JPH07308871A - Power tool - Google Patents

Abstract

PURPOSE:To prevent the burning of a motor due to the over-current by changing a reference current value for preventing the burning of the motor due to the over-current so as to follow up the variation of the input voltage, while always effectively developing the characteristic of the motor. CONSTITUTION:A motor 47 is incorporated inside a housing. A cover 52 is provided to the place where the upper part of the tool body 41 is positioned when it is used. In the inside of the cover 52, a LED base 53 is arranged, so that a user can visually recognize from above the lighting condition or extinguishing condition of a LED 54. To the LED base 53, a signal wire 55 for controlling the lighting condition is connected to a control unit 42 via a cable 56 for supplying the driving power to the tool body 41.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive device.

[0002]

2. Description of the Related Art For example, in a high frequency electric power tool such as a grinder (hereinafter referred to as an electric power tool), a microcomputer provided in a drive circuit of a motor has been conventionally used to prevent burnout due to overcurrent of the motor. A reference current value for determining overcurrent is set. Further, this drive circuit compares a current circuit for detecting a load current of the motor and a current value of the load current of the motor detected by the current detection circuit with a predetermined reference current value, and the detected load current value is When the reference current value is exceeded, it is determined that the current is an overcurrent, and an overcurrent detection circuit that outputs an overcurrent detection signal is provided. In the motor drive circuit of this conventional example, when the overcurrent detection signal is output from the overcurrent detection circuit, the output voltage and the output frequency from the inverter unit are reduced, the slip of the motor is increased, and the motor is temporarily operated. To prevent the burnout due to the overcurrent of the motor by either shutting down the motor or installing a thermal relay so that the thermal relay is activated and the motor is tripped at the time of overcurrent. There is.

[0003]

In the motor drive circuit of the conventional example, the reference current value set for preventing burnout due to overcurrent of the motor depends on what condition the input voltage to the inverter section is. It is a fixed value even when set to. Therefore, as an example, fluctuations of ± 10% at 200V specifications
When the input voltage is supplied to the drive circuit of the motor, even if the input voltage is 220V, which is advantageous for the characteristics of the motor, the above-described burnout prevention operation is performed as in the case of the input voltage 180V, which is disadvantageous for the characteristics of the motor. Therefore, the input voltage 22
The characteristics of the motor, which should be exhibited at 0 V, are
There is a problem that it is not actually exhibited.

Further, in the conventional power tool, driving power is supplied to the power tool body held by the user via a cable. The tool main body has a built-in motor, and a disk-shaped round file or the like that is rotationally driven by a rotary shaft of the motor is fixed.

In the conventional power tool, when the overcurrent to the motor as described above is generated, the power tool body is not provided with a structure for notifying the overcurrent state. Therefore, there is a problem that the user cannot take an appropriate and prompt countermeasure.

The present invention has been made in order to solve the above problems. When an overcurrent state of a motor occurs, a user can easily recognize this overcurrent state, and It is an object of the present invention to provide an electric power tool that allows a user to take appropriate and prompt measures against the occurrence.

[0007]

SUMMARY OF THE INVENTION An electric power tool of the present invention includes a tool main body having a built-in motor for working, drive power to the motor, and detection of an overcurrent state of the motor.
And a control unit for outputting an overcurrent signal, the tool body,
Informing means for informing the overcurrent state in response to the overcurrent signal from the control unit is provided, and by doing so, the above object can be achieved.

In the present invention, the notification means may be arranged at the upper end of the tool body.

[0009]

According to the present invention, when the motor built in the tool body is rotationally driven by the drive power from the control unit to perform work, the control unit detects the overcurrent state of the motor and outputs the overcurrent signal. Is output. When the overcurrent signal is output, the notification means provided in the tool body notifies the user of the overcurrent state in response to the overcurrent signal from the control unit. As a result, when an overcurrent state occurs in the motor, the user can easily recognize this overcurrent state, and the user can take appropriate and prompt countermeasures against the occurrence of the overcurrent. .

[0010]

EXAMPLES The present invention will be described below with reference to examples. Although the present embodiment is described as a high frequency power tool such as a grinder (hereinafter, power tool) as an example, the present invention is not limited to this embodiment. FIG. 1 is a system diagram showing an electrical configuration of an electric power tool 1 according to an embodiment of the present invention.
In the present embodiment, the electric power tool 1 is configured to include a tool main body 41 that is held by a user to perform work such as polishing, and a control device 42 in which the tool main body 41 is connected by a cable 56. .

The tool body 41 is provided with a cylindrical housing 43 as an example, and has a so-called pot type shape. A stator 44 and a rotor 45 are arranged in the housing 43 to form a motor 47. The rotor 45
The rotary shaft 46 fixed to the above is rotatably attached to the housing 43 by bearings 47 and 48. One end of the rotary shaft 46 projects outward from the housing 46, a support base 49 is fixed, and a round file 50 is attached near the tip of the rotary shaft 46 that further projects from the fixed base 49, and a fixing tool 51.
It is sandwiched and fixed between the support base 49 and the support base 49.

