detailed configuration of mold  31  will be described later. 
     Four load sensors  35  are arranged on lower mold  33 , the load applied to lower mold  33  is measured, and a load signal indicating the measured load is output to load amplifier  36 . Load amplifier  36  amplifies the input load signal to obtain an amplified load signal, and outputs the amplified load signal to computer  37 . Computer  37  determines whether or not foreign matter  22  is present inside mold  31  based on the input amplified load signal. When it is determined that foreign matter  22  is present, computer  37  controls control device  58  to stop the punching, or notifies the operator of the generation of foreign matter  22  via display device  38 . When it is determined that foreign matter  22  is present, computer  37  may control device  58  to stop the punching, or further, notify the operator of the generation of foreign matter  22  via display device  38 . 
       FIG.  2 A  is a side view illustrating a detailed configuration example of mold  31  of  FIG.  1   .  FIG.  2 B  is a perspective view illustrating a detailed configuration example of mold  31  of  FIG.  1   . 
     In  FIG.  2 A , mold  31  includes upper bolster  11 , lower bolster  12 , linear guide  13 , upper mold  32 , lower mold  33 , and stripper part  34 . Upper mold  32  includes punch  1 , punch base  2  for fixing punch  1 , and punch holder  3 . Lower mold  33  includes die  7 , die base  8  for fixing die  7 , and die holder  9 . Stripper part  34  is configured with stripper spring  4 , stripper  5 , and stripper guide  6 . 
     Upper mold  32  moves up and down by being fixed to the upper bolster that moves up and down along linear guide  13 . Die  7  has a hole having any predetermined shape such as a circle or a polygon. Punch  1  has a columnar shape having the same shape. Workpiece  21  (not illustrated) is sandwiched between die  7  and punch  1 , and upper mold  32  is moved downward so as to introduce punch  1  into the hole of die  7 , and accordingly, a hole in a shape of punch  1  is punched into workpiece  21 . 
     Stripper  5  of stripper part  34  is disposed such that the lower surface thereof is positioned below the tip end of punch  1 . Stripper  5  can move in the up-down direction along stripper guide  6 . Stripper  5  comes into contact with workpiece  21  before punch  1  as upper mold  32  moves downward, and the elastic force of stripper spring  4  presses and holds workpiece  21  during the punching. 
     Four load sensors  35  are arranged between the lower surface of die base  8  and the upper surface of lower bolster  12 . The detailed arrangement of load sensor  35  will be described later. Load sensor  35  measures the load applied to die  7  during the punching, and outputs a load signal indicating the measured load to load amplifier  36 . 
       FIG.  3    is a top view illustrating an arrangement example of load sensor  35  of punching device  51  of  FIG.  1   . In  FIG.  3   , the paper surface illustrates the upper surface of lower bolster  12 . Elements unnecessary for the description except for lower bolster  12  and load sensor  35  are omitted. 
     In  FIG.  3   , in the exemplary embodiment, in punching device  51 , four load sensors  35 , such as load sensors  351  to  354 , are arranged. Load sensors  351  to  354  are arranged such that the X-Y plane with punching shaft  122  at the center of hole  121  of die  7  as the origin is symmetrical with respect to both the X axis and the Y axis. Specifically, load sensors  351  to  354  are arranged in order respectively at each of the four points where the coordinates on the X-Y plane are (a, -b), (-a, -b), (-a, b), and (a, b) with respect to lengths a and b. 
     The load in the punching direction applied to load sensors  351  to  354  is represented by Fz 1  to Fz 4 , respectively. At this time, the total punching load Fz, moment Mx around the X axis, and moment My around the Y axis are represented by the following equations, respectively.
 
 Fz=Fz 1+ Fz 2+ Fz 3+ Fz 4
 
 Mx=b  (− Fz 1− Fz 2+ Fz 3+ Fz 4)  (1)
 
 My=a  (− Fz 1+ Fz 2+ Fz 3− Fz 4)  (2)
 
     However, moment Mx around the X axis is considered as positive in the clockwise direction with respect to the X-axis positive direction, and moment My around the Y axis is considered as positive in the clockwise direction with respect to the Y-axis positive direction. 
