Patent ID: 7850648

Claim:
A needle unit for an injection device having an injection needle and a needle holder, the needle unit comprising: a guiding part securable to the needle holder; a cover longitudinally slidable along the guiding part, the cover comprising a longitudinally extending guiding rib on an inner surface thereof and a switching ramp extending in a proximal direction from the cover; and a substantially planar tensing wheel longitudinally slaved to the guiding part, the tensing wheel comprising: a recess extending through the wheel and adapted to receive the switching ramp thereby causing rotational motion of the tensing wheel; and a radially extending blocking element adapted to interface with the guiding rib, wherein: proximal motion of the cover relative to the injection device causes rotation of the tensing wheel via interaction between the switching ramp and the recess, the rotation causing the blocking element to flexibly engage the guiding rib; and subsequent distal motion of the cover causes a proximal end of the guiding rib to clear the blocking element allowing the blocking element to release to a position generally in line with the guiding rib thereby preventing additional proximal motion of the cover.