WO2021105776A1

WO2021105776A1 - System and method for positive balancing of rotors

Info

Publication number: WO2021105776A1
Application number: PCT/IB2020/052668
Authority: WO
Inventors: Ranjan Kumar; Sunil BAILY THOMAS; Navya IP; Aravind REDDY S; S R Riyaz
Original assignee: Ifb Industries Ltd
Priority date: 2019-11-25
Filing date: 2020-03-23
Publication date: 2021-06-03

Abstract

The present invention discloses a system and a method for positive balancing of rotors such as rotors in electrical motors. The system includes a shaft 202, permanent magnets 216 and silicon steel 218 being molded with plastic 214 and assembled with the shaft 202, the plastic mold 214 and silicon steel 218 defining an operative first outer surface 212a and an operative second outer surface 212b, one or more recesses 208 configured on the operative first 212a and second outer surfaces 212b at predetermined angular locations; and the one or more recesses 208 configured to receive a predetermined amount of a mass. The positive balancing is done using a first fixture 300 and a second fixture.

Description

SYSTEM AND METHOD FOR POSITIVE BALANCING OF ROTORS

FIELD OF INVENTION

The present invention relates to positive balancing of rotors, and in particular, the present invention relates to positive balancing of rotors in electrical motors, wherein the efficiency and quality of the motors comprising the rotors is enhanced.

BACKGROUND

Rotating machinery is ubiquitous in the contemporary world. We are surrounded by rotating machines employed in mechanical and electrochemical systems that include rotors of motors and engines, machining tools, industrial turbo machinery and the like. When unbalanced distribution of rotating masses around an axis of rotation occurs, due to reasons such as constraints in manufacturing processes, tolerances and uneven material density distribution, the rotor unbalance arises. An undesired aspect of this causes excessive vibrations especially at high rotational speed, which may lead to damage of bearings and may also result in destruction of the machines. At very high speeds, a tiny imbalance in weight can create detrimental effects on rotating machines due to exponentially high centrifugal force generated by the eccentric mass. In particular, vibrations set in the rotating machine due to interaction of the unbalanced mass component with the radial acceleration due to rotation which together generates a centrifugal force. As the redundant mass component rotates, the force acts on the rotor and tries to move the rotor therewith, due to the departure of centre of mass away from the axis of rotation.

Vibration of the rotating machinery can be suppressed by eliminating the root cause of vibration that is the system unbalance. The vibrations can be reduced to a minimum value though they cannot be completely eliminated. Balancing of rotors prevents excessive loading of bearings and avoids fatigue failure thereby increasing life of machinery as well as performance of the rotor. Further, balancing is essential as it improves mass distribution of the rotating machine and the rotating machine rotates without any unbalanced centrifugal force. Therefore, balancing a rotating machine is of paramount significance to warrant that the machine operates consistently.

In the known art, the balancing of the rotating machine comprises addition or removal of small amounts of weight at various axial locations and angular position from a rotor of the rotating machine that contributes rotating forces thereto. In particular, the rotor of the rotating machine is balanced by removing rotor material from the periphery of the rotor. In certain cases, a considerably amount of rotor material or mass may have to be removed from the rotor.The removal of mass or material from a rotor of an electrical motor causes disruption in free flow of flux and results in uneven air gap flux density distribution. Negative balancing also increases torque ripple, vibration and reduces RMS torque. Another drawback of rotors with negative balancing in electrical motor rotors wherein material is removed from the periphery of rotor is that, it increases audible noise levels due to the uneven texture of rotor periphery. Further, the process described hereinabove essentially requires considerable time and longer the process takes, the more is the cost associated therewith. In addition, a Brushless DC motor’s rotor depends on magnetic field generated on rotor periphery (by virtue of permanent magnets embedded within) and subsequent interaction between stator of the motor. If there are cuts on this periphery, it causes disruption in free flow of magnetic flux/field lines and results in uneven air gap flux density distribution, which in turn translates to torque ripple and distorted shaft output of the motor. Thus, there is felt an acute need for overcoming one or more drawbacks associated with the conventional negative balancing systems and methods for rotors, especially for rotors used in electrical motors of high speed applications (>15000RPM). In particular, there is felt a need for providing a system and method for dynamic balancing of rotors such as the electrical motor rotors.

