the injection device shown in fig1 to 3 has a carpule part 1 and a transmission 2 which is easily attachable and detachable , for example by means of a thread or a bayonet socket . the carpule part 2 comprises a container 3 for liquids , hereinafter called &# 34 ; carpule &# 34 ; 3 , filled with the liquid to be injected , a carpule holder 4 , a piston 5 which is in contact with the liquid at all times and displaces the liquid to be injected during the act of injecting , a needle holder 6 and a needle 7 from which the liquid to be injected is ejected . the transmission 2 is incorporated in a transmission sleeve 8 . it comprises a drive member 12 , comprised of a guide button 32 and a carrier sleeve 13 firmly attached thereto , said drive member being disposed rotatably and shiftably in the advance direction of the piston 5 in the transmission sleeve 8 , a driven member 9 , comprised of a threaded rod 39 and a flange 10 , said driven member being shiftable in the advance direction of the piston 5 and being carriable over a certain distance under the influence of the drive member 12 , 13 executing longitudinal shifts , a transmission element 11 being screwably disposed on the threaded rod 9 and having the effect of the driven member 9 , 10 being carried along by the drive member 12 , 13 , a compression spring 14 held by a spring sleeve 15 and acting between the transmission sleeve 8 and the carrier sleeve 13 . the injection device according to the invention has the following constructive features : a locking device 16 , 17 , 20 , 21 engages with the drive member 12 , 13 . the threaded rod 9 of the driven member 9 , 10 is disposed non - rotatably but shiftably in the longitudinal direction in the transmission sleeve 8 . the transmission element 11 is non - rotatable but attached shiftably in the longitudinal direction to the drive member 12 , 13 . the flange 10 of the drive member 9 , 10 is contiguous to the piston 5 being in contact with the liquid as long as the carpule 3 is connected to the transmission 2 . at the end of each injection , the transmission 2 is in a locked end position ( fig1 ) in which end position ( fig1 ) it may also be stored and transported . in this end position ( fig1 ), the drive member 12 , 13 protrudes relative to the transmission sleeve 8 so far in the advance direction towards the piston 5 that the lock 16 , 17 , 20 , 21 between the transmission sleeve 8 and the drive member 12 , 13 engages and secures it against rotation and shifting in the longitudinal direction . in addition , the transmission element 11 is in contact with a first stopper 18 on the transmission sleeve 8 in the direction of the piston 5 which limits said transmission sleeve in the direction of the piston . when the lock 16 , 17 , 20 , 21 is engaged , the drive member 12 , 13 is neither rotatable nor shiftable . therefore , it is not possible to operate the injection device -- not even intentionally -- while it is in the final position ( fig1 ) and thus it cannot lose any liquid . this distinguishes it from the injection devices known previously . the lock 16 , 17 , 20 , 21 , for example , consists of a locking ring 16 encircling the drive member 12 , 13 and a cam 20 connected therewith . said cam is positioned in the transmission sleeve 8 and when pressed by a spring 17 engages in the drive member 12 , 13 in the final position . said cam can only be released from the groove 21 by pressing the locking ring 16 against the spring 17 . once the lock 16 , 17 , 20 , 21 has been released , the drive member 12 , 13 is once again rotatable and shiftable and is pushed by the compression spring 14 into the home position ( fig2 ) described below . however , a lock having comparable properties may also be designed in a different manner . in order to carry out another injection , the transmission 2 is first brought into a home position ( fig2 ). in said home position , the drive member 12 , 13 is pushed as far as possible away from the piston 5 opposed to the advance direction of the piston and this is effected by the compression spring 14 which pushes the drive member 12 , 13 by a distance h up to a second stopper 19 on the transmission sleeve 8 . said second stopper 19 is , for example , an annular ring on the surface of the inner jacket of the transmission sleeve 8 . the transmission element 11 is still contiguous to the first stopper 18 of the transmission sleeve ( 8 ) in the direction of the piston 5 . the shift from the final position ( fig1 ) to the home position ( fig2 ) is effected by releasing the lock ( 16 , 17 , 20 , 21 ) of the transmission sleeve 8 and the drive member 12 , 13 , said drive member 12 , 13 becoming rotatable and shiftable in the