FORM 2 THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
System and method for designing a cam profile
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Dutta Ujjal of Crompton Greaves Ltd, S3 Division, Switchgear Complex, A-3, MIDC, Ambad, Nashik-422010, Maharashtra, India; an Indian National.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

Field of the Invention:
This invention relates to the field of mechanical engineering and mathematical modeling relating to mechanical assemblies.
Particularly, this invention relates to a cam and system and method for designing a cam profile.
Background of the invention:
Cams are used in Circuit Breakers to utilize the energy stored in the closing spring for charging the tripping spring as well as closing the breaker efficiently. It plays a pivotal role in important working conditions of the circuit breaker, typically during its closing operation.
Closing operation of a Circuit Breaker is described as follows: Once the closing command of the Circuit breaker is given to the closing coil, it pushes the close holding trigger. Following this action, the closing spring is free to move. The closing spring is connected to the cam shaft with the help of a link such that as the closing spring begins to discharge the cam, it starts to rotate. After a few degrees of rotation of the cam, it hits the follower connected to the main shaft lever. The main shaft lever has three arms; one connected to the tripping spring, one connected to the interrupter and one connected to the follower. Rotation of the follower simultaneously charges the tripping spring as well as closes the interrupter. At the end of the operation, the Trip Holding Latch prevents the reverse movement of the

Main Shaft Lever, thus, preventing the breaker from opening and holding the trip spring in charged condition.
An efficient design of a circuit breaker acknowledges the following working parameters:
1) halfclose condition
2) overtravel and Closing Operation (CO) condition
3) C2 speed
Half Close in a Circuit Breaker:
This condition occurs when the Cam is not able to push the follower after a certain amount of rotation of the Main Shaft Lever. The primary cause is that one the Tripping Spring force equals the Closing Spring force the momentum of the Cam is not sufficient to push it further.
CO in a circuit Breaker:
In an ideal condition at the end of the Closing Operation the rotation of the main shaft lever moves the Trip Holding Latch in anti clockwise direction and the Main Shaft Lever arm on the Trip Spring Side further moves upward so that the trip holding latch has sufficient time to reset to its original position thus preventing the reverse rotation of Main Shaft Lever.
if the Main Shaft Lever is not able to move sufficiently upwards, then the Trip Holding Latch will not get sufficient time to reset as result it won't be able to hold the main shaft lever thus causing the Breaker to open instead of holding it in Closed Condition. This phenomenon is known as CO in a Circuit Breaker.

Overtravel is the excess travelling energy in the moving components which result in circuit breaker operation. An optimum amount of overtravel is necessary for providing the sufficient time as well as space for the latching system. Excess overtravel may lead to unnecessary stress in the components consisting of the latching system. On the other side less overtravel may lead to CO condition which in itself is extremely detrimental for the mechanism as well as the pole components.
Existing Breaker Cam Design is highly inefficient as the amount of energy required by the Closing Spring is very high.
The existing cams in use do serve the necessary requirements, but it was found to be energy inefficient, while optimizing the cam profile for boosting the C2 speed does serve the purpose but at the same time when the closing spring is discharged even a little halfclose condition is reached. An inefficient cam leads to having closing spring energy higher than required increasing the material cost for the components associated with closing spring as well as generating unnecessary noise and vibrations.
Prior Art:
US5310971 discloses an operating mechanism of circuit breaker , where cams are chosen to enable re-closing of the contact bridge.
US6015959 discloses the usage of cam assembly having energy storage spring mechanism.

'An Optimum Design of a Gas Circuit Breaker Using Design of Experiments', by Sung Pil Jung et al. discloses a cam profile synthesis program developed using MATLAB.
In view of the prior art, though different methods are disclosed for cam profile designs, there is no approach of studying and determining the tripping & closing spring energy balancing points with respect to time for the purpose of optimization of cam profile design in circuit breaker operation.
Objects of the Invention:
An object of the invention is to provide an improved cam profile designed to produce optimum working conditions for associated assemblies.
Another object of the invention is to achieve an optimized cam profile design for effective C2 speed and lower halfclose condition.
Summary of the Invention:
For the purposes of this specification, a cam profile is designed to provide calculated effect on its associated assemblies in mechanical communication. A cam profile, typically includes a curve in its auxiliary view and includes an 'initial loading point' which is the start point of the curve, a 'release point' which is the end point of the curve, and an intermediate 'energy balance point' which defines the degree of curvature of the curve.

