MXPA99000239A - Flexi piston rod - Google Patents

Abstract

The present invention relates to a syringe for receiving an ampoule having a cylindrical interior of a first specific diameter, the syringe is characterized in that it comprises: a flexible piston rod having a tape-shaped body, the body includes upper and lower surface opposite and opposite sides, wherein the piston rod also includes a plurality of support members axially spaced along the body and projecting from the upper surface, wherein the support members have distal ends spaced away from the body, and wherein the sides and distal ends, when the piston rod is observed in cross section, lie at least generally along a circle having a diameter that is approximately the same as the first diameter, so that when the rod of the piston extends inside the cylindrical interior of a vial, the sides and the distal ends will remain a stopper with the inside of the bulb in at least three contact positions and where one of the contact positions is located in the middle of the circle, opposite the other two contact positions, and a guide member of the rod piston to guide a portion of the piston rod, which is located outside the interior of the vial, along a guide surface.

Description

FLEXIBLE PISTON ROD DESCRIPTION OF THE INVENTION The invention relates to flexible piston rods for injection syringes. The injection syringes are mainly provided with a rigid piston rod by means of which a piston is pressed on one end of a cartridge to press out the contents of the cartridge through an injection needle mounted on the other end. Such injection syringes will mainly have a length, which is at least twice the length of the cartridge. It has been proposed to provide flexible piston rods of shorter syringes. Such piston rods may be bent so that their outer end is parallel to the cartridge near this cartridge and not as an axial continuation thereof. WO 95/09021 discloses a flexible piston rod for a syringe comprising a cartridge holder and a part for fixing the dose. The fixed doses are pressed out of the cartridge by means of a flexible piston rod, which is bent 180 ° by a piston rod guide placed immediately behind the cartridge. When the syringe is of the type in which an empty cartridge can be replaced by a new one after the piston rod REF. 29133 has been removed from the empty cartridge, the piston rod guide can be designed so that it can support the piston rod when a pressure is transmitted, and moving the rod through piston. This is obtained by using a piston rod guide that has the shape of a curved tube that supports all sides of the piston rod, which is made as a tightly wound steel spring. For use in a disposable syringe with a flexible piston rod the piston rod guide only has to support the piston rod during its transmission of pressure to a piston in the cartridge, and consequently a piston rod guide can be used more simple. Furthermore, it is desired to manufacture the piston rod of a material of the same type as the material from which the disposable syringe is made, ie plastic, since the combination of metal parts and plastic parts reduces the possibilities for recycling. Also the piston rod must meet the need for a piston rod that is rigid enough to be bent and the desire for a minimum consumption of material. From EP 110 687 it is known how to use a flexible drive belt to drive a piston in a cartridge. The tape is made of a molded polypropylene plastic and necessary stiffness is obtained by giving the tape a curved and ribbed cross section along the side edges of the tape. The curved shape of the cross section corresponds to the curvature of the inner wall of the cartridge, so that the tape can come into contact with this inner wall over its full width. However, when a tape or a curved cross section is curved to follow an arc of a circle, the tape has to assume a linear cross section. In addition, the plastic has memory, so that a cross section, which has been maintained for some time linearly will not automatically reach the original curved shape when the part in question no longer follows an arc of a circle, consequently a cross section, the which is intended to follow the curved shape of the inner wall of a cartridge can not be reliable. The object of the invention is to provide a flexible piston rod made of plastic and which can be bent out of a cartridge and used to press a piston into a cartridge without bending inside this cartridge. This is obtained by means of a piston rod, which comprises a body in the form of a belt, which along its length is provided with supports projecting from at least one side of the belt, the belt has a width and supports a length, so that the sides of the tape and the ends of the supports come into contact with the outer wall of an ampoule in at least three positions along the internal perimeter of the ampoule with not all of the support points being in the same half of the circular cross-section. In a preferred embodiment of a piston rod according to the invention, the body formed of a belt has a width corresponding to the length of a cord covering an arc of approximately 120 ° of the circular internal cross-section of the ampule and supports which project perpendicularly from the side of the face oriented towards the axis of the vial in contact with the inner wall of this vial in a displaced position 120 ° from each