OBJECTS OF THE INVENTION Some of the objects of the present disclosure, of which at the minimum one object is fulfilled by at least one embodiment disclosed herein, are as follows:

An object of the present disclosure is to provide an alternative, which overcomes at least one drawback encountered in the existing prior art;

Another object of the present disclosure is to provide a system and a method for balancing a rotating machine; Still another object of the present disclosure is to provide a system and a method for balancing a rotating machine which reduces vibrations, audible and signal noises, structural fatigue stresses, enhances bearing life, power losses, torque ripple and/or cogging torque, cycle time as milling operation is not required; and reduces maintenance frequency, due to reduced wear and moving parts in the balancing setup.

Yet another object of the present disclosure is to provide a system and method for balancing a rotating machine, which enhances efficiency and quality thereof.

Other objects and benefits of the present disclosure will be more apparent from the following description, which is not intended to bind the scope of the present invention.

SUMMARY OF THE INVENTION

In an aspect, the present invention provides a system for positive balancing of electrical motor rotors. Typically, balancing of rotating equipments is of two types - single plane or static balancing and two plane or dynamic balancing. The present invention relates but not limited to two plane or dynamic balancing. The system comprises a shaft having a first end and a second end, permanent magnets and silicon steel being molded with plastic and assembled with the shaft, the plastic mold and the silicon steel defining an operative first outer surface and an operative second outer surface on a first end and a second end of the plastic mold, respectively, one or more recesses being configured on the operative first and second outer surfaces at predetermined angular locations, the one or more recesses configured to receive a predetermined amount of a mass, a first fixture comprising, a first support configured to receive a first bearing and the first end of the shaft operatively therein, a second support configured to receive a second bearing and the second end of the shaft operatively therein, a driving means, operatively connected torotor periphery, configured to drive therotor, an accelerometer operatively mounted on at least one of the first support and the second support and configured to measure vibrations due to imbalance mass of the rotor during rotations thereof, wherein the accelerometer generates a vibration signal, a filter configured to receive and filter the vibration signal from the accelerometer to obtain a filtered signal, a vibration meter configured to receive the filtered signal and determine and display magnitude of the vibrations, a tachometer configured to measure speed of rotation of rotor, a phase angle meter configured to measure a phase angle delay between the signal from the tachometer and the filtered signal for detecting the angular location of the imbalance on the rotor relative to a datum position, a display unit for displaying the phase angle, the magnitude of bearing vibration and mass of imbalance, a second fixture comprising a first support configured to receive a first bearing and the first end of the shaft operatively therein, a second support configured to receive a second bearing and the second end of the shaft operatively therein, a driving means, operatively connected to one of the first end and the second end of the shaft, configured to drive the shaft, wherein the balancing mass(es) being received in the one or more recesses to reduce the mass imbalance, and permanently. In accordance with another aspect, the present invention discloses a method for positive balancing of electrical motor rotors. The method comprises the steps of providing a rotor having a mass imbalance, mounting the rotor on a first fixture, wherein a first end and a second end of a shaft of the rotor are received in a first bearing and a second bearing supported on a first and second support, respectively, rotating the rotor while being mounted on the first fixture at a predetermined rotational speed, by coupling the rotor with a driving means, measuring vibrations of the rotating rotor by using an accelerometer to determine vibrations due to imbalance mass of the rotor during rotation thereof and generating a vibration signal, filtering the vibration signal employing a filter to obtain a filtered signal, determining and displaying magnitude of the filtered signal employing a vibration meter, measuring rotation speed of the rotor by employing a tachometer and generating a corresponding signal therefrom, determining a phase angle between the filtered vibration signal and the signal generated by a tachometer, thereby detecting the angular location of the imbalance on the rotor at both the sides of the rotor relative to a datum position, determining the position of mass imbalance and the amount of mass to be inserted, providing a second fixture and operably securing the rotor on to the second fixture, receiving and securing one or more balancing mass(es) in the one or more recesses to reduce the mass imbalance, and repeating the above steps till mass imbalance of the rotor is below a predetermined value.