     In a case where load sensors  351  to  354  are not arranged symmetrically with respect to the X axis and the Y axis, the equation for this moment becomes more complicated. In order to stably support die base  8 , load sensors  351  to  354  are preferably arranged symmetrically. 
     The foreign matter detecting operation of punching device  51  configured as described above will be described below with reference to  FIGS.  4 A to  7   . 
     In the exemplary embodiment, as foreign matter  22 , the punching scrap generated by the phenomenon called “scrap floating” is assumed. The scrap floating is a phenomenon in which the punching scrap generated during the punching adheres to punch  1  due to, for example, electrostatic force, surface tension, and the like, and is removed from punch  1  after the punching is completed, and accordingly, foreign matter  22  is generated on workpiece  21  or die  7 . Scrap floating occurs particularly frequently in a case where workpiece  21  is a thin plate having a thickness of 0.1 mm or less, or in a case where a small hole having a small punching shape is punched. It is considered that this is because the mass of the generated punching scrap is small and the punching scrap easily adheres to punch  1  due to the surface tension, magnetic force, electrostatic force, and the like of the lubricating oil. 
       FIG.  4 A  is a side view illustrating an appearance example of a case where foreign matter  22  is generated on the upper surface of workpiece  21 . Since foreign matter  22  is generated on the upper surface of workpiece  21  on the negative side of the X axis, and accordingly, stripper  5  that presses workpiece  21  is in contact with foreign matter  22  thereon instead of workpiece  21 . Of stripper springs  4  connected to stripper  5 , those in the X-axis negative direction shrink more than those in the positive direction by the thickness of foreign matter  22 . Therefore, the load applied to die  7  by stripper  5  in the punching direction increases toward the negative side in the X axis. Due to the generation of foreign matter  22 , as illustrated by the arrow in  FIG.  4 A , the center of gravity of the object on die  7  is biased in the X-axis negative direction, and thus, the load applied to die  7  in the punching direction by workpiece  21  and foreign matter  22  also becomes larger on the negative side (Fz 2 , Fz 3 ) of the X axis than on the positive side (Fz 1 , Fz 4 ). 
       FIG.  4 B  is a side view illustrating an appearance example of a case where foreign matter  22  is generated beside workpiece  21 , that is, directly on die  7 . Unlike the case of  FIG.  4 A , stripper  5  comes into contact with workpiece  21  horizontally, and thus, the load is not biased by stripper spring  4 . Meanwhile, since foreign matter  22  is generated on the negative side of the X axis of workpiece  21 , similar to  FIG.  4 A , as illustrated by the arrow in  FIG.  4 B , the center of gravity of the object on die  7  is biased in the X-axis negative direction, and the load (Fz 2 , Fz 3 ) on the negative side of the X axis becomes larger than that on the positive side (Fz 1 , Fz 4 ). 
     The values of measured loads Fz 1  to Fz 4  of load sensors  351  to  354  are output to load amplifier  36  as load signals indicating measured loads Fz 1  to Fz 4 , respectively. Load amplifier  36  amplifies the load signal to obtain an amplified load signal, and outputs the amplified load signal to computer  37 . 
       FIG.  5 A  is a view illustrating the relationship between loads Fz 1  to Fz 4  and moments Mx and My around the X axis and the Y axis when foreign matter  22  is generated without overlapping workpiece  21 . In  FIG.  5 A , moments Mx and My around the X axis and the Y axis of the load are moments in which the clockwise direction with respect to each axis is positive, respectively, indicated by the arrows in the drawing. In a case where foreign matter  22  is not generated, measured loads Fz 1  to Fz 4  of load sensors  351  to  354  arranged symmetrically with respect to the X axis and the Y axis all have the same value. Therefore, when moments Mx and My are calculated according to the equations (1) and (2), Mx=0 and My=0 are substantially established. Such moments Mx and My in a case where no foreign matter 22 is generated are called initial moments Mx 0  and My 0 . 
