U.S. patent application number 10/360957 was filed with the patent office on 2004-08-12 for method for sensing switch closure to prevent inadvertent startup.
Invention is credited to Brotto, Daniele C..
Application Number | 20040155532 10/360957 |
Document ID | / |
Family ID | 32824094 |
Filed Date | 2004-08-12 |
United States Patent
Application |
20040155532 |
Kind Code |
A1 |
Brotto, Daniele C. |
August 12, 2004 |
Method for sensing switch closure to prevent inadvertent
startup
Abstract
A method for preventing sudden inadvertent operation of a motor
of a tool or appliance when the motor is initially electrically
connected to a power source while an On/Off switch for controlling
the motor is in a closed (i.e. `On`) position. The method includes
electrically connecting the motor to a power source and determining
a position of the On/Off switch when the motor is initially
electrically connected to the power source by sensing whether
current is flowing through the motor. Additionally, the method
includes supplying insufficient power for the motor to function
when the motor is initially electrically connected to the power
source by controlling the operation of an electronic valve
associated with the motor.
Inventors: |
Brotto, Daniele C.;
(Baltimore, MD) |
Correspondence
Address: |
Harness, Dickey & Pierce, P.L.C.
Mark D. Elchuk
P.O. Box 828
Bloomfield Hills
MI
48303
US
|
Family ID: |
32824094 |
Appl. No.: |
10/360957 |
Filed: |
February 7, 2003 |
Current U.S.
Class: |
307/326 |
Current CPC
Class: |
H02H 7/0816 20130101;
H02P 1/18 20130101; H02H 11/00 20130101 |
Class at
Publication: |
307/326 |
International
Class: |
H02H 001/00 |
Claims
What is claimed is:
1. A method for preventing startup of a motor when the motor is
initially electrically connected to a power source while an On/Off
switch for controlling the motor is in an `On` position, said
method comprising: electrically connecting the motor to a power
source; utilizing a microcontroller to determine a position of the
On/Off switch when the motor is initially electrically connected to
the power source; and utilizing the microcontroller to control an
amount of power provided to the motor based on the position of the
On/Off switch when the motor is initially electrically connected to
the power source.
2. The method of claim 1, wherein utilizing a microcontroller to
determine the position of an On/Off switch comprises utilizing the
microcontroller to sense whether current is flowing through the
motor.
3. The method of claim 1, wherein utilizing a microcontroller to
determine the position of an On/Off switch comprises utilizing the
microcontroller to sense whether a voltage is present across the
motor.
4. The method of claim 1, wherein electrically connecting the motor
to a power source comprises electrically connecting the motor to an
AC power source.
5. The method of claim 4, wherein utilizing the microcontroller to
control an amount of power provided to the motor comprises
utilizing the microcontroller to fire an electronic valve at a low
conduction angle when the motor is initially electrically connected
to the AC power source, such that power provided to the motor is
insufficient for the motor to function.
6 The method of claim 4, wherein utilizing the microcontroller to
control an amount of power provided to the motor further comprises
utilizing the microcontroller to disable normal operation of the
motor when the On/Off switch is determined to be in a closed (i.e.
`On`) position when the motor is initially connected to the AC
power source.
7. The method of claim 6, wherein utilizing the microcontroller to
disable normal operation of the motor comprises utilizing the
microcontroller to disable normal operation of the motor until the
microcontroller determines the On/Off switch is in an open (i.e.
Off) position.
8. The method of claim 1, wherein electrically connecting the motor
to a power source comprises electrically connecting the motor to a
DC power source.
9. The method of claim 8, wherein utilizing the microcontroller to
control an amount of power provided to the motor comprises
utilizing the microcontroller to switch an electronic valve at a
narrow duty cycle when the motor is initially electrically
connected to the DC power source, such that power provided to the
motor is insufficient for the motor to function.
10 The method of claim 8, wherein utilizing the microcontroller to
control an amount of power provided to the motor further comprises
utilizing the microcontroller to disable normal operation of the
motor when the On/Off switch is determined to be in a closed
position when the motor is initially connected to the DC power
source.
11. The method of claim 10, wherein utilizing the microcontroller
to disable normal operation of the motor comprises utilizing the
microcontroller to disable normal operation of the motor until the
microcontroller determines the On/Off switch is in an open
position.
12. A system for preventing inadvertent startup of a motor when the
motor is initially electrically connected to a power source while
the motor is in an `On` operational status, the system comprising:
a motor control switch configured to control the operational status
of the motor; an electronic valve configured to control the flow of
current through the motor when the motor is electrically connected
to a power source; and a microcontroller configured to determine a
position of the motor control switch when the motor is initially
connected to the power source, and control an amount of power
provided to the motor based on the position of the motor control
switch when the motor is initially connected to the power
source.
13. The system of claim 12, further comprising a shunt resistor,
wherein to determine the position of the motor control switch, the
microcontroller is further configured to monitor voltage across the
shunt resistor, thereby sensing whether current is flowing through
the motor.
14. The system of claim 12, wherein to determine the position of
the motor control switch, the microcontroller is further configured
to determine the presence or absence of a voltage across the
motor.
