in its preferred embodiment , the invention is intended to be used in conjunction with a conventional blood collection tube and holder ; however , it is anticipated that the present invention may be modified for use with nearly any medical or laboratory device ; such as a syringe , without departing from the contemplated scope of the present invention as defined by the claims attached hereto . in describing the present invention , the term &# 34 ; distal end &# 34 ; of an element refers to the end of the element closest to the needle point of the device which is designed to pierce the skin of the patient . the term &# 34 ; proximal end &# 34 ; of an element refers to the end of the element furthest from the needle point which is designed to pierce the skin of the patient . the terms &# 34 ; inner &# 34 ; or &# 34 ; inwardly &# 34 ; and &# 34 ; outer &# 34 ; or &# 34 ; outwardly &# 34 ; are used herein to refer to the orientation of an element with respect to the reference plane designated as a -- a in fig1 and 10 . the reference plane a -- a extends generally through the central axis of the blood collection tube holder and along the proximal needle section . as illustrated in the attached drawings , the present invention generally includes a blood collection device 10 consisting of a blood collection tube ( not shown ), a blood collection tube holder 14 and a needle housing 16 . the blood collection tube described herein is a conventional evacuated tube having a needle pierceable stopper thereon . the blood collection tube holder 14 described herein is a conventional blood collection tube holder consisting of a pair of proximal finger flanges ( not shown ), an elongate barrel section 20 and a preferably threaded needle hub mounting section 22 positioned on the distal end of the blood collection tube holder 14 . in the preferred embodiment , the needle housing 16 preferably consists of a foldable , one - piece molded element which may be molded as illustrated in fig4 a and 4b and then folded and bonded around the nonlinear needle referred to here in as needle 24 to form the needle housing 16 illustrated in fig1 . it is anticipated that the needle housing 16 may also be formed by a pair of molded elements bonded together to retain the needle 24 therein . the needle housing 16 as illustrated in fig4 a and 4b , includes a needle recess 18 , a bonding surface 19 , a needle protecting lip 21 and a shield alignment lip 23 . the needle recess 18 is located on each half of the needle housing 16 to retain the needle 24 therein in a fixed position . the bonding surface 19 consists of a protrusion on one of the halves of the needle housing 16 and a matching recess on the other half to irreversibly retain the needle housing 16 in the assembly position . the needle protecting lip 21 extends outwardly from the top of one half of the needle housing 16 in an overlapping manner into a corresponding recess on the opposing half of the needle housing 16 to maintain the sterility of the needle 24 and to prevent access to the needle 24 when the needle housing 16 is assembled . the shield alignment lip 23 extends into the cylindrical shield support member 32 to contact the elongate slit 40 on the protective shield 28 to prevent rotational movement of the protective shield 28 as it is moved between the retracted and extended positions . the assembled needle housing 16 preferably includes the nonlinear needle 24 , a needle hub section 26 , a shield support member 32 and a shield assembly 27 consisting of a protective shield 28 and a finger member 30 . the needle 24 of the present invention consists generally of a proximal needle section 34 which is preferably straight and extends proximally beyond the proximal end of the needle hub section 26 to a sharpened proximal point 35 ; a curved intermediate needle section 36 is contained within the needle hub section 26 to create the preferred nonlinear orientation of the needle 24 and a distal needle section 38 which is preferably straight and extends distally beyond the distal end of the needle hub section 26 . the proximal needle section 34 and the distal needle section 38 of the needle 24 are preferably oriented in a generally parallel and offset manner with respect to each other to facilitate single handed operation of the present invention . the distal end of the needle 24 includes a bevelled distal needle point 39 oriented to facilitate the insertion of the distal needle section 38 into the vein of the patient . the proximal needle point 35 on the proximal end of the needle 24 is designed to pierce the stopper of a blood collection tube once the proximal end of the needle hub section 26 has been threaded onto the hub mounting section 22 of the blood collection tube holder 14 . the needle hub section 26 of the present invention preferably consists of a separately molded element having a threaded section thereon to facilitate the attachment of the blood collection tube holder 34 thereto . the needle hub section 26 is preferably adhesively bonded or welded to a recess on the inner , proximal side of the needle housing 16 . the protective shield 28 of the present invention preferably consists of an elongate tubular member constructed of a semi - rigid polypropylene having a sufficient rigidity to protect against being deflected off the distal needle section 38 while having sufficient flexibility to