Abstract:
The invention provide a cylindrical pushrod for the syringe needle-retracting safety injector, comprising an outer cylinder ( 1 ), an inner cylinder ( 2 ), a push pole ( 3 ), an underpinned piece ( 4 ) and a seal gasket ( 5 ); the push pole ( 3 ) is set at the front end of chamber of outer cylinder ( 1 ), its front end appears as a tubular shape or projects partially in the longitudinal direction, the back end of push pole ( 3 ) is supported on the underpinned piece ( 4 ); the underpinned piece ( 4 ) is set at the front end of the chamber of outer cylinder ( 1 ) and supports the push pole ( 3 ); the cylinder wall of the inner cylinder ( 2 ) supports the underpinned piece ( 4 ); a clamping structure is set at the tail of this cylindrical pushrod. With the safety injector with the cylindrical pushrod according to the invention, the medical personnel can control the time of the needle retraction as desired, and is not necessary to change their habitual injection practice, and thereby the safety injector is easy to operate. The invention also provide a safety injector, which can not only carry out the controllable retraction of the needle but also has a simple and crafty fixed structure of the needle stand to achieve the effect of reliable fixation as well as releasing with ease.

Description:
FIELD OF THE TECHNOLOGY  
       [0001]     This invention relates to a medical instrument, and particularly to a cylindrical pushrod for the needle-retracting safety injector, and the needle-retracting controllable safety injector having the said pushrod.  
       BACKGROUND OF THE INVENTION  
       [0002]     The injector is a medical instrument used commonly and in large quantities in the medical field. If the injector is used repeatedly, it is apt to lead to the spread of diseases between various patients and result in the cross contamination, which endanger the public health. Some people collect the waste single-use injectors that have already been used, and sale them in the medical market again for the illegal benefits, which bring the enormous hidden dangers of propagation and spread of various diseases. Moreover, when the medical personnel injects, the exposed needle may stab the medical personnel or the collector of castoff thereby causing the infection and propagation of diseases. In order to prevent the injector from being reused and achieve the object of single use by destructing the injector automatically after being used once, and in order to prevent the occurrence of accidental stabbing by the used injector, the technical schemes of the single-use injector with retractable syringe needle are proposed, such as the Chinese utility model patent No. ZL01221139.7, which disclosed a safety self-destructing single-use injector with the needle retracting into the inside of the injector after injecting. This technical schemes includes fixing the needle in the needle stand with a casing spring, the needle stand then being fixed in the head portion of the injector with the needle gasket, and at the end of injection, the pushrod&#39;s bottom plug fixed on the head of pushrod releasing the fit between the needle stand and the gasket through pushing and pressing, while the pushrod&#39;s bottom plug being pressed into the inside of hollow pushrod, and the whole needle together with the needle stand being retracted backward to the inside of the pushrod under the action of the spring, thereby achieving the self-destruction of injector so as to its reuse is avoided and the occurrence of stabbing accident due to the exposure of the needle after injection is excluded.  
         [0003]     Though this technical scheme can carry out the retraction of the injector&#39;s needle after injection, the retraction process is performed automatically and is uncontrollable. Therefore, the technical solution exists the disadvantages as follows: first, the retraction is performed when the needle still stays in the patient&#39;s body while the injection is finished, which may cause the needle to push forward or sway when releasing the fixed structure of needle stand, thereby paining the patients or even hurt them; second, according to the operation criterion, the medical personnel should press the injection location with the sterilized cotton ball at the end of injection and then draw out the needle. However, the retraction of needle is automatic in this technical scheme and can not be controlled by the medical personnel, so the medical personnel must press the injection location with the sterilized cotton ball before the end of injection, which brings the operational inconvenience for the medical personnel because they must change their customary injection practice.  
         [0004]     And in the technical scheme, the fixed structure of needle stand also exists defects that it can not obtain the fixed effect of being firm as well as releasable. Furthermore, the technical scheme also exists the defects that the needle stand is pushed forward to further penetrate into the patient&#39;s body when the bottom plug of the pushrod pushs and presses the fixed structure of needle stand and that the residual liquor is too much.  
       SUMMARY OF THE INVENTION  
       [0005]     One purpose of the invention is to overcome the abovesaid defects of prior art, and provides a cylindrical pushrod that is used for the syringe needle-retracting safety injector and can carry out the controllable retraction of needle, and a needle-retraction-controllable safety injector with the cylindrical pushrod.  