15. The system of claim 12, wherein the motor is electrically
connected to an AC power source, and wherein the microcontroller is
further configured to fire the electronic valve at a low conduction
angle when the motor is initially connected to the AC power source,
such that the power provided to the motor is insufficient for the
motor to function.
16. The system of claim 15, wherein the microcontroller is further
configured to: disable normal operation of the motor when the motor
control switch is determined to be a closed position when the motor
is initially connected to the AC power source; and continue to
disable normal operation of the motor until the microcontroller
determines that the motor control switch has been placed in an OFF
position.
17. The system of claim 12, wherein the motor is electrically
connected to a DC power source, and wherein the microcontroller is
further configured to switch the electronic valve at a narrow duty
cycle when the motor is initially connected to the DC power source,
such that the power provided to the motor is insufficient for the
motor to function.
18. The system of claim 17, wherein the microcontroller is further
configured to: disable normal operation of the motor when the motor
control switch is determined to be a closed position when the motor
is initially connected to the DC power source; and continue to
disable normal operation of the motor until the microcontroller
determines that the motor control switch has been placed in an OFF
position.
19. An electro-mechanical system adapted to prevent inadvertent
operation of the system when the system is initially electrically
connected to a power source while the system is in an `On`
operational status, said system comprising: a motor for providing a
force used by the system to perform a function; a control circuit
configured to control operation of the motor, the control circuit
comprising: a On/Off switch configured to control an operational
status of the motor; an electronic valve configured to control the
flow of current through the motor when the motor is electrically
connected to a power source; and a microcontroller configured to
sense at least one of whether current is flowing through the motor
and whether voltage is present at the motor when the motor is
initially connected to the power source, thereby determining a
position of the On/Off switch when the motor is initially connected
to the, and control an amount of power provided to the motor based
on the position of the On/Off switch when the motor is initially
connected to the power source.
20. The system of claim 19, wherein the system is electrically
connected to an AC power source, and wherein the microcontroller is
further configured to fire the electronic valve at a low conduction
angle when the system is initially connected to the AC power
source, such that the power provided to the motor is insufficient
for the motor to function.
21. The system of claim 20, wherein the microcontroller is further
configured to: disable normal operation of the motor when the
On/Off switch is determined to be in an On position when the motor
is initially connected to the AC power source; and continue to
disable normal operation of the motor until the microcontroller
determines that the On/Off switch has been placed in an OFF
position.
22. The system of claim 20, wherein the electronic valve is a
triac.
23. The system of claim 19, wherein the system is electrically
connected to a DC power source, and wherein the microcontroller is
further configured to switch the electronic valve at a narrow duty
cycle when the system is initially connected to the DC power
source, such that the power provided to the motor is insufficient
for the motor to function.
24. The system of claim 23, wherein the microcontroller is further
configured to: disable normal operation of the motor when the
On/Off switch is determined to be in an On position when the motor
is initially connected to the DC power supply; and continue to
disable normal operation of the motor until the microcontroller
determines that the On/Off switch has been placed in an OFF
position.
25. The system of claim 23, wherein the electronic valve is an
electronic switching device
26. A system for preventing inadvertent operation of a motor driven
device when a motor of the device is initially electrically
connected to a power source, the system comprising: an electronic
valve configured to control the flow of current through the motor
when the motor is electrically connected to a power source; and a
microcontroller configured to sense whether current is flowing
through the motor when the motor is initially connected to the
power source, and disable normal operation of the motor if current
is sensed flowing through the motor when the motor is initially
connected to the power source.
27. The system of claim 26, further comprising a shunt resistor,
wherein to sense whether current is flowing through the motor when
the motor is initially connected to the power source, the
microcontroller is further configured to monitor voltage across the
shunt resistor.
28. The system of claim 26, wherein the motor is electrically
connected to an AC power source, and wherein the microcontroller is
further configured to fire the electronic vavle at a low conduction
angle when the motor is initially connected to the power source,
such that insufficient power for motor operation is provided to the
motor.
29. The system of claim 28, wherein the electronic valve is a
triac.
30. The system of claim 26, wherein the motor is electrically
connected to an DC power source, and wherein the microcontroller is
further configured to switch the electronic valve at a narrow duty
cycle when current is sensed flowing through the motor when the
motor is initially connected to the power source, such that
insufficient power for motor operation is provided to the
motor.
31. The system of claim 30, wherein the electronic valve is an
electronic switching device.
32. The system of claim 26, wherein the microcontroller is further
configured to continue to disable normal operation of the motor
until the microcontroller senses that current has stopped flowing
through the motor.
33. A method for preventing inadvertent startup of a motor as the
motor is being electrically connected to a power source, said
method comprising: electrically connecting the motor to a power
source; sensing whether current is flowing through the motor as the
motor is being connected to the power source, thereby determining a
position of a motor control switch as the motor is being
electrically connected to the power source; and providing
insufficient power for the motor to function as the motor is being
electrically connected to the power source by controlling the
operation of an electronic valve.
34. The method of claim 33, wherein the method further comprises
utilizing a control circuit to sense whether current is flowing
through the motor as the motor is being electrically connected to
the power source, and to provide insufficient power for the motor
to function as the motor is being electrically connected to the
power source.
