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THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - A RACK-PINION BASED MECHANISM FOR ELECTRICAL SWITCHING DEVICE
2. Applicant(s)

(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY: An Indian Company.
(c) ADDRESS: L & T House, Ballard Estate, Mumbai 400 001,
State of Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
The present invention relates generally to actuating mechanisms for low voltage switchgear, and more particularly, to actuating mechanisms for low voltage contactor,
BACKGROUND OF THE INVENTION
As per the current scenario in electrical switching devices a typical actuating mechanism of the prior art is bulky, involving large number of components and hardware, which makes it difficult to assemble. Further, particularly in case of vacuum contactors the vacuum interrupters for multiple phases (i.e. here, 3 phases) are to be aligned so that they operate at the exact same instant, which is difficult to achieve in the presently available mechanisms.
For instance, US 5069077 discloses an actuating mechanism for a vacuum-type interrupter with a contact spring. The actuating mechanism of a vacuum-type interrupter has a pivotally positioned two-armed lever and a spring which holds the contact force ready and which engages with the lever. The two-armed lever is guided with limited displacement in a bearing in a direction which runs approximately parallel to the actuation direction of the interrupter. While enabling, the two-armed lever pivots about a bearing bolt around the end of the bolt guiding until the contact elements engage each other. The further pivoting of the lever takes place around a linkage assembly between the two-armed lever and the actuating impact rod. The two-armed lever can be formed from two parallel split levers with a clearance such that the spring can engage between the split levers. The actuating mechanism is suitable for one or multiple vacuum circuit breakers, e.g., for use in gas insulated switchgear.
US 4247745 A (corresponding to application no.GB2030777) disclosed a vacuum-type contactor assembly is provided having an operating linkage such that a fault, or heavy overload currents, will cause a maintenance of the contact-closed position, and a pair of springs are provided in the operating linkage, one of which is purely an atmospheric pressure compensating, or "kickoff, spring, whereas the other is a heavy contact pressure spring compressed following contact closure, and serving to provide both a hammer action at contact separation to break any welds occurring at the contact

structure, and an accelerating force during contact opening. Preferably, an electromagnetic actuating mechanism is utilized to affect the short travel and high contact forces typically required by vacuum-type switches.
However, the aforesaid mechanisms in the prior art suffer from drawbacks of complex assembly and lower efficiency.
The present invention overcomes these limitations by providing a simpler, more robust and more efficient mechanism involving rack pinion arrangement, which is effectively used to convert the forces and displacements in different planes to achieve different travels of the actuation system and the contact system. The mechanism of the present invention has a fewer number of components than in the prior art mechanism, which are interlinked without much use of hardware, which makes the mechanism easy to assemble in its housing with other sub assemblies.
OBJECTS OF THE INVENTION
The object of the invention is to overcome the above-specified disadvantages/drawbacks of the prior art by providing a rack-pinion based mechanism for electrical switching device.
The advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

In one aspect of the present invention, there is provided an actuating mechanism for an electrical switching device, said system comprising:
an actuator raovably connected to a spring arrangement;
a substantially vertical rack bridge means and a substantially horizontal rack bridge means, said bridge means being in co-operative engagement with said actuator such that movement of the said actuator facilitates upward and downward movement of said bridge means;
a gear assembly operatively coupled with said actuator, said gear assembly being movable corresponding to the movement of said actuator;
wherein said gear assembly comprises a small pinion and a large pinion mounted on a shaft assembled with said horizontal rack bridge and vertical rack bridge respectively, which provide actuating mechanism between said actuator and a contact system of the electrical switching device.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.
Figure 1 shows the layout of the mechanism and how it couples the actuator to the contact system. The working is explained below.

Figure 2 shows the mechanism of the present invention when the switching device is in ON condition.
Figure 3 shows the mechanism of the present invention when the switching device is in OFF condition.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.
Throughout the drawings, it should be noted that like reference numerals are used to depict the same or similar elements, features and structures.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.
Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.
By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.
It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
Accordingly the present invention provides a rack pinion based actuating mechanism for an electrical switching device. The mechanism is designed to serve the basic function of an electrical switching device and acts as a coupler to the actuator and the contact system of the switching device. The gear assembly comprising the pinions is mounted on the shaft is assembled into the housing by locating the shaft alone. Then the vertical rack bridge is assembled onto the larger pinions. Then the horizontal racks are assembled onto the smaller pinions and coupled to the contact system.
The diameters of the pinions were selected in such a way that the gear ratio obtained provided the desired ratio of actuator travel and the contact travel. The ratio of diameters of the pinions decides the gear ratio which directly gives the ratio in which the displacement of the actuator is related to the displacement of the contact system. If the ratio is 3:1, it means that the contact travel is 1 mm when the actuator travel is 3

