GB2575571A

GB2575571A - Motor control apparatus and power tool

Info

Publication number: GB2575571A
Application number: GB1913570.6A
Authority: GB
Inventors: Endo Daisuke; Shimizu Hiroyuki; Miyagi Takanori
Original assignee: Nitto Kohki Co Ltd
Current assignee: Nitto Kohki Co Ltd
Priority date: 2017-04-25
Filing date: 2018-04-19
Publication date: 2020-01-15
Anticipated expiration: 2038-04-19
Also published as: JPWO2018198928A1; JP6811850B2; GB2575571B; KR20190128696A; TW201843018A; CN110521108A; KR102342214B1; TWI685404B; CN110521108B; GB201913570D0; DE112018002164T5; WO2018198928A1

Abstract

A motor control apparatus 32 has: an on/off switch 22; a main control unit 36; a motor control circuit 38; an operating voltage generation circuit 40; a SW/AC monitoring unit 46; and an operating voltage monitoring unit 48. The SW/AC monitoring unit 46 monitors the state of the on/off switch SW or the state of a power supply line 35 between the on/off switch SW and a motor 30. The operating voltage monitoring unit 48 monitors the voltage level of an operating voltage Vcc outputted from the operating voltage generation circuit 40. The main control unit 36 controls activation or stopping of the motor 30 by double-checking a SW/AC monitor signal MS from the SW/AC monitoring unit 46 and an operating voltage monitor signal MV from the operating voltage monitoring unit 48.

Description

DESCRIPTION

TITLE OF THE INVENTION: MOTOR CONTROL APPARATUS AND POWER TOOL

TECHNICAL FIELD [0001] The present invention relates to a motor control apparatus and a power tool utilizing electric power from an external power source to operate and control a motor therein.

BACKGROUND ART [0002] Nowadays, motors are used for various applications in wide range of fields such as household appliances, industrial uses, etc. In our personal circumstances, there are many portable electrical devices that are supplied with electric power from an external power source, for example, a commercial AC power source to make a built-in motor operate with a plug, which is provided through an electrical code on the device body, being inserted in an outlet. In general, an electrical device of this type needs the user to manually operate an on/off switch attached to the device body so that the user can control operation and stopping of the device with his own will.

[0003] However a user sometimes inadvertently plugs in an outlet with the on/off switch being on. In that case various troubles may occur when the motor in the device unexpectedly starts. The same is true for a case that the motor stops due to a sudden power failure in the external power source while the device is operating and then the motor unexpectedly restarts due to an immediate recovery of the power failure.

[0004] Conventionally, in the field of power tool, there have been provided various motor control apparatuses with such capability as to prevent a motor therein from unexpectedly starting or restarting when meeting re-plugin or recovery of power failure, thus intending to improve safety and workability (Patent Documents 1, 2 and 3).

PRIOR ART DOCUMENT

PATENT DOCUMENT [0005]

Patent Document 1: Japanese Laid-Open Patent Publication No. 1985-174079

Patent Document 2: Japanese Laid-Open Patent Publication No.

1996-308098

Patent Document 3: Japanese

Laid-Open Patent Publication No.

1996-336779

SUMMARY OF THE INVENTION

PROBLEM TO BE SOLVED BY THE

INVENTION

[0006] The portable electrical device of the external power supply type described above can avoid unexpected starting or restarting of a motor therein when re-plugin or recovery of power failure occurs after a while (generally after a few seconds or more) since stopping of the motor due to an inappropriate plugin or a temporary power failure. Because a motor control apparatus in the device resets once and then responds to the situation. However, when re-plugin or recovery of power failure occurs within 1 to 2 seconds of the motor stopping, the motor control apparatus responds without resetting to the re-plugin or the recovery of power failure under an unstable or indeterminate operating voltage, causing the motor to unexpectedly start or restart contrary to the user's intention.

[0007] The present invention aims to solve the above problems of the prior art and provides a motor control apparatus and a power tool equipped therewith that can properly and surely prevent starting or restarting of a motor therein not intended by the user.

MEANS FOR SOLVING THE PROBLEM [0008] A motor control apparatus according to a first aspect of the invention is for controlling operation of a motor utilizing power supplied from an external power source to rotate, comprising an on/off switch provided electrically in series with the motor to the external power source, an operating voltage generation unit inputting power from the external power source to generate a DC operating voltage, and a first monitoring unit for monitoring the state of the on/off switch or the state of a power supply line between the on/off switch and the motor to generate a first monitoring signal indicating whether or not power from the external power source is being supplied to the power supply line, characterized by comprising:

a second monitoring unit for monitoring the operating voltage to generate a second monitoring signal indicating whether the voltage level of the operating voltage is higher or lower than a preset monitoring value; and a control unit adapted to operate under the operating voltage to control activation or stopping of the motor based on information of the first and second monitoring signals.

[0009] In the motor control apparatus with the above configuration, the second monitoring unit serves to monitor the voltage level of the operating voltage while the first monitoring unit serves to monitor the state of the on/off switch or the state of the power supply line between the on/off switch and the motor, and the control unit double checks the first monitoring signal from the first monitoring unit and the second monitoring signal from the second monitoring unit to control activation or stopping of the motor, enabling to properly and surely prevent starting or restarting of the motor not intended by the user even when input of power from the external power source stops unexpectedly and resumes immediately.

[0010] A motor control apparatus according to a second aspect of the invention is for controlling operation of a motor utilizing power supplied from an external power source to rotate, comprising an on/off switch provided electrically in series with the motor to the external power source, an operating voltage generation unit inputting power from the external power source to generate a DC operating voltage, and a first monitoring unit for monitoring the state of the on/off switch or the state of a power supply line between the on/off switch and the motor, characterized by comprising:

a second monitoring unit for monitoring whether the operating voltage is higher or lower than a preset monitoring value; and a control unit adapted to operate under the operating voltage to control activation or stopping of the motor based on monitoring information from the first and second monitoring units; wherein when the first monitoring unit provides its monitoring information indicating that the on/off switch has changed from the OFF state to the ON state while the second monitoring unit is providing its monitoring information indicating that the voltage level of the operating voltage is higher than the monitoring value, the control unit responds to the monitoring information from the first monitoring unit to activate the motor;

when the first monitoring unit provides its monitoring information indicating that input of power from the external power source to the power supply line has stopped while the second monitoring unit is providing its monitoring information indicating that the voltage level of the operating voltage is higher than the monitoring value, the control unit responds to the monitoring information from the first monitoring unit to stop the motor; and while the second monitoring unit is providing its monitoring information indicating that the voltage value of the operating voltage is lower than the monitoring value, the control unit does not activate the motor even when the first monitoring unit provides its monitoring information indicating that input of power from the external power source to the power supply line has started or resumed.