A cover 52 is fixed to the side of the housing 46 opposite to the side where the round file 50 is arranged.
The cover 52 is provided at a position corresponding to the upper portion when the tool body 41 is used. An LED substrate 53 is arranged inside the cover 52, and an LED 54 is provided on the LED substrate 53. The LED 54 is the cover 52
When the tool main body 41 is used, the user can visually recognize the lit state or the extinguished state by projecting from the above. The LED board 53 includes
A signal line 55 for externally supplying a signal for controlling the lighting state of the LED 54 is connected, and the signal line 55 is connected to the control device 42 via a cable 56 for supplying driving power to the tool body 41. It

FIG. 2 is a block diagram showing the electrical construction of the electric power tool 1 of this embodiment. The electric power tool 1 includes the tool main body 1 shown in FIG. 1 including the motor 47 and the LED board 53 in FIG. 2, and the control device 42 shown in FIG. 1 including the rest of the configuration in FIG. Composed of. Controller 4
As an example, a three-phase AC power supply (hereinafter referred to as a power supply) 2 that outputs an input voltage with a fluctuation of ± 10% in a 200V specification is connected to 2. The power supply line 60 to which the drive voltage is supplied from the power supply 2 is connected to the rectifier 8 via the fuse 2, the current transformer 4, and an ON / OFF switch (hereinafter, power supply switch) 5 in series. The varistor board 7 is connected in parallel to the power supply line 60.

The relay 9 is connected to one power supply line 61 of the pair of power supply lines 61 connected to the output terminal of the rectifier 8.
Are connected in series, and the pair of power supply lines 61 has a capacitance 6
2 and a resistor 63, the input voltage detection unit 16 for detecting the input voltage to the inverter circuit 11 and the current transformer 10 are connected in series, and as an example, a power transistor of two stages is provided for each phase. Inverter circuit 1
1 is connected to the input terminal. The transformer 28 is connected to two power supply lines 64 of the three power supply lines 64 connected to the output terminal of the inverter circuit 11, and the output voltage from the inverter circuit 11 is output. The power line 6
4 is connected to the motor 47, and the motor 47 is provided with a soft start switch 13.

The output terminal of the current transformer 4 has a ground fault detection circuit 19
Is connected, and the output of the ground fault detection circuit 19 causes the motor 47 to trip as will be described later.
Is input to the protection function control circuit 30 for preventing burning due to overcurrent.

In relation to the relay 9, the relay drive circuit 2
0 is provided, and the relay drive circuit 20 has a CPU to be described later.
When the output of 15 is supplied and the motor 47 is driven in an overcurrent state as described later, and there is a risk of burnout,
The relay 9 is cut off by the CPU 15 via the relay drive circuit 20, and the supply of drive power from the rectifier 8 to the inverter circuit 11 is cut off.

The output of the input voltage detector 16 is DC-
The input voltage value is input to the DC converter control power supply unit 17, the output is input to the voltage detection circuit 18, and the input voltage value input from the rectifier 8 to the inverter circuit 11 is detected. The output of the voltage detection circuit 18 is input to an A / D (analog / digital) converter 21, the input voltage value is converted into a digital signal and input to the CPU 15, and also to the protection function control circuit 30. To be done. The output of the current transformer 10 is input to the overcurrent detection circuit 22 and the overcurrent detection circuit 2
2 outputs the protection function control circuit 30 and the A
It is input to the / D converter 21.

The output of the transformer 28 is converted into a digital signal by the A / D converter 21 via an output current feedback circuit 29, and the converted digital signal is input to the CPU 15. The CPU 15 controls the PWM generator 23 to generate a pulse width modulation signal for rotationally driving the motor 47 at a predetermined rotation speed. The output of the PWM generator 23 is input to the dead time generation circuit 24 and sets a dead time for eliminating an unstable state at the time of switching on / off of the transistor in the inverter circuit 11. The output of the dead time generation circuit 24 is input to the inverter drive circuit 26 that drives the inverter circuit 11 via the buffer 25.

The CPU 15 includes an LED control circuit 31.
Is connected to the LED substrate 53 via the signal line 55 built in the cable 56 shown in FIG.

