Title: Motor speed sensor advancement emulation and compensation
Abstract: A microcontroller emulates advancement of a speed sensor for a motor, rather than having a physical movement of the speed sensor. The microcontroller calculates an advancement time based on the motor's efficiency. The microcontroller measures a motor speed utilizing a tachometer signal transmitted from the speed sensor. The microcontroller subtracts the emulated advancement time from the motor speed to generate a commutation countdown time. The microcontroller switches or commutates outputs when the commutation countdown time has elapsed. The microcontroller measures an actual advance time, which is a time between the commutating of the outputs and a receipt of the next speed sensor interrupt. The microcontroller calculates an anticipated motor speed by adding the actual advance time to the commutation countdown time.
Patent Number: 7,002,311 Issued on 02/21/2006 to Strike, et al.
| Inventors:
|
Strike; Nigel (Phoenix, AZ);
Brewer; Carl (Chandler, AZ)
|
| Assignee:
|
Minebea Co., Ltd. (Tokyo, JP)
|
| Appl. No.:
|
803328 |
| Filed:
|
March 18, 2004 |
| Current U.S. Class: |
318/439; 318/254 |
| Current Intern'l Class: |
H02P 6/12 (20060101) |
| Field of Search: |
318/138,254,439,720-724
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Ro; Bentsu
Attorney, Agent or Firm: Pillsbury Winthrop Shaw Pittman LLP
Claims
The invention claimed is:
1. A method of driving a motor comprising:
calculating an emulated advancement time based on the motor's efficiency;
measuring a time for one revolution of a rotor of the motor;
subtracting the emulated advancement time from the time for the one revolution
of the rotor to generate a commutation countdown time; and
commutating outputs from a controller to the motor when the commutation countdown
time has elapsed.
2. The method of claim 1, further including measuring an actual advance time,
the actual advance time being a time between the commutating of the outputs and
a receipt by the controller of a next speed sensor interrupt.
3. The method of claim 2, further including calculating an anticipated motor
speed by adding the actual advance time to the commutation countdown time.
4. The method of claim 3, further including
(a) calculating a new commutation countdown time by subtracting the emulated
advancement time from the anticipated motor speed;
(b) commutating outputs from the controller when the new commutation countdown
time has elapsed;
(c) measuring the actual advance time between the commutating of the outputs
and the next speed sensor interrupt;
(d) calculating the anticipated motor speed by adding the actual advance time
to the new commutation countdown time; and
continuing the steps (a), (b), (c), and (d) until the anticipated motor speed
is lower than a pre-determined motor speed threshold.
5. The method of claim 4, further including decrementing the emulated advancement
time by a pre-determined advancement time to created a decremented emulated advancement
time if the anticipated motor speed is lower than a pre-determined threshold;
calculating the new commutation countdown time by subtracting the decremented
emulated advancement time from the anticipated motor speed;
commutating the outputs from the controller when the new commutation countdown
time has elapsed;
measuring the actual advance time, the actual advance time being the time between
the commutating of the outputs from the controller and the receipt by the controller
of the next speed sensor interrupt; and
calculating the anticipated motor speed by adding the actual advance time to
the new commutation countdown time.
6. A method of initializing neutral commutation, comprising:
initializing a first driving signal to drive a motor;
receiving a tachometer signal from a speed sensor for the motor;
measuring a pulse time based on the received tachometer signal;
calculating a commutation countdown value by subtracting an initial advancing
time from the pulse time if the calculated motor speed is lower than a minimum
pre-determined threshold; and
commutating outputs to the motor including generating a second driving signal
if the commutation countdown value has elapsed.
7. The method of claim 6, further including measuring an actual advance time
as a period between the commutating of the outputs and a receipt of a next speed
sensor interrupt.
8. The method of claim 7, further including creating an anticipated motor speed
by adding the actual advance time to the commutation countdown time.
9. The method of claim 8, further including determining if the initial advancing
time is less than a threshold advancing time.
10. The method of claim 9, further including
(a) creating a new advancing time by adding an incremental advancing time to
the initial advancing time if the initial advancing time is less than the threshold
advancing time;
(b) calculating a new commutation countdown time by subtracting the new advancing
time from the anticipated motor speed;
(c) commutating the outputs including generating the first drive signal when
the new commutation countdown time has elapsed;
(d) measuring the actual advance time between the commutating of the outputs
and the next speed sensor interrupt;
(e) creating a new anticipated motor speed by adding the actual advance time
to the new commutation countdown time, and
repeating steps (a), (b), (c), (d), and (e) until the new advancing time is greater
than threshold advancing time.
11. A method of driving a motor, comprising:
calculating an advancement time based on a motor's efficiency;
utilizing a tachometer signal transmitted from a speed sensor for the motor to
to measure a time between pulses of the tachometer signal;
subtracting the advancement time from the the time between pulses to generate
a commutation countdown time; and
commutating outputs from a controller to the motor when the commutation countdown
time has elapsed.
12. The method of claim 11, further including
(a) utilizing the tachometer signal transmitted from the speed sensor at a new
measurement time to measure a new time between pulses,
(b) calculating a new commutation countdown time by subtracting the advancement
time from the new time between pulses;
(c) commutating outputs to the motor from the controller when the new commutation
countdown time has elapsed; and
continuing the steps (a), (b), and (c) until the new time between pulses is lower
than a pre-determined threshold.
13. A method of initializing neutral commutation, comprising:
initializing a first driving signal to drive a motor;
receiving a tachometer signal from a speed sensor for the motor;
calculating a time between pulses of a tachometer signal based on the received
tachometer signal;
calculating a commutation countdown value by subtracting an initial advancing
time from the time between pulses of the tachometer signal if the time between
pulses of the tachometer signal is lower than a minimum pre-determined threshold; and
commutating outputs to the motor, including generating a second driving signal,
if the commutation countdown value has elapsed.
