in the exemplary embodiment of a piston pump i for use in a dosing device constructed in accordance with the principles of the present invention , the piston pump 1 has an inlet channel 2 and an outlet channel 3 for a liquid to be conveyed . the piston pump 1 can be a component , for example , of an implantable medication dosing device operated by a battery implanted as a part of the device . if so used , the inlet channel 2 is connected to a reservoir ( not shown ) for the liquid medication , for example insulin , and the outlet channel 3 will be connected to a catheter arrangement ( not shown ) for delivering the medication to a selected location in the body of the patient in whom the device is implanted . the piston pump i has a piston 4 which is contained in a cylinder housing 5 . the drive of the piston 4 ensues by means of an electromagnetic actuation system formed by a permanent magnet 6 arranged in the region of the inlet channel 2 , a stator 7 seated on the cylinder housing 5 and having a stator winding 8 , and an encapsulated armature 9 rigidly connected to the piston 4 , and disposed substantially between the permanent magnet 6 and the stator 7 . the pole pieces of the permanent magnet 6 and of the stator 7 are respectively referenced 10 . the stator winding 8 is connected via terminal lines 11 and 12 to a control circuit , shown in greater detail in fig2 . the displacement region 13 ( stroke length ) of the piston 4 is limited by the end face 14 of the piston 4 facing toward the outlet channel 3 , by the cylinder housing 5 , and by a valve 15 which is seated in a position which seals the displacement region 13 with the force of a magnet 16 . the piston 4 is maintained in the quiescent position illustrated in fig1 by the permanent magnet 6 . upon excitation of the stator winding 8 , the piston 4 is accelerated out of its quiescent position in the direction toward the valve 15 , and thereby presses the liquid situated in the displacement region 13 through the valve 15 , which opens against the restoring force of the magnet 16 , and into the outlet channel 3 . at the same time , liquid from the reservoir is caused by suction to flow in through the channel 2 at the back side of the piston 4 . this liquid is drawn by suction through the gap between the piston 4 and the portion of the cylinder housing 5 surrounding the piston 4 into the displacement region 13 , when the piston 4 is moved back to its quiescent position by the force of the permanent magnet 6 , upon disconnection of the excitation of the stator winding 8 . a detector in the form of a noise sensor 17 is disposed in the region of the outlet channel 3 , concentrically relative to the channel 3 . the noise sensor 17 is formed by piezoceramic annular disc 20 provided with metal layers 18 and 19 at both sides . the annular disc 20 is secured at one side to a flange 22 of the piston pump i via an insulating layer 21 , and is connected at an opposite side to a coupling compound 24 via a further insulating layer 23 . the metal layers 18 and 19 serve as sensor electrodes , and are connected to terminal lines 25 and 26 which are conducted to the exterior of the pump 1 . the noise sensor 17 is contained in a housing 27 which is fixed to the piston pump 1 . the armature 9 , rigidly connected to the piston 4 , has an annular surface 28 facing in the direction toward the outlet channel 3 . a surface of the cylinder housing 5 in the form of a detent 29 is disposed opposite the annular surface 28 with the annular surface 28 , in the quiescent position shown in fig1 being spaced from the detent 29 . for each complete pump stroke , the annular surface 28 of the armature 9 of the piston 4 strikes against the detent 29 , causing the generation of an impact noise which is distinct from the general pump noise . this impact noise is transmitted to the noise sensor 17 via the cylinder housing 5 and the flange 22 , and is therein converted into an electrical output signal , which can be tapped across the terminal lines 25 and 26 . a schematic circuit diagram of a control and monitoring circuit for the piston pump i is shown in fig2 . the circuit includes a voltage multiplier 31 , having output terminals 32 and 33 connected to a charging capacitor 34 and having supply terminals connected to a battery 30 . the stator winding 8 of the piston pump 1 , together with a free - running diode 35 connected between its terminal lines 11 and 12 are connected in parallel with the charging capacitor 34 via a controllable switch 36 . the control of the excitation of the stator winding 8 ensues with a higher - ranking control unit 37 , which is connected to a data memory 38 . a telemetry unit 39 is connected to the memory 38 for two - way communication with an external programming device 40 . a number of different conveying ( pumping ) rates can be stored in the memory 38 , which can be called automatically according to a prescribed program sequence , or can be called upon actuation of the programming device 40 . the selected rate is transmitted to a pump rate generator 42 via a control line 41 . the pump rate generator 42 generates a sequence of individual pulses at an output line 43 , each individual pulse defining an individual pump stroke of the piston pump 1 . the pulse repetition rate is proportional to the conveying rate currently in force . the output line 43 of the pump rate generator 42 is connected to an activation input of the voltage multiplier 31 . the voltage multiplier 31 is switched on ( enabled ) at each individual pulse , and generates a signal at a monitoring output 44 as soon as the charging capacitor 34 is charged to a prescribed , minimum voltage . upon the appearance of the signal at the monitoring output 44 , and the prior appearance of an individual pulse on the control line 43 , a logic circuit 45 generates an output signal on an output signal line 46 which is supplied both to the control unit 37 and to the setting input s of a bistable trigger circuit 47 . the bistable trigger circuit 47 generates a signal at its output q , which is supplied to the controllable switch 36 as a turn - on ( beginning energization ) signal . simultaneously , the counting of a time duration is started in the control unit 37 , the bistable trigger circuit 47 being reset at its reset input r via a control line 48 after the expiration of this time duration , and thereby generating a turn - off ( end energization ) signal at its output q for the controllable switch 36 . both terminal lines 25 and 26 of the noise sensor 17 are connected to the control unit 37 . the output signal of the noise sensor 17 is analyzed in an evaluation means ( not separately shown ) which is an integral component of the control unit 37 . an error detector 49 is connected to the control unit 37 , which generates an error message such as , in the illustrated embodiment , an acoustic signal . it is also possible that the error message may be in the form of an electrical stimulation pulse ( tickle ) to the patient , or a talemetric transmission of the error message to the programming device 40 . three curves are shown in fig3 which , from top to bottom , illustrate the current i through the stator winding 8 , the velocity v of the piston 4 , and the output signal s of the noise sensor 17 for three different on - time durations t a , t b and t c , during which the controllable switch 36 is closed . the curves for the current i , the piston velocity v and the output signal s allocated to the different time intervals t a , t b and t c are correspondingly indexed with subscripts a , b and c . a pump stroke is started at time t = 0 , by closing the switch 36 as a result of a turn - on signal at the output q of the trigger circuit 47 . the charging capacitor 34 is discharged across the stator winding 8 , in which a current i flows in the form of an attenuated sinusoidal oscillation . when the stator magnetic field generated by the current i in the stator winding 8 exceeds the retaining force of the permanent magnet 6 , the stator friction of the piston 4 in the cylinder housing 5 ( occurring at t = t 1 in fig3 ), the piston 4 is accelerated in a direction toward the valve 15 , whereby the piston velocity v progressively increases . in the case denoted by the subscripts a , which corresponds to the pump control disclosed by the aforementioned european application 0 317 705 , the switch 36 remains closed until the piston 4 strikes the detent 29 . the typical output signal s a of the noise sensor 17 thereby arising exceeds the sensitivity threshold s o thereof for the detection of the impact of the piston 4 against the detent 29 , and is used for triggering a turn - off signal for the switch 36 , which ends the on - time duration t a . as shown in fig3 the piston velocity v a reaches its maximally possible value at the end of the on - time duration t a , so that the piston 4 strikes the detent 29 with the highest possible impact energy . during continuous operation of the piston pump 1 , this high impact energy can lead to mechanical damage to the piston pump 1 , and to an undesirably high mechanical stressing of the liquid to be conveyed . as can be seen from the curve i a of the current , moreover , the energy consumption is comparatively high . additionally , the impact noise can be burdensome to the patient and to those around the patient . in a first embodiment of the invention , a fixed value t b is provided for the on - time duration , this being calculated , for example , on the basis of experimental trials and being dimensioned so short that the excitation of the stator winding 8 is disconnected before the piston 4 strikes the detent 29 but being sufficiently long to obtain a sufficiently high impact energy of the piston 4 given malfunction - free operation of the piston pump 1 . this means that the output signal s b of the noise sensor 17 is sure to exceed the sensitivity threshold s o . at the beginning of the pump stroke , therefore , a turn - on signal for the switch 36 is generated by setting the trigger circuit 47 . after the expiration of the predetermined on - time duration t b , the trigger circuit 47 is reset and the switch 36 is opened by a turn - off signal at the output q of the trigger circuit 47 . the magnetic energy stored in the stator winding 8 at the time of turn - off results in the current i b continuing to flow through the stator winding 8 and the free - running diode 35 , with the current i b exponentially decaying due to the internal resistance of the stator winding 8 . due to the kinetic energy of the piston 4 and of the liquid in front of and behind the piston 4 , as well as due to the magnetic energy stored in the stator winding 8 at the turn - off time , the piston 4 continues to be driven toward the detent 29 , and upon impact with the detent 29 generates the output signal s b in the noise sensor 17 . as can be seen in fig3 both the current consumption and the maximum piston velocity , as well as the impact energy of the piston 4 , are lower than