FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
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 sensor arrangement for high resolution position sensing in closed loop motor control.
APPLICANTS
Crompton Greaves Limited, CG House, 6th Floor, Dr. Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India; an Indian Company.
INVENTOR
Balakrishnan Manu and Upadhayay Pranshu of Crompton Greaves Limited, Global R&D Center, Aryabhatta Building, Kanjur Marg (East), Mumbai - 400042, Maharashtra, India; both Indian Nationals.
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 electrical engineering.
Particularly, this invention relates to motors, and sensors and control mechanisms, thereof.
Specifically, this invention relates to a sensor arrangement for high resolution position sensing in closed loop motor control.
BACKGROUND OF THE INVENTION:
An electric motor is an electric machine that converts electrical energy into mechanical energy. In normal motoring mode, most electric motors operate through the interaction between an electric motor's magnetic field and winding currents to generate force within the motor.
Brushless DC electric motor also known as electronically commutated motors are synchronous motors that are powered by a DC electric source via an integrated inverter/switching power supply, which produces an AC electric signal to drive the motor. Additional sensors and electronics control the inverter output amplitude and waveform and frequency.
A brushless DC motor or an electronically commutated motor has permanent magnets which rotate with a fixed armature, eliminating the problems of connecting current to the moving armature. An electronic controller replaces the brush / commutator assembly of the brushed DC motor, which continually switches the phase to the windings to keep the motor turning. The controller performs similar timed power distribution by using a solid-state circuit rather than the brush / commutator system.
Because the controller must direct the rotor rotation, the controller requires some means of determining the rotor's orientation/position (relative to the stator coils.) Some designs use Hall-effect sensors or a rotary encoder to directly measure the rotor's position.

A Hall-effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall-effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications. Hall sensors are commonly used to time the speed of wheels and shafts. They are used in brushless DC electric motors to detect the position of the permanent magnet.
Encoders are typically expensive devices and have complexity in attaching and working with a motor.
There is a need for an improved sensor arrangement in order to obtain better resolution / accuracy of sensing in a cost-effective manner.
PRIOR ART:
US7453225 discloses the use of 4 Hall-effect sensors. These four Hall-elements (120a-d) are disposed in two pairs (120a,c;120b,d) and the Hall-elements in each pair are arranged to deliver signals with a 180 degrees phase lag relative to each other and with a 90 degrees phase lag relative to the Hall-elements of the other pair.
EP1093210 discloses the use of an analog type Hall sensor for outputting an analog magnetism detecting signal the phase of which is shifted by 90 degrees from that of the analog type Hall sensor or a digital type Hall sensor for out-putting a digital magnetism detecting signal.
US7965004 discloses the use of two analog rotor position sensors which are arranged at a distance from one another such that, during operation, they generate two sinusoidal signals having a phase shift of 90 degrees to each other. A signal generator serves to generate at least one pulse-shaped signal from the two sinusoidal rotor position signals that are phase-shifted by 90 degrees.
OBJECTS OF THE INVENTION:
An object of the invention is to provide a sensor arrangement for high resolution position sensing in closed loop motor control.

Another object of the invention is to improve resolution of sensing of speed for motors or rotating machines.
Yet another object of the invention is to improve resolution of sensing of speed for motors or rotating machines in a cost-effective manner.
Still another object of the invention is to provide increased speed/position feedback pulses in one mechanical revolution, for motors or rotating machines using closed loop motor control.
An additional object of the invention is to derive sensor positions such that pulse width is not unequal, thereby increasing accuracy, which sensors are used in motors or rotating machines using closed loop motor control.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a sensor arrangement for high resolution position sensing in closed loop motor control for a motor, said motor comprising a main set of sensors consisting of a first main sensor, a second main sensor, and a third main sensor, each of said main sensors being spaced apart 120° electrically from each other, said sensor arrangement further comprises:
• at least a first level of auxiliary set of sensors consisting of at least three sensors including a first level first auxiliary sensor, a first level second auxiliary sensor, a first level third auxiliary sensor, each of said auxiliary sensors per level being displaced in a predetermined manner with respect to a corresponding main sensor.
Typically, each of said sensors is a Hall-effect sensor.
Typically, each of said first level auxiliary sensors is spaced apart 30° electrical from a corresponding main sensor.

