JPS649868B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a syringe, such as a hypodermic syringe, used in the pharmaceutical field, and in particular to a locking device for such a syringe.

BACKGROUND OF THE INVENTION Syringes have a variety of medical and non-medical applications. In the field of medicine, syringes can be used to draw blood, inject drugs, and, in conjunction with other devices, to assist in biopsies and bone grafts. In the field of engineering, syringes (generally modified or used as medical syringes) are used, for example, to withdraw samples of liquids or gases from reactors.
It can be used to dispense adhesives and other liquid compounds. Generally, a medical syringe includes a body - usually made of plastic - and a plunger that is slidable within the body and includes a piston that fits and seals the body. I'm here. The plunger generally has a single finger grip at its proximal end for pushing or pulling the plunger into and out of the body, and the body itself also has an opposing finger grip at its proximal end. A lip can be provided. Medical syringes come in a variety of sizes and shapes and are well known in the medical and industrial communities.

Syringe barrels often include volume markings, and in widely used commercial syringes, the barrel is made of translucent plastic material such that the location of the piston at the end of the plunger is visible through the barrel wall. There is. Therefore, you can read the capacity by aligning the capacity mark on the body with the end of the piston.

It is often desirable to lock the plunger of a syringe in a fixed position within the barrel. for example,
The soft tissue biopsy method outlined in U.S. Pat. Therefore, it is absolutely necessary to prevent it from moving backwards toward its initial position. In another example, it may be desirable to withdraw a specific amount of fluid from one internal organ, as is commonly done with amniocentesis;
In this case, the liquid is retained within the syringe until it is discharged into a suitable container. Care must be taken to prevent accidental movement of the plunger while liquid is in the syringe. It may be desirable to draw a specific amount of a reactive chemical into each of a pair of syringes. For example, one syringe contains an epoxide resin to react with, and the other contains a specified amount of an amine "hardener" to react with the resin. Because the relative amounts of resin and curing agent dispensed determine the properties of the resin being synthesized, the plunger must be placed within the syringe barrel until the resin and curing agent are dispensed from the syringe. It is preferable not to move.

U.S. Pat. No. 3,882,849 discloses a biopsy needle having a toothed plunger, the teeth of the plunger engaging a plate at the proximal end of the barrel at a given location of the plunger within the barrel. .

Yay, a syringe similar to this has a US patent number 3938505.
has been disclosed. This type of syringe requires additional manufacturing steps and high costs, and the US patent
The sharp edges of the teeth as disclosed in 3882849,
For example, there is a risk of getting caught in surgical gloves worn by doctors and nurses.

The present invention provides a locking device for a syringe having a body and a plunger pivotable within the body.

Means for Solving the Problems The syringe locking device of the present invention includes a cam means located within the body between the body and the plunger, and carried by the body, and a cam means for restraining the plunger in contact with the body. and means for moving the cam means for the purpose of moving the cam means.

Preferably, the means for moving the cam means includes a handle fixed to the cam means and an arm extending outside the body.

Further, it is preferable that the syringe locking device configured as described above is provided with a holding means for restraining the movement of the cam means in the axial direction of the body. Preferably, the retaining means is a groove that receives an annular lip formed in the body.

Further, the cam means has a cam surface that slides against the web of the plunger and the interior surface of the body;
The cam surface has a first sector that is generally circular and has a substantially constant radius, a second sector that has a larger radius that approximates the radius of the interior surface of the fuselage, and first and second sectors. It is preferable to form a closed curve with a third fan-shaped portion that extends between the first and second fan-shaped portions and extends at least in part considerably beyond the locus of points created by the radius of the first fan-shaped portion.

(Function) According to the above configuration, the cam means is moved by means such as the handle and the arm to bring the plunger into contact with the body, thereby restricting movement of the plunger in the axial direction and locking the plunger.

Further, since the holding means prevents the cam means from moving in the axial direction, the plunger is more reliably locked.

Furthermore, if the cam surface is formed by three sectors, the first, second, and third, when the cam means rotates from the unlocked position to the locked position, the longest chord of the third sector (the cam A force is applied from the web to return the cam means to the unlocked position until the angle between the web and the line connecting the center of rotation of the means and the tip of the third fan-shaped portion becomes a right angle.
When the angle between the string and the web exceeds a right angle, a force is applied to the cam means such that it is rotated into a locked position. Therefore, the cam means is reliably held in position at both the locked and unlocked positions.