         [0006]     Another purpose of the invention is to provide a needle-retraction-controllable safety injector wherein the needle stand is fixed firmly at the head portion of injector with a simple fixed structure and is easy to be released, and which can realize that the needle stand and the needle will not moves further forward or sways unintentionality, and the residual drug liquor can be reduced effectively after injection.  
         [0007]     In order to attain the said purposes of the invention, there provides a cylindrical pushrod for the syringe needle-retracting safety injector, wherein the cylindrical pushrod comprises an outer cylinder  1 , an inner cylinder  2 , a push pole  3  and an underpinned piece  4 ; the head of outer cylinder  1  is provided with a sealing gasket  5 ; the push pole  3  is set at the front end of chamber of outer cylinder  1 , the front end of push pole  3  closes the frontend opening of outer cylinder  1  and outstands outside of the seal gasket  5 , and appears as a tubular shape or projects partially in longitudinal direction, and the back end of said push pole  3  is supported on the underpinned piece  4 ; the underpinned piece  4  has a through hole  401  for allowing the push pole  3  to pass through and a underpinned patch  402  for opening or closing the through hole  401 , and the underpinned patch  402  is set at the front end of the chamber of outer cylinder  1  and supports the push pole  3 ; the inner cylinder  2  is set inside the outer cylinder  1  with its front end openend and its back end closed, and the top end surface of its cylinder wall supports the underpinned piece  4  or the underpinned patch  402  thereof to close the through hole  401 ; the tail of cylindrical pushrod is provided with a clamping structure for clamping the inner cylinder and the outer cylinder in a releasable manner, the clamping structure may make the inner cylinder  2  slide backward for a distance for allowing the push pole  3  pass through after opening the through hole  401  under the action of retractive force of the needle, and is clamped within the outer cylinder  1  again after it is released to.  
         [0008]     As a modified cylindrical pushrod for the needle-retracting safety injector of the invention, wherein the clamping structure is a supporting piece  6 , which is composed of one O-shape ring part  601 , two elastic strips  602  and two raised blocks  603 ; the two elastic strips  602  are set opposing to each other at both sides of the O-shape ring part  601 ; the two raised blocks  603  are set respectively at the position on the outside of two elastic strips  602  with the same height, and the two raised blocks  603  are of the semispherical, triangle shape or the other shapes with a slope on its upside; the cylinder wall of outer cylinder  1  is provided respectively with the holes  101  having a matched shape with the raised blocks  603  in the position matching with the two raised blocks  603 ; after the supporting piece  6  is mounted, the two raised blocks  603  engage into the holes  101  respectively and protrude beyond the holes  101 ; the cylinder wall of rear portion of inner cylinder  2  exists two long holes  201  opposing to each other; the supporting piece  6  is set around the rear portion of inner cylinder  2  in the position of the long hole  201  and engaged in the holes  101  of outer cylinder  1 , and the upper end of elastic strips  602  supports the superior border&#39;s surface of the long hole  201  of inner cylinder  2 .  
         [0009]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein the cylinder wall of rear portion of the outer cylinder  1  has at least one long hole  102 ; the cylinder wall of mid-back portion of inner cylinder  2  has the corresponding long holes  202  at the position matched with the long hole  102 , the superior border of the long holes  202  extends downward to form an upright or inclining outward elastic strips  203 , and there are two raised blocks, the upper raised block and the lower raised block, on the outside wall of the elastic strips  203 , the distance between the lower end surface of upper raised block  204  and the lower end surface of lower raised block  205  equals to or exceeds the distance of inner cylinder  2  sliding backward for opening the through hole  401  to allow the push pole  3  passes through, the height of the upper raised block  204  equals to or exceeds that of the lower raised block  205 , and a slope is formed on the top thereof, the upper and lower raised blocks are fixed in and protrude outside the long holes  102 , and the lower raised block  205  is supported on the inferior border of the long hole  102  so that the inner cylinder  2  can be locked releasably on the outer cylinder  1 .  
         [0010]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein the chamber of outer cylinder  1  contracts inward to form a shoulder  103  at the front end of outer cylinder  1 , and extends forward to form a hollow chamber with a smaller diameter; the underpinned piece  4  is a O-shape sheet with a through hole  401  at its center, and is provided with a plurality of upwarping elastic underpinned patchs  402 ; the underpinned piece  4  is set at the front end of the chamber of outer cylinder  1 , and the top end surface of inner cylinder  2  pushs and presses the underpinned piece  4  to the shoulder  103  of the front end of chamber of outer cylinder  1  to press down the elastic underpinned patchs  402  which then occlude the through hole  401  and support the push pole  3 ; the push pole  3  is set in the hollow chamber with the smaller diameter at the front end of outer cylinder  1 .  