[0011] In the motor control apparatus with the above configuration, the second monitoring unit serves to monitor the voltage level of the operating voltage while the first monitoring unit serves to monitor the state of the on/off switch or the state of the power supply line between the on/off switch and the motor, and the control unit double checks the monitoring information from the first monitoring unit and the second monitoring information from the second monitoring unit to control activation or stopping of the motor, enabling to properly and surely prevent start or restart of the motor not intended by the user even when input of power from the external power source stops unexpectedly and resumes immediately.

[0012] A power tool according to a first aspect of the invention comprises :

a body;

a movable tool mounted on the body so as to be able to do a certain movement;

a motor provided in the body that is supplied with power from an external power source to drive the tool; and a motor control apparatus provided in the body for controlling operation of the motor supplied with power from an external power source, including an on/off switch provided electrically in series with the motor to the external power source, an operating voltage generation unit inputting power from the external power source to generate a DC operating voltage, and a first monitoring unit for monitoring the state of the ON/OFF switch or the state of a power supply line between the on/off switch and the motor;

characterized in that the motor control apparatus comprises a second monitoring unit for monitoring the operating voltage to generate a second monitoring signal indicating whether the voltage level of the operating voltage is higher or lower than a preset monitoring value, and a control unit adapted to operate under the operating voltage to control activation or stopping of the motor based on information of the first and second monitoring signals.

[0013] In the power tool with the above configuration, because of the motor control apparatus of the first aspect being provided therein, it is permitted to properly and surely prevent start or restart of the motor not intended by the user even when input of power from the external power source stops unexpectedly and resumes immediately, thus improving safety and workability.

[0014] A power tool according to a second aspect of the invention comprises :

a body;

a movable tool mounted on the body so as to be able to do a certain movement;

characterized by comprising:

[0015] In the power tool with the above configuration, because of the motor control apparatus of the second aspect being provided therein, it is permitted to properly and surely prevent starting or restarting of the motor not intended by the user even when input of power from the external power source stops unexpectedly and resumes immediately, thus improving safety and workability.

EFFECT OF THE INVENTION [0016] A motor control apparatus according to the present invention providing the configuration and operation described above can properly and surely prevent a motor therein from starting or restarting contrary to the user's intention when input of power from the external power source stops and immediately resumes.

[0017] A power tool according to the present invention providing the configuration and operation described above can properly and surely prevent a motor therein from starting or restarting contrary to the user's intention, achieving improved safety and workability.

BRIEF DESCRIPTION OF DRAWINGS [0018] Fig.l is a perspective view showing an appearance configuration of a motorized belt grinding machine as a power tool in an embodiment of the present invention.

Fig. 2 is a block diagram showing a system configuration of a motor and a motor control apparatus incorporated in the motorized belt grinding machine.

Fig. 3 is a circuit diagram showing of a specific circuit configuration of the motor control apparatus in the embodiment.

Fig. 4 is a flow chart showing a basic control procedure in a main control unit to activate and stop the motor in the motor control apparatus.

Fig. 5 is a timing diagram showing the changes of state in various parts in a case that the motor control apparatus is normally supplied with power from an external power source when plugging in an outlet with an on/off switch being off.

Fig. 6 is a timing diagram showing the changes of state in various parts in a case that the motor control apparatus is normally supplied with power from an external power source when plugging in an outlet with an on/off switch being on in the embodiment.

Fig. 7 is a timing diagram showing the changes of state in various parts in an exemplary case that input of power from the external power source stops once in operation and resumes immediately after that in the embodiment.

Fig.8 is a timing diagram showing the changes of state in various parts in another exemplary case that input of power from the external power source stops once in operation and resumes immediately after that in the embodiment.

Fig. 9 is a flow chart showing a basic control procedure in the main control unit of the motor control apparatus in a case (comparative example) of removing the operating voltage monitoring unit therefrom.

Fig.10 is a timing diagram showing the changes of state in various parts in the comparative example (Fig.9).

Fig. 11 is a flow chart showing a variation of the control procedure in the main control unit of the motor control apparatus.

MODES FOR CARRYING OUT THE INVENTION [0019] Next there will be described an embodiment of the present invention in conjunction with the attached drawings.

[0020] [Appearance Configuration of Power Tool]

Referring to Fig.l, there is shown an appearance of a motorized belt grinding machine as a power tool in accordance with an embodiment of the present invention. The motorized belt grinding machine 1 includes a cylindrical body 10, a plug 14 provided through an electrical cable 12 on the rear end portion of the body 10, a grinding head 16 mounted to be turnable on the front end portion of the body 10, a movable grinding belt 18 extending between the rear end portion and the front end portion of the grinding head

16, a rod-like handle 20 fixed to the grinding head 16, and an on/off switch 22 and a display 24 provided at appropriate positions on the surface of the body 10.

[0021] The body 10 has a function of one grip pairing with the handle 20. The body 10 builds in a motor 30 and the circuit board of a motor control apparatus 32 (Fig.2 and Fig.3) that will be described later. Furthermore the body 10 accommodates at the front end portion thereof a transmission mechanism (not shown) including gears for transmitting a rotational driving force from the motor 30 to the grinding head 16. The grinding head 16 has a drive pulley (not shown) housed in the rear end portion thereof, a driven pulley (not shown) mounted on the front end portion thereof, and the endless grinding belt 18 stretched between the pair of pulleys. In operation, a rotational driving force from the motor 30 is transmitted through the transmission mechanism and the pair of pulleys to the grinding belt 18 which moves straight between the pair of pulleys while rubbing a workpiece (not shown) to be grinded or polished.