In accordance with the embodiments, the balancing mass(es) for positive balancing is at least one of brass, aluminum and a combination thereof, the balancing mass(es) being received in the one or more recesses permanently while the rotor is stationary, the balancing mass(es) being in form of cylindrical strips.

In accordance with the embodiments, the number of recesses configured on the first and second outer surfaces being in the range of 6 to 10, preferably 8. BRIEF DESCRPTION OF THE ACCOMPANYING DRAWING

The detailed description is set forth with reference to the accompanying figures, in which:

FIG. 1 illustrates a schematic diagram of a rotor, wherein the rotor is balanced by the conventional negative balancing technique; FIG. 2A illustrates a schematic diagram of a rotor, wherein the rotor is balanced by positive balancing technique in accordance with the embodiments herein;

FIG. 2B illustrates a schematic diagram of a side view of the rotor of FIG. 2A;

FIG. 2C illustrates a schematic diagram of an exploded view of the rotor of FIG. 2A; FIG. 3 A illustrates a block diagram of a system for positive balancing of rotors in accordance with the embodiments herein;

FIG. 3B illustrates a schematic diagram of a system for positive balancing of rotors in accordance with the embodiments herein; and FIG. 4 illustrates a schematic diagram of an exploded view of the rotor with the balancing mass(es) in accordance with the embodiments herein.

LIST OF NUMERALS 0 - Rotor 2 - Shaft 2a - First end 2b - Second end 4 - Rotor body 4a - First outer surface 4b - Second outer surface 10 - Cuts or recesses 0 - Rotors 0c - Exploded view of rotor 2 - Shaft 2a - First end 2b - Second end 4 - Rotor body 4a - First end 4b - Second end 6 - Rotor periphery 8 - Recesses 12a - Operative first outer surface 12b - Operative second outer surface 14 - Plastic mold 16 - Permanent magnets 18 - Silicon steel 0 - First fixture 0a Block diagram of system 0b Schematic diagram of system 2 First support 4 First bearing 6 Pulley 8 Belt 10 Accelerometer 12 Vibration signal 14 Filter 16 Filtered signal 18 Vibration meter 0 Tachometer 2 Signal from tachometer 4 Phase angle meter 6 Adjustable tachometer support 8 Datum position 0 Second bearing 2 Base plate 0 Rotor with balancing mass(es) 2 Balancing mass(es)

DETAILED DESCRIPTION

All technical terms and scientific expressions used in the present disclosure have the same meaning as understood by a person skilled in the art to which the present invention belongs, unless and otherwise specified. As used in the present specification and the claims, the singular forms “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. The term "comprising” as used in the present specification will be understood to mean that the list following is non-exhaustive and may or may not include any other extra suitable things, for instance one or more additional feature(s), part(s) and /or constituent(s) as applicable. Further, the terms “about” and “approximately" used in combination with ranges of sizes of parts, and/or any other physical properties or characteristics, are meant to include small variations that may occur in the upper and/or lower limits of the ranges of sizes.

The embodiments disclose a system and a method for positive balancing of rotors. In particular, the preferred embodiments disclose a system and a method for positive balancing of rotors in electrical motors, wherein the efficiency and quality of the motors comprising the rotors are enhanced.

