Injector display

The invention concerns a display for a medical injection device (1) wherein an injection dose is pre-selected by rotating an operating head (2) and then is administered by axially displacing said head. Switching devices (7, 8) are apposed to the operating head (2) to actuate switches (7, 8) of which the switch positions are transmitted to a printed circuit board (13). The printed circuit board (13) preferably contains a processor, so that values such as set injection dose, the sum of administered injection doses etc. and signals concerning operational states are shown on a display system (15).

FIELD OF THE INVENTION 
The invention relates to a medical-injection display for an injection 
device used to inject selectable doses of liquid from an ampoule or the 
like. 
BACKGROUND OF THE INVENTION 
Injection devices (hereafter called merely "devices") are used in medicine 
to inject liquids for instance into the human body. The present 
application relates to devices constructed so that patients are able to 
administer to themselves the injections at any time. Significant criteria 
are the compactness of the device which must be carried on one's person, 
the possibility to carry out several injections using one ampoule in the 
device, and accurately preselected injection doses, as well as reliability 
and simple handling of the device. 
Such devices are known. European patent document B10 293 958 describes one 
employing ampoules with plungers. The plunger is advanced by a rod driven 
by an electric motor and the injection liquid in the ampoule is thereby 
expelled from the ampoule and through a needle. A sensor measures the 
dose-setting adjustment of the rod and hence of the plunger. The 
electrical signal magnitude measured is compared at a comparator with an 
electrical reference value previously set by the patient and can be 
displayed. When the dose set by the reference value has been reached, an 
electric check is performed each time to see whether the set dose is still 
present in the ampoule. If not, the electrical motor is locked up to 
preclude injection and this state is then displayed. 
While this device can be carried on one's person, it is fairly bulky 
because of the electric motor and the gear sets. Also, the sensor provides 
an analog output and if there were a change in amplification, the desired 
rod adjustment conforming to the reference value might differ from the 
actually set value and the patient would inject the wrong dose. The 
patient lacks checking means. Moreover, the battery condition is not 
displayed, and it might be at such a Level, previous to a required 
injection, adequate still to control the device and feed the displays but 
insufficient to lower the motor and therefore the injection could not be 
carried out. The complexity of the electronic control of this device 
includes further functions not cited herein and therefore it is 
comparatively large. 
A further device is known from WO 87/02895. It is actuated solely manually 
and has the bulk of a fountain pen with clip; in other words, it is easily 
carried on the patient's person. The injection dose can be set at a rod by 
rotating an operating head; this rod moreover does not touch the ampoule 
which is used in this device and which is filled with the injection 
liquid. When the operating head is displaced axially, the rod is made to 
touch the plunger and the adjusted dose is then expelled through a needle 
by said plunger. Thereupon the rod and operating head snap back and the 
next dose can then be set by rotating said operating head. The size of the 
dose is determined by the number of revolutions undergone by the operating 
head and illustratively may be detected by acoustic signals emitted every 
quarter turn. 
The set dose can be checked acoustically only during setting, but not 
later. This constitutes to a substantial drawback because erroneous doses 
cannot be ruled out. 
SUMMARY OF THE INVENTION 
An object of the invention is to alleviate the shortcomings of both 
devices. To that end, it provides a display for an injection device 
whereby the patient is able to check reliably and subsequently the set 
dose and is provided information how much injection liquid remains for 
further injections.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A display according to the invention mounted on an injection device 1 
partly shown in FIGS. 1 and 2 and moreover illustratively similar to that 
of WO 87/02895 comprises an axial operating head 2 with a cylindrical part 
3, said head being rotatable in order to set the magnitude of the dose to 
be thereupon injected and further being slidably movable axially to carry 
out the injection. The rotations of the operating head 2 are composed of 
continuous fractional turns of which a given number amounts to one 
revolution. Illustratively the fractional turns may be quarter-turns. 