[0022] The on/off switch 22 comprises a sliding manual switch, for example. The switch 22 is so configured as to be locked in either the ON and OFF positions thereof when the user takes his finger off the switch 22 in the current position. The display 24 comprises a plurality of LEDs or lamps, for example. The display 24 is adapted to light or blink in specific emitting colors to indicate the operating status of the belt grinding machine or give an alarm in abnormal situation.

[0023] [Configuration of Motor Control Unit]

Referring to Fig.2, there is shown in block diagram a system configuration of the motor 30 and the motor control apparatus 32 incorporated in the motorized belt grinding machine.

[0024] The motor 30 comprises a single-phase AC motor, for example. In order to rotate under control of the motor control apparatus 32, the motor 30 is supplied with AC power E of commercial frequency having a fixed effective value V_E (for example 100 volts) from a commercial AC (Alternating Current) power source 34 as an example through the plug 14, the electrical cable 12 (Fig.l) and the on/off switch 22.

[0025] The motor control apparatus 32 in a basic form comprises the on/off switch 22, a main control unit 36, a motor control circuit 38, an operating voltage generation circuit 40, a reference clock and timing unit 42, a motor rotational speed measurement unit 44, a SW/AC monitoring unit 46 and an operating voltage monitoring unit 48 .

[0026] The operating voltage generation circuit 40 is provided electrically in parallel with the motor 30 to the AC power source 34 and is supplied with AC power E from the AC power source 34 to generate a DC operating voltage V_cc with a predetermined rated value (for example 5 volts) . The operating voltage V_cc outputted from the operating voltage generation circuit 40 is supplied through an operating voltage supply line to every unit or integrated circuit that needs operating voltage in the motor control apparatus 32.

[0027] The motor control circuit 38 is provided electrically in series with the on/off switch 22 and the motor 30 to the AC power source 34 . When AC power E from the AC power source is being inputted through the plug 14 and the electrical cable 12 with the on/off switch 22 being on, the motor control circuit 38 serves to control a current flowing through the motor 30 under control of the main control unit 36.

[0028] The reference clock and timing unit 42 includes an oscillator 50 and a zero-cross detection unit 52. The oscillator 46 comprises for example a crystal oscillator to generate a basic clock signal CK required for calculation and other processing in the main control unit 36. The zero-cross detection unit 52 is adapted to detect each of timings at which an alternating current of commercial frequency supplied from the AC power source 34 crosses the zero level to generate a basic timing pulse signal CZ required for ignition control or phase control of the motor 30 by the main control unit 36.

[0029] The motor rotational speed measurement unit 44 includes a rotation detection sensor 54 which detects the position of a rotating body (rotor) in the motor 30, and a rotational speed calculation unit 56 which calculates the rotational speed of the motor 30 based on the signal outputted from the rotation detection sensor 54 .

[0030] The SW/AC monitoring unit 46, a first monitoring unit in the embodiment, is configured to monitor the state of the on/off switch SW or the state of a power supply line 35 between the on/off switch SW and the motor 30, and to generate a SW/AC monitoring signal (first monitoring signal) MS indicating whether or not power from the AC power source 34 is being inputted to the power supply line 35.

[0031] The operating voltage monitoring unit 48, a second monitoring unit in the embodiment, is configured to input and monitor the same voltage as the operating voltage V_cc supplied to the main control unit 36 from the operating voltage generation circuit 40, and to generate an operating voltage monitoring signal (second monitoring signal) MV indicating whether the voltage level of the operating voltage V_cc is higher or lower than a preset monitoring value.

[0032] As described above, the main control unit 36 inputs the operating voltage V_cc from the operating voltage generation circuit 40, inputs the basic clock signal CK and the basic timing pulse signal CZ from the reference clock and timing unit 42 (50,52), inputs the measurement value of rotational speed of the motor 30 from the motor rotational speed measurement unit 44 (54,56), inputs the SW/AC monitoring signal MS from the SW/AC monitoring unit 46, and inputs the operating voltage monitoring signal MV from the operating voltage monitoring unit 48. The main control unit 36 has signal processing function as well as calculation processing function, and serves to control activation, rotational operation and stopping of the motor 30 through the motor control circuit 38.

[0033] Referring to Fig.3, there is shown a specific circuit configuration of the motor control apparatus 32 in the embodiment. The main control unit 36 and the rotational speed calculation unit 56 in a preferable form comprise a microcomputer. The rotation detection sensor 54 in a preferable form comprises a Hall IC. In a preferable form, the operating voltage generation circuit 40 comprises an AC/DC conversion circuit, preferably including an input capacitor 60, a full wave rectification circuit 62 composed of bridged four diodes, Zener diodes 64,66 and resistors 68, 70 for smoothing or ripple suppression, and an output circuit 74 with a capacitor 72.

[0034] The zero-cross detection circuit 52 in a preferable form comprises a photo coupler 76. With AC power E being inputted from the AC power source 34, the photo transistor 76a of the photo coupler 76 momentarily turns off only when the alternating current of commercial frequency crosses the zero level to obtain a timing pulse signal CZ, which indicates the timing of start of each half cycle of commercial AC frequency, at the collector terminal of the photo transistor 76a. The timing pulse signal CZ is applied to a specific input port of the main control unit 36.

[0 035] The motor control circuit 38 in a preferable form comprises a bidirectional thyristor 78 and a photo triac 80. The bidirectional thyristor 78 composing a switching element is electrically connected in series with the on/off switch 22 and the motor 30 to the AC power source 34. The photo triac 80 that is in combination with nearby capacitor 82 and resistors 83 and 84 to compose an ignition circuit or phase control circuit has its light emitting diode 80a connected to a specific output port of the main control unit 36. The main control unit 36 is adapted to control ON (light up) and OFF (turn off) of the light emitting diode 80a so as to perform switching control of the bidirectional thyristor 78 at a desired firing angle or phase angle synchronized to the timing pulse signal CZ through the photo triac 80, thereby permitting flexible control of a current flowing through the motor 30 .

[0036] In this way the motor control circuit 38 comprises the ignition circuit or phase control circuit utilizing the photo triac 80, providing electrical isolation between the circuit of the motor drive system that operates under the high voltage (AC 100 volts) of the AC power source 34 and the circuit of the control system that operates under the operating voltage (DC 5 volts).