The embodiments of the present invention is described hereinbelow with reference to the figures, wherein FIG. 1 illustrates a schematic diagram of a rotor, wherein the rotor is balanced by the conventional negative balancing technique, FIG. 2A illustrates a schematic diagram of a rotor, wherein the rotor is balanced by positive balancing technique in accordance with the embodiments of the present invention, FIG. 2B illustrates a schematic diagram of a side view of the rotor of FIG. 2 A, FIG. 3A illustrates a block diagram of a system for positive balancing of rotors, FIG. 3B illustrates a schematic diagram of a system for positive balancing of rotors and FIG. 4 illustrates a schematic diagram of an exploded view of the rotor with the balancing mass(es) in accordance with the embodiments of the present invention.

FIG. 1 illustrates a schematic diagram of a rotor 100, wherein the rotor 100 is balanced by the conventional negative balancing technique. The rotor 100 comprises a shaft 102 having a first end 102a and a second end 102b, a rotor body 104 having a first outer surface 104a and asecond outer surface 104b, wherein the rotor body 104 is disposed around the shaft 102, and is molded in plastic, the rotor body 104 comprising one or more permanent magnets disposed and embedded within the plastic mold. Further, the rotor 100 includes recesses or cuts 110 configured on the rotor body 104, wherein the recesses or the cuts 110 are the areas or positions from where the mass of the rotor body 104 is removed to balance the rotor 100.

A typical method of negative balancing of the rotor 100 by which mass distribution of the rotor 100 is balanced includes the following steps, wherein the shaft 102 is supported on two supports, one each for supporting the ends (102a, 102b). One of the ends (102a, 102b) is coupled to a driving means which drives (rotates) the shaft 102 about its axis and hence the rotor lOO.This is also referred to as the measurement phase. A sensor is connected to determine the mass distribution of rotor 100 at some particular angle on both the first end 102a and the second end 102b of the rotor 100. A cutting tool is provided in proximity of the rotor 102, wherein the cutting tool is configured to cut or remove some material from the rotor body 104 to configure one or more cuts or recesses 110 thereon. The cutting tool is configured so that the cutting speed and the depth of the cut or recess 110 can be controlled with accuracy and precision. The same procedure is repeated until the both sides of the rotor mass is below 65mg or a target unbalance level.This is also called the correction phase. In accordance with an aspect of the present invention, a system for positive balancing the electrical motor rotor is disclosed, wherein the system overcomes one or more drawbacks of the conventional negative balancing technique.

The embodiments of the present invention is now described with reference FIG. 2A, FIG. 2B , FIG. 2C FIG. 3A, FIG. 3B, and FIG. 4 wherein FIG. 2A illustrates a schematic diagram of a rotor, wherein the rotor is balanced by positive balancing technique in accordance with the embodiments of the present invention, FIG. 2B illustrates a schematic diagram of a side view of the rotor of FIG. 2A, FIG. 2C illustrates a schematic diagram of an exploded view of the rotor of FIG. 2A, FIG. 3A illustrates a block diagram of a system for positive balancing of rotors, FIG. 3B illustrates a schematic diagram of a system for positive balancing of rotors and FIG. 4 illustrates a schematic diagram of an exploded view of the rotor with the balancing mass(es) in accordance with the embodiments herein. In accordance with the embodiments of the present invention, the system comprises a rotor 200 having a mass imbalance, the rotor 200 comprising a shaft 202 having a first end 202a and a second end 202b, permanent magnets 216 and silicon steel 218 being molded with plastic 214 and assembled with the shaft 202 to define a rotor body 204, the plastic mold 214 and the silicon steel 218 defining an operative first outer surface 212a and an operative second outer surface 212b on a first end 204a and a second end 204b of the plastic mold 214, respectively.

In accordance with an embodiment, one or more recesses 208 are configured on the operative first surface 212a and second outer surface 212b at predetermined angular locations on the rotor body 204. The one or more recesses 208 are configured to receive a predetermined amount of a mass or weights therein, and hence instead of removing or cutting mass or weight or material from rotor periphery 206, some predetermined amount of weight or mass is added to the rotor 200 in these recesses 208. In accordance with an embodiment the system includes, a first fixture 300 provided to receive and operably rotate the rotor 200. In accordance with an embodiment, the first fixture 300 comprises a base plate 332 provided with a first support 302 configured to receive a first bearing 304 and the first end 202a of the shaft 202 operatively therein, a second support configured to receive a second bearing 330 and the second end 202b of the shaft 202 operatively therein.