14. The method of claim 13, further including determining if the initial advancing
time is less than a threshold advancing time.
15. The method of claim 14, further including
(a) creating a new advancing time by adding an incremental advancing time to
the initial advancing time if the initial advancing time is less than the threshold
advancing time;
(b) calculating a new commutation countdown time by subtracting the new advancing
time from the time between pulses in the tachometer signal;
(c) commutating the outputs to the motor, including generating the first drive
signal when the new commutation countdown time has elapsed, and
repeating steps (a), (b), and (c) until the new advancing time is greater than
threshold advancing time.
16. A microcontroller to drive a motor, comprising:
a determination module to receive a tachometer signal from a speed sensor for
the motor, to to determine a time between pulses of the tachometer signal from
the tachometer signal, and to transmit the time between pulses of the tachometer signal;
an advancing analyzation module to receive the time between pulses of the tachometer
signal, to calculate a commutation countdown time by subtracting an advancement
time from the time between pulses of the tachometer signal, and to transmit the
commutation countdown time,
a counting module to receive the commutation countdown time, and to transmit
a commutation signal once the commutation countdown time has expired; and
a commutation output module to receive the commutation signal and to switch outputs
of the microcontroller to the motor upon receipt of the commutation signal.
17. The microcontroller of claim 16, wherein the commutation output module notifies
the advancing analyzation module that the outputs to the motor are switched, the
advancing analyzation module transmits a second signal to the counting module to
begin an actual advance count, the speed determination module transmits a signal
identifying that a next speed sensor interrupt has been received, and the counting
module stops the actual advance count upon receipt of the next speed sensor interrupt.
18. The microcontroller of claim 17, wherein an anticipated motor speed is calculated
by adding the commutation countdown time and the actual advance count.
19. The microcontroller of claim 17, further including, after the commutation
of the microcontroller outputs, the determination module determining the time between
the pulses of the tachometer signal for a new measurement time, and transmitting
the time between the pulses of the tachometer signal for the new measurement time
to the advancing analyzation module; and
the advancing analyzation module calculating the commutation countdown time for
the new measurement time by subtracting the advance time from the time between
the pulses of the tachometer signal.
20. The microcontroller of claim 19, wherein the determination module utilizes
a second counting module to determine the time between the pulses of the tachometer
signal for the new measurement time.
21. A device, comprising:
a driving device to receive a driving signal and to transmit the driving signal;
a motor to receive the driving signal and to operate the device based on the
driving signal;
a speed sensor to monitor the speed of the motor and to transmit a tachometer
signal; and
a microcontroller to receive the tachometer signal and to generate the driving
signal, including,
a speed determination module to receive the tachometer signal from the speed
sensor, to measure a time between pulses of the tachometer signal, and to transmit
the time between the pulses of the tachometer signal;
an advancing analyzation module to receive the time between the pulses of the
tachometer signal, to calculate a commutation countdown time by subtracting an
advancement time from the time between the pulses of the tachometer signal, and
to transmit the commutation countdown time,
a counting module to receive the commutation countdown time, and to transmit
a commutation signal once the commutation countdown time has expired; and
a commutation output module to receive the commutation signal and to switch outputs
of the driving signal generated by the microcontroller upon receipt of the commutation signal.
22. The device of claim 21, wherein the commutation output module notifies the
advancing analyzation module that the outputs are switched, the advancing analyzation
module transmits a second signal to the counting module to begin an actual advance
count, the speed determination module transmits a signal identifying that a next
speed sensor interrupt has been received, and the counting module stops the actual
advance count upon receipt of the next speed sensor interrupt.
23. The device of claim 22, wherein an anticipated motor speed is calculated
by adding the commutation countdown time and the actual advance count.
24. The device of claim 21, further including, after commutation of the microcontroller
outputs, the determination module determining the time between the pulses of the
tachometer signal for a new measurement time, and transmitting the time between
the pulses of the tachometer signal for the new measurement time to the advancing
analyzation module, and
the advancing analyzation module calculating the commutation countdown time for
the new measurement time by subtracting the advance time from the time between
the pulses of the tachometer signal.
25. A computer-readable medium having encoded thereon a computer-readable program
code which when executed causes a microcontroller to:
calculate an emulated advancement time based on a motor's efficiency;
measure a time for one revolution of a rotor of the motor;
subtract the emulated advancement time from the time for the one revolution of
the rotor to generate a commutation countdown time; and
commutate outputs from a controller when the commutation countdown time has elapsed.
26. The computer readable medium of claim 25, having encoded thereon computer
readable program code, which when executed causes the microcontroller to
measure an actual advance time, the actual advance time being a time between
the commutating of the outputs and a receipt by the controller of a next speed
sensor interrupt.
27. The computer readable medium of claim 26, having encoded thereon computer
readable program code, which when executed causes the microcontroller to calculate
an anticipated motor speed by adding the actual interrupt time to the commutation
countdown time.
28. A computer-readable medium having encoded thereon computer-readable program
code which when executed causes a microcontroller to:
initialize a first driving signal to drive a motor;
receive a tachometer signal from a speed sensor for the motor;
calculate a time between pulses of the tachometer signal based on the received
tachometer signal;
calculate a commutation countdown value by subtracting an initial advancing time
from the time between the pulses of the tachometer signal if the time between the
pulses of the tachometer signal is lower than a minimum pre-determined threshold; and
commutate outputs for the motor, including generating a second driving signal
if the commutation countdown value has elapsed.
