JP2010012547A - Power tool - Google Patents

Abstract

The present invention provides an electric tool capable of setting an overcurrent set value of a motor in accordance with use conditions of a tip tool driven by a motor.
[Solution]
When the motor 103 for driving the tip tool 5 and the load current (I) flowing through the motor 103 exceeds the overcurrent set value (I2), the motor 103 is stopped or the rotation speed (N ), And the overload protection means 123 can set the overcurrent set values (I1, I2) according to the use conditions of the tip tool 5. Overcurrent set value switching means 142 is provided.
[Selection] Figure 2

Description

  The present invention relates to an electric tool having a constant rotation control means for controlling the rotation speed of a motor for driving a tip tool to be constant, and in particular, an overload protection means capable of setting an overcurrent set value corresponding to a load state by the tip tool. It is related with the provided electric tool.

  Conventionally, in a power tool such as a disc grinder or a circular saw, the rotational speed control of the motor that applies rotational force to the tip tool does not change the motor speed even if the motor load varies depending on the load condition of the tip tool. Rotational speed is detected, and the detection result is fed back to the conduction angle for power supply such as triac that drives the field winding of the motor, and phase control is performed so that the rotational speed of the motor is always constant. Has been done. Also, in general, a drive motor detects a current flowing through the motor so that the motor does not burn out due to an excessive load current, compares it with a preset overcurrent set value, and when the overcurrent set value is exceeded, the motor An overload protection means for stopping the operation is provided.

  However, in the conventional overload protection means, the overcurrent set value is uniformly set in the vicinity of the load current value at which the motor does not burn out, so when the electric tool is continuously used in the vicinity of the overcurrent set value Depending on the overload condition, the motor may burn out and its life may be deteriorated. On the other hand, when the overcurrent set value is set low so as to extend the life of the motor, there is a risk that the operation of a relatively heavy load cannot be performed. That is, if the motor overcurrent set value is set to be relatively low from the viewpoint of safety, the overload protection means always operates conservatively and cannot effectively use the performance of the motor as an electric tool.

  Therefore, an object of the present invention is to solve the above-mentioned problems, set an appropriate overcurrent set value corresponding to the load state by the tip tool of the electric power tool, and effectively use the motor performance. It is providing the electric tool provided with a protection means.

  Among the inventions disclosed in accordance with the present invention in order to solve the above problems, the summary of typical ones will be described as follows.

  According to one aspect of the present invention, when the load current flowing through the motor exceeds the overcurrent set value and the motor for driving the tip tool, the motor is stopped or the rotational speed of the motor is reduced. An overload protection means for reducing the overload protection means, wherein the overload protection means comprises overcurrent set value switching means capable of setting the overcurrent set value according to use conditions of the tip tool. Have.

  According to another feature of the invention, the overcurrent set value switching means is constituted by a switch means, and the overcurrent set value can be switched in two stages by the switch means.

  According to the above feature of the present invention, the user can set the overcurrent set value according to the work application (load state) of the tip tool by the overcurrent set value switching means. The motor performance can be used effectively. Further, since the overcurrent set value corresponding to the load state is set, the motor can be used with a long life and the power consumption of the entire work can be reduced.

  The above and other objects, and the above and other features and advantages of the present invention will become more apparent from the following description of the present specification and the accompanying drawings.

Hereinafter, an embodiment in which the electric power tool of the present invention is applied to a disc grinder will be described in detail with reference to FIGS. 1 to 9. Note that in the drawings for describing the embodiments, members having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

[About the configuration of the power tool]
FIG. 1 is a schematic outline view of a disc grinder according to the present embodiment. The disc grinder 100 includes a motor housing portion 1 that houses a commutator motor (AC motor) 103 described later, a gear cover portion 3 connected to one end side of the motor housing portion 1, a main switch 102 of the commutator motor 103, and In order to supply electric power by electrically connecting a switch handle portion 2 that