Patent Publication Number: US-11389973-B2

Title: Gripping tool, gripping system, and evaluation method of gripping performance

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application of U.S. application Ser. No. 16/360,877, filed Mar. 21, 2019, which is a continuation application of International Application PCT/JP2017/034441, filed on Sep. 25, 2017. This application also claims priority to Japanese Application No. 2017-047885, filed on Mar. 13, 2017. The entire contents are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a gripping tool, and a gripping system, and an evaluation method of gripping performance. 
     BACKGROUND 
     There is a gripping tool that grips an object and transfers the object. It is desirable for the gripping performance of the gripping tool to be high. For example, it is desirable to be able to grip various objects having different sizes and/or shapes with a larger force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective cross-sectional view illustrating a gripping tool according to an embodiment; 
         FIG. 2  is a perspective cross-sectional view illustrating the gripper of the gripping tool according to the embodiment; 
         FIGS. 3A to 3D  are cross-sectional views illustrating a gripping method using the gripping tool according to the embodiment; 
         FIGS. 4A to 4C  are cross-sectional views illustrating the gripping mechanism of the gripping tool according to the embodiment; 
         FIG. 5  is a perspective view illustrating the gripping tool according to the conventional example; 
         FIG. 6  shows experimental results illustrating the characteristics of the gripping tools according to the embodiment and the conventional example; 
         FIG. 7  describes the evaluation method of the gripping performance according to the embodiment; 
         FIG. 8  is an experimental result illustrating the characteristics of the gripping tool according to the embodiment; 
         FIG. 9  is an experimental result illustrating the characteristics of the gripping tool according to the embodiment; 
         FIG. 10  shows experimental results illustrating other characteristics of the gripping tool according to the embodiment; 
         FIG. 11  is a perspective cross-sectional view illustrating a gripping tool according to a first modification of the embodiment; 
         FIG. 12  is a perspective cross-sectional view illustrating a gripping tool according to a second modification of the embodiment; 
         FIG. 13  is a perspective cross-sectional view illustrating a gripping tool according to a third modification of the embodiment; and 
         FIG. 14  is a schematic view illustrating a gripping system  5  according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a gripping tool includes a gripper. The gripper is flexible. A plurality of granular materials is provided in an interior of the gripper. The gripping tool grips a workpiece by depressurizing the interior of the gripper in a state in which the gripper is caused to contact the workpiece. A diameter of at least a portion of the granular materials is less than 1774 μm. 
     Various embodiments are described below with reference to the accompanying drawings. 
     The drawings are schematic and conceptual; and the relationships between the thickness and width of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values. The dimensions and proportions may be illustrated differently among drawings, even for identical portions. 
     In the specification and drawings, components similar to those described previously or illustrated in an antecedent drawing are marked with like reference numerals, and a detailed description is omitted as appropriate. 
       FIG. 1  is a perspective cross-sectional view illustrating a gripping tool  1  according to an embodiment. 
     The gripping tool  1  according to the embodiment includes a gripper  10  that is flexible. A granular material  15  is provided in the interior of the gripper  10 . 
