FIELD OF THE INVENTION
[0003] The present invention relates to the field of motion control and electric motors, in
particular brushless DC electric motors, and pertains to commutation and encoding for such
motors.
BACKGROUND OF THE INVENTION
[0004] Commutation for brushless DC (BLDC) electric motors typically employ Hall-effect
sensors to sense movement of permanent magnets in operation of the motors. Hall-effect
sensors, however, have not been successfully incorporated to encode DC motors to a high degree
of accuracy and granularity without the use of additional position sensors and/or encoder
hardware, and as such their usefulness in this context is limited. In many instances, the
successful operations and application, of motor-driven elements requires a high degree of
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precision and resolution in determining the position (and changes in position) of the motordriven
elements. This is particularly important for small scale devices, for example, driving
pumps and syringes to manipulate fluid samples in analytic processes in diagnostic systems.
Another difficulty is precision-controlled motion of such motors. Motion control ofbrushless
DC motors is well-known in the art by incorporation of a hardware encoder for position feedback
and speed control. However, when implementing motion control by conventional means,
such as an electronic, motor, and/or optical encoder, the mechanical packaging of such motors
becomes large, more complex and expensive.
[0005] There is a need, therefore, for systems and methods that allow for determination of
displacement of a motor, for example, encoding of a BLDC motor, to a very high degree of
resolution and positional accuracy. It is further desirable to provide motion control for such
motors without use of an additional hardware encoder and with relatively simple hardware and
control software.
BRIEF SUMMARY OF THE INVENTION
[0006] In one aspect, the invention herein pertains to the field ofBLDC motors and motion
control, in particular, an absolute encoder integrated within the motor in a small package. In
some embodiments, the invention pertains to integrated motion which combines the motor with
an integrated absolute encoder and controller functions in a relatively small package. This
approach enables a new generation of robotic, human augmentation, automation equipment,
military, and space flight uses because of its compactness, performance, light weight, and
competitive price.
[0007] In some embodiments, this approach is embodied by a BLDC motor that is modified to
include a rotor having a first inner magnetic ring, and a second outer magnetic ring and an
additional sensors (e.g., analog Hall-effect sensors), thereby generating a second high-resolution
encoder. A first encoder is generated by the "inner ring" of magnets which also serve the dual
purpose for motor driving. The second encoder is generated by the second ring of magnets on the
"outer ring" which are for encoder use only. In one aspect, the due to the manner in which the
signals are processed, the encoder is absolute within one period, or electrical cycle. This enables
instant-on from a positioning and commutation standpoint. Thus, the position of the motor can
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be determined with minimal rotor movement, in contrast to a motor with an incremental encoder.
Similarly the second encoder is also absolute but over a different period. By using the "Vernier"
relationship between the two absolute encoders-each absolute over a segment of the rotor
displacement, an absolute displacement within a single rotor rotation can be derived.
[0008] In some embodiments, the motor system utilizes this approach to generate a highresolution
ABSOLUTE encoder that allows for determination of an absolute position of the rotor
by utilizing geometric and algebraic interpolation between the sensor signals received by one or
more sensors detecting passage of the magnets of the inner and outer magnet rings upon rotation
of the rotor. In one aspect, the motor system analyzes only the linear portions of the sensor
signals from the inner and outer magnet rings. While these concepts are described in regard to a
motor having a rotatably-mounted rotor, it is appreciated that these concepts may also be applied
to a linear motor having a linear stage that moves in a linear fashion.
[0009] In some embodiments, the BLDC motor utilizes a common microcontroller with
integrated Analog-to-Digital Converter (ADC) to drive a three-phase half bridge to perform
motor commutation. The controller can drive the motor via sinusoidal, trapezoidal, sync, or any
other form of commutation and motor drive for theN number of motor phases.
[0010] In some embodiments, the BLDC motor utilizes the same microcontroller, or an
additional microcontroller integrated into the motor, to interpolate the high-resolution
incremental or absolute encoder and perform commutation and motor drive. In some
embodiments, the controller can further provide any of: communication with a host system; PID
feedback control; state-space feedback and feedforward control; and execution of motion
trajectories. In some embodiments, the host communicates to the motor to move according to a
predefined trajectory, for example, a pre-defined "curve" with constant acceleration, constant
velocity and constant acceleration, or some other movement. Here the term trajectory will be
taken to mean a time sequence of points on a path.
[0011] In one aspect, the motor can include a communication unit that provides wireless
communication with this integrated solution over a wireless interface, for example, such as
Bluetooth, BLE, Wi-Fi, 2.4 or 900 ISM bands, Zigbee, or any suitable communication means.
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[0012] In another aspect, the motor can be configured with a power-line communication unit
that is configured for communication with the integrated solution on a signal over power
communications scheme. In some embodiments, select wires (e.g. two or more) connect to the
motor which are used to power the motor drive bridge as well as motion control electronics. A
voltage regulator can be used to take the higher voltage used for the motor drive and adjust this
voltage for use with the processing electronics. In some embodiments, a specially designed
circuit is used to modulate a signal onto the powerline, and demodulate a signal from the
powerline, by the host controller. In some embodiments, two-way communication is achieved
over the powerline from host controller and motor controller. It is appreciated that each of the
above features can be used in an embodiment in combination with one or more other features.
[0013] Any of the aspects or features described above can be utilized with systems having
multiple motors connected to a single powerline system, for example, by use of a single master
host controller controlling all motors. Some such embodiments can utilize wireless
communications where an additional "sync" line is used to ensure, synchronized ("lock step")
motion of all motors in the system.
[0014] Some embodiments can utilize a controller that synchronizes multiple integrated motor,
encoder, control and drive solutions to work in tandem with each other through a digital
communications interface, for example, as Ethernet, EtherCAT (Ethernet for Control
Automation Technology), SPI, i2c, UAR, RS232, RS485, or any other suitable fieldbus or digital
communications interface. In some embodiments with multiple motor units, the controller can
be configured for synchronization of multiple integrated motor units (with encoder and control
and drive).
[0015] In another aspect, the motor includes a high-resolution linear motor encoder using two
or more analog hall-effect sensors and a "standard" linear actuator magnetic array. In some
embodiments, the motor uses the same magnets as already exist for motor drive of the linear
motor. In some embodiments, a silicon device with integrated ADC and controller is used to
perform the measurement, calculation and communication to a host system.
