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, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)


TITLE OF THE INVENTION
Former of a winding machine for making shunt field coils
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Moudghil Ashish Saurabh of Crompton Greaves Ltd, Engineering, M7 Division, Madhya Pradesh, 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 a former of a winding machine for making shunt field coils
BACKGROUND OF THE INVENTION
Heavy duty DC machines like DC motors include a stator comprising a shunt field coil mounted on a stator body. A shunt field coil is generally rectangular in shape and is made by winding a conductor coil around a former with a window formed within. The former is rotatably mounted on the winding machine to facilitate winding of the shunt field coil on the former. The width and thickness of the wound coil structure and window size are critical for proper mounting of the shunt field coil on the stator body and for the efficient performance of the stator. In one configuration of the former, the former comprises four spaced guide pins held between a bottom plate and a top plate and forming the four corners of the shunt field coil to be wound. The shunt field coil is wound around the guide pins during the rotation of the former on the winding machine. Due to the gaps between the pins, it is extremely difficult to maintain uniformity in the thickness and width of the winding and the size of the window within the winding. It is also extremely difficult to maintain perfect rectangularity of the winding, especially at the corners due to the unyielding or unbending nature of the conductors at the corners formed by the pins. This requires hammering during winding as well as during assembly of the field coil on the stator body and as a result productivity is reduced. Also the resin being applied during winding, invariably forms bubbles at the sides of the winding, especially at the inner side thereof. These bubbles will affect the uniformity of the window within the winding. As result of dimensional inaccuracy of the coil resulting from thickness and width variations
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and window size variation, fitment of the coil in the stator body becomes problematic. In another configuration of the former, a solid metallic block, generally rectangular in shape, is sandwiched between the bottom and top plates to form a former element around which conductor coil is wound to form the shunt field coil. Such a block is very heavy and requires a lot of man power for handling. It also increases the material cost of the former. Further, all the four sides and the top and bottom surfaces of the block are also required to be machined to achieve perfect dimensional accuracy of the shunt field coil in thickness, width and window size. Maching of the top and bottom surfaces of the block are necessary to maintain parallelarity between the bottom and top plates. Machining is also expensive and increases the cost and time, besides resulting in wastage of material.
OBJECTS OF THE INVENTION
Another object of the invention is to provide a former of a winding machine for making shunt filed coil, which former produces shunt field coils of excellent dimensional accuracy and eliminates hammering and increases productivity.
Another object of the invention is to provide a former of a winding machine for making shunt field coils, which former reduces the material cost and efforts for handling the former.
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Another object of the invention is to provide a former of a winding machine for making shunt field coil which is easy to manufacture and reduces the manufacturing cost and time and wastage of material..
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a former of a winding machine for making shunt coils, the former comprising a former element sandwiched between a bottom plate and a top plate, wherein the former element comprises a block formed with atleast one window within.
The following is a detailed description of the invention with reference to the accompanying drawings, in which Figs 1 and 2 are assembled and disassembled views of a former of a winding machine for making shunt field coils according to an embodiment of the invention. The former 1 as illustrated in Figs 1 and 2 of the accompanying drawings comprises a former element 2 sandwiched between a bottom plate 3 and a top plate 4. The former element comprises a rectangular block and is formed with a rectangular window 5 within. The former is also formed with bolt holes 6 matching with bolt holes 7 in the bottom plate and bolt holes 8 in the top plate. The former element and the top and bottom plates are held together with the former element sandwiched between the bottom plate and top plate with bolts 9 tightened in the bolt holes. The former element also comprises a pair of spaced ribs 10 formed across the window and provided with stud holes 11 matching with stud holes 12 in the bottom plate and stud holes 13 in the top plate. The former is mounted
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on a winding machine (not shown) with studs (not shown) tightened in the stud holes in the former element and top and bottom plates and in the winding machine. During rotation of the former on the winding machine, conductor coil is wound on the former with application of resin in the usual manner. According to the invention, the window extends over substantial area of the former element and only the sidewalls of the window of the former element are required to be machined on ail the surfaces to achieve perfect dimensional accuracy of the former element and the coil being wound on the former element. The window size of the wound coil will remain dimensionally accurate because of the four side walls of the former element being dimensionally accurate. The thickness and width of the wound coil will also be dimensionally accurate as the coil is getting wound on the four side walls of the former element. There is perfect parallelarity between the inner surfaces of the bottom and top plates because of the uniform and even top and top surfaces of the side walls of the former element. As a result, the dimensional accuracy of the field coil is maintained during winding, hammering is avoided, productivity is increased and fitment of the field coil on the stator body is rendered easy and convenient. The coil can be easily bent against the corners of the former element. The resin being applied during the winding of the coil does not form bubbles on the inner surfaces of the coil because of the inner surfaces of the coil being in close contact with the evenly and uniformly machined four sides of the former. As a result of this also, the window size of the wound coil is maintained. Because of the window within the former element, the weight and material cost of the former element are considerably reduced. Handling of the former element is much easier. Man power required for handling the former element is also considerably reduced. Because of the window within the former element, the surface area to be
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machined is considerably reduced. As a result machining time and cost are reduced. Wastage of material is also reduced. The former element is preferably made of steel which is mechanically very strong, easy to clean and maintain. However, the former element can be made of any other mechanically strong and easy to clean and maintain material. The former element need not be rectangular. The shape of the former element and the shape of the window within the former element will depend upon the shape of the field coil. There can be more than one window and more than one rib within the window. The former can be assembled together by any other known means besides using bolts. The former can be mounted on the winding machine by any other means besides using studs. Such variations of the invention are obvious to those skilled in the art and the scope of the invention should be construed and understood accordingly.
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We claim:
1. A former of a winding machine for making shunt coils, the former comprising a former element sandwiched between a bottom plate and a top plate, wherein the former element comprises a block formed with atleast one window within.
2. The former as claimed in claim 1, wherein the forming element is rectangular shape and is formed with a rectangular window within and a plurality of bolt holes matching with boit holes in the bottom plate and top plate for bolting the former element and the top plate and bottom plate together with the former element sandwiched between the bottom plate and top plate, the former element further comprising a pair of spaced reinforcing ribs across the window, the ribs being formed with stud holes matching with stud holes in the bottom plate and top plate for mounting the former on the winding machine with studs.
3. The former as claimed in claim 1 or 2, wherein the window extends over substantial area of the block.
4. The former as claimed in anyone of claims 1 to 3, wherein the former is made of steel.
Dated this 22nd day of December 2008
(Jose M A)
ofKhaitan&Co
Agent for the Applicants
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