35. The method of claim 34, wherein electrically connecting the
motor to a power source comprises, electrically connecting the
motor to an AC power source.
36. The method of claim 35, wherein utilizing the control circuit
to provide insufficient power for the motor function comprises
utilizing the control circuit to fire an electronic valve at a low
conduction angle.
37. The method of claim 34, wherein electrically connecting the
motor to a power source comprises, electrically connecting the
motor to a DC power source.
38. The method of claim 37, wherein utilizing the control circuit
to provide insufficient power for the motor function comprises
utilizing the control circuit to switch an electronic valve at a
narrow duty cycle.
39 The method of claim 34, wherein the method further comprises
utilizing the control circuit to disable normal operation of the
motor when the motor control switch is determined to be in a closed
position as the motor is being connected to the power source.
40. The method of claim 39, wherein utilizing the control circuit
to disable normal operation of the motor comprises utilizing the
control circuit to disable normal operation of the motor until the
control circuit determines the motor control switch is in an open
position.
41. The method of claim 34, wherein utilizing a control circuit to
sense whether current is flowing through the motor, and to provide
insufficient power for the motor to function as the motor is being
electrically connected to the power source comprises, utilizing a
microcontroller to sense whether current is flowing through the
motor as the motor is being electrically connected to the power
source, and to provide insufficient power for the motor to function
as the motor is being electrically connected to the power
source.
42. A method for preventing inadvertent start-up of a motor of a
tool when the motor is initially connected to a power source while
an On/Off switch for controlling the motor is in an `On` position,
said method comprising: electrically connecting the motor to a
power source; sensing whether a voltage is present across the motor
when the motor is initially connected to the power source, thereby
determining a position of the On/Off switch when the motor is
initially electrically connected to the power source; and providing
insufficient power for the motor to function when the motor is
initially electrically connected to the power source by controlling
the operation of an electronic valve.
43. The method of claim 42, wherein the method further comprises
utilizing a control circuit to sense whether a voltage is present
across the motor, and to provide insufficient power for the motor
to function when the motor is initially electrically connected to
the power source.
44. The method of claim 43, wherein electrically connecting the
motor to a power source comprises, electrically connecting the
motor to an AC power source.
45. The method of claim 44, wherein utilizing the control circuit
to provide insufficient power for the motor function comprises
utilizing the control circuit to fire a triac at a low conduction
angle.
46. The method of claim 43, wherein electrically connecting the
motor to a power source comprises, electrically connecting the
motor to a DC power source.
47. The method of claim 46, wherein utilizing the control circuit
to provide insufficient power for the motor function comprises
utilizing the control circuit to switch an electronic switch at a
narrow duty cycle.
48 The method of claim 43, wherein the method further comprises
utilizing the control circuit to disable normal operation of the
motor when the On/Off switch is determined to be in a closed
position when the motor is initially connected to the power
source.
49. The method of claim 48, wherein utilizing the control circuit
to disable normal operation of the motor comprises utilizing the
control circuit to disable normal operation of the motor until the
control circuit determines the On/Off switch is in an open
position.
50. The method of claim 43, wherein utilizing a control circuit to
sense whether voltage is present at the motor, and to provide
insufficient power for the motor to function when the motor is
initially electrically connected to the power source comprises,
utilizing a microcontroller to sense whether voltage is present at
the motor, and to provide insufficient power for the motor to
function when the motor is initially electrically connected to the
power source.
51. A tool comprising: an electric motor; an On/Off switch for
controlling the application of power to the motor; a motor control
circuit including: a processor for sensing if a current is flowing
through the motor substantially upon coupling a power cord of the
tool to a power source to thereby detect if the On/Off switch is in
a closed position when power is initially applied to the tool; and
an electronic switch for regulating the application of power to the
motor to prevent the application of sufficient power to the motor
for the motor to startup when power is initially applied to the
tool with the On/Off switch is engaged, and for continuing to
prevent the application of sufficient power to the motor until the
On/Off switch is first released and re-engaged.
Description
FIELD OF INVENTION
[0001] The invention relates generally to control systems for
electric motors, and more particularly to a control system and
method for preventing inadvertent startup of the motor when the
motor is initially connected to a power source while an On/Off
switch controlling the motor is being held in an `On` position.
BACKGROUND OF THE INVENTION
[0002] Typically, in motor driven devices, such as power tools and
household appliances, if the device is connected to a power source
with an On/Off switch of the device in the `On` position, the motor
of the device would suddenly startup. If the sudden startup of the
motor was inadvertent and unexpected by a user of the device,
damage to other objects in the vicinity of the tool, or to the tool
itself, could occur. Some known methods have used dedicated
circuitry connected to the On/Off switch of the motor driven device
to directly monitor the position of the On/Off switch and prevent
the motor from starting up if power is connected to the tool or
appliance while the On/Off switch is in the `On` position. Other
known methods have utilized separate devices to prevent such
inadvertent startup. With such separate devices, the motor driven
device is connected to a first device and the first device is
connected to the power source. Thus, the first device disconnects
the power source from the motor driven device when hazardous
conditions occur. The use of such known methods and devices
however, incur additional expense, inconvenience, and additional
interconnects.
