BACKGROUND OF THE INVENTION

The present invention relates generally to limit switches and, more particularly, to a neutral position limit switch that includes a simplified head assembly design with less moving parts therein.

Electrical limit switches comprise a widely employed class of switching apparatus for selectively completing and/or interrupting one or more electrical connections depending upon the position of a displaceable switch-sensing member. Many electrical limit switches include a head assembly that incorporates a rotary actuator that translates rotary motion into a linear motion to actuate the limit switch. A typical head assembly has a crank or other lever for rotating an actuator shaft, and an output member driven by the actuator shaft with linear output movement. The output member engages and drives an element of the displaceable switch-sensing member for selectively completing and/or interrupting one or more electrical connections. In some embodiments, the electrical limit switch may be constructed as a neutral position switch where the actuator shaft of the head assembly is rotatable in both clockwise and counterclockwise directions for effecting movement of the output member and a corresponding translation of the displaceable switch-sensing member from a neutral position to two distinct positions in different modes.

It is recognized, however, that presently constructed head assemblies of the above described design possess certain disadvantages as far as their operating characteristics and construction are concerned. For example, neutral position limit switches where the actuator shaft of the head assembly is rotatable in both clockwise and counterclockwise directions typically require a large degree of pre-travel rotation (e.g., approaching 15-20°) of the actuator shaft before the rotation is translated into linear movement of the output member, which results in an increased switching/tripping time for the limit switch. While it is possible to reduce this large degree of pre-travel rotation, such reduction of the pre-travel rotation angle is commonly achieved by making the head assembly more complex with more moving parts, such as by having separate cam members and provision for mounting these cam members in different orientations with respect to the actuator shaft and output member to obtain the desired operation. It is thus recognized that head assemblies with such a construction include a large number of moving parts, which increases the cost and complexity of the head assembly and may lead to reliability issues in the field.

It would therefore be desirable to provide a head assembly for a neutral position limit switch require a small degree of pre-travel rotation (e.g., approaching 5°) of the actuator shaft before the rotation is translated into linear movement of the output member, in order to provide a quicker switching/tripping time for the limit switch. It would further be desirable for the head assembly to achieve this reduced degree of pre-travel rotation via a simplified head assembly design with a reduced number of moving parts that would require less time and cost for assembly thereof and that would enhance reliability of the limit switch due to the reduction of moving components therein.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one aspect of the invention, an operating head for providing actuation in a limit switch includes a housing, a shaft rotatable in clockwise and counter-clockwise directions, a cam member supported on the shaft and that is rotatable in the clockwise and counter-clockwise directions responsive to rotation of the shaft, and a follower actuated by the cam member responsive to rotation of the cam member in the clockwise and counter-clockwise directions, with the follower further including a pivot pin secured to the housing, a lever portion positioned on the pivot pin and pivotable thereabout in opposing directions, and a rolling pin mounted to the lever portion and in contact with the cam member. The operating head also includes an actuator member in contact with the lever portion and that translates linearly in a first direction or a second direction responsive to the pivoting of the lever portion. The rolling pin moves along a profile of the cam member upon rotation of the cam member in the clockwise or counter-clockwise direction so as to cause the lever portion to pivot, with the actuator member linearly translating in the first direction or the second direction responsive to the pivoting of the lever portion.

In accordance with another aspect of the invention, an electrical limit switch includes a switch subassembly having a plurality of fixed electrical terminals and a contact carrier comprising electrical contacts thereon, the contact carrier movable between a plurality of distinct switching positions to selectively shift a location of the electrical contacts to different electrical terminals to make and break different circuits in the switch subassembly. The electrical limit switch also includes an operating head subassembly having a shaft rotatable in clockwise and counter-clockwise directions, a cam member supported on the shaft and that is rotatable in the clockwise and counter-clockwise directions responsive to rotation of the shaft, an actuator member configured to move linearly in a first direction or a second direction responsive to rotation of the cam member in the clockwise or counter-clockwise direction to cause a corresponding movement of the contact carrier, and a follower in contact with each of the cam member and the actuator member to translate rotation of the cam member in the clockwise or counter-clockwise direction into linear movement of the actuator member in the first or second direction, with the follower directly actuating the actuator member.

In accordance with yet another aspect of the invention, an operating head for providing actuation in a limit switch includes a shaft rotatable in clockwise and counter-clockwise directions, a cam member supported on the shaft and that is rotatable in the clockwise and counter-clockwise directions responsive to rotation of the shaft, and an actuator member that moves linearly from a normal position in a first direction or a second direction responsive to rotation of the cam member in the clockwise or counter-clockwise direction, the actuator member movable between a first actuated position and a second actuated position. The operating head also includes a follower in contact with each of the cam member and the actuator member to translate rotation of the cam member in the clockwise or counter-clockwise direction into linear movement of the actuator member in the first or second direction. In operation of the operating head, there is approximately 5° of pre-travel rotation of the shaft to move the actuator member to the first actuated position and the second actuated position.

Various other features and advantages of the present invention will be made apparent from the following detailed description and the drawings.