be positioned along the length dimension of the distal needle section 38 in an overlapping or encircling manner . the protective shield 28 includes an elongate slit 40 extending proximally from the distal end thereof to a location approximately midway along the shield assembly 122 and a pair of radial tabs 41 near the distal end of the protective shield 28 . the proximal end of the shield assembly 27 includes the finger member 30 which extends proximally from the proximal end of the protective shield 28 . the protective shield 28 and finger member 30 are slidably retained in the shield support member 32 and are preferably positioned to slide in the shield support member 32 adjacent to the barrel section 20 of the blood collection tube holder 14 . the protective shield 28 is further axially aligned to slide along the distal needle section 38 of the needle 24 . although the shield assembly 27 is preferably constructed as a two - piece molded or extruded element wherein the protective shield 28 and finger member 30 are formed as separate elements which are then assembled together with either a frictional fit , adhesives or nearly any other convenient method of attachment , it is readily anticipated that the shield assembly 27 may also be formed as a single - piece molded or extruded element . in this embodiment , a generally wedge - shaped start detent recess 42 is positioned on the outer side of the shield support member 32 adjacent to the proximal end of the protective shield 28 . a needle recess ( not shown ) is located near the proximal end of the inner surface of protective shield 28 adjacent to the finger member 30 . the needle recess is preferably an enlarged opening on the proximal end of the elongate slit 40 to allow the protective shield to enclose the proximal end of the distal needle section 38 when the protective shield 28 is in the extended position . a biased locking tab 46 is positioned on the inner surface of the shield assembly 27 on the finger member 30 . the locking tab 46 is biased inwardly from the finger member 30 to form a contacting relation with a locking recess 48 located on the inner side surface of the shield support member 32 when the protective shield 28 is in the fully extended position . the shield support member 32 of the shield assembly 27 includes an enclosed elongate groove or channel along the outer side of the needle housing 16 to enclose a portion of the shield assembly 27 therein . the distal end of the shield support member 32 includes an enlarged recess 43 to releasably retain the radial tabs 41 therein when the protective shield 28 is in the retracted position . the proximal end of the shield support member 32 is semicircular and extends beyond the proximal end of the needle housing 16 to allow the shield assembly 27 to be slidably moved therein a sufficient distance to allow the protective shield 28 to expose the distal needle section 38 when the protective shield 28 is moved to the retracted position . the groove or channel section of the shield support member 32 extends to the distal end of the needle housing 16 to form a distal shield opening 62 which is adjacent to the enlarged recess 43 and positioned generally at the intersection of the intermediate needle section 36 and the distal needle section 38 . a locking recess 48 is positioned approximately midway along the inner side surface of the shield support member 32 to retain the locking tab 46 from the shield assembly 27 therein when the protective shield 28 is in the fully extended position . the outer side surface of the shield support member 32 includes an inwardly biased start detent 50 . the start detent 50 is positioned in a side recess 52 on the needle housing 16 . the proximal end of the start detent 50 preferably includes a pair of contacting lips 42 to frictionally contact the sides of the side recess 52 to retain the start detent 50 in the neutralized position once the shield assembly 27 is moved proximally from the initial start position . fig2 and 3 illustrate the blood collection device 10 of the preferred embodiment assembled for shipping and storage . the proximal end of the blood collection device 10 includes a rectangularly shaped proximal hard case 56 which is preferably heat staked to the needle housing 16 . the proximal hard case 56 encloses and maintains the sterility of the proximal end of the shield assembly 27 and the shield support member 32 during shipping and storage . a rubber needle sleeve 58 is also preferably positioned on the proximal needle section 34 to prevent accidental needle sticks when the proximal hard case 56 is removed and prior to the insertion of the proximal needle section 34 into the blood collection tube holder 14 . once the hub mounting section 22 of the blood collection tube holder 14 is threaded into the needle hub section 26 of the needle housing 16 , the elongate barrel section 20 of the blood collection tube holder 14 protects the user from accidentally contacting the proximal needle point 35 of the proximal needle section 34 . the distal end of the blood collection device 10 includes a distal hard case 60 which is heat staked to the distal end of the needle housing 16 . the distal hard case 60 encloses and maintains the sterility of the distal needle section 38 and protects the distal needle point 39 during shipping and storage . when the health care worker desires