(Example) A typical standard medical syringe is shown in FIG.
Set it to 2. This syringe has an open proximal end 12.2.
and a constricted end 12.3.
Contains 2.1. For illustrative purposes, a hypodermic needle 12.4 is shown connected to the distal end of a syringe by conventional attachment means such as a Luey locking device 12.5. At its proximal end 12.2, the body 12.1 is provided with an inwardly directed annular lip 12.6 which is connected to one distally directed annular shoulder 1.
2.7 is formed. The smooth internal surface 12.8 of the fuselage 12.1 spans substantially the entire length of the fuselage, and the fuselage 12.1 is preferably of uniform diameter. Finger grips 12.9 (FIG. 1) extend outwardly from the open proximal end 12.2 of the body 12.1. A commercially designed plunger 14
It is housed within the fuselage 12.1. Plunger 14
comprises one shank 14.1, one piston 14.2 attached to the distal end of the shank 14.1, and one handle or finger grip 14 attached to the proximal end of the shank 14.1. .3. The piston 14.2 is typically made of rubber or other resilient material and engages and seals against the smooth internal surface 12.8 of the body 12.1. This sealing can also be achieved by providing a slidable outer ring on the piston 14.2, but this engagement and sealing can be done in any known manner. The shank 14.1 typically has a cross section (sixth
) is generally "X" shaped and defines radially extending webs 145, 14.6, 14.7 and 14.8. The outer edge of the web is usually square and forms a fairly sharp, right angle. The web 14.6 in FIG. 6 has a typical angular outer edge 14.9 forming a right angle with the walls of the web (15 and 15.1). In FIG. 6, the shaft 14.1 loosely penetrates the interior of the body 12.1;
The slightly constricted open proximal end 1 of the body 12.1 is also formed by an annular lip 12.6.
2.2 also penetrates loosely, and the proximal end 12.2
has a diameter slightly larger than the maximum diameter of the webbed shaft 14.1.

A typical example of the locking means of the present invention, indicated at 20, is shown in FIGS. 1-7 as cam means 22, handle 24, and cam means 22 and handle 24.
It is shown as including connector means 26 for connecting the two.

Cam means 22 illustrated in FIGS. 2, 3 and 7
includes a generally cylindrical cam 22.1, the outer surface 22.2 of which is generally cylindrical, but with a relatively flat surface on one side, as best seen in FIG. has a surface portion 22.3 which is
This cam 22.1 therefore has a large diameter "x" and a small diameter "y". This relatively flat surface portion 22.3 is preferably generally cylindrical and has a radius approximately equal to half the diameter of the interior of the fuselage 12.1 defined by the smooth interior surface 12.8. The large diameter "x" means that the flat surface portion 22.3 of the cam 22.1 is connected to the smooth inner surface 2 of the hole in the fuselage.
2.3 so that it is supported by the facing walls 15.2 and 15.3 of the webs 14.5 and 14.8 of the shaft 14.1 located approximately in the center of this hole, Set. All of these conditions are shown in FIG.

Axially outwardly of the cam 22.1, extending as far as the proximal end 12.2 of the body 12.1, there is a generally cylindrical connector means 26 whose cross-section, outer circumference, The outer circumference of cam 22.1 is similar to that of cam 22.1, but smaller.
It forms one annular shoulder 22.4 facing approximately proximally (FIGS. 2 and 3). A handle 2 is attached to the proximal end of this connector means 26.
4, the handle 24 extending approximately radially outwardly of the proximal end 12.2 of the barrel 12.1 and thus accessible to the syringe user.
It has one arm 24.1. This handle 24 has a substantially circular boss 24.3 which is slightly larger than the connector means 26 and forms an annular shoulder 24.3 facing the annular shoulder 22.4 of the cam 22.1. 2 can be provided.
Therefore, these facing annular shoulders 22.4
and 24.3 form a groove 24.4, which is a typical retaining means for restricting the axial movement of the locking means 20 relative to the fuselage 12.1. The annular lip 12.6 at the open proximal end 12.2 of the body 12.1 fits into this groove 24.4.
Annular shoulder 22.4 and lip 1 of the fuselage 12.1
2.6 and the distal annular shoulder 12.7, the locking means 20 lock onto the plunger 1.
4 is retracted, the proximal end 12.1 of the body 12.1.
2. They are prevented from escaping to the outside. boss 2
The annular shoulder 24.3 of 4.2 (the shoulder of the handle 24 when the boss 24.2 is not present) is connected to the plunger 1.
4 is pushed into the body 12.1, the cam 2
2.1 prevents it from sliding in the distal direction of the fuselage 12.1.

