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
A fixture for assembling stator of an AC motor


APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli,
Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Bhujbal Ekanath Ramdas, Crompton Greaves Ltd, LT Motors, A6/2 MIDC Area, Ahmednagar, 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 fixture for assembling stator of an AC motor.
BACKGROUND OF THE INVENTION
An AC motor comprises a rotor rotatably mounted within a stator in spaced apart relationship therewith. Uniform air gap is required between the rotor and the stator for efficient functioning of the motor. Non-uniform air gap may also cause the rotor to rub against the stator during rotation thereof and get damaged. It may also lead to jamming of the motor. A stator comprises a wound stator pack assembled within a stator case. A fixture generally used for assembling a stator comprises a hydraulic cylinder, the piston rod of which extends upwardly through a stator case support plate. A wound stator pack is held at the top of the piston rod of the hydraulic cylinder and the hydraulic cylinder is operated to lower the wound stator pack and assemble it within the stator case located on the stator case support plate. The wound stator pack is very heavy and difficult to handle. It is lifted and held at the top of the piston rod of the hydraulic cylinder with the help of a tackle. Therefore, handling and mounting of the wound stator pack at the top of the piston rod is difficult and cumbersome. During handling of the wound stator pack, damages can occur to the wound stator pack. It can also cause accidents. While lowering the wound stator pack into the stator case, misalignment between the wound stator pack and the stator case invariably occurs due to vibrations and wobbling of the piston rod, especially due to the heavy weight of the wound stator pack. As a result, concentricity between the stator case and wound stator pack is not maintained. This will give rise to
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non-uniform air gap between the stator and the rotor and to the disadvantages discussed above. Such a fixture also cannot handle stator of different sizes.
OBJECTS OF THE INVENTION
An object of the invention is to provide a fixture for assembling stator of an AC motor, which fixture maintains concentricity between the stator case and wound stator pack.
Another object of the invention is to provide a fixture for assembling stator of an AC motor, which fixture renders assembly of the stator easy and convenient and prevents damages to the stator and accidents.
Another object of the invention is to provide a fixture for assembling stator of an AC motor, which fixture can handle stator of different sizes and has flexibility.
Another object of the invention is to provide a fixture for assembling stator of an AC motor, which fixture does not require any electric power for its operation.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a fixture for assembling a stator, the fixture comprising a support means for supporting a wound stator pack, the support means being mounted on a base plate supported on a rigid surface, a holder means for holding a stator case, the holder means being held above the support means with a stator case disposed coaxially with a wound stator pack supported on the support means,
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drive means for moving down the holder means along with the stator case held therein and engaging the stator case over the wound stator pack supported on the support means concentrically and guide means for guiding the downward movement of the holder means with the stator case.
The following is a detailed description of the invention with reference to the accompanying drawings, in which
Fig 1 is a cross-sectional view of the fixture for assembling the stator of an AC motor according to an embodiment of the invention with the piston rod of the hydraulic cum pneumatic cylinder at its extreme top position and with the stator case mounted at the top of the piston rod and the wound stator pack located on the support member mounted on the base plate;
Fig 2 is a cross-sectional view of the fixture of Fig 1 with the piston rod of the hydraulic cum pneumatic cylinder lowered and the stator case assembled over the wound stator pack; and
Fig 3 is a plan view of the fixture of Fig 1.
The fixture 1 as illustrated in Figs 1 to 3 of the accompanying drawings comprises a base plate 2 supported on a rigid surface. 3 is a closed end cylindrical support member for supporting a wound stator pack 4. The support member is provided with a collar 5
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projecting upwardly from the center of the closed end thereof and a mounting flange 6 at the opposite end thereof. The support member is removably mounted on the base plate with screws 7 tightened in screw holes (not marked but can be visualised in Figs 1 and 2) provided in the flange and corresponding screw holes (not shown but can be visualised in Figs 1 and 2) in the base plate. 8 is a hydraulic cum pneumatic cylinder located below the base plate. Four hydraulic cylinders 9 are located below the base plate around the hydraulic cum pneumatic cylinder out of which only two hydraulic cylinders can be seen in Figs 1 and 2. Mandrel 10 with the wound stator pack 4 wound thereon is held in a cup shaped member 11 with bolts 12. The cup shaped member with the wound stator pack and mandrel is supported on the closed end of the support member against the collar thereof. The over hanging portion of the windings of the stator pack are marked 13. 14 is a support plate for holding a stator case 15. The support plate is formed with a central opening 16 having a stepped side wall 17. 18 is a correspondingly profiled spigot located in the opening 16 against the stepped side wall 17. The support plate is supported at the top of the four piston rods 19 of the four hydraulic cylinders projecting upwardly through the base plate. The stator case is located on the spigot and tightly held in position at the top end of the telescopic piston rod 20 of the hydraulic cum pneumatic cylinder extending upwardly through the base plate, support member 3 and collar 5 and mandrel 10 with the help of a cap shaped member 21. The cap shaped member is tightly held in position with the help of a closed end tubular retainer member 22 having an external step 21a. The external step of the tubular member abuts against the cap shaped member and the tubular member is tightly held at the top end of the telescopic piston rod of the hydraulic cum pneumatic cylinder with a screw 23 tightened in a corresponding hole
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(not shown but can be visualised in Figs 1 and 2) at the top end of the telescopic piston rod through a hole (not marked but can be visualised in Figs 1 and 2) in the closed end of the tubular member. The wound stator pack and stator case are held coaxially. The stator case is lowered and assembled onto the wound stator pack by operating the hydraulic cum pneumatic cylinder and the hydraulic cylinders. While the stator case is being lowered, the downward movement of the stator case is guided and balanced by the piston rods of the hydraulic cylinders. Therefore, the downward movement of the stator case is not subjected to vibrations and wobbling and is smooth. As a result the concentricity between the stator case and wound stator pack is maintained. After the stator case is fully assembled onto the wound stator pack, the cap shaped member and the tubular member are disassembled from the telescopic piston rod of the hydraulic cum pneumatic cylinder by removing the screw 23. The telescopic piston rod of the hydraulic cum pneumatic cylinder and the piston rods of the hydraulic cylinders are retracted to their extreme bottom position below the stator level and the stator with the cup shaped member is removed from the support member for further processing. The telescopic piston rod of the hydraulic cum pneumatic cylinder reduces the overall height of the fixture in its non-operative position.