[0016] In yet another aspect, the invention pertains to a linear motor that includes any of the
features described above alone or in combination. In still another aspect, the invention pertains
to a combination of a rotary and linear motor that includes any of the features described above
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alone or in combination. In some embodiments, such motors having a combination of rotary and
linear motors are all controlled by a single controller chip.
[0017] In some embodiments, a processing module is configured to process the signals from at
least two sensors by utilizing a matrix transformation from which the motor displacement (e.g.
angular displacement of rotor) is determined. Advantageously, utilizing matrix transformation
from the signals of at least two sensors eliminates the velocity ripple arising from decoding
methods that employ mathematical approximations. The velocity ripple can adversely affect the
accuracy of a signal from an individual sensor and introduce vibration and instability in the drive
train. The use of a mathematical transformation when decoding purely sinusoidal or other
deterministic, periodic signal models provide increased resolution and fidelity for determination
of motor displacement. In some embodiments, the encoder includes a processor
communicatively coupled to the n magnetic field sensors and configured to determine
displacement of the movable element based on n signals from the n magnetic field sensors by
processing the n signals utilizing a transformation matrix.
[0018] In still another aspect, the encoder approach can be modified for a multi-speed
mechatronic system. Such an encoder system can include: a movable element that applies at
least two of a spatially-varying field, a first applying a field of period, S 1 and a second, S2 where
S2 is an integer multiple of the period, S 1; and a stationary support having nl sensors arranged
within the period S 1 and n2 sensors arranged within the period S2, where nl and n2 are each
greater than or equal to two, the sensors being configured to measure the magnetic field of the
movable element. The system can further includes a processor that obtains the signals from the
sensors and applies a transformation matrix to determine field angles, ~ 1 and~ 2. In some
embodiments, the processor is configured to: process nl and n2 sensor signals from the nl and
n2 sensors; apply a mathematical transformation to compute sine and cosine of the field angles, ~
1 and~ 2, respectively; and compute~ 2 with substantially equivalent resolution to~ 1. The
above described approaches can be utilized with the absolute encoder configuration described
previously.
[0019] In some embodiments of the multi-speed approach, each of S1 and S2 can be a rotary
displacement while in other embodiments, each can be a linear displacement. The mathematical
transformation can be configured such that calculation of each field angle, ~' is independent of
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an amplitude and bias of the magnetic field sensors. The magnetic field sensors are uniformly
distributed within each period, S 1 and S2. In some embodiments, the system is configured such
that the applied magnetic field is represented by a sum of first and at least one of higher-order
harmonics. In some embodiments, the processor of the control unit can store a run out
represented by a spatially-varying signal representing the difference between the true field angle
and the sensed field angle for each of field angles S 1 and S2 and utilizes the run out to
compensate for the difference thereby removing any runout error.
[0020] The above described encoder can be utilized in a BLDC motor configured for operation
of a mechatronic system within a diagnostic assay system. In some embodiments, the
mechatronic system of the diagnostic assay system comprises any of: a syringe, valve, or door
mechanism. the processor can be configured to process only the substantially linear portions of
the signals or can process the entire signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIGS. 1A-1B show perspective view of a BLDC motor in an exemplary embodiment
of the invention.
[0022] FIGS. 2A-2B show top and side views, respectively, of the BLDC motor of FIG. 1A.
[0023] FIG. 3 shows an exploded view of the BLDC motor of FIG. 1A.
[0024] FIG. 4 shows a top schematic view of an BLDC motor with encoder in accordance with
some embodiments.
[0025] FIGS. 5A-5B show top schematic views of an BLDC motor with encoder in
accordance with some embodiments.
[0026] FIG. 6 shows top schematic views of an BLDC motor with encoder in accordance with
some embodiments.
[0027] FIGS. 7-8 shows waveforms of the voltage signals from sensors of an exemplary
BLDC motor with encoder in accordance with some embodiments.
[0028] FIG. 9 shows closed loop control of a BLDC motor with encoder in accordance with
some embodiments.
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[0029] FIGS. 10-11 shows a relationship between the inner and outer rings of magnets of a
BLDC motor with an integrated, absolute encoder in accordance with some embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[0030] In the foregoing specification, the invention is described with reference to specific
embodiments thereof, but those skilled in the art will recognize that the invention is not limited
thereto. As used throughout, the term "about" can refer to the ±10% of the recited value.
Various features and aspects of the above-described invention can be used individually or jointly.
It is appreciated that any of the aspects or features of the embodiments described herein could be
modified, combined or incorporated into any of the embodiments described herein, as well as in
various other types and configurations. Further, the invention can be utilized in any number of
environments and applications beyond those described herein without departing from the broader
spirit and scope of the specification.
[0031] FIG. IA and IB are perspective top and bottom views, respectively, of a brushless DC
(BLDC) electric motor 100 having an integrated absolute encoder in accordance with some
embodiments. FIGS. 2A and 2B shows top and elevational side views, respectively of the BLDC
motor 100, and FIG. 3 shows an exploded view. As shown, the motor 100 includes: a blockshaped
base 1, a bearing assembly 2 that rotatably supports the rotor assembly; a substrate 3,
typically a printed circuit board (PCB); a stator 4 having multiple poles (each having pole teeth
and a pole shoe); and an outer housing cover 10. The PCB substrate can include a controller and
control circuitry for encoding and commutation. The rotor assembly includes a ring frame 5,
outer magnets 6, inner magnets 7, and a rotor portion that includes a lid 8 and shaft 9. In this
embodiment, the stator has 12 poles (each having pole teeth and pole shoes), while the rotor ring
5 has twenty outer magnets 6 and fourteen inner magnets 7.
[0032] Substrate 3 can include sets of sensors arranged for detection of the magnets of the
inner and outer magnet rings during operation of the motor. In this embodiment, the PCBA
substrate 3 include a series of three outer sensors lla, lib, lie and a series of three inner sensors
12a, 12b, 12c distributed along a partial arc around the central opening through which the
rotatable shaft 9 extends for detection of the inner and outer magnets, respectively. Additional
outer sensors 13a, 13b, 13c (partly visible), can be included on the opposite side of the opening
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as well, although such sensors are optional. The optional additional sensors compensate the rotor
run out, hysteresis, and the placement tolerance of the outer magnets which in turn enhance the
position accuracy.
