Encoding mechanism integral to the motor and using the permanent magnets embedded in the rotor eliminates the need for external devices to encode information relating the position and velocity of the rotating member

Berard, C. A.

Furia, T. J.

Goldberg, E. A.

Greene, R. C.

English

NASA Technical Reports Server

or 
S 
May 1970	 Brief 70-10188 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Hall Effect Encoding of Brushless DC Motors 
Figure 1. Element Location 
To operate a brushless dc motor, an encoder and 
external circuitry must be employed to provide com-
mutation of the windings. In order to eliminate the 
need for external devices to encode information relat-
ing the position and velocity of the rotating member, 
an encoding mechanism integral to the motor, and 
using the permanent magnets embedded in the rotor, 
has been developed. Brushless dc motors are construc-
ted with the magnetic field created by permanent mag-
nets in the rotating member (rotor) and the windings 
in the stationary member (stator). While a two-pole 
machine is described here, the scheme is useful in ma-
cnines with numerous poles. 
As shown in Figure 1, a Hall-effect element, at-
tached to the stator, is mounted in the motor gap. 
When driven with a constant current, the output of the 
element is proportional to the magnetic induction, B, 
including both direction (or sense) and magnitude 
of the rotor field. Thus the output is maximum in one 
direction when the north pole is under the Flail cle-
ment, maximum in the other direction when the 
south pole is under the Hall element, and at some 
intermediate level when the position of the rotor is 
in between. 
For the brushless motor type having two windings 
in quadrature, sine and cosine driving signals are re-
quired. Two Hall elements are used to replace the sine-
cosine resolver. The field of the rotor is a sinusoidal 
function of position. Position is described by the angle 
0, where 6 equals zero when Hall element #1, as shown 
in Figure 2 is energized by the north pole of the rotor. 
The sine and cosine outputs are amplified and applied 
to the proper motor winding by external control 
electronics. 
For a switched-winding type motor, where the wind-
ings are energized sequentially as a function of motor 
rotor position, a slightly different arrangement is used. 
Here, one sensor is used for each pair of windings. 
All windings are energized sequentially over 360 elec-
trical degrees where for multi-winding or multi-pole 
machines: 
360 electrical degrees = 
360 mechanical degrees of rotation

number of pole pairs 
If there are X pairs of windings, then each winding 
is energized for 360/2X electrical degrees. Detection 
of positive and negative outputs from each Hall ele-
ment is performed to energize the proper windings 
by external commutation and control logic. 
Notes: 
1. In this design, the encoding function uses the per-
manent magnets integral to the motor so that size 
and weight are minimized through the elimination 
of conventional encoders, disks, or magnets. 
(continued overical) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19700000181 2020-03-17T00:29:19+00:00Z
Hall El 
#2 on P 
:ation 
2. Requests for further information may be directed to 
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B70-10188
Patent status: 
No patent action is contemplated by NASA. 
Source: Clement A. Berard, Thomas J. Furia, 
Richard C. Greene, and Edwin A. Goldberg of 
Astro-Electronics Division of RCA 
under contract to 
Goddard Space Flight Center 
(GSC- 10789) 
Hall Output #1	 0=0	 Hall Element #1 on Stator 
Cosine 0 
Output 
0	 90 1,,,,< ^80 1 ^22 7 0 1 
Hall Output #2	 I 
E 2 
Sine 0 
Output
0 Position 
Degrees 
	
I	 I	
9Position 
0	 90	 1	 Degrees 
Figure 2. Sine and Cosine Outputs During Rotor Movement 
Brief 70-10188	 Category 01


Hall effect encoding of brushless dc motors

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