Alternatively, each of said first level auxiliary sensors is spaced apart 90° electrical from a corresponding main sensor.
Typically, said arrangement comprises a multiplexing means adapted to multiplex signal outputs from each of said main sensors and auxiliary sensors to provide a final multiplexed signal, Fmux.
Typically, said arrangement comprises at least a further level of auxiliary set of sensors wherein number of total auxiliary sensors provided in correlation with the number of levels of sets of auxiliary sensors, in conformation with said pre-determined manner, being given by: number of auxiliary sensors forNth level = 3* (2N -1).
Typically, said arrangement comprises at least a further level of auxiliary set of sensors, each further level comprising at least a pre-defined number of first auxiliary sensors, said pre-defined number, for level N, in conformation with said pre-determined manner, being given by: number of first auxiliary sensors for Nth level = (2N-1)
Typically, said arrangement comprises at least a further level of auxiliary set of sensors, each further level comprising at least a pre-defined number of second auxiliary sensors, said predefined number, for level N, in conformation with said pre-determined manner, being given by: number of second auxiliary sensors for Nth level = (2N-1)
Typically, said arrangement comprises at least a further level of auxiliary set of sensors, each further level comprising at least a pre-defined number of third auxiliary sensors, said pre-defined number, for level N, in conformation with said pre-determined manner, being given by: number of third auxiliary sensors for N,h level = (2N-1)
Typically, said arrangement comprises a multiplexing means adapted to multiplex signal outputs from each of said main sensors and auxiliary sensors to provide a final multiplexed signal, Fmux, wherein number of transitions in the multiplexed signal per electrical cycle for Nth level of auxiliary sensors, in conformation with said pre-determined manner, being given by 6 * 2N

Typically, said arrangement comprising a multiplexing means adapted to multiplex signal outputs from each of said main sensors and auxiliary sensors to provide a final multiplexed signal, Fmux, wherein three main sensors and Nlh level auxiliary sensors [obtained by 3* (2N -1) no. of auxiliary sensors] provide (6 * 2N) transitions in said final multiplexed signal per electrical cycle).
Typically, angular position of all first-auxiliary sensors, for a given level N, with respect to its corresponding main sensor, in conformation with said pre-determined manner, is given by:

and further wherein angular position of all corresponding level N second auxiliary sensors
(HB[k]) being 120 degree apart with respect to its corresponding level N first auxiliary sensor
(HA[k]).
and further wherein angular position of all corresponding level N third auxiliary sensors (HC[k])
being 240 degree apart with respect to its corresponding level N first auxiliary sensor (HA[k]),
Alternatively, angular position of all first auxiliary sensors, for a given level N, with respect to its corresponding main sensor, in conformation with said pre-determined manner, is given by;

and further wherein angular position of all corresponding level N second auxiliary sensors
(HB[k]) being 120 degree apart with respect to its corresponding level N first auxiliary sensor
(HA[k]).
and further wherein angular position of all corresponding level N third auxiliary sensors (HC[k])
being 240 degree apart with respect to its corresponding level N first auxiliary sensor (HA[k]).
Typically, each of said auxiliary sensors is mechanical spaced apart from a main sensor based on the following formula, in conformation with said pre-determined manner being:
mechanical angle = electrical separation angle /[(number of poles in the motor/2)].
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figures 1 and 2 illustrate cross sectional views of a motor assembly;

Figure 3 illustrates outputs from three Hall-effect sensors with corresponding phase voltages and the current waveforms; and
Figure 4 illustrates three output sensors being multiplexed together to form an output signal, F
1 mux-
The invention will now be described in relation to the accompanying drawings, in which: Figure 5 illustrates output signals from 3 main sensors and output signals from 3 auxiliary sensors; all six signals being multiplexed to provide a final multiplexed signal, Fmux;
Figure 6, of the accompanying drawings, illustrates placement of sensors in a vector format; and
Figure 7 illustrates, schematically, positions of the sensors (main and auxiliary).
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figures 1 and 2 illustrate cross sectional views of a motor assembly. Reference numeral 12 refers to a stator. Reference numeral 14 refers to a rotor. Reference numeral 16 refers to magnets which circumferentially envelope the rotor. Reference numeral 18 refers to a shaft about which rotor rotates. Reference numeral 20 refers to drive end of the shaft 18. Reference numeral 22 refers to Hall-effect sensor magnets located in order to sense magnet position. Reference numeral 21 refers to sensor magnet.
Figure 3 illustrates outputs from three Hall-effect sensors with corresponding phase voltages and the current waveforms.
According to the prior art, typically, three sensors are used in permanent magnet brushless DC motors. These three sensors are displaced 120°, electrically. Each sensor is a Hall-effect sensor, and each sensor relays an output signal.
Thus, output of these three sensors are multiplexed together to an output signal, Fmux, as shown in Figure 4 of the accompanying drawings. The X-axis refers to electrical angles of separation