mm. This reduction ratio is needed as the desired contact travel is less as compared to the designed actuator travel.
Switching on:
When the switching device is turned on, Actuator (1) moves in the downward direction. Vertical Rack Bridge (2) moves along with Actuator (1) being coupled together with fasteners. Rack Bridge (2) meshes with Larger pinion(5) and rotates in clock-wise sense as seen in Figure 1. Being on the same shaft, Smaller pinion (3) rotates by the same angle. Meshed with the Horizontal rack (4), it translates in right direction as seen in Figure 1. This translation makes the contacts, housed in (6) and the device is ON
As per figure 1, the pinions along with the shaft will rotate in clockwise direction, looking from the direction in which the vacuum interrupter (6). Then once the vertical rack bridge (2) moves down, it rotates the large pinion and hence the shaft in clockwise sense, which in turn translates the horizontal rack (4) to the right, thereby closing the contacts in the vacuum interrupter. This is device on state.
Switching Off:
When the device is turned off, the Actuator (1) returns to its original position by spring arrangement. There are compression springs which are connected to the actuator (1). Once the device is turned off, i.e. the supply to the actuating coil is cut off, the springs which are compressed when the device is on, return to their original position by pushing the actuator (1) upwards. By this the mechanism returns back to its original position. The position of the springs is shown in figure 3. Through the coupling of the proposed mechanism, the racks return to their original position and the contacts are broken, the device is OFF.
ADVANTAGES:
1. More efficient coupling mechanism as compared to existing ones, since in the existing systems the linear motion is converted to rotary motion and converted

back to linear motion using cam type joints. Whereas in the current case, this is achieved using rack pinion mechanism where efficiency of conversion is very high.
2. Extremely easy assembly as compared to currently available mechanism assemblies.
3. Intricate shapes of components to achieve cam type joint is eliminated
4. Longer life as compared to lever actuated mechanisms because of optimized force requirements due to rack - pinion mechanism. Rack-pinion based mechanism provides higher efficiency as compared to cam based mechanism.
5. In order to achieve the synchronization between the travels of the actuator and the contact system, the existing mechanisms incorporate a large leverage, which increases the overall size of the device. Whereas in the present invention it is achieved by the right combination of racks and pinions to suit the travels of actuator and contact system, thereby reducing the dimensions of the device. Hence a compact system is developed.

WE CLAIM:
1. An actuating mechanism for an electrical switching device, said system
comprising:
an actuator (1) movably connected to a spring arrangement;
a substantially vertical rack bridge means (2) and a substantially horizontal rack bridge means (4), said bridge means (2 and 4) being in co-operative engagement with said actuator such that movement of the said actuator facilitates upward and downward movement of said bridge means (2);
a gear assembly operatively coupled with said actuator, said gear assembly being movable corresponding to the movement of said actuator;
wherein said gear assembly comprises a small pinion (3) and a large pinion (5) mounted on a shaft assembled with said horizontal rack bridge (4) and vertical rack bridge (2) respectively, which provide actuating mechanism between said actuator and a contact system of the electrical switching device.
2. The mechanism as claimed in claim 1, wherein said horizontal rack bridge (4) is coupled with said contact system (6).
3. The mechanism as claimed in claim 1, wherein said vertical rack bridge (2) is coupled with said actuator (1).
4. The mechanism as claimed in claim 1, wherein when said switching device is switched ON , said actuator (1) moves downward thereby said vertical rack

bridge (2) moves downward resulting into rotating of said larger pinion (5) clockwise interconnected with said vertical rack bridge (2).
5. The mechanism as claimed in claim 4, wherein said large pinion (5) and said small pinion (3) connected on the same shaft results into rotation of the small pinion in clockwise direction with same angle.
6. The mechanism as claimed in claim 5, wherein said horizontal rack bridge (4) being connected with said small pinion (5) translates into right direction results into coupling of contact between actuator (1) and contact system(6).
7. The mechanism as claimed in claim 1, wherein when said switching device is switched OFF , said actuator (1) moves upward by said spring arrangement thereby said vertical rack bridge (2) moves upward resulting into rotating of said larger pinion (5) anti-clockwise interconnected with said vertical rack bridge (2).
8. The mechanism as claimed in claim 7, wherein said large pinion (5) and said small pinion (3) connected on a same shaft results into rotation of said small pinion (3) in anti-clockwise direction with same angle.
9. The mechanism as claimed in claim 8, wherein said horizontal rack bridge (4) being connected with said small pinion (5) translates into left direction results into breaking of contact (s) between actuator (1) and contact system{6).

10. The mechanism as claimed in claim 1, wherein diameters of said large pinion (5) and small pinion (3) is selected in a way to provide a gear ratio.
11. The mechanism as claimed in claim 10, wherein said gear ratio provides a desired ratio of actuator travel and contact travel.