Further, for the embodiment of FIGS. 1-7, the handle 24 of the locking means 20 was shown in FIG. 1 facing the smooth inner surface 12.8 of the plunger 14
allows easy movement in and out of the fuselage 12.1. The walls 15.2 and 15.3 of adjacent webs 14.5 and 14.8 slide smoothly along the cylindrical outer surface 22.2 of the cam 22.1 and
As shown, the cam 22.1 is attached to the inner wall of the body 12.1, and the lip 12.6 is attached to the groove 2 of the locking means 20.
4.4 to prevent the locking means 20 from moving axially relative to the fuselage 12.1. When the cam 22.1 is rotated into the locked position of FIG. 7 (for example, by moving the handle in the direction indicated by the arrow in FIG. 6), the cam 22.1 moves the shaft 14.1. ,
The cam 2 is pressed against the opposite side of the fuselage 12.1.
The outer circumference of the fuselage 12.1 is the inner surface 12.2 of the fuselage 12.1.
8, and the adjacent webs 14.5 and 1
There is also a sliding movement against walls 15.2 and 15.3 of 4.8. In this position, the outer ends 14. of the webs 14.6 and 14.7 of the plunger 14.
9 is strongly pressed against the inner circumferential surface 13 of the lip 12.6, as a result of which the plunger 14
further axial movement relative to the fuselage 12.1 is restricted. Movement of handle 24 from the position of FIG. 6 to the position of FIG. 7 causes cam 22.
The large diameter "x" of 1 rotates in the axial direction of the body 12.1, so that the shank 14.1 of the plunger 14
and the inner surface 12.8 of the body 12.1 adjacent to the cam 22.1, the distance between
is inserted or restrained between the body 12.1 and the cam 22.1, and the plunger 14 is locked.

When the locking means 20 is in the position shown in FIGS. 1 and 6, the end 24.5 of the handle 24 is attached to the web 1.
4.5 along and in contact with the wall 15.2; likewise, when the handle 24 is moved to the position shown in FIG.
It is further noted that along and in contact with the wall 15.3 of the
4.5 and 14.8 in this way, cam 22.1
The lock and unlock positions of the lock are defined and defined.

The shank 14.1 of the medical syringe outlined above is at least slightly flexible, so that the locking means 20 of the invention has a cam 22.1 thereof.
by pushing radially inwardly and distally to release lip 12.6 and walls 1 of webs 14.5 and 14.8.
It is possible to insert such a syringe simply and easily by inserting it into the approximately sector-shaped gap defined by 5.2 and 15.3. In the embodiment shown in Figures 1-7, this operation takes only a second or two and the locking means 20 is set into position with an audible click.

As illustrated in FIG. 7, when the locking means 20 is in the locked position, the plunger 14
2.1 and is sandwiched or restrained between the body 12.1 and the cam 22.1.
The plunger 14 is thus locked against axial movement relative to the body 12.1. The plunger 14, the cam 22.1 or the body 12.1, or a combination thereof, may be provided with slots or sharp or serrated edges, if desired, to further stabilize the plunger 14 in its position. can be retained.

3, 6 and 7 that the restraining force exerted by the plunger 14 on the body 12.1 and on the cam 22.1 is determined primarily by the shape and dimensions of the cam means 22. will be understood by. For example, the force acting in this manner to lock plunger 14 in position can be reduced in the embodiment of FIGS. 1-7 by reducing the cylindrical diameter of the "x" portion of the cam. However, this kind of decrease also
The manual force required to rotate the cam 22.1 to the position of FIG. 7 can also be reduced. Furthermore, the ease with which the plunger 14 can be moved axially within the body 12.1 when the locking means 20 is in the unlocked state as shown in FIG. This can be changed by reducing the proximity to the internal surface 12.8 of the fuselage 12.1.

It is ensured that the locking means 20 are held in position axially relative to the fuselage 12.1, i.e.
It is of course important that the lip 12.6 is securely retained within the groove 24.4 in the embodiment of FIGS. 1-7. Even more desirable is
It is possible to rotate the handle 24 from the position of FIG. 6 to the position of FIG. 12.1 and the cam 22.1.

