with regard to fastening , mounting , attaching or connecting components of the present invention , unless specifically described as otherwise , conventional mechanical fasteners and methods may be used . other appropriate fastening or attachment methods include adhesives , welding and soldering , the latter particularly with regard to the electrical system of the invention , if any . in embodiments with electrical features or components , suitable electrical components and circuitry , wires , wireless components , chips , boards , microprocessors , inputs , outputs , displays , control components , etc . may be used . generally , unless otherwise indicated , the materials for making the invention and / or its components may be selected from appropriate materials such as metal , metallic alloys , ceramics , plastics , etc . unless stated otherwise , identical reference characters refer to the same parts . fig1 - 9 show one exemplary preferred embodiment of an injection device in accordance with the present invention . referring to fig1 a and 1 b , the injection device comprises a casing 1 consisting of a proximal ( rear ) casing part 1 a and a distal ( forward ) casing part 1 b which is axially and fixedly connected to the proximal casing part 1 a by a latching connection 1 c . the latching connection 1 c is formed from or by a window or opening contained in or associated with the proximal casing part 1 a , into which an elastic tab formed or carried by the distal casing part 1 b snaps . a product container 2 is accommodated in the casing 1 , on the distal end of which an injection needle 4 is situated for delivering a liquid product contained in the product container 2 . the proximal end of the product container 2 comprises a shifting piston 3 which , when moved relative to the product container 2 and in the direction of the injection needle 4 , delivers the product , for which reason this may also be referred to as a delivery movement . the product container 2 is accommodated in the device such that it can be shifted in the distal direction , such that the injection needle 4 protrudes from the distal end of the injection device . this may therefore be referred to as an injection movement . the product container 2 is axially and fixedly connected to a holder 10 for the product container 2 . the casing 1 , e . g . its distal and proximal casing parts 1 a , 1 b , comprise a viewing window 12 through which the user of the injection device can view the product container 2 . the holder 10 surrounds the product container 2 in the shape of a sleeve , such that it either comprises a viewing window itself or , as in this example , comprises a transparent material , to enable the container 2 to be viewed . the product container 2 is axially and fixedly connected to a functional sleeve 11 arranged proximally ( rearwardly ) relative to it by a clamp formed at the proximal end of the holder 10 . the proximal end of the product container 2 comprises a radially projecting collar which is encompassed by the clamp . the functional sleeve 11 also comprises a radially projecting collar at its distal end , which is also enclosed by the clamp . the product container 2 , the functional sleeve 11 and the holder 10 are thus axially and fixedly connected to each other , such that they can be moved as a single part . this combination is referred to in the following as the advancing structure . the functional sleeve 11 surrounds a piston rod 5 which can act on the piston 3 in order to deliver product . the piston rod 5 comprises a sleeve - shaped part which surrounds an advancing spring 6 , wherein the advancing spring 6 is distally supported on the piston rod 5 and proximally supported on a switch sleeve 8 , in or on a socket 8 a formed on it . a signalling unit is arranged on or associated with the piston rod 5 , using which a haptic and / or acoustic signal , in some preferred embodiments at least three or more haptic and / or acoustic signals , can be generated for an injection procedure or operation and / or a delivery procedure or operation . the signalling unit comprises a catch rod 23 connected to the switch sleeve 8 , and an engaging sleeve 22 which surrounds the catch rod 23 and is axially and fixedly connected , e . g . latched , to the piston rod 5 . the engaging sleeve 22 comprises an engaging element 26 which engages with a groove 27 formed in or by the catch rod 23 . the proximal end of the catch rod 23 comprises a head 24 which can be moved in the proximal direction in a sliding guide 25 formed by the activating element 13 . the distal end of the head is in an engagement with a socket 8 a formed by the switch sleeve 8 , wherein the engagement prevents the head 24 and therefore the catch rod 23 from moving in the distal direction relative to the switch sleeve 8 . the exact functionality of this arrangement is explained below with reference to fig1 and 11 which show in detail