[0033] Rotor assembly engages physically with stator by drive shaft 9, which engages the
bearing assembly 2 of the stator to guide rotation of the rotor with precision. Bearing 2 assembly
includes two parts that rotatably engage the shaft from opposite sides of the PCB substrate.
Details of the bearings are not shown, although it is appreciated that there are many conventional
ways such bearings can be implemented. Drive shaft 9 passes through an opening in cover 10
and can be engaged to drive mechanical devices or torque transfer mechanism. The rotor rotates
in either direction depending on details of commutation. It is appreciated that the approaches
described herein can be used regardless of the direction of rotation of the rotor.
[0034] Individual components can be understood further by referring to FIG. 3, which shows
an exploded view of the integrated actuator. In this embodiment, the design comprises a 20 W
motor, a true 16+ bit absolute encoder, and the control electronic within a relatively small
package. At top is the upper cover 10, in which an opening in the center of the cover allows the
motor to couple with the interface equipment. In this embodiment, the central opening is
relatively small (e.g. 10-50 mm, 20-40 mm, 35 mm). The rotor shaft 9 extends upward through
the central opening for interfacing with equipment (the OD and shaft length can vary as needed).
Rotor lid 8 includes a precise spacer for alignment with magnets of the inner and/or outer rings.
[0035] Ring 5 is calculated to an appropriate thickness to accommodate the flux density of the
inner and outer magnets. As shown, the inner and outer magnets are mounted on the ring 5. It is
appreciated however, that the inner and outer magnets can be included on separate rings that
interface, or can be integral with one or more rings. In some embodiments, the outer magnet ring
6 and inner magnet ring 7 each includes magnets of any even number. In some embodiments, the
number of magnets in inner magnet ring 7 is different from that of the outer magnet ring. In this
embodiment, the outer magnet ring has twenty magnets, while the inner magnet ring has fourteen
magnets. The combination of the outer magnet and inner magnet is central to generating an
absolute encoder as described herein.
[0036] Also shown is stator core 4. In some embodiments, the stack length (e.g., height of the
stator) of the stator including the winding is smaller or equal to the length of the magnets of the
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inner ring 6. This dimension allows for generating a noise free sine wave. In some embodiments,
the sensors are separated from the magnets by a small distance. In small-scale devices, this
separation is typically less than 5 mm, such as 4 mm, 3 mm, 2 mm or 1 mm or less depending on
the overall size of the device and the strength of the magnetic fields. It is advantageous for the
space between the sensors and the permanent magents to be minimized in order to substantially
eliminiate noise in the detection signal. It is appreciated that any of the aspects described in U.S.
Patent Application No. 15/217,893 entitled "Encoderless Motor with Improved Granularity and
Methods of Use," for example, in regard to arrangement and dimensioning of magnets relative
the rotor or magnetic core, can be utilized for either inner or outer magnet rings to provide noise
free signals.
[0037] One or more sensors are disposed adjacent the path of the magnets during operation of
the rotor. The rotor includes one or more inner sensor rings to detect a signal from the inner
magnets and one or more outer sensors to detect the signal from the outer magnets. Typically,
the rotor includes sets of multiple sensors disposed along the paths of the inner and outer rings,
which are spaced apart and can be offset to provide improved resolution. In some embodiments,
spacing within the sensors is calculated as follows:
s = 120/P
where:
S : Spacing between hall sensors, in degree.
P: Pole pair
[0038] In one aspect, the inner sensor(s) is the coarse encoder signal and also serves as the
motor commutation, while the outer sensor(s) is the fine encoder signal which incorporates with
the coarse signal to allow determination of an absolute position. This embodiment includes two
sets of three sensors each. The two sets are placed 90° electrical and 180° mechanical apart to
improve the resolution and position accuracy. It is appreciated that additional sensors or sensor
arrangements could be used.
[0039] The above-noted sensors are typically mounted on the PCB substrate 3 for detection of
the magnets, but can be placed on any suitable surface. The PCB also implements a silicon
device with integrated ADC and microcontroller, which can be used to perform the motion
control, measurement, calculation and communication to a host system.
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[0040] In accordance with the applications noted above, it is noted that the absolute encoder
features described herein allows the entire motor to be of a considerably small size. For
example, the embodiment described herein can be of a dimension of about less than 4" square
(length and width, as shown in FIG. 2A) and less than 2" in height (as shown in FIG. 2B). In
some embodiments, this design allows for the motor with integrated actuator to be less than 2"
square (length and width) and 2" or less in height. It is appreciated that the concepts described
herein are not limited to these particular dimensions or small-scale mechanisms and could be
used in various other motor designs of any size for various applications.
[0041] In another aspect, a control unit (not shown in FIG. 1A) can switch current in the coils
102 providing electromagnetic interaction with permanent magnets 106 to drive the rotor, as
would be known to one of skill in the art ofBLDC motors. The control unit can be connected via
connector 14, such as the 12-pin connector shown in FIG. 2A-2B. The connector can provide
means for communication as well as for powering the motor, as described previously. It is
appreciated that the control unit can be separately provided or integrated within the PCB of the
motor.
[0042] It is appreciated that this embodiment is a non-limiting exemplary prototype. It should
be noted that the number of pole teeth and poles, and indeed the disclosure of an internal stator
and an external rotor are exemplary, and not limiting in the invention, which is operable with
motors of a variety of different designs. For example, while an internal stator and external rotor
are described here, it is appreciated that this approach can also be used in a motor having an
internal rotor and external stator as well.
[0043] Such a motor could be used in a wide variety of applications, and is of particular use for
operation of a small-scale mechanical mechanism requiring a high level of accuracy and
granularity. Some embodiments include a motor system having improved resolution in the
determination of rotor position and/or displacement without use of hardware encoders and/or
noise-filtering, for example, a resolution of about 0.1 degrees of mechanical rotation, or
preferably about 0.01 degrees mechanical rotation, or even about 0.001 degrees of mechanical
rotation or less. One such application is operation of a syringe drive to effect highly precise fluid
metering, or operation of a valve assembly of a diagnostic assay system that interfaces with a
sample cartridge in order to facilitate a complex sample processing and/or analysis procedure
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upon fine-tuned movement of the valve assembly. Examples of such applications can be found
in U.S. Patent Application No. 15/217,893 entitled "Molecular Diagnostic Assay System"; U.S.