[ 0 037 ] The SW/AC monitoring unit 4 6 in a preferable form comprises a branch line or branch circuit 86 electrically connected in parallel with the power supply line 35 or the motor 30. The branch circuit 86 includes a photo coupler 88 and a resistor 90 for current limit that are connected in series with each other. The photo transistor 88a of the photo coupler 88 has its collector terminal connected to a voltage supply line or terminal with the operating voltage V_cc through a pull-up resistor 92 as well as to a specific input port of the main control unit 36 and has its emitter terminal connected to a ground potential terminal.

[0038] In the SW/AC monitoring unit 46 with the above configuration, when power E from the AC power source 34 is being inputted to the power supply line 35 through the on/off switch 22, a current is flowing through the branch circuit 86 regardless of the state (rotating or stop) of the motor 30, keeping the photo transistor 88a of the photo coupler 88 on so that the SW/AC monitoring signal MS obtained at the collector terminal thereof is at the ground level or L level. On the contrary, when AC power E is not being inputted to the power supply line 35 despite being inputted to the operating voltage generation circuit 40 (or when the on/off switch 22 is in the OFF state), the photo transistor 88a of the photo coupler 88 is off to obtain the SW/AC monitoring signal MS with the operating voltage V_cc level or H level at the collector terminal thereof. The main control unit 36 inputs and monitors the SW/AC monitoring signal MS without interruption and judges that the SW/AC monitoring signal MS is at H level (MS=H) when the voltage level of the signal MS is higher than a preset H level threshold V_H (for example 2.0 volts), and judges that the

SW/AC monitoring signal MS is at level of the signal MS is lower V_L (for example 0.8 volts) . Note

SW/AC monitoring signal MS has a

L level (MS=L) when the voltage than a preset L level threshold that it is indeterminate when the voltage level between the L level threshold V_L and the H level threshold V_H.

[0039] In this way the SW/AC monitoring unit 46 comprises the current detection unit using the photo coupler 88 to determine whether or not a current is flowing through the branch circuit 86, providing electrical isolation between the current detection circuit that operates under the high voltage (AC 100 volts) of the AC power source 34 and the monitoring signal output circuit that operates under the operating voltage (DC 5 volts).

[0040] The operating voltage monitoring unit 48 in a preferable form comprises an integrated circuit. Although not shown, the operating voltage monitoring unit 48 includes a comparator, which compares the voltage level of the operating voltage V_cc supplied from the operating voltage generation circuit 40 with a preset monitoring value V_K to generate a comparison result indicative of the magnitude relationship between V_cc and V_K, and an output circuit which provides the comparison result from the comparator to the main control unit 36 as the binary operating voltage monitoring signal MV. More specifically, the monitoring signal MV is provided with H level when the voltage level of the operating voltage V_{c c} is higher than the monitoring value V_K, and provided with L level when the voltage level of the operating voltage V_cc is lower than the monitoring value V_K . It may be determined as either MV=H or MV=L when the operating voltage V_cc has the same level as the monitoring value V_K. The monitoring value V_K is set to be higher than the limit value of the operating voltage V_cc that enables the main control unit 36 to operate normally. For instance, when the rated value V_s of the operating voltage V_cc is 5 volts, the monitoring value V_K is set to 4.5 volts.

[0041] The display unit 24 comprises three LEDs 94R,94Y and 94B whose emission colors are red, yellow and blue (or green), respectively, for example. The LEDs 94R, 94Y and 94B are connected in parallel with each other to specific output ports of the main control unit 36 that controls turn-on, blink or turn-off of each LED individually.

[0042] [Operation of Motor Control Apparatus]

The operation of the motor control apparatus 32 in the embodiment will hereinafter be described with reference to Figs.4 to 11.

[0043] The flowchart of Fig.4 shows a basic control procedure in the main control unit 36 to activate and stop the motor 30 in the motor control apparatus 32. Moreover the timing diagrams of Figs. 5 and 6 show the changes of state in various parts in a case that the motor control apparatus 32 is normally supplied with AC power from the AC power source 34 in operation of the motorized belt grinding machine.

[0044] In the motor control apparatus 32, upon insertion of the plug 14 into the outlet of the AC power source 34, AC power E from the AC power source 34 is inputted regardless of the state of the on/off switch 22 to the operating voltage generation circuit 40 which then generates the operating voltage V_cc. At that time, the operating voltage V_cc rises instantly to the rated value V_s (DC 5 volts) from the previous value or zero volts. When the operating voltage V_cc has risen to the rated value V_Sf the main control unit 36, the motor rotational speed measurement unit 44 (54,56), the operating voltage monitoring unit 48,etc. each of which is adapted to operate under the operating voltage V_cc become active, respectively. On the other hand, the zero-cross detection unit 52 starts supplying the timing pulse signal CZ to the main control unit 36 at the same time as the start of input of AC power E.

[0045] At first the main control unit 36 carries out the initialization (step S₁₀₁) to make necessary initial setting for the resisters, input ports and output ports therein to be used in this operation. In the initialization, the unit delay time T_P is assigned a setting value (for example 10ms), while the number of delays N_s is assigned another setting value (for example 5 times) and then initialized as N=0 (step S_R). The unit delay time T_P is set sufficiently shorter than the monitoring value reaching time T_K. Next, the main control unit 36 inputs through its specific input port the SW/AC monitoring signal MS from the SW/AC monitoring unit 46 and reads the logic value of the signal MS (step S₁₀₂) · [0046] Normally, as shown in Fig. 5, when the user inserts the plug 14 into an outlet of the AC power source 34 (at the point of time t₀), the on/off switch 22 is in the OFF state. In that case, the photo transistor 88a of the photo coupler 88 in the SW/AC monitoring unit 46 is off because of no current flowing through the branch circuit 86. Thus, at the same time as start of input of AC power E, namely at the time point t₀ , the SW/AC monitoring signal MS changes from the previous level or L level to H level in conjunction with the rise of the operating voltage V_cc. Thus the main control unit 36 judges MS=H and after the passage of the delay time T_P (step S_F) reads the value of the operating voltage monitoring signal MV provided from the operating voltage monitoring unit 48 (step S_{x 03}) . At this time, the operating voltage V_cc has risen to the rated value (5 volts) and the monitoring signal MV is at H level (MV=H) .

