Circular knitting machine, particularly of the medium-diameter type, with improved needle actuation

A circular knitting machine, comprising:

• a footing;
• a needle cylinder supported on said fooling and rotationally actuatable, with respect to said footing about an axis thereof, which is orientated substantially vertically;
• a plurality of axial slots being formed on an outer lateral surface of the needle cylinder, each slot accommodating a needle;
• actuating means for actuating the needles provided and interacting with said needles during rotation of the needle cylinder about said axis thereof in order to actuate the needles along a corresponding axial slot of the needle cylinder so that the needles form knitting with at least one yarn dispensed to the needles at at least one drop or feed of the machine;
• and wherein said needle actuation means comprise, for each needle, a sub-needle arranged in the corresponding axial slot of the needle cylinder below said needle;
• said sub-needle being connected bilaterally to the needle for motion along the corresponding axial slot and having, along an extension thereof, a heel that is orientated radially with respect to the needle cylinder;
• sub-needle actuation cams, said sub-needle being able to oscillate on a radial plane of the needle cylinder in order to pass from an active position, in which the sub-needle is extracted radially with the heel thereof from the corresponding axial slot of the needle cylinder so as to engage paths formed by said sub-needle actuation cams, which are arranged around the needle cylinder and are suitable to produce, or allow a movement of said sub-needle along the corresponding axial slot of the needle cylinder, to an inactive position, in which the sub-needle is embedded with the heel thereof in the corresponding axial slot of the needle cylinder so as to avoid engaging said sub-needle actuation cams;
• and sub-needle actuation means which act on said sub-needle for transition thereof from said active position to said inactive position and vice versa, wherein said actuation means for actuating the sub-needle comprises an actuation element that is arranged in each one of said axial slots below a corresponding sub-needle and is moveable on command along the corresponding axial slot in order to interact with a lower end of the sub-needle and produce transition and retention of said sub-needle in said active position or in said inactive position, the lower end of said sub-needle being shaped complementarily to an upper end of said actuation element in order to move said sub-needle from said inactive position to said active position or vice versa as a consequence of an axial movement of said actuation element along the corresponding axial slot of the needle cylinder, and wherein said lower end of said sub-needle is forked, with a first prong that protrudes downward with respect to the second prong;
• said first prong lying closer to the bottom of the corresponding axial slot of the needle cylinder than said second prong;
• said first prong being engageable by an upper portion of said actuation element to move or stably retain said sub-needle in its inactive position, and said second prong being engageable by said upper portion of said actuation element to move or stably retain said sub-needle in the active position.