Further, the system includes a driving means (not shown in the figures), which may be an electric motor or any other means which is capable of coupling and rotating the rotor 200 in the first fixture. The driving means is connected to the rotor 200 by means of a belt 308 at the rotor periphery 206. In an embodiment, the rotor periphery 206 is coupled to a pulley 306 and the pulley 306 can be coupled to the driving means using a belt 308. Any other coupling means is also well within the ambit of the present invention and the present invention is not limited to these embodiments.

In accordance with an embodiment, the system further includes a plurality of accelerometers 310 configured to measure vibrations at a first end 202a side and a second end 202b side of the rotor due to imbalance mass of the rotor 200 during rotations thereof, wherein the accelerometers 310 generate vibration signals 312. In an embodiment, load cell can be used to measure vibrations due to imbalance mass of the rotor 200. Further, a plurality of filters 314 is configured to receive and filter the vibration signals 312 from the corresponding accelerometer 310 to obtain filtered signals 316. A plurality of vibration meters 318 is configured to measure the vibrations of the rotor 200 at the first end 202a side and the second end 202b side. A tachometer 320 is mounted on an adjustable tachometer support 326 and configured to measure speed of rotation of rotor 200. A phase angle meter 324is provided and is configured to measure a phase angle delay between the signal 322 from the tachometer 320 and the filtered signals 316 for detecting the angular location of the imbalance at the first end 202 side and the second end 202b side of the rotor 200 relative to a datum position 328. Further, one or more display units may be provided to display one or more data and details generated including the phase angle, the magnitude of bearing vibration and mass of imbalance.

Further, the system includes a second fixture, which comprises a first support configured to receive a first bearing 304 and the first end of the shaft 202a operatively therein, a second support configured to receive a second bearing 330 and the second end of the shaft 202b operatively therein, a driving means, operatively connected to one of the first end and the second end of the shaft, configured to drive the shaft, such that the rotor 200 is set at a desired angular position, wherein the second fixture is employed to add the balancing mass(es) 402 permanently into the recesses 208 to achieve reduction in the mass imbalance in response to the imbalance and corresponding angular location detected during the run in the first fixture.

In accordance with an embodiment, the balancing mass(es) 402 for positive balancing can be at least one of brass, aluminum and a combination thereof, wherein the balancing mass(es) 402 are received in the one or more recesses permanently. The balancing mass(es) 402 can be permanently added while the rotor is stationary. Further, the balancing mass(es) 402 can be in the form of strips. In an embodiment, the strips can have a cylindrical cross section. In accordance with an embodiment, the rotor 200 can have any number of recesses for receiving the balancing mass(es) 402. In an embodiment, the recesses configured on the first and second outer surfaces being in the range of 6 to 10, preferably 8 recesses on the first outer surface and second outer surface.

In accordance with another aspect of the present invention, a method for positive balancing of electrical motor rotors is disclosed. The method comprises providing a rotor 200 having a mass imbalance, mounting the rotor 200 on a first fixture