in the known drive mode referred to by subscripts a set forth above . it should be noted that the impact energy is a quadratic function of the impact velocity . the piston acceleration also becomes lower in comparison to the aforementioned known drive mode , which is advantageous in order to prevent cavitation . as a result , the mechanical stressing of both the piston pump 1 and the liquid to be pumped is lower . if , due to disturbances of any type , the number of impacts of the piston 4 detected by the noise sensor 17 for a given number of past strokes falls below a prescribed value , this is registered by the control unit 37 . the control unit 37 thereupon lengthens the on - time duration , and after the expiration of the on - time duration the bistable trigger circuit 47 is reset in the subsequent pump strokes . this occurs either by the time interval t b being lengthened by a prescribed amount t b , or by not generating the turn - off signal for the switch 36 until the appearance of an output signal s from the noise sensor 17 indicating the detection of the impact of the piston 4 against the detent 29 . simultaneously , the occurrence of the malfunction event together with other pump parameters such as , for example , the current pump rate , the time interval t a and the time t 1 are stored in the memory 38 , so that this information can recalled by a physician using the programming device 40 for error evaluation . moreover , the patient is informed of the occurrence of a malfunction by the error detector 49 , by an acoustic signal or by a stimulation current pulse . alternatively , the patient can be informed of the error message upon the next interaction with the telemetry means , or upon his or her next visit to the physician . the lengthened time interval can be manually reset to the earlier value t b via the programming device 40 . it is also possible , however , that resetting to the earlier value t b can automatically ensue upon the expiration of a programmed time within the control unit 37 . in a further embodiment of the invention explained with reference to fig4 the turn - on time interval t is variable . the beginning of each pump stroke is marked with individual pulses p generated by the pump rate generator 42 . proceeding from a value for the on - time duration t at which an output signal s of the noise sensor 17 which is sure to exceed the sensitivity threshold s o is obtained ( i . e . with the value t a , for example ), the time interval t is shortened by a prescribed step width t s after a prescribed number of pump strokes ( two pump stroked in the embodiment of fig4 ). this procedure is repeated until the output signal s of the noise sensor 17 falls below the sensitivity threshold s o . at that time , the time duration is lengthened to the value t c by at least one step width t s ( fig3 ) and the new value is retained for a given time , or for a number of pump strokes until a new value for the on - time duration is calculated again by step - by - step shortening of the on - time duration t . this procedure is also initiated when the output signal of the noise sensor 17 is suddenly absent . due to changes in the pump 1 , changes in the catheter system , or due to external conditions such as pressure or temperature , or due to changes in the liquid to be conveyed , the piston motion may change , so that different output signals of the noise sensor 17 are obtained even with an unaltered on - time duration t for the electromagnetic excitation . the drive of the piston pump 4 is automatically matched to altered pump conditions by the step - by - step shortening of the on - time duration , until the absence of an impact of the piston 4 against the detent 29 , which results in the subsequent lengthening of the on - time duration by at least one step width . if the length of the on - time duration exceeds a prescribed maximum value , or falls below a prescribed minimum value , an error message is generated by the error detector 49 . information by means of which malfunctions in the pump operation can be identified , and possibly impending malfunctions can be detected in advance , are obtained by storing the occurrence of a failure to detect the piston impact , together with the pump rate . in addition to or instead of detection by a noise sensor 17 , the impact of the piston 4 against the detent 29 may be detected by types of sensors , for example an optical sensor or a magnetic proximity switch . although modifications and changes may be suggested by those skilled in the art , it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art .
in a dosing device of the type suitable for human implantation for delivering a liquid medicament , a piston of a pump is accelerated against a detent by energization of an electromagnetic actuation system , with the electromagnetic actuation system being controlled so that it is de - energized slightly before the piston reaches the detent , with the inertia of the piston carrying the piston against the detent to complete the piston stroke . by shortening the amount of time during which the electromagnetic actuation system is energized , energy is saved . control of the electromagnetic actuation system is undertaken by identifying a nominal stroke time for the piston by detecting the impact of the piston against the detent , and calculating an on time for the electromagnetic actuation system which is so short that the impact of the piston against the detent can still be just barely detected .