[0003] It would therefore be highly desirable to provide a system
and method for preventing the inadvertent startup of a motor driven
device, in the event that power is initially provided to the device
while the On/Off switch of the device is in the `On` position, but
that does not present the problems and additional cost described
above.
BRIEF SUMMARY OF THE INVENTION
[0004] In one preferred embodiment of the present invention, a
method is provided for preventing inadvertent startup of a motor
when the motor is initially connected to a power source while a
motor control (i.e. On/Off) switch controlling the motor is
switched into the `On` position. The method includes electrically
connecting the motor to a power source and determining the position
of the motor control switch when the motor is initially
electrically connected to the power source by sensing whether
current is flowing through the motor. Additionally, the method
includes momentarily providing insufficient power for the motor to
function when the motor is initially electrically connected to the
power source by controlling the operation of an electronic
valve.
[0005] In another preferred embodiment, a system is provided for
preventing inadvertent startup of a motor when the motor is
electrically connected to a power source. The system includes a
motor control (i.e. On/Off) switch for manually controlling an
operational status of the motor and a electronic valve for
controlling the flow of current through the motor when the motor is
initially electrically connected to a power source. The system
additionally includes a microcontroller for determining a position
of the motor control switch when the motor is initially connected
to the power source. The microcontroller also controls an amount of
power provided to the motor based on the position of the motor
control switch when the motor is initially connected to the power
source.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The present invention will become more fully understood from
the detailed description and accompanying drawings, wherein;
[0007] FIG. 1 is a simplified illustration of an exemplary power
tool of appliance incorporating the system and method of the
present invention for preventing inadvertent startup of a motor of
the tool when power is first coupled to the tool while the tool's
On/Off switch is in the `On` position;
[0008] FIG. 2 is a simplified electrical schematic of the system
shown in block form in FIG. 1, wherein the system is connectable to
an AC power source and an AC motor of the exemplary tool of
appliance;
[0009] FIG. 3 is simplified electrical schematic of an alternative
preferred embodiment of the system shown in FIG. 2;
[0010] FIG. 4 is another simplified electrical schematic of an
alternative preferred embodiment of the system shown in FIG. 2;
[0011] FIG. 5 is a simplified electrical schematic of an
alternative preferred embodiment of the system shown in FIG. 1,
wherein the system is connectable to an AC power source and an AC
motor of the exemplary power tool or appliance; and
[0012] FIG. 6 is a simplified electrical schematic of the system
shown in FIG. 1, wherein the system is connectable to a DC power
source and a DC motor of an associated power tool or appliance.
DETAILED DESCRIPTION OF THE INVENTION
[0013] FIG. 1 is a highly simplified block diagram of a system 10
of the present invention included in a motor driven device 14 for
preventing inadvertent startup of the motor driven device 14 when
power is initially provided to the motor driven device 14. In this
preferred embodiment of the present invention, the system 10
prevents the operation of a motor 18 included in the motor driven
device 14 if the motor 18 is initially connected to a power source
when a motor control switch 22, also known as an On/Off switch or
trigger, is in a closed (i.e. `On`) position.
[0014] The motor 18 provides force, such as torque or linear force,
utilized by the device 14 to perform a function, for example rotate
a blade of a mitre saw or spin a drill bit of a drill. It will be
appreciated that although motor driven device 14 is shown in FIG. 1
as a mitre saw, device 14 can be any electro-mechanical device that
utilizes force provided by an electric motor to perform an intended
mechanical function. For example, device 14 could also comprise a
power tool or an appliance such a table saw, a circular saw, a
drill, a belt sander, a mixer, a blender, a can opener, food
processor, or an automated knife. Additionally, it will be
appreciated that although FIG. 1 shows the device 14 having a power
cord 26 for providing AC power to the motor 18, device 14 could be
a portable motor driven device that utilizes DC power to operate
the motor 18. Thus, the system 10 is applicable with AC and DC
powered motor driven devices 14.
[0015] The motor 18, while described as an AC motor with the device
14, could instead be a DC motor suitable for use with a motor
control scheme that utilizes current measurement to control the
operation of the motor 18, as needed for the particular tool or
appliance with which it is being used. For example, the motor 18
could be an AC or DC powered universal motor, a permanent magnet
motor, or a linear motor. The system 10 includes a control module
30 and the motor control switch 22. The control module 30 is
preferably suitable for use with a plurality of motor driven tools
or appliances, such as device 14, that utilize a plurality of
different motors having different operating specifications and
different operational parameters specific to the particular
application of the motor 18.