29. The computer-readable medium of claim 28 having encoded thereon computer-readable
program code, which when executed causes the microcontroller to measure an actual
advance time as a period between the commutating of the outputs and a receipt of
a next speed sensor interrupt.
30. The computer-readable medium of claim 29 having encoded thereon computer
readable program code, which when executed causes the microcontroller to create
an anticipated motor speed by adding the actual advance time to the commutation
countdown time.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to motors for driving devices, e.g., cooling fans.
More particularly, the present invention relates to motors for driving devices,
e.g., cooling fans, for use in electronic systems and for software emulation and
compensation within the driven devices to achieve efficient operation.
2. Discussion of the Related Art
In electronic systems, such as computer systems, cooling fans play an important
role in maintaining the system's capabilities. The inability to remove excessive
heat from electronic systems may lead to permanent damage of the system. Because
of the complexity of existing electronic systems, cooling fans have added functionalities
other than just providing cooling air, such as the ability to control the speed
of a fan, the ability to monitor a tachometer pulse on a fan to determine instantaneous
fan speed, and the ability to detect if a fan has failed or is slower than its
preset speed.
Brushless D.C. motors, utilized today in electronic devices such as personal
computers, servers, laptops, and desktop computers, include a rotating permanent
magnet rotor, a stator carrying field coils, and a drive circuit for sequentially
exciting the field coils with digital pulses, thereby creating electronic commutation.
Electronically commutated motors eliminate or reduce the disadvantages inherent
in motors with mechanical structures for a commutator. Specifically, radio frequency
interference losses and electromagnetic induction (EMI) losses are reduced or eliminated.
Power consumption attributed to armature-brush arcing is also eliminated.
The electronic driving circuitry incorporates active electronic components such
as MOSFETs, to provide pulse width modulated signals. Drive pulse generation is
synchronized with rotor position by the incorporation of monitoring or feedback
circuitry, including the use of position sensors, such as Hall effect devices.
In a cooling fan, a circuit board may include a position sensor, such as a hall
effect sensor, a rotor, a stator, and a microcontroller.
A DC brushless motor may include a driving circuit based on an integrated circuit
that is soldered to the printed circuit board. The printed circuit board is contained
inside a motor casing together with the stator and the rotor. The rotor, supported
by bearings, may thus be propelled inside the stator to produce mechanical rotation
under control of the electronic driving circuitry. A stator is comprised of a selected
number of turns of conductor coils wound around a bobbin reel.
In operation, the stator field winding acts as an electromagnetic source that
produces magnetic flux as a result of the excitation current it receives. The generated
magnetic flux flows in a longitudinal direction of the generally cylindrical-shaped
body of the stator along the magnetic circuit inside the upper and lower magnetic
pole pieces, which are located at both ends of the stator cylindrical body. The
magnetic flux flows either into or out from the pole plates of the pole pieces
respectively and then into or out from the rotor. Depending on the polarity of
the current excitation in the stator field windings, the flux passes across an
air gap in the radial direction either to or out from the corresponding magnetic
poles in the ring magnet of the rotor. As the magnetic flux passes through closed
loops of magnetic circuits formed in the stator, the air gap and the rotor, mechanical
driving force is developed and the rotor is propelled to rotate.
Depending on the relative angular position of the rotor, the drive circuit
alternatively feeds driving current of clockwise or counter-clockwise orientation
into the stator field winding. As a result, the pole plates and the upper and lower
magnetic pieces respectively may become alternatively energized as north and south
poles respectively. With proper driving control, the rotor can thus be propelled
to rotate by the stator in the desired direction and speed of rotation.
Apparatus for sensing angular position and speed of a rotary shaft have
moved to utilizing less expensive components. Hall sensors and magnorestrictive
sensors may be utilized to generate electrical signals when exposed to a rotating
magnetic field. Hall effect sensors utilize a current-carrying semiconductor membrane
to generate a low voltage perpendicular to the direction of current flow when subjected
to a magnetic field normal to the surface of the membrane. The rotation of the
rotor's magnetic field is detected by, for example, a Hall sensor (Hall generator
circuit) which senses the rotor position and speed and provides synchronizing pulses.
If a hall sensor is placed in a neutral position, as illustrated in FIG. 1(
a),
the fan does not run efficiently and in some cases may not be able to reach the
higher speeds required to cool the electronics or computing device enclosure. In
order to combat this inefficiency, the hall sensor may be physically moved to an
advanced position, as illustrated in FIG. 1(
b), so that the hall sensor
is activated slightly before the pole pass. The hall sensor interrupt is sent to
a microcontroller, and the microcontroller switches the outputs, slightly before
the magnet passes the actual pole. The switching of outputs is referred to as switching
or commutation. This allows the fan to reach the higher speeds and operate in an
efficient manner.
The amount of advancement of the hall sensor depends on the operating speed of
the motor. Conventionally, the appropriate advancement of the hall sensor is based
on the maximum motor speed. Unfortunately, this means that when the speed control
of the fan is being utilized and the fan is running at a lower speed than maximum,
the motor is not running as efficiently as possible.
Problems arise when the hall sensor is physically advanced as described
above. A permanently advanced hall sensor causes an "oscillating effect" problem
on startup and also may cause a locked rotor condition. The net result of the "oscillating
effect" can prevent the fan from starting up or from rotating. The "oscillating
effect" is illustrated in FIGS. 1(
c) and
1(
d). If the hall
sensor is placed in a neutral position as shown in FIG. 1(
c), the rotational
torque for the motor shaft and the hall sensor is in one direction, whether momentum
is present or not. If the hall sensor is placed in an advanced position, as illustrated
in FIG. 1(
d), a negative torque and a positive torque exist. If the fan
is rotating, momentum overcomes the negative torque. If there is no momentum, such
as during startup, the positive and the negative torques can pull back and forth
indefinitely, causing an "oscillating effect." The "oscillating effect" frequency
is determined by the Gauss of the hall sensor, and could be interpreted by the
microcontroller as the frequency of a running fan.