         [0011]     As a cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein the underpinned piece  4  is compose of a plug  7  and an underpinned patch  8 , the connection between the underpinned patch  8  and the plug  7  is a flexible connection, and a hinge structure, a gemel structure or the like can be set between the underpinned patch  8  and the plug  7 , or the joint part can be formed as a flexional feeble layer, to realize the flexible connection between the two parts; an aperture through which the underpinned patch  8  passes and which has a shape matching with the plug is provided on the cylinder wall of the front end of outer cylinder  1 ; after the underpinned patch  8  is inserted into the aperture, the plug  7  closes the aperture and secures one end of the underpinned patch  8  on the cylinder wall of outer cylinder  1 , the other end of the underpin patch  8  is supported on the top end surface of the cylinder wall of inner cylinder  2 .  
         [0012]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein the underpinned piece  4  is a ring part, on which a through hole  401  and an underpinned patch  402  are provided, and a round of groove or flange  403  playing the function of clamping is provided on its side wall, one end of the underpinned patch  402  is free, and the other end of the underpinned patch connects to the underpinned piece  4  with a hinge, a gemel or the like, or a flexional feeble layer to achieve a flexible connection; the underpinned piece  4  is set at the front end of the chamber of outer cylinder  1 , a round of flange or groove  105  are provided on the cylinder wall of the front end of outer cylinder  1  to match with the groove or flange  403  on the underpinned piece  4 , and the underpinned piece  4  is fixed at the front end of chamber of outer cylinder  1  through the clamping function of the groove and flange; the top end surface of the cylinder wall of inner cylinder  2  supports the free end of the underpinned patch  402  to close the through hole  401 .  
         [0013]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, it further comprises a protective sleeve  9  which function to protect the clamping structure set at the tail of the cylindrical pushrod from being disengaged unintentionally due to accidental touch, the protective sleeve  9  is a jointed body of a thick cylinder  901  and a thin cylinder  902 ; a round of flange  106  is set on the outer wall of the rear portion of outer cylinder  1 ; the inner diameter of thin cylinder  902  matches with the outer diameter of outer cylinder  1 , a round of groove  903  is set on the inside wall of the thin cylinder  902  to clamp with the flange  106 , the protective sleeve  9  is connected to the rear end of outer cylinder  1  and is fixed by the clamping relation between the groove  903  and the flange  106 , the thick cylinder  901  of the protective sleeve  9  covers the clamping structure after being mounted.  
         [0014]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein it further comprises a sealing gasket  10 ; the chamber of outer cylinder  1  contracts inward to form a shoulder  103  at the front end of outer cylinder  1 ; an annular dummy club  301  is set at the lower end of push pole  3 ; the sealing gasket  10  is mounted between the annular dummy club  301  and the shoulder  103  at the front end of the chamber of outer cylinder  1 .  
         [0015]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein it further comprises a compressible needle-stopping piece  11 ; a hollow chamber is set at the front end of push pole  3 ; the needle-stopping piece  11  is set within the hollow chamber at the front end of push pole  3 , the needle-stopping piece  11  has an exposed part at the front end which is higher than the front end of push pole  3  after plugging the opening of the hollow chamber of push pole  3 , and the compressive force of the needle-stopping piece  11  is larger than or equal to the retractive force of the needle.  
         [0016]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein the needle-stopping piece  11  is composed of a piston head  1101  and a compressible part, the compressible part may be a hollow thinwall pipe  1102  or a hollow corrugated pipe, and also may be a spring supporting the piston head.  
         [0017]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein a groove  1105  is set on the top surface of the needle-stopping piece  11 ; a slot  302  communicated with the groove  1105  is set in the chamber wall of the hollow chamber at the front end of push pole  3 . The purpose of the groove  1105  and the slot  302  is to push out the drug liquor in the syringe as much as possible to reduce the remains of drug liquor.  
         [0018]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein the outer cylinder  1  shows up a front end in a tubular shape or with partial longitudinal projection after the seal gasket  5  is installed thereon; the push pole  3  is changed into a compressible needle-stopping piece  12 , the front end of the needle-stopping piece  12  plugs into the opening of the hollow chamber of outer cylinder  1  and has an exposed part at its front end which is higher than the front end of outer cylinder  1 , the rear end of the needle-stopping  12  is compressible and is supported on the underpinned piece  4 , the compressive force of the needle-stopping piece  12  exceeds or equals to the retractive force of the needle.  