Patent No. 8,048,386 entitled "Fluid Processing and Control;" and U.S. Patent No. 6,374,684
entitled "Fluid Control and Processing System," which are incorporated herein by reference.
[0044] FIG. 4 shows an exemplary motor 400 having a rotor and stator design and PCB layout
that indicates the positions of three sensors, H (e.g. Hall-effect sensors). In accordance with a
typical BLDC motor, the motor 400 includes a stator 410 with anchored windings on ferrous
cogs, while the rotor 420 includes a rotating shroud with permanet magnets. In this embodiment,
the sensors are spaced at 0, 120 and 240 "electrical degrees" where 360 electrical degrees is
equal to the angle of one pole pair.
[0045] For a motor with 12 poles, for example, the Hall-effect Sensors are spaced at:
where:
A (degrees)
A+ 20 + (N*60) (degrees)
A+ 40 + (M*60) (degrees)
A is an arbitrary position about the circumference of the magnetic rotor
N is some number of"electrical cycles" to offset the Hall-effect sensor
M is a second number of electrical cycles to offset the Hall-effect sensor
[0046] In some embodiments, for a motor rotor with any number of poles, it is advantageous if
the three sensors (e.g. Hall-effect sensors) are placed as follows about the circumference of the
rotor magnets:
A (degrees)
A+ 120/P + (N*180/P) (degrees)
A + 240/P + (M* 180/P) (degrees)
where P is the number of Poles in the Rotor
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[0047] In some embodiments, for a motor rotor with any number of poles and any number of
sensors (e.g. Hall-effect Sensors), the sensors are placed as follows (angles in degrees):
where:
N is number of iteration
His number of Hall-effect Sensors
A is some starting angle (degrees)
P is the number of total magnetic poles (pole pairs I 2)
X is an arbitrary value to allow the Hall-effect sensors to be spaced (this could be equal
toN, but could be larger if required for very large Hall-effect sensors or very many poles.
If the Hall-effect sensors are sufficiently small and the poles sufficiently large, then X
could be zero. X=N in the exemplary case).
[0048] In one aspect, an added benefit of using the same number of sensors on the inner ring
and outer ring is that a commutation cycle will match the electrical cycle of the Hall-effect
sensors. For example, as the rotor moves, the electrical angle at which one drives the motor
windings cycles at the same rate as the Hall-effect sensors. This reduces processing power
needed for the purpose of commutation as described further below.
[0049] Orientation of Hall-effect Sensors
[0050] In another aspect, it is advantageous to orient the sensors (e.g. Hall-effect sensors)
relative the rotor so that the locations of adjacent sensors corresponds to adjacent magnets, as
shown in FIGS. SA-6.
[0051] FIG. SA shows another exemplary BLDC motor 500 which shows the position of the
sensors, H, relative the magnets of the rotor (note the position of sensors Hand magnets on the
inner ring 521 ). FIG. 5B shows a detail view with the stator removed to better illustrate the
relative positions of the magnets and sensors H. In accordance with a typical BLDC motor, the
motor 500 includes a stator 510 with anchored windings on ferrous cogs, while the rotor 520
includes a ring 520 having an inner magnet ring 521 with permanet magnets as well as the outer
magnet ring 522 with permanent magents. In this embodiment, there are a series of inner sensors
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H inner disposed along or adjacent the path of the inner magnets and there are a series of outer
sensors, H outer, disposed along or adjacent the path of the outer magnets. FIG. 6 shows
substantially the same exemplary motor as FIG. 5 with the housing cover 10 and rotor lid 8 and
shaft 9 shown as transparent.
[0052] In one aspect, commutation of the BLDC motor 500 can be performed using only three
sensors. The specific embodiment described here is for a three-phase, fourteen-pole, brushless,
direct-current, motor. It is appreciated that the concepts of the invention described herein are not
limited to this specific embodiment. This same approach can be utilized for encoder
interpolation and commutation of many different kinds of motors as well as many different
motor poles. In some embodiments, the magnets used for encoding/position detection can be the
same magnets that are used for motor drive, which reduces total number of magnets needed in
the system thereby allowing for additional integration.
[0053] Hall-effect Waveforms
[0054] FIGS. 7-8 shown below displays the analog voltage signal waveforms output from a
logical set of properly biased analog Hall-effect sensors, properly spaced such that the permanent
magnets in the motor produce waveforms separate by 60°. FIG. 7 depicts a rotor moving
clockwise, while FIG. 8 shows counter clockwise motion.
[0055] In this embodiment, for analog Hall-effect sensors that are powered off of 5 V, zero
crossing (where the Hall-effect sensor is not experiencing a magnetic induced Hall-effect) is very
close to 2.5V, which is typical for most Hall-effect sensors. Zero crossings can be utilized to
divide up the sampled Hall-effect sensor data. In one aspect, additional algorithms can be used
to interpolate rotor position with even finer granularity than zero-crossing, for example, a
"Center of mass" or "Centroid" algorithm.
[0056] In one aspect, the control unit can utilize operating instructions recorded on a readable
memory thereof, which include such an algorithm. For example, in some embodiments, the
control unit is configured to perform the centroid based interpolation, which can be firmware that
is programmed into the ASIC in the exemplary motor system.) An example of such an algorithm
is provided in the following code, which is written in ANSI C:
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InterruptServiceRoutine(commutationHandler)
{
commutationState = 0;
if(ADC_SAR_Seq_finalArray[O] > 0)
commutationState I= Ob001;
if(ADC SAR_Seq_fina1Array[1] > 0)
commutationState I= Ob010;
if(ADC SAR_Seq_fina1Array[2] > 0)
commutationState I= Ob100;
switch(commutationState)
{
case Ob101:
firstParam = 0;
secondParam = 2;
//signage = 0;
adder = 2 << extraResolutionForEncoder;
break;
case Ob001:
firstParam = 2;
secondParam = 1;
//signage = 1;
adder = 3 << extraResolutionForEncoder;
break;
case Ob011:
firstParam = 1;
secondParam = 0;
//signage = 0;
adder = 4 << extraResolutionForEncoder;
break;
case Ob010:
firstParam = 0;
secondParam = 2;
//signage = 1;
adder = 5 << extraResolutionForEncoder;
break;
case Ob110:
firstParam = 2;
secondParam = 1;
//signage = 0;
adder = 6 << extraResolutionForEncoder;
break;
case Ob100:
firstParam = 1;
secondParam = 0;
//signage = 1;
adder = 7 << extraResolutionForEncoder;
break;
default:
break;
temp = ADC_SAR_Seq_finalArray[firstParam] +
PCT/US2021/015877
ADC SAR Seq finalArray[secondParam] + ADC_SAR_Seq_finalArray[secondParam];
//assuming zero point of 0 ... May need to eventually calibrate ..