In addition, different designs of the cooling fan may result in hall placement
changes. If a design of a cooling fan needs to be changed, the hall advancement
angle or advancement amount from a neutral position may need to change to achieve
max efficiency or desired speed. That results in a PCB layout change.
For example, if a fan is running at 4000 RPM, then the hall sensor or speed sensor
may be adjusted to 3 degrees from neutral position, and the PCB is laid out to
allow this position. If the same or similar fan needs to run at 6000 RPM, the PCB
would need to be reconfigured to adjust the hall sensor or speed sensor to 5 degrees
from neutral position for maximum efficiency. The design change or new circuit
board layout results in an increase in monetary and time costs.
Accordingly, a need exists to allow the fan to operate at high speeds
and to run in an efficient manner, while minimizing the "oscillating effect" and
minimizing any additional costs associated with board layout changes.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(
a) illustrates a neutral placement of a hall sensor according
to the prior art;
FIG. 1(
b) illustrates an advanced placement of a hall sensor according
to the prior art;
FIG. 1(
c) illustrates a torque relationship caused by a neutral placement
of a hall sensor according to the prior art;
FIG. 1(
d) illustrates a torque relationship caused by an advanced placement
of a hall sensor according to the prior art;
FIG. 2 illustrates a cooling fan including speed sensor advancement emulation
and compensation according to an embodiment of the present invention;
FIG. 3(
a) illustrates a microcontroller incorporating speed sensor advancement
emulation and compensation according to an embodiment of the present invention;
FIG. 3(
b) illustrates a second embodiment of a microcontroller incorporating
sensor sensor advancement emulation and compensation according to an embodiment
of the present invention;
FIG. 4(
a) illustrates a flowchart for the initialization stage for driving
a motor according to an embodiment of the present invention;
FIG. 4(
b) illustrates a flowchart for the initialization stage for driving
a motor where a tachometer signal is utilized to determine a calculated motor speed
according to an embodiment of the present invention;
FIG. 5(
a) illustrates a flowchart of an advancing emulation algorithm
after an initialization stage according to an embodiment of the present invention; and
FIG. 5(
b) illustrates a flowchart of an advancing emulation algorithm
after an initialization stage and when a tachometer signal is utilized to determine
a calculated fan speed according to an embodiment of the present invention.
DETAILED DESCRIPTION
FIG. 2 illustrates a cooling fan including speed sensor advancement emulation
and compensation according to an embodiment of the present invention. The cooling
fan
100 includes a fan module
110, which has a fan
112 (including
fan blades), a motor
114 rotatably coupled to the fan
112 to drive
the fan
112, and a driving circuit
150. The fan may be referred to
as an impeller. The motor
114 includes a stator
151 and a rotor
153.
The driving circuit
150 may include a first driver
152 and a second
driver
154. A microcontroller
120, such as a PIC16C717 microcontroller
device manufactured by Microchip Technology, Inc., is in direct communication with
the fan module
110. Any suitable microcontroller, controller, processor,
or processing device may be utilized. The microcontroller
120 may drive
the motor
114 through the driving circuit
150, in a manner as described
above. In other words, the microcontroller
120 may be coupled to a first
driving device
152 and a second driving device
154. The first driving
device
152 and the second driving device
154 in the driving circuit
150 may be coupled to the motor
114.
Although the invention is described in embodiments utilizing a motor to
drive a cooling fan, the present invention may be utilized in any apparatus or
device where a motor is being utilized to drive a shaft, and where a speed sensor
is utilized to sense, magnetically or otherwise, a rotational speed of the shaft.
In the application, a fan speed is mentioned but similarly the term "fan speed"
may be replaced with the term "motor speed." Many apparatus or devices may encounter
the "oscillating effect" described above due to an advancement of the speed sensor.
The teachings of the present invention apply to these areas also. For example,
a pump motor that moves water or another liquid through a medium may utilize the
teachings of the present invention. Motors for vacuum cleaners or other small household
appliances may also benefit from utilizing this technique. In addition, motors
in automatic breaking systems and electronic power steering systems may benefit
from the utilization of this technique.
The microcontroller
120 is preferably fixed internally within the cooling
fan
100. In an embodiment of the invention, the microcontroller
120
may be directly coupled to the motor
114. In this embodiment of the invention,
the functionality of the first driving device
152 and the second driving
device
154 may be incorporated into the microcontroller.
A bus interface
130 is in communication with the microcontroller
120.
In an embodiment of the invention, the bus interface may be an Inter-IC (I2C) bus
("I2C-Bus Specification", Version 2.1, January 2000, from Philips Semiconductors).
The bus interface
130 facilitates transfer of data to and from the microcontroller
120 from outside devices such as a system
140 or another cooling
fan
100 located within the same system
140. The bus interface
130
may be interconnected by bus lines
132, such as I2C bus lines, to the system
140. Illustratively, the I2C bus lines
132 have two lines: a data
(SDA) line and a clock (SCL) line. Inter-IC (I2C) may be accessed serially so that
each individual device utilizing the I2C protocol has a specific identification
(ID), but may all be connected to the same communication line(s) or bus(es) (i.e.,
it may be connected as a parallel bus). Inter-IC (I2C) is a useful protocol because
it is familiar to thermal design engineers who utilize cooling fans in their system
designs, and a fair number of digital logic devices utilize the I2C protocol. However,
any other bus interface systems and protocols may also be utilized. For example,
the Controller-Area Network (CAN) protocol (Controller-Area Network (CAN) Specification,
version 2.0, 1991, Robert Bosch GmbH, Stuttgart, Germany), utilized in the automotive
industry, may also be utilized with the bus interface
130 according to an
embodiment of the present invention.