         [0019]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein the needle-stopping piece  12  is composed of a piston head  1201  and a compressible part; the piston head  1201  plugs into the opening of the hollow chamber of outer cylinder  1  and has an exposed part which is higher than the front end of outer cylinder  1 ; the compressible part may be a hollow thinwall pipe  1202  or a hollow corrugated pipe  1203 , and also may be a spring supporting the piston head.  
         [0020]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein the rear end of the needle-stopping piece  12  is provided with a supporting dummy club  1205  which matchs with the shoulder positioned at the top end of chamber of the outer cylinder  1 .  
         [0021]     As a modified cylindrical pushrod for the needle-retracting safety injector according to the invention, wherein on the top surface of needle-stopping piece  12  is provided with a groove  1206 ; a slot communicated with the groove is provided on the cylinder wall at the position of the frontend opening of outer cylinder  1 .  
         [0022]     In order to attain the said purposes of the invention, there also provides a needle-retraction controllable safety injector, wherein the said safety injectoris mounted with a cylindrical pushrod for the needle-retracting safety injector structured as above.  
         [0023]     As a modified needle-retraction controllable safety injector according to the invention, wherein the safety injector comprises a needle syringe  13 , a needle stand  14  for fixing a needle, a needle stand sheath  15 , a spring  16 , a needle stand fixture and a cylindrical pushrod with the abovesaid structure; the needle syringe  13  forms a shoulder of contracting inward at its distal end, and the shoulder extends outward to form a cannula  17  with a less diameter than that of the needle syringe  13 , the inside wall is provided with a round of flange  18  at the connection position of the shoulder with the cannula  17 , and the outer wall of cannula  17  is provided with a round of flange or groove  1701 ; the needle stand  14  is a tubular body with a through hole  1401  in its center, the needle is fixed in the through hole  1401  of the needle stand  14 , the lower end of needle stand  14  is provided with a dummy club  1402 , and the needle stand  14  is installed within the cannula  17 ; the said needle stand fixture comprises the flange  18 , the dummy club  1402  and an O-shape seal ring  19 , the said O-shape seal ring  19  is set around the lower portion of dummy club  1402  of the needle stand  14 , the flange  18  supports the O-shape seal ring  19 , and the O-shape seal ring  19  supports the dummy club  1402  of the needle stand  14 , thereby the needle stand  14  is removably fixed in the cannula  17 ; the spring  16  is set around the needle stand  14  with its lower end supported on the dummy club  1402  of the needle stand  14 ; the needle stand sheath  15  has a hollow chamber opening rearward, the inner diameter of the chamber matches with the outer diameter of cannula  17 , and the inside wall is provided with a round of groove or flange  1501  clamping with the flange or groove  1701  on the outer wall of cannula  17 , the closed top end of needle stand sheath  15  has a through hole  1502 , the needle stand sheath  15  is installed on the cannula  17  mounted already with the needle stand  14 , the needle  1  extendes out from the through hole  1502 , the closed top end of needle stand sheath  15  press the upper end of spring  16  and prepress the spring  16  between the closed top end and the dummy club  1402  of the needle stand  14 , and then the lower border surface of the closed top end joints with the upper border surface of the top end of needle stand  14 ; the said cylindrical pushrod is installed within the needle syringe  13 , the thick cylinder  901  of its protective sleeve  9  is connected around partly on the outer wall of the rear end of needle syringe  13 , when the cylindrical pushrod is pushed to the top end of the chamber of needle syringe  13 , i.e. when the injection is complete, the top end of cylindrical pushrod drives the O-shape seal ring  19  to slide as a whole or partially so as to loose the needle stand fixture and release the needle stand  14 , at the same time, the lower border surface of needle syringe  13  push to disengage the clamping structure of the rear end of the cylindrical pushrod and releases the inner cylinder  2 .  