the signalling unit shown in fig1 - 9 . the signalling unit from fig1 and 11 can alternatively be replaced with a different signalling unit in accordance with fig1 to 14 or with yet another signalling unit in accordance with fig1 and 16 . the injection device shown in fig1 - 9 does not have to be significantly modified to accommodate these or other suitable embodiments of signalling units . in the initial state of the injection device , shown in fig1 a and 1 b , the advancing spring 6 is biased such that it can advance the needle 4 and in particular the advancing structure ( comprised of components 2 , 10 , 11 ) for an injection movement and can shift the piston 3 for a delivery movement . the functional sleeve 11 comprises a blocking element 16 on which a shoulder is formed which is directed radially inwardly and which , in the initial state , co - operates with a shoulder which projects radially outwardly and is formed at the distal end of the piston rod 5 , such that the piston rod 5 is blocked against moving relative to the functional sleeve 11 . the blocking element 16 is held in the engagement with the piston rod 5 by a surface of the switch sleeve 8 which points radially inwardly . in some preferred embodiments , the blocking element 16 is elastically connected , e . g . in one piece , to the functional sleeve 11 via an elastic arm . the elastic arrangement can be configured such that the blocking element 16 tends to move radially outwardly , wherein this is prevented by the surface of the switch sleeve 8 which points radially inwardly . the proximal end of the functional sleeve 11 comprises at least one snapping element 15 which snaps into the switch sleeve 8 in the initial state to prevent the functional sleeve 11 and therefore the advancing structure from moving , hence the biased spring 6 cannot yet be relaxed and cannot yet move the advancing structure in the distal direction . at the proximal end of its casing 1 , the injection device comprises an activating element 13 which is arranged such that it is axially fixed but rotatable relative to the casing . the activating element 13 accommodates a restoring spring 21 which is distally supported on the proximal end of the switch sleeve 8 and proximally supported on the activating element 13 . the restoring spring 21 has the task of charging the switch sleeve 8 , and an operating sleeve 9 which acts axially on the switch sleeve 8 , with a force which acts in the distal direction , such that the switch sleeve 8 and the operating sleeve 9 are pressed in the distal direction . the activating element 13 comprises an activation lock 14 which , in the switching states of the injection device shown in fig1 a , 1 b , 2 a and 2 b , grips behind the snapping element 15 such that the snapping element 15 is blocked , locked and / or secured against moving out of the engagement with the switch sleeve 8 . this advantageously prevents the injection device from being inadvertently triggered . the activation lock can be moved out of the engagement with the snapping element 15 by rotating the activating element 13 , for example by 90 °, relative to the casing 1 . a retracting spring 7 which acts in the longitudinal direction of the device is distally supported on the switch sleeve 8 and proximally supported on the functional sleeve 11 . as shown in this example , the retracting spring 7 surrounds the switch sleeve 8 and the functional sleeve 11 . the retracting spring 7 is proximally supported on a collar 11 a which is formed by the functional sleeve 11 and grips radially outwardly through a breach formed in the switch sleeve 8 . in selected or particular switched positions , the retracting spring 7 can therefore generate a relative movement between the switch sleeve 8 and the functional sleeve 11 . the retracting spring 7 is a compression spring which can move the functional sleeve 11 relative to the switch sleeve 8 in the proximal direction . the retracting spring 7 is not biased or is biased with only a small biasing force . when the injection device is in the state shown in fig1 a and 1 b , for example , the biasing force of the retracting spring 7 is smaller than the biasing force of the advancing spring 6 . the operating sleeve 9 is arranged distally relative to the switch sleeve 8 and such that it can be moved relative to the casing 1 . the switch sleeve 8 and the operating sleeve 9 can reciprocally charge each other with a pressing force , and can be latched , operably coupled or connected to each other and thus shift each other . in order that it does not block the view onto the product container 2 , the operating sleeve 9 also comprises a window in the region of the window 12 . alternatively , the operating sleeve 9 can be formed from a transparent material . in the initial state , the operating sleeve 9 is distally advanced beyond the distal end of the casing 1 by the restoring spring 21 via the switch sleeve 