A hypodermic jet injector employing self-contained, patient fillable, thin-walled disposable ampules. Each ampule includes an elongate plastic body with an injection orifice at a first end, an internal propellant at a closed second end, and a double piston slidably and sealingly mounted within the body entirely between the orifice and the internal propellant, and also includes an auxiliary access opening in the ampule side wall. An ampule chamber with a corresponding access opening in its side wall is provided to receive and support the thin-walled ampule. The main body of the ampule is molded with draft angles, and the double piston construction includes a soft rubber plunger and a relatively hard plunger to the front and rear, respectively, of the auxiliary access opening in the ampule, with the two plungers interconnected by a connecting rod spanning the central section of the ampule. The ampule chamber is provided with a draft angle in the front section of its bore adjacent to the soft plunger in the ampule, and a straight bore in the rear section adjacent to the hard plunger in the ampule. The injector includes a high-resolution metered filling device located parallel to the ampule chamber and including a piston engagement member which is laterally movable into contact with the connecting rod, which consequently moves under control of the filling device. The metered filling device includes a digital dosage display including a drum bearing a plurality of dosage values in integer form arranged in a spiral pattern on its surface, and a dosage selection window positioned so as to expose a single dosage value at a time.

BACKGROUND OF THE INVENTION 
This invention relates generally to hypodermic injection devices, and more 
particularly to reusable hypodermic jet injectors, or needleless 
injectors, in which a dosage of medicine and a powering charge are 
contained within a disposable ampule. 
Hypodermic injection devices capable of administering a dosage of medicine 
in the form of a fine, high-velocity jet delivered with sufficient force 
as to pass through skin tissue without the need of a hypodermic needle 
have been known since at least the 1960s. Perhaps the widest application 
of jet injectors is in the administration of insulin to individuals 
afflicted with diabetes, although such devices are also known for use in 
vaccinations as well as the administration of vitamins, anesthetics and 
other medicines in liquid form. Examples of jet injectors employing 
disposable ampules are disclosed in the following patents: 
______________________________________ 
U.S. Pat. No. 
Inventor Issue Date 
______________________________________ 
3,335,722 Lowry et al. Aug. 15, 1967 
4,089,334 Schwebel et al. 
May 16, 1978 
4,124,024 Schwebel et al. 
Nov. 7, 1978 
4,518,385 Lindmayer et al. 
May 21, 1985 
4,940,460 Casey et al. Jul. 10, 1990 
5,312,335 McKinnon et al. 
May 17, 1994 
______________________________________ 
Cost is normally a factor in the selection of any disposable device, and 
the cost of a disposable ampule is directly affected by the amount of 
material required for a particular ampule design as well as by 
manufacturing costs. In a number of the devices disclosed in the above 
patents a disposable ampule extends out of the forward end of the injector 
and, as such, must be designed to withstand the high internal pressures 
developed during injection. For example, disposable ampules have been made 
according to the principles of U.S. Pat. No. 4,089,334 to Schwebel et al. 
using polycarbonate, and a wall thickness of 0.100" has been found 
necessary with such a material. Reinforcement of the exposed exterior 
portion of an ampule as shown in U.S. Pat. No. 4,124,024 to Schwebel et 
al. can provide the strength required to withstand the pressures 
encountered during an injection, but at the cost of additional material 
incorporated into the ampule for reinforcement. 
Lowry et al. discloses a disposable ampule having a stainless steel nose 
piece over the front end of a plastic sleeve, with the complete ampule 
except for the tip of the nose piece enclosed within the bore of the jet 
injector. Lowry et al. indicates a maximum thickness of about 0.020" for 
the stainless steel nose piece, and a greater thickness for the plastic 
sleeve. The ampule does not include a propellant charge; instead, a 
stopper of neoprene rubber or like elastomer is exposed at the rear of the 
ampule and is contacted from the rear by a piston which is forced forward 
into the ampule under pressure developed from the ignition of a propellant 
charge contained in a separate part of the hypodermic device. 
Manufacturing concerns also come into play in connection with the cost of a 
disposable ampule. For example, the cycle time for a molding operation 
increases as a function of increased wall thickness and has a 
corresponding impact on labor costs and operating expenses. 
In addition, we have discovered that injection molding of plastic ampules 
can be made more efficient by molding the ampules with draft angles, i.e., 
slightly tapered surfaces as opposed to uniform cylindrical surfaces. 
Draft angles on the inside and outside surfaces of an ampule will 
facilitate the separation of a newly molded ampule from an outer mold 
section or sections as well as from a core pin or insert or other inner 
mold part. It is further believed that such a construction will eliminate 
the need for a mold release, and thereby eliminate the associated material 
cost as well as the time required to apply the mold release to the mold 
surfaces and to thereafter remove all residual mold release from the 
molded ampule to prevent contamination. 