         [0024]     As a modified needle-retraction controllable safety injector according to the invention, which comprises a needle syringe  13 , a needle stand  14  for fixing a needle, a needle stand sheath  15 , a spring  16 , a needle stand fixture and a cylindrical pushrod with the abovesaid structure but without the protective sleeve  9 ; the needle syringe  13  forms a shoulder of contracting inward at its distal end, and the shoulder extends outward to form a cannula  17  with a less diameter than that of the needle syringe  13 , the inside wall is provided with a round of flange  18  at the connection position of the shoulder with the cannula  17 , and the outer wall of cannula  17  is provided with a round of flange or groove  1701 ; the needle stand  14  is a tubular body with a through hole  1401  in its center, the needle is fixed in the through hole  1401  of the needle stand  14 , the lower end of needle stand  14  is provided with a dummy club  1402 , and the needle stand  14  is installed within the cannula  17 ; the said needle stand fixture comprises the flange  18 , the dummy club  1402  and an O-shape seal ring  19 , the said O-shape seal ring  19  is set around the lower portion of dummy club  1402  of the needle stand  14 , the flange  18  supports the O-shape seal ring  19 , and the O-shape seal ring  19  supports the dummy club  1402  of the needle stand  14 , thereby the needle stand  14  is removably fixed in the cannula  17 ; the spring  16  is set around the needle stand  14  with its lower end supported on the dummy club  1402  of the needle stand  14 ; the needle stand sheath  15  has a hollow chamber opening rearward, the inner diameter of the chamber matches with the outer diameter of cannula  17 , and the inside wall is provided with a round of groove or flange  1501  clamping with the flange or groove  1701  on the outer wall of cannula  17 , the closed top end of needle stand sheath  15  has a through hole  1502 , the needle stand sheath  15  is installed on the cannula  17  mounted already with the needle stand  14 , the needle  1  extendes out from the through hole  1502 , the closed top end of needle stand sheath  15  press the upper end of spring  16  and prepress the spring  16  between the closed top end and the dummy club  1402  of the needle stand  14 , and then the lower border surface of the closed top end joints with the upper border surface of the top end of needle stand  14 ; the said cylindrical pushrod is installed within the needle syringe  13 , when the cylindrical pushrod is pushed to the top end of the chamber of needle syringe  13 , the top end of cylindrical pushrod drives the O-shape seal ring  19  to slide as a whole or partially so as to loose the needle stand fixture and release the needle stand  14 , at the same time, the lower border surface of needle syringe  13  push to disengage the clamping structure of the rear end of the cylindrical pushrod and releases the inner cylinder  2 .  
         [0025]     As a modified needle-retraction controllable safety injector according to the invention, wherein a protective patch  21  is provided between the roll rim  20  of the needle syringe  13  and the protective sleeve  9  to prevent the cylindrical pushrod from being pushed to the top end of the chamber of needle syringe  13  and the needle stand  14  and the clamping structure being loosed prior to the use of the injector due to a misoperation; the protective patch  21  can be fixed on the lower end surface of the roll rim  20 , and also can be fixed on the cylinder wall of the needle syringe  13  or the protective sleeve  9 .  
         [0026]     By comparison with the prior art, the cylindrical pushrod and the safety injector provided by the invention can achieve the following advantageous technical effects:  
         [0027]     First, in the safety injector mounted with the cylindrical pushrod according to the invention, even the needle stand  14  and the inner cylinder  2  are all in a releasing state after the injection is complete, the released needle stand still maintain its original position without retractation, because the operator still presses the rear end of the cylindrical pushrod with his/her finger, which makes the released inner cylinder  2  can not slide backward and the through hole  401  on the underpinned piece  4  can not be opened. As such, the operator can loose the finger pressing on the rear end of cylindrical pushrod after he(she) draws out the needle soas to let the needle retract into the injector. Therefore, the operator can control the time of the needle&#39;s retraction at his own will, and need not to change his operation practice. It facilitate the operation.  
         [0028]     Second, the safety injector according to the invention not only can carry out the controllable needle-retraction but also has a simple and crafty fixed structure of the needle stand, to achieve the effect of reliability as well as releasing with ease, and the needle stand can not move forward or sway unintentionally during being released to injure the patient.  
