DRIVMEKANISME TIL AKSIAL FREMDRIVNING AF EN STEMPELSTANG, ISAER TIL EN INJEKTIONSSPROEJTE

In a drive mechanism of the type where a rotating drive wheel deforms and partly works into engagement with a rod of deformable material to axially displace the rod as the drive wheel rotates, the drive wheel is a wheel (15) which is provided with worm threads (17) and whose axis of rotation is substantially parallel with the said rod (11). According to the invention, such a structure results in an unprecedented great metering accuracy with indication of very small doses from e.g. an injection syringe (13) whose plunger (14) is driven by said rod (11). The invention is characterized in that the worm threads work into the deformable material of the rod under the action of essentially completely continuous forces. The preferred embodiment comprises two worms (in Fig. 4 behind the worm (17) on the opposite side of the rod (11) driven by their respective shafts (19), which are driven by a common worm (22) via helical toothed wheels (21). An antibackup roller (12) placed in an opening cover (27) serves to press the rod (11) down between the two worms so as to provide some wedge effect. Complete balance in the mechanism is obtained because the two worms rotate in the opposite direction.