Patent ID: 8641390

Claim:
A linear rod pumping apparatus, for imparting reciprocating substantially vertical motion to a rod of a sucker-rod pump having a pump stroke, the apparatus comprising: a linear mechanical actuator arrangement, having a substantially vertically movable member attached to a polished rod of the sucker-rod pump for imparting and controlling vertical motion of the polished rod of the sucker-rod pump, the linear mechanical actuator arrangement comprises: a rack and pinion gearing arrangement, with the rack being disposed for operation in a substantially vertical direction for reciprocating motion along a pumping axis; and the rack being operatively connected in gear mesh relationship with the pinion; a motor operatively connected to the vertically movable member of the linear mechanical actuator arrangement with the pinion operatively coupled to the rotating output of the motor establishing a fixed relationship between the rotational position of the motor and the vertical position of the vertically movable member with the motor configured to exert a force on the rack in one direction and in another opposite direction; and a control arrangement operatively connected to the motor, for controlling the motor, the control arrangement operates the motor in a driving mode, for applying torque to the pinion in a first direction to urge rotation of the pinion in the first direction, to urge upward movement of the rack on an upward portion of the stroke of the polished rod, and the control arrangement operates the motor in a braking mode, for applying a net torque to the pinion in the first direction for resisting rotation of the pinion in the opposite direction, during downward movement of the rack on a downward portion of the stroke of the polished rod, the control arrangement includes, sensing arrangements for sensing one or more parameters of the group of parameters consisting of: linear position of the rack along the pumping axis, rotational position of the pinion about the pinion axis, motor torque, motor speed, motor acceleration, and motor input power.