Patent ID: 8088110

Claim:
A safety injector comprising: a needle hub connecting a needle, the needle hub comprising a inserting part therein and a hollow track connecting with the inserting part, the inserting part being for accommodating the needle and the hollow tract further comprising a distal end and a proximal end, the distal end of the hollow tract having a first inner diameter and the proximal end having a second diameter, and the first inner diameter being larger than the second inner diameter, wherein the needle hub further comprises a plurality of slots, slopes, turning chutes and guiding chutes connected serially; a hollow barrel connecting the needle hub for guiding the needle hub to retract into the hollow barrel after an injection is completed, wherein the hollow barrel comprises a plurality of hooks, the plurality of hooks engage with the slots to clamp the needle hub; and a collapsable plunger combination settled in the hollow barrel, the collapsable plunger combination comprising a rod, a retractable plunger and hollow plunger, the rod extending from one end of the retractable plunger toward the needle hub, the hollow plunger comprising a first telescoping part and the retractable plunger comprising a second telescoping part, the first telescoping part telescoping with the second telescoping part, there being at least one raised portion formed on an outside wall of the second telescoping part to be correspondingly embedded in at least one depression formed on an inside wall of the first telescoping part, the raised portion and the depression engaging to each other; wherein the engagement between the raised portion and the depression is released to make the retractable plunger retract into the hollow plunger when a following press on the hollow plunger after an injection is completed, and thereby spare a space of the hollow barrel for accommodating the needle hub, and when the following press is applied on the hollow plunger after the injection is completed, the hooks of the hollow barrel disengage with the slots and slide along the slopes, the turning chutes, and the guiding chutes, so that the needle hub is guided and retracted into the hollow barrel.