to obtain a blood sample from a patient , the health care worker initially applies lateral pressure to the proximal hard case 56 to break the heat stake on the needle housing 16 . next , the blood collection tube holder 14 is threaded onto the needle hub section 26 of the needle housing 16 . once the appropriate site on the patient &# 39 ; s arm has been prepared , the health care worker may remove the distal hard case 60 from the needle housing 16 by rotating the distal hard case 60 until the heat stake is broken . next , the health care worker moves the shield assembly 27 from the start position wherein the protective shield 28 substantially encloses the distal needle section 38 to the retracted position by placing their thumb on the finger member 30 to move the finger member 30 proximally along the shield support member 32 until the distal needle section 38 is uncovered by the protective shield 28 . as the shield assembly 27 is moved proximally along the shield support member 32 , the protective shield 28 and the elongate slit 40 are moved over the distal portion of the intermediate needle section 36 and the distal needle section 38 . the start detent 50 is also moved from an initial start position in the start detent recess 42 to a neutralized position wherein the contacting lips 54 of the start detent 50 frictionally contact the sides of the side recess 52 to create a generally planar relation along the interior surface of the shield support member 32 so that the start detent 50 does not interfere with any further movement of the shield assembly 27 in the shield support member 32 . the shield assembly 27 is moved proximally in the shield support member 32 until the radial tabs 41 reach the enlarged recess 43 which prevents further proximal movement of the shield assembly 27 in the shield support member 32 . once the shield assembly 27 is in the retracted position , the blood collection device 10 and the distal needle section 38 of the needle 24 may then be aligned parallel to the vein of the patient so that the bevelled end of the distal needle point 39 is adjacent to the skin of the patient . the distal needle section 38 of the needle 24 is then inserted into the vein of the patient and an evacuated blood collection tube is inserted into the blood collection tube holder 14 . as the blood collection tube is inserted into the blood collection tube holder 14 , the stopper of the blood collection tube contacts the rubber needle sleeve 58 and causes the proximal needle point 35 to pierce the rubber needle sleeve 58 . the stopper then compresses the rubber needle sleeve 58 against the needle hub section 26 of the needle housing 16 as the blood collection tube is pushed into the blood collection tube holder 14 . once the proximal needle section 34 passes through the stopper of the blood collection tube , blood is drawn from the vein of the patient into the evacuated blood collection tube . when a sufficient blood sample has been obtained from the patient , the blood collection tube is removed from the blood collection tube holder 14 and the rubber needle sleeve 58 resiliently covers the proximal needle section 34 . if a further blood sample is desired , a second blood collection tube may be inserted into the blood collection tube holder 14 and the blood collection procedure is repeated . once a sufficient number of blood samples have been obtained and the final blood collection tube has been removed from the blood collection tube holder 14 , the health care worker may remove the distal needle section 38 of the needle 24 from the vein of the patient . immediately after the distal needle section 38 of the needle 24 has been removed from the vein of the patient , the health care worker may single handedly hold the blood collection device 10 and move the finger member 30 distally along the shield support member 32 until the protective shield 28 encloses the distal needle section 38 and the distal needle point 39 of the blood collection device 10 . as the finger member 30 and protective shield 28 are moved distally along the shield support member 32 , the inwardly biassed locking tab 46 will frictionally contact the inner surface of the shield support member 32 until the locking tab 46 reaches the locking recess 48 on the inner surface of the shield support member 32 when the protective shield 28 reaches the fully extended position . the locking tab 46 and locking recess 48 are located in an enclosed portion of the needle housing 16 to prevent access to the locking mechanism of the present invention so that the locking mechanism cannot be defeated unless extraordinary force is used . fig8 illustrates an alternate embodiment of the present invention wherein the shield support member 32 includes a reduced diameter section 64 to compress the protective sheath 28 around the distal needle section 38 as the protective sheath is moved distally from the retracted position to the extended position as illustrated , the reduced diameter section 64 is positioned at the distal shield opening 62 on the needle housing 16 and adjacent to the intersection of the intermediate needle section 36 and the distal needle section 38 to compress the protective shield 28 after the needle 24 has passed through the elongate slit 40 . this embodiment provides additional protection against needle sticks caused by accidental deflection of the protective