According to the invention, the wound stator pack and the stator case of the stator are assembled together maintaining their concentricity. Besides, the wound stator pack which is heavy and difficult to handle is located on the support member supported on the base plate and the stator case which weights comparatively less is mounted at the top of the telescopic piston rod of the hydraulic cum pneumatic cylinder. Therefore,
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handling of the wound stator pack is easy and convenient. Damage to the wound stator pack during handling is eliminated. Accidents are also prevented. The invention does not require a tackle to hand the wound stator pack. The spigot can be changed to handle stator of different sizes. Therefore, the fixture of the invention has flexibility. It also does not require any electric power for its operation and is compact because of the telescopic piston rod.
The stator case can be mounted at the top end of the telescopic piston rod of the hydraulic cum pneumatic cylinder with a different arrangement. The geometry / construction of the support member can be different. There can be more than four or less than four hydraulic cylinders to guide the downward movement of the stator case. The piston rod of the hydraulic cum pneumatic cylinder need not be telescopic. Such variations of the invention are to be construed and understood to be obvious to those skilled in the art and within the scope of the invention.
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We claim
1. A fixture for assembling a stator, the fixture comprising a support means for supporting a wound stator pack, the support means being mounted on a base plate supported on a rigid surface, a holder means for holding a stator case, the holder means being held above the support means with a stator case disposed coaxially with a wound stator pack supported on the support means, drive means for moving down the holder means along with the stator case held therein and engaging the stator case over the wound stator pack supported on the support means concentrically and guide means for guiding the downward movement of the holder means with the stator case,
2. The fixture as claimed in claim 1, wherein the said support means comprises a closed end cylindrical support member provided with a collar projecting upwardly from the center of the closed end thereof and a mounting flange at the opposite end thereof, the support member being removably mounted on the base plate with bolts tightened in bolt holes provided in the mounting flange and in the base plate and a cup shaped member located on the closed end of the support member against the collar thereon, the cup shaped member having the wound stator pack wound on a mandrel and located against edge of the cup shaped member with the over hanging portion of the wound stator pack disposed in the cup shaped member, the mandrel being removably fitted at the bottom of the cup shaped member.
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3. The fixture as claimed in claim 1 or 2, wherein the drive means comprises a hydraulic cum pneumatic cylinder located below the base plate with the piston rod of the hydraulic cum pneumatic cylinder projecting upwardly through the base plate and the center of the closed end of the support member and the collar and the mandrel of the wound stator pack, the piston rod of the hydraulic cum pneumatic cylinder being telescopic, the guide means comprises four hydraulic cylinders located below the base plate around the main cylinder with their piston rods projecting upwardly through the base plate and the holder means comprises a support plate formed with a central opening having a stepped sidewall and a spigot matching with the stepped side wall of the centra] opening and located in the central opening of the support plate against the stepped sidewall of the support plate, the support plate being held at the top of the piston rods of the hydraulic cylinders, the stator case being disposed coaxial with the wound stator pack and a cap shaped member adapted to be removably held at the top end of the piston rod of the hydraulic cum pneumatic cylinder against the stator case supported on the spigot.
4. The fixture as claimed in claim 3, wherein the cap shaped member is removably held at the top end of the piston rod of the hydraulic cum pneumatic cylinder by a closed end tubular retainer member formed with a step on the outer surface thereof adapted to be engaged against the cap shaped member, the retainer member being clamped at the top end of the hydraulic cum pneumatic cylinder
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by a screw passing through a hole at the closed end thereof and tightened in a correspondingly threaded hole at the top end of the hydraulic cum pneumatic cylinder.
Dated this 20th day of November 2008
(Jose M A)
of Khaitan & Co
Agent for the Applicants
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