300, wherein a first end 202a and a second end 202b of a shaft 202 of the rotor 200 are received in a first bearing 304 and a second bearing 330 supported on a first support 302 and second support, respectively. The rotor 200 is rotated while being mounted on the first fixture 300 at a predetermined rotational speed, by coupling the rotor 200 with a driving means. Thereafter, the vibrations of the rotating rotor 200 are measured by using a plurality of accelerometers 310 to determine vibrations due to imbalance mass of the rotor 200 at both the sides, first end 202a side and second end 202b side, during rotation thereof and generating vibration signals 312, filtering the vibration signals 312 employing a plurality of filters 314 to obtain filtered signals 316, determining and displaying magnitude of the filtered signals 316 by employing a plurality of vibration meters 318, measuring rotation speed of the rotor by employing a tachometer 320 and generating a corresponding signal 322 there from, determining a phase angle between the filtered signal 316 and the signal 322 generated by a tachometer 320, thereby detecting the angular location of the imbalance on the rotor 200 at both the sides, first end 202a side and second end 202b side, relative to a datum position 328, determining the position of mass imbalance and the amount of mass to be inserted, providing a second fixture and operably securing the rotor on to the second fixture, receiving and securing one or more balancing mass(es) 402 in the one or more recesses to reduce the mass imbalance, and repeating the above steps till mass imbalance of the rotor is below a predetermined value.

The following is an example for the positive balancing of the rotor 200 in accordance with the embodiments of the present invention. For positive balancing of the rotor 200 some material such as brass or aluminum is employed in the range of 50 mg to 500 mg, which is inserted into the recesses 208 of the rotor 200. The rotor is mounted on a fixture and a driving means is coupled to the rotor via a belt. A sensor is connected to the fixture to sense the mass distribution of rotors at some particular angle on both drive and non-drive ends of the rotor. A rotor pole is marked for reference and is considered as 0 degree. In particular, the marking is done over the shaft end 202b of the rotor. Here pole of the rotor considered as an angular increment, depending on the no of poles available on the rotor. Here 1 pole angle is the fraction of total no of poles and 360 degrees (45 degree in this case= 360/8 -see FIG. 2B). Thereafter, the rotor 200 is placed over the first fixture. Here rotor is rotated by the belt in a clockwise direction and the sensor is allowed to sense the mass distribution of rotor about axis of rotation at some angles. Bearing position on the shaft is held by the fixture’s roller to hold the rotor and the sensed reading in the digital form, from the sensor is noted/determined, wherefrom the unbalanced weight at some particular angular position on both drive and non-drive ends is determined. Thereafter, the position of unbalance is then physically identified by counting the no of poles towards clockwise direction.

Further, a second fixture is provided to operably secure the rotor in position during balancing mass insertion. The rotor is placed in the same second fixture and using a driving tool, calculated balancing mass/inserts/are inserted from that angle (pole of the rotor) of the rotor to just opposite rotor pole hole on drive end. Similar process is followed for the non-drive end of the rotor also. Same procedure will be repeated until both side of the rotor mass is below 58mg or target unbalance level. It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention may be embodied in other specific forms without departing from the essential attributes thereof, and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

TECHNICAL ADVANCES AND ADVANTAGES The present disclosure, as described herein above, provides several advances including, but that are not limited to, a system and method for positive balancing of electrical motor rotors, wherein the system and method: minimizes vibrations of the rotor; minimizes audible and signal noises; - minimizes structural fatigue stresses; enhances bearing life; reduces power losses; minimizes torque ripple and/or cogging torque; enhances efficiency; - reduces cycle time as milling operation is not required; and reduces maintenance frequency.

Claims

WE CLAIM: 1. A system for positive balancing of electrical motor rotors having a mass imbalance, said rotor 200 comprising: o a shaft 202 having a first end 202a and a second end 202b; o permanent magnets 216 and silicon steel 218 being molded with plastic 214 and assembled with said shaft 202, ■ said plastic mold 214 and silicon steel 218 defining an operative first outer surface 212a and an operative second outer surface 212b on a first end 202a and a second end 202b of said plastic mold 214, respectively;

^■ one or more recesses 208 being configured on said operative first 212a and second outer surfaces 212b at predetermined angular locations; and