8 . the distal end of the operating sleeve 9 serves to place the device onto an injection location on a patient . the holder 10 comprises a switching cam 17 which engages with a cavity 18 in the operating sleeve 9 which can be a breach or opening as shown in this example . the switching cam 17 is elastically connected , e . g . in one piece , to the holder 10 , for example via an elastic arm . the switching cam 17 is biased such that it tends to engage with the cavity 18 and / or move radially outwardly . the switching cam 17 , which projects radially outwardly from the holder 10 , distally comprises an oblique surface which assists in pressing the switching cam 17 out of the engagement with the cavity 18 . the switching cam 17 also proximally comprises a contact surface which extends transversely or perpendicularly to the longitudinal direction and can pass into an axial abutment with the proximal boundary of the cavity 18 , which prevents the switching cam 17 from moving out of the cavity 18 . the operating sleeve 9 comprises an axial abutment 19 , against which the distal end of the holder 10 can abut at the end of an injection movement . as shown in fig1 a and 1 b , a cap 32 is arranged on the distal end of the injection device and protects the interior of the injection device from contamination and keeps the needle 4 sterile . the cap 32 is removed before using the injection device , such that the needle 4 and the operating sleeve 9 are exposed , as shown in fig2 a and 2 b . the state of the injection device shown in fig2 a and 2 b differs from the state shown in fig1 a and 1 b in that the cap 32 has been removed . the force exerted on the injection device when the needle cap 32 is removed is channeled via the holder 10 onto the functional sleeve 11 , where it is transmitted via the snapper 15 onto the switch sleeve 8 which is supported on the operating sleeve 9 . the operating sleeve 9 is in turn latched to the casing 1 via a projection 1 d formed by the distal casing part 1 , such that removing the cap 32 from the injection device does not exert any undesirable effect on the mechanism . in the switching state shown in fig2 a and 2 b , the operating sleeve 9 cannot be slid or can only be slid or moved very slightly into the distal end of the injection device , since this shifting movement is relayed to the snapper 15 via the switch sleeve 8 , wherein the snapper 15 is prevented from moving in the proximal direction by the activating element 13 . fig3 a and 3 b show the injection device in an activated state , i . e . in which the injection device can be triggered . the injection device is activated or unlocked by a rotational movement of the activating element 13 by , for example , 90 °. this releases the snapping elements 15 for a movement directed radially inwardly , in that the activation lock 14 moves out of the engagement with the snapping elements 15 and is rotated . this creates space for the snapping elements 15 to be deflected inwardly . the activating element 13 , like the snapping element 15 , also comprises an activating cam 13 a which is moved into axial alignment with the snapping element 15 by the rotational movement of the activating element 13 . the snapping element 15 proximally comprises — and the activating cam 13 a arranged proximally relative to it distally comprises — a contour which can deflect the snapping element 15 radially inwardly when the snapping element 15 is moved in an engagement with the activating cam 13 . in this example , the contours are two inclined planes which slide off on each other . to trigger the injection device , the user of the device places its distal end onto the injection location , which has usually been disinfected beforehand . this shifts the operating sleeve 9 relative to the casing 1 in the proximal direction , in some preferred embodiments until the distal end of the operating sleeve 9 is approximately flush with the distal end of the distal casing part 1 b . the movement of the operating sleeve 9 slaves the switch sleeve 8 in the proximal direction , wherein the snapping elements 15 are pressed , radially inwardly , out of the engagement with the switch sleeve 8 by the activating cams 13 a . as long as the snapping elements 15 are snapped into the switch sleeve 8 , the elements of the advancing structure are also slaved or moved in the proximal direction by the movement of the operating sleeve 9 in the distal direction . since the piston rod 5 is in a blocking engagement with the functional sleeve 11 , the piston rod 5 is also slaved in the proximal direction . the signalling unit , which is accommodated in the piston rod 5 , is also slaved in the proximal direction . the head 24 formed proximally on the catch rod 23 can slide along in the guide 25 formed by the activating element 13 . since a relative movement between the activating sleeve 11 and the switch sleeve 8 is still not possible during