When, and only when, the rotatable head is in a position of a terminated 
fractional turn can the operating head 2 can be displaced only axially: 
the cylindrical part 3 of the operating head 2 has a number of axial 
lengthwise bosses 4 corresponding to the number of fractional turns and 
which, upon axial displacement of the operating head 2, engage the same 
number of longitudinal channels 6 in a housing wall 5 and thereby prevent 
rotation. The final axial position, that is the position wherein the 
longitudinal bosses 4 fully engage the longitudinal channels 6, is smitted 
from the drawing, but their rest positions are shown, namely, in which 
rotation of the operating head 2 is possible because then there is no 
engagement between the longitudinal bosses 4 and the longitudinal channels 
6. The operating head 2 advanced into the end position is returned into 
the rest position by elastic means omitted from the drawing but located in 
the lower part of the device 1. 
Switch operation means 7, 8 are apposed to the operating head 2 and can be 
actuated by its motion. They engage a switch part 9 and in turn actuate 
switches 10, 11 and 12. Switch part 9 is connected to a printed-circuit 
board 13 powered by a battery 14 and said board in turn is electrically 
connected to a display 15 such as an LCD system. 
These switch means 7, 8 may form signals as a result of the rotation, in 
which event they will be called "boss" or "cam" rings 7, or they may form 
signals by means of the axial displacement, in which case they are called 
"switch rings" 8. Preferably the cylindrical part 3 of the operating head 
2 passes through the switch means 7, 8. 
The cam rings 7 rotate together with the operating head 2, being driven for 
instance by the longitudinal bosses 4 on the cylindrical part 3 of the 
operating head 2. However, other transmission means may be provided for 
rotation. Advantageously they comprise an equal number of 
circumferentially equidistant bosses 18. A cam ring 7 may comprise several 
cam surfaces 16, 17 adjoining one another at its outer circumference and 
with axially offset bosses or shoulders 18. If, as shown in the drawing, 
cam ring 17 comprises a first cam surface 16 and a second cam surface 17, 
then the former can actuate a first switch 10 and the latter can actuate a 
second switch 11 in switch part 9. Advantageously the shoulders 18 of a 
cam surface 16, 17 are designed in such manner that during the rotation of 
the operating head 2 the switches 10, 11 located in the plane of a 
shoulder 18 will always be turned ON by means of a first angular excursion 
and OFF by means of a second angular excursion. As elucidated further 
below, the switchover implemented by the shoulders 18 of the switches 10, 
11 each time entails the setting of the next injection dose and its 
display. 
Other switch means are designed as switch rings 8 which do not take part in 
the rotation of the operating head 2. They are prevented from doing so for 
instance by a stop 20 of the switch ring 8 being rigidly mounted in a hole 
of the housing wall 5. The cylindrical part of the operating head 2 also 
passes through the switch ring 8. 
A third switch 12 of the switch part 9 is kept in a first position by a 
switch ring 8 during the rest position and during the transition from rest 
position to the end position, and back, when the operating head 2 is 
displaced axially. For the omitted axial end position of the operating 
head 2, switch ring 8 moves the third switch 12 of the switch part 9 into 
a second position. For that purpose cylindrical part 3 of operating head 2 
is illustratively fitted with an annular channel 19 entered by switch ring 
8 for the axial end position, whereby it moves third switch 3 into the 
second position. 
The above procedure is implemented for instance in that switch ring 8 is 
pressed by a spring behind switch 12 into the annular channel 19 and 
thereby makes room, as a result of which spring-loaded switch 12 is 
simultaneously reversed from the first: into the second position. Because 
the end position of the axial displacement takes place only at the end of 
injection, switch ring 8 allows counting the number of administered 
injections. 
Cam rings 7 and switch rings 8, through switches 10, 11, 12, drive an 
electric part of the display essentially consisting of a printed-circuit 
board 13, a battery 14 and an LCD system 15. Printed-circuit board 13 
contains a processor receiving its inputs from the switch positions of 
switches 10, 11, 12 and allowing performance of the following functions, 
counting the time of display 
counting the fractional turns when setting an injection dose, 
counting a "reserve" which is computed from the difference between the 
volume of injection liquid when the ampoule was inserted minus all the set 
injection doses up to that time based on the partial rotations, and 
counting the output of injection doses based on the fractional turns. 
Accordingly the number of fractional turns of the operating head 2 to 
increase the set injection dose is added by the display over the entire 
capacity range of the liquid receptacle or to enlarge the pre-set dose, or 
it is subtracted when reversing the direction of rotation. 
