[ 0037 ] fig1 . a and 1 . b show the basic principles of a medication delivery system according to the invention . a medication delivery system 1 is schematically shown in fig1 . a . a cylindrical medication cartridge 11 ( e . g . a replaceable one ) comprising a piston 112 at one end and an outlet 111 at its opposite end is shown in its operational position to be fixedly held relative to an electromotor 15 for actuating the movement of the piston 112 by ( schematically indicated ) holding means 12 . a needle 113 for leading a dose of medication from the cartridge to a body is connected to the outlet 111 of the cartridge 11 . the piston 123 has an inner 1121 and an outer surface 1122 . the inner surface 1121 is in contact with the liquid medication contained in the cartridge 11 . the outer surface 1122 is adapted to engage with one end 136 of the piston rod 13 . a piston rod 13 is shown to be operable to engage and displace the piston 112 . the piston rod cooperates with driving means 161 , 162 to transfer the angular movement ( as indicated by arrows 150 ) of the electromotor 15 to a linear displacement ( as indicated by arrows 130 ) of the piston rod 13 . the piston rod 13 in fig1 . a is mainly cylindrical , axially stiff , and provided with threads ( not shown ) that , together with a corresponding driving nut 162 ( fixedly held in an axial direction of the piston rod by holding means 163 ) provided with a gear wheel ( not shown ) on its outer periphery and a corresponding cooperating gear wheel 161 on the motor , constitute the driving means for converting movement from the motor 15 to the piston rod 13 . the piston rod 13 is prevented from rotating about its longitudinal axis by holding means 134 that are adapted to follow the axial movement of the rod . in the embodiment in fig1 . a , the piston rod is assumed to have a longitudinal axis of rotational symmetry . this need , of course , not be the case . the piston rod may take any convenient form , cf . e . g . fig3 - 5 and our copending patent application “ medication delivery device with bended piston rod ”. the medication delivery system consists of a replaceable part , comprising the medication cartridge ( including the piston ), a needle and possibly the piston rod , and a fixed part comprising the remaining parts of the system . the movement 150 of the electromotor 15 is illustrated in fig1 . a by the circle 155 and the circular section 151 corresponding to an actual movement of the electromotor from a minimum or start position d am , min of the electromotor to the position d am ( 1 ) i . e . corresponding to a certain fraction of a turn ( or a rational number of turns ). a corresponding movement of the piston rod 13 is indicated by arrows 132 and 131 illustrating a movement of the piston rod from a minimum or start position d p , min to the position d p ( 1 ) corresponding to a specific dose v d ( 1 ). in fig1 . a . a movement of the electromotor and the piston rod from their respective start positions is indicated . the movement may of course commence at any instance within the operational range between the minimum and maximum positions [ d am , min ; d am , max ] and [ d p , min ; d p , max ], respectively . the movement of the electromotor ( and hence the piston rod ) is controlled by a processing circuit , e . g . a micro processor 18 . the processor has access to a memory 17 ( either as a separate unit or as an integral part of the processor ) . prior to the use of the medication delivery system 1 , data 19 describing the actual movement 130 of the piston rod 13 as a function of the movement 150 of the electromotor 15 are loaded into a non - volatile part of the memory 17 . a battery 14 supplies electric energy to the electromotor 15 , the processor 18 and the memory 17 ( and to any other relevant parts of the system ) via conductors 141 . the data 19 describing the actual movement 130 of the piston rod 13 as a function of the movement 150 of the electromotor 15 may be loaded in the form of an algebraic function d p = f ( d am ) ( if at hand ) describing corresponding values of angular position d am of the electromotor and linear position d p of the end 136 of the piston rod 13 engaging the piston 112 at its outer surface 1122 . alternatively , data 19 may consist of a table of corresponding values of d am and d p over the operating range of the device with an appropriate density of data ( e . g . 100 values per turn of the motor ) . in a preferred embodiment the data 19 are obtained by a calibration procedure , optionally carried out during the production and configuration of the medication delivery system , preceding the normal use of the device . a very simple example of inaccuracies that influence the ejected dose in an injection device is the case of a threaded piston rod that is driven by a corresponding nut . if , e . g ., the thread is specified to a pitch of 0 . 70 mm per turn +− 0 . 05 mm and if the extreme case of the thread per turn is 0 . 