Lindmayer et al. discloses a syringe for a needleless injector in which the 
barrel of the syringe tapers slightly from front to rear and the injector 
barrel in which it fits is tapered internally to match the taper of the 
syringe barrel in order to use a thin-walled syringe barrel which is 
capable of resisting the high pressures required to create a high-velocity 
jet. The patent refers, without explanation or illustration, to a barrel 
and plunger tapered slightly for insertion into a similarly tapered casing 
of an injector, but the syringe plunger as disclosed is an elongated hard 
plastic body described as a cylindrical body with a conical front end for 
abutting the conical front end of the syringe barrel. Internally, the 
syringe barrel, which may be formed of polypropylene, similarly appears 
uniformly cylindrical in shape except for its conical front end. Without a 
draft angle on the inside wall surface of an ampule, however, injection 
molding of the ampule is made more difficult and consequently more 
expensive. 
There is also an ever-increasing need for devices for rapidly and easily 
but very accurately filling jet injectors with a required medicine dosage, 
especially for home health care. Injectors suited for self-administration 
of medicine in a home care setting are desirable from a cost standpoint as 
well as from the standpoint of patient convenience, especially for 
long-term care which would otherwise necessitate frequent appointments 
with medical personnel. Cost constraints practically dictate reusable jet 
injectors, because it is impractical to dispose of a complete device after 
one use, and reusable jet injectors need to be filled prior to each use. 
Some reusable injectors permit filling of medicine directly into an 
injection chamber, while others are designed to receive a prefilled 
ampule. After an injection with the former type, the injection chamber and 
any passageways leading to it from a supply vial inevitably contain some 
residual amount of medicine which can be difficult to remove. Periodic 
cleaning is typically required with such injectors, as exemplified by the 
Medi-Jector.RTM., commercially available from Derata Corporation. Without 
proper cleaning, the residual amounts of medicine can lead to 
complications, particularly when different types of medicine are to be 
injected, as is fairly common in insulin administration regimens. 
Patients are more likely to accept, and properly use, a jet injector that 
is simple to set up for use and that requires little or no cleaning after 
use. Prefilled ampules can help meet these criteria, but it is not 
practical to maintain a large inventory of ampules prefilled with various 
different amounts of different types of medicine. Physicians commonly 
prescribe different dosages of medicine for different medical conditions 
including the type and severity of an illness as well as the age and 
weight of an individual patient. In such situations it is highly desirable 
to have a single type of ampule that can accommodate different dosages. It 
would be most advantageous for patients in home care settings to be able 
to quickly and confidently fill such an ampule with a prescribed dosage 
from a conventional medicine vial, without help from medically trained 
personnel. However, this would require a filling mechanism that is fast 
and simple to use and still capable of precise measurement by untrained 
individuals. 
Casey et al. discloses a patient-fillable ampule for a hypodermic injection 
device which can accommodate different dosages and which is filled via an 
adapter from a separate medicine bottle. The injection device assembly 
comprises a sleeve attached to a housing containing a gas cartridge and 
trigger mechanism, with the ampule contained within the sleeve during use. 
The sleeve must be separated from the housing to provide access to the 
ampule for replacement and/or filling. U.S. Pat. No. 4,338,980 to Schwebel 
et al. discloses a filling device for disposable ampules for use in jet 
injectors, but that device requires a special medicine vial as well as an 
ampule holder, a housing and a dispensing handle which a user must 
assemble in order to fill the ampule. Moreover, the device with its 
multiple parts is separate from the jet injector, and, thus, various parts 
of the device or the entire device may be misplaced between uses of the 
injector, particularly by those who are afflicted with poor vision or poor 
memory, such as elderly diabetics. There is thus a continuing need for a 
hypodermic injector combined with a precise, easily used ampule filling 
device in a single unit. 
Ease of use for any patient-fillable ampule or jet injector is affected by 
the ease with which the user can read dosage indications during the 
filling process. Vernier scales, for example, are difficult for many 
people to read and understand, and other types of dosage indicators are 
hard to read for any patient with impaired vision. Such factors can reduce 
patient confidence in self-administration and, worse, can cause dosage 
errors. 
SUMMARY OF THE INVENTION 
The present invention overcomes these and other disadvantages of the prior 
art with an improved disposable ampule and a hypodermic jet injector with 
an internal filling mechanism. 
