Patent Publication Number: US-2009223762-A1

Title: Shock Absorber

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a shock absorber that uses the flow resistance of fluid flowing through a narrow gap to alleviate the impact of collision by absorbing the collision energy. 
     BACKGROUND ART 
     Factory assembly lines or the like frequently entail a step for causing a carrying table to travel to and stop at a predefined position, so that a component or work(s) loaded on the carrying table may be brought to and stopped at such predefined position, and/or may undergo a pressing process or other required process thereat. In doing so, if the carrying table moves too fast, when the carrying table stops, the component etc. or the counterpart may get broken. It can also cause a loud noise, or depending on circumstances, can deform the carrying table. 
     Therefore, factory assembly lines or the like employ a shock absorber for stopping the carrying table to gradually reduce the traveling speed of the carrying table so that such inconvenience can be prevented. 
       FIG. 11  shows an example of such shock absorbers that are generally known to be used for the above described purpose. 
     In the same drawing, a tubular cylinder part is indicated by  10 , and the cylinder part  10  has an opening at one end and is closed at the other end. A threaded hole for filling with silicon oil into an after-mentioned enclosed space  34  is concentrically formed at the other end of the cylinder part  10 . A small screw  12  is screwed into the threaded hole via an O-ring  14 . A thread is formed on the circumference of the cylinder part  10  and a couple of hex nuts  16  are screwed on it. 
     A piston  18  is concentrically inserted into the cylinder part  10  from one end. The piston  18  is composed of a rod part  20  and a piston part  22  which is configured at the end of the rod part  20 . The rod part  20  is covered or surrounded by a sleeve  24  at the part proximal to the piston part  22 , and the part distal to the piston part  22  projects from the one end of the cylinder part  10 . The projecting end is covered with a protection cap (not indicated in the drawing). 
     Outside the sleeve  24 , that is, between the sleeve  24  and the cylinder part  10 , an accumulator  26  and an O-ring  28  are inserted. Inside the sleeve  24 , that is, between the sleeve  24  and the rod part  20 , a rod packing  30  is inserted. The ring-shaped gap between one end of the cylinder part  10  and the rod part  20  is enclosed with a ring-shaped plug  32 . 
     Regarding the space inside the cylinder part  10 , the area in front of the sleeve  24  is an enclosed space  34 . The enclosed space  34  is filled with silicon oil. The internal space of the cylinder part  10  that is the space towards the other end from the piston part  22  accommodates a spring  36  along the inner surface of the cylinder part  10 , biasing the piston part  22  to the one direction. 
     For example, the above described shock absorber can be installed so that the end of the rod part  20  projecting from the cylinder part can hit the carrying table on which a component is carried, at a point immediately before a predetermined position where that particular carrying table is to be stopped. 
     When the end of the rod part  20  hits the carrying table carrying a component, the rod part  20  is forced into the cylinder part  10 , and the piston  18  is pushed to the other side into the cylinder part  10 . Thus the silicon oil is pushed by the piston part  22  at the end of the piston  18 , and the pushed silicon oil flows back through the gap between the piston part  22  and the cylinder part  10  while the flow resistance of the silicon oil absorbs the kinetic energy of the rod part  20 , thus gradually reducing the pushing force of the rod part  20  so that the carrying table together with the component can be stopped at a desired position. 
     Patent Document 1: Japanese Utility Model Unexamined Publication H4-19225 (Registration No.1952561) 
     Patent Document 2: Japanese Utility Model Unexamined Publication S60-97432   
     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     In recent years, various products have been downsized and accordingly those components have become smaller and more sensitive. Therefore the impact acceleration during deceleration is preferable to be as small as possible and the development of a shock absorber with such a characteristic is desired. 
     It is an object of this invention to provide a shock absorber with a minimum peak value of the impact acceleration during a collision. 
     Means of Solving the Problems 
