the present safety device described herein is directed to a needle guard for a syringe having the safety device triggering mechanism independent of the syringe and stopper tolerances . the fully assembled safety device 10 is shown in fig1 . the assembly of the device 10 comprises a main body 60 with a plunger 22 emanating proximally from the proximal end 68 and a rigid needle shield ( rns ) 40 and rns removal tool 50 emanating distally from the main body 60 . inside the device 10 , as shown in fig2 , is a prefilled syringe 20 with an attached needle 24 with the rns 40 covering over the needle 24 to protect the needle and maintain a sterile barrier for the medication injection pathways . at the distal end of the assembly is the rns removal tool 50 , which is a removable covering over the rns 40 that facilitates its removal just before injecting medication into the patient . the plunger 22 is attached to a syringe stopper 26 . at the distal end of the assembly inside the main body 60 is the needle guard body 80 , which is a tube that is concentric and interior to the main body 60 ( see fig2 , 5 , and 6 ). as shown in fig2 and 3 , the needle guard body 80 is axially slide - able with respect to the rest of the main body 60 and is biased in a distal direction by a compression spring 61 positioned between a syringe flange 34 and the needle guard body 80 , and acting on a proximal end 82 of the needle guard body 80 . initially , the needle guard body 80 is held in a proximal position by the rns removal tool 50 . the rns removal tool 50 is held in this position against the force of the spring 61 by retention barbs 54 that project outwardly at the proximal end 55 of the rns removal tool 50 and that mate with corresponding retention windows 62 in the wall 63 of the main body 60 of the device 10 ( see fig3 , 11 , 13 - 16 ). immediately before injecting medication into a patient , the rns 40 , as depicted in fig5 , is removed by squeezing the rns removal tool 50 , which collapses along two slits 52 that run along the side of the tool 50 starting at its proximal end 55 . the collapsed configuration of the tool 50 allows the retention barbs 54 at the proximal end 55 to disengage from the corresponding retention windows 62 in the main body 60 of the device 10 . an inwardly projecting capture lip 75 , at the proximal inside surface of the rns removal tool 50 , grasps the proximal edge 42 of the rns 40 , which in combination with the compressive force transmitted by the collapsed rns removal tool 50 walls allows it to pull the rns 40 from the distal end of the syringe 20 when the user pulls it in a distal direction ( see fig5 and 17 ). as the rns removal tool 50 is withdrawn from the end of the device 10 , the needle guard body 80 slides forward , as shown in fig6 , to an intermediate stop point b as shown in fig4 a and 4c , governed by the interference between one or more inwardly projecting protrusions 64 from the main body 60 and corresponding grooves 90 in the outer surface of the needle guard body 80 . the outer side of one protrusion 64 on the main body 60 is shown in fig3 b - 4e , 5 and 6 . they are positioned at the end of cut - out sections that provide flexibility to the protrusions arms 65 . the protrusions 64 interfere with the needle guard body grooves 90 by projecting into the groove space and controlling the movement of the needle guard body 80 against the distally directed force of the spring 61 and the proximally directed reaction force from the patient &# 39 ; s skin . prior to removal of the rns 40 , the protrusion 64 is in position a of the needle guard body grooves 90 as shown in fig4 a and 4b . after the rns 40 is removed , the needle guard body 80 moves distally in response to the force of the spring 61 , so that the protrusion 64 travels along a first groove section 91 to position b as shown in fig4 c . this includes some rotational movement of the needle guard body 80 as the protrusion 64 pushes against the angled wall of the first groove section 91 just before position b . this transition to position b includes a step 92 prior to groove deepening of the guard body groove 90 just prior to entering position b in a second groove section 93 to prevent the protrusion 64 from retracing its path back along the first groove section 91 toward position a . as the needle 24 is inserted into the patient , the patient &# 39 ; s skin pushes the needle guard body 80 proximally against the force of the spring 61 , such that the groove - protrusion 90 - 64 interface moves from position b along the second groove section 93 to position c as shown in fig4 a . toward the distal end of the second groove section 93 , the groove depth steps down to a fourth , deeper groove section 94 along an edge 96 that is angled to the axis of the needle guard body 80 . at this point , the user must hold the device 10 against the skin working against the force of the spring 61 and perform the injection . after the injection is complete and the device 10 is pulled away from the patient , the needle guard body 80 moves distally , as shown in fig4 d , under the force of the spring 61 from position c to position d with the protrusions 64 in the deeper groove section 94 such that the protrusions 64 encounter the stepped surface 96 causing the needle guard body 80 to rotate with respect to the main body 60 and enter a final groove section 98 in route to position d . as shown in fig4 a , 4e and 4f , upon further distal movement of the needle guard body 80 , the protrusion 64 drops into a further deepening