temp<<= extraResolutionForEncoder; //12 bits of centroid
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algorithm
temp /= ADC_SAR_Seq_finalArray[firstParam] +
ADC SAR_Seq_finalArray[secondParam];
PCT/US2021/015877
temp-= (2AextraResolutionForEncoder); //remove offset from
centroid algorithm.
II we get two clock pulses per ZC
if(ADC SAR Seq_finalArray[firstParam] == 0)
//if the first parameter is zero, then keep track of boundary
condition ...
temp -= 1;
adder temp;
//FW based quaderature decoder
if( (adder< 768) && (commutationWheel last > 2304))
hwEncoder += 3072;
else if( (adder > 2304) && (commutationWheel last < 768))
hwEncoder -= 3072;
commutationWheel last = adder;
encoder = hwEncoder + adder-encoderOffset;
//end FW based quad decoder
adder /= 6;
commutationWheel = adder;
It is appreciated that such algorithms could utilize the same or similar approach by use of any
suitable programming languages.
[0057] The above routine is performed at a sampling rate of 1/ L1ts. where L1ts is the time
interval between samples in the discrete-time implementation. All three channels ofHall-effect
sensor are sampled in this period. In an exemplary case, the three Hall-effect sensors are
sampled at 100 ksps rate and are run through an analog mux. On-chip DMA resources can be
used to transfer the samples from the ADC to the processor's SRAM memory, which end up in
an array called: "ADC_SAR_Seq_final Array". In the exemplary case, the L1ts is programmable
down to 100 !J.S. This function provides two different outputs. One output is a parameter called
"Commutation Wheel". Commutation wheel is a 512 count (9 bit) representation ofwhere the
rotor is located within the A-F electrical commutation cycle. The other output is a parameter
called "encoder". "Encoder" is a continuous encoder ( 64-bits in this case) which continues to
increment with each electrical cycle. "Encoder" in this case has 3072 counts of resolution per
electrical cycle and billions of counts of integrated resolution.
[0058] Simple Centroid Approach
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[0059] In some embodiments, the control unit can be configured to utilize the "Simple
Centroid" approach to interpolate the hardware encoders utilizing the analog levels of each AH
waveform individually. For example, in Commutation state 100, note that waveforms Band C
cross each other in a near-linear fashion within this commutation section. The following
algorithm is used in this section to add additional encoder resolution to the hardware encoder
already running. The hardware encoder already has six (6) counts of resolution per pole: any
additional resolution (AR) may be used to augment this resolution with the "Simple Centroid"
algorithm.
EP =((HE)* (AR) I 2) + { [ (B*AR) + (C*AR*2)] I AR}- AR
where:
EP =Encoder Position
HE = Hardware Encoder
AR = Additional Resolution
B = ADC of Analog B phase AH waveform
C = ADC of Analog C phase AH waveform
[0060] Additional Functionality
[0061] In addition to commutation and encoding, this specific embodiment performs closed
loop PID control of rotor position, current measurement and command and control. In this
embodiment, control can include a floating point rotation translation for a worm drive with 284
rotor revolutions per revolution over a UART interface.
[0062] The hardware system described above allows the firmware to be somewhat isolated
from the low-level motor driving functionality. It is appreciated that PID control can be used to
control the motor, as would be readily understood by one of skill in the art. However, suffice it
to say that the firmware may simply drive the direction and PWM of the instantiated hardware
system. An example of such a PID control is shown in FIG. 9. Such a control method can
include the following steps: 1. Measure the Encoder Position ~ 2. Compare this to desired
position ~ 3. Input these desired and actual positions into the PID control system. ~ 4.
Adjust direction and PWM of motor control based upon output ofPID control. In addition to the
PID control, a Delta Sigma based (Low Pass Filtering) ADC can be utilized to measure current.
This current may be requested over the UART interface and reported to the control unit.
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[0063] "OUTER MAGNET RING"
[0064] In order to include an absolute encoder in the design, a secondary "outer ring" can be
utilized. In some embodiments, the outside ring of magnets utilizes Hall-effect sensors for
measurement that are spaced with the same calculations as the inside ring described above.
[0065] The outer ring can utilize the same ADC techniques and algorithms to generate a
"Commutation Wheel" and "Encoder" parameter for the outside ring. In some embodiments, the
same mathematical approach that was used with the inner ring, described above, can be used
with the outer ring.
[0066] The mechanical placement of the magnets on the rotor and the vertical relationship of
the magnets to the Hall-effect sensors are precisely controlled. In this embodiment, the outer ring
magnets are placed 20 mils closer to the Hall-effect sensors in the vertical direction.
[0067] The relationship between the number of poles in the inner and outer rings is another
factor to consider. In one aspect, the number of pole pairs for the inner ring and the number of
pole pairs for the outer ring must not share a common denominator. In one aspect of some
embodiments, the magnets position on the inner ring and outer ring should not repeat over one
revolution, which means the value of the outer pole pairs divided by the inner pole pairs is not a
whole number. In the exemplary embodiment, the inner ring has seven pole pairs and the outer
ring has ten pole pairs.
[0068] ABSOLUTE ENCODER CALCULATIONS
[0069] FIGS. 10-11 illustrate a relationship between the absolute position and the commutation
of the outer and inner rings. The relationship between the absolute position and the
"Commutation Wheel" of the inner ring and "Commutation Wheel" of the outer ring is utilized
to determine which electrical cycle the motor is in of the "P/2" number of electrical cycles in a
revolution. For example, in a motor with "P" poles, there are "P/2" electrical cycles such that
there are seven electrical cycles on the inner ring and ten electrical cycles on the outer ring per
revolution. As can be seen in the figure, by utilizing differing numbers of pole pairs defined by
the magnet, the linear portions of the signals from the inner and outer magnet rings cross each
other, thereby providing improved granularity. It is appreciated that the number of magnets and
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pole pairs of the outer ring can be greater than the inner ring (for example, 1 0-to-7 as shown in
FIG. 1 0), or less than (for example, 2-to-7 as shown in FIG. 11 ).
