Apparatus for monitoring the action of electromagnetically operated printing hammers

Claim 2

Apparatus for monitoring the operation of printing hammers in printers, each hammer being operable by an electromagnet having a coil and an armature wherein each printing hammer is provided with an actuating element which in the vicinity of the point of motion reversal of the hammer operates the armature associated with the electromagnet to induce a voltage pulse in the coil of the electromagnet, and evaluating means coupled to said coil to indicate that the hammer has made a printing stroke.

Claim 3

Apparatus according to claim 1, wherein said magnet armature is a lever and said actuating element comprises a wedge-shaped projection on said hammer and which adjacent the point of hammer motion reversal deflects the magnet armature relative to the core.

Claim 4

Apparatus according to claim 1, wherein the magnet armature is one arm of a two-armed lever, the other arm extending into the path of the actuating element.

Claim 5

Apparatus according to claim 3, wherein each said hammer includes a holding member and said apparatus further includes a compression spring, means holding the printing hammer in a normal cocked position against the thrust of said spring by one arm of said lever, said one arm having a hook-shaped end engaging said holding member said one arm being deflected to operate the printing hammer when the state of excitation of the magnet is changed, the actuating element comprising a ramp cooperation with the other arm to restore the two-armed lever to its position of rest when the printing hammer reaches the point of motion reversal.

Claim 6

Apparatus according to claim 4, including a spring attached to said other arm to oppose the force of the magnet on said one arm but which develops a force less than the force of attraction of the magnet, and that the current for energizing the magnet is so changed in time that the retaining force of the magnet on said one arm at the instant said other arm causes said one arm to be forcibly retracted from the magnet in the region of the point of hammer motion reversal is in the range of one-fifth to one-tenth of the initial force of attraction of the magnet.