of the groove 90 at a groove recess 99 such that the protrusion 64 is substantially captured in the groove recess 99 in a locked out state . this engagement prevents relative motion of the needle guard body 80 with respect to the main body 60 . as the needle guard body 80 moves from position c to position d as the needle 24 is pulled from the patient , it is projected distally around the needle 24 to the extent that it protects the caregiver and others from inadvertently being stuck by the needle tip 25 . as shown in fig4 e and 4f , the needle guard body 80 is held in this needle - shielding position by interference of the protrusions 64 in the groove recess 99 at position d so that the needle guard body 80 cannot be pushed proximally with respect to the main body 60 , or pulled distally with respect to the main body 60 . for patients that have limited hand strength , holding the device against the skin while the needle 24 is in the injection site , requires maintaining a force against the spring 61 that pushes against the needle guard body 80 ( position c in fig4 a ). an alternative embodiment of the device to lessen this axial force could be accomplished by increasing the angle of the stepped surface 96 in the deeper groove section 94 that starts proximally to point c as shown in fig4 a and 4d and deflects the main body protrusion 64 over to the straight groove section 98 that ends at position d . in fig4 a and 4d , this angle is shown at about 45 degrees . an angle of perhaps 60 degrees would place a greater axial component of force against the spring force at some reduction of the lateral force . of course , an angle of 90 degrees would hold the needle guard body 80 completely against the force of the spring 61 if the main body protrusion 64 could stay down in the deeper groove section 94 , but there would be no lateral deflection to get the main body protrusion 64 over to position d where the device 10 locks out into the desired safety configuration . depending on the coefficient of friction between the main body protrusion 64 and the needle guard body 80 , the angle can be optimized to reduce the holding force for the patient , but still allow the main body protrusion 64 to lockout at position d shown in fig4 a , 4e and 4f . the sequence of steps to operate the device is described in fig5 through 10 . first , as shown in fig5 , the rns removal tool 50 is squeezed and pulled distally to remove the rns 40 from the device . squeezing the rns removal tool 50 disengages the retention barbs 54 from the barb retention windows 62 and the capture lips 75 grip the proximal end of the rns 40 , thus removing the rns 40 as the rns removal tool 50 is pulled distally outward from the device . as a result of the removal of the rns 40 and the rns removal tool 50 , the needle guard body 80 moves distally to the position shown in fig6 , under the force of the spring 61 . a composite of 3 steps to inject medication is shown in fig7 and 8 . in step 1 , the needle guard body 80 is placed against the patient &# 39 ; s injection site 100 . in step 2 , the device 10 is pushed against the injection site 100 , causing the needle guard body 80 to move proximally with respect to the main body 60 allowing the needle 24 to enter into the injection site 100 . in step 3 , the plunger rod 22 is pushed forward to dispel the medication into the injection site 100 . fig8 also shows a cross - section of the device 10 with the needle guard 80 fully retracted and after the plunger 22 has been fully depressed . in fig9 , the device 10 is being withdrawn from the injection site while the spring 61 pushes the needle guard body 80 distally . as the device 10 is fully withdrawn from the injection site 100 , the needle guard body 80 fully extends forward as shown in fig1 . at this point the main body protrusions 64 have entered position d in the groove 98 of the needle guard body 80 as shown in fig4 e and 4f and locked the needle guard body 80 from further motion with respect to the main body 60 to prevent any needle sticks . to facilitate movement of the main body 60 and its protrusions 64 with respect to the grooves 90 of the needle guard body 80 , one or both components can be made using a plastic resin with ample lubrication ( e . g . high content of mold release ). alternatively , dissimilar plastic resins exhibiting a low mutual coefficient of friction can be used for the components . it is to be understood that there exist alternative arrangements of components that would still fall within the scope of what is described and claimed within this application . for instance , the needle guard body 80 could be positioned on the outside of the main body with interior - facing grooves and outwardly facing protrusions on the main body 80 . an alternative embodiment for the safety device is presented for use with light - sensitive drugs that require only minimal exposure to light . in this embodiment , the components of the device are made of opaque materials ( e . g . plastic resins with pigments , tinted glass , etc .) that effectively block light from reaching the drug in the medication delivery device . however , drug injection instructions normally require the caregiver to inspect the drug to check that it is not cloudy , etc . prior to giving the injection . to achieve this , as shown in fig1 and 12 the main body 60 and needle guard body 80 of the device 10 have diametrically opposed windows that are positioned with respect to each other such that they are not aligned until the rns removal tool 50 and