number of motor shaft revolutions has occurred while both motor torque and motor speed are controlled within desired ranges of values this method of pump control has the effect of providing control of discrete pump output volumes at desired output pressures and at desired pump output rates within the range of the capacity of the pump fig7 a is a schematic cross sectional view of an embodiment of a planetary roller screw 700 with a hollow central bore planetary roller screws with solid central cores are commercially available a plurality of roller screws with helical splines on the outer surfaces thereof 704 are disposed between a nut 701 and a lead screw 705 comprising a helical spline on the outer surface thereof gear teeth are provided on each end of the roller screws to mate with two ring gears 702 while circumferential spacing of the plurality of roller screws is maintained by two spacer inserts 703 fig7 b is a schematic cross sectional view of an embodiment of a recirculating roller screw 710 with a hollow central bore recirculating roller screws with solid central cores are commercially available a plurality of roller screws with circumferential grooves on the outer surfaces thereof 712 are disposed between a nut 711 and a lead screw 715 comprising a helical spline on the outer surface thereof engagement between the roller screw circumferential grooves and the lead screw helical spline is made possible through the use of even multiples of multi start threading for the helical spline circumferential spacing of the plurality of roller screws is maintained by a roller cage 713 which is held in position by two.