The count of display duration determines the duration during which one of 
the above listed magnitudes can be displayed by LCD system 15 unless 
another magnitude is already displayed. Illustratively, this duration is 
128 seconds for the device shown. When setting the injection dose in the 
illustratively shown device of FIGS. 1 and 2, the fractional turns, which, 
as mentioned above are quarter-turns of the operating head 2, are counted 
by means of a cam ring 17 and switch 10, 11 with a 2-position binary 
counter of the processor, and according to the position of operating head 
2, the binary numbers 00, 10, 11, and 01 will be the outputs at LCD system 
15. 
Again as mentioned above, because the first and second switches 10, 11 
actuated by the rotation of operating head 2 and by cam ring 7 and 
shoulders 18 axe reversed shortly before the end of the corresponding 
fractional turns, operating head 2 can be rotated arbitrarily clockwise or 
counter-clockwise without giving rise to errors in ascertaining its 
position from the readout of the LCD system. The signals formed are shown 
in FIG. 3. 
The x-axis of FIG. 3 shows the angular excursion and the y-axis the signal 
magnitudes at the display output for setting the injection dose, while the 
abscissa below shows the associated readout of a binary counter and below 
that the associated display of an LCD system. 
Shortly before the end of the first fractional turn (prior to 90.degree.), 
first boss 18 of the first cam surface 16 reverses first switch 10 and 
raises the signal A. Illustratively the binary number 10 appears at the 
LCD system which in this case is counting in the binary mode. 
Shortly before the end of the second fractional turn (prior to 180.degree.) 
second shoulders 18' of the second cam surface 17 reverses second switch 
11 and raises the second signal B. The first signal remains at its 
previous amplitude. The binary number 11 appears at the LCD system. 
Shortly before the end of the third fractional turn (prior to 270.degree.) 
first shoulder 18 of the first cam surface 16 moves back first switch 10 
and moves down the first signal A. The second signal remains high. The 
binary number 01 appears at the LCD system. 
Shortly before the end of the fourth fractional turn (prior to 360.degree.) 
second shoulder 18' of the second cam surface 17 moves back the second 
switch and moves down the second signal B. The first signal remains low. 
The LCD system 15 displays the binary number 00. 
This procedure continues to the end of the rotation of operating head 2 
after the injection dose has been set. The binary numbers also may be 
stated in another sequence. 
The number of fractional turns moreover is summed by an LCD counter and 
appears as a decimal number, after the end of the rotation, at the LCD 
system 15. It indicates the magnitude of the set injection dose based on 
the number of fractional turns. This display will be erased for the axial 
end position of operating head 2, that is, after the injection of the set 
injection dose, by the processor and through switch ring 8 and third 
switch 12 with the time-delay of the display-duration count. 
The number of the injected fractional turns is subtracted from a reserve 
counter automatically set, upon new-ampoule insertion, to the total 
injection quantity from this ampoule, based on the number of possible 
fractional turns. This reserve counter shows a conspicuous special alarm 
character, for instance a flickering "tt" on LCD system 15 in lieu of the 
set dose if the set dose exceeds the still extent reserve of injection 
liquid. 
The processor may contain a timer. If the maximum allowed time to 
administer an injection from the inserted ampoule is exceeded, then a 
special alarm character such as a flickering "bb" can be displayed at the 
LCD system 15 after an attempt was made to set an injection dose. 
Moreover the processor monitors the battery power output. If the power has 
become too low, it will display a warning sign such a flickering "bt" at 
the LCD system 15 after an attempt was made to set an injection dose. 
Furthermore discrete circuits with preset functions may be used in lieu of 
a processor on the printed-circuit board 13 to carry out the above 
operations. Speaking broadly, one may consider that the said operations 
can be implemented by the printed-circuit board 13. 
Also different and advantageous display means may be used with the device 
of the invention. Illustratively the display may be integrated into an 
injection device wherein the injection dose can be set and the injection 
itself can be carried out using electrical means. 
Following setting of the desired dose, the patient is able to check it 
thereafter in the injection device by means of the display according to 
the invention and obtains information how much injection liquid remains 
for further injections. The display of the invention therefore meets its 
objective.