rns 40 have been removed . after removal , when the diametrically opposed windows on the two components align , as shown in fig1 , they form a line of sight through the device 10 , which enables the caregiver to inspect the drug volume . referring to fig1 , prior to the removal of the rns 40 and rns removal tool 50 , the main body window 69 is blocked internally by the outer surface of the opaque needle guard body 80 . in fig1 , after the rns 40 has been removed and the needle guard body 80 has moved forward , the window 69 of the main body 60 is aligned with the window 85 of the opaque needle guard body 80 allowing visibility into the syringe 20 . a similar window is provided on the diametrically opposite side of the device 10 . the rns 40 , rns removal tool 50 , and plunger rod 22 components would also be made of opaque materials to prevent light exposure at the ends of the device 10 . a covering ( not shown ) over the proximal end of the syringe with a hole for the plunger rod could also be created to provide additional light protection . similarly , a second cover ( 158 ; see fig1 a ) could be placed over the distal end of the rns removal tool to block light from entering the distal end . the rns 40 not only protects the needle 24 from being bent or its tip 25 from being damaged but it also forms one of the sterile barriers for the drug closure system . it must perform these functions before , during , and after sterilization and is therefore a complicated component that receives a tremendous amount of testing during the drug development and approval process . since it has potential contact with the drug inside the syringe 20 , it becomes part of the specific drug closure system that receives regulatory approval and is therefore difficult to change after approval . they have become industry standard devices produced by specialized third party manufacturers . nevertheless , they have limitations and deficiencies , namely that they can become difficult to remove from the syringe 20 after sterilization and storage , often requiring greater than 20n of force to remove . on a small part ( approximately 0 . 25 inches in diameter , 1 inch long ) such as this , it makes it difficult for healthcare workers to remove due to the small grasping area . patients that perform self - administration , especially those with limited manual dexterity or strength ( e . g . arthritic or multiple sclerosis patients ) will find it extremely difficult to remove . therefore , an added improvement of the present device 10 is to facilitate the rns 40 removal . this is accomplished by the rns removal tool 50 , which , as shown in fig1 , 14 , 15 , 23 and 24 , in addition to presenting a bigger surface area with which the user can grab , it also features some cam mechanisms to provide mechanical leverage in removing the rns 40 . as depicted , the rns removal tool retention barbs 54 reside inside the main body barb retention window 62 before the rns 40 is removed . the lateral sides 110 of the barb 54 and the corresponding edges of the main body barb retention window 62 are angled , as shown in fig1 , such that as the rns removal tool 50 is rotated , the barbs 54 push against the edge of the window 62 and are deflected radially inward as shown in fig1 and 17 . the axial cam follower 56 on the rns removal tool 50 , as shown in fig1 , has not yet acted against the main body axial cam profile 66 . the mechanical advantage of the barbs 54 engaging the edges of the retention windows 62 provides a strong radial squeeze so that the inwardly projecting capture lips 75 on the rns removal tool 50 further engages the proximal edge 42 of the rns 40 as shown in fig1 and 22 . this engagement cannot pre - exist sufficiently since the syringe 20 and rns 40 must assemble into the device 10 , from the proximal to distal end of device 10 , with minimal resistance or disturbance to the rns 40 seal as shown in fig1 . after the proximal end 42 of the rns 40 is engaged by the rns removal tool 50 , the axial cam follower 56 engages a sloped surface 67 of the main body axial cam profile 66 as shown in fig1 which places a mechanically advantaged axial force on the rns removal tool 50 in a distal direction , creating a distal axial displacement and forming a gap between the main body 60 and the rna removal tool 50 . because of the radial and axial cam surface between the rns removal tool 50 and the main body 60 , the rns removal tool 50 pushes the rns 40 off of the syringe 20 and needle 24 with much less effort on the part of the user than would normally be required . although this description has used a rns 40 as an example , soft needle shields , which do not have a hard plastic outer shell , could equally be used in this application with minor changes to account for different geometry . a further improvement to the device could be a distal end cap 158 ( fig1 a ) on the rns removal tool 50 and a proximal inwardly projecting lip ( not shown ) that together would help contain the rns 40 after it had been removed from the syringe 20 , preventing it from falling to the floor , etc . the rns removal tool 50 can also have large cut - through arrows 51 indicating the direction of rotation to the end user . it could also have large wings 53 extending radially outward to provide greater rotational mechanical advantage for the end user ( see fig1 ). the rns removal tool 50 , as described above , pulls the rns 40 off the syringe / needle 24 by radially collapsing at the proximal end of the rns 40 . when the rns removal tool 50 has