     More specifically, the gripper  10  includes a first portion  11  and a second portion  12 . The first portion  11  contacts a workpiece to be gripped. The second portion  12  opposes the first portion  11 . The first portion  11  and the second portion  12  include flexible materials such as a silicone resin, a rubber material, an acrylic resin, etc. The granular material  15  is provided in a first space SP 1  between the first portion  11  and the second portion  12 . The gripper  10  is configured by, for example, bonding the first portion  11  and the second portion  12  via a bonding agent. The first portion  11  and the second portion  12  may be bonded by thermal compression bonding. 
     The outer perimeter of the first portion  11  and the outer perimeter of the second portion  12  are held by a holder  20 . Thereby, the first space SP 1  is separated from an external space. The holder  20  has, for example, a circular ring configuration. Because only the outer perimeter of the gripper  10  is held by the holder  20 , the gripper  10  can deform inside the holder  20  in the direction of a line connecting the first portion  11  and the second portion  12 . 
     The direction of the line connecting the first portion  11  and the second portion  12  is, for example, the vertical direction. The direction of the line connecting the first portion  11  and the second portion  12  includes a first direction (up) from the first portion  11  toward the second portion  12 , and a second direction (down) from the second portion  12  toward the first portion  11 . Hereinbelow, the description of the embodiments is performed using “vertical direction,” “up/above,” and “down/below” based on the positional relationship between the first portion  11  and the second portion  12 . 
     As an example, the holder  20  includes a first flange  21  and a second flange  22 . The first flange  21  abuts the outer perimeter lower surface of the first portion  11 . The second flange  22  abuts the outer perimeter upper surface of the second portion  12 . The gripper  10  is held by fastening the first flange  21  and the second flange  22  using a fastener  25  such as a screw, etc. 
       FIG. 2  is a perspective cross-sectional view illustrating the gripper  10  of the gripping tool  1  according to the embodiment. 
     The first portion  11  and the second portion  12  of the gripper  10  are illustrated as being separated in  FIG. 2 . 
     As illustrated in  FIG. 2 , the first portion  11  includes a concave portion  11   r  and a convex portion  11   p . The concave portion  11   r  is recessed upward. The concave portion  11   r  is provided at the center of the gripper  10 . The upper surface of the concave portion  11   r  contacts the second portion  12 . The convex portion  11   p  protrudes downward. The convex portion  11   p  is provided around the concave portion  11   r . The concave portion  11   r  and the convex portion  11   p  are continuous with each other. 
     The concave portion  11   r  contacts the second portion  12 . The convex portion  11   p  is separated from the second portion  12  in the vertical direction. In the gripping tool  1  illustrated in  FIG. 1  and  FIG. 2 , the first space SP 1  is formed between the convex portion  11   p  and the second portion  12 . 
     A second space SP 2  that is surrounded with the concave portion  11   r  and the convex portion  11   p  is formed below the first portion  11 . Specifically, the top of the second space SP 2  is covered with the concave portion  11   r . The side of the second space SP 2  is surrounded with the convex portion  11   p . The bottom of the second space SP 2  is open. As described below, the second space SP 2  is sealed from the external space by the workpiece to be gripped being positioned below the second space SP 2 . 
     As illustrated in  FIG. 1  and  FIG. 2 , the gripper  10  further includes a first port  31  and a second port  32 . The first port  31  communicates with the first space SP 1 . The second port  32  pierces the second portion  12  and the concave portion  11   r  of the first portion  11 . The second port  32  communicates with the second space SP 2 . A first pipe  41  for depressurizing the first space SP 1  is connected to the first port  31 . A second pipe  42  for depressurizing the second space SP 2  is connected to the second port  32 . 
       FIGS. 3A to 3D  are cross-sectional views illustrating a gripping method using the gripping tool  1  according to the embodiment. 
       FIGS. 3A to 3D  illustrate a case where a workpiece W to be gripped has a cross section in which three triangles are connected. 
