Liquid medicine administration device

A liquid medicine administration device comprising:

• a liquid medicine container filled with liquid medicine, the liquid medicine container including a tip at which is located an opening through which the liquid medicine is discharged during administration of the liquid medicine;
• a gasket positioned inside the liquid medicine container and connected to a plunger, the gasket being movable in the liquid medicine container toward the opening of the liquid medicine container to discharge the liquid medicine through the opening;
• a housing in which is housed the liquid medicine container and the plunger;
• a motor which operates to output a drive torque, the motor being operatively connected to a feed screw so that the drive torque rotates the feed screw;
• at least one guide wall that engages the plunger to restrict rotation of the plunger relative to the housing;
• the plunger including a threaded portion and a plunger body, the threaded portion of the plunger threadedly engaging the feed screw, the plunger body being movable in the liquid medicine container toward the tip by virtue of the rotation of the feed screw that is threadedly engaged with the threaded portion of the plunger and the at least one guide wall that engages the plunger to restrict rotation of the plunger with respect to the housing;
• and
• the plunger being configured so that when the plunger body receives an axial reaction force equal to or greater than a preset pressing force from the gasket during advancement of the plunger through the rotation of the feed screw, a pressing force applied by the plunger body to the gasket to advance the gasket toward the tip ceases.

A method comprising:

• inserting a needle tube into a living body, the needle tube being connected to a liquid medicine container containing liquid medicine so that sliding movement of a gasket connected to a plunger and positioned in the liquid medicine container causes the liquid medicine to flow from the liquid medicine container to the needle tube, the liquid medicine container being housed in a housing together with a motor that outputs a drive torque and that is operatively connected to a feed screw so that the drive torque rotates the feed screw, rotation of the plunger being restricted, the plunger including a threaded portion and a plunger body, the threaded portion of the plunger threadedly engaging the feed screw, the plunger body being movable in the liquid medicine container toward the tip by virtue of the rotation of the feed screw and the restriction on rotation of the plunger,
• operating the motor to produce the drive torque, and transferring the drive torque to the feed screw to move the plunger so that the plunger body applies a pressing force to the gasket to discharge liquid medicine from the liquid medicine container by way of the tip;
• and
• cancelling the pressing force applied by the plunger body to the gasket when the plunger body receives an axial reaction force equal to or greater than a preset pressing force from the gasket so that the gasket stops moving toward the tip and the discharge of the liquid medicine from the liquid medicine container by way of the tip stops.