JP2010082761A - Electric tool - Google Patents

Abstract

The present invention has been made in view of the above circumstances, and an object thereof is to provide an electric tool having both workability and safety.
When the detected current value of the motor current exceeds a second overcurrent set value, it is determined that the motor 103 is locked, and the gate signal input by the triac 125 is immediately stopped ( Step 210). When the current value of the motor current exceeds the first overcurrent set value, it is determined whether or not this state has been continued for 3 seconds or more (step 209). Therefore, the gate signal input to the triac 125 is stopped (step 210).
[Selection] Figure 1

Description

The present invention relates to an electric tool having a rotation control function for controlling the rotation speed of a motor.

In conventional power tools, the rotation speed of the motor is controlled by detecting the rotation speed of the motor so that the rotation speed of the motor does not fluctuate even if the load on the motor fluctuates, and the detection result is fed back to the conduction angle such as triac. Thus, a constant rotation control is generally performed to keep the motor rotation number constant. Further, in order to protect the motor, a control method for stopping the motor when a current flowing through the motor is detected and a preset overcurrent set value is exceeded is performed.

JP-A-4-208002

  In the above prior art, for example, when the cutting tool is engaged with a circular saw or the like and the tip tool bites into the member and the motor is locked, the motor current exceeds the overcurrent value and the motor stops. When the biting state of the tip tool is relatively shallow, even when the cutting tool can be immediately removed from the biting state and the cutting operation can be continued, the motor stops and it is difficult to increase the working efficiency. On the other hand, when the biting state is deep or is not easily removed from the biting state, it is necessary to reliably stop the motor in order to prevent the motor from burning.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an electric tool having both workability and safety.

  In order to achieve the above object, in the invention of claim 1, a voltage applying means for applying a driving voltage to the motor, a rotational speed detecting means for detecting the rotational speed of the motor, and a rotational speed setting for setting the rotational speed of the motor And a control means for controlling the drive voltage to the motor by comparing the rotational speed detection signal output from the rotational speed detection means with the rotational speed setting signal set by the rotational speed setting means, and detecting the current flowing through the motor The current detecting means and the control means for stopping the motor or reducing the rotation speed when the current detected by the current detecting means exceeds the first overcurrent value for a predetermined time, and detecting the current detected by the current detecting means. Is characterized in that the drive voltage is controlled to stop the motor when a second overcurrent value larger than the first overcurrent value is exceeded.

  The invention according to claim 2 is characterized in that the control unit calculates the other from one of the first overcurrent value and the second overcurrent value.

  According to the present invention, when the biting state of the tip tool is relatively shallow, the cutting operation can be continued by exiting from the state where the first overcurrent value is exceeded. In addition, when the biting state is deep or when it is difficult to get out of the biting state, the first overcurrent value continues for a predetermined time or the second overcurrent value is reached and the motor is reliably stopped. Can be made.

  In addition, since the other overcurrent value is set by calculation from one of the first overcurrent value and the second overcurrent value, the storage area of the overcurrent value can be suppressed, and the cost can be reduced. .

  A power tool according to an embodiment of the present invention will be described with reference to FIGS. First, the configuration of the rotational speed control device for an electric tool according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 1, the rotation speed control device 104 is connected to an AC power source 101 and is supplied with electric power. The rotation speed control device 104 is connected to the motor 103 via the switch 102 and is driven by applying a voltage to the motor 103.

  The rotational speed control device 104 controls the rotational speed of the motor according to the function for detecting the rotational speed reduction rate that controls the rotational speed of the motor according to the rotational speed reduction rate, and the rate of increase of the current flowing through the motor. It has a function for detecting the motor current increase rate. Therefore, the rotation speed control device 104 includes a power supply circuit 107, a rotation sensor 106, a rotation speed amplification circuit 105, a zero cross detection circuit 108, a motor voltage adjustment circuit 140, a microcomputer 123, a dial type volume 134 for setting the rotation speed, and a resistor 133. , And a variable resistor 135.

  The rotation speed control device 104 has a function for setting the motor start time for setting the time until the rotation speed of the motor 103 is increased to the set rotation speed, and the motor 103 when a predetermined current or more flows to the motor 103. It further has a function for detecting overcurrent that stops the rotation of the motor. Therefore, the rotation speed control device 104 includes a motor start time setting circuit 150 and an overcurrent setting circuit 160.