According to this invention, there is provided a system for designing a cam profile, adapted to be used in a circuit breaker having a tripping spring and a closing spring, said system comprises:
a. Initial loading point sensing means adapted to sense and measure
energy at said initial loading point of a cam profile;
b. Release point sensing means adapted to sense and measure energy at
said release point of a cam profile;
c. Energy sensing means adapted to sense energy at an array of points
located in between said measured initial loading point and said
measured release point;
d. Energy measuring means adapted to measure energy at each of said
array of points with respect to tripping spring energy and closing
spring energy at each of said sensed energy balance points;
e. Energy balance sensing means adapted to sense the point at which
both the spring energies balance;
f. Curve fitting means adapted to fit a curve for said sensed initial
loading point, sensed released point with respect to sensed energy
balance point;
g. Comparator mans adapted to compare different cam profile results
with pre-defined cam results in relation to pre-defined working
parameters; and
h. Iteration means adapted to iterate steps of sensing initial loading point, release point, or energy balance point or the combination in order to achieve a fitting curve for achieving an improved cam profile.

According to this invention, there is provided a method for designing a cam profile, adapted to be used in a circuit breaker having a tripping spring and a closing spring, said system comprises:
a. Sensing and measuring energy at said initial loading point of a cam
profile;
b. Sensing and measuring energy at said release point of a cam profile;
c. Sensing energy at an array of points located in between said measured
initial loading point and said measured release point;
d. Measuring energy at each of said array of points with respect to
tripping spring energy and closing spring energy at each of said
sensed energy balance points;
e. Sensing the point at which both the spring energies balance;
f. Fitting a curve for said sensed initial loading point, sensed released
point with respect to sensed energy balance point;
g. Comparing different cam profile results with pre-defined cam results
in relation to pre-defined working parameters; and
h. Iterating steps of sensing initial loading point, release point, or energy balance point or the combination in order to achieve a fitting curve for achieving an improved cam profile.
Brief Description of the Accompanying Drawings:
The invention will now be described in relation to the accompanying drawings, in which:
Figure 1 illustrates a schematic configuration of the circuit breaker device;

Figure 2 illustrates various cam profiles; and
Figure 3 illustrates graphical representation of analysed parameters.
Detailed Description of the Accompanying Drawings:
Figure 1 illustrates a schematic configuration of the circuit breaker device. In a circuit breaker device, once the closing command of the Circuit breaker is given to the closing coil, it pushes the close holding trigger. Following this action, the closing spring is free to move. The closing spring is connected to the cam shaft (12) with the help of a link such that as the closing spring begins to discharge the cam (14), ft starts to rotate. After a few degrees of rotation of the cam, it hits the follower connected to the main shaft lever (16). The main shaft lever has three arms; one connected to the tripping spring (18), one connected to the interrupter (20) and one connected to the follower (22). Rotation of the follower simultaneously charges the tripping spring as well as closes the interrupter. At the end of the operation, the Trip Holding Latch (24) prevents the reverse movement of the Main Shaft Lever, thus, preventing the breaker from opening and holding the trip spring in charged condition.
According to this invention, there is provided a system and method for designing a cam profile.
Figure 2 illustrates various cam profiles according to this invention.

In accordance with an embodiment of this invention, there is provided an energy sensing means and an energy measuring means adapted to sense and measure the tripping spring energy and closing spring energy with respect to time.
In accordance with another embodiment of this invention, there is provided an energy balance sensing means adapted to sense the point at which both the spring energies balance. This is the energy balance point (270). It is observed that this point is achieved when it is very close to the close condition of the breaker. While optimizing the cam for boosting the C2 speed results in the energy balance point quite far away from the close condition of the breaker.
This helps in deciding the energy balance point followed by the cam profile optimization. This ensures efficiency at the same time preventing of the halfclose condition.
In initial systems and methods, to optimize the Cam it was found that the Closing speed of the interrupter was excessively high as well as huge amount of over travel leading to huge amount of stress in the Trip Holding Latch.
A further dig into the reasons helped to find that the Force Balance Point in the old Cam was very high i.e. the point where the tripping spring force point is balanced by the closing spring force. In the other highly optimized cam, it was further found that a energy balance point can be achieved where force is much low. So, in the current invention, for designing a Cam the

