A control circuit for an electromagnetic cutting apparatus includes auxiliary power impulse systems and auxiliary condensers for accelerating an already moving plunger of the cutting apparatus. The basic control circuit includes photoelectric sensors for sensing the leading and trailing edges of components. The sensors are part of an electronic circuit for rapidly charging a coil surrounding a core on the plunger for driving a blade downwardly to cut the tape. Condensers in the electronic circuit are normally charged and, in response to signals from the photoelectric sensors, instantaneously discharge into the coil to actuate the plunger. The auxiliary power impulse systems and auxiliary condensers are controlled by timers for discharging the auxiliary condensers into the coil a short time after the condensers of the basic circuit and while the plunger is moving to accelerate the latter.
A synchronized subharmonic controller for a dual coil electromagnetic vibrator, which derives both power and timing from a single phase AC line, having a trigger circuit which operates the coils at one-third the power line frequency. A timing circuit is optically coupled to alternately fire a pair of oppositely-directed SCR's with each SCR connecting one of the coils across the AC line. The optical coupling reduces feedback from the coil circuitry to the timing circuit. A pair of capacitors supply additional power to operate the coils and to reduce the peak values of current supplied by the power line.
An electromagnet hammer of the type described in U.S. Pat. No. 4,215,297 is autosynchronized by triggering the discharge thyristor in response to the detection of the position of the armature by a proximity detector, or by direct detection of the zero passage of the negative amplitude of the discharge current, or at a reference point representing the position of the armature, with a delay equal to at least half the period of the natural period of oscillation of the armature/plunger and its elastic suspension.
To obtain high accuracy of the control current in spite of tolerances of operation of the positioned element, a current mirror circuit (18) is provided having two current paths (17, 23). A low resistance resistor (11) is connected in series with the positioned element and the first current path (17) of the current mirror circuit. A command element (22) is connected in the second current path (23) of the current mirror circuit and connected to a command value--actual value comparator (24, 26). Thus, high accuracy of operation and control current is obtained in spite of wide tolerances of the positioning element. Losses in the system are minimized by using pulse width--modulated control thereof.