  The power supply circuit 107 is a half-wave rectifier circuit including a Zener diode 118 and a capacitor 119 connected in parallel to each other, and a resistor 107 and a diode 116 connected in series to one end of the Zener diode 118. The power supply circuit 107 converts the AC voltage into a DC constant voltage Vcc and supplies it to the rotation control device 104. In this embodiment, the voltage Vcc is lower than the ground potential.

  The rotation speed amplification circuit 105 includes a coupling capacitor 109, an NPN transistor 113, a bypass capacitor 115, and resistors 110, 111, 112, and 114, and amplifies the rotation speed detection signal from the rotation sensor 106. The rotation sensor 106 is a sensor that outputs a rotation speed detection signal corresponding to the rotation speed by detecting an electromotive force induced by a magnetic pole provided on the rotation shaft of the motor 100, for example.

  One end of the rotation sensor 106 is connected to one end of the coupling capacitor 109. The other end of the coupling capacitor 109 is connected to a connection point between the resistor 110 and the resistor 111 connected in series between the voltage Vcc and the ground potential, and is connected to the base of the NPN transistor 113. The collector of the NPN transistor 113 is connected to the ground potential via the resistor 112 and is also connected to the microcomputer 123. The emitter of the NPN transistor 113 is applied with a voltage Vcc via a resistor 114 and a bypass capacitor 115 connected in parallel with each other. In the rotation speed amplification circuit 105, the output of the rotation sensor 106 is input to the NPN transistor 113 as a biased alternating current signal based on the voltage dividing ratio between the resistor 110 and the resistor 111, thereby having a frequency corresponding to the rotation speed. The amplified substantially rectangular wave signal is output to the microcomputer 123. The microcomputer 123 calculates the number of rotations of the motor by detecting and counting, for example, the falling edge of the rectangular wave.

  In order to set the rotation speed of the motor 103, a resistor 133, a dial volume 134, and a variable resistor 135 are connected in series between a predetermined voltage Vcc and a ground potential. A contact point of the dial type volume 134 is connected to the microcomputer 123. Here, the dial type volume 134 is configured such that the user can freely set it from the outside depending on the work application. The variable resistor 135 is an adjustment variable resistor for suppressing variations in the rotation speed control device 104. A voltage corresponding to a desired set value of the rotation speed of the motor 103 is input to the microcomputer 123 by setting a predetermined resistance value with the dial type volume 134 and performing fine adjustment with the variable resistor 135.

  The zero cross detection circuit 108 includes a photocoupler 122, a resistor 120, and a resistor 121. The photocoupler 122 includes an LED 171 and an LED 172 connected in parallel with opposite polarities, and a photodiode 173. One end of the resistor 120 is connected to the AC power source 101, and the other end is connected to the LED 171 and the LED 172. The collector of the phototransistor 173 is connected to the ground potential through the resistor 121 and is connected to the microcomputer 123, and the emitter is applied with the voltage Vcc. When the LED 171 or the LED 172 emits light, the collector voltage of the phototransistor 173 becomes the voltage Vcc. When the voltage of the AC power supply 101 is close to the ground potential and neither LED emits light, the collector voltage becomes the ground potential. The microcomputer 123 detects a zero cross when the ground potential is reached.

  The motor voltage adjustment circuit 140 includes a triac 125 and a resistor 126. The T2 terminal of the triac 125 is connected to the motor 103 and the resistor 124, and the T1 terminal is connected to the ground potential via the resistor 127. The gate terminal of the triac 125 is connected to the microcomputer 123 via the resistor 126. The triac 125 adjusts the voltage supplied to the motor 103 by controlling the conduction angle while referring to the zero cross detected by the zero cross circuit 108 by the microcomputer 123.

  The resistor 124 is connected between the motor 103 and the microcomputer 123, and outputs a predetermined voltage to the microcomputer 123 when the switch 102 is turned on.

  The resistor 127 is a shunt resistor for detecting a current flowing through the motor 103, and outputs a voltage value corresponding to the current flowing through the motor 103 to the microcomputer 123 via the resistor 128.