between three Hall-effect sensors. Reference numerals HA. HB, HC correspond to signals from three Hall-effect sensors. Reference numeral Fmux corresponds to the multiplexed signal. Therefore, from the waveform of Fmux, it can be seen that the transition from high to low or vice a versa occurs at 60° electrical. This is the maximum resolution which can be achieved with the three Hall-effect sensor type arrangement of the prior art (which is separation of 60° electrical). Thus, there are six transitions per electrical cycle, which is captured for calculating the speed of the motor (where the Hall-effect sensors are employed).
Typically, in a closed loop speed control (for a motor), the speed is calculated using position signals (received, in this case, as signal outputs, from the Hall-effect sensors). The speed can, thus, be calculated by counting the transition time of the Fmux signal.
As mentioned earlier, there is a need for a better resolution, in that, there is a need to figure out a way to add additional sensors for having additional signals which provide a multiplexed signal with equal pulse w7idth,
According to this invention, there is provided a sensor arrangement for high resolution position sensing in closed loop motor control.
In accordance with an embodiment of this invention, there are two sets of sensors; a main set of sensors (HA, HB, HC) and an auxiliary set of sensors (HA1, HB1, HC1).
Each of the sensors, typically, is a Hall-effect sensor. East set of sensors comprises three sensors. In at least one embodiment of this invention, there are three main sensors and three auxiliary sensors. The main set of sensors, typically, comprises a first main sensor (HA), a second main sensor (HB), and a third main sensor (HC). The auxiliary set of sensors, typically, comprises a first level first auxiliary sensor (HA1), a first level second auxiliary sensor (HA2), a first level third auxiliary sensor (HC1).
The number of sensors can be further increased in conformation with the principles of this invention, which are further described below.

In at least the one embodiment where there are three main sensors and three auxiliary sensors, the main sensors (HA, HB, HC) are displaced 120° electrically from each other. Similarly, the auxiliary sensors (HA1, HB1, HC1) are displaced 120° electrically from each other but the auxiliary sensors are displaced by 30° or 90° elec. from their respective main sensors. E.g. First level first auxiliary sensor HA1 is displaced 30° or 90° electrically from main sensor HA. First level second auxiliary sensor HB1 is displaced 30° or 90° electrically from main sensor HB. First level third auxiliary sensor HC1 is displaced 30° or 90° electrically from main sensor HC. Thus, the maximum resolution, in position, which can be achieved with a six Hall-effect sensor type arrangement is 30° electrical.
Figure 5 illustrates output signals from 3 main sensors and output signals from 3 auxiliary sensors; all six signals being multiplexed to provide a final multiplexed signal, Fmux
In accordance with a non-limiting exemplary embodiment of this invention, an 8-pole motor provides 24 speed / position feedback pulses in one mechanical revolution for a 3-sensor arrangement, but a 6-sensor arrangement, in accordance with this invention, provides 48 speed / position feedback pulses in one mechanical revolution. If other positions for the sensors are chosen, it results in feedback pulses of unequal width, which, in turn, results in lesser accuracy.
Figure 6, of the accompanying drawings, illustrates placement of sensors in a vector format. Figure 7 illustrates, schematically, positions of the sensors (main and auxiliary).
Therefore, in accordance with at least one embodiment of this invention, the 6-sensor arrangement, described above, provides double the pulses over the prior art's 3-sensor arrangement and aids in providing more resolution for speed / position feedback (from the multiplexed 6-output signal). The above arrangement also gives a closed loop control bandwidth double that of a 3-sensor arrangement, which is critical while controlling motor (or rotating machine) at low speeds of 10-50 rpm.
There are 6 transitions in the above stage, which can be increased by using a set of auxiliary sensors. The main sensors are taken as the reference for placing the auxiliary sensors. Increasing sets of auxiliary sensors relates to increases levels of auxiliary sensors (for the purposes of