side of the body formed of tape. According to the invention, the supports can be provided with a spacing that allows the piston rod to bend towards the side containing the supports. The supports can be provided on both sides of the belt to increase the rigidity of the piston rod in the bulb. By such piston rods, the guide of the piston rod must be provided with a groove in the direction of movement of the piston rod to accommodate the protruding brackets. Alternatively, the supports can be placed adjacent to each other, so that the piston rod can be bent only towards the side of the supports. The piston rod guide should be designed with a groove, which can accommodate the projected supports. In one embodiment of the piston rod according to the invention, the supports can have the shape of plates oriented in the longitudinal direction of the body of the piston rod perpendicular to this body and connected to the piston rod body by connections that they have a small length in the longitudinal direction of the piston rod. This construction has greater rigidity and the connections of the plates to the piston rod are small, for example in the same order of size as the thickness of the belt that forms the piston rod, in the longitudinal direction of this rod, will not reduce the flexibility of this piston rod. In another embodiment of the piston rod according to the invention, this rod can be composed of pieces in the form of a belt, each of which have a support formed of a plate fixed thereto along the length of the piece, the pieces they are connected by articulations that allow the curvature of the pieces towards the side that does not contain the supports. In this mode, the tape-shaped parts that form the piston rod have obtained a good rigidity considering the total flexibility of the piston rod. For the advancement of the piston rod according to the invention, racks can be provided on any side that does not contain the supports or near such supports along the edge of the piston rod on the same side as those supports. In embodiments with rigid tape pieces, the zipper may be composed of a rack in the form of sectors in contact with a drive pinion. In the following Xo, the invention will be described in greater detail with reference to the drawings, in which Figure 1 shows a side view of an embodiment of a piston rod according to the invention inserted in an ampoule and curved by a guide of piston rod, Figure 2 shows a sectional view along the line II-II in Figure 1, Figure 3 shows another embodiment of a curved piston rod according to the invention, Figure 4 shows another embodiment more than one curved piston rod according to the invention, figure 5 shows a further embodiment of a piston rod according to the invention, and figure 6 shows a further embodiment of a piston rod according to the invention. In Figure 1 a piston rod in the form of a belt 1 is along one of its sides provided with separate supports 2. The piston rod is shown inserted into an ampoule 3 and in contact with a piston 4 in the bulb . Immediately outside the bulb the piston rod is bent by a piston rod guide 5. The piston rod guide 5 has a curved surface supporting the convex side of the curved piston rod. On its sides the guide of the piston rod 5 has flanges 5 ', each supporting another flange 5"parallel to the curved surface of the piston rod guide at a distance corresponding to the thickness of the belt forming the connecting rod This way a guide path can be formed, which prevents the piston rod from taking a short cut along a rope, towards the curved surface when compressive forces do not act on the piston rod. Figure 2 shows how the side edges of the tape-shaped piston rod 1 and the ends of the supports are in contact with the internal perimeter of the bulb. The tape-shaped piston rod is in contact with the inner perimeter of the bulb so that the rectangular cross-section of the belt forms a cord in the circular cross-section of the bulb. The supports are projected perpendicular to the side of the tape oriented to the center of the circular cross-section of the vial to avoid bending the tape in this direction. Bending in a direction towards the center of the circular cross section is avoided by the fact that the tape has reached a curved cross section to allow such bending outwards. When the width of the tape is small, the tape will have enough rigidity to avoid such a bend. However, ampoules with supports of a larger diameter may be appropriate on the side of the tape not oriented towards the center of the cross section of the ampoule as shown by the supports 2 'in Figure 3. In the embodiment shown in FIG. Figure 1 The piston rod guide curves the piston rod in the direction of the supports. This will make the radius of curvature which can allow the curvature to depend on the spacing between the supports. Figure 4 shows a type of piston rod, in which the supports are in contact with each other when the piston rod is linear and not curved. This gives the linear piston rod good stiffness. The piston rod can be bent by means of a piston rod guide not shown if only the curvature is made towards the side of the piston rod made of belt having no projecting supports. The piston rod guide should be provided with a groove which can accommodate the brackets which now project from the side of the belt in contact with the guide of the piston rod.