It will be obvious that the shape and size of the cam 22.1 shown in Figures 3, 6 and 7 can be varied as desired to obtain the desired results.
In one satisfactory embodiment, a cam having the shape shown in FIG. When the locking means 20 used in a standard commercial syringe having an inner diameter of approximately 15.9 mm (approximately 5/8 inch) and as shown in the drawing is not locked as shown in FIG. 14
The force required to smoothly retract the lock was approximately 395 grams (0.87 pounds), but the locking means 20
Without it, it was about 340 grams (0.75 pounds). When the locking means 20 was rotated to the locked position of FIG. 7, approximately 5.5 pounds was required to move the plunger 14 axially against the locking force thus applied.
It should be noted that the arm 24.1, which has a length of about 5/8 of about 25.4 mm (1 inch) and extends laterally from the open end of the body 12.1, can be easily attached to the sixth arm by finger pressure.
I was able to move it from the position shown in the figure to the position shown in Figure 7.

Another embodiment of the locking means of the present invention is shown in the eighth embodiment.
Abbreviated in the figure. In this embodiment, which is identical to the embodiment of FIGS. 1-7 except for the shape of the cam, the cam 28
is a generally rectangular shape having dimensions such that the ends of the cam 28 are in light sliding contact with the facing walls 15.2 and 15.3 of the webs 14.5 and 14.8 when the locking means are not locked. It has a cross section of When the cam 28 has been rotated through approximately 90 DEG to the position shown in phantom, the cam 28 locks the plunger 14 against the opposite side of the body 12.1, also shown in phantom. Except for the shape of the cam 28, the
In FIG. 9, which is the same as the embodiment shown in FIGS. 7 to 7, the cam 29 has an oval cross section and can be rotated from the unlocked position shown by the solid line to the locked position shown by the broken line. If possible, the plunger 14 is similarly moved from the solid line position to the dashed line position.

A preferred embodiment of the invention is shown in Figures 10-14. This embodiment is similar to that shown in FIGS. 1-7, but the cam 30 is modified. The generally cylindrical cam 30 is connected to a handle 32 by a generally cylindrical connector means 34, which handle 32 and connector means 34 are generally identical in shape to the embodiment shown in FIGS. It has The connector means 34 and the cam 30 form a proximally directed annular shoulder 34.1 that is connected to the distally facing surface of the handle 32 and to the connector means 34. An annular shoulder 3 facing in the opposite direction is thus formed.
2.1 and together with the surface of the connector means 34 form a groove 34.2 which is a typical retaining means. As in the previous embodiment, this groove 34.
2 is sized to accommodate the lip 12.6 of the fuselage 12.1.

The intersection of the cam 30 and a plane perpendicular to the direction of movement of the plunger 14 forms a closed curve drawn as a boundary line of the solid line in the cross-sectional view shown in FIG. One fan-shaped part a of this closed curve
(corresponding to the first fan-shaped portion) is approximately circular, and its radius r ₁ remains approximately constant. Another sector c of this curve (corresponding to the second sector) is also circular, but its radius r ₂ is considerably larger than _the radius of the sector a; approximately the same as the radius of the inner surface 12.8 of 1. radius r ₁
The circle formed by is completed with a dotted line in FIG. 14 for illustration. The remaining sector b (corresponding to the third sector) of the closed curve extends quite far, almost outside the trajectory of the point created by radius r ₁ , and becomes a single smooth curve.
is adjacent to substantially circular sectors a and c. The surface of the cam 30 formed by the fan-shaped portion b is
A support surface is provided, as described in more detail below. The surfaces formed by sectors c and b merge into one smoothly rounded nose tip, labeled 30.1 in FIG. 14.
The protrusion of the cam surface beyond the circular shape defined by radius r ₁ creates a slightly distracting cam 30 with an asymmetrical cross-sectional shape. By referring again to FIG. 14, the longest chord across the closed curve passes through the nose tip 30.1, and this chord is significantly larger than the longest chord passing through the closed curve perpendicular to this chord. It is understood that it will preferably have a length of at least 1.2 times.

FIG. 12 shows the locking means in an unlocked state, with the surface portion 30.2 of the cam 30 corresponding to the sector c being in sliding contact with the internal surface of the body, and the surface portion 30.2 corresponding to the sector a .3
is along and in sliding contact with one of the webs 14.5 of the plunger 14, and the nose end 30.1 corresponding to the sector b is along the web 14.5.
4.8 along the surface. In this state,
Although the plunger 14 is off-centered within the fuselage 12.1, it can move smoothly and effortlessly into and out of the fuselage 12.1. When it is desired to lock the position of the plunger 14, the handle 32 of the locking means is rotated downward (clockwise in the drawing) to the position shown in FIG. When the cam is rotated in this manner, the nose end 30.1 touches the wall 15.3 of the web 14.8.
web 1 and at the same time
The wall 15.2 of 4.5 is also connected to these two webs 14.
5 and 14.8 from the part of the fuselage 12.1. In this way, the plunger
It is moved downward to the left in Figure 3 and is clamped between the fuselage wall and the cam.