  The motor start time setting circuit 150 includes a resistor 129 and a resistor 130 connected in series with each other between the voltage Vcc and the ground potential. A connection point between the resistor 129 and the resistor 130 is connected to the microcomputer 123, and the motor start time setting circuit 150 outputs a voltage corresponding to a voltage dividing ratio between the resistor 129 and the resistor 130 to the microcomputer 123. The voltage corresponding to the voltage dividing ratio between the resistor 129 and the resistor 130 is set according to the time from when the motor 103 starts rotating until it reaches the set rotational speed.

  The overcurrent setting circuit 160 includes a resistor 131 and a resistor 132 connected in series with each other between the voltage Vcc and the ground potential. The connection point between the resistor 131 and the resistor 132 is connected to the microcomputer 123, and the overcurrent setting circuit 160 outputs a voltage corresponding to the voltage dividing ratio between the resistor 131 and the resistor 132 to the microcomputer 123. The voltage corresponding to the voltage dividing ratio between the resistor 131 and the resistor 132 is set according to the maximum current that can be safely passed through the motor 103.

  The microcomputer 123 is a control unit of the rotation speed control circuit 104. The microcomputer 123 is applied with a predetermined voltage Vcc by the power supply circuit 107. In addition, the microcomputer 123 is connected to the rotation speed amplification circuit 105, the zero cross detection circuit 108, the motor start time setting circuit 150, the overcurrent value setting circuit 160, the resistors 124 and 128, and the dial type volume 134, and inputs signals from each of them. Has been. Further, it is connected to the gate terminal of the triac 125 through the resistor 126 and outputs a signal for controlling the conduction angle of the triac 125.

In the present embodiment, the power supply circuit 107 and the motor voltage adjustment circuit 140 operate as voltage application means of the present invention, and the rotation sensor 106 and the rotation speed amplification circuit 105 are rotation speed detection means. The shunt resistor 127 is current detection means, and the microcomputer 123 is control means.
Next, a series of operations of the rotation speed control device 104 will be described with reference to the flowchart of FIG. When an AC voltage is first supplied from the AC power supply 101, a DC constant voltage is supplied to the microcomputer 123 and the control circuit by the power supply circuit 107. Thereafter, the microcomputer 123 detects the start time setting voltage of the motor 103 set by the resistors 129 and 130, and sets the start time (step 201). The start time is a soft start time in which the rotation speed is smoothly increased to the target rotation speed after a certain period in order to suppress the reaction when the motor 103 is rapidly rotated. Specifically, it is set in 5 steps within the range between the reference voltage VCC and GND in the circuit. When the start time setting voltage is 0 to 1/5 × VCC, the start time is 0 second, and 1/5 × VCC. Start up time is 1 second for up to 2/5 × VCC, start up time of 2 seconds for 2/5 × VCC to 3/5 × VCC, start up for 3/5 × VCC to 4/5 × VCC If the time is 3 seconds and 4/5 × VCC to VCC, the start time is set to 4 seconds. It is preferable that the start-up time is set longer for a motor having a larger size to suppress a reaction at the time of start-up. Next, the microcomputer 123 detects the first overcurrent value setting voltage of the motor 103 set by the resistors 131 and 132, and sets the first overcurrent value (step 202). This overcurrent value is set so that the motor 103 will not burn out due to overload. Next, the microcomputer 123 calculates a second overcurrent set value from the first overcurrent value set voltage detected in step 202. This second overcurrent set value is for detecting that the motor 103 is locked, and needs to be set to be equal to or less than the lock current of the motor 103. Specifically, a value calculated 3 to 4 times the first overcurrent set value is set as the second overcurrent set value (step 203). Next, the microcomputer 123 detects the target rotation speed setting voltage of the motor 103 set by the resistor 133 and the variable resistors 134 and 135, and sets the target rotation speed (step 204). The variable resistor 134 can be freely set by the user from the outside depending on the work application. The variable resistor 135 is an adjustment variable resistor for suppressing variations in the control circuit. Next, when the switch 102 is turned on, the resistor 124 is returned and a switch ON signal is input to the microcomputer 123. The microcomputer 123 returns the resistor 126 and inputs a gate signal to the gate terminal of the triac 125. Thereafter, the triac 125 is turned on, a current starts to flow through the motor 103, and the motor 103 starts to rotate (step 205). At this time, the microcomputer 123 gradually widens the conduction angle from the zero cross point detected by the zero cross detection circuit 108 according to the start time of the motor 103 set by the resistors 129 and 130, and the rotational speed of the motor 103 becomes the resistance. The soft start operation is performed so that the target rotational speed set by the resistor 133 and the variable resistors 134 and 135 is obtained. Next, the microcomputer 123 monitors the rotational speed of the motor 103 detected by the rotational speed sensor 106 and the rotational speed signal amplification circuit 105, and when the rotational speed of the motor 103 is lower than the target rotational speed. Controls the gate signal input to the triac 125 so that the conduction angle of the triac 125 is widened and the conduction angle of the triac 125 is narrowed when the rotational speed of the motor 103 is high, so that the rotational speed of the motor 103 is always constant. Thus, phase control is performed (step 206). Next, the microcomputer 123 detects the current value flowing through the motor 103 and monitors whether the second overcurrent set value has been exceeded (step 207). The current flowing through the motor 103 is converted into a voltage signal by the shunt resistor 127. The converted voltage signal is returned to the resistor 128 and input to the microcomputer 123. The microcomputer 123 compares the input voltage signal with the second overcurrent set value set in step 203. When the detected current value exceeds the second overcurrent set value, it is determined that the motor 103 is in a locked state, and the gate signal input to the triac 125 is instantaneously stopped (step 210). If the detected current value does not exceed the second overcurrent value, the process proceeds to the next step, and the microcomputer 123 detects the current value flowing in the motor 103 and sets the first value set in step 202. It is monitored whether or not the overcurrent set value is exceeded (step 208). If the current value detected at this time exceeds the first overcurrent set value, it is determined whether or not this state has continued for 3 seconds or more (step 209). When the detected current value continues the first overcurrent set value for 3 seconds or more, it is determined that the motor 103 may be burned out, and the gate signal input to the triac 125 is stopped (step 210).
In steps 208 and 209, if the value of the current flowing through the motor 103 does not exceed the first overcurrent set value or has not been continued for 3 seconds or more, the process returns to step 202, and the constant rotation control of the motor 103 is continued. , And the locked state and overcurrent of the motor 103 are monitored.