[0047] After confirming the condition of MS=H and MV=H, the main control unit 36 runs the loop [C] (steps S_P^S_x04C^S_x05^S_{x0 2}—>S _F—>S _{x 0 3}—>S _p—> ) five times. When the number of delays N has reached the set number N_s (five times), namely when 50ms (10ms><5) have elapsed from the time point t₀, the main control unit 36 exits from the loop [C], preparing activation of the motor 30 (steps S_P^S_{4 06}). Then the main control unit 36 keeps running the loop [D] (steps Sio7^S₁₀₈^S₁₀₇^··) repeatedly while waiting for the SW/AC monitoring signal MS to change from H level to L level.

[0048] As shown in Fig.5, the SW/AC monitoring signal MS changes from H level to L level when the user switches the on/off switch 22 on (at the time point t_x) . In the SW/AC monitoring unit 46, a current starts flowing through the branch circuit 86 at this time whereby the photo transistor 88a of the photo coupler 88 turns on so that the SW/AC monitoring signal MS changes from H level to L level.

[0049] When the SW/AC monitoring signal MS changes from H level to L level (at the time point t_x) , the main control unit 36 activates the motor 30 through the motor control circuit 38 (steps S₁₀₇^S ₁₀₉) . Then the main control unit 36 continues to monitor the SW/AC monitoring signal MS and run the loop [E] repeatedly (steps S_{10 9}^S _xx0^S_xxX^^S_x0 g^· · ) while confirming that the monitoring signal MS is at L level, thus keeping the motor 30 rotating.

[0050] While keeping the motor 30 rotating in that way, the main control unit 36 carries out measuring the rotational speed and load of the motor 30 through the motor rotational speed measurement unit 44 (54,56), controls a current flowing through the motor 30 by means of the motor control circuit 38 and notifies in real time the user of the operating status (particularly load status) through the display 24. For instance, the main control unit 36 turns on the blue (green) LED 94B when normal or no load (the maximum rotational speed), turns on the yellow LED 94Y when light load (rotational speed 80%), and blinks the red LED 94R when high load (rotational speed 60%). Moreover, when overload, the main control unit 36 can perform display control to blink the red LED 94R at a high rate of for example 0.2 second intervals before stopping the motor 30 and to change the blinking speed from the high rate to a low rate of for example 1.0 second intervals immediately after stopping the motor 30.

[0051] When the grinding process by the motored belt grinding machine is complete and the user switches the on/off switch 22 off (at the time point t₂) , the SW/AC monitoring signal MS changes from the previous level or L level to H level. At this time, the current no longer flows through the branch circuit 86 whereby the photo transistor 88a of the photo coupler 88 in the SW/AC monitoring unit 46 turns off.

[0052] When the SW/AC monitoring signal MS changes from L level to H level, the main control unit 36 completely turns off the switching element 78 of the motor control circuit 38 to stop the motor 30 at the timing of the change in the signal MS (steps S_xio^S₁₁₂) . Then the main control unit 36 initializes the number of delays to zero (N=0) (steps S _{x x 3}^S_R) and runs the loop [C] repeatedly in the same way as for the start of input of AC power E while repeating confirmation of MS=H and MV=H for the set number of delays N s (five times) and thereafter prepares activation of the motor 30 (steps S_P^S₁₀₆) . Then the main control unit 36 runs the loop [D] repeatedly while waiting for the on/off switch 22 to be switched on.

[0053] The example of Fig.5 shows a case that the user unplugs the plug 14 from the outlet after a while, for example, at the time point t₃ after a few seconds. In that case, upon unplugging the plug 14 from the outlet, AC power E from the AC power source 34 is no longer inputted to the operating voltage generation circuit 40 of which the output voltage or the operating voltage V_cc then drops from the rated value to zero volts. In this time, the charge stored in the output capacitor 72 in the operating voltage generation circuit 40 is discharged through the resistor 70 so that the operating voltage V_cc gradually drops with a time constant.

Thus the main control unit 36 becomes inactive when the operating voltage V_cc becomes lower than a specified operation limit value (for example about 1.8 volts).

[0054] Referring to Fig.6, there is shown a case that the user inserts the plug 14 into the outlet of the AC power source 34 with the on/off switch 22 being in the ON state. Even in this case, regardless of the state of the on/off switch 22, the operating voltage generation circuit 40 generates and raises the operating voltage V_cc to the rated value V_s whereby the operating voltage monitoring signal MV rises from the previous level or L level to H level at the same time as the start of input of AC power E from the AC power source 34 (at the time point t₀).

[0055] In that case, when the main control unit 36 reads the SW/AC monitoring signal MS (step S₁₀₂) immediately after the initialization setting (step S₁₀₁) , the SW/AC monitoring signal MS remains at L level. That is, in the SW/AC monitoring unit 46, a current starts to flow through the branch circuit 86 at the same time as the start of input of AC power E because of the on/off switch 22 being on, and thereby the photo transistor 88a of the photo coupler 88 turns on so that the SW/AC monitoring signal MS is held at L level. Thus the main control unit 36 keeps running the loop [A] repeatedly (steps S _{4 0 2}^S _{4 0 4 a}^S_R^S _{4 0 2}^S _{4 0 4 a}·· ) while waiting for the SW/AC monitoring signal MS to change from L level to H level.

[0056] Then, when the user switches the on/off switch 22 off, the current stops flowing through the branch circuit 86 whereby the photo transistor 88a of the photo coupler 88 in the SW/AC monitoring unit 46 turns off, causing the SW/AC monitoring signal MS to change from L level to H level. Thus the main control unit 36 confirms the condition of MS=H and MV=H and then runs the loop [C] five times. And, when the number of delays N has reached the set number of times (5 times) or when 50ms (10ms*5) have elapsed from the point of time t₀, the main control unit 36 prepares activation of the motor 30 (steps S_P^S₁₀₆) and then runs the loop [D] repeatedly until the on/off switch 22 is switched on.

