A flexible piston rod

Details A flexible piston rod A flexible piston rod

A - Human Necessities

61

M

A61M 5/315 (2006.01) A61M 5/145 (2006.01)

Patent

CA 2403843

A flexible piston rod for an injection device, which piston has the form of a helical spring made up from a number of narrowly adjacent turns of windings. These turns provide an external thread, which thread fits into the internal thread of a nut element. When the nut element is rotated the piston rod is advanced forward, which movement is used to displace a piston inside a cartridge containing a fluid to be expelled. In order to prevent the piston rod from rotating when the nut element is rotated, the helical spring making up the piston rod is provided with a longitudinal spine, which is located at a peripheral area of the helical spring. The spine can either be a mechanical removal of a part of the out-turned area of each winding, or it can be a reduction or removal of an initial tension in a longitudinal area of the helical spring.

L'invention concerne une tige de piston flexible pour dispositif à injection, ayant la forme d'un ressort hélicoïdal qui comporte un certain nombre de spires d'enroulement adjacentes, lesquelles constituent un filet externe qui s'emboîte dans le filet interne d'un écrou. Lorsque l'écrou est mis en rotation, la tige de piston avance, ce qui permet de déplacer le piston à l'intérieur d'une cartouche contenant un fluide à éjecter. Pour éviter la rotation de la tige avec celle de l'écrou, le ressort est pourvu d'une arête dorsale longitudinale située à sa périphérie, ladite arête pouvant être obtenue par extraction mécanique d'une partie de la zone tournée vers l'extérieur de chaque enroulement, ou bien par réduction ou extraction de tension initiale dans une zone longitudinale du ressort.

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