shield 28 off the distal needle section by causing the sides of the protective shield 28 to overlap once the protective shield 28 passes distally beyond the reduced diameter section 64 . fig8 illustrates yet another feature of the present invention wherein the protective shield 28 includes a distal notched section 66 to assist in aligning the needle 24 with the elongate slit 40 and a modified shield support member 32 &# 39 ;. in this embodiment , the protective shield 28 is moveable to a retracted position wherein the notched section 66 of the protective shield 28 is spaced apart from the needle 24 a predetermined distance the radial tabs 41 on the distal end of the protective shield 28 contact the enlarged recesses 67 on the distal end of the needle housing 16 . this allows the health care worker to visually observe the entire distal needle section 38 of the needle 24 prior to or during the insertion of the needle into the patient while the protective shield 28 is in the retracted position . the modified shield support member 32 &# 39 ; is shorter than the shield support member 32 of the previous embodiment and functions as a guide and locking means for the shield assembly 27 in the same manner as described above for fig1 - 7 . another form of the present invention is illustrated in fig9 - 14 . in this embodiment , the needle housing 110 consists of a pair of preferably molded elements which may be snap fit or adhesively bonded together to retain the nonlinear needle referred to herein generally as needle 124 in a sterile , fixed position within the needle housing 110 . the needle housing 110 of this embodiment consists generally of a needle cover 112 , a needle platform 114 , a shield assembly 127 and a nonlinear needle 124 . as with the first embodiment , the needle 124 of the present embodiment , consists of a generally straight proximal needle section 134 , a curved intermediate needle section 136 and a generally straight distal needle section 138 . the proximal end of the proximal needle section 134 and the distal end of the distal needle section 138 include bevelled needle points , 135 and 139 , respectively . the needle platform 114 of the present embodiment includes a threaded needle hub section 125 , a generally flat platform surface 116 , a shield locking section 118 , and an angled needle positioning surface 120 . the needle hub section 125 extends proximally along the inner side of the flat platform surface 116 and includes a threaded proximal section and hub thereon to facilitate the attachment of a standard blood collection tube holder 14 and rubber needle sleeve 164 thereto . the shield locking section 118 extends proximally from the outer side of the flat platform surface 116 to frictionally contact the shield assembly 127 . the shield locking section 118 consists of a semi - circular extension having a pair of inwardly biased locking detents 122 on the sides thereof and a ramped start detent recess 123 on the inner surface thereof . the angled positioning surface 120 is a quadrilaterally shaped element which extends distally from the center of the platform surface 116 between needle hub section 126 and the shield locking section 118 . the sides of the angled positioning surface 120 include a pair of cover retaining tabs 126 extending outwardly therefrom . the top surface of the angled positioning surface 120 is angled to match the general angle of the intermediate needle section 136 of the needle 124 and includes a needle groove 128 to retain the intermediate needle section 136 of the needle 124 therein . the needle cover 112 is preferably a molded element which encloses and retains the intermediate needle section 136 of the needle 124 in a fixed position . the outer side of the needle cover 112 includes a cylindrical shield support cylinder 130 which slidably encloses and retains the shield assembly 127 therein the sides of the needle cover 112 include a pair of tab retaining slots 132 which irreversibly retain the tabs 126 from the needle platform 114 therein . a perimeter flange 140 is located along the proximal surface of the needle cover 112 . the perimeter flange 140 is spaced slightly above the proximal end of the needle cover 112 to provide support for the proximal hard case 156 which is preferably heat staked thereto . the shield assembly 127 is generally a rigid elongate tubular element having a distal section 142 and a proximal section 144 . the distal section 142 of the shield assembly 127 includes an elongate needle slot 146 extending the entire length of the distal section 142 . the distal end of the needle slot 146 includes a notched section 148 to facilitate the passage of the needle 124 into the needle slot 146 and a pair of radial tabs 141 to limit the proximal movement of the shield assembly 127 . the proximal section 144 of the shield assembly 127 includes a start detent 148 , a start detent slot 150 and a pair of shield locking recesses 152 thereon . the start detent slot 150 is located on the inner surface of the shield assembly 127 . the start detent 148 is a generally wedge shaped , moveable element having its proximal end hingedly positioned on the outer surface of the shield assembly 127 . the distal end of the start detent 148 includes a positioning tab 154 thereon which is angled inwardly to releasably project through start detent slot 150 and into the start detent recess 