When the handle 32 is rotated from the position shown in FIG. Web 14.8 Wall 15.
3, the cam 30 is subjected to a force from the web 14.8 in the direction of returning it to the position of FIG. 12. and said string and web 14.8
When the cam 30 is rotated in the direction of the position shown in FIG. 13 beyond a right angle with the wall, the cam 30 is subjected to a force from the web 14.8 to the position shown in FIG.

That is, the cam 30 moves from the position shown in FIG.
When rotated to the position shown in FIG. 3, the elastic force of the web 14.8 applies the 12th
After being applied in the direction of returning to the position shown in the figure and sliding into contact, the elastic force of the web 14.8 is applied to the cam 30 so that it is in the position shown in FIG.

Therefore, the cam 30 is always held in the unlocked or locked position. And arm 24.
If the cam 30 is rotated slightly beyond the nose end 30.1 by holding the cam 30, the cam 30 will automatically rotate and move to the unlocked position or the locked position, resulting in good operability. There is also no risk of the syringe becoming loose and unlocked during use.

As shown in FIG. 13, when the locking means is locked, the webs 14.5 and 14.8 are slightly elastically deformed or bent into the position shown in FIG. In response to the cam force applied to the cam, the fuselage wall near the open end deforms slightly outward. When the locking means returns to the unlocked position, the plunger web and body will, of course, substantially resume their original shapes.

The locking means depicted in FIGS.
In the form shown in the figure, the inner diameter of the fuselage is approximately 15.9 mm (approximately 5/8
inch) used in standard commercial syringes. As mentioned above, the longest chord across cam 30 is on the order of approximately 7.9 mm (0.310 inch), and perpendicular to this chord, the longest chord across cam 30 is approximately
It was around 6.3mm (approximately 0.247 inches). When the locking means are locked, the axial force required to move the plunger 14 within the body 12.1 is approximately
It weighed around 4.08 kilograms (9 pounds). In comparison, the locking means of Figures 1-7 weighed approximately 2.49 kilograms (approximately 5.5 pounds).

The locking means of the present invention can be modified in various ways, and the syringe using it can also be modified. For example, in the above description, the syringe has been described as having a plunger shaft having a generally "X" shaped cross section, but the present invention is applicable to plungers of various other shapes. For example, the shank of the plunger may be of generally circular cross-section, and the web may be of "Y"-shaped cross-section. All that is required is that the plunger and the body form an open space in which the cam means is housed so that the cam, when locked, places the plunger in restraining contact between the cam and the body. have the effect of

The locking means of the invention may be made of any suitable rigid material, such as metal or plastic. Preferably, the locking means, including the cam means, connector and handle, are molded as a single piece of plastic, such as polyethylene, polypropylene, etc., for high volume, low unit cost production.

Although the preferred embodiments of the present invention are as described above, it goes without saying that various modifications may be made thereto without departing from the spirit of the invention and the scope of the claims.

(Effects of the Invention) In the present invention, since the plunger is locked by the cam means, the operation is simple and the manufacturing cost is low. Furthermore, it can be used without modifying the structure of current medical syringes.

Furthermore, by providing a holding means that reliably stops the axial movement of the cam means, the plunger can be locked more reliably, making it possible to accurately extract a specific amount of liquid or gas or dispense a liquid compound. Ru.