75 mm constantly over the whole operational range of the rod is assumed , the deviation between actual dose and intended dose would reflect a corresponding inaccuracy , i . e . resulting in a constant relative overdose of approximately 7 % ( assuming that this tolerance is the decisive parameter in deciding the dose accuracy ). the table below illustrates an example of expected d ep and actual d p values of displacement of the piston rod 13 as a function of the rational number of turns d am of the actuating means 15 . in the example a linear relationship between expected piston rod displacement d ep and the rational number of turns d am of the actuating means is anticipated . the deviation of the actual displacement d p therefrom ( denoted ‘ ld error ’ in the table ) has a stochastic character . actual ld 2 ad 1 expected ld 2 ld 2 error dose 3 dose error 3 d am [ turns ] d ep [ mm ] d p [ mm ] [ mm ] v d [ iu ] v d [ iu ] 0 0 0 0 0 0 0 . 5 0 . 35 0 . 34 − 0 . 01 2 . 43 − 0 . 07 1 0 . 70 0 . 75 0 . 05 5 . 33 0 . 33 1 . 5 1 . 05 1 . 08 0 . 03 7 . 71 0 . 21 2 1 . 40 1 . 40 0 . 00 10 . 00 0 . 00 2 . 5 1 . 75 1 . 72 − 0 . 03 12 . 29 − 0 . 21 3 2 . 10 2 . 14 0 . 04 15 . 29 0 . 29 3 . 5 2 . 45 2 . 44 − 0 . 01 17 . 43 − 0 . 07 4 2 . 80 2 . 71 − 0 . 09 19 . 36 − 0 . 64 — — — — — — d am , max [ d am , max * 0 . 70 ] — — — — the density of measurement points may of course be as fine as wished by subdividing each turn into smaller fractions of a turn . in the table above a linear relationship between the actual displacement of the piston and the dose volume v d is anticipated ( nominally 1 turn corresponding to a displacement of 0 . 70 mm and a dose of 5 iu ). this need not be the case , however . the expected relationship could be a known non - linear relationship and the compensation procedure could take care of deviations from this known non - linear relationship . the rightmost column of the table shows deviation from the expected dose ( denoted ‘ dose error ’) as a function of the rational number of turns d am of the actuating means . in general , fix points on the medication cartridge and the piston rod to which all measurements are referred , must be defined . in fig1 . a and in the table above , the displacement of the piston rod relative to the medication cartridge is calculated as the displacement of the end 136 of the piston rod 13 engaging with the outer surface 1122 of the piston 112 ( denoted d p ( 1 ) or 131 ) relative to the end 115 of the cartridge opposite the outlet 111 ( denoted d p , min or 132 ). [ 0052 ] fig1 . b shows a graphical example of the relationship between the movement dam 150 of the electro motor 15 and the expected d ep 20 and actual d p 21 displacement of the piston rod 15 . the graphical representation includes the interval [ d am , min , d am , max ] ( 152 , 153 ) of the movement of the electromotor corresponding to the operating range [ d p , min , d p , max ] ( 132 , 133 ) of the piston rod . corresponding values of the position d am ( 1 ) 151 of the electromotor relative to a start value ( d am , min ) and the expected d ep ( 1 ) 231 and actual d p ( 1 ) 131 values of the displacement of the piston rod relative to a start value ( d p , min ) for a given dose vd ( 1 ) relative to a start value ( 0 ) are indicated . in a preferred embodiment , calibration data corresponding to the table above are measured and stored for every individual piston rod and corresponding driving means ( e . g . a driving nut ) and actuating means in a test setup where driving means and actuating means are those of the final medication delivery device . alternatively the test setup may apply driving means and actuating means equivalent to those of the final medication delivery device , if convenient . the data for a given piston rod and corresponding driving means are stored in the memory means of the relevant medication delivery device either directly during calibration or at a later stage , e . g . by storing the data in a relevant storage device together with data identifying the individual medication device in question ( possibly together with corresponding data for other devices ) for later retrieval and loading . [ 0054 ] fig2 shows a possible appearance of a medication delivery system ( without a housing ) according to the invention . the embodiment in fig2 comprises a partially curved piston rod 13 cooperating with driving means 16 ( in the form of a gear box ) to transfer movement from the electromotor 15 to the piston rod 13 . the electromotor is controlled by a processor 18 based on data stored in a memory 17 , both electronic circuits being located on a printed circuit board ( pcb ) 22 . the piston rod shows a 180degrees bending to provide a compact device . the piston rod engages a piston ( not shown ) in the replaceable medication cartridge 11 . the device delivers a specific dose to a user through an outlet 111 of the cartridge to which a replaceable needle ( not shown ) may be attached . the dose is delivered by activating the electromotor 15 under control of the processing circuit 18 on the basis of prerecorded data stored in the memory 17 . the dose may be preset in the device ( e . g . by preloading such data in a memory ) or based on a user input ( through i / o means not