description in this specification). Thus, a first set of auxiliary sensors is referred to first level (LEVEL 1) auxiliary sensors which comprise 3 auxiliary sensors; one auxiliary sensor per main sensor. The maximum resolution, in electrical position, which can be achieved with LEVEL 1 auxiliary sensors is 30 degrees.
Therefore from the above arrangement, the following parameters can be observed (as also seen
in Figure 5 of the accompanying drawings):
Number of auxiliary sensors in LEVEL 1 = 3.
No of transitions from high to low and vice versa in one electrical cycle = 12.
Angular position of LEVEL 1 sensors with respect to their corresponding main sensors = 30 deg
or 90 deg.
In at least one more embodiment, the number of auxiliary sensors (per main sensor) can be increased in a pre-defined progressive manner. This arrangement allows increase in number of transitions from high to low and from low to high, in one electrical cycle. The three main sensors are known and absolutely required to drive a rotating machine.
If 'N' is the level of auxiliary sensors that are provided, the total number of auxiliary sensors to beused at Level N = 3*(2N-l).
Therefore, the number of first auxiliary sensors (per main first sensor) (i.e. HA's) for LEVEL N = (2N-1)
E.g. if N = 3, Total number of auxiliary sensors to be used for LEVEL 3 = 21. Number of first auxiliary sensors (per main first sensor) (HA's) for LEVEL 3 = 7 i.e. there will be HA[1], HA[2],..., HA[7] and corresponding second auxiliary sensors (per main second sensor) (HB's) i.e. there will be HB[1], HB[2],.... HB[7] and corresponding third auxiliary sensors (per main
third sensor) (HC's) i.e. there will be HC[1], HC[2],..., HC[7]. HB's and HC's would be 120 and

240 degree apart from their corresponding first auxiliary sensor HA's respectively.
Number of transitions in one electrical cycle with LEVEL N set of auxiliary sensors = 6 * 2N

Therefore, the angular position of all the first auxiliary sensors (HA's) for LEVEL N is as below:


Electrical Angular position of HA[k] w.r.t. HA

And corresponding second and third auxiliary sensors (HB's and HC's) should be placed 120 and 240 deg apart from their corresponding first auxiliary sensors (HA's).
E.g., if N = 3, Electrical Angular position of HA[k] vv.r.t. HA will be as follows:

HA[k] Position k[60/2ΛN ] Or Position 60+k[60/2ΛN]
HA[1] 7.5
67.5
HA[2] i5
75
HA[3] 22.5
82.5
HA[4] 30
90
HA[5] 37.5
97.5
HA[6] 45
105
HA[7] 52.5
112.5
In accordance with another non-limiting exemplary embodiment in relation to a 6-sensor arrangement of this invention, the six sensor arrangement is relatively inexpensive as compared to an equivalent incremental quadrature encoder i.e. the six sensor arrangement only has 6 sensors and a PCB providing 48 speed / position feedback pulses and costing approximately 7 times lesser than an encoder of similar pulses range. Therefore, the six sensor arrangement (in accordance with the principles of main and auxiliary sensors of this invention) is very cost effective. There is no need for an extra sensor magnet to sense the six sensing states, as main magnet can be used as sensor magnet. It is a very cost effective solution in providing better closed loop performance at low speeds as compared to a similar encoder being used for position