[0070] The electrical cycle relationships for an entire revolution of two exemplary motor
embodiments are illustrated in FIGS. 10 and 11. Notably, for every position in every electrical
cycle, the relationship between the inside ring and outside ring will determine which electrical
cycle within the entire revolution the rotor is positioned. The following algorithm can used to
make this determination. (This utilizes 512 counts per electrical cycle. This number is not a
required for proper operation, but is used because it is a convenient binary value for
multiplication and division in two's compliment.)
[0071] For each value of the inner Commutation wheel there is an IPP number of outer
commutation wheel values possible as shown here:
OW[N]
/PP-1
where:
N =Number of iteration
IW = "Commutation Wheel" Value corresponding to electrical position on inner ring
OW = "Commutation Wheel" Value corresponding to electrical position on outer ring
IPP = number of inner ring pole pairs
OPP = number of outer ring pole pairs
[0072] In one aspect, the inner and outer rings must NOT have a common denominator of pole
pairs of each ring. If the inner and outer ring have a common denominator then the series
OW[N] will have two or more values of equal magnitude. It will then be impossible to make the
determination of location around the absolute rotation. Therefore, the set of all valid inner and
outer ring pole pair combinations is the infinite set where IPP% OPP != 0
[0073] The above series could be calculated with each iteration of measurement given enough
processing power. However, it is advantageous to accelerate this equation for the benefit of
absolute encoder output. This is accomplished through the following ANSI C equation.
#define INNER POLE PAIRS 7 - -
#define RESOLUTION OF COMM WHEEL 512
int modulationValueTable[INNER POLE PAIRS +1]
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37
110
183
256
329
402
475
549
} ;
[0074] The values in the modulationValueTable table are given by:
modValueTable[N]
N=O
PCT/US2021/015877
I round [-2-*-~-P-P + ~;PR]
IPP
where:
IPP is the Pole Pairs in the inner ring.
R is the Resolution of the commutation wheels
N is the number of iteration
int modulationindexTable[S]
o , I I
5 , I I
3 , I I
1 , I I
6 , I I
4 ,II
2 ,II
0 ,II
} ;
[0075] The values in the modulationlndexTable table are given by:
N=O
i[N] I [-R_*_~p-Pp_P_*_i o/oR]
where:
IPP
IPP is the Pole Pairs in the inner ring.
R is the Resolution of the commutation wheels
N is the number of iteration
i is the modulation index table value
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int absBotTable[512] = .....
The values in the absBotTable table are given by:
N=O
absBotTable[N] I round
R-1
[{
N * OPP} ]
R * IPP o/oR
where:
IPP is the Pole Pairs in the inner ring.
OPP is the Pole Pairs in the outer ring.
R is the Resolution of the commutation wheels
N is the number of iteration
int32 absoluteEncoderFunction(void)
{
int i;
int32 temp;
if(commutationWheelOutside < 0)
commutationWheelOutside += 512;
if(commutationWheelOutside >= 512)
commutationWheelOutside -= 512;
if(commutationWheelinside <0)
commutationWheelinside += 512;
if(commutationWheelinside >= 512)
commutationWheelinside -= 512;
temp = commutationWheelOutside -
absBotTable[commutationWheelinside];
while(temp < 0)
temp += 512;
for(i=O;i<8;i++)
{
if( temp < modulationValueTable[i]
{
temp 12288;
temp *= modulationindexTable[i]+1;
temp -= extremeAbsoluteResolution;
return(temp);
return(Oxffffffff);
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[0076] Where commutationWheelOutside and commutationWheellnside are the inside and
outside commutation wheel parameters and "extremeAbsoluteResolution" is a higher resolution
version of the inside commutation wheel (12288 counts to be exact) given by the same simple
centroid algorithm as before. If the inside and outside rings are not perfectly aligned, then an
alternate table can be utilized to compensate for the offset between rings. This can be performed
by adding an offset which is proportional to the offset between inner and outer ring commutation
wheels. The offset between outside and inside commutation wheel counts can be measured in
outside commutation wheel counts. These counts can then be subtracted from the line above as
shown:
temp = commutationWheelOutside -
absBotTable[commutationWheelinside]- OFFSET;
while(temp < 0)
temp += 512;
[0077] As described above in the non-limiting exemplary embodiments, an ADC is used to
produce the division of the straight, linear portions of the phase-separated waveforms and motor
100, which can be driven by any suitable driver circuitry (for example, a DRV83 13 Texas
Instruments motor driver circuit). It is understood that there are other arrangements of circuitry
that might be used while still falling within the scope of this approach. In some embodiments the
circuitry and coded instructions for sensing the Hall-effect sensors and providing motor
encoding may be implemented in a programmable system on a chip (PSOC) on the PCB.
[0078] The above-described approach is one way of determining the absolute encoder value by
looking at the phase-shift in the substantially linear portions of the Hall-effect sine waves.
However, it is appreciated that the matrix transformation approach can also be used. Using the
matrix transformation method, the absolute position is calculated on each of the inner-ring and
outer ring respectively and then an absolute position can be determined within one rotor
revolution using the Vernier effect. This is the same concept as described above in that the
phase-shift between the inner and outer ring provides an unambiguous way of determining the
absolute position.
[0079] It is appreciated that a variety of alterations can be made in the embodiments described
herein without departing from the scope of the invention. For example, electric motors of
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different designs might be incorporated and controlled in alternative embodiments of the
invention by placement of sensors to generate substantially sinusoidal phase-separated
waveforms in a manner that the circuitry takes into account only the substantially straight, linear
portions of the resulting, intersecting curves, with additional resolution provided by dividing the
straight portions into equal length segments, effectively dividing the voltage increments into
equal known segments to be associated with fractions of rotor or stator rotation, depending on
mechanical design of the motor.