this movement , neither the retracting spring 7 nor the advancing spring 6 are tensed or relaxed . the force which the user of the device has to exert on the casing 1 for the operating sleeve 9 to be shifted in the proximal direction is substantially determined by the force of the restoring spring 21 against which the switch sleeve 8 and the operating sleeve 9 are moved . the spring 21 is a compression spring and is formed from a plastic material . alternatively , it is of course also possible to use springs made of a spring steel material or other suitable material . the activating element 13 is axially attached to the casing 1 by an annular snapping connection with the casing . if the operating sleeve 9 is not pressed far enough onto the injection location , such that the snapping elements 15 are not released from the engagement with the switch sleeve 8 , then the trigger mechanism , for example the switch sleeve 8 and the operating sleeve 9 , is restored by the restoring spring 21 when the injection device is removed from the injection location . as can be seen from fig4 b , the movement of the operating sleeve 9 in the proximal direction forms a blocking window 20 which is distally bounded by the casing 1 , the projection 1 d , and proximally bounded by the operating sleeve 9 . since there is no relative movement between the advancing structure and the operating sleeve 9 during the movement of the operating sleeve 9 in the proximal direction , the switching cam 17 remains in the cavity 18 . once the snappers 15 have latched out of the engagement with the switch sleeve 8 , the advancing spring 6 can be partially relaxed , which shifts the advancing structure in the distal direction , whereby the injection needle 4 protrudes beyond the distal end of the injection device . since the functional sleeve 11 is moved relative to the switch sleeve 8 during this injection movement , the retracting spring 7 is compressed , i . e . tensed . the spring force of the advancing spring 6 is greater than the spring force of the retracting spring 7 during the entire injection procedure , i . e . also at the beginning and end of the injection procedure . the advantage of this is , for example , that the injecting force is reduced , which helps to avoid wear on the injection device . as can be seen from fig5 a and 5 b , which show the situation at the end of the injection procedure , the blocking element 16 engages with the cavity 18 in a movement which is directed radially outwardly , as indicated by the arrows in fig5 b . to facilitate this engagement , the blocking element 16 comprises a projection which is directed radially outwardly . the blocking element 16 fulfils a dual function . when the blocking element 16 latches into the cavity 18 , the blocking element 16 simultaneously latches out of the piston rod 5 in the movement directed radially outwardly , such that the latter is released for a delivery movement . conversely , the movement of the advancing structure axially , in the proximal direction , is blocked or prevented . this procedure decouples the advancing spring 6 from the retracting spring 7 , i . e . the advancing spring 6 has no effect on the bias of the retracting spring 7 in this state . a delivery movement then follows , during which a time - constant clicking sound is emitted by the signalling unit and can also be sensed by the user of the device . the user of the device does not sense any additional force caused by the injection procedure , which is collected by the snapping action between the operating sleeve 9 and the switch sleeve 8 and is not supported on the casing . the force for the injection procedure is channeled onto the collar of the product container 2 via the functional sleeve 11 . the injection procedure is thus forcibly controlled , since the functional sleeve 11 advances the product container 2 until the end of delivery , and the piston rod 5 cannot deliver until the blocking elements 16 have engaged with the cavities 18 . the injection movement is stopped by the abutment 19 on the operating sleeve 9 . during the injection movement , the switching cam 17 is pressed out of the engagement with the cavity 18 , due to its distal design , by the distal boundary of the cavity 18 of the operating sleeve 9 and is shifted in the distal direction , such that it latches into the blocking window 20 , as shown in fig5 a and 5 b . the blocking element 16 , latched into the cavity 18 , is in contact with the proximal boundary of the cavity 18 . since the blocking element 16 and the switching cam 17 are at a defined distance from each other due to their axially fixed arrangement , it is preferable if there is a commensurate or defined distance , e . g .— a small distance , 0 . 