     First, the position in the horizontal direction of the gripper  10  and the position in the horizontal direction of the workpiece W are aligned. After aligning the position of the gripper  10  and the position of the workpiece W, the gripper  10  is lowered toward the workpiece W as illustrated in  FIG. 3A . 
     The gripper  10  is flexible. When the gripper  10  contacts the workpiece W, the convex portion  11   p  of the first portion  11  is pressed outward to envelope the workpiece W as illustrated in  FIG. 3B . The second space SP 2  that was open is sealed by the workpiece W. 
     Then, the lowering of the gripper  10  is stopped. As illustrated in  FIG. 3C , the first space SP 1  is depressurized via the first port  31  and the first pipe  41 . For example, the first space SP 1  is depressurized to about 0.1 atmosphere. At this time, the granular material  15  in the first space SP 1  jams and solidifies. The configuration of the gripper  10  enveloping the workpiece W and in close contact with the workpiece W is fixed thereby; and a force for gripping the workpiece W is generated. 
     Then, as illustrated in  FIG. 3D , the second space SP 2  is depressurized via the second port  32  and the second pipe  42 . For example, the second space SP 2  is depressurized to about 0.1 atmosphere. Thereby, the workpiece W is pulled by suction toward the second space SP 2 ; and the gripping force is increased further. 
     Subsequently, the gripping tool  1  that grips the workpiece W is raised. The gripping tool  1  is moved in the horizontal direction. After the workpiece W is transferred to the prescribed position, the first space SP 1  and the second space SP 2  are opened to the atmosphere. Thereby, the gripping force is eliminated; and the workpiece W is released from the gripping tool  1 . By the method described above, the workpiece W to be gripped is transferred to the prescribed position. 
       FIGS. 4A to 4C  are cross-sectional views illustrating the gripping mechanism of the gripping tool  1  according to the embodiment. 
     The gripper  10  of the gripping tool  1  is partially simplified in  FIGS. 4A to 4C . 
     In the gripping tool  1  according to the embodiment as illustrated in  FIG. 4A , the outer perimeter of the gripper  10  is held by the holder  20 . Accordingly, as illustrated in  FIG. 4B , the gripper  10  can deform upward with respect to the workpiece W when the gripper  10  is caused to contact the workpiece W. 
     Air is suctioned via the first port  31  and the second port  32  in this state. Thereby, as illustrated in  FIG. 4C , the contact surface area between the gripper  10  and the workpiece W increases while the gripper  10  deforms further upward with respect to the workpiece W. 
     As described above, the gripper  10  is held by the holder  20  to be deformable upward with respect to the workpiece W. According to this configuration, the gripping force can be increased when the workpiece W is gripped by the gripper  10 . 
     A gripping tool  100  according to a conventional example that is generally sold will now be described with reference to  FIG. 5 . Comparison results of the gripping forces for the gripping tool  1  according to the embodiment and the gripping tool  100  according to the conventional example will be described with reference to  FIG. 6 . 
       FIG. 5  is a perspective view illustrating the gripping tool  100  according to the conventional example. 
     As illustrated in  FIG. 5 , the gripping tool  100  includes a suction pad  101 . The gripping tool  100  grips the workpiece by causing the suction pad  101  to abut the workpiece to be gripped and by suctioning. 
       FIG. 6  shows experimental results illustrating the characteristics of the gripping tools according to the embodiment and the conventional example. 
     In  FIG. 6 , the horizontal axis is the curvature (the reciprocal of a curvature radius R) of the object surface to be gripped. The vertical axis illustrates the gripping force at each curvature. Multiple gripping tools  100  and the gripping tool  1  according to the embodiment are used in the experiment. The diameter of the suction pad  101  is different between the gripping tools  100 . 
     In the experiment, the gripping force was measured using the following procedure. 