[0057] When the user switches the on/off switch 22 on (at the time point t₄), the SW/AC monitoring signal MS changes from H level to L level whereby the main control unit 36 exits from the loop [D] to activate the motor 30 (steps S₁₀₇^S₁₀₉) . Then the main control unit 36 runs the loop [E] repeatedly to keep the motor 30 rotating. And, when the user switches the on/off switch 22 off or unplugs the plug 14 from the outlet, the monitoring signal MS changes from

H level to level, causing the motor 30 to stop (steps S₁₁₀^S₁₁ ₂) . The subsequent control procedure and operation are the same as in Fig.5.

[0058] In this embodiment, as described above, the motor 30 does not start rotating even when the user inserts the plug 14 into the outlet of the AC power source 34 with the on/off switch 22 being on, and the motor 30 starts rotating only when the user switches the on/off switch 22 off once and then switches it on.

[0059] Ref erring to Fig. 7, there may be a case that a sudden power failure occurs or the plug 14 unintentionally comes out of the outlet while the motor 30 is rotating, for example, at the time point t _a . In that case, due to stopping of AC power E input, supplying of power stops not only to the power supply line 35 and the motor 30 but also to the operating voltage generation circuit 40. In the operating voltage generation circuit 40, however, the power stored in the capacitor 72 of the output circuit 74 is discharged at a time constant so that the output voltage or operating voltage V _cc drops exponentially from the previous value or the rated value V_s in the same manner as a case of unplugging the plug 14 from the outlet when normal.

[0060] In this way, at the same time as the stopping of AC power E input, the current that has been flowing through the branch circuit 86 until just before is cut off so that the photo transistor 88a of the photo coupler 88 in the SW/AC monitoring unit 46 turns off, causing the SW/AC monitoring signal MS to change from the previous level or L level to H level. The main control unit 36 stops the motor 30 through the motor control circuit 38 at the timing of the change (MS= L^H)in the SW/AC monitoring signal MS (steps S_xiii2)· [0061] The case of Fig.7 shows that the user reinserts the plug into the outlet to resume AC power E input immediately after the passage of a certain time or monitoring value reaching time T_K (for example 30ms) , which is from the time point t_a when AC power E input stopped to when the voltage level of the operating voltage V_cc becomes lower than the specific monitoring value V_K, for example, at the time point t_c, 40 ms after the time point t_a .

[0062] In that case, when AC power E input from the AC power source resumes at the time point t_c, the operating voltage generation circuit 40 instantly restores the operating voltage V_cc to the rated value V_s, and furthermore the operating voltage monitoring unit 48 makes the operating voltage monitoring signal MV change from L level to H level in an instant. On the other hand, at the same time as the resume of AC power E input, the SW/AC monitoring unit 4 6 turns on the photo transistor 88a of the photo coupler 88, causing the voltage level of the SW/AC monitoring signal MS to drop from the previous level or H level to zero volts (L level) in an instant. It is noted that the voltage level of the SW/AC monitoring signal MS rises once to near the rated value V_s at the stopping of AC power E input and then drops exponentially according to the operating voltage V_cc. The main control unit 36 judges MS=H until the voltage level of the SW/AC monitoring signal MS becomes lower than the H level threshold V_H.

[0063] The procedure in the main control unit 36 in that case is as follows. Namely, the main control unit 36 carries out the initialization (N=0) for the number of delays (steps S₁₁₃^S_R) after stopping the motor 30, then confirms MS=H and MV=H, and then continues to run the loop [C] repeatedly. Soon, when the monitoring value reaching time T_K (30ms) has elapsed, the operating voltage monitoring signal MV changes from H level to L level whereby the main control unit 36 transitions from the loop [C] to the loop [B] (steps S _{x 0 3}—*S _{x 0 4 b}^S_R^S _{x 0 2}—>S_F—>S _{x 0 3}—* * ’ ) . Immediately after that, when AC power E input resumes and thereby the operating voltage monitoring signal MV returns from L level to H level at the time point t_c, the main control unit 36 exits from the loop [B] to check the number of delays (steps S _{x 0 3}^S_P) . In that time, since the number of delays has not reached the set number of times (five times) yet, the main control unit 36 enters the loop [C] to check the SW/AC monitoring signal MS (steps S_P^S_x04C^S_x05^S_x02). Then, because of MS=L, the main control unit 36 enters the loop [A] (steps S₁₀2^S_104a^S_R^· j and continues to run the loop [A] repeatedly.

[0064] In this embodiment, even when the time point t_c of resume of AC power E input passes the time (50ms) obtained by multiplying the unit delay time (10ms) by the set number of delays N_Sf the main control unit 36 does not transition to preparation of motor activation (step S₁₀₆) but stays in the loops [A]~[C]. More specifically, when the main control unit 36 has run the loop [C] four times, namely at the time point t^ after 40ms from the time point t_a when AC power input stopped, the operating voltage monitoring signal MV changes from H level to L level so that the main control unit 36 transitions from the loop [C] to the loop [B] (steps S_x03—*S_x04_b^S_R^· · ) . Thereafter, when AC power E input resumes at the time point t_Cf the main control unit 36 exits from the loop [B] (steps S₁₀₃^S_P) and then enters the loop [C] once (steps Sp^S4₀4_C^S4₀5—*S4₀₂) because the number of delays has not reached the set number of times N_s (five times). But, since the SW/AC monitoring signal MS remains at L level in that time, the main control unit 36 transitions from the loop [C] to the loop [A] (steps S104₀4_a^S_R^· · ) and then stays in the loop [A].

[00 65] The example of Fig. 8 shows that the user reinserts the plug 14 into the outlet to resume input of AC power E at the time point t^ before the monitoring value reaching time T_K (30ms) has elapsed from the time point t_a when AC power E input stopped , for example, at the time point t₃ when 20ms have elapsed from the time point t a · [0066] The procedure in the main control unit 36 in this case is as follows. Namely, after stopping the motor 30, the main control unit 36 carries out the initialization (N=0) (steps S₁₁₃^S_R) and then checks the logical values of the SW/AC monitoring signal MS and the operating voltage monitoring signal MV (steps S_102iS₁₀₃) .

