US20040155532A1

US20040155532A1 - Method for sensing switch closure to prevent inadvertent startup

Info

Publication number: US20040155532A1
Application number: US10/360,957
Authority: US
Inventors: Daniele Brotto
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 2003-02-07
Filing date: 2003-02-07
Publication date: 2004-08-12
Also published as: US20040155529A1; CN1748276A; JP4685758B2; JP2006518181A; CN100431235C; ATE544216T1; US7112900B2

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.

Description

FIELD OF INVENTION

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

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.

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

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.

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

The present invention will become more fully understood from the detailed description and accompanying drawings, wherein; [0006]
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; [0007]
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; [0008]
FIG. 3 is simplified electrical schematic of an alternative preferred embodiment of the system shown in FIG. 2; [0009]
FIG. 4 is another simplified electrical schematic of an alternative preferred embodiment of the system shown in FIG. 2; [0010]
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 [0011]
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.[0012]

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a highly simplified block diagram of a [0013] 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.
The [0014] 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.
The [0015] 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.
FIG. 2 is a simplified electrical schematic of the system [0016] 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.
The [0017] 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 38 a and begins to operate the electronic valve 42 via signals output from a port 38 b. 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 38 a, the microcontroller 38 begins to fire the triac 42 via port 38 b. 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 38 a. 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 38 a. 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.
When the [0018] 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 38 a. 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° and 175° for the positive half cycle and between 340° and 355° for the negative half cycle. The conduction angle may be derived from an analog representation of the AC voltage produced at port 38 a by voltage divider circuit 46 or determined via time delays posted at the zero crossing of the AC signal at port 38 a.
For current to be flowing through the [0019] 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.
Substantially simultaneously with beginning to fire the [0020] 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 38 c 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 38 c 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 38 c to amplify the voltage sensed across shunt resistor 62 to a level suitable for detection by microcontroller 38.
In one preferred embodiment, the voltage signal provided at [0021] port 38 c 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 38 c 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.
FIG. 3 is a simplified electrical schematic of another preferred embodiment in which the [0022] 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 38 d. In one preferred embodiment, the voltage across the triac 42 is amplified by an amplifier 70 for analysis by the microcontroller 38, via port 38 d. 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 38 d, 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.
FIG. 4 is simplified electrical schematic of yet another preferred embodiment in which the [0023] 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 38 d. The voltage across the motor 18 is amplified by an amplifier 74 for analysis by microcontroller 38, via port 38 d. 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 38 d, 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.
Thus, referring to FIGS. 2, 3 and [0024] 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.
In operation, if the [0025] 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 38 c or port 38 d 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
Therefore, the [0026] 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.
Still referring to FIGS. 2, 3 and [0027] 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.
FIG. 5 is a simplified electrical schematic of an alternative preferred embodiment of the system [0028] 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.
In one preferred embodiment, [0029] port 38 d 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 38 d 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.
FIG. 6 is a simplified electrical schematic of the system [0030] 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.
In the DC application of [0031] 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 138 b, 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.
In one preferred embodiment, when the motor is initially connected to the DC power source, the [0032] 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.
Substantially simultaneously to beginning to attempt to fire the [0033] 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.
In operation, if the [0034] 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.
It will be appreciated that although FIG. 6 shows the [0035] 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.
In another preferred embodiment, similar to the AC embodiment described above in reference to FIG. 5, to determine the position of the [0036] 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.
Although the [0037] 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).
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. [0038]
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. [0039]
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. [0040]

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

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;

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

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:

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.