     First, the object to be gripped is placed at the prescribed position. The object is gripped by the gripping tool. The gripping tool is raised at a constant rate while measuring the force applied to the gripping tool. The gripping tool is raised until the gripping tool separates from the object. The maximum value of the measured force is recorded. The experiment is repeated three times for each gripping tool. The average of the measured maximum values is used as the gripping force (N (newtons)). 
     As illustrated in  FIG. 6 , a large gripping force is obtained for the workpieces having relatively flat surfaces for the gripping tool  100  including the suction pad  101  having a diameter of 30 cm and the gripping tool  100  including the suction pad  101  having a diameter of 50 cm. When the surface of the workpiece has curvature, the gripping forces of these gripping tools  100  abruptly decrease; and it was difficult to grip the workpieces. 
     For the gripping tool  100  including the suction pad  101  having a diameter of 10 cm, a similar gripping force is obtained when the surface of the object has a small curvature and when the surface is flat. However, this gripping tool  100  is problematic in that the gripping force is small. 
     For the gripping tool  1  according to the embodiment, a gripping force substantially equal to that of a flat surface is obtained even in the case where the surface of the object has a small curvature. The gripping force of the gripping tool  1  according to the embodiment is larger than that of the gripping tools  100  in which the diameters of the suction pad  101  are 10 cm and 30 cm; and a sufficient value was obtained. 
     It can be seen from  FIG. 6  that the gripping force of the gripping tool may be greatly dependent not only on the form of the gripping tool but also on the shape of the object to be gripped. For example, the gripping tool  1  according to the embodiment and the gripping tool  100  including the suction pad  101  having the diameter of 50 cm are compared. When the surface of the object has curvature, the gripping force of the gripping tool  1  is larger than that of the gripping tool  100 . When the surface of the object is flat, the gripping force of the gripping tool  100  is larger than that of the gripping tool  1 . Accordingly, it is a challenge to quantitatively evaluate the gripping performance of the gripping tool. 
     The inventors of the application devised the method described below as an evaluation method of the gripping performance of the gripping tool. 
       FIG. 7  describes the evaluation method of the gripping performance according to the embodiment. 
     The experimental results of the gripping tool  1  according to the embodiment illustrated in  FIG. 6  are used in  FIG. 7 . 
     First, similarly to the experimental results of  FIG. 6 , the curvature of the object surface is changed while measuring the gripping force of the gripping tool at each curvature. Then, the integral of the gripping force over the curvature is calculated from the measurement results. 
     The integral corresponds to calculating the surface area of a region S illustrated in  FIG. 7 . By plotting the experimental results of the curvature and the gripping force, the region S is surrounded with the horizontal axis, 1/R=C min , 1/R=C max , and line segments connecting the gripping forces to each other. C min  is the minimum curvature of the curvature 1/R for which the measurements of the gripping force are performed. C max  is the maximum curvature of the curvature 1/R for which the measurements of the gripping force are performed. 
     The gripping performance of the gripping tool is defined as the calculated integral. According to the evaluation method, the gripping performance of the gripping tool can be evaluated quantitatively and includes the dependence of the gripping force on the shape of the object to be gripped. 
     Table 1 recited below illustrates the evaluation results of the gripping performance of the gripping tools  100  according to the conventional example and the gripping tool  1  according to the embodiment. The gripping performance of the gripping tool is evaluated using the evaluation method described above based on the experimental results illustrated in  FIG. 6 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 GRIPPING 
               