Immediately after input of AC power E has stopped, because of MS=H and MV=H, the main control unit 36 runs the loop [C] repeatedly. Then, when input of AC power resumes at the time point t^ before the monitoring value reaching time T_K (30ms) has elapsed, the main control unit 36 checks the SW/AC monitoring signal MS in the loop [C] (steps S₁₀3^S_104c^S₁₀₅^S₁₀₂) . Thus, since the SW/AC monitoring signal MS has changed from H level to L level at the time point t|3,the main control unit 36 enters the loop [A] and stays therein.

[0067] In this embodiment, as described above, the main control unit 36 double checks the monitoring information (MS) provided from the SW/AC monitoring unit 46 and the monitoring information (MV) provided from the operating voltage monitoring unit 48. As long as the operating voltage monitoring unit 48 is issuing the monitoring information (MV=L) indicating that the voltage level of the operating voltage V_cc is lower than the specified monitoring value V_K, the main control unit 36 does not activate the motor 30 even if the SW/AC monitoring unit 46 is issuing the monitoring information (MS=H'%L) indicating that input of AC power from the AC power source 34 to the power supply line 35 has started or resumed.

[0068] Thus, even when the plug 14 comes out of the outlet in a grinding process using the motored belt grinding machine contrary to the user's intention and then the user reinserts the plug 14 into the outlet in a hurry, the motor 30 will never start. The same is true for a case that the AC power source 34 suddenly shuts down during a grinding process and resumes soon. In that case, the user can make the motor 30 restart by switching the on/off switch 22 off once and then switching it on again.

[0069] It is noted that when preventing the motor 30 from restarting in the above manner, the main control unit 36 makes the display 24 issue an alarm, for instance, makes the green LED 94G blink at a low rate so as to prompt the user to operate the on/off switch 22.

[0070] By the way, in a comparative example or case of removing the operating voltage monitoring unit 48 from the motor control unit in the embodiment, the main control unit 36 performs such control procedure as shown in Fig.9, leading to changes in the voltage levels or logical values of various parts therein as shown in Fig.10. In this case, the control procedure does not include the process (step S₁₀₃) of checking the monitoring information (the operating voltage monitoring signal MV) provided from the operating voltage monitoring unit (48), the delay related processes (steps S_R, S_F,S_P) and the loops [B] and [C], etc., the main control unit 36 controls activation and stopping of the motor 30 based only on the monitoring information (the SW/AC monitoring signal MS) from the SW/AC monitoring unit 46. Therefore, when input of AC power E stops suddenly and resumes immediately (at the time point t_c) in a grinding operation, the SW/AC monitoring signal MS changes from H level to L level, to which the main control unit 36 responds, causing the motor 30 to restart (steps S₁₀₆^S₁₀₉) . However, such restart of the motor not intended by the user is dangerous for the user himself and those around him as well as undesirable for work.

[0071] [Other embodiments and variations]

Although description of the preferred embodiment has been made, the present invention is not limited by the embodiment above. It is possible for a person skilled in the art to make various changes or modifications to the embodiment without departing from the technical idea or scope of the present invention.

[0072] In the embodiment described above, for instance, it is possible to modify the control procedure in the main control unit 36 (Fig.4) as shown in Fig.11. According to the modification or second embodiment, the delay initialization process (step S_R) , the process of checking the number of delays (step S_P) and the loop [C] are removed while a process of rechecking the SW/AC monitoring signal (step S_G) and the loop [F] are added instead. The delay time T_P in the delay process (step S_F) is set to a value (for example 30~35ms) that is the same as or slightly longer than the monitoring value reaching time T_K (30ms). The same operations as those of Fig. 7 and Fig.8 are also performed according to the control procedure of the second embodiment.

[0073] More specifically, in the case of Fig.7, the monitoring value reaching time T_K (30ms) has elapsed during clocking of the delay time T_P from the time point t_a when AC power E input stopped, causing the operating voltage monitoring signal MV to change from

H level to L level. Thus, when the main control unit 36 checks the operating voltage monitoring signal MV after the delay time T_P has elapsed, MV is at L level (MV=L) , and therefore the main control unit 36 enters the loop [B] (steps S₄₀₃^S _404b^S ₄₀₂^S_F^S₄₀₃^S_404b··) · Then, when AC power E input resumes at the time point t_c, the SW/AC monitoring signal MS changes to L level whereby the main control unit 36 enters the loop [A] (steps S _{4 0 2}^S _{4 0 4 a}^S _{4 0 2}·· ) and thereafter stays therein.

[0074] In the case of Fig.8, during clocking of the delay time T_P from the time point t_a when AC power E input stopped, AC power E input resumes at the time point tp, causing the operating voltage monitoring signal MV to change from L level to H level (step S_{4 03}) . However, since the SW/AC monitoring signal MS is at L level, the main control unit 36 enters the loop [A] through the loop [F] (steps S_G^S _{4 0 4 a}^S _{4 0 2}· ·) and thereafter stays therein.

[0075] In regard to the peripheral circuits around the main control circuit 36, for instance, the operating voltage generation circuit 40 may generate multiple operating voltages. In that case, the operating voltage monitoring unit 48 may monitor any one of the multiple operating voltages, normally monitor the voltage level of what is supplied to the main control unit 36. The external power source 34 is not limited to a single-phase commercial AC power source but may be a single-phase or three-phase AC power source having any frequency or a DC power source. Therefore the operating voltage generation circuit 40 is not limited to a single-phase AC/DC conversion circuit but may be a three-phase AC/DC conversion circuit or a switching power supply circuit, an inverter circuit or the like. Furthermore, the motor 30 is not limited to a single-phase AC motor but may be any kind of motor. The SW/AC monitoring unit 46 in the above embodiment uses a photo coupler to obtain a high speed current detector, but may use a relay or the like instead of the photo coupler.

[0076] The motored belt grinding machine in the embodiment described above is an example of power tools in accordance with the present invention. The present invention can be applied to a motored beveling machine, a disc grinding machine, a disc polishing machine, a peeling machine, a cutting machine, a drilling machine and any other power tools of the external power supply type using a motor for a motive power source therein. Moreover the motor control apparatus of the present invention is not only applicable to a power tool but also to any electrical device of the external power supply type using a motor for a motive power source therein.