sensing. Therefore this invention provides competitive advantage in terms of cost and performance.
The INVENTIVE STEP lies in provisioning a first main set of sensors intermittently disposed with a second auxiliary set of sensors with the electrical configuration defined above. The multiplexed signals from the sensors provide increased feedback pulses in one revolution, thereby increasing accuracy. Further, this aids in criticality of achieving control of motor at low speeds.
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. A sensor arrangement for high resolution position sensing in closed loop motor control for
a motor, said motor comprising a main set of sensors consisting of a first main sensor, a
second main sensor, and a third main sensor, each of said main sensors being spaced apart
120° electrically from each other, said sensor arrangement further comprising:
• at least a first level of auxiliary set of sensors consisting of at least three sensors including a first level first auxiliary sensor, a first level second auxiliary sensor, a first level third auxiliary sensor, each of said auxiliary sensors per level being displaced in a pre-determined manner with respect to a corresponding main sensor.
2. The sensor arrangement as claimed in claim 1, wherein each of said sensors is a Hall-effect sensor.
3. The sensor arrangement as claimed in claim 1, wherein each of said first level auxiliary sensors being spaced apart 30° electrical from a corresponding main sensor.
4. The sensor arrangement as claimed in claim 1, wherein each of said first level auxiliary sensors being spaced apart 90° electrical from a corresponding main sensor.
5. The sensor arrangement as claimed in claim I, wherein said arrangement comprising a multiplexing means adapted to multiplex signal outputs from each of said main sensors and auxiliary sensors to provide a final multiplexed signal. Fmux.
6. The sensor arrangement as claimed in claim 1, wherein said arrangement comprising at least a further level of auxiliary set of sensors wherein number of total auxiliary sensors provided in correlation with the number of levels of sets of auxiliary sensors, in conformation with said pre-determined manner, being given by:
number of auxiliary sensors for Nth level = 3* (2N-1).
7. The sensor arrangement as claimed in claim 1, wherein said arrangement comprising at
least a further level of auxiliary set of sensors, each further level comprising at least a pre-

defined number of first auxiliary sensors, said pre-defined number, for level N, in conformation with said pre-determined manner, being given by:
number of first auxiliary sensors for Nth level = (2N-l)
8. The sensor arrangement as claimed in claim 1, wherein said arrangement comprising at
feast a further level of auxiliary set of sensors, each further level comprising at least a pre
defined number of second auxiliary sensors, said pre-defined number, for level N, in
conformation with said pre-determined manner, being given by:
number of second auxiliary sensors for Nth level = (2N -1)
9. The sensor arrangement as claimed in claim 1, wherein said arrangement comprising at
least a further level of auxiliary set of sensors, each further level comprising at least a pre
defined number of third auxiliary sensors, said pre-defined number, for level N, in
conformation with said pre-determined manner, being given by:
number of third auxiliary sensors for Nth level = (2N-1)
10. The sensor arrangement as claimed in claim 1, wherein said arrangement comprising a multiplexing means adapted to multiplex signal outputs from each of said main sensors and auxiliary sensors to provide a final multiplexed signal, Fmux, wherein number of transitions in the multiplexed signal per electrical cycle for Nl level of auxiliary sensors, in conformation with said pre-determined manner, being given by 6 * 2N
11. The sensor arrangement as claimed in claim 1. wherein said arrangement comprising a multiplexing means adapted to multiplex signal outputs from each of said main sensors and auxiliary sensors to provide a final multiplexed signal, Fmux, wherein three main sensors and Nth level auxiliary sensors [obtained by 3* (2N -1) no. of auxiliary sensors] provide (6 * 2N) transitions in said final multiplexed signal per electrical cycle).
12. The sensor arrangement as claimed in claim 1. wherein angular position of all first auxiliary sensors, for a given level N, with respect to its corresponding main sensor, in conformation with said pre-determined manner, being given by:


and further wherein angular position of all corresponding level N second auxiliary sensors (HB[k]) being 120 degree apart with respect to its corresponding level N first auxiliary sensor (HA[k]).
and further wherein angular position of all corresponding level N third auxiliary sensors (HC[k]) being 240 degree apart with respect to its corresponding level N first auxiliary sensor (HA[k]).
The sensor arrangement as claimed in claim 1, wherein angular position of all first auxiliary sensors, for a given level N, with respect to its corresponding main sensor, in conformation with said pre-determined manner, being given by:

and further wherein angular position of all corresponding level N second auxiliary sensors (HB[k]) being 120 degree apart with respect to its corresponding level N first auxiliary sensor (HA[k]).
and further wherein angular position of all corresponding level N third auxiliary sensors (HC[k]) being 240 degree apart with respect to its corresponding level N first auxiliary sensor (HA[k]).
4. The sensor arrangement as claimed in claim 1, wherein each of said auxiliary sensors is mechanical spaced apart from a main sensor based on the following formula, in conformation with said pre-determined manner being: mechanical angle = electrical separation angle /[(number of poles in the motor/2)].