123 on the platform surface 116 in the initial assembled position the shield locking recesses 152 are positioned proximal to the start detent 148 and form a pair of generally wedge shaped recesses on the outer proximal surface of the shield assembly 127 . the proximal end of the shield assembly 127 forms a finger pad 158 to facilitate the single handed operation of the present embodiment . assembly of this embodiment is relatively simple and may be accomplished quickly and inexpensively . initially , the intermediate needle section 136 of the needle 124 is positioned in the needle groove 138 so that the proximal needle section 134 of the needle 124 extends through the threaded proximal section of the platform surface 116 . the needle 124 may be adhesively bonded or welded to any convenient surface of the platform surface 116 to retain the needle 124 therein the needle cover 112 is then snapped onto the platform surface 116 so that the retaining tabs 126 extend through the retaining slots 132 to retain the needle cover 112 on the platform surface 116 and the distal needle section 142 extends through the shield support cylinder 130 . the rubber needle sleeve 164 is then placed on the proximal needle section 134 and the shield assembly 127 is inserted into the shield support cylinder 130 on the needle cover 112 . the start detent 148 is then pressed inwardly as the shield assembly 127 is moved distally through the shield support member 130 . the shield assembly 127 slides distally through the shield support member 130 until the positioning tab 154 on the start detent 148 passes through the start detent slot 150 and contacts the start detent recess 123 on the shield locking section 118 of the needle platform 114 . in this position , the distal section 142 of the shield assembly 127 partially encloses the distal needle section 138 and is prevented from further distal movement by contact between the positioning tab 154 on the start detent 148 and distal side of the start detent recess 123 . finally , the proximal hard case 156 and the distal hard case 160 are heat staked to the respective ends of the assembly . once the device has been sterilized , it may then be shipped and stored without losing sterility . the present embodiment operates similar to the first embodiment described above for fig1 - 7 . when the health care worker desires to obtain a blood sample from a patient , the health care worker may apply lateral pressure to the proximal hard case 156 to break the heat stake between the proximal hard case 156 and the perimeter flange 140 . next , the blood collection tube holder 14 is threaded onto the needle hub section 125 . once the appropriate site on the patients arm has been prepared , the health care worker may remove the distal hard case 160 from the needle housing 110 by rotating the distal hard case 160 until the heat stake on the distal end of the needle cover 112 is broken . the health care worker may then move the shield assembly 127 from the initial start position to the retracted position by placing their thumb on the finger pad 158 and moving the shield assembly 127 proximally along the shield support member 130 . as the shield assembly 127 is moved proximally along the shield support member 130 , the start detent 148 is moved from the start detent recess 123 and the start detent slot 150 to a neutralized position on the shield assembly 127 . a pair of supplemental detents 162 on the interior surface of the shield assembly 127 prevent the start detent 148 from returning to the initial start position . once the shield assembly 127 is moved to the retracted position , the blood collection device 10 and the distal needle section 138 of the needle 124 may be aligned parallel to the vein of the patent so that the distal needle point 139 is adjacent to the skin of the patient . next , the distal needle section 138 of the needle 124 is inserted into the vein of the patient and an evacuated blood collection tube is inserted into the blood collection tube holder 14 . as the blood collection tube is inserted into the blood collection tube holder 14 , the stopper of the blood collection tube contacts the rubber needle sleeve 164 and causes the proximal needle point 135 to pierce the rubber needle sleeve 164 . the stopper then compresses the rubber needle sleeve 164 against the needle hub section 125 of the needle housing 110 while the stopper is pierced by the proximal needle point 135 . once the stopper is pierced by the proximal needle point 135 , blood is drawn from the vein of the patient into the evacuated blood collection tube 12 . when a sufficient amount of blood has been obtained , the blood collection tube 12 is removed from the blood collection tube holder 14 and the resilient rubber sleeve recovers the proximal needle point 135 . if a further blood sample is desired , a second blood collection tube 12 may be inserted into the blood collection tube holder 14 and the blood collection procedure is repeated . once a sufficient number of blood samples have been obtained and the final blood collection tube 12 has been removed from the blood collection tube holder 14 , the health care worker may remove the distal needle section 138 from the vein of the patient . immediately after removing the needle 124 from the vein of the patient , the health care worker may single handedly hold the blood collection device 