Print hammer damping mechanism for typewriters and like printing machines

A print device for typewriters and like printing machines comprising a platen roller having a point of typing;

• a character-carrying element having radial flexible spokes, wherein each spoke bears a print character which can be selectively positioned in front of the point of typing;
• a print hammer which can be selectively actuated to move the selected print character against the platen roller, wherein said print hammer has a given weight;
• an actuating solenoid for actuating the print hammer including a casing having a front core, a rear core and a movable armature;
• a flange connected with the rear core and including a fixed bush having an opening disposed adjacent to the character-carrying element, wherein the front core comprises a projection portion having a seat;
• a travel limit element disposed opposite to the fixed bush with respect to the front core and rear core, to limit said seat frontwardly;
• a return coil spring for return to rest of the print hammer;
• a damping mechanism for damping the return to rest of the print hammer, wherein said damping mechanism includes an intermediate stop element to limit said seat rearwardly and a movable bush movably guided by said seat between the travel limit element and the intermediate stop element and comprising an opening;
• and means for defining the rest position of said print hammer;
• wherein the print hammer comprises a rear end for cooperating with the spoke of the selected character, a cylindrical portion adjacent to said rear end and a cylindrical stem on which is fixed said armature, wherein said stem is disposed adjacent to said cylindrical portion, and comprises a groove and a front end, wherein said movable armature is positioned between said cylindrical portion and said groove and said return coil spring operates on said armature adjacent to said cylindrical portion, and wherein said print hammer is guided by the rear end housed in the opening of said fixed bush and by the front end housed in the opening of said movable bush and is held spaced from the platen roller in said rest position by means of said return coil spring;
• wherein said solenoid is energizable for moving the movable armature toward said rear core, against the action of said return coil spring to actuate said print hammer;
• wherein said damping mechanism further comprises a first damping element of resilient material engaged with said groove between the movable armature and the movable bush, a counteracting coil spring coaxial with the cylindrical stem and disposed between the movable bush and the travel limit element for biasing the movable bush toward the intermediate stop element and the platen roller and a second damping element of resilient material, coaxial with the cylindrical stem and disposed between the movable bush and the travel limit element wherein said means for defining the rest position include the movable bush, the first damping element which bears on said movable bush and one of said intermediate stop member and travel limit element and wherein said counteracting coil spring urges the movable bush to be arrested against the intermediate stop element upon actuation of the print hammer toward the print position;
• and
• wherein said damping mechanism is provided for producing sequential damping functions, including a first damping phase effected by said first damping element as compressed by the action of the movable armature and the movable bush, transmission of movement from the armature to the movable bush in order to move the movable bush from the arrest against said intermediate stop element to the travel limit element, compression of said counteracting coil spring and a following damping phase effected by the second damping element as compressed between the movable bush and said travel limit element at said rest position under the action of said rest position defining means, thereby minimizing the time for the print hammer to settle down at said rest position.

A print device for printing machines comprising a platen roller having a point of typing;

• a character-carrying element having radial flexible spokes provided at the periphery with a series of characters which can be selectively positioned in front of the point of typing;
• a print hamber which can be actuated from a rest position to a printing position for moving a selected character against the platen roller;
• and a solenoid for actuating the print hammer comprising a magnetic armature, a winding and an internal housing having a travel limit element disposed opposite to the character-carrying element, and an intermediate stop element disposed opposite to the character-carrying element, a return coil spring for returning the spring hammer to the rest position after printing of the selected character, a damping mechanism for damping the return to rest position of the print hammer, and means for defining the rest position of said print hammer;
• wherein the print hammer comprises a rear end for cooperating with a spoke of the selected character, and a stem on which is fixed the magnetic armature;
• wherein the print hammer provides an intermediate surface and the damping mechanism comprises a series of damping elements which produce sequential damping functions, minimizing the time for the print hammer to settle down, said series comprising a movable bush operating a as a counteracting weight for the print hammer, housed in said internal housing, accommodating a front portion of said stem and movable between the travel limit element and the intermediate stop element, a first damping element disposed between said intermediate surface and said movable bush, a counteracting coil spring disposed between the movable bush and the travel limit element, and a second damping element disposed between the movable bush and the travel limit element;
• wherein said winding is energizable for moving said armature against the action of said return coil spring to actuate the print hammer, wherein said means for defining the rest position comprise said movable bush and said first damping element sandwiched between said intermediate surface and said movable bush and one of said intermediate stop element and said travel limit element;
• wherein in the rest position of the print hammer the return coil spring urges the intermediate surface toward the movable bush to compress said first damping element and the counteracting coil spring urges the movable bush toward said intermediate stop;
• wherein said counteracting coil spring is provided to cause said movable bush to be arrested against said intermediate stop element, upon the actuation of said print hammer;
• and
• wherein said sequential damping functions comprise a first damping phase by said first damping element as compressed by the action of said intermediate surface against the movable bush, transmission of movement from said intermediate surface to the movable bush, compression of said counteracting coil spring, and a following damping phase effected by said second damping element as compressed between the movable bush and said travel limit element.

A print device for typewriter and like printing machines comprising a platen roller defining a point of printing;

• a character-carrying element having flexible spokes provided at the periphery with a series of characters which can be selectively positioned in front of the point of printing;
• a print hammer movable rearwardly along a printing direction from a rest position to a printing position for moving a selected character against the platen roller, whenin said print hammer comprises a stem, having an intermediate portion, a front portion and a rear portion;
• a solenoid including an actuating armature fixed to the intermediate portion of said stem, a return coil spring for rapidly returning the print hammer to the rest position after printing of each character, and a casing comprising a rear core having rear guide means for guiding the rear portion of said stem and a front core including an internal housing having an intermediate stop and a travel limit stop;
• damping means for reducing the time for damping of the print hammer after printing of each character;
• and means for defining the rest position of said stem, wherein said damping means are housed into the internal housing and comprise:
• a counteracting weight movable for a pre-set gap of small amount along said printing direction between the intermediate stop and the travel limit stop, wherein said internal housing comprises front guide means for guiding said counteracting weight along said printing direction, wherein said counteracting weight comprises guide means for guiding the front portion of said stem between the rest position and the printing position of said print hammer, a first damping element having an elastomeric disc for damping purposes disposed between the actuating armature and the counteracting weight, a counteracting coil spring disposed between the counteracting weight and the travel limit element and a second damping element having an elastomeric disc for damping purposes disposed between the counteracting weight and the travel limit element, wherein said means for defining the rest position comprise said counteracting weight, said actuating armature, said first damping element and one of said intermediate stop and said travel limit stop;
• wherein said counteracting coil spring is provided to urge frontwardly the counteracting weight in order to ensure arrest of said counteracting weight against said intermediate stop upon actuation of said print hammer;
• wherein said actuating armature is provided to strike against the counteracting weight through the first damping element for a rearward movement of said counteracting weight upon returning of the print hammer to said rest position;
• and
• wherein said damping means are provided to produce a first damping phase by the first damping element upon the striking of said armature against the counteracting weight through the first elastomeric element, a second damping phase by the rearward movement of the counteracting weight through said pre-set gap and compression of said counteracting spring by the counteracting weight and a third damping phase by the second damping element compressed between the counteracting weight and the travel limit stop up to arrest of said print hammer by said means for defining the rest position of said stem.