     The shock absorber according to the present invention is characterized by a tubular cylinder part with an opening at one end and the other end closed; a seal part configured to seal the internal space of this cylinder part at a part closer to this one end inside this cylinder part; fluid filled in the enclosed space formed by this seal part inside this cylinder part; a piston part configured to be slidable inside this enclosed space; and a rod part that slidably penetrates this seal part concentrically and is connected to the piston part at one end while projecting out to the other side; wherein the shock absorber has a tapered inner surface of this cylinder part inside this enclosed space, reducing its internal diameter from the one end to the other end, and the rate of this taper is within the range from 1/50 to 1/130. 
     The reason why the rate of taper is set to be within the range from 1/50 to 1/130 is to lower the peak value of the impact acceleration during a collision. If the rate of taper exceeds 1/50, it results in an inconvenience of causing a large impact acceleration by the collision of the piston part  22  into the other end of the cylinder part  10  at the end of the impact absorption after the collision. If the rate of taper is less than 1/130, it results in an inconvenience of causing a large impact acceleration at the beginning of the impact absorption. If the rate of taper is between 1/50 and 1/130, it will not result in such inconveniences. 
     It is also preferable that the gap between the cylinder part and the piston part is within the range from 1/100 to 5/100 millimeter (mm) in proximity to the other end of the cylinder part. If the gap is less than 1/100 mm, it results in an inconvenience of prolonging the activation time. If the gap exceeds 5/100 mm, it results in an inconvenience of not completing the impact absorption at the end of the stroke. However if the gap is between 1/100 to 5/100 mm, it will lower the peak value of the impact acceleration during a collision, fulfilling its function as a shock absorber. 
     It is also preferable to use oil with a viscosity of 32 to 300 centi Stokes (cSt) for the fluid. If the fluid viscosity is less than 32 cSt, it results in an inconvenience of not gaining a sufficient impact absorbency. If the fluid viscosity exceeds 300 cSt, it results in inconveniences of exceeding an appropriate impact absorbency and prolonging the recovery time of the piston rod. However, if the fluid viscosity is between 32 to 300 cSt, it will lower the peak value of the impact acceleration during a collision, fulfilling its function as a shock absorber. 
     In addition, the enclosed space of the cylinder part may have the same range of the internal diameter as that of the side of the other end. 
     Advantageous Effect of the Invention 
     The shock absorber of the present invention has the effect of minimizing the peak value of the impact acceleration during a collision, thereby making it possible to reduce an impact given to an object or work used, to a lowest possible degree. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is an illustration of the shock absorber according to an embodiment of the present invention. 
         FIG. 2  is an outline illustration of the experimental device that was used in the collision experiment. 
         FIG. 3  is a graph to indicate the relationship between the stroke of the piston part and the impact acceleration when the rate of taper on the inner surface of the cylinder part is straight. 
         FIG. 4  is a graph to indicate the relationship between the stroke of the piston part and the impact acceleration when the rate of taper on the inner surface of the cylinder part is 1/130. 
         FIG. 5  is a graph to indicate the relationship between the stroke of the piston part and the impact acceleration when the rate of taper on the inner surface of the cylinder part is 1/100. 
         FIG. 6  is a graph to indicate the relationship between the stroke of the piston part and the impact acceleration when the rate of taper on the inner surface of the cylinder part is 1/80. 
         FIG. 7  is a graph to indicate the relationship between the stroke of the piston part and the impact acceleration when the rate of taper on the inner surface of the cylinder part is 1/70. 
         FIG. 8  is a graph to indicate the relationship between the stroke of the piston part and the impact acceleration when the rate of taper on the inner surface of the cylinder part is 1/60. 
         FIG. 9  is a graph to indicate the relationship between the stroke of the piston part and the impact acceleration when the rate of taper on the inner surface of the cylinder part is 1/50. 
         FIG. 10  is a graph to indicate the relationship between the stroke of the piston part and the impact acceleration when the rate of taper on the inner surface of the cylinder part is 1/30. 
         FIG. 11  is a section view of an example of a traditional shock absorber. 
     