According to an embodiment of the present invention, the microcontroller
120 is programmed with program code that enables the microcontroller
120
to read byte communications provided by a system or device
140 that utilizes,
for example, the I2C protocol. In a particular embodiment of the present invention,
the microcontroller
120 includes a program memory into which the program
code is stored. The PIC16C717 microcontroller, for example, is capable of handling
14-bit words and has a capacity of 2 kilobytes. The program or instruction code
may be programmed only once into the microcontroller
120 at the factory,
and if so, it is not re-programmable or re-writeable by an end user or cooling
fan customer. The PIC16C717 microcontroller, for example, also includes a small
data memory, or "scratch pad memory", having a capacity of 256 bytes available
to the microcontroller
120 to conduct its operations. In an embodiment of
the invention, the data memory of the microcontroller
120 is volatile and
does not store any programming or instructions, but rather it is only a working memory.
The cooling fan
100 and specifically the fan module
110 may include
a speed sensor
117. The speed sensor
117 may be a hall sensor or
a magnorestrictive sensor. In embodiments of the invention utilizing the hall sensor,
the hall sensor
117 provides a signal to the microcontroller based on the
positions of magnetic poles of the rotor
153 of the fan motor
114
in relation to the hall sensor. In an embodiment of the invention, the signal may
be referred to as a tachometer signal. The hall sensor utilizes the hall effect,
which occurs when charge carriers moving through a material experience a deflection
because of an applied magnetic field. The deflection results in a measurable potential
different across the side of the material which is transverse to the magnetic field
and the current direction.
In an embodiment of the invention utilizing a hall sensor as the speed sensor
117, a digital hall sensor may be utilized. In an embodiment of the invention,
an analog hall sensor may be utilized. In one embodiment of the invention, the
hall sensor
117 may provide a 50% duty cycle signal. As the rotor (containing
the permanent magnet) passes by the hall sensor, the output signal of the hall
sensor
117 transitions from low to high, or from high to low, depending
on the polarity of the magnet at the time of passing.
In an embodiment of the present invention, there are four stator teeth and four
magnetic poles. For each complete revolution of the rotor, the hall sensor will
transition four times, corresponding to the four magnetic poles on the rotor. Four
transitions will generate two evenly spaced square wave pulses. This corresponds
to two pulses being transmitted for each revolution of the fan. In other embodiments
of the present invention, additional magnetic poles may be used. For example, the
stator can utilize six stator teeth and the magnet can utilize six magnetic poles.
In this embodiment, the hall sensor would transition six times for each revolution,
generating three evenly spaced square wave pulses for each revolution. Based on
the signal provided by the speed sensor
117, e.g., the tachometer signal,
the microcontroller
120 is capable of determining the speed of the cooling
fan
100.
In order to avoid the "oscillating effect" at startup, avoid the locked-rotor
problem discussed above, maximize motor efficiency, and in order to minimize hall
sensor placement changes due to different designs and different loads created by
the fan on the motor, software code in the microcontroller
120 predicts
when the drive signals from the microcontroller should be activated, switched,
or commutated. In other words, software code may emulate the position of a speed
sensor
117 and also compensate for the advancement in position of the speed
sensor
117. Outputs from the microcontroller are switched at a commutation
time, which may be before the speed sensor interrupt signal or tachometer signal
is received at the microcontroller
120. In the embodiment of the invention
illustrated in FIG. 2, the microcontroller
120 may switch from generating
a first driving signal that is transmitted to the first driving device
152
to generating a second driving signal that is transmitted to the second driving
device
154.
The commutation time is determined by subtracting a pre-determined advancing
time from a calculated fan speed. The calculated fan speed is determined by the
microcontroller
120 after the microcontroller
120 receives the tachometer
signal and analyzes the tachometer signal generated by the speed sensor
117.
In an embodiment of the invention, the calculated fan speed may have a measurement
of revolutions per minute (RPM).
After the outputs from the microcontroller
120 are switched, the microcontroller
120 monitors or measures the time at which a next speed sensor interrupt
is received from the speed sensor
117. In other words, in an embodiment
of the invention utilizing a hall sensor, an actual advance time is measured between
the time of commutation or switching and when the next hall sensor interrupt is
received from the hall sensor
117.
In an embodiment of the invention, the microcontroller
120 calculates
an
anticipated fan speed by adding the actual advance time to the commutation time.
In this embodiment of the invention, the anticipated fan speed may be utilized
by the microcontroller
120 in place of the calculated fan speed. In an embodiment
of the invention, the microcontroller
120 determines the calculated fan
speed after the outputs have been commutated. In other words, the microcontroller
120 does not utilize the anticipated fan speed, i.e., the speed calculated
using the actual advance time and the commutation time.
The microcontroller
120 utilizes the anticipated fan speed or the calculated
fan speed to calculate a new commutation time for the next switching of the microcontroller
outputs. For example, the new commutation time is calculated by subtracting the
pre-determined advancing time from the anticipated fan speed or calculated fan
speed. The pre-determined advancing time may also be referred to as the emulated
advancing time. For example, the outputs of the microcontroller
120 are
switched, e.g., from a second driving signal back to a first driving signal.
In the embodiment of the invention utilizing the anticipated fan speed, the microcontroller
120 measures the elapsed time between the switching of the outputs and the
next speed sensor interrupt to produce the actual advance time. The new anticipated
fan speed is the summation of the actual advance time and the new commutation time.
