Linear actuator with feedback position sensor device

An electrically powered volumetric pump, comprising:

• (a) a cylinder having an input port and an output port;
• (b) a piston disposed within the cylinder and slidable along a pumping axis;
• and
• (c) a linear actuator operatively connected to drive the piston in the cylinder, the linear actuator including:
• (i) a housing assembly;
• (ii) an energizable stator supported by the housing assembly;
• (iii) elongated cylinder means of a magnetic material having means mounted about an outer circumference thereof for forming an armature with the cylinder means, the elongated cylinder means having an internally threaded bore to thereby define an armature drive cylinder;
• iv) means for rotatably supporting the cylinder means relative to the housing assembly;
• v) an actuator assembly including an output shaft operably coupled to the piston and a thread engaging portion operably coupled with the threaded bore of the cylinder means, the thread engaging portion being moved along the threaded bore of the cylinder means to provide bidirectional linear movement of the output shaft in an axis parallel to the pumping axis, the extent of the thread engaging portion being smaller than the extent of the internal threads extending along the cylinder means such that the difference therebetween defines a maximum actuation stroke for the actuator assembly, and the thread engaging portion including a plurality of transmission rollers interposed between and engaging both the output shaft and the threaded bore of the cylinder means;
• and
• (vi) rotational position sensing means for sensing the rotational position of the armature drive cylinder and providing a positional signal representative thereof.

A method of controlling linear positioning in an electrically powered linear actuator of the type including an actuator assembly movable among a plurality of positions along a linear axis by an armature drive cylinder rotatably mounted within a housing having an energizable stator disposed about the armature drive cylinder, the actuator assembly including an output shaft coupled to the armature drive cylinder through a plurality of transmission rollers interposed therebetween, the method comprising the steps of:

• (a) actuating an electrically powered linear actuator to rotate an armature drive cylinder disposed therein, including the step of transferring a force transferred to a plurality of transmission rollers by the armature drive cylinder directly to an output shaft;
• (b) sensing the rotational position of the armature drive cylinder;
• (c) determining a linear position of the actuator assembly from the sensed rotational position of the armature drive cylinder;
• and
• (d) terminating actuation of the electrically powered linear actuator when a desired linear position of the actuator assembly has been reached.

An electrically powered linear actuator comprising:

• (a) a housing assembly;
• (b) an energizable stator supported by the housing assembly;
• (c) elongated cylinder means of a magnetic material having means mounted about an outer circumference thereof for forming an armature with the cylinder means, the elongated cylinder means having an internally threaded bore to thereby define an armature drive cylinder;
• (d) means for rotatably supporting the cylinder means relative to the housing assembly;
• (e) an actuator assembly including an output shaft and a thread engaging portion operably coupled with the threaded bore of the cylinder means, the thread engaging portion being moved along the threaded bore of the cylinder means to provide bidirectional linear movement of the output shaft, the extent of the thread engaging portion being smaller than the extent of the internal threads extending along the cylinder means such that the difference therebetween defines a maximum actuation stroke for the actuator assembly, wherein the thread engaging portion includes:
• (1) a plurality of transmission rollers circumferentially spaced about a portion of the output shaft and axially aligned therewith, the rollers including camming surfaces, the internal threads of the cylinder means contacting the camming surfaces to move the transmission rollers along the threaded extent of the cylinder means in response to the selective rotation of the armature drive cylinder;
• and
• (2) surfaces along a portion of the output shaft which are engaged by the camming surfaces of the transmission rollers to cooperatively move the output shaft along the threaded extent of the cylinder means in combination with the transmission rollers, wherein the force transferred to the transmission rollers is directly transferred to the output shaft;
• and
• (f) rotational position sensing means for sensing the rotational position of the armature drive cylinder and providing a positional signal representative thereof.

An electrically powered volumetric pump, comprising:

• (a) a cylinder having an input port and an output port;
• (b) a piston disposed within the cylinder and slidable along a pumping axis;
• (c) a linear actuator operatively connected to drive the piston in the cylinder, the linear actuator including:
• (i) a housing assembly;
• (ii) an energizable stator supported by the housing assembly;
• (iii) elongated cylinder means of a magnetic material having means mounted about an outer circumference thereof for forming an armature with the cylinder means, the elongated cylinder means having an internally threaded bore to thereby define an armature drive cylinder;
• (iv) means for rotatably supporting the cylinder means relative to the housing assembly;
• (v) an actuator assembly including an output shaft operably coupled to the piston and a thread engaging portion operably coupled with the threaded bore of the cylinder means, the thread engaging portion being moved along the threaded bore of the cylinder means to provide bidirectional linear movement of the output shaft in an axis parallel to the pumping axis, the extent of the thread engaging portion being smaller than the extent of the internal threads extending along the cylinder means such that the difference therebetween defines a maximum actuation stroke for the actuator assembly;
• and
• (vi) rotational position sensing means for sensing the rotational position of the armature drive cylinder and providing a positional signal representative thereof;
• (d) input and output valves configured to selectively allow fluid communication through the input and output ports, respectively, wherein when the linear actuator moves the piston in a first direction, flow is induced from the input port to the cylinder, and when the linear actuator moves the piston in a second direction, flow is induced from the cylinder to the output port;
• and
• (e) control means, operatively connected to the linear actuator and the input and output valves, for coordinating actuation of the linear actuator and the input and output valves, wherein the control means opens the input valve when the linear actuator is actuated to move the piston in the first direction and wherein the control means opens the output valve when the linear actuator is actuated to move the piston in the second direction.