Spring return worm gear drive actuator and method

Abstract

A worm gear drive actuator having an output gear for controlling movement of a component between a default position and an activation position. The actuator includes a spring return connected to a return gear mounted in meshing engagement with a spur gear coaxially mounted to one end of the worm. As the worm is driven by a motor to rotate the output gear and thus the component to the activation direction, the spring turns and accumulates a torsional load. When the motor is deactivated, the spring releases its torsional load which rotates the return gear, spur gear, worm and output gear in the opposite direction which returns the component to its default position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of a spring return drive actuator in accordance with an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, an electrically driven actuator 10 is seen having a housing 12 encasing the various components of the actuator 10. An output gear 14 is mounted in the housing 10 and includes an output shaft 16 for connecting to a component to be rotated such as a butterfly valve, for example (not shown). A worm gear 18 is mounted in housing 12 in meshing engagement with output gear 14. Worm gear 18 includes a first end 18a and second end 18b, the first end 18a adapted for connecting to an electric DC motor 20 for driving worm gear 18 in an activation rotational direction.

A spur gear 22 is coaxially connected to worm gear second end 18b and is rotatable with the worm gear 18. A return gear 24 is mounted in meshing engagement with spur gear 22. A return spring 26 has a first end 26a connected to and moveable with return gear 24 and a second end 26b which is fixed relative to the housing 10 and thus not movable with return spring 26. Upon activation of motor 20, motor 20 rotates worm gear 18 which in turn rotates spur gear 22 which in turn rotates return gear 24 which causes return spring 26 to turn and accumulate a torsional load. The tensioned return spring 26 biases return gear 24 in a default rotational direction opposite to the activation rotational direction. Upon deactivation of motor 20, return spring 26 releases its torsional load thereby rotating return gear 24, and thus also spur gear 22, worm gear 18 and output gear 14, in the default rotational direction.

The ratio between return gear 24 and spur gear 22 is relatively high to allow a relatively large rotational movement of the spur gear 22 and worm gear 18 with a relatively small rotational movement of the return gear 24. As such, spring 26 need only be turned a small amount to accumulate the torsional load necessary to move the gears and ultimately the valve blade to its default position. In one embodiment, the spur gear 22 may have a diameter approximately the same size as the diameter of the worm gear 18 while the return gear 24 has a diameter which is more than twice the diameter of the worm and spur gears.

While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have the full scope as defined by the language of the following claims.

Claims

1. An electrically driven actuator comprising: a) an output gear;b) a worm gear in meshing engagement with said output gear, said worm gear having first and second ends, said first end adapted for connecting to an electric motor for driving said worm gear in an activation rotational direction;c) a spur gear coaxially connected to and rotatable with said worm gear second end;d) a return gear in meshing engagement with said spur gear; ande) a return spring having a first end connected to and moveable with said return gear and a second end which is fixed and not movable with said return spring, said return spring rotating and accumulating a torsional load upon said motor driving said worm gear in said activation rotational direction,whereby said torsionally loaded return spring biases said return gear in a default rotational direction opposite to said activation rotational direction, said return gear thereby rotating said spur gear, said worm gear and said output gear in said default rotational direction.

2. The actuator of claim 1 wherein said spur gear has a diameter approximately equal to the diameter of said worm gear.

3. The actuator of claim 2 wherein said return gear has a diameter more than twice the diameter of said spur gear.

4. A method of controlling movement of a component between a default position and an activation position, said method comprising the steps of: a) providing an output gear;b) providing a worm gear in meshing engagement with said output gear, said worm gear having first and second ends, said first end adapted for connecting to an electric motor for driving said worm gear in an activation rotational direction which moves said component to said activation position;c) providing a spur gear coaxially connected to and rotatable with said worm gear second end;d) providing a return gear in meshing engagement with said spur gear; ande) providing a return spring having a first end connected to and moveable with said return gear and a second end which is fixed and not movable with said return spring, said return spring rotating and accumulating a torsional load upon said motor driving said worm gear in said activation rotational direction,whereby said torsionally loaded return spring biases said return gear in a default rotational direction opposite to said activation rotational direction, said return gear thereby rotating said spur gear, said worm gear and said output gear in said default rotational direction which moves said component to said default position.

5. The method of claim 4 wherein said spur gear has a diameter approximately equal to the diameter of said worm gear.

6. The method of claim 5 wherein said return gear has a diameter more than twice the diameter of said spur gear.