This process continues as the fan continues to operate. In an embodiment of the
invention utilizing the calculated fan speed, the microcontroller
120 determines
new calculated fan speeds after the outputs have been commutated.
FIG. 3(
a) illustrates a microcontroller incorporating speed sensor advancement
emulation and compensation according to an embodiment of the present invention.
FIG. 3(
b) illustrates a second embodiment of a microcontroller incorporating
speed sensor advancement emulation and compensation according to the present invention.
The microcontroller may be utilized to send signals to drive a motor, which in
turn drives another device, such as a cooling fan. For simplicity and ease of illustration,
the description below refers to cooling fan speed, but the present invention applies
to further embodiments of motors in which other devices are driven or rotated by
the motor. The cooling fan microcontroller
200 includes a speed determination
module
204, an advancing analyzation module
206, a commutation/output
module
208, and a counting module
216. In an embodiment of the invention
illustrated in FIG. 3(
b), the cooling fan microcontroller may include a
first counter
216 and a second counter
218. The cooling fan microcontroller
200 may include a memory
212. The counters may be implemented as
timers in the microcontroller
200. The speed determination module
204,
the advancing analyzation module
206, and a commutation/output module
208
may be implemented in software within the microcontroller
200.
The cooling fan microcontroller
200 may start the fan
112 (see
FIG. 1). In an embodiment of the invention, a signal may enable the fan motor to
be turned on from the initialization or the power-up of the system
140.
In an embodiment of the invention, the microcontroller
200 may send a driving
signal to the motor
114 through a driving circuit
150. In an embodiment
of the invention, the microcontroller may transmit a first driving signal to cause
the motor
114 to turn on or activate the fan
112.
The advancing analyzation module
206 is deactivated as the fan is initialized.
In other words, the advanced analyzation module is not operating during initialization
or turning on of the fan. The advance analyzation module
206 is deactivated
to avoid the "oscillating effect" which is caused because when there is no momentum
and the torques can pull back and forth indefinitely. After initialization, the
speed determination module
204 receives the tachometer signal from the speed
sensor
117 and determines the speed of the fan
112 from the tachometer
signal. The speed of the fan may be referred to as the calculated fan speed.
In an embodiment of the invention, the speed determination module
204
may
receive the tachometer signal and utilize the second counter
218 to determine
the calculated fan speed, as illustrated in FIG. 3(
b). For example, the
speed determination module
204 may monitor the tachometer signal and notify
the second counter
218 (or timer) that a pulse has been received by the
speed determination module. The second counter
218 may measure the pulse
time in the tachometer signal or the time between pulses in order to determine
the calculated fan speed.
The speed determination module
204 continues to monitor the tachometer
signal. During this time, the microcontroller
200 switches the outputs in
sync with the tachometer signal interrupt. This may be referred to as "neutral
switching." Once the speed determination module
204 identifies that the
calculated fan speed has increased above an initial speed threshold, the advancing
analyzation module
206 is activated. The microcontroller
120 may
store a value of the initial speed threshold in a memory
212. The memory
212 may be a volatile or non-volatile memory. In an embodiment of the invention,
the initial speed threshold may be stored in a first register. In an embodiment
of the invention, the initial speed threshold may be stored in a memory address
in a common microcontroller memory, such as illustrated by memory
212 in
FIGS. 3(
a) and
3(
b).
In one embodiment of the invention, after the initial speed threshold has been
reached, i.e., the calculated fan speed is greater than the initial speed threshold,
the advancing analyzation module
206 emulates the advancing of a hall sensor
interrupt by calculating a commutation countdown value. The commutation countdown
value is calculated by subtracting an initial advancing amount from the calculated
fan speed. The initial advancing amount is a value calculated to be the smallest
amount of advancement possible while being large enough to overcome the microcontroller's
speed sensor interrupt overhead. In an embodiment of the invention, the initial
advancing amount may stored in a register. In an embodiment of the invention, as
illustrated in FIG. 3, the initial advancing amount may be stored in an address
in the common memory
212. In an embodiment of the invention, the initial
advancing amount may be referred to as an initial emulation amount. A motor
114
operates in the most efficient manner if the current being delivered to it maintains
a uniform value. In other words, a current waveform representing the current drawn
by the motor should be free of spikes having large magnitudes and also should maintain
a value within a narrow range of current values.
The advancing analyzation module
206 utilizes the commutation countdown
value to notify the commutation/output module
208 to switch outputs, i.e.,
perform commutation. In an embodiment of the invention, the commutation output
module
208 may switch from outputting a first driving signal to outputting
a second driving signal. For example, the commutation countdown value may be transmitted
to a counting module
216 (or first counting module in FIG. 3(
b))
from the commutation/output module
208. The counting module
216 may
decrement a time equal to the commutation countdown value, or let a time period
corresponding to the commutation countdown period expire. After the time equal
to the commutation countdown value has expired, a signal may be transmitted from
the commutation/output module
208 to switch outputs. The counting module
216 may be implemented in hardware or software.
In the embodiment of the invention illustrated in FIG. 3(
a), after commutation,
or switching of the outputs, the commutation output module
208 may transmit
a signal to a counting module
216 to initiate a measurement of an actual
interrupt time. In an embodiment of the invention, the counting module
216
for measuring the actual advance time may be the same counting module
216
as utilized above, or it may be a physically separate counting module (not shown).