According to a first aspect of the invention, a self-contained, 
patient-fillable ampule for a jet injector includes an elongate ampule 
body having an injection orifice at a first end, a propellant at a second 
end, and a hollow portion therebetween, along with a piston slidably and 
sealingly mounted in the hollow portion of the ampule body, wherein the 
ampule also includes an auxiliary access opening in the body in proximity 
to the piston. The term "self-contained ampule" is used herein to mean an 
ampule containing a propellant, a piston or plunger, a hollow portion or 
chamber for fluid medicine, and an injection orifice in an ampule body. 
According to another aspect of the invention, a self-contained disposable 
ampule for a jet injector includes an elongate ampule body having an 
injection orifice at a first end, a propellant at a second end, and a 
hollow portion therebetween which is internally tapered along its 
longitudinal axis. The hollow portion has an expandable wall structure. 
The ampule also includes a plunger slidably and sealingly mounted in the 
hollow portion of the ampule body. 
According to a further aspect of the present invention, a self-contained 
disposable ampule includes an elongate plastic body with an injection 
orifice at a first end, an internal propellant at a closed second end, and 
a piston slidably and sealingly mounted within the body entirely between 
the orifice and the internal propellant. The ampule side wall structure is 
such that it requires external support to withstand normal peak operating 
pressures developed during an injection. 
A high-resolution metered filling device constitutes another aspect of the 
present invention. The filling device comprises a rotary-to-linear filling 
actuator including a linear drive member threaded to a rotary drive 
member, and a digital dosage display connected to said actuator and 
synchronously responsive to the rotary drive member. A drive block and 
drive screw as disclosed herein constitute one form of linear and rotary 
drive members, respectively, although other forms are contemplated. The 
digital dosage display includes a drum bearing a plurality of dosage 
values in integer form arranged in a spiral pattern on its surface, and a 
drum cover threadedly connected to the drum with a thread pitch matching 
the pitch of the spiral pattern. The drum cover extends over the drum and 
has a dosage selection window therein slightly greater in size than a 
single integer value and in registry with the spiral pattern, whereby a 
single dosage value is visible at a time through the window during 
rotation of the drum relative to the window. 
It is a general object of the present invention to provide an improved 
hypodermic jet injector. 
Another object of the invention is to provide a hypodermic jet injector 
with an improved type of disposable ampule. 
Another object of the invention is to provide a hypodermic jet injector 
which includes a filling mechanism in a single unit. 
A further object is to provide a filling mechanism that is fast and simple 
for untrained or vision-impaired individuals to use without sacrificing 
measurement precision. 
These and other objects and advantages of the present invention will become 
more apparent upon reading the following detailed description of the 
preferred embodiment in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purposes of promoting an understanding of the principles of the 
invention, reference will now be made to the embodiment illustrated in the 
drawings and specific language will be used to describe the same. It will 
nevertheless be understood that no limitation of the scope of the 
invention is thereby intended, such alterations and further modifications 
in the illustrated device, and such further applications of the principles 
of the invention as illustrated therein being contemplated as would 
normally occur to one skilled in the art to which the invention relates. 
With reference to FIGS. 1 and 2, the preferred embodiment of a jet injector 
according to the present invention includes a housing having a top case 1 
and bottom case 2 which together enclose an ampule chamber 3 and 
associated multifunction assembly 4, a trigger assembly 5, an extendable 
cocking lever 6, and a metered filling mechanism 7. Briefly described, the 
injector is designed to receive and fill a self-contained, disposable 
ampule having a piston which is externally accessible, preferably through 
the ampule side wall. The trigger assembly is cocked by extending and 
rotating the cocking lever 6 and then lifting the handle 36 on assembly 4. 
The latter action also raises the ampule chamber for loading and resets 
the trigger to the firing position for the next injection. An empty ampule 
is loaded into the ampule chamber and then the handle is lowered to return 
the ampule chamber to its original position in order to fill the ampule. 
The cocking lever is rotated back to its forward position and its 
extension is used as a platform for securely attaching a medicine vial and 
adapter to the front end of the ampule. The filling mechanism is then 
operated to engage and move the ampule piston rearwardly to draw fluid 
medicine into the ampule through its injection orifice, after which the 
vial and adapter are removed. The filling mechanism is automatically 
disengaged from the ampule and an injection is given, in sequence, by 
actuating the trigger assembly with the injector in contact with a 
patient's skin. 
More specifically, the ampule chamber is designed to receive and support a 
self-contained, disposable, thin-walled ampule 10 having, as shown in 
FIGS. 3 and 4, an explosive charge 12 at the rear end 14 thereof, an 
injection orifice 16 at its front end 18, a double piston 20 and a fluid 
medicine chamber 22, and further having an access opening 24 for access to 
the piston for the purpose of filling the ampule after it is loaded into 
the ampule chamber, as will be described. The ampule chamber is provided 
with a corresponding access opening 26 in its side and bottom walls. 