energy balance point is firstly designed and then the remaining design of Cam profile may be considered.
In accordance with yet another embodiment of this invention, there is provided an initial loading point sensing means adapted to sense and measure energy at said initial loading point (250).
In accordance with yet another embodiment of this invention, there is provided a release point sensing means adapted to sense and measure energy at said release point (260).
In accordance with an additional embodiment of this invention, there is provided a curve fitting means adapted to fit a curve for said sensed initial loading point, sensed released point with respect to sensed energy balance point. The fitted curve realises the profile for the new cam, in accordance with the system and method of this invention.
In accordance with yet an additional embodiment of this invention, there is provide a comparator means adapted to compare different Cam profile results are compared with the original Cam data, for various working parameters relating to halfclose condition, CO condition, C2 speed and optimum overtravel condition. In instances where comparative analysis fails for each or any of the working parameters, a new energy balance point may be sought using the above method.

In accordance with yet an additional embodiment of this invention, there is provided an iteration means adapted to iterate steps of sensing initial loading point, release point, or energy balance point or the combination in order to achieve a fit.
The new Cam profiles are obtained with a spine fit between the initial and final points.
In the case of energy balance approach a third point is figured out which is the energy balance point between the Tripping spring energy and the closing spring energy.
Reference numeral 200 refers to a cam. Reference numeral 240 refers to an original profile of a cam (in relation to prior art). Reference numeral 230 refers to a harmonic profile of a cam. Reference numeral 220 refers to a profile of a cam in accordance with this invention.
Figure 3 illustrates graphical representation of analysed parameters according to this invention. Reference numeral 310 refers to energy balance curve for old closing condition. Reference numeral 320 refers to energy balance curve for old tripping condition. Reference numeral 330 refers to energy balance curve for intermediate closing condition. Reference numeral 340 refers to energy balance curve for intermediate tripping condition. Reference numeral 350 refers to energy balance curve for new closing condition. Reference numeral 360 refers to energy balance curve for new tripping condition.

We claim,
1. A system for designing a cam profile, adapted to be used in a circuit breaker having a tripping spring and a closing spring, said system comprising:
a. Initial loading point sensing means adapted to sense and measure
energy at said initial loading point of a cam profile;
b. Release point sensing means adapted to sense and measure energy
at said release point of a cam profile;
c. Energy sensing means adapted to sense energy at an array of points
located in between said measured initial loading point and said
measured release point;
d. Energy measuring means adapted to measure energy at each of
said array of points with respect to tripping spring energy and
closing spring energy at each of said sensed energy balance points;
e. Energy balance sensing means adapted to sense the point at which
both the spring energies balance;
f. Curve fitting means adapted to fit a curve for said sensed initial
loading point, sensed released point with respect to sensed energy
balance point;
g. Comparator mans adapted to compare different cam profile results
with pre-defined cam results in relation to pre-defined working
parameters; and
h. Iteration means adapted to iterate steps of sensing initial loading point, release point, or energy balance point or the combination in order to achieve a fitting curve for achieving an improved cam profile.

2. A method for designing a cam profile, adapted to be used in a circuit breaker having a tripping spring and a closing spring, said system comprising:
a. Sensing and measuring energy at said initial loading point of a cam
profile;
b. Sensing and measuring energy at said release point of a cam profile;
c. Sensing energy at an array of points located in between said measured
initial loading point and said measured release point;
d. Measuring energy at each of said array of points with respect to
tripping spring energy and closing spring energy at each of said
sensed energy balance points;
e. Sensing the point at which both the spring energies balance;
f. Fitting a curve for said sensed initial loading point, sensed released
point with respect to sensed energy balance point;
g. Comparing different cam profile results with pre-defined cam results
in relation to pre-defined working parameters; and
h. Iterating steps of sensing initial loading point, release point, or energy balance point or the combination in order to achieve a fitting curve for achieving an improved cam profile.