[0016] FIG. 2 is a simplified electrical schematic of the system 10
(shown in FIG. 1), connectable to an AC power source and the motor
18, wherein the motor 18 is an AC motor, in accordance with one
preferred embodiment of the present invention. The control module
30 includes a control circuit, generally indicated at 32, that
determines a position of the motor control switch 22 and controls
an amount of power provided to the motor 18 based on the position
of the motor control switch 22. In one preferred embodiment, the
control circuit 32 includes a power supply 34 that supplies power
to a microcontroller 38 programmed to control an electronic valve
42, such as a triac, a field effect transistor (FET), an insulated
gate bipolar transistor (IGBT), a silicone-controlled rectifier
(SCR), or a voltage control device. Microcontroller 38 can be any
suitable microcontroller, for example one microcontroller
especially well suited for use with system 10 is an AT26
microcontroller commercially available from ATMEL, Inc. of San
Jose, Calif. The motor 18 is connected to the power source at AC
mains via the power cord 26 (shown in FIG. 1). Operation of the
motor 18 is controlled by the control module 30. To control
operation of the motor 18, the control module 30 controls the
amount of current flowing through the motor 18 by using the
microcontroller 38 to control the amount of current flowing through
the electronic valve 42. One function of the control module 30 is
to monitor the position of the motor control switch 22 and prevent
starting of the motor 18 if AC power is applied to motor 18 with
the motor control switch 22 in a closed (i.e. `On`) position.
[0017] The control module 30 is powered-up whenever the AC power
cord 26 is connected to an AC mains power source, regardless of the
position of the motor control switch 22. When the control module 30
is powered-up the microcontroller 38 senses AC power at a port 38a
and begins to operate the electronic valve 42 via signals output
from a port 38b. The electronic valve 42 can be any current or
voltage controlling device controllable by the microcontroller 38,
such as a triac or other suitable electronic valve device. In one
preferred embodiment, the electronic valve 42 is a triac. For
exemplary purposes, with regard to FIGS. 2, 3 and 4, the electronic
valve 42 will be referred to as triac 42. When the microcontroller
38 senses AC power at port 38a, the microcontroller 38 begins to
fire the triac 42 via port 38b. The control module 30 further
includes a voltage divider circuit 46 comprised of resistors 50,
52, 54, and clamping diodes 56 and 58. The voltage divider circuit
is coupled via a circuit line 60 to the microcontroller 38 at port
38a. The resistors 50, 52, and 54 divide the AC source voltage to a
voltage level usable by the microcontroller 38, and the clamping
diodes 56 and 58 protect the microcontroller 38 from damage if a
voltage spike occurs in the AC source voltage. The microcontroller
38 senses AC power by measuring the divided voltage from the AC
power source via port 38a. Alternatively, the microcontroller 38
can sense AC power by monitoring a digital signal provided by a
subsystem, wherein the digital signal would represent a zero
crossing of the AC voltage.
[0018] When the motor 18 is initially connected to the AC power
source, the control module 30 is powered-up and the microcontroller
38 senses voltage at port 38a. In one preferred embodiment, the
microcontroller 38 is programmed to immediately begin attempting to
fire triac 42 at a low conduction angle, for example between
160.degree. and 175.degree. for the positive half cycle and between
340.degree. and 355.degree. for the negative half cycle. The
conduction angle may be derived from an analog representation of
the AC voltage produced at port 38a by voltage divider circuit 46
or determined via time delays posted at the zero crossing of the AC
signal at port 38a.
[0019] For current to be flowing through the motor 18 and the triac
42, motor control switch 22 must be in the closed position.
However, regardless of whether current is flowing through the motor
18 and the triac 42, when the control module 30 is first
powered-up, that is, when the motor is initially connected to the
AC power source, the microcontroller 38 attempts to fire the triac
42 at a low conduction angle. Therefore, if the motor 18 is
inadvertently or unexpectedly connected to the AC power source with
the motor control switch 22 in a closed position, the triac 42 is
being fired at a sufficiently low conduction angle such that power
provided to the motor is insufficient for the motor to function.
Thus, regardless of the position of the motor control switch 22,
the motor 18 of the device 14 will not suddenly be pulsed on when
being initially connected to the AC power source.
[0020] Substantially simultaneously with beginning to fire the
triac 42 at a low conduction angle, the microcontroller 38 is
programmed to determine whether the motor control switch 22 is in
an open or closed position (i.e. `On` or `Off`). In one preferred
embodiment, to determine the position of the motor control switch
22 the microcontroller 38 is programmed to sense whether current is
flowing through the motor 18. FIG. 2 shows one preferred embodiment
in which the microcontroller 38 senses whether current is flowing
through the motor 18 by monitoring a voltage across a shunt
resistor 62, via a port 38c of the microcontroller 38. In the
embodiment shown in FIG. 2, the value of shunt resistor 62 is
sufficiently small such that when current is flowing through the
motor 18, indicating the motor control switch 22 is in the closed
position, the voltage signal is supplied to port 38c via an
amplifier 66. However, in an alternative preferred embodiment,
shunt resistor 62 has a larger resistance value such that amplifier
66 is not needed and the voltage across shunt resistor is directly
presented to microcontroller 38. In another alternative preferred
embodiment, the value of shunt resistor 62 is sufficiently small,
and the microcontroller 38 includes internal circuitry to detect
current flow through the shunt resistor 62 such that amplifier 66
is not needed. For example, the microcontroller 38 may include an
internal amplifier at port 38c to amplify the voltage sensed across
shunt resistor 62 to a level suitable for detection by
microcontroller 38.