shown , but which may e . g . take the form of a keypad and a display ). a cap ( not shown ) to protect and optionally support the piston rod at its 180degrees path and to cover the electromotor , pcb and other vital parts of the device is provided . [ 0057 ] fig2 . a and 2 . b show orthogonal plane views of the medication delivery system , whereas fig2 . c presents a perspective view of the system . [ 0058 ] fig3 . a , 3 . b and 3 . c show a tape - shaped piston rod and corresponding driving means according to the invention for which periodic as well as stochastic non - linearities may be present . the piston 33 comprises a tape with centrally situated , regularly spaced circular holes 331 adapted to cooperate with corresponding protruding circular cylindrical members 361 on the driving drum 36 . the driving drum is activated by an electromotor through appropriate driving means ( e . g . a gear box ) . the holes are shown to be positioned along a centerline of the tape , but may of course be located at one or both longitudinal edges of the tape or along a line off the center line or in any other convenient way as long as the protruding means on the driving drum follow a corresponding pattern . likewise the individual holes and corresponding protruding members may take on any convenient form , e . g . edged as opposed to circular , as long as the holes in the tape and the protruding members on the driving drum correspond . [ 0060 ] fig3 . a and 3 . b show orthogonal plane views of the piston rod and driving drum , whereas fig3 . c shows a perspective view of a coiled piston rod . in fig3 . a - 3 . c , the driving means on the piston rod and driving drum are shown as individual holes and corresponding protruding members , respectively . they might of course take on any other appropriate form , e . g . corresponding indentations or grooves and projecting members . likewise , the receiving members may be located on the driving drum and the corresponding protruding members on the piston rod , if convenient . the non - linearities in the transfer of angular movement from the electromotor to linear movement of the piston rod may have several origins . one source involved in the interaction between the driving drum and the piston rod is the built - in variations in the distance between adjacent holes in the tape and in the geometrical form of each individual hole due to production tolerances . these deviations from ideality have their counterpart in the corresponding features of the driving drum . together these inaccuracies will result in a non - linear variation in the actual displacement of the piston rod with angular movement of the electromotor . the deviation from the expected displacement will be of a stochastic nature . other contributions to non - linearity may e . g . come from the interaction of gear wheels , etc . these contributions may be partly stochastic in nature and partly periodic . another source of non - linearity has its origin in the construction of the piston rod . as appears from fig3 . c , the tape may be coiled on the driving drum . depending on the thickness of the tape and the diameter of the drum , the length of tape provided by each turn of the driving drum will decrease the fewer the number of times that the tape is coiled on the driving drum , and vice versa . this source of non - linearity is predictable in principle , however , since it has a geometric origin . a mathematical expression including the geometrical dimensions of the tape and the drum may be set up . yet another source of non - linearity is a possible nonconcentric suspension of the driving wheel or drum , which result in a periodic non - linearity that may be compensated by the present invention . the contributions to non - linearity in the transfer of angular movement from the electromotor to linear movement of the piston rod are thus partly of a stochastic nature and partly of a ‘ geometrical ’ nature . the latter may in principle be mathematically described and included in the correction algorithm of the processing unit . the former , however , can only be compensated for by a proper calibration of each individual device . such a calibration will conveniently include all contributions ‘ automatically ’ ( be they of a stochastic or geometric nature ), so that a complete correction of the movement of the piston may be achieved on this basis . a limiting factor in the correction process is of course the accuracy with which the processing unit controls the angular movement of the electromotor . if , however , the geometric contributions are dominating , a purely mathematical correction is of interest . in this case , a calibration of each unit prior to their ( first ) use is not necessary . [ 0068 ] fig4 . a and 4 . b show a toothed piston rod and corresponding driving means according to the invention for which periodic well as stochastic non - linearities may be present . [ 0069 ] fig4 . a and 4 . b illustrate only a part of a medication delivery system , namely the cartridge 11 with outlet 111 and piston 112 , the latter being engaged with a serrated piston rod 43 