5 to 1 mm in this example — between the proximal end of the switching cam and the distal end of the blocking window 20 when the blocking element 16 is in engagement with the cavity . as explained further below , this distance is used to generate a haptic or acoustic signal intended to signal that the product has been completely delivered . the small distance z arises from the difference of the distance between the contact surface of the switching cam 17 pointing in the proximal direction and the contact surface pointing in the proximal direction , and the distance between the proximal boundaries of the cavity 18 and the blocking window 20 . fig6 a and 6 b show the injection device in a state after the product has been delivered . while the product is being delivered , the outer circumferential surface of the sleeve - shaped part of the piston rod 5 presses the blocking element 16 into the cavity 18 , which secures the blocking element 16 against latching out of the cavity 18 while the product is being delivered . the piston rod 5 can comprise a cavity or its length can be dimensioned such that once the product has been delivered , the securing lock applied to the blocking element 16 by the outer circumferential surface of the piston rod 5 is dropped , such that the blocking element 16 can latch out of the cavity 18 , as shown in fig6 b , either due to an elastically biased arrangement of the blocking element 16 or due to the geometry of the blocking element 16 , which causes the blocking element 16 to be pressed out of the cavity 18 . at the end of the product delivery , the advancing spring 6 has been relaxed again , while the tension on the tensed retracting spring 7 has remained constant . the spring force of the advancing spring 6 is then less than the spring force of the biased retracting spring 7 . by releasing the engagement between the blocking element 16 and the cavity 18 , the retracting spring 7 and the advancing spring 6 are coupled to each other again . as shown in fig7 a and 7 b , this coupling causes the small distance z to disappear ( see fig5 b and 6 b ), by moving the proximal end of the advancing structure and / or the switching cam 17 , abruptly onto the distal end of the blocking window 20 . as the switching cam 17 impacts , a haptic and / or acoustic signal is generated . this movement by the small path z does not yet , however , completely remove the needle 4 from the patient . the patient or user of the device can then wait any length of time before completely removing the needle from the patient , since he can initiate the automatic needle retraction of the device at will . it is not yet possible to move the needle completely into the distal end of the casing 1 , since — as can be seen in fig7 b — the switching cam 17 is in engagement with the blocking window 20 and thus blocks or prevents the spring 7 against relaxing . to release the needle 4 for retraction , the user of the device merely has to remove it from the injection location . the restoring spring 21 can then move the operating sleeve 9 in the distal direction via the switch sleeve 8 , wherein the advancing structure is fixed relative to the operating sleeve 9 , such that the switching cam 17 — driven due to its distal design by the spring 21 in conjunction with the operating sleeve 9 — is pressed radially inwardly , out of the blocking window 20 , by the projection 1 d . as soon as the switching cam 17 has been pressed inwardly , the needle 4 is released for retraction . releasing the engagement also releases the retracting spring 7 for a retracting movement . due to the greater spring force of the biased retracting spring 7 , the entire advancing structure is pressed or urged in the proximal direction , wherein the spring 6 is tensed again and the spring force of the retracting spring 7 is greater than the spring force of the advancing spring 6 during the entire retracting procedure , i . e . up to and including the end of the retracting procedure . fig9 a and 9 b show the injection device in an end state . in this state , the dimensions of the injection device are again the same as at the beginning . thus , the cap 32 can be fitted again and the injection device disposed of . in the end position , the needle is completely retracted into the distal end of the device . the snapping element 15 is again latched to the switch sleeve 8 , as at the beginning . however , it is not possible to trigger the injection device again , since this would require the advancing spring 6 to be biased , as for example shown in fig1 a . fig1 and 11 show in detail the signalling unit of fig1 to 9 . the catch rod 23 comprises a catch 30 comprising a plurality of latching elements 31 arranged along the longitudinal direction at incrementally reduced distances . these distances are reduced as a function of the diminishing spring force . the proximal end and / or the head of the catch rod is connected to the switch sleeve 8 such that it is axially fixed at least in one direction ( for example fig1 ). the catch rod 23 is surrounded by a catch sleeve 22 which is connected to the distal