[0021] In one preferred embodiment, the voltage signal provided at
port 38c is an analog signal. However, alternatively, a separate
subsystem could be employed to measure the voltage across shunt
resistor 62 and to present a digital signal at port 38c to indicate
whether current is flowing through the motor 18. Additionally,
although FIG. 2 shows the triac 42, the shunt resistor 62 and the
amplifier 66 as being included in the control module 30, it will be
appreciated that in preferred alternate embodiments, one of, two
of, or each of the triac 42, the shunt resistor 62 and the
amplifier 66 could be external to the control module 30.
[0022] FIG. 3 is a simplified electrical schematic of another
preferred embodiment in which the microcontroller 38 is programmed
to sense whether current is flowing through the motor 18. Instead
of using the voltage differential due to current flowing through
shunt 62 to sense current flowing through the motor 18, the triac
42 provides the necessary impedance to create a voltage detected by
the microcontroller 38 at a port 38d. In one preferred embodiment,
the voltage across the triac 42 is amplified by an amplifier 70 for
analysis by the microcontroller 38, via port 38d. Alternatively,
the amplifier 70 may be replaced by any other circuit or component
suitable to condition the voltage signal for detection by the
controller 38 at port 38d, for example a resistor. It will also be
appreciated that the amplifier 70 may be omitted if the
microcontroller 38 has internal circuitry suitable to detect
voltage across the triac 42. In the embodiment shown in FIG. 3, the
shunt resistor 62 and the amplifier 66 are not utilized by the
microcontroller 38 to sense current flowing through the motor 18,
but are rather utilized for other control functions of the motor
18.
[0023] FIG. 4 is simplified electrical schematic of yet another
preferred embodiment in which the microcontroller 38 is programmed
to sense whether current is flowing through the motor 18 when AC
power is initially applied to the motor 18. In this embodiment,
instead of using the voltage differential due to current flowing
through shunt 62 or the voltage across the triac 42 to sense
current flowing through the motor 18, the motor 18 provides the
necessary impedance to create a voltage detected by the
microcontroller 38 at port 38d. The voltage across the motor 18 is
amplified by an amplifier 74 for analysis by microcontroller 38,
via port 38d. Alternatively, the amplifier 74 may be replaced by
any other circuit or component suitable to condition the voltage
signal for detection by the controller 38 at port 38d, for example
a resistor. It will also be appreciated that the amplifier 74 may
be omitted if the microcontroller 38 has internal circuitry
suitable to detect a voltage across the triac 42. In the embodiment
shown in FIG. 4, the shunt resistor 62 and the amplifier 66 are not
utilized by the microcontroller 38 to sense current flowing through
the motor 18, but are rather utilized for other control functions
of the motor 18.
[0024] Thus, referring to FIGS. 2, 3 and 4, when the motor 18 is
initially connected to the AC power source, the microcontroller 38
attempts to begin firing the triac 42 at a low conduction angle to
prevent the motor 18 from `jerking` if the motor control switch 22
is closed. If the motor control switch 22 is in fact closed, the
firing of the triac 42 allows current to flow through the motor 18,
the triac 42, and the shunt resistor 62. As current flows through
the motor 18, the microcontroller 38 senses the current flow, as
described above, and prevents operation of the motor 18 until such
time as the microcontroller 38 determines that the motor control
switch 22 has been place in the open (i.e. `On`) position.
[0025] In operation, if the motor control switch 22 is open when AC
power is initially applied to the motor 18, no current can flow
through the motor 18. Therefore, via the voltage signal monitored
at port 38c or port 38d as described above, the microcontroller 38
recognizes that no current is flowing through the motor 18 and
enables normal operation of the motor driven device 14. That is,
upon a subsequent closure of the motor control switch 22, the
microcontroller 38 will fire the triac 42 at a conduction angle
suitable to produce sufficient power for the motor 18 to function
in accordance with desired operational parameters of the motor
driven device 14. Conversely, if the motor control switch 22 is
closed and current flows through the motor 18 when the motor 18 is
initially connected to the AC power source, the microcontroller 38
senses the current flow and prevents the motor 18 from functioning.
For example, the microcontroller 38 may continue to limit the
current flowing through the motor by continuing to fire the triac
42 at a low conduction angle insufficient to cause rotation of the
motor 18, or the microcontroller 38 may stop firing the triac 42
altogether so that no current flows through the motor 18.
Thereafter, the microcontroller 38 prevents operation of the motor
18 until the microcontroller 38 senses that current is no longer
flowing through the motor 18, indicating that the motor control
switch 22 has been opened. Once the motor control switch 22 is
opened, the microcontroller 38 will enable normal functioning of
the motor 18
[0026] Therefore, the microcontroller 38 is programmed to attempt
to fire the triac 42 at a low conduction angle as the control
module 30 is initially powered-up, and to detect closure of the
motor control switch 22 very soon thereafter. By only firing the
triac 42 at low conduction angles to sense the position of the
motor control switch 22, insufficient power is provided to the
motor 18 to cause rotation of the motor 18, thereby preventing
suddenly pulsing on the motor 18. Additionally, if the
microcontroller 38 senses that the motor control switch 22 is
closed when power is initially applied to the motor 18, the
microcontroller 38 disables normal operation of the motor 18 until
the motor control switch 22 is opened. Once the microcontroller 38
senses that the motor control switch 22 has been opened, the
microcontroller 38 enables normal motor start-up operation upon a
subsequent closure of motor control switch 22.
