Hammer lock releasing mechanism for a printing device

A hammer lock releasing mechanism for a printing device comprising:

• (a) a rotary type wheel provided on its outer surface with a plurality of types disposed in the circumferential direction at equal angular intervals, and driven in rotation at a specific speed;
• (b) a plurality of printing hammer heads disposed confronting said type wheel and undergoing displacement, during a printing operation, to selectively strike a desired type onto a sheet of paper, thereby carrying out printing, said sheet of paper being fed between said hammer heads and said rotary type wheel, each of said hammer heads having a convex part;
• (c) a plurality of first urging means for constantly urging said hammer heads to move in the direction of carrying out a printing action, each of said first urging means being attached to one of said hammer heads;
• (d) a plurality of locking means for locking said hammer heads in a non-printing position, each of said locking means being engageable with a plurality of said hammer heads, thereby preventing said first urging means from discharging their urging force, each of said locking means being attached to one of a plurality of second uring means;
• (e) trigger means for displacing said locking means against a force exerted by said second urging means, so as to unlock said hammer heads and permit said hammer heads to carry out said printing action;
• and
• (f) a rotary cam structure rotatable in correspondence with the rotation of said type wheel and engageable by said convex parts of said hammer heads, said rotary cam struoture having a circumferential surface comprising a plurality of sequences of connected portions, each sequence comprising a portion for permitting the corresponding one of said hammer heads to carry out said printing action, a portion for resetting the corresponding one of said hammer heads connected to said portion for permitting said printing action, first and second peripheral portions of equal radius for holding the corresponding one of said hammer heads in a non-printing position, and an intermediate portion having a radius smaller than the radius of and lying between said first and second peripheral portions, said first peripheral portion and said portion for resetting the corresponding one of said hammer heads being connected in a continuous manner, and said second peripheral portion being connected in a discontinuous manner to an ajdacent portion for permitting said printing action, wherein
• (i) said portion for permitting said printing action comprises a concave part for permitting said convex part of the corresponding one of said hammer heads, which is unlocked from the non-printing position by said trigger means, to enter therein, thereby permitting said hammer head to rotate under the influence of the corresponding one of said first urging means;
• (ii) said portion for resetting the corresponding one of said hammer heads comprises a continuous surface of increasing radius for guiding said hammer head in a direction opposite the direction taken by said hammer head during said printing action so that the corresponding one of said locking means is engageable with said hammer head;
• (iii) said first and second peripheral portions comprise surfaces of maximum radius on said rotary cam structure, said maximum radius being such that the corresponding one of said hammer heads is displaced from engagement with said locking means in response to said convex part of said hammer head contacting either of said peripheral portions;
• and
• (iv) said intermediate portion comprises a noncontact portion having a radius less than said maximum radius, such that said convex part of the corresponding one of said hammer heads is not in contact with said noncontact portion when said hammer head is locked by the corresponding one of said locking means.