A lead screw, a lead screw nut (7) and a drive member (8) are aligned with an axis defining an axial direction and an opposite axial direction. A coupling between the lead screw and the lead screw nut allows a helical movement of the lead screw with respect to the lead screw nut at least in the axial direction. The lead screw is coupled with the drive member, the coupling generating a helical movement of the lead screw with respect to the drive member when the drive member is moved in the axial direction with respect to the lead screw. A dispense stop feature (19) of the lead screw nut and a dispense stop feature (20) of the drive member prevent the generation of the helical movement of the lead screw when a specified end position of the drive member is approached.一導螺桿、一導螺桿螺帽(7)以及一驅動構件(8)對齊於一軸線,該軸線定義一軸向方向以及一相反的軸向方向。導螺桿與導螺桿螺帽間之聯結允許導螺桿依軸向方向相對於導螺桿螺帽進行一螺旋運動。導螺桿會與驅動構件聯結,當驅動構件相對於導螺桿依一軸向方向運動時,該聯結會產生導螺桿相對於驅動構件的螺旋運動。當到達驅動構件的一特定末端位置時,導螺桿螺帽的一給藥終止特製件(19)以及驅動構件的一給藥終止特製件(20)能夠避免導螺桿的螺旋運動。5...導螺桿6...螺紋16...給藥終止特製件17...止動特製件