In the embodiment of the invention illustrated in FIG. 3(
a), the speed
determination module
204 receives a speed sensor interrupt from the speed
sensor. The speed determination module
204 transmits a notification to the
advanced analyzation module
206 identifying that the next speed sensor interrupt
has been received. The advanced analyzation module
206 receives the speed
sensor interrupt notification from the speed determination module
204 and
notifies the counting module
216 to stop the measuring of the actual advance
time. In other words, the counting module
216 is measuring an actual advance
time between when the speed sensor interrupt is received and when commutation or
switching of the outputs from the microcontroller occurred.
In the embodiment of the invention illustrated in FIG. 3(
a), the advanced
analyzation module
206 adds the commutation countdown value and the actual
advance time to generate the anticipated fan speed. The advanced analyzation module
206 utilizes the value for the anticipated fan speed in the next iteration
or next measure time of the calculation of the commutation countdown time. In an
embodiment of the invention illustrated in FIG. 3(
a) when one counting module
216 is utilized, the commutation countdown value may be retained in the
counting module and then added to the measured actual advance time, which is also
stored in the counting module.
In the embodiment of the invention illustrated in FIG. 3(
b), the speed
determination module
204 may receive the tachometer signal and utilize the
second counter
218 to determine the calculated fan speed, after commutation
has occurred. This may be utilized for the next measured time period. For example,
the speed determination module
204 may monitor the tachometer signal and
notify the second counter
218 (or timer) that a pulse has been received
by the speed determination module
204. In this embodiment of the invention,
the calculated fan speed may be utilized for the next measured time or period to
determine the new commutation time.
The speed determination module
204 determines if the current advancing
time is greater than a first advancing threshold. For example, the first advancing
threshold may be 90 microseconds and the current advancing time may only be 30
microseconds. If the speed determination module
204 identifies that the
current advancing time is not greater than a first advancing threshold, the speed
determination module
204 adds an incremental advancing time to the current
advancing time. The incremental advancing time may be stored in a register. In
an embodiment of the invention, the incremental advancing time may be stored in
a memory address in a common memory
212. Illustratively, if the incremental
advancing time is 20 microseconds, then the new advancing time is 50 microseconds.
The countdown commutation time and the new anticipated fan speed (FIG. 3(
a))
or calculated fan speed (FIG. 3(
b)) are then calculated utilizing the new
advancing time and anticipated fan speed or calculated fan speed. The speed determination
module
204 transmits the anticipated fan speed or calculated fan speed and
the new advancing time to the advancing analyzation module
206. The advancing
analyzation module
206 calculates the countdown commutation value by subtracting
the new advancing time from the anticipated fan speed or calculated fan speed.
The advancing analyzation module
206 alerts the commutation output module
208 to switch outputs.
The speed determination module
204 determines if the current advancing
time is greater than a first advancing threshold. If the current advancing time
is greater than the advancing time threshold, then initialization is complete.
During operation of the cooling fan where the current advancing time is greater
than the first advancing threshold, the speed determination module
204 may
receive either the anticipated fan speed, in the embodiment illustrated in FIG.
3(
a), or the calculated fan speed, in the embodiment illustrated in FIG.
3(
b). The speed determination module
204 may transmit the speed to
the advancing analyzation module
206. The advancing analyzation module
206
may determine if the anticipated fan speed or the calculated fan speed is above
an efficient speed threshold. If the advancing analyzation module
206 determines
that the anticipated fan speed or the calculated fan speed is below the efficient
speed threshold, the advancing analyzation module
206 determines if the
fan is stopped or in a locked rotor condition. If the advancing analyzation module
206 identifies that the cooling fan is stopped or in a locked rotor condition,
the initialization process for the fan begins. In other words, the cooling fan
is reset. If the advancing analyzation module
206 determines that the fan
is not stopped or in a locked rotor condition, then the current advancing time
is decremented by a second pre-determined amount.
The advancing analyzation module
206 calculates the commutation countdown
time utilizing the supplied variables, e.g., calculated fan speed and current advancing
amount; calculated fan speed and decremented advancing amount; anticipated fan
speed and current advancing amount, etc. The advancing analyzation module
206
transmits this commutation value to a first counter
216 which times the
elapsing of the countdown commutation time. After the countdown commutation time
has elapsed, a signal is sent from the advancing analyzation module
206
to the commutation output module
208, which enables the outputs from the
microcontroller to be commutated.
As described above, in one embodiment of the invention, after commutation, or
switching of the outputs, the commutation output module
208 may transmit
a signal to a counting module
216 to initiate a measurement of an actual
advance time. The speed determination module
204 receives a speed sensor
interrupt from the speed sensor
117. The speed determination module
204
transmits a notification to the advanced analyzation module
206 identifying
that the next speed sensor interrupt has been received. The advanced analyzation
module
206 receives the speed sensor interrupt notification from the speed
determination module
204 and notifies the counting module
210 to
stop the measuring of the actual advance time. The advanced analyzation module
206 adds the commutation countdown value and the actual fan speed which
results in the new anticipated fan speed.
In an embodiment of the invention, the speed determination module
204
may
receive the next speed sensor interrupt and may determine the calculated fan speed
based on the timing of the next speed sensor interrupt and the previous speed sensor
interrupt. In this embodiment the speed determination module may utilize the second
counting module
218, as illustrated in FIG. 3(
b).
FIG. 4 illustrates a flowchart for the initialization stage of a motor driven
device according to an embodiment of the present invention. In this illustration,
a cooling fan is the motor driven device. In other embodiments of the invention,
other devices may be driven by a motor and the motor speed may be monitored. For
ease of illustration, this description utilizes fan speed, but motor speed may
be substituted for fan speed. The cooling fan is initialized and the fan is turned
on
300. The advancing modification is disabled during power-on or initialization
of the fan to eliminate the "oscillating effect."
