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 dual stator variable air gap axial flux windmill generator
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Dr. Samsul Ekram of Crompton Greaves Ltd, APDTC,CG Global R&D Centre, Crompton Greaves Ltd., Kanjur (E), Mumbai 400042, Maharashtra, India, an Indian National and Dr. Min-Fu Hsieh, Associate Professor, Department of Systems and Naval Mechatronic Engineering of the National Cheng Kung University, No. 1 University Road, Tainan City -701, Taiwan (ROC), a Taiwanese 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
The invention relates to a windmill generator and more particularly towards a windmill generator having dual stators and a variable air gap for generating axial flux. BACKGROUND OF THE INVENTION
Windmill generators are environment friendly and non-polluting machines employing naturally, abundantly and freely available wind energy for generation of electricity. A windmill generator usually comprises of a rotor disposed between a pair of stators all of which are mounted on a shaft. The stators are mounted rigidly onto the shaft while rotor is -adapted to be rotated around the shaft and is in a spaced apart relationship maintaining an air gap with each of the stators. The rotor and the stators are rigidly mounted on the shaft. Blades are mounted on the rotor for rotating the rotor by wind force which in turn generates an EMF in stator windings. EMF voltage depends on the speed of the rotor and the air gap between the rotor and the stators. However, since the rotor and the stators are rigidly mounted on the shaft, the output voltage in such a windmill generator is directly proportional only to the speed of the rotor. Therefore the windmill generator generates optimum electricity only during high wind speed. During low wind speed, the generation of electricity reduces drastically owing to a low speed of the rotor. OBJECTS OF THE INVENTION
An object of the invention is to provide a dual stator variable air gap axial flux windmill generator which tracks maximum possible power at all wind speeds.
Another object of the invention is to provide a dual stator variable air gap axial flux windmill generator which tracks maximum possible power at all wind speeds, is cost effective and simple in design.

DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a dual stator variable air gap axial flux windmill generator comprising a rotor axially slidably mounted on a shaft between a pair of stators in a spaced apart relationship with each of the stators, one of the stators being rigidly mounted at a distant end of the shaft and the other stator being slidably mounted on the shaft, the proximal end of the shaft being mounted to a tracking arrangement, a tension means provided between the rotor and the slidable stator and between the slidable stator and an arrester fitted on the shaft, the slidable stator comprising a wind trapper.
The following is a detailed description of the invention with reference to the accompanying drawings, in which
Fig 1 is a side view of a dual stator variable air gap axial flux windmill generator;
Fig 1 is a side view of a dual stator variable air gap axial flux windmill generator. The windmill generator 1 comprises of a rotor 2 and a pair of stators 3 & 4 mounted on a shaft 5 such that the rotor 2 remains disposed between the pair of stators 3 & 4 maintaining a constant air gap with each of the stators 3 & 4 during the operation of the windmill generator 1. The rotor 2 is axially slidably mounted on the shaft 5. One of the stators 3 is rigidly mounted at a distant end 6 of the shaft 5 and the other stator 4 is slidably mounted on the shaft 5. The proximal end of the shaft 5 is mounted to a tracking arrangement 7 to rotate the windmill generator 1 in the direction of the wind so as to align or self set the windmill generator 1 in the wind direction. A mechanical spring 8 is provided between the rotor 2 and
the slidable stator 4 and between the slidable stator 4 and an arrester 9 fitted on the shaft 5.
*
The slidable stator 4 comprises of a canonical disc 10 for trapping the wind. The rotor 2 is mounted with blades 11. Due to wind forces acting on the blades 11, the blade 11 rotates

around the shaft 5 along with the rotor 2. The entire windmill generator 1 assembly is mounted on a pole support 12 to place the windmill generator 1 well above the ground level. Due to the wind forces, the tracking arrangement 7 causes the shaft 5 to rotate in the direction of the wind so as to align or self set the windmill generator 1 in the wind direction for capturing the maximum wind energy blowing in the direction of the windmill generator 1 and correspondingly increase electric power generation. As the wind forces rotates the blades 11 and consequently the rotor 2, an axial magnetic flux is generated round the magnetic material core of the stators 3 & 4 and an electric current is induced in the electric coils wound around the magnetic material core.
During high wind speed, the blades 11 and consequently the rotor 2 rotates at a high speed. The rotor 2 slides axially towards the slidable stator 4 due to high force of wind. Simultaneously, the canonical disc 10 traps the wind to push the slidable stator 4 away from the rotor 2 thereby maintaining a constant air gap between the rotor 2 and the stators 3 & 4. The size and shape of the canonical disc 10 as well as the tension in the mechanical springs 8 is so designed to maintain an optimum and const air gap between the rotor 2 and the stators 3 & 4 at high wind speed for tracking a rated power from the windmill generator 1. The electricity" generated from a windmill generator 1 or the emf voltage induced in the stator windings of a windmill generator 1 is directly proportional to the rate of speed of the rotor 2 and the air gap between the rotor 2 and stators 3 & 4. Therefore, at high wind speed, the rated power is tracked out of the windmill generator owing to the high speed of rotor 2 and an optimum air gap between the rotor 2 and the stators 3 & 4.
In case of a reduction in the speed of the wind, the slidable rotor 4 slides backs towards the rotor 2 as the canonical disc 10 no longer pushes the slidable stator 4 with the

same force as it would have done during high wind speed. Simultaneously, the rotor 2 too moves away from the slidable stator 4 to maintain a constant yet decreased air gap with the stators 3 & 4 as compared to the air gap maintained during high wind speed. Hence the reduction in the speed of the rotation of the rotor 2 is compensated by decreasing the amount of air gap between the rotor 2 and the stators 3 & 4 thereby generating substantially the same amount of electricity as being generated at high wind speed.
According to the invention, the dual stator variable air gap axial flux windmill generator is cost effective and simple in design. The windmill generator varies the air gap between the rotor and the stators at high and low wind speeds to track maximum power at both high and low wind speeds using a simple and low cost technique.
Instead of a canonical disk, a disk of some other shape can be used to trap wind and provide a pushing force to the slidable stator. The wind trapper can either be an integrated structure with the slidable stator or a structure affixed to the slidable stator.
Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the invention as defined.

We claim:

1. A dual stator variable air gap axial flux windmill generator comprising a rotor axially slidably mounted on a shaft between a pair of stators in a spaced apart relationship with each of the stators, one of the stators being rigidly mounted at a distant end of the shaft and the other stator being slidably mounted on the shaft, the proximal end of the shaft being mounted to a tracking arrangement, a tension means provided between the rotor and the slidable stator and between the slidabie stator and an arrester fitted on the shaft, the slidable stator comprising a wind trapper.
2. The windmill generator as claimed in claim 1, wherein the wind trapper comprises of a canonical disc fitted to the slidable stator at its face confronting the rotor.
Dated this 25th day of March 2009.
Crompton Greaves Limited By their Agent & Attorney

(Ivan Bernard Fuller) of Khaitan & Co