^■ said one or more recesses 208 configured to receive a predetermined amount of a mass; said system comprising: a first fixture 300 comprising: o a first support 302 configured to receive a first bearing 304 and said first end 202a of said shaft 202 operatively therein; o a second support configured to receive a second bearing 330 and said second end 202b of said shaft 202 operatively therein; o a driving means, operatively connected to rotor periphery 206 of said rotor 200, configured to drive said rotor 200; a plurality of accelerometers 310 configured to measure vibrations due to imbalance mass of said rotor 200 at first end 202a side and second end 202b side during rotations thereof, wherein said accelerometers 310 generate vibration signals 312; a plurality of filters 314 configured to receive and filter said vibration signals 312 from said accelerometers 310 to obtain filtered signals 316; a plurality of vibration meters 318 configured to receive said filtered signals 316 and determine and display magnitude of said vibrations; a tachometer 320 configured to measure speed of rotationand generate a signal 322; a phase angle meter 324 configured to measure a phase angle delay between the signal 322 from said tachometer 320 and said filtered signals 316 for detecting the angular location of the imbalance on said rotor 200 at first end 202a side and second end 202b side, relative to a datum position

328; a display unit for displaying the phase angle, the magnitude of bearing vibration and mass of imbalance; - a second fixture comprising: o a first support 302 configured to receive a first bearing 304 and said first end 202a of said shaft 202 operatively therein; o a second support configured to receive a second bearing 330 and said second end 202b of said shaft 202 operatively therein; o a driving means, operatively connected to one of said first end 202a and said second end 202b of said shaft 202, configured to drive said shaft 202; wherein the balancing mass(es) 402 being received in said one or more recesses 208 · to reduce the mass imbalance; and

• permanently.

2. The system as claimed in claim 1, wherein said balancing mass(es) 402 for positive balancing is at least one of brass, aluminum and a combination thereof.

3. The system as claimed in claim 1, wherein said balancing mass(es) 402 being in form of strips.

4. The system as claimed in claim 4, wherein said strips having a cylindrical cross section.

5. The system as claimed in claim 1, wherein the number of recesses 208 configured on said first outer surface 212a and second outer surface 212b being in the range of 6 to 10, preferably 8.

6. A method for positive balancing of electrical motor rotors, said method comprising: providing a rotor 200 having a mass imbalance; mounting said rotor 200 on a first fixture 300, wherein a first end 202a and a second end 202b of a shaft 200 of said rotor 200 are received in a first bearing 304 and a second bearing 330 supported on a first 302 and second support, respectively; - rotating said rotor 200 while being mounted on said first fixture 300 at a predetermined rotational speed, by coupling said rotor 200 with a driving means; measuring vibrations of said rotating rotor 200 by using a plurality of accelerometers 310 to determine vibrations due to imbalance mass of said rotor 200 at first end 202a side and second end 202b side during rotation thereof and generating vibration signals 312; filtering said vibration signals 312 employing a plurality of filters 314 to obtain filtered signals 316; - determining and displaying magnitude of said filtered signals 316 employing a plurality of vibration meters 318; measuring rotation speed of said rotor 200 by employing a tachometer 320 and generating a corresponding signal 322 therefrom; determining a phase angle between said filtered signals 316 and said signal 322 generated by a tachometer 320, thereby detecting the angular location of said imbalance on said rotor 200 at first end 202a side and second end 202b side relative to a datum position 328; determining the position of mass imbalance and the amount of mass to be inserted; - providing a second fixture and operably securing said rotor 200 on to said second fixture; receiving and securing one or more balancing mass(es) 402 in said one or more recesses 208 to reduce the mass imbalance; and

Repeating the above steps till mass imbalance of said rotor 200 is below a predetermined value.

7. The method as claimed in claim 6, wherein said balancing mass(es) 402 for positive balancing is at least one of brass, aluminum and a combination thereof.

8. The method as claimed in claim 6, wherein said balancing mass(es) being received in said one or more recesses permanently.

9. The method as claimed in claim 6, wherein said balancing mass(es) 402 being in form of strips.

10. The method as claimed in claim 10, wherein said strips having a cylindrical cross section.

11. The method as claimed in claim 6, wherein the number of recesses 208 configured on said first outer surface 212a and second outer surface 212b being in the range of 6 to 10, preferably 8.