         [0029]     Third, the safety injector with the cylindrical pushrod according to the invention can push out the drug liquor in the needle syringe as much as possible before the needle-retraction to reduce the remains of drug liquor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]      FIG. 1  is a section view of a cylindrical pushrod as one of the embodiments of the invention;  
         [0031]      FIG. 2  is a section view of the outer cylinder of the cylindrical pushrod as shown in  FIG. 1 ;  
         [0032]      FIG. 3  is a section view of the inner cylinder of the cylindrical pushrod as shown in  FIG. 1 ;  
         [0033]      FIG. 4  is a section view of the outer cylinder used in another embodiment of the invention;  
         [0034]      FIG. 5  is a section view of the inner cylinder matching with the outer cylinder as shown in  FIG. 4 ;  
         [0035]      FIG. 6  is a section view of a push pole according to the invention;  
         [0036]      FIG. 7  is a top view of an underpinned piece according to the invention;  
         [0037]      FIG. 8  is a side view of the underpinned piece shown in  FIG. 7 ;  
         [0038]      FIG. 9  is a schematic drawing of another underpinned piece according to the invention;  
         [0039]      FIG. 10  is schematic drawing of the underpinned piece shown in  FIG. 9  when the underpinned patch is unfolded;  
         [0040]      FIG. 11  is a schematic drawing of the other underpin piece put forward by the invention;  
         [0041]      FIG. 12  is a schematic drawing of another underpinned piece according to the invention;  
         [0042]      FIG. 13  is a section view of the protective sleeve in the cylindrical pushrod shown in  FIG. 1 ;  
         [0043]      FIG. 14  is a partial section view of the cylindrical pushrod with the underpinned piece shown in  FIG. 9 ;  
         [0044]      FIG. 15  is a section view of a cylindrical pushrod according to another embodiment of the invention;  
         [0045]      FIG. 16  is a schematic drawing of the inner cylinder of cylindrical pushrod shown in  FIG. 15 ;  
         [0046]      FIG. 17  is a schematic drawing of the supporting piece of cylindrical pushrod shown in  FIG. 15 ;  
         [0047]      FIG. 18  is a section view of a needle-stopping piece according to the invention;  
         [0048]      FIG. 19  is a section view of a push pole according to the invention;  
         [0049]      FIG. 20  is a partial section view of another cylindrical pushrod according to the invention;  
         [0050]      FIG. 21  is a section view of a safety injector according to one of the embodiments of the invention;  
         [0051]      FIG. 22  is a section view of another safety injector according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0052]     The embodiments of the invention will be explained detailedly with reference to the accompanying drawings hereinafter.  
         [0053]     The first embodiment: as shown in  FIGS. 1-8  and  13 , the cylindrical pushrod for the needle-retracting safety injector according to this embodiment, comprises an outer cylinder  1 , an inner cylinder  2 , a push pole  3 , an underpinned piece  4  and a protective sleeve  9 ;  
         [0054]     Around the head of outer cylinder  1  is provided with a sealing gasket  5 ;  
         [0055]     The chamber of outer cylinder  1  contracts inward to form a shoulder  103  at the front end of outer cylinder  1 , and extends forward to form a hollow chamber with a smaller diameter;  
         [0056]     The push pole  3  is set in the hollow chamber with the smaller diameter at the front end of outer cylinder  1 , with its outer wall jointing with the inside wall of the front end of outer cylinder  1 , the front end of push pole  3  closes the frontend opening of outer cylinder  1  and outstands outside of the seal gasket  5 , and appears as a tubular shape or projects partially in longitudinal direction, and the back end of push pole  3  is supported on the underpinned piece  4 ;  
         [0057]     The underpinned piece  4  is a O-shape sheet with a through hole  401  at its center, and is provided with four upwarping elastic underpinned patchs  402 ;  
         [0058]     The underpin piece  4  is set at the front end of the chamber of outer cylinder  1 , and the top end surface of inner cylinder  2  pushs and presses the underpinned piece  4  to the shoulder  103  of the front end of chamber of outer cylinder  1  to press down the elastic underpinned patchs  402  which then occlude the through hole  401  and support the push pole  3 ;  
         [0059]     The inner cylinder  2  is set inside the outer cylinder  1  with its front end openend and its back end closed, and the top end surface of its cylinder wall supports the underpinned piece  4  to close the through hole  401 ;  
         [0060]     An annular dummy club  301  is set at the lower end of push pole  3 ; a sealing gasket  10  is mounted between the annular dummy club  301  and the frontend wall of the chamber of outer cylinder  1 ;  
         [0061]     The protective sleeve  9  is a jointed body of a thick cylinder  901  and a thin cylinder  902 ;  
         [0062]     A round of flange  106  is set on the outer wall of the rear portion of outer cylinder  1 ; the inner diameter of thin cylinder  902  matches with the outer diameter of outer cylinder  1 , a round of groove  903  set on the inside wall of the thin cylinder  902  to clamp with the flange  106 , the protective sleeve  9  is connected around the rear end of outer cylinder  1  and is fixed by the clamping relation between the groove  903  and the flange  106 , the thick cylinder  901  of the protective sleeve  9  covers the clamping structure after being mounted;  
         [0063]     The clamping structure of the rear portion of cylindrical pushrod has the following structure:  
         [0064]     The cylinder wall of rear portion of the outer cylinder  1  has two long hole  102 ;  
         [0065]     The cylinder wall of mid-back portion of inner cylinder  2  has two corresponding long holes  202  at the position matched with the long hole  102 , the upper border of long hole  202  extends downward to form an upright elastic strip  203 , and there are two raised blocks, the upper raised block and the lower raised block, on the outside wall of the elastic strip  203 , the distance between the lower end surface of upper raised block  204  and the lower end surface of lower raised block  205  equals the distance of inner cylinder  2  sliding backward for opening the through hole  401  to allow the push pole  3  passes through, the height of the upper raised block  204  exceeds that of the lower raised block  205 , and a slope is formed on the top portions, the upper and lower raised blocks are fixed in and protrude outside the long holes  102 , and the lower raised block  205  is supported on the lower border of the long hole  102  so that the inner cylinder  2  can be locked releasably on the outer cylinder  1 ;  
         [0066]     After the inner cylinder disengages with the outer cylinder, the inner cylinder  2  slides backward under the action of retractive force of the pinhead to a distance so that the through hole  401  is opened to allow the push pole  3  passes through, and then the inner cylinder  2  is locked on the outer cylinder  1  again with the upper raised block  204 .  
