A printer is provided with a plurality of print hammers, each of which is maintained in a rest position engaging a deformed elastic body. Individual magnetic circuits in combination with a single permanent magnet are provided for selectively maintaining each of said print hammers in said rest position and for selectively releasing said print hammers to effect printing. Each magnetic circuit consists of a first portion including a device for adjusting the reluctance of said second portion upon release of the associated print hammer. The first and second portions are connected in parallel with a permanent magnet common to at least two print hammers. Each of said print hammers is released from its rest position by exciting a control coil in said magnetic circuit in a direction such that the magnetomotive force applied to said print hammer to hold said print hammer in position is decreased, the displacement of the print hammer being the product of the release of the energy of the elastic body.
A dot-matrix printing device for a printing office machine, comprising a series of striking bars in the proximity of the recording medium movable transversely of the medium for printing dots in different locations. The bars are adapted to be actuated by the armatures of corresponding electromagnets for impressing individual dots of characters. The striking bars are guided in the proximity of the recording medium by a movable guide which effects the transverse movement and each electromagnet has a fixed core and a movable armature in articulated engagement with the corresponding bar. Each armature is provided with an actuating spring which tends to move the armature away from the core of the electromagnet. A permanently magnetized rubber establishes a bias magnetic flux such as to keep the armatures at rest in opposition to the action of the actuating springs and a plurality of windings can be energized selectively to generate a flux opposed to the bias flux so as to allow the actuating springs to move the armatures away from the cores for impression of the dots. The device further includes a reloading member which acts on the armatures to bring them back into contact with the cores of the electromagnets.
A high-speed print hammer and magnetic actuator is provided which operates with a minimum of power dissipation, can achieve high speed, and has very little flux leakage beyond the mechanical structure. The magnetic actuator is made up of two pole pieces having a high magnetic permeability, with a permanent magnet therebetween. A print hammer, also having a portion constructed of a material with a high magnetic susceptiblity, is pulled away from its unsprung position by the permanent magnet and contacts the faces of the pole pieces, providing a very low reluctance magnetic path between them. The print hammer is released from this cocked position by a pulsed electromagnetic field applied in a direction opposite that of the permanent magnet, the pulse pattern corresponding to the desired impact pattern of the print hammer. Lower drive power to the electromagnet is achieved by providing an alternate magnetic path having a reluctance intermediate between that provided by the print hammer when it is in contact with the pole faces, and the reluctance between the pole faces (i.e., through the air) when the print hammer is not in contact with the pole faces.
A droppage in a power source voltage below a prescribed value is prevented by using an electro-magnetic device of low power consumption type in a single lens reflex camera, and at the same time when the power source voltage is lower than the prescribed value, an erroneous function prevent circuit is activated to make the control circuit of a camera electronically inoperative and an indication of warning is made.