Loading of an ampule into the ampule chamber is facilitated by a guide 
channel 27 located on the top case to the rear of the ampule chamber and 
aligned with the inside surface of the ampule chamber in its raised 
(loading) position. The ampule chamber has an opening 28 approximately 
0.25" in diameter in the center of its front end 30 which mates with the 
tip 17 of the ampule such that the front surface of the ampule tip is 
flush with the front surface of the ampule chamber. Thus, medicine may be 
discharged through the ampule orifice and directly into the skin of a 
patient against which the jet injector is held for an injection. 
The ampule chamber is attached to the top case by a pair of integral guide 
tabs or keys 32 formed to fit into slots 34 in the top case, whereby the 
ampule chamber is constrained to vertical motion. The ampule chamber is 
raised for loading and lowered for filling and for injection, as alluded 
to above, by means of handle 36, which fits through an opening 38 in the 
top case. The handle has a hollow underside permitting parallel contact 
with the top of the ampule chamber when in the lowered position, as shown 
in FIG. 1. A recess is provided on either side of guide channel 27 to 
receive the sides of the end of the handle for this purpose. 
Handle 36 forms part of multifunction parallelogram assembly 4, shown in 
further detail in FIG. 8. The ampule chamber and a horizontal slider 39 
constitute the top and bottom segments of the parallelogram, respectively, 
and they are interconnected by the loading handle and by a pair of rear 
links 40. The horizontal slider is limited to horizontal motion by 
constraints in the case, i.e., by a pair of horizontal surfaces 41 and a 
pair of horizontal surfaces 43 (FIG. 9) in sliding contact with the top 
and bottom surfaces, respectively, of a pair of legs 44 on slider 39. 
Surfaces 41 are formed on a base 42 which is fastened to the bottom case; 
surfaces 43 are the bottom surfaces of the sidewalls defining the opening 
38 in the top case. The horizontal and vertical constraints and the 
corresponding action of the parallelogram assembly can perhaps be better 
appreciated from FIGS. 9A and 9B, which schematically illustrate the 
parallelogram assembly in its two operating positions. FIG. 9A illustrates 
the position of the assembly with loading handle 36 down, which is the 
proper position for filling and firing as well as when the injector is not 
in use. FIG. 9B illustrates the assembly in its position with the loading 
handle up, which is the proper position for loading an ampule into the 
ampule chamber and for completion of the cocking sequence. 
The trigger assembly is mounted on base 42 in the bottom case, and it 
includes a firing pin 45 affixed by a conical rear portion thereof to a 
mounting block 46 connected to a horizontally movable spring linkage 48 
which is biased forward by means of a compression spring 50 so as to cause 
the firing pin to move rapidly toward the charge at the rear end of the 
ampule when the injector is triggered. A space is provided in the top case 
under guide channel 27 for mounting block 46, and a wall 49 is provided 
under the forward end of the guide channel as a rear support for the 
ampule chamber when the injector is triggered. The wall is provided with a 
hole to allow passage of the firing pin. 
With combined reference to FIGS. 2 and 6, the spring linkage consists of 
two pivot links 52 and 54 and a spring support link 56 affixed to firing 
pin mounting block 46. Compression spring 50 is mounted on support link 56 
and extends between a pivot block 58 on the front end of the support link 
and a stop 60 on a plate 62 which holds the linkage in place on the base 
in the bottom case. The forward pivot point 64 of forward link 52 is fixed 
to the base by a pivot pin and associated hole in the base. A trigger 
button 66 is slidably mounted by means of a tongue 67 between the bottom 
case and base 42 in a guideway formed in the bottom case for this purpose. 
The trigger button is connected to a button slider 68 which is slidably 
mounted on base 42 by means of a set of guide rails 69 and mating guide 
channels 71. One of the guide rails on the button slider comes into 
contact with and moves forward link 52 when the trigger is pressed, and 
thereby releases the compression spring which then drives the firing pin 
forward, as will be explained. 