FIG. 3 is a graph for explaining various electric characteristics of the electric power tool 1 of this embodiment. The solid line in FIG. 3 indicates the case where the input voltage is 180 V, and the broken line indicates the input voltage is 220 V.
The case of V is shown. The operation of the electric power tool 1 of the present embodiment will be described below with reference to FIG. Power tool 1
Is a reference current value Ith in order to prevent the risk of burnout of the motor 47 due to overcurrent flowing to the motor 47 due to overload or the like, and the drive current exceeds the reference current value. The state is detected and the LED 54 is turned on. As a result, the user holding the tool body 41 and performing a polishing operation or the like is informed of the occurrence of the overcurrent state. Further, when this overcurrent state occurs, the output voltage and the output frequency from the inverter circuit 11 are lowered, the slip of the motor 47 is increased, and the motor 47 is rotated.
To stop temporarily, or relay 9
Is operated and the motor 47 is tripped to prevent the motor 47 from burning due to overcurrent. Further, when the overcurrent state of the motor 47 is detected, the reference current value Ith is made to follow the drive voltage so that the reference current value that makes good use of the characteristics of the motor 47 can be set. These operations will be described below.

In the electric power tool 1, an initial value Ith0 of a predetermined reference current value is set. CPU15 of power tool 1
Is an inverter circuit 11 detected by the current transformer 10.
The differential voltage ΔV between the input voltage Vin to the inverter 28 and the output voltage Vout from the inverter circuit 11 detected by the transformer 28 is calculated. The input voltage Vin is the difference voltage Δ
When it changes so as to increase V, the CPU 15 increases the reference current value Ith from the initial value Ith0,
A new reference current value Ith is set. On the other hand, when the input voltage Vin changes so as to reduce the difference voltage ΔV, the CPU 15 reduces the reference current value Ith from the initial value Ith0 and sets a new reference current value Ith. When the input voltage fluctuates to further increase or decrease, the CPU 15 further increases or decreases the reference current value Ith as described above.

Line L1 in FIG. 3 shows the case where the reference current value is fixed as described in the prior art. In the following description, the fixed reference current value is 7.3 A as an example. In this case, if the input voltage is 180V, the output is P
When 1 (W), overcurrent protection is activated. On the other hand, when the input voltage is 220V, the overcurrent protection is activated when the output is P2 (W). As a result, the maximum output P3 (W) when the input voltage is 220V is not reached.

In the case of the electric power tool 1 of the present embodiment, the reference current value can fluctuate between 7.35A and 8.55A shown in FIG. 3 as an example, corresponding to the difference voltage ΔV. become. Therefore, in this embodiment, the input voltage is 220V
In the case of, it becomes possible to output the output P3 (W),
The motor 47 can be used by making good use of the electrical characteristics of the motor 47 shown in FIG.

In the electric power tool 1 of this embodiment, when an overcurrent flows through the motor 47 due to an overload or the like, the CPU 15 controls the PWM generator 23 to output the output from the inverter circuit 11. The voltage and the output frequency are reduced, the slippage of the motor 47 is increased, and the motor 47 is temporarily stopped, or the relay 9 is operated and the motor 47 is tripped. The burnout due to the overcurrent of the motor 47 is prevented.

Further, the electric power tool 1 detects the overcurrent state to prevent the risk that the motor 47 is burned due to an overload due to an overload in the motor 47, and the LE
Turn on D54. As a result, the user holding the tool body 41 and performing a polishing operation or the like is informed of the occurrence of the overcurrent state. As a result, the situation where the user inadvertently works in the overcurrent region of the motor 47 is eliminated, and it is possible to preferably prevent burnout due to overload.
At this time, since the LED 54 is installed on the upper end portion of the pot-type tool main body 41, the user can easily visually recognize the LED 54 and the burnout can be efficiently prevented.

[0026]

By using the power tool of the present invention,
The following effects can be achieved. According to the invention, when the motor built in the tool body is rotationally driven by the drive power from the control unit to perform work, the control unit detects the overcurrent state of the motor and outputs the overcurrent signal. When the overcurrent signal is output, the notification means provided in the tool body notifies the user of the overcurrent state in response to the overcurrent signal from the control unit. As a result, when an overcurrent state occurs in the motor, the user can easily recognize this overcurrent state, and the user can take appropriate and prompt countermeasures against the occurrence of the overcurrent. .

[Brief description of drawings]

FIG. 1 is a system diagram showing an electrical configuration of a power tool 1 according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of the electric power tool 1 of the present embodiment.

FIG. 3 is a graph illustrating various electric characteristics of the electric power tool 1 of this embodiment.

[Explanation of symbols]

 1 power tool 2 power source 4, 10 current transformer 8 rectifier 9 relay 11 inverter circuit 15 CPU 16 input voltage detection unit 18 voltage detection circuit 20 relay drive circuit 28 transformer 41 tool body 42 controller 43 housing 47 motor 54 LED 55 signal Wire 56 cable

Claims (2)

[Claims] 1. A tool main body comprising a tool main body having a built-in motor for performing work, and a control section for supplying drive power to the motor and detecting an overcurrent state of the motor and outputting an overcurrent signal. An electric power tool provided with a notifying means for notifying an overcurrent state in response to an overcurrent signal from the control unit. 2. The electric power tool according to claim 1, wherein the notification means is arranged at an upper end portion of the tool body.