         [0067]     The second embodiment: as shown in  FIGS. 15-19 , the basic structure of this embodiment is similar to that of the first embodiment, the differences include:  
         [0068]     The clamping structure of the rear portion of the cylindrical pushrod comprises a supporting piece  6 :  
         [0069]     The supporting piece  6  is composed of one O-shape ring part  601 , two elastic strips  602  and two raised blocks  603 ;  
         [0070]     The two elastic strips  602  are set opposing to each other at both sides of O-shape ring part  601 ;  
         [0071]     The two raised blocks  603  are set respectively at the position on the outside of two elastic strip  602  with the same height, and the two raised blocks  603  each has a slope on the top;  
         [0072]     The cylinder wall of outer cylinder  1  is provided respectively with the holes  101  having a matched shape with the raised blocks  603  respectively in the position matching with the two raised blocks  603 ;  
         [0073]     After the supporting piece  6  is mounted, the two raised blocks  603  engage into the holes  101  respectively and protrude beyond the holes  101 ;  
         [0074]     The cylinder wall of rear portion of inner cylinder  2  exists two long holes  201  opposing to each other;  
         [0075]     The supporting piece  6  is set around the rear portion of inner cylinder  2  in the position of the long holes  201  of and engaged in the holes  101  of outer cylinder  1 , and the upper end of elastic strip  602  supports the superior border&#39;s surface of the long holes  201  of inner cylinder  2 .  
         [0076]     The cylindrical pushrod in this embodiment further comprises a compressible needle-stopping piece  11 ;  
         [0077]     The needle-stopping piece  11  is composed of a piston head  1101  and a compressible part, the compressible part is a hollow thinwall pipe  1102 ;  
         [0078]     At the front end of push pole  3  is provided with a hollow chamber; the needle-stopping piece  11  is set within the hollow chamber at the front end of push pole  3 , the needle-stopping piece  11  has an exposed part at the front end which is higher than the front end of push pole  3  after plugging the opening of the hollow chamber of push pole  3 , and the compressive force of the needle-stopping piece  11  is larger than the retractive force of the needle;  
         [0079]     A groove  1105  is set on the top surface of the needle-stopping piece  11 ;  
         [0080]     A slot  302  communicated with the groove  1105  is set in the the chamber wall of the hollow chamber at the front end of push pole  3 .  
         [0081]     The third embodiment: as shown in  FIGS. 9, 10 ,  14 ,  20  and  21 , the basic structure of this embodiment is similar to that of the first embodiment, the differences include:  
         [0082]     The underpinned piece  4  is a ring part on which a through hole  401  and the underpinned patch  402  are provided, and a round of flange  403  playing the function of clamping is provided on its side wall, one end of the underpinned patch  402  is free, and the other end of the underpinned patch connects to the underpinned piece  4  with a flexional feeble layer;  
         [0083]     The underpinned piece  4  is set at the front end of the chamber of outer cylinder  1 , a round of groove  105  are provided on the cylinder wall of the front end in the chamber of outer cylinder  1  to match with flange  403  on the underpinned piece  4 , and the underpinned piece  4  is fixed at the front end of the chamber of outer cylinder  1  through the clamping effect of the groove and flange;  
         [0084]     The top end surface of the cylinder wall of inner cylinder  2  supports the free end of the underpinned patch  402  to close the through hole  401 ;  
         [0085]     The push pole  3  can be changed into a compressible needle-stopping piece  12 ;  
         [0086]     The needle-stopping piece  12  comprises a piston head  1201  and a compressible part, and its rear end is provided with a supporting dummy club  1205  matching with the shoulder at the top end of chamber of outer cylinder  1 ;  
         [0087]     The front end of the piston head  1201  plugs into the opening of the hollow chamber of outer cylinder  1  and has an exposed part which is higher than the front end of outer cylinder  1 ;  
         [0088]     The compressible part is a hollow thinwall pipe  1202 , also may be a hollow corrugated pipe  1203 , or may be a spring supporting the piston head  1201  (not shown in drawings);  
         [0089]     The outer cylinder  1  shows up a front end in a tubular shape or with partial longitudinal projection after the seal gasket  5  is mounted thereon;  
         [0090]     The front end of the needle-stopping piece  12  plugs into the opening of the hollow chamber of outer cylinder  1  and has an exposed part at its front end which is higher than the front end of outer cylinder  1 , the rear end of this needle-stopping piece is compressible and is supported on the underpinned piece  4 , the compressive force of the needle-stopping piece  12  is higher than the retractive force of the needle;  
         [0091]     On the top end surface of the needle-stopping piece  12  is provided with a groove  1206 ;  
         [0092]     On the cylinder wall of front end of outer cylinder  1  is provided with a slot for communicating with the groove (not shown in drawings).  