The jet injector employs a two-stage cocking mechanism which includes the 
cocking lever and an associated cam 70, as well as a vertical pin 72 
descending from horizontal slider 39 through a hole 73 in the button 
slider to a position in front of the spring linkage. Cam 70 is integrally 
formed within the main portion 80 of the cocking lever, which is 
horizontally rotatably mounted in the bottom case. A cam follower 74 is 
mounted on the bottom of the firing pin mounting block 46 at the level of 
the cam and is held in contact with the cam by spring 50. A longitudinal 
slot 76 (FIG. 6A), corresponding in length to the stroke length of the 
firing pin, is provided in base 42 for connection of the firing pin 
mounting block to cam follower 74, which preferably includes a roller 78 
for low-friction contact with the cam surface. A telescopic extension 81, 
which may be spring-biased toward its retracted position, is provided on 
the cocking lever for increased leverage during cocking and also as a 
platform for a vial and filling adapter, as will be described in 
connection with the filling mechanism. 
FIGS. 6A, B and C illustrate the trigger mechanism in its released, 
semi-cocked and fully cocked positions, respectively, along with pertinent 
portions of the cocking mechanism including the vertical pin on the bottom 
of the horizontal slider. The trigger button and other parts of the 
injector are removed for ease of illustration. With the cocking lever in 
its resting position, shown in FIG. 2, the cam follower 74 is at its 
forwardmost position, as determined by the shape of cam 70, and the spring 
linkage and firing pin are correspondingly in their forwardmost position 
as illustrated in FIG. 6A. 
FIG. 6B illustrates the trigger mechanism with the cocking lever rotated 
180.degree. clockwise, as viewed from above. By rotation of the cocking 
lever, and correspondingly the cam, to this position, the firing pin and 
linkage are pulled back against the force of the spring to the position 
shown. It will be appreciated by those skilled in the art that this 
semi-cocked position of the spring linkage is unstable in that the spring 
force will be immediately released upon return of the cocking lever to its 
original position. 
However, as shown in FIG. 6C, the trigger mechanism is placed in a stable, 
fully cocked position by rearward motion of pin 72 into contact with link 
52 while the cocking lever is still in its outer position. The pin is 
moved by lifting handle 36 on the parallelogram assembly, which causes 
slider 39 to slide back in the housing. Pin 72 thereby forces link 52 to 
pivot counterclockwise until the pivot pin 53 interconnecting links 52 and 
54 crosses the center line of the spring linkage, at which point the 
spring causes the linkage to snap into the position shown in FIG. 6C. The 
linkage is restrained by the adjacent wall of base 42, as illustrated, and 
remains stationary in that position after the cocking lever is returned to 
its original position and until the trigger is pressed to fire the device. 
The cam shape illustrated in FIGS. 2 and 6 and shown particularly clearly 
in FIG. 7 has been determined to provide an increasing mechanical 
advantage during rotation of the cocking lever, thereby compensating for 
increasing spring resistance during spring compression and also for 
angle-dependent changes in components of spring force and friction during 
rotation of the lever. As a result, the force required to rotate the lever 
rises initially with displacement but substantially levels off and thereby 
provides a more even feel for a user cocking the trigger mechanism. 
The preferred embodiment of a disposable ampule according to the present 
invention includes a double piston, as mentioned above. The ampule piston 
is referred to as a double piston because it includes two plungers or 
seals interconnected by a connecting rod. The connecting rod is sized and 
shaped to provide an air space extending between the two seals. This 
double piston construction, in conjunction with the access openings in the 
walls of the ampule and ampule chamber, serves two purposes: 1) it enables 
a mechanical arm or other engagement member to access, engage and move the 
piston and thereby draw fluid medicine into the ampule; and 2) it prevents 
contamination of the medicine during the firing process by means of a vent 
to the outside atmosphere from a space between the medicine chamber and 
the combustion chamber within the ampule. The medicine chamber and 
combustion chamber both experience high pressures during an injection, 
whereas the space around the connecting rod between the front and rear 
seals is at atmospheric pressure. Should any combustion gases leak past 
the rear seal, they would be vented to the atmosphere through access 
opening 24 in the ampule and access opening 26 in the ampule chamber and 
would not be able to mix with any medicine in the medicine chamber. This 
is because it is impossible for gases to travel against a pressure 
gradient into the medicine chamber. 
Disposable ampule 10 is disclosed in further detail in FIGS. 3-5, from 
which it can be seen that the ampule has a main body 90 in which the 
double piston 20 is slidably and sealingly mounted, with the double piston 
having a plunger 92 snapped on the front end 94 of an integrally molded 
combination of a connecting rod 96 and rear seal 98. Preferably, the 
plunger is soft rubber and the connecting rod and rear seal are relatively 
hard and non-compressible. The connecting rod is preferably formed with 
two spaced sets of four elongated ribs as shown in FIG. 5, for purposes of 
a low-cost substantially rigid construction and large vent passageways. 