comprising driving means 431 in the form of individual teeth placed beside each other in the length of the piston rod . a driving wheel 46 with individual teeth 461 adapted to cooperate with the teeth 431 of the piston rod 43 comprises another part of the driving means that are responsible for transferring the angular movement of the electromotor ( not shown ) to a linear displacement of the piston rod 43 . as discussed above for the tape - shaped piston rod of fig3 . a - 3 . c , a contribution to the non - linearity in the transfer of angular movement from the electromotor to linear movement of the piston rod will have its origin in inaccuracies in piston rod and driving means due to production tolerances and possible other defects ( e . g . due to mechanical damage ) of these parts . another source , however , resulting in a cyclical and predictable contribution to the non - linearity , has its origin in the interaction of the teeth of the circular driving wheel and the teeth of the linear piston rod . the point of contact between a tooth of the driving wheel and a tooth of the piston rod will move during the ‘ cycle ’ of a given tooth of the driving wheel from its first contact with the actual tooth of the piston rod to its last contact with said tooth ( before the next tooth of the driving wheel ‘ takes over ’) . this movement will give rise to a non - linear contribution to the movement of the piston rod with respect to the angular movement of the driving wheel ( and thus the electromotor ). a mathematical expression based on the geometrical dimensions of driving wheel and piston rod including the teeth on both may be set up and included in the correction algorithm . alternatively , the combined effects of material inaccuracies and builtin geometrical non - linearities may be corrected for by making a calibration of each device prior to its ( first ) use . [ 0072 ] fig5 shows a chain - like piston rod and corresponding driving means according to the invention for which periodic as well as stochastic non - linearities may be present . [ 0073 ] fig5 again illustrates only a part of a medication delivery system , namely the cartridge 11 with outlet 111 ( with needle 113 ) and piston 112 , the latter being engaged with a ‘ chain - like ’ piston rod 53 comprising driving means in the form of individual links 531 placed beside each other in the length of the piston rod . each link comprises a hole ( not shown ) and is connected to its neighbouring link by a connecting member 532 . a driving wheel 56 with individual protruding members 561 adapted to cooperate with the holes of the links 531 of the piston rod 53 comprises another part of the driving means that are responsible for transferring the angular movement of the electromotor ( not shown ) to a linear displacement of the piston rod 53 . as discussed for the embodiments in fig3 and 4 , the contribution to the non - linearity in the transfer of angular movement from the electromotor to linear movement of the piston rod is likewise composed of a stochastic part and a geometrical part . the geometrical part may in principle be compensated for by mathematical means and the combined effects of material inaccuracies and builtin geometrical non - linearities may be corrected for by making a calibration of each device prior to its ( first ) use . some preferred embodiments have been shown in the foregoing , but it should be stressed that the invention is not limited to these , but may be embodied in other ways within the subject - matter defined in the following claims . for example , the actuating means are exemplified as an angular electromotor . the actuating means could of course be any other convenient type including a linear motor .
the invention relates to : a medication delivery device for delivering a specific dose comprising a medication cartridge having an outlet and a piston , and means for holding said cartridge , and a piston rod being operable to engage and displace said piston , and electrically driven actuating means , and driving means for transferring movement from said actuating means to said piston rod , and memory means for storing data , and processing means for evaluating said data and for controlling said actuating means . the object of the present invention is to provide a medication delivery system that combines a relatively high dose accuracy with the use of relatively low quality mechanical components and which enables compensation for built - in non - linearities . the problem is solved in that a first set of data describing the actual movement of said piston rod relative to said medication cartridge as a function of the movement of said actuating means is stored in said memory means , and the movement of the piston rod governing the delivered dose is controlled by the processing means on the basis of said first set of data . this has the advantage of allowing compensation for mechanical inaccuracies and built - in non - linearities linearities . the invention may e . g . be used in injection or infusion devices for a person &# 39 ; s self - treatment of a disease such as diabetes .