longitudinal direction and the compression spring 14 shifting the drive member 12 , 13 opposed to the advance direction of the piston ( 5 ) into the home position ( fig2 ). from the home position ( fig2 ), the transmission 2 is brought into an intermediate position ( fig3 ) which is determined by the amount of liquid to be injected with the next injection . in said intermediate position , the lower end of the transmission element 11 is shifted by a distance x relative to the first stopper 18 on the transmission sleeve 8 opposed to the advance direction of the piston 5 , said distance x being determined by with i being the amount of liquid to be injected and f being the inner cross sectional area of the carpule . the shift from the home position ( fig2 ) to the intermediate position ( fig3 ) is effected by rotating the drive member 12 , 13 in such a direction that the transmission element 11 which is connected shiftably in the longitudinal direction and rotatable with the drive member 12 , 13 is rotated around its axis , the threaded rod 9 , in such a manner that it is shifted along said threaded rod 9 opposed to the advance direction of the piston 5 by the distance x . the transmission element 11 is shiftable to a third stopper 22 on the carrier sleeve 13 at most . said stopper is positioned against the advance direction of the piston on the inner jacket surface of the drive member at a distance a + h from the first stopper 18 , with h being the travel distance of the drive member between the final position ( fig1 ) and the home position ( fig2 ). from the intermediate position ( fig3 ), the transmission is brought into the final position ( fig1 ). during this time the injection procedure is carried out . for this purpose , the drive member 12 , 13 is shifted by the distance h in the advance direction of the piston . during this advance shift , the drive member 12 , 13 carries the transmission element 11 forward which is positioned at a distance x from the first stopper 18 on the transmission sleeve 8 . from that point onwards , the transmission element 11 carries the driven member 9 , 10 which is shiftable only the longitudinal direction along by the distance x . during this operation , the flange 10 thereof pushes the piston 5 in the carpule 3 forward so that the amount of liquid i = f × x is displaced on the whole and ejected through the needle 7 ( injection ). when the drive member 12 , 13 has travelled the distance h and the transmission element 11 has travelled the distances x at the same time , the lock 16 , 17 , 20 , 21 engages into the drive member 12 , 13 . thus the transmission 2 comes to rest in the final position , the drive member 12 , 13 is no longer rotatable or shiftable in the longitudinal direction and the injection device thus protected against a loss of liquid . after the entire liquid in the carpule 3 has been consumed , the carpule part 1 is detached from the transmission 2 in the home position ( fig2 ). then the driven member 9 , 10 must be pushed back by rotating the drive member 12 , 13 in the reverse direction of the shift from the home position ( fig2 ) into the intermediate position ( fig3 ) until the flange 10 comes to rest on the stopper 23 of the transmission sleeve 8 . advantageously the new carpules 3 to be inserted are filled in such a manner that the piston 5 is pushed forward a little by the flange 10 during incorporation into the injection device and some liquid is ejected from the needle 7 . this ensures that no air is injected even during the first injection with the new carpule 3 . the injection devices according to the invention may be equipped with electrical , optical or acoustic means capable of indicating the selected distance x . this may , for example , be a ratchet which acts between the driven member ( 9 , 10 ) and the transmission sleeve ( 8 ). the injection device according to the invention has a lock 16 , 17 , 20 , 21 which prevents even intentional operation while it is in the final position ( fig1 ). this means that it may be stored and transported more reliably even with the carpule 3 attached than devices according to the prior art . moreover , it is comprised of fewer components some of which are easier to manufacture so that the required production costs are lower .
an injection device is described which is lockable in its end position in such a manner that the reliability of storing or transporting it with a carpule attached is improved in comparison with devices according to the prior art . it is comprised of fewer components than comparable devices , with these components being easier to manufacture so that production costs are low . the injection device is used for medical purposes .