         [0093]     The forth embodiment: as shown in  FIG. 21 , the needle-retraction controllable safety injector according to this embodiment, comprises a needle syringe  13 , a needle stand  14  for fixing a needle, a needle stand sheath  15 , a spring  16 , a needle stand fixture and a cylindrical pushrod as said in the third embodiment;  
         [0094]     The needle syringe  13  forms a shoulder of contracting inward at its distal end, and the shoulder extends outward to form a cannula  17  with a less diameter than that of the needle syringe  13 , the inside wall is provided with a round of flange  18  at the connection position of the shoulder with the cannula  17 , and the outer wall of cannula  17  is provided with a round of flange  1701 ;  
         [0095]     The needle stand  14  is a tubular body with a through hole  1401  in its center, the needle is fixed in the through hole  1401  of the needle stand  14 , the lower end of needle stand  14  is provided with a dummy club  1402 , and the needle stand  14  is installed within the cnnula  17 ;  
         [0096]     The needle stand fixture comprises a flange  18 , a dummy club  1402  and an O-shape seal ring  19 , the O-shape seal ring  19  is set around the lower portion of dummy club  1402  of the needle stand  14 , the flange  18  supports the O-shape seal ring  19 , and the O-shape seal ring  19  supports the dummy club  1402  of the needle stand  14 , thereby the needle stand  14  is removably fixed in the cannula  17 ;  
         [0097]     The spring  16  is set around the needle stand  14  with its lower end supported on the dummy club  1402  of the needle stand  14 ;  
         [0098]     The needle stand sheath  15  has a hollow chamber opening rearward, the inner diameter of the chamber matches with the outer diameter of cannula  17 , and the inside wall is provided with a round of groove  1501  clamping with the flange or groove  1701  on the outer wall of cannula  17 , the closed top end of needle stand sheath  15  has a through hole  1502 , the needle stand sheath  15  is installed on the cannula  17  mounted with the needle stand  14 , the needle  1  extends out from the through hole  1502 , the closed top end of needle stand sheath  15  press the upper end of spring  16  and prepress the spring  16  between the closed top end and the dummy club  1402  of the needle stand  14 , and then the inferior border surface of the closed top end joints with the superior border surface of the top end of needle stand  14 ;  
         [0099]     The cylindrical pushrod is installed within the needle syringe  13 , the thick cylinder  901  of its protective sleeve  9  is connected around partly on the outer wall of the rear end of needle syringe  13 , when the cylindrical pushrod is pushed to the top end of the chamber of needle syringe  13 , the top end of cylindrical pushrod drives the O-shape seal ring  19  to slide as a whole or partially so as to loose the needle stand fixture and release the needle stand  14 , at the same time, the inferior border surface of needle syringe  13  pushs to disengage the clamping structure of the rear end of the cylindrical pushrod and releases the inner cylinder  2 ;  
         [0100]     A protective patch  21  is set between the roll rim  20  of the needle syringe  13  and the protective sleeve  9 , the protective patch  21  is fixed on the inferior end surface of the roll  20  and on the cylinder wall of needle syringe  13 .  
         [0101]     The fifth embodiment: as shown in  FIG. 22 , the basic structure of the needle-retraction controllable safety injector of this embodiment is similar to that of the forth embodiment, the difference include:  
         [0102]     The said needle-retraction controllable safety injector comprises the cylindrical pushrod as said in the second embodiment.