Abstract: An electromechanical chest compressor is provided with a reciprocating member for contacting a patient's chest; the reciprocating member extends from and retracts into a housing positioned on a patient's chest maintained in contact with a patient by a circumscribing thoracic cavity belt. The reciprocating member is driven by a follower in contact with a rotating drive screw. The drive screw is mounted coaxially with and internally of a permanent magnet DC motor and is connected to the motor's rotor. The current supplied to each of the individual stator windings of the motor is independently controlled by a control system that accesses addresses in a look-up table to determine the value of the current to be supplied to the individual windings.

Abstract: A field control for permanent magnet motors is provided with a memory lookup table containing several addresses corresponding to each coil of the motor. Each address corresponds to the value of current to be supplied to the corresponding coil at the moment that the address location is interrogated. The address to be addressed is modified by a phase shifter to alter the value of the current to be supplied to the corresponding coil. The phase shifter modifies the address being accessed to thereby access an address representing a greater or lesser value of the current being supplied to the corresponding coil. The modification of the address being accessed results in the modification of the current being supplied to the corresponding coil to minimize the total current being supplied to the motor under the given RPM and load conditions.