[0027] Still referring to FIGS. 2, 3 and 4, in an alternative
preferred embodiment, the microcontroller 38 is not programmed to
attempt to fire the triac 42 at a low conduction angle when the
control module 30 is first powered-up. Rather, the microcontroller
38 immediately begins to attempt to fire the triac 42 at a
conduction angle sufficient for the motor 18 to begin to function.
Thus, if the motor control switch 22 is closed when the motor 18 is
initially connected to the AC power source, the motor 18 will begin
to function. However, substantially simultaneous with the
powering-up of the control module 30, the microprocessor 38
determines the position of the motor control switch 22. Thus, if
the motor control switch 22 is closed when the motor 18 is first
connected to the AC power source, the microcontroller 38 will
virtually immediately sense current flowing through the motor 18
and prevent powering on of the motor 18 until the motor control
switch is placed in an open position. Thus, the motor 18 will not
be powered up if the AC power is initially supplied with the motor
control switch 22 in the closed position.
[0028] FIG. 5 is a simplified electrical schematic of an
alternative preferred embodiment of the system 10 (shown in FIG.
1), connectable to an AC power source. The operation of the system
10 in this embodiment is essentially the same as the operation
described above in reference to FIGS. 2, 3 and 4, except instead of
determining the position of the motor control switch 22 by sensing
the current flowing through the motor 18, the position of the motor
control switch 22 is determined by sensing the presence or absence
of a voltage across motor 18. The presence of a voltage across
motor 18, when AC power is initially applied to motor 18, indicates
that the motor control switch 22 is closed, while the absence of a
voltage indicates that the motor control switch 22 is open.
[0029] In one preferred embodiment, port 38d of the microcontroller
38 is connected to the motor 18 via a circuit line 78 that includes
a resistor 82. If the motor control switch 22 is closed when the AC
power source is initially applied to the motor 18, the
microcontroller 38 detects the presence of a voltage signal at port
38d and prevents the motor 18 from functioning. For example, the
microcontroller 138 may couple the resistor 82 to ground, thereby
shorting the motor 18 and preventing the microcontroller 138 from
firing the triac 42 so that no current is allowed to flow through
the motor 18. Thereafter, the microcontroller 38 continues to
prevent operation of the motor 18 until the microcontroller 38
senses that voltage is no longer present across the motor 18,
indicating that the motor control switch 22 has been opened. Once
the motor control switch 22 is opened, the microcontroller 38
enables normal function of the motor 18. Although FIG. 5
illustrates line 78 connected to motor 18 at an electrical node
internal to the control module 30, it will be appreciated that line
78 can be connected to the motor 18 at a node external to the
control module 30.
[0030] FIG. 6 is a simplified electrical schematic of the system 10
(shown in FIG. 1) connectable to a DC power source and the motor
18, wherein the motor 18 is a DC motor, in accordance with one
preferred embodiment of the present invention. For clarity and
convenience, components of system 10 in FIG. 6 identical to
components in FIGS. 2, 3, 4 and 5 are identified in FIG. 6 using
reference numerals increased by 100 over those used in FIGS. 2, 3,
4 and 5. The system 10 functions in a DC application very similar
to the way the system 10 functions in the AC application described
above in reference to FIGS. 2, 3, 4 and 5. Essentially, in one
preferred embodiment, the microcontroller 138 prevents initial
sudden motor startup, determines whether the motor control switch
122 is in the closed position when DC power is initially applied to
the motor 18, and if so, prevents the motor 18 from functioning
until motor control switch 122 is subsequently opened and closed
again.
[0031] In the DC application of system 10, the motor 18 is
connected to a DC power source at a positive terminal 190 and a
negative terminal 192. The control module 130 is powered-up
whenever the terminals 190 and 192 are connected to a DC power
source. When the control module 130 is powered-up the
microcontroller 138 senses DC power and begins to attempt to
operate the electronic valve 142, via port 138b, such that, if
current is flowing through the motor 18, insufficient power is
provided to the motor 18 for the motor 18 to function. In one
preferred embodiment the electronic valve 142 is a transistor, such
as a FET or IGBT. For exemplary purposes, with regard to FIG. 6,
the electronic valve 142 will be referred to as transistor 142.
[0032] In one preferred embodiment, when the motor is initially
connected to the DC power source, the microcontroller 138 is
programmed to immediately attempt to begin switching transistor 142
at a narrow duty cycle, for example between a 5% and 15% duty
cycle. For current to be flowing through the motor 18 and the
transistor 142, the motor control switch 122 must be in the closed
position. Therefore, if the motor 18 is inadvertently or
unexpectedly connected to the DC power source with the motor
control switch 122 in a closed position, the transistor 142 is
being fired at a sufficiently narrow duty cycle such that power
provided to the motor is insufficient for the motor to function.
Thus, the motor driven device 14 will not `jerk` due to the motor
18 abruptly beginning to rotate.