The rear end 14 of the ampule is closed by a piston stop and primer 
support 100 which is press fitted into the rear end of main body 90, as 
shown in FIG. 4, by primer 12 and by a primer holder 102 press fitted over 
the rear of piston stop 100. Piston stop 100 is hollow and includes a seat 
104 in its rear end which cooperates with a cup 106 in the rear of primer 
holder 102 to hold primer 12 which is preferably a Winchester large rifle 
primer, which contains approximately 350 mg of azide. The primer cap is 
exposed to the rear by an access hole 107, which the firing pin enters to 
engage and mechanically actuate the primer cap. The conical rear portion 
of the firing pin and the access hole cooperate to ensure that the firing 
pin is centered when it engages the primer cap, and also to maintain a 
seal at the rear end of the ampule during detonation of the charge. 
An opaque sleeve 108 is provided to cover the portion of the main ampule 
body 90 to the rear of access opening 24 as well as the piston stop and 
primer holder as shown in FIG. 4. A thin gap 109 approximately 0.010" is 
provided between the sleeve and the central portion of the ampule body to 
allow for expansion of the ampule body to facilitate forward motion of the 
piston during an injection. The main ampule body, the sleeve, the 
connecting rod and rear seal, the piston stop and primer holder are all 
preferably formed of polypropylene or other inexpensive plastic material. 
The main ampule body is preferably formed of a transparent polypropylene, 
with sidewalls preferably in the range of 0.025-0.040" for medicine 
chamber 22 and combustion chamber 110, with an average wall thickness of 
0.030". Alternatively, the ampule may be constructed of high density 
polyethylene. Front end 18 is tapered and sized so as to fit in the 
approximately 0.25" diameter opening in the front end of the ampule 
chamber. The ampule body defines tapered surfaces 112 and 114 which lead 
from the injection orifice 16, which preferably has a diameter of 0.005", 
to medicine chamber 22. The ampule sleeve is preferably opaque so as to 
obscure the view of the combustion chamber in the ampule which may become 
unsightly after discharge due to soot or other residue from the primer 
discharge. Rear seal 98 may be a polypropylene disk of sufficient hardness 
and axial thickness, preferably approximately 0.030" or more, to be 
substantially non-compressible, whereas the main body of the ampule is 
readily expandable and requires external support to withstand the normal 
operating pressures developed within it during an injection. 
Alternatively, a hard Velbron or butadiene rubber may be employed for the 
rear seal. The ampule main body is preferably molded with draft angles on 
the interior and exterior surfaces of its front and rear chambers as well 
as its central section, for more efficient injection molding. The interior 
surfaces preferably have a draft angle of approximately 0.25.degree., and 
the exterior surfaces preferably have a draft angle of approximately 
0.5.degree.-1.0.degree.. The ampule construction as described above offers 
significant advantages including lower cost due to less material and 
shorter molding cycle times, as well as greater ease of manufacturing due 
to the use of draft angles. 
The ampule chamber is molded from a strong, high-grade, transparent plastic 
such as polycarbonate, and has a draft angle on the front chamber section 
to match the draft angle on the front section of the ampule. A draft angle 
is suitable in this section of the ampule chamber because the soft rubber 
plunger inside the ampule will compress as it moves forward during an 
injection. The rear section of the ampule chamber is provided with a 
straight bore to provide expansion space for the ampule to "balloon out" 
as the harder, non-compressible rear seal is forced forward through the 
decreasing diameter of the thin-walled ampule. The central section of the 
ampule chamber may also have a straight bore, although a draft angle on 
that section may be suitable in some applications. With straight bores in 
the central and rear sections of the ampule chamber, and with draft angles 
on the ampule as indicated above, gaps of approximately 0.010" are 
obtained at points A and B, respectively, in FIG. 4 (draft angles slightly 
exaggerated for illustration of the gaps). 
Access opening 24 in the ampule preferably extends approximately 90.degree. 
circumferentially around main body 90, and is designed to be oriented as 
shown in FIG. 3 when loaded into the ampule chamber, whereby the access 
openings in the ampule and ampule chamber are aligned for filling 
purposes. For this purpose, sleeve 108 is provided with a key 116 
approximately 0.200-0.250" in length and of suitable width and is 
precisely attached to the main body of the ampule such that key 116 is in 
line with the bottom edge of opening 24. A mating slot 118 is provided in 
the ampule chamber at the bottom rear end of the bore therein. Thus, an 
empty ampule can be readily loaded into the ampule chamber with the proper 
orientation. The double piston is preferably installed in its forwardmost 
position in the ampule, corresponding to a zero dosage, and oriented with 
the ribs on the connecting rod in horizontal and vertical planes as shown 
in FIG. 4. 