    
    
     DESCRIPTION OF SYMBOLS 
     
         
           10  Cylinder part 
           12  Small screw 
           14  Ring 
           16  Hex nut 
           18  Piston 
           20  Rod part 
           22  Piston 
           22  Piston part 
           24  Sleeve 
           26  Accumulator 
           28  O-ring 
           30  Rod packing 
           32  Plug 
           34  Enclosed space 
           36  Spring 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The purpose of minimizing the impact acceleration during a collision as much as possible can be achieved by limiting the rate of taper on the inner surface of the cylinder part to the range between 1/50 and 1/130. 
       FIG. 1  is an illustration of the shock absorber according to an embodiment of the present invention. Although the basic configuration of the shock absorber in this drawing is generally the same as the one described in BACKGROUND ART, details are omitted for convenience of explanation. 
     In  FIG. 1 , a tubular cylinder part is indicated by  10 , and the cylinder part  10  has an opening at one end and is closed at the other end. A piston  18  is concentrically inserted into the cylinder part  10  from one end. A piston  18  is composed of a rod part  20  and a piston part  22  which is configured at the end of the rod part  20 . 
     The rod part  20  is surrounded by a sleeve  24  at the part proximal to the piston part  22 , and the part distal to the piston part  22  projects from the one end of the cylinder part  10 . Outside the sleeve  24 , that is, between the sleeve  24  and the cylinder part  10 , an accumulator  26  is inserted. Inside the sleeve  24 , that is, between the sleeve  24  and the rod part  20 , a rod packing  30  is inserted. 
     Regarding the space inside the cylinder part  10 , the area in front of the seal part composed of the sleeve  24 , the accumulator  26 , and the rod packing  30  is the enclosed space  34 . The enclosed space  34  is filled with silicon oil. 
     The inner surface of the cylinder part  10  inside this enclosed space  34  is tapered reducing its internal diameter from the one end to the other end. The preferred rate of this taper is within the range from 1/50 to 1/130. 
     The gap between the cylinder part  10  and the piston part  22  is within the range from 1/100 to 5/100 mm. The fluid viscosity of the oil is within the range from 32 to 300 cSt. In addition, the enclosed space of the cylinder part may have the same range of the internal diameter as that of the side of the other end. 
     Next, the principle of operation of the impact absorption by this shock absorber is described. 
     The above described shock absorber can be installed so that the end of the rod part  20  can hit the table on which a component is carried, at a point immediately before a predetermined position where that particular carrying table is to be stopped. 
     When the end of the rod part  20  hits the table, the rod part  20  is forced into the cylinder part  10 , and the piston part  22  is pushed to the other side of the cylinder part  10 . Thus the fluid is pushed by the piston part  22 , and the fluid flows back through the gap between the piston part  22  and the cylinder part  10  while the flow resistance of the fluid absorbs the kinetic energy of the rod part  20 , thus reducing the pushing force of the rod part  20  so that the rod part  20  and the table can be stopped at a desired position. 
     EXAMPLE 
     An experimental device as shown in  FIG. 2  was prepared. Here, a 2.0 kg block shaped test object is indicated by  50 , and an accelerometer  52  is placed at the back of the test object  50 . The test object  50  together with the accelerometer  52  is mounted on a rodless cylinder  54  and can be horizontally transferred to the direction indicated by an arrow. A shock absorber  58  supported by a support  56  is placed right in front of the carrying direction of the test object  50 . A laser displacement meter  60  is also placed right in front of the test object  50  towards the carrying direction allowing to measure the traveling speed of the test object  50 . 
     This experimental device was used to transfer the test object  50  in the direction indicated by arrow A with the air pressure inside the cylinder of the rodless cylinder  54  of 0.5 MPa, and the test object was collided at the speed of 1.0 m/s into a shock absorber with various rates of taper ranging from straight to 1/30 on the inner surface of the enclosed space of the cylinder part  10  to obtain each impact acceleration. The results are shown in  FIGS. 3 to 10 , and the peak values of the impact acceleration are shown in TABLE 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Peak value of the impact 
               
               
                   
                 Rate of taper 
                 acceleration (G) 
               
               
                   
                   
               
             
            
               
                   
                 0 
                 22.5 
               
               
                   
                      1/130 
                 11.1 
               
               
                   
                      1/100 
                 10.2 
               
               
                   
                  1/80 
                 14.4 
               
               
                   
                  1/70 
                 13.3 
               
               
                   
                  1/60 
                 15.0 
               
               
                   
                  1/50 
                 14.1 
               
               
                   
                  1/30 
                 20.9 
               
               
                   
                   
               
            
           
         
       
     
     According to this experiment, if the rate of taper exceeds 1/50, it results in an inconvenience of causing a large impact acceleration by a collision of the piston part  22  into the other end of the cylinder part  10  at the end of the impact absorption after the collision into the shock absorber  58 . If the rate of taper is less than 1/130, it results in an inconvenience of causing a large impact acceleration at the beginning of the impact absorption. However, if the rate of taper is between 1/50 and 1/130, it will not result in such inconveniences, thus lowering the peak value of the impact acceleration during a collision.