[0033] Substantially simultaneously to beginning to attempt to fire
the transistor 142 at a narrow duty cycle, the microcontroller 138
is programmed to determine whether the motor control switch 122 is
in an open or closed position (i.e. `On` or `Off`). In various
preferred embodiments, similar to the AC embodiments described
above, to determine the position of the motor control switch 122
the microcontroller 138 is programmed to sense whether current is
flowing through the motor 18. For example, the microcontroller 138
senses whether current is flowing through the motor 18 by
monitoring a voltage across the shunt resistor 162, the electronic
valve 142, or the motor 18. If current is flowing through the motor
18, indicating the motor control switch 122 is in the closed
position when the motor 18 is initially connected to the DC power
source, the microcontroller 138 begins to fire the transistor 142
at a narrow duty cycle, thereby preventing the motor 18 from
abruptly beginning to rotate. The microcontroller 138 continues to
prevent operation of the motor 18 until such time as the
microcontroller 138 determines that the motor control switch 122
has been placed in the open (i.e. `Off`) position.
[0034] In operation, if the motor control switch 122 is open when
DC power is initially applied to the motor 18, no current can flow
through the motor 18. Therefore, the microcontroller 138 recognizes
that no current is flowing through the motor 18 and enables normal
operation of the motor driven device 14. That is, upon a subsequent
closure of the motor control switch 122, the microcontroller 138
will fire the transistor 142 at a duty cycle suitable to produce
sufficient power for the motor 18 to function in accordance with
desired operational parameters of the motor driven device 14.
Conversely, if the motor control switch 122 is closed and current
flows through the motor 18 when the motor 18 is initially connected
to the DC power source, the microcontroller 138 senses the current
flow and prevents the motor 18 from functioning. For example, the
microcontroller 138 may continue to limit the current flowing
through the motor 18 by continuing to fire the transistor 142 at a
narrow duty cycle, or the microcontroller 138 may stop firing the
transistor 142 altogether so that no current flows through the
motor 18. Thereafter, the microcontroller 138 prevents operation of
the motor 18 until the microcontroller 138 senses that current is
no longer flowing through the motor 18, indicating that the motor
control switch 122 has been opened. Once the motor control switch
122 is opened, the microcontroller 138 enables normal functioning
of the motor 18 by firing the transistor 142 at a duty cycle
suitable to operate the motor 18 in accordance with the operational
parameters of the motor driven device 14.
[0035] It will be appreciated that although FIG. 6 shows the
transistor 142, the shunt resistor 162 and the amplifier 166 as
being included in the control module 130, in preferred alternate
embodiments of the present invention, one of, two of, or each of
the transistor 142, the shunt resistor 162 and the amplifier 166
could be readily located external to the control module 130.
[0036] In another preferred embodiment, similar to the AC
embodiment described above in reference to FIG. 5, to determine the
position of the motor control switch 122 the microcontroller 138 is
programmed to sense the presence or absence of a voltage across the
motor 18. If, when the motor 18 is initially connected to the DC
power source, the microcontroller 138 senses the presence of a
voltage at the motor 18, indicating the motor control switch 122 is
in the closed position, the microcontroller 138 prevents startup of
the motor 18 until such time as the microcontroller 138 determines
that the motor control switch 122 has been place in the open (i.e.
`On`) position.
[0037] Although the control circuits 32 and 132 have been described
above in FIGS. 2, 3, 4, 5 and 6 to include a microcontroller it
will be appreciated that the control circuit 32 can include any
electrical and semiconductor devices suitable to perform the
operations described above. That is, the control circuits 32 and
132 can include any electrical and semiconductor devices suitable
to determine a position of a motor control switch based on either
current flowing through the motor 18 or the presence of a voltage
across the motor, and control an amount of power provided to the
motor 18 based on the position of the motor control switch. For
example, control circuit 32 or circuit 132 could each include an
application specific integrated circuit (ASIC).
[0038] Thus, the present invention provides a system that utilizes
a control circuit to determine the position of a control switch of
a motor driven device and to prevent inadvertent startup of the
motor if the device is connected to a power source with the control
switch in a closed position. More specifically, upon connecting the
motor driven device to a power source, the control circuit operates
an electronic valve such that if current is flowing through the
motor, the motor will not suddenly startup. Additionally, if the
control circuit senses that current is flowing through the motor
when power is first applied, indicating that the motor control
switch is closed, the control circuit continues to prevent the
motor from operating. The control circuit then continues to prevent
the motor from operating until such time as the control circuit
senses that current has stopped flowing through the motor,
indicating that the motor control switch has been placed in the
open (i.e. `Off`) position.
[0039] Even more specifically, in one preferred embodiment, upon
connecting the motor driven device to the power source, a
microcontroller is programmed to attempt to operate the electronic
valve such that if current is flowing through the motor, the motor
will not suddenly be pulsed on. Additionally, substantially
simultaneously, the microcontroller determines whether current is
flowing through the motor. If the microcontroller senses that
current is in fact flowing through the motor, indicating that the
motor control switch is closed, the microcontroller takes
appropriate action to continue to prevent the motor from operating.
The microcontroller then continues to prevent the motor from
operating until such time as the microcontroller senses that
current has stopped flowing through the motor, indicating that the
motor control switch has been placed in the open position.
[0040] While the invention has been described in terms of various
specific embodiments, those skilled in the art will recognize that
the invention can be practiced with modification within the spirit
and scope of the claims.
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