               
                   
                   
                 PERFORMANCE 
               
               
                   
                 UNIT 
                 (N/mm) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 CONVENTIONAL 
                 Φ 10 
                 1.50 
               
               
                   
                 EXAMPLE 
                 Φ 30 
                 2.27 
               
               
                   
                   
                 Φ 50 
                 5.90 
               
               
                   
                   
                 AVERAGE 
                 3.22 
               
            
           
           
               
               
               
            
               
                   
                 EMBODIMENT 
                 6.21 
               
               
                   
                   
               
            
           
         
       
     
     From Table 1, it can be seen that the value of the gripping performance of the gripping tool  1  according to the embodiment is greater than the values of the gripping performance of the gripping tools according to the conventional example. This shows that the gripping performance of the gripping tool  1  according to the embodiment is superior to those of the gripping tools according to the conventional example. 
     The inventors discovered in further experiments that the diameter and the shape of the granular material  15  in the gripper  10  interior affects the gripping performance. Therefore, the inventors performed similar experiments for multiple gripping tools  1  having mutually-different diameters and shapes of the granular material  15 . The inventors evaluated the gripping performance of each gripping tool  1  using the evaluation method described above. 
       FIG. 8  and  FIG. 9  are experimental results illustrating the characteristics of the gripping tool  1  according to the embodiment. 
     In  FIG. 8 , the horizontal axis and the vertical axis are respectively the curvature and the gripping force similarly to  FIG. 6 . In  FIG. 9 , the horizontal axis is the diameter of the granular material  15 ; and the vertical axis is the gripping performance. 
     For example, microbeads, silicone resin beads, coffee beans, glass beads, etc., can be used as the granular material  15 . In the experiment, a spherical first granular material and an angular second granular material are used. The spherical first granular material includes one material (a material A) selected from the group consisting of microbeads, silicone resin beads, coffee beans, and glass beads. The angular second granular material includes another one material (a material B) selected from the group recited above.  FIG. 8  illustrates the change of the gripping performance of the gripping tool  1  as the diameter of the first granular material is changed, and the gripping performance of the gripping tool  1  in the case where the second granular material is used. In  FIG. 8 , the numerical value in parentheses beside the material illustrates the diameter of the first granular material. An intermediate value between the minimum diameter and the maximum diameter of the second granular material was used as the diameter of the second granular material. 
     From the experimental results of  FIG. 8 , it can be seen that a high gripping force is obtained at each curvature as the diameter of the granular material  15  decreases. For the first granular material and the second granular material  15 , it can be seen that a higher gripping force is obtained for the first granular material than for the second granular material. The gripping performance was calculated for each diameter based on the experimental results of  FIG. 8 .  FIG. 9  illustrates the calculation results. From the results of  FIG. 9 , it can be seen that a higher gripping performance is obtained when the granular material  15  is spherical and the diameter of the granular material  15  is smaller. 
     As illustrated in Table 1, the average gripping performance of the gripping tools  100  according to the conventional example that are generally sold is 3.22 (N/mm). Comparing this result to the experimental results of  FIG. 9 , it can be seen that the diameter of the gripping tools  100  according to the conventional example corresponds to 1774 μm. Accordingly, the gripping tool  1  that has a higher gripping performance than the average gripping tool according to the conventional example is obtained by setting the diameter of the granular material  15  to be less than 1774 μm. 
     From the results of Table 1 and  FIG. 9 , it can be seen that the gripping performance obtained when the granular material  15  is spherical and the diameter is 500 μm or less is superior to the highest gripping performance of the gripping tools  100  according to the conventional example. Accordingly, it is more desirable for the granular material  15  to be spherical and to have a diameter of 500 μm or less. 
       FIG. 10  shows experimental results illustrating other characteristics of the gripping tool according to the embodiment. 
       FIG. 10  illustrates the experimental results in the case where the granular materials  15  having mutually-different diameters are mixed. In this experiment, a granular material having a diameter of 500 μm and a granular material having a diameter of 900 μm were mixed; and the proportion of the granular material (the major material) having the diameter of 500 μm was changed. 
     From the experimental results of  FIG. 10 , a large change of the gripping force is not seen even in the case where the granular materials having different diameters are mixed. This result shows that the gripping tool  1  that has a high gripping performance is obtained when the diameter of at least a portion of the multiple granular materials  15  is in the range described above. 