[0080] Some non-limiting exemplary uses and applications for a DC electric motor according
to the invention include the following:
[0081] Diagnostic applications: With increasing use of robotics for use in high-throughput
processing of fluid samples and performing of diagnostic assays, high resolution control of
mechanical mechanisms has become extremely useful. Particularly, as diagnostic devices have
trended toward small-scale and microdevices, which are more efficient and require smaller
sample sizes, control over small-scale movements is of particular interest.
[0082] Medical applications: With increasing use of robotics for remote surgery techniques,
extremely well controlled movement of remotely controlled implements have become essential.
For example, in ophthalmology or neurology procedures where manipulation of retinal cells or
nerve endings require movements with microscopic resolution. In order to effect these
movements, which are far finer than is possible with a human hand with eye coordination,
computers are used to move actuators in concert with feedback from suitable sensors. A motor
with high resolution positional encoding capabilities as disclosed herein can assist the computer,
and therefore the surgeon, in performing these delicate procedures.
[0083] Semiconductor fabrication: Systems for fabrication of semiconductor devices rely on
fine movement of the silicon wafer and manipulator arms. These movements are regulated by
means of positional feedback. A motor with high res olution positional encoding capabilities as
disclosed herein suitable in these applications.
[0084] Aerospace and satellite telemetry: High resolution angular position feedback can be
used for precise targeting and for antenna positioning. In particular, satellite communication
antenna dishes need to precisely track orbiting satellites. Satellite trajectory combined with
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precise angle feedback from a motor as described herein mounted to the antenna and power
spectrum from the antenna can assist precise tracking. In addition, because the motor as
described herein is small, inexpensive and robust, it is an ideal choice for use on satellites and in
other extra-terrestrial applications that will be well known to persons of skill in the art.
[0085] Remote controlled vehicles: the small size and reduced cost of the motor disclosed
herein makes it desirable for use in remote controlled vehicle applications, including drones.
In particular the high resolution positional encoding features of the motor make it ideal for
steering (directional control) and acceleration (power control) in both commercial and
recreational uses of remote controlled vehicles. Additional uses will be apparent to persons of
ordinary skill in the art.
[0086] Further to the above, the skilled person will be aware that there are a variety of ways
that circuitry may be arranged to provide granular control for a motor thusly equipped and
sensed. The invention is limited only by the claims that follow.

WHAT IS CLAIMED IS:
1. A DC electric motor system comprising:
a stator mounted to a substrate, the stator comprising a coil assembly having a
core of magnetic material and electrical windings;
a rotor mounted to the stator, the rotor comprising:
an inner magnet ring having a first set of permanent magnets adjacent to the core
of magnetic material, the first set of permanent magnets being arranged to facilitate
rotation of the rotor;
an outer magnet ring having a second set of permanent magnets, the second set of
permanent magnets arranged to facilitate determination of a displacement of the rotor
based on relative positions of the first and second set of permanent magnets;
one or more sensors mounted on the substrate and disposed about the circumference of
the rotor, wherein the one or more sensors are arranged to obtain voltage signals from the first
and second set of magnets during rotation of the rotor, the voltage signals corresponding to
positions of the first and second set of permanent magnets.
2. The system of claim 1, wherein the rotor comprises a common ring wherein the
first set of magnets are mounted on an inside surface of the common ring thereby defining the
inner magnet ring, and the second set of magnets are mounted on an outside surface of the
common ring thereby defining the outer magnet ring.
3. The system of claim 1, wherein the rotor comprises any of:
a ring having magnetized poles that defines the inner magnet ring, while the outer magnet
ring is defined by the second set of magnets mounted on the ring;
a ring having magnetized poles that define the outer magnet ring, while the inner magnet
ring is defined by the first set of magnets mounted on the ring.
4. The system of claim 1, wherein the rotor comprises:
a first ring having magnetized poles that define the inner magnet ring, and
a second ring concentric with the first ring and having magnetized poles that define the
outer magnet ring.
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5. The system of claim 1, wherein the inner and outer magnets each comprise an
even number of magnets.
6. The system of claim 5, wherein the inner magnet ring comprises a different
number of magnets than the outer magnet.
7. The system of claim 6, wherein the inner magnet ring comprises fewer magnets
than the outer magnet.
8. The system of claim 6, wherein the outer magnet ring comprises fewer magnets
than the inner magnet ring.
9. The system of claim 1, wherein each of the inner and outer magnet rings
comprises one or more pole pairs, wherein the number of pole pairs of the inner and outer
magnet rings do not share a common denominator.
10. The system of claim 1, wherein the stator is mounted on a substrate, and the one
or more sensors are mounted on the substrate and arranged along the path of the magnets of the
inner and/or outer magnet ring.
11. The system of claim 1, wherein the one or more sensors comprise:
a first set of sensors arranged for detection of the inner magnet ring, and
a second set of sensors arranged for detection of the outer magnet ring.
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12. The system of claim 11, wherein the first set of sensors comprises two or more
sensor disposed along or adjacent a path of the inner magnets of the inner magnet ring
13. The system of claim 11, wherein the first set of sensors comprises at least three
sensors spaced apart and disposed within one quadrant of rotation of the rotor, and the second set
of sensors comprises at least three sensors that are spaced apart and disposed within one quadrant
of rotation of the rotor.
14. The system of claim 11, wherein the inner magnet ring has an even number of
magnets with two or more pole pairs.
15. The system of claim 14, wherein the first set of sensors are spaced apart, wherein
the spacing= 120/P where Pis the number of pole pairs.
16. The system of claim 11, wherein the second set of sensors comprises two or more
sensors disposed along or adjacent a path of the outer magnets of the inner magnet ring.
17. The system of claim 11, wherein the outer magnet ring has an even number of
magnets with two or more pole pairs.
18. The system of claim 17, wherein the second set of sensors are spaced apart,
wherein the spacing= 120/P, where Pis the number of pole pairs of the outer magnet ring.
19. The system of claim 11, further comprising:
a controller configured for operation of the motor based on an absolute position of
the rotor, wherein the controller is further configured to determine displacement by:
position.
obtaining a first set of sinusoidal signals from the first set of sensors;
obtaining a second set of sinusoidal signals from the second set of sensors;
analyzing the first and second set of signals to determine an absolute
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20. The system of claim 19, wherein the controller is further configured to:
receive, with the controller, a desired position of the rotor;
compare the desired position with the absolute position or displacement
determined; and
adjust pulse width modulation and drive direction of the motor based on the
comparison to achieve the desired position of the rotor.