An annular groove 19 with square edges as shown in FIG. 4 is formed in the 
tip of the ampule for filling purposes, and, more specifically, to 
facilitate a sealed connection to a filling adapter having a mating 
annular protrusion with a slightly oversize curved surface designed for 
primary contact with the outer corners of the groove. An outlet orifice is 
provided in the center of the annular protrusion in communication with a 
needle adapted to penetrate the septum of a medicine vial pressed against 
the other end of the adapter. A second needle, different in length from 
the first, may be included in the adapter to provide a vent for the 
medicine vial to reduce the pressure required for medicine withdrawal. The 
needle lengths should be sufficiently different that one needle tip can be 
positioned near the top of the medicine vial with the other tip near the 
bottom of the vial. A support adapted for mounting on extension 81 of the 
cocking lever is provided to firmly hold the medicine vial and adapter 
together and maintain a seal between the adapter and ampule. Preferably, 
spring loading is provided for these purposes, by means of a spring-loaded 
extension on the cocking lever and/or spring loading in the support for 
the vial and adapter. 
As shown in detail in FIG. 12, the metered filling mechanism 7 includes a 
rotatably mounted drive screw 120 the front end 121 of which is threadedly 
attached to a drive block 122 which is in turn slidably connected to a 
guide rod 123 and to a piston connecting pin 124, which is the preferred 
form of piston engagement member. Pin 124 is in turn slidably connected to 
button slider 68, which is connected to the trigger button and slidably 
mounted on base 42 by mating guide rails and channels, as described 
earlier. The drive block, piston connecting pin and button slider are 
interconnected by dovetail slots and rails as shown in FIG. 12, whereby 
the connecting pin moves axially with the drive block when the drive screw 
is turned, sliding upon the button slider at this time, and is also free 
to move laterally with the button slider, sliding under the drive block at 
this time. The button slider moves and carries the connecting pin toward 
the ampule during the cocking process, primarily in response to the motion 
of pivot link 52 and, if desired, also in response to vertical pin 72 
contacting an optional angled surface 75 of hole 73. The button slider 
carries the connecting pin away from the ampule when the injector is 
triggered. Guide rod 123 is provided to reduce play due to tolerancing. It 
is slidably mounted in an unthreaded hole 129 in the drive block and 
supported on each end by the top case, with the rear end of the rod 
mounted in a vertical wall or bracket formed in the top case and the front 
end mounted in the front wall of the top case. A through-hole may be 
provided in the front hole of the top case for insertion of the guide rod 
to facilitate assembly of the injector. 
Referring to FIGS. 10 and 13 in addition to FIG. 2, a button lock 130 is 
provided as a safety lock for the trigger, and also for the purpose of 
moving the piston connecting pin into position for engagement with the 
double piston in an ampule lowered into position for filling. The button 
lock slides axially in a guide channel 131 provided in base 42 for this 
purpose, and its axial position is controlled from underneath the housing 
by a thumb tab 133 extending down from the button lock through a slot 135 
(FIG. 7) in the bottom case. 
Piston connecting pin 124 is sized and shaped to snugly fit within a slot 
132 (FIGS. 4 and 5) formed within the connecting rod of the piston for 
this purpose, and desirably includes a tapered upper surface to compensate 
for potential misalignments with respect to the slot in the connecting 
rod. It is preferably set at the zero position (zero dosage) before an 
ampule is lowered onto it, and, as mentioned above, the ampule piston is 
correspondingly set at the zero position. With the connecting pin in its 
extended position, shown in FIG. 10, and with the pin in engagement with 
the connecting rod of an ampule loaded in the ampule chamber, the ampule 
can be filled by turning the drive screw to move the drive block 
rearwardly and thereby move the ampule piston back the same distance. The 
motion of the piston within the ampule causes medicine to be drawn through 
the ampule orifice from a medicine vial to which the jet injector is 
attached for this purpose via a suitable adapter such as described above. 
The drive screw has relatively fine threads on its front end for engagement 
with the drive block, which is provided with matching threads, and also 
includes a number drum 134 and a section 136 of coarse threads to the rear 
thereof, as shown in detail in FIG. 11. The number drum bears numerical 
dosage values in a spiral arrangement conforming to the spiral shape of 
the coarse threads on the rear end of the drive screw. A dosage selection 
window 138 is provided in a drum cover 140 which is mounted over the 
number drum and moved axially with respect thereto by an internally 
threaded ring 142 which engages the coarse threads 136 on the drive screw. 