Tachometer signals are received
302 and a fan speed is calculated
based on the tachometer signal from the speed sensor. In an embodiment of the invention,
a fan speed is calculated by the microcontroller and may be referred to as a calculated
fan speed.
The calculated fan speed is analyzed to determine
304 if the calculated
speed has reached an initial fan speed threshold. In an embodiment of the invention,
the pre-determined threshold may be 500 revolutions per minute (RPM). In an embodiment
of the invention, the initial fan speed threshold may be 2500 RPMs. The initial
fan speed threshold may be set for the fan and may identify an operating speed
at which the advancing emulation produces results that enable efficient operation
of the cooling fan. If the calculated speed is not above the initial fan speed
threshold, the microcontroller receives a new value in the tachometer signal and
calculates a fan speed based on, for example, the pulse duration or time between
pulses in the tachometer signal. The microcontroller
120 continues to calculate
the fan speed until the initial fan speed threshold is reached.
If the initial fan speed threshold for the fan speed is exceeded, the advancing
modification is enabled
306 utilizing an initial advancing time. In an embodiment
of the invention, the initial advancing time may be, for example, 20 microseconds.
In an embodiment of the invention, the initial advancing time may be 25 microseconds.
The initial advancing time may any value. The initial advancing time may need to
be greater than the time required for the microcontroller to receive and process
the speed sensor interrupt. This time which is required to receive and process
the speed sensor interrupt may be referred to as the interrupt overhead. If the
initial advancing time is not greater than the interrupt overhead, then the calculations
made by the microcontroller may not meaningful.
A commutation countdown value is calculated
308 by the microcontroller
for
a certain timeframe. For example, the commutation countdown value may be calculated
for ½ revolution of the fan. In another example, the commutation countdown
value may be calculated for a whole revolution of the fan or a ⅓ revolution
of the fan. In the first iteration of the initialization routine, the commutation
countdown value may be the calculated fan speed minus the initial advancing time.
The commutation countdown value may be utilized, for example, to countdown a
timer or counter within the microcontroller. Once the commutation countdown value
has elapsed, the microcontroller switches outputs or commutates
310 the
output signals. As described above, commutation is the switching of direction of
the current that flows through coil or stator winding, which results in the switching
of the stator polarities. Illustratively, this occurs when the microcontroller
sends an output signal to a different driver within a driving circuit.
In one embodiment of the invention, an actual advance time is calculated
312
between the commutation of the output signals and the next received speed sensor
interrupt, as illustrated in FIG. 4(
a). The microcontroller may calculate
the actual advance time. In this embodiment of the invention, an anticipated fan
speed is calculated
314 by adding the actual advance time and the commutation time.
In one embodiment of the invention illustrated in FIG. 4(
b), the tachometer
signal is received
330 from the speed sensor. The calculated fan speed is
determined
332 based on the tachometer signal received from the speed sensor,
as illustrated in FIG. 4(
b).
The current advancing time is compared
316 to a threshold advancing time.
In an embodiment of the invention, the threshold advancing time may be 70 microseconds.
In an embodiment of the invention, the threshold advancing time may range anywhere
from 60-120 microseconds, depending on different motors, loads, or fan speeds required
for the operation of the cooling fan.
If the current advancing time is less than the threshold advancing time, then
a new advancing time is calculated
318. The new advancing time is created
by adding an incremental time to the current advancing time. In an embodiment of
the invention, the incremental time could be 5 microseconds. In an embodiment of
the invention, the incremental time could be 10 or 20 microseconds. A new commutation
countdown value is calculated utilizing the new advancing time and the anticipated
fan speed or calculated fan speed and the process returns to
308.
If the current advancing time is greater than the threshold advancing time, then
the initialization stage of the fan has been completed
320.
FIG. 5(
a) illustrates a flowchart of an advancing emulation algorithm
after an initialization stage utilizing an anticipated fan speed according to an
embodiment of the present invention. FIG. 5(
b) illustrates a flowchart of
an advancing emulation algorithm after an initialization stage utilizing a calculated
fan speed according to an embodiment of the present invention. When the fan is
operating at a speed greater than the initial fan speed threshold, the anticipated
fan speed (in one embodiment) and the calculated fan speed (in one embodiment)
is received
400 by the microcontroller for the previous iteration of the
advancing emulation and compensation.
The anticipated fan speed or calculated fan speed is verified or checked or compared
402 against an efficient fan speed threshold to verify that the fan is still
operating above the speed as defined by the fan speed threshold.
If the anticipated fan speed or calculated fan speed is less than the efficient
fan speed threshold, the microcontroller determines
404 whether the fan
is stopped or in a locked rotor condition. If the fan is stopped, i.e., there is
no fan speed or the fan is in a locked rotor condition, the microcontroller may
set the current advancing time to zero. In this case, if the microcontroller is
utilizing the anticipated fan speed, with the current advancing time equal to zero,
the microcontroller may have to utilize the tachometer signal from the hall sensor
in order to determine the next fan speed. This operation is described above with
respect to FIG. 4. In an embodiment of the invention utilizing the calculated fan
speed, the microcontroller may operate to determine the calculated fan speed, as
illustrated in FIG. 5(
b).
If the anticipated fan speed of calculated fan speed is below the threshold fan
speed and the fan is not stopped or in a locked rotor position, the advancing time
is decremented
408 by a second time amount or pre-determined decrement of
time. This creates a decremented advancing time.
The countdown commutation value is calculated
410 by subtracting either
the decremented advancing time (if the anticipated fan speed or calculated fan
speed was not greater than the pre-determined fan speed threshold) or by utilizing
the existing advancing time, e.g., in the range of 60 to 120 microseconds, (if