21. The system of claim 19, wherein the controller is a proportional-integralderivative
(PID) controller.
22. The system of claim 19, wherein the control unit is further configured with
programmable instructions recorded on a memory thereof, the instructions configured to apply in
algorithm to analyze the linear portions of the first and second set of signals.
23. The system of claim 22, wherein the control unit is further configured such that
the algorithm utilizes a center-of-mass interpolation.
24. The system of claim 22, wherein the control unit is further configured such that
the algorithm utilizes a centroid interpolation.
25. The system of claim 22, wherein the control unit is further configured such that
the algorithm utilizes a matrix transformation method.
26. The system of claim 19, wherein the substrate is a printed circuit board (PCB)
comprising circuitry enabling analog-to-digital conversion (ADC) of voltage values in the
defined linear portions of the signals from the first and second set of sensors.
27. The system of claim 19, wherein the circuitry is implemented in a programmable,
system-on-a-chip (PSOC).
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28. The system of claim 1, wherein the outer magnet ring has a single pole pair and
the inner magnet ring has two or more pole pairs.
29. The system of claim 28, wherein the out magnet ring is a continuous ring with
each halfbeing magnetized to a pole of the single pole pair.
30. A method for encoding a DC electric motor, the method comprising:
operating a motor by powering a coil assembly of a stator of the motor, the coil assembly
having a core of magnetic material and electrical windings, thereby rotating a rotor having an
inner magnet ring having a first set of permanent magnets adjacent to the core of magnetic
material, wherein the rotor further includes an outer magnet ring having a second set of
permanent magnet; and
determining an absolute position of the rotor by:
obtaining, with one or more sensors of the motor, a first signal from the first set of
permanent magnets passing by the one or more sensors during rotation of the rotor;
obtaining, with one or more sensors of the motor, a second signal from the second
set of permanent magnets passing by the one or more sensors during rotation of the rotor;
analyzing the first and second signal and correlating to a position of the rotor.
31. The method of claim 30, further comprising:
adjusting operation of the motor based on the determined absolution position of the rotor.
32. The method of claim 31, wherein adjusting operation comprises adjusting the
pulse-width-modulation and/or the drive direction of the motor.
33. The method of claim 30, wherein the motor is operated via a controller, the
method further comprising:
receiving, with the controller, a desired position of the rotor;
comparing the desired position with the absolute position determined; and
adjust pulse width modulation and drive direction based on comparison to achieve
the desired position of the rotor.
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34. The method of claim 33, wherein the controller is a proportional-integralderivative
(PID) controller.
35. The method of claim 33, wherein the controller employs a state-space determined
feedback controller.
36. The method of claim 33, wherein the controller also employs feedforward control
37. The method of claim 30, wherein the stator is mounted on a substrate, and the one
or more sensors are mounted on the substrate along a path of the magnets of the inner and outer
magnet rings, respectively.
38. The method of claim 30, wherein the rotor comprises a common ring wherein the
first set of magnets are mounted on an inside surface of the common ring defining the inner
magnet ring, and the second set of magnets are mounted on an outside surface of the common
ring defining the outer magnet ring.
39. The method of claim 30, wherein the rotor comprises any of:
a ring having magnetized poles therein that define the inner magnet ring, while the outer
magnet ring is defined by the second set of magnets mounted on the ring; and
a ring having magnetized poles therein that define the outer magnet ring, while the inner
magnet ring is defined by the first set of magnets mounted on the ring.
40. The method of claim 30, wherein the inner and outer magnets each comprise an
even number of magnets.
41. The method of claim 40, wherein the inner magnet ring comprises a different
number of magnets than the outer magnet.
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42. The method of claim 30, wherein each of the inner and outer magnet rings
comprise a one or more pole pairs, wherein the number of pole pairs of the inner and outer rings
do not share a common denominator.
43. The method of claim 30, wherein determining the absolute position of the rotor
comprises analyzing only the linear portions of signals from the one or more sensors.
44. The method of claim 43, wherein analyzing comprises applying a center of mass
or centroid based interpolation.
45. An encoder for a mechatronic system, the encoder comprising:
a movable element that applies at least two of a spatially-varying field, a first applying a
field of period, S1 and a second, S2 where S2 is an integer multiple of the period, S1;
a stationary support having nl sensors arranged within the period S 1 and n2 sensors
arranged within the period S2, where nl and n2 are each greater than or equal to two, the sensors
being configured to measure the magnetic field of the movable element; and
a processor configured to:
process nl and n2 sensor signals from the nl and n2 sensors;
apply a mathematical transformation to compute sine and cosine of the field
angles, ¢ 1 and¢ 2, respectively; and
compute ¢ 2 with substantially equivalent resolution to ¢ 1.
46. The encoder in claim 45, where an absolute displacement is determined within a
period larger than either S 1 and S2 by using the Vernier effect arising from the difference
between S 1 and S2.
47. The encoder in claim 45, where each of S 1 and S2 is a rotary displacement.
48. The encoder in claim 45, where each of S 1 and S2 is a linear displacement.
49. The encoder in claim 45, wherein the mathematical transformation is configured
such that calculation of each field angle, ¢, is independent of an amplitude and bias of the
magnetic field sensors.
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50. The encoder in claim 45, where the magnetic field sensors are uniformly
distributed within each period, S 1 and S2.
51. The encoder claim 45, where the system is configured such that the applied
magnetic field is represented by a sum of first and at least one of higher-order harmonics.
52. The encoder of claim 45, wherein the processor is configured to:
store a runout represented by a spatially-varying signal representing the difference
between the true field angle and the sensed field angle for each of field angles S 1 and S2 and
utilizes the runout to compensate for the difference thereby removing any runout error.
53. The encoder in claim 45, where the encoder is utilized in a BLDC motor
configured for operation of a mechatronic system within a diagnostic assay system.
54. The encoder in claim 45 wherein the mechatronic system of the diagnostic assay
system comprises any of: a syringe, valve, door or cartridge loading mechanism.
55. The encoder in claim 45 wherein the processor is configured to process only the
substantially linear portion of the signals.