completely pulled the rns 40 off the syringe / needle 24 and the user relaxes their grip , the collapsed capture of the proximal end of the rns 40 may no longer be present allowing the rns 40 to unexpectedly separate and fall from the rns removal tool 50 . an improved version of the rns removal tool 150 is shown in fig1 a and 18b , wherein an elastomeric insert 157 is placed inside the rns removal tool 150 such that it nominally has a slight press fit against the rns 40 , the fit being moderate enough to allow for installation of the rns 40 from the proximal direction during syringe 20 insertion yet sufficient enough to maintain a frictional grip on the rns 40 to prevent it from separating from the rns removal tool 150 in the absence of any collapsing grip from the rns removal tool 150 . the size and durometer of the elastomeric insert 157 is such that when the rns removal tool 150 is rotated as in fig1 , the radial squeezing of the rns removal tool 150 transmits a sufficient squeezing force against the rns 40 through the elastomeric insert 157 so as to pull the rns 40 from the syringe / needle 24 . internal circumferential ribs may assist for transmitting a gripping force onto the rns 40 . for those applications where full inspection of the syringe drug contents is required before injection , the main body window 69 shown in fig1 can be elongated the amount of the syringe body as shown in fig1 . this would also require that the needle guard body 80 be transparent or have a corresponding window since the drug inspection may need to occur before the device is readied for administration . in an alternate embodiment shown in fig2 - 24 , the capture lip 75 of the rns removal tool 50 , may come up over the syringe barrel 20 slightly when the device 10 is fully assembled . consequently , when the rns removal tool 50 is rotated during rigid needle shield 40 removal , the cam surface 110 on the rns retention barbs 54 , presses against the main body retention window 62 , forcing the rns removal tool arms 58 to press radially inward , causing the rns removal tool capture lip 75 to press against the barrel of the syringe 20 rather than the rns 40 . this is advantageous during the rotational portion of rns 40 removal to avoid rotation of the soft needle shield 46 with respect to the syringe needle , which can affect the quality or sharpness of the needle prior to insertion into a patient . in this embodiment , as the rns removal tool capture lip 75 presses against the barrel of the syringe 20 as it is rotated , the friction created between the two components will impart a force on the barrel of the syringe 20 to encourage rotation of the entire syringe — rns assembly 200 ( fig2 ). it is expected that either the syringe — rns assembly 200 will rotate with the rns removal tool 50 , or due to the friction between the syringe flange 34 , spring 61 , and main body 60 ( fig2 ), the syringe — rns assembly 200 will remain fixed and the rns removal tool 50 will rotate around it . as the rns removal tool 50 rotates the axial cam follower 56 will encounter the main body axial cam profile 66 forcing the rns removal tool 50 to move axially away from the syringe 20 . once the axial cam follower 56 on the rns removal tool 50 reaches the end of the main body axial cam profile 66 the user will be required to continue to pull the rns removal tool 50 from the device 10 , which will be aided by the needle guard body 80 , powered by the spring 61 . as the rns removal tool 50 is moving axially away from the syringe 20 , the rns removal tool capture lip 75 will be pressed against the barrel of the syringe 20 ( fig2 ). it will continue to remain in contact with the syringe 20 , even as it reaches the syringe neck down area 28 . consequently , the rns removal tool capture lip 75 will capture the rns 40 as the rns removal tool 50 is removed from the device 10 ( fig2 ). by captured , it is meant that the surface of the rns removal tool capture lips 75 will slide radially inward and over the proximal end surface 42 of the rns 40 . as the rns removal tool 50 is removed from the device 10 it will pull the rns 40 axially from the syringe 20 , ultimately removing it from the syringe 20 . in the foregoing specification , the invention has been described with reference to specific embodiments thereof . it will , however , be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention . for example , the reader is to understand that the specific ordering and combination of process actions described herein is merely illustrative , unless otherwise stated , and the invention can be performed using different or additional process actions , or a different combination or ordering of process actions . as another example , each feature of one embodiment can be mixed and matched with other features shown in other embodiments . features and processes known to those of ordinary skill may similarly be incorporated as desired . additionally and obviously , features may be added or subtracted as desired . accordingly , the invention is not to be restricted except in light of the attached claims and their equivalents .
a device that is used in conjunction with a needle - based medication injection device that prevents needle stick injuries . the used needle is shielded by a needle guard that surrounds and extends beyond the needle tip . in a preferred embodiment , before the needle is inserted into the patient , the needle guard projects forward to substantially hide visibility of the needle for safety and to reduce patient anxiety .