EXPLANATIONS OF LETTERS OR NUMERALS [0077] motored belt grinding machine on/off switch motor motor control apparatus

AC power source main control unit

38	motor control circuit
40	operating voltage generation	circuit
46	SW/AC monitoring unit
48	operating voltage monitoring	unit
78	bidirectional thyristor
88	photo coupler

Claims

1. A motor control apparatus for controlling operation of a motor that utilizes power supplied from an external power source to rotate, comprising an on/off switch provided electrically in series with the motor to the external power source, an operating voltage generation unit inputting power from the external power source to generate a DC operating voltage, and a first monitoring unit for monitoring the state of the on/off switch or the state of a power supply line between the on/off switch and the motor to generate a first monitoring signal indicating whether or not power from the external power source is being supplied to the power supply line, characterized by comprising:

2 . The motor control apparatus of claim 1 wherein the first monitoring unit comprises a branch circuit that is electrically connected in parallel with the motor in the stage behind the on/off switch as seen from the external power source and a current detection unit for detecting whether or not a current is flowing through the branch circuit.

3. The motor control apparatus of claim 2 wherein the current detection unit includes a photo coupler provided in the branch circuit, and the photo transistor of the photo coupler has a first terminal connected through a resistor to a voltage supply terminal of the operating voltage and a second terminal connected to a ground potential terminal, obtaining the first monitoring signal at the first terminal.

4. The motor control apparatus of claim 3 wherein the first monitoring signal is generated as a binary signal with a first threshold that is set between the rated value of the operating voltage and the ground potential and with a second threshold lower than the first threshold, and the control unit judges that the first monitoring signal has the first logical value when the voltage level of the first monitoring signal is higher than the first threshold, and judges that the first monitoring signal has the second logical value when the voltage level of the first monitoring signal is lower than the second threshold.

5. The motor control apparatus of claim 4 wherein the control unit activates the motor when the first monitoring signal changes from the first logical value to the second logical value while the second monitoring signal is indicating that the voltage value of the operating voltage is higher than the monitoring value, and the control unit stops the motor when the first monitoring signal changes from the second logical value to the first logical value while the second monitoring signal is indicating that the voltage value of the operating voltage is higher than the monitoring value .

6. The motor control apparatus of claim 5 wherein the control unit does not activate the motor even when the first monitoring signal changes from the first logical value to the second logical value while the second monitoring signal is indicating that the voltage value of the operating voltage is lower than the monitoring value.

7. The motor control apparatus of claim 5 wherein the monitoring value is so set that when input of power from the external power source stops with the on/off switch being on, the voltage value of the operating voltage becomes lower than the monitoring value before the voltage level of the first monitoring signal becomes lower than the threshold.

8. The motor control apparatus of any one of claims 5 to

7 wherein the second monitoring unit generates the second monitoring signal with the first logical value when the voltage value of the operating voltage is higher than the monitoring value, and generates the second monitoring signal with the second logical value when the voltage value of the operating voltage is lower than the monitoring value.

9. The motor control apparatus of claim 8 wherein the control unit does not activate the motor regardless of the value of the first monitoring signal as long as the second monitoring signal has the second logical value.

10. The motor control apparatus of claim 1 wherein when stopping the motor, the control unit keeps the motor stopped regardless of either the values of the first and second monitoring signals until a specified delay time has passed from the stopping of the motor.

11. The motor control apparatus of claim 10 wherein the delay time is so set to be the same as or slightly longer than a time required for the voltage level of the operating voltage to drop from the rated value to the monitoring value when input of power from the external power source to the power supply line has stopped with the on/off switch being on.

12. The motor control apparatus of claim 1 wherein when stopping the motor, the control unit repeatedly checks the first and second monitoring signals a fixed number of times across a specific delay time immediately after the stopping of the motor .

13. The motor control apparatus of claim 12 wherein the delay time is so set as to be slightly shorter than a time required for the voltage level of the operating voltage to drop from the rated value to the monitoring value.

14. The motor control apparatus of claim 1 wherein a switching element is provided electrically in series with the motor and the on/off switch to the external power source, and the control unit performs switching control of the switching element at a constant frequency to perform control of rotational operation of the motor, and makes the switching element off to stop the motor.

15. The motor control apparatus of claim 1 wherein the external power supply comprises an AC power source, the operating voltage generation circuit comprises an AC/DC conversion circuit for converting AC power inputted from the AC power source to DC power, and the AC/DC conversion circuit has in its output stage a capacitor to output the charging voltage as the operating voltage.

16. A motor control apparatus for controlling operation of a motor that utilizes power supplied from an external power source to rotate, comprising an on/off switch provided electrically in series with the motor to the external power source, an operating voltage generation unit inputting power from the external power source to generate a DC operating voltage, and a first monitoring unit for monitoring the state of the on/off switch or the state of a power supply line between the on/off switch and the motor, characterized by comprising:

17. A power tool comprising:

a body;

a movable tool mounted on the body so as to be able to do a certain movement;

characterized in that the motor control apparatus comprises a second monitoring unit for monitoring the operating voltage to generate a second monitoring signal indicating whether the voltage level of the operating voltage is higher or lower than a preset monitoring value, and a control unit adapted to operate under the operating voltage to control activation and stopping of the motor based on information of the first and second monitoring signals.

18. A power tool comprising:

a body;

a movable tool mounted on the body to be able to do a certain movement;

characterized by comprising:

a second monitoring unit for monitoring whether the operating voltage is higher or lower than a preset monitoring value; and a control unit adapted to operate under the operating voltage to control activation or stopping of the motor based on monitoring information from the first and second monitoring units;

wherein when the first monitoring unit provides its monitoring information indicating that the on/off switch has changed from the OFF state to the ON state while the second monitoring unit is providing its monitoring information indicating that the voltage level of the operating voltage is higher than the monitoring value, the control unit responds to the monitoring information from the first monitoring unit to activate the motor;

when the first monitoring unit provides its monitoring information indicating that input of power from the external power source to the power supply line stops while the second monitoring unit is providing its monitoring information indicating that the voltage level of the operating voltage is higher than the monitoring value, the control unit responds to the monitoring information from the first monitoring unit to stop the motor; and while the second monitoring unit is providing its monitoring information indicating that the voltage value of the operating voltage is lower than the monitoring value, the control unit does not activate the motor even when the first monitoring unit provides its monitoring information indicating that input of power from the external power source to the power feeding line has started or resumed.