10 and move the finger pad 156 distally along the shield support member 130 until the distal section 152 of the shield assembly 127 encloses the distal needle section 138 and distal needle point 139 of the blood collection device 10 . as the shield assembly 127 is moved distally along the shield support member 130 , the locking detents 122 will be biased against sides of the shield assembly 127 until the locking detents 122 reach the locking recesses 152 on the proximal section 144 of the shield assembly 127 . when the shield assembly 127 is in the locked extended position , the cooperation between the locking detents 122 and the locking recesses 152 will prevent the shield assembly 127 from being retracted unless excessive force is applied to the shield assembly 127 . fig1 - 19 illustrate yet another form of the present invention wherein the protective shield 70 is slidable in a nonlinear manner along a preferably straight needle 72 . in this embodiment , the blood collection tube holder 74 and the proximal needle section 76 are preferably the same as the blood collection tube holder 14 and the proximal needle section 34 described above . as illustrated in fig1 , the needle hub section 78 is threadedly mounted on the distal end of the blood collection tube holder 74 and includes an offset protective shield passageway 80 through which the protective shield 70 is moved between the retracted and extended positions . the distal end of the needle hub section 78 preferably includes a reduced diameter section 82 to compress the protective shield 70 as it passes from the protective shield passageway 80 onto the distal needle section 84 of the needle 72 . the protective shield 70 of the present invention is preferably constructed of a semi - rigid polypropylene having sufficient rigidity to adequately protect the needle while having sufficient flexibility to pass nonlinearly through the protective shield passageway 80 . the distal end of the protective shield 70 includes a hardened tip 86 to protect the health care worker from accidental needle sticks . as illustrated in fig1 , the hardened tip 86 includes a needle hole 88 and a flexible lip 90 thereon . the proximal end of the protective shield 70 includes a finger member 92 thereon to facilitate the movement of the protective shield 70 between the retracted and extended positions . the elongate slit 94 of this embodiment extends between the hardened tip 86 and the finger member 92 to allow the protective shield 70 to pass over the proximal end of the distal needle section 84 . when the protective shield 70 is in the retracted position , the hardened tip 86 is positioned on the proximal end of the distal needle section 84 immediately adjacent to the distal end of the needle hub section 78 while the finger member 92 extends proximally from the proximal side of the protective shield passageway 80 . as the protective shield 70 is moved to the extended position , the hardened tip 86 moves distally along the distal needle section 84 and the elongate slit 94 of the protective shield 70 is opened as it passes over the proximal end of the distal needle section 84 . once the elongate slit 94 has passed over the proximal end of the distal needle section 84 , the reduced diameter section 82 of the needle hub section 78 compresses the elongate slit 94 to cause the sides of the protective shield to overlap once they have passed beyond the needle hub section 78 . in the extended position , the hardened tip 86 extends beyond the distal point 96 a sufficient distance to allow the flexible lip 90 to prevent the distal needle point 96 from returning through the needle hole 88 . the finger member 92 on the proximal end of the protective shield 70 is positioned adjacent to the proximal end of the protective shield passageway 80 and cannot be retracted unless extraordinary force is used to force the distal needle point 96 through the flexible lip 90 and into the needle hole 88 of the hardened tip 86 . in another form of the present embodiment , the finger member 92 is movable into an enlarged area ( not shown ) in the proximal end of the protective shield passageway 80 so that the finger member is substantially flush with the proximal end of the protective shield passageway 80 in the extended portion . fig1 and 19 illustrate yet another alternate form of the protective shield 70 of fig1 , wherein the respective sides of the protective shield 70 &# 39 ; are oriented in an interlocking relationship once the protective shield 70 &# 39 ; pass beyond the proximal end of the distal needle section 84 . the foregoing is intended to be descriptive of the preferred form of the various embodiments described above . it is readily anticipated that certain features of the embodiments are interchangeable or may be modified without departing from the scope of the invention which is defined by the following claims .
a medical device particularly adpated for use with a blood collection tube including a nonlinear needle having first and second needle points wherein the first needle point is selectively protected by a movable protective shield and the second needle point is designed to pierce the stopper of an evacuated blood collection tube . the needle guard is movable axially along a portion of the nonlinear needle between a needle tip exposing retracted position and a needle covering locked extended position .