The rear end of the drive screw is rotatably fixed with respect to a 
rotatable metering knob 144 such that it rotates with the knob. The 
forward end 146 of the metering knob is rotatably mounted within a support 
block 148 which is retained in base 42 in a recess 150 adapted to mate 
with the bottom of the support block so as to prevent any horizontal 
motion thereof. As shown in more detail in FIG. 10, a shoulder 152 on the 
metering knob is positioned between the upper rear surface 153 of support 
block 148 and the rear end wall 154 of recess 150, thereby fixing the 
metering knob axially with respect to the case. Drum cover 140 is keyed to 
support block 148 so as to limit the drum cover to axial motion with 
respect to the case. A calibration screw 156 is rotatably mounted on the 
rear of and axially fixed with respect to the metering knob and threadedly 
engages the interior of the rear end of the drive screw, whereby rotation 
of the calibration screw causes axial motion of the drive screw for 
purposes of minor calibration adjustments. 
Window 138 is covered by a shade 158 when button lock 130 is in its 
unlocked position, which is illustrated in FIG. 13, such that the dosage 
value is not visible to a user at such times. Window shade 158 is axially 
fixed with respect to the case by a flange 160 and by a corresponding 
surface formed in the upper case for this purpose. A helical rib 162 on 
the shade and a mating slot on the inside surface of upper portion 164 of 
the button lock cooperate to rotate the shade when the button lock is 
moved axially. As shown in FIG. 10, when the button lock is moved 
forwardly to its locked position, the proper position for filling the 
ampule, the shade is rotated away from the window and the dosage value is 
visible to the user. The user can also see, through window 37 in the top 
case, the forward surface 166 of drum cover 140, and forward surface 166 
is preferably colored blue or another appropriate color to present the 
appearance of fluid medicine in a syringe and thereby provide a user with 
additional visual feedback on a filling operation in process. Of course, 
with a transparent ampule chamber and ampule as described above, the 
actual medicine content of an ampule is visible, along with any air 
bubbles that may be present, through the front section of the ampule 
chamber as can readily be appreciated from FIG. 1. 
However, the primary display is by means of the dosage selection window, 
which presents the user with the precise dosage value, preferably within a 
range of 0 to 100 units of medicine, and with one number visible at a time 
to eliminate confusion. Smaller and larger ranges are also contemplated 
for particular applications, as are different units of measure. 
The number drum as described above provides a high resolution digital 
display, by which is meant a display of values in integer form, in a 
limited space. The numbers are placed along a spiral path on the number 
drum that matches the pitch of the coarse threads on the drive screw. The 
difference in pitch between the fine and coarse threads on the drive screw 
provides a mechanical scale factor which results in a high resolution 
digital readout of up to 100 units of insulin, for example, with less than 
10 turns of the metering knob. Another advantage of the metering device 
according to the present invention is that it makes possible a nonlinear 
display, which is particularly desirable where, as here, the inside 
diameter of the ampule varies along its length. The distance between 
consecutive numbers on number drum 134 is mathematically calculated 
according to the interior ampule geometry. More specifically, the spacing 
between high dosage values is less than that for low dosage values because 
the ampule diameter increases with distance from the tip in the preferred 
embodiment. 
The button lock is moved to its unlocked position (FIG. 13) after filling, 
when the user desires to give an injection. The injector is then ready for 
firing. When the trigger button is pressed, it moves the button slider and 
thereby moves the piston connecting pin out of engagement with the piston, 
and then, as part of the same continuous motion, forces pivot pin 53 
across the center line of the spring linkage and thereby releases the 
compression spring, which then drives the firing pin into contact with the 
charge in the ampule, causing detonation which drives the piston forward 
to force the medicine out of the injector. The above sequential motion is 
important in order to ensure that the filling mechanism does not inhibit 
piston motion within an ampule during an injection. For this purpose, the 
button slider guide rail which contacts the pivot link 52 in the trigger 
assembly is preferably dimensioned such that there is a gap of 
approximately 0.100-0.125" between it and pivot link 52 when it is in the 
filling position. 
While the invention has been illustrated and described in detail in the 
drawings and foregoing description, the same is to be considered as 
illustrative and not restrictive in character, it being understood that 
only the preferred embodiment has been shown and described and that all 
changes and modifications that come within the spirit of the invention are 
desired to be protected. For example, although the disclosed ampule 
chamber is especially suited for use with patient-fillable ampules, it is 
also capable of accommodating prefilled ampules. Also, the principles of 
the high-resolution metered filling device disclosed herein are applicable 
to independent or integral filling devices designed for connection to the 
orifice end or opposite end of a jet injector, a hypodermic syringe, a 
self-contained ampule with or without an auxiliary opening, or other 
injection devices.