end of the advancing spring 6 or / and to the distal end region of the piston rod 5 . the engaging sleeve comprises an engaging element 26 which engages with an annular groove 27 . the engaging element 26 engages with the groove 27 in the initial position . during the advancing movement for injecting , i . e . the injection movement , the engaging element latches out of the groove 27 and is moved over a first section of the catch rod up to the beginning of the plurality of latching elements 31 . the first section does not comprise any other latching element , but is rather substantially cylindrical or tapered , such that no signals are emitted during the injection movement . the length of the first section is dimensioned such that the engaging element 26 has substantially traveled the whole of the first section once the injection movement is complete . at the start of the delivery movement , the rod 23 and the sleeve 22 are drawn even further apart , such that the engaging element 26 is moved over the second section , i . e . the section with the latching element 31 , such that the latching elements 31 are respectively crossed . a brief clicking signal is emitted as each of the latching elements are crossed . the time intervals from one clicking signal to the next are constant , even though the diminishing spring force reduces the speed of the engaging element 26 as the path increases . in accordance with the present invention , the distances from one latching element to the next are reduced as the spring path increases , thus allowing for the varying speed . on the radially opposite side , on which the engaging element 26 is arranged , another engaging element 26 could be provided . however , in the depicted embodiment , an additional engaging element 26 is not provided , but , as shown here , a support which is formed by the sleeve wall and serves as a thrust bearing . fig1 to 14 show an alternative embodiment of the signalling unit for the injection device of fig1 to 9 . the catch 30 is arranged in a groove 29 , namely on its flank . the latching elements 31 project from the groove flank in the circumferential direction . an axially movable carriage 28 is arranged in the groove 29 and is axially and fixedly coupled to the piston rod 5 . during the delivery movement , the carriage 28 is slaved by the piston rod 5 , hence the engaging element 26 elastically arranged on the carriage 28 crosses the individual latching elements 31 of the catch 30 . here , too , the latching elements 31 respectively have distances from each other which allow for the varying force of the advancing spring to emit time - constant signals . the distance between the serrated teeth is thus selected such that the individual clicks occur at uniform time intervals , even though the carriage 28 with the piston rod 5 exhibits a lower delivery speed at the end of delivery than at the beginning . fig1 and 16 show another embodiment of the signalling unit , in which the catch 30 is formed from cavities , e . g . windows , which are also attached to the piston rod 5 at varying distances . the engaging element 26 is elastically arranged on the functional sleeve 11 . during the delivery movement , the piston rod 5 and thus the hole catch 30 are moved past the engaging element 26 , which respectively latches into each hole catch 31 and thus generates the signal . the advantage of this embodiment is that the engaging element 26 can be formed by the blocking element 16 , such that this embodiment involves few parts . embodiments of the present invention , including preferred embodiments , have been presented for the purpose of illustration and description . they are not intended to be exhaustive or to limit the invention to the precise forms and steps disclosed . the embodiments were chosen and described to provide the best illustration of the principles of the invention and the practical application thereof , and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated . all such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth they are fairly , legally , and equitably entitled .
an injection device for administering a liquid product , the device including a drive mechanism , an engaging member and a catch including a number of latching elements , wherein at least one of the engaging member and the number of latching elements is relatively moveable to the other to generate a haptic and / or acoustic signal comprising a number of discrete signals during a relative movement , wherein one of the catch and the engaging member is coupled to the drive mechanism and the drive mechanism generates a variable drive speed during the relative movement , and wherein the latching elements are a distance from each other such that a time interval between each of the number of discrete signals is constant . a method for generating a haptic and / or acoustic signal in use of an injection device is encompassed .