  According to this embodiment, when the biting state of the tip tool is relatively shallow, the cutting operation can be continued by exiting from the state where the first overcurrent value is exceeded. Also, when the biting state is deep or it is not possible to easily escape from the biting state, the first overcurrent value continues for a predetermined time or reaches the second overcurrent value, so the motor is surely stopped. Can be made.

  In addition, since the second overcurrent value is set by calculation from the first overcurrent value, the storage area of the microcomputer can be suppressed, and the cost can be reduced.

  In the present embodiment, the motor is stopped when the first overcurrent value continues for 3 seconds.For example, when the first overcurrent value continues for 3 seconds or more, the motor is set according to the duration time of 3 seconds or more. You may control so that a drive voltage may be decreased sequentially.

It is a block diagram of the rotation speed control apparatus which concerns on one Example of this invention. It is a series of operation | movement flowcharts of the rotation speed control apparatus which concerns on one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101: AC power supply 102: Switch 103: Motor 104: Rotational speed control apparatus 105: Rotational speed signal amplification circuit 106: Rotational speed sensor 107: Power supply circuit 108: Zero cross detection circuit 123: Microcomputer
124, 126, 128, 129, 130, 131, 132, 133: resistor 125: triac 127: shunt resistor 134, 135: variable resistor

Claims (2)

Voltage application means for applying a drive voltage to the motor;
A rotational speed detecting means for detecting the rotational speed of the motor;
A rotational speed setting means for setting the rotational speed of the motor;
A control means for controlling a drive voltage to the motor by comparing a rotation speed detection signal output from the rotation speed detection means with a rotation speed setting signal set by the rotation speed setting means;
Current detecting means for detecting a current flowing through the motor;
The control means stops the motor or reduces the rotational speed when the current detected by the current detection means exceeds the first overcurrent value for a predetermined time, and the current detected by the current detection means An electric tool characterized by controlling the drive voltage to stop the motor when a second overcurrent value larger than the first overcurrent value is exceeded.   2. The power tool according to claim 1, wherein the control unit calculates the other from one of the first overcurrent value and the second overcurrent value by calculation.

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