Further, the cam surface of the cam means is composed of three sector-shaped portions, which applies force to the cam means to maintain it in the locked and unlocked positions, thereby providing good operability, and furthermore, the plunger is easily removed during use of the syringe. Loosening of the locked or unlocked state is reliably prevented.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a syringe with locking means of the present invention. 2 is a plan view of the locking means of FIG. 1; FIG. FIG. 3 is a cross-sectional view taken along line 3--3 in FIG. 2. FIG. 4 is a cross-sectional view taken along line 4--4 in FIG. Figure 5 is 5-5 in Figure 1.
FIG. FIG. 6 is a cross-sectional view taken along line 6--6 in FIG. 5. FIG. 7 is a cross-sectional view similar to that of FIG. 6, showing the locking means in a different position. FIG. 8 is a cut away cross-sectional view of another embodiment of the invention. FIG. 9 is a broken cross-sectional view showing a third embodiment of the present invention.
FIG. 10 is a plan view of a modified locking means of the present invention. FIG. 11 is a bottom view of the locking means of FIG. 10. FIG. 12 is a partially cut-away cross-sectional view of a syringe having the locking means of FIGS. 10 and 11, but with the locking means shown in the unlocked state; Towards the end, it is taken. Figure 13 is the first
FIG. 2 is a cross-sectional view similar to FIG. 2, with the locking means shown in the locked state. Figure 14 is 14-1 in Figure 10.
FIG. 4 is a cross-sectional view taken approximately along line 4; 12...Syringe, 12.1...Torso, 12.6
... Lip, 12.8 ... Internal surface, 14 ... Plunger, 14.1 ... Shaft, 14.5,1
4.6, 14.7, 14.8...web, 20...
...Lock means, 22...Cam means, 24...Handle, 26...Connector means, 24.1...Arm, 24.4...Groove, a, b, c...Sector shaped portion.

Claims (1)

Claims: 1. A syringe having a body and a plunger, the plunger having a radially and axially extending web and being movable axially within the body, wherein the body is located within the body. and said plunger, said cam means being carried by said body, and means for moving said cam means for bringing said plunger into contact with and restraining said body. A syringe locking device for securing the plunger to the body. 2. A patent further characterized in that said means for moving said cam means includes a handle fixed to said cam means, said handle including an arm extending outside said body for manual operation. A syringe locking device according to claim 1. 3. The plunger includes a plurality of webs extending in the longitudinal direction and the radial direction thereof, the body includes a smooth cylindrical inner wall, and the inner wall and the adjacent web have an open cylindrical shape between them. a cam forming a sector, the cam means being located within one of the sectors near the open end of the body and capable of contacting an inner wall of the body and a wall of each of the adjacent webs; said cam means having an unlocked position to permit axial movement of said plunger within said body and an axial position of said body for restraining said plunger between said body and said cam means. A syringe locking device according to claim 1, further characterized by being rotatable between a locking position displaced in a direction perpendicular to the syringe locking device. 4. Claim 1 further characterized in that said cam means has a cam surface for bringing said plunger into contact with said body when said cam means moves, said cam surface having a generally rectangular cross-section. The device described. 5. The invention of claim 1, further characterized in that the cam means has a cam surface for bringing the plunger into contact with the body when the cam means moves, the cam surface having a generally elliptical cross-section. syringe locking device. 6. A syringe having a body and a plunger, wherein the plunger has a web extending in the radial and axial directions and is movable in the axial direction within the body, between the body and the plunger within the body. cam means located at and carried by said body; and means for moving said cam means for bringing said plunger into contact with said body and restraining said body; A syringe locking device for fixing the plunger relative to the body, characterized in that it has retaining means for restraining axial movement with respect to the body. 7. said retaining means being a groove for receiving an annular lip formed inwardly in the body for retaining said cam means in a substantially fixed axial position relative to said body; 7. A device according to claim 6, further characterized in that: 8. The patent further characterized in that said means for moving said cam means includes a handle fixed to said cam means, said handle including an arm extending outside said body for manual operation. A syringe locking device according to claim 6. 9 having a body and a plunger, the body having a smooth cylindrical interior surface, the plunger moving axially within the body, and radial and axially spaced circumferentially from each other; a syringe having a shank including a plurality of webs extending in the direction, including cam means carried between two adjacent webs of the plunger and the interior surface of the body; A line of intersection between the cam surface and a plane perpendicular to the direction of movement of the plunger approximates the radius of a first sector-shaped portion that is substantially circular and has a substantially constant radius and the cylindrical inner surface of the body. a cam surface configured to form a closed curve having a second sector having a radius greater than the second sector, and a third sector extending between the first and second sector; 3
at least a portion of the sector of the first sector extends significantly beyond the locus of points caused by the radius of the first sector, and the cam means allows the plunger to move axially within the body. an unlocked position and a cam surface perpendicular to the axis of the body for contacting an interior surface of the body and the wall of the adjacent web to constrain the plunger between the cam surface and the body; A syringe locking device for fixing the plunger relative to the barrel, characterized in that it is rotatable between a locking position and a locking position in which the plunger is displaced in a direction. 10 The length of the maximum chord that crosses the closed curve is
The syringe lock of claim 9 further characterized by being at least about 1.2 times the length of the longest chord across a closed curve taken perpendicular to the longest chord. Device.