In the embodiments shown in FIG. 1, the supports have only a small extension in the longitudinal direction of the piston rod if they do not impede the curvature of the piston rod. In the embodiment shown in FIG. 4, the supports are formed as plate-shaped members 6 which are connected to the piston rod 1 by means of connections 7 having only a small extension in the longitudinal direction of the piston rod. Yet another embodiment of the piston rod according to the invention is illustrated in FIG. 5. The piston rod in the form of a belt is comprised of belt parts 8 and each part 8 has a longitudinal wall 9 projecting perpendicularly from one. from its sides. The tape parts 8 are hinged together by the links 10 to form a piston rod which can only be bent by bending its joints. The piston rod can be advanced by adding pressure to its end outside the bulb as shown by arrow 11 in figure 1. Alternatively the piston rod can be provided on its body in the form of a belt with a flexible rack 12 as Figure 4 is shown as a rack by means of which the piston rod is advanced by means of a pinion which engages the rack and rotates according to the required advancement of the piston rod. The rack can be provided on one side of the piston which does not contain supports as shown in figure 4 or near the supports along the edges of the piston rod body in ribbon form (not shown). Alternatively, a bore may be provided along the edge of the piston rod and advancement of the piston rod may be obtained by means of gears coupling such a bore. When the piston rod is not fully flexible but is flexible only in the joints the parts in the joints are rigid and not flexible, a rack on the side that does not contain supports can be formed as sectors of an inwardly gear meshing coupling the toothed pinion external actuator driving the piston rod as illustrated in figure 6, wherein the rigid parts 13 of the piston rod are provided with curved racks which are coupled by a pinion 14. On the side of the piston rod opposite to curved zips are provided in the form of plate 16. The curvature of the piston rod is obtained by bending the piston rod in the joints 15 connecting the rigid parts forming the piston rod. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following:

Claims (10)

1. A flexible piston rod for use in cylindrical ampules, characterized in that the piston rod comprises a ribbon-shaped body which along its length is provided with supports projecting from at least one side of the belt, the it has a width and the supports a length so that the sides of the tape and the ends of the supports are in contact with the inner wall of the lamp in at least three positions along the internal perimeter of the lamp and that not all the contact points are on the same half of the circular cross section.

2. The flexible piston rod according to claim 1, characterized in that the belt-shaped body has a width corresponding to the length of a cord covering an arc of approximately 120 ° of the circular internal cross-section of the ampoule and supports projecting perpendicular from the side of the tape oriented towards the axis of the vial in contact with the inner wall of this vial in a position displaced approximately 120 ° from each side of the sides of the body in the form of a tape.

3. The flexible piston rod according to claim 1 or 2, characterized in that the supports are provided with a spacing that allows the piston rod to curve towards the side containing the supports.

4. The flexible piston rod according to claim 1 or 2, characterized in that the supports are placed adjacent to each other so that the piston rod can only be bent towards the side of the supports.

The flexible piston rod according to claim 4, characterized in that the supports are in the form of plates oriented in the longitudinal direction of the piston rod body perpendicular to this body and connected to the piston rod body by connections that have a small length in the longitudinal direction of the piston rod, ^

6. The flexible piston rod according to claim 4, characterized in that the piston rod is composed of pieces in the form of a ribbon each of which have supports in the form of plates fixed to them along the piece, the pieces are connected by joints that allow the curvature of the pieces towards the side that does not contain the supports.

7. The flexible piston rod according to any of the preceding claims, characterized in that a rack is provided on the side that does not contain supports.

8. The flexible piston rod according to any of the preceding claims, characterized in that a rack is provided on the side containing the supports along the edge of the piston rod body.

9. The flexible piston rod according to claim 6, characterized in that the side of the tape-shaped parts that do not contain supports is provided with rack pieces in the form of sectors each of which have a curvature that allows them attach to a pinion.

10. The flexible piston rod according to claim 2, characterized in that the supports are provided on the side of the piston rod in the form of a tape not oriented towards the axis of the ampule.