     In  FIG.  5 A , a case is considered in which, in die  7 , in a region (first quadrant) where both the X and Y coordinates are positive, foreign matter  22  is generated without overlapping workpiece  21 . As described above regarding  FIG.  4 B , since the position of the center of gravity of the object on die  7  is biased toward foreign matter  22 , the load applied to load sensors  351  to  354  becomes larger as foreign matter  22  is generated. Therefore, measured load Fz 4  of load sensor  354  on foreign matter  22  side with respect to the X axis becomes larger than measured load Fz 1  of load sensor  351  on the opposite side, and similarly, measured load Fz 3  of load sensor  353  becomes larger than measured load Fz 2  of load sensor  352 . Similarly, regarding the Y axis, measured load Fz 4  becomes larger than measured load Fz 3 , and measured load Fz 1  becomes larger than measured load Fz 2 . 
     When moments Mx and My are calculated according to the equations (1) and (2) using these measured loads Fz 1  to Fz 4 , Mx&gt;0 and My&lt;0 are established. Computer  37  determines that foreign matter  22  is generated in a case where at least one of moments Mx and My is not 0. 
     A case is considered in which foreign matter  22  is generated in another quadrant of die  7 . In a case where foreign matter  22  is generated in the second quadrant (a region where the X coordinate is negative and the Y coordinate is positive) of die  7 , measured load Fz 3  becomes large and measured load Fz 1  becomes small, and thus, when moments Mx and My are calculated based on the equations (1) and (2), Mx&gt;0 and My&gt;0 are established. Similarly, in a case where foreign matter  22  is generated in the third quadrant (a region where both X and Y coordinates are negative) of die  7 , Mx&lt;0 and My&gt;0 are established, and in a case where foreign matter  22  is generated in the fourth quadrant (X coordinate is positive and Y coordinate is negative) of die  7 , Mx&lt;0 and My&lt;0 are established. Therefore, by confirming whether moments Mx and My are positive or negative around the X axis and the Y axis, it is possible to estimate in which quadrant of die  7  foreign matter  22  is generated. 
     Computer  37 , which determined that foreign matter  22  was generated, estimates in which quadrant foreign matter  22  is generated as described above, controls display device  38 , displays screen  380  as illustrated in  FIG.  5 B , warns the operator, and controls control device  58  to stop the operation of punching device  51 . On screen  380 , frames corresponding to the first to fourth quadrants of die  7  are displayed, and the frames corresponding to the quadrants in which foreign matter  22  is estimated to be generated are displayed in a warning color different from that of the others. By looking at screen  380 , the operator can confirm in which quadrant of die  7  foreign matter  22  is generated and remove foreign matter  22 . 
     In the exemplary embodiment, the moments around the X axis and the Y axis are used to estimate where foreign matter  22  is generated in the region divided into four by the X and Y axes. However, when there are at least three load sensors  35 , the purpose of estimating the position of foreign matter  22  can be achieved. However, when multiple load sensors are used, the detection accuracy of foreign matter  22  can be improved, and the region of die  7  can be divided into more regions to estimate the more detailed position of foreign matter  22 . 
     In  FIG.  5 B , display device  38  is a display device such as a liquid crystal display. However, any display device may be used as long as the display device can notify the operator in which of the plurality of regions divided from the region of die  7  foreign matter  22  is generated. For example, the operator can be notified of the generation position of foreign matter  22  by using four LED lamps arranged on punching device  51 . 
       FIG.  6    is a front view illustrating a display example of a setting screen for determining generation of the foreign matter. In the procedure for determining that foreign matter  22  is generated, when it is determined that foreign matter  22  is generated in a case where the values of moments Mx and My are not 0, it is considered that a slight measurement error or shaking will be erroneously detected as the generation of foreign matter  22 . Therefore, punching device  51  in the exemplary embodiment determines that foreign matter  22  is generated in a case where at least one of the absolute values of moments Mx and My is larger than a predetermined threshold value. This threshold value can be set by presenting a screen illustrated in  FIG.  6   , for example, to the operator and having the operator input the threshold value for moments Mx and My. 
     Since initial moments Mx 0  and My 0  were 0 in the exemplary embodiment, the quadrant of die  7  in which foreign matter  22  was generated was estimated depending on positive and negative moments Mx and My. However, there is a case where initial moments Mx 0  and My 0  are not 0 depending on the arrangement number and arrangement location of load sensors  35 . In this case, the same estimation can be performed based on the magnitude relationship between moments Mx and My and initial moments Mx 0  and My 0 . In this case, the threshold value for moment Mx may be set not for the absolute value |Mx| of moment Mx but for the absolute value |Mx−Mx 0 | of the difference between moment Mx and initial moment Mx 0 . The upper limit value and the lower limit value may be set individually, and in a case where the magnitude of moment Mx exceeds the range of the values, it may be determined that foreign matter  22  was generated. This also applies to moment My. 
