Constant energy drive circuit for electromagnetic print hammers
AssigneeInternational Business Machines Corporation
InventorRobert W. Arnold
Life of this patent
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Abstract
A constant energy drive circuit for an electromagnetic print hammer has a chopping circuit including a comparator which cycles a switch connecting the energizing coil of the print hammer to an unregulated power supply. Changes in the drive voltage of the unregulated source are compensated for by altering the switching rate of the switch by adjusting the amplitude of a reference signal applied to the comparator. The reference signal adjustment is inverse to changes in the drive voltage.
Claims13
A constant energy drive circuit for an electromagnet having a coil connectable to an unregulated source of drive voltage by a switch means activated by a turn on signal of fixed time duration causing current to flow in said coil, and a chopping circuit means for cycling said switch means activatable at a preset level of current in said coil during said time duration for chopping the current in said coil during said time duration at an average peak current for at least a portion of the remainder period of said time duration, characterized by,
- said chopping circuit including means for altering the switching rate of said switch means in response to changes in said drive voltage to vary the average peak current in said coil during said remainder period to compensate for changes in the drive voltage of said source.
A constant energy drive circuit for an electromagnet comprising
- an inductive coil,
- switch means having an open and a closed state for operatively connecting an unregulated source of drive voltage in circuit with said coil,
- current sense means for providing a sense signal indicative of the level of current in said coil,
- reference signal means associated with said source of drive voltage for providing a threshold signal the level of which establishes the threshold level of current in said coil,
- means for enabling said switch means to a closed state in response to a turn on signal of fixed time duration representing the total time for energizing said coil,
- chopping circuit means for cycling said switch means between said open and closed states including means for generating cycling signals in response to periodically occurring correspondence between said sense and reference signals,
- means responsive to said cycling signals from said chopping circuit means for cycling said level of said threshold signals from said reference signal means to said chopping circuit means, and
- means associated with said reference signal means for changing the amplitude levels of said threshold signals inversely in response to changes in said drive voltage.
A constant energy drive circuit for an electromagnet comprising
- a coil
- switch means having an open and a closed state for operatively connecting an unregulated source of drive voltage in circuit with said coil,
- current sense means for providing a sense signal the level of which is indicative of the level of the current in said coil,
- means for enabling said switch means to a closed state in response to a turn on signal having a fixed time duration, and
- means activated at a preset level of said sense signal for cycling said switch means between said closed and open states and for adjusting the cycling rate to compensate for changes in said drive voltage.
Dependencies are inferred from the claim text.