     The range of the diameter of the granular material  15  described above can be used favorably by the gripping tool  1 . In the gripping tool  1  as illustrated in the gripping mechanism of  FIGS. 4A to 4C , the gripper  10  is deformable upward with respect to the workpiece W. In the case where the gripper  10  is deformable upward with respect to the workpiece W, the diameter of the granular material  15  greatly affects the deformation amount of the gripper  10 . The contact surface area between the first portion  11  and the workpiece W increases as the deformation amount of the gripper  10  increases. Accordingly, the gripping performance of the gripping tool  1  can be improved further by setting the diameter of at least a portion of the granular material  15  of the gripping tool  1  to be less than 1774 μm (more desirably 500 μm or less). 
     The gripping tool according to the embodiment is not limited to the gripping tool illustrated in  FIG. 1  and  FIG. 2 . As described below, various modifications of the gripping tool according to the embodiment are applicable. In the gripping tools described below as well, the gripping performance of the gripping tool can be improved by setting the diameter of at least a portion of the granular material  15  to be in the range described above. 
       FIG. 11  is a perspective cross-sectional view illustrating a gripping tool  2  according to a first modification of the embodiment. 
     The gripping tool  2  illustrated in  FIG. 11  differs from the gripping tool  1  in that the holder  20  is not included. Therefore, the outer perimeter of the first portion  11  and the outer perimeter of the second portion  12  are fixed by being bonded to each other. 
       FIG. 12  is a perspective cross-sectional view illustrating a gripping tool  3  according to a second modification of the embodiment. 
     In the gripping tool  3  illustrated in  FIG. 12 , compared to the gripping tool  1 , the configuration of the gripper  10  is different; and the second port  32  is not included. 
     In the gripper  10 , the first portion  11  is curved to be convex downward. The second portion  12  is curved to be convex upward. The granular material is provided in the first space SP 1  between the first portion  11  and the second portion  12 . 
     Unlike the gripping tool  1  illustrated in  FIG. 1 , the first portion  11  of the gripping tool  3  does not include the concave portion  11   r  and the convex portion  11   p . Therefore, in the gripping tool  3 , the second space SP 2  is not formed below the first portion  11 . The second port  32  is not provided. In the gripping tool  3  according to the modification as well, similarly to the mechanism illustrated in  FIGS. 3A to 3D , the gripper  10  is deformable upward with respect to the workpiece W when gripping the workpiece W. The gripping force of the gripper  10  can be increased thereby. 
       FIG. 13  is a perspective cross-sectional view illustrating a gripping tool  4  according to a third modification of the embodiment. 
     The gripping tool  4  illustrated in  FIG. 13  differs from the gripping tool  3  in that the holder  20  is not included. The outer perimeter of the first portion  11  and the outer perimeter of the second portion  12  are fixed by being bonded to each other. 
       FIG. 14  is a schematic view illustrating a gripping system  5  according to the embodiment. 
     The gripping system  5  of the embodiment includes the gripping tool  1 , a transfer robot  90 , a first depressurizing apparatus  91 , a second depressurizing apparatus  92 , and a controller  93 . 
     The transfer robot  90  includes an arm  90   a . For example, the arm  90   a  includes multiple joints. The gripping tool  1  is mounted to the tip of the arm  90   a . The transfer robot  90  operates the arm  90   a  according to a command from the controller  93  and grips and transfers the workpiece W. 
     The first depressurizing apparatus  91  and the second depressurizing apparatus  92  include vacuum pumps. The first depressurizing apparatus  91  is connected to the first pipe  41  of the gripping tool  1  illustrated in  FIG. 1 . The second depressurizing apparatus  92  is connected to the second pipe  42  of the gripping tool  1 . The first depressurizing apparatus  91  and the second depressurizing apparatus  92  are driven according to commands from the controller  93 . Thereby, the first space SP 1  and the second space SP 2  are depressurized or opened to the atmosphere. 
     The controller  93  includes a CPU (Central Processing Unit), ROM (Read Only Memory), nonvolatile flash memory, etc. Various processing of the controller  93  is performed by the CPU. Various control algorithms, various constants, and the like that are necessary for the operation of the gripping system  5  are stored in the ROM. The transfer procedure, the transfer conditions, and the like of the workpiece W are stored as appropriate in the flash memory. 
     According to the transfer procedure stored in the flash memory, the controller  93  sends commands to control the operations of the transfer robot  90 , the first depressurizing apparatus  91 , and the second depressurizing apparatus  92 . 
     Because the gripping system  5  includes the gripping tool  1  having a high gripping performance, the workpiece W can be gripped and transferred more reliably. 
     The gripping system  5  according to the embodiment may include any of the gripping tools  2  to  4  according to the modifications described above instead of the gripping tool  1 . In the case where the gripping system  5  includes the gripping tool  3  or  4 , the gripping system  5  may not include the second depressurizing apparatus  92 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.