     In the exemplary embodiment, in a case where the absolute values of moments Mx and My exceed the threshold value, it is determined that foreign matter  22  was generated, a warning is displayed on display device  38 , and control device  58  is controlled to stop punching device  51 . However, each different threshold value may be set for displaying a warning and stopping punching device  51 . For example, it is assumed that a warning is displayed in a case where the absolute value of moment Mx exceeds 1.0 m⋅N, and punching device  51  is stopped in a case where the absolute value exceeds 2.0 m⋅N. 
       FIG.  7    is a table illustrating an operation example of punching device  51 . In  FIG.  7   , the threshold value illustrated in  FIG.  6    is set as a threshold value for determining the generation of foreign matter  22 . The “number of punches” indicates the number of times of performing the punching with respect to workpiece  21 . The values in the column “moment difference” indicate the difference between moments Mx and My and initial moment Mx 0  and My 0 . “Determination” indicates determination result on whether or not any of the above moment differences with respect to the X and Y axes exceeds the threshold value, that is, whether or not foreign matter  22  is generated. “NG” indicates that the moment difference exceeded the threshold value, and “OK” indicates that the moment difference did not exceed the threshold value. “Response” indicates a response automatically taken by punching device  51  in response to the above-described determination result. 
     In  FIG.  7   , since none of the moment difference values exceeded the threshold value during the first punching, it was determined that no foreign matter  22  was generated, and the punching was continued as it was. At the time of the second punching, it was determined that the value of the moment difference with respect to the Y axis exceeded the threshold value and foreign matter  22  was generated. Therefore, a warning was displayed to the operator based on the sign of the moment difference for each of the X and Y axes, and the punching was stopped. 
     After this, after receiving a warning and removing foreign matter  22 , the operator starts the operation of punching device  51  again to perform the third punching. In the third punching, none of the moment difference values exceed the threshold value, it was determined that no foreign matter  22  was generated, and the punching was continued. 
     In this manner, punching device  51  according to the exemplary embodiment measures the load applied to die  7  by load sensors  351  to  354 , and calculates moments Mx and My based on measured loads Fz 1  to Fz 4 . After this, it is determined whether or not foreign matter  22  is generated based on the difference in magnitude between calculated moments Mx and My and initial moments Mx 0  and My 0 . In a case where foreign matter  22  is generated, punching device  51  displays the determination result including the quadrant of die  7  in which foreign matter  22  is generated to the operator, or stops the punching of punching device  51 . In a case where foreign matter  22  is generated, punching device  51  may display the determination result including the quadrant of die  7  in which foreign matter  22  is generated to the operator, and further stop the punching of punching device  51 . Accordingly, even in a case where foreign matter  22  is generated in a place where foreign matter  22  does not overlap workpiece  21 , the generation of foreign matter  22  can be detected and the punching can be stopped. By knowing the place where foreign matter  22  is generated in advance, the operator can smoothly remove foreign matter  22  and restart the next punching. 
     In the exemplary embodiment, the punching scrap generated by “scrap floating” is assumed as foreign matter  22 , but punching device  51  can detect not only the scrap floating but also, for example, the mixing of foreign matter from the outside. At least two of load amplifier  36 , computer  37 , display device  38 , control device  58 , and the like of the exemplary embodiment may be configured as the same element. 
     Furthermore, in the exemplary embodiment, load sensor  35  is disposed below die base  8 , but may be disposed anywhere as long as the load applied to three or more points of the die is transmitted, respectively. For example, a plurality of load sensors  35  may be disposed on stripper part  34 . 
     The punching device of the disclosure can detect foreign matter even in a case where the distance between the stripper and the lower mold does not change, such as when foreign matter is placed next to the workpiece, or in a case where the punching cycle is accelerated, and despite the high detection sensitivity, there are few error detection. Therefore, it is possible to provide a punching device capable of performing highly accurate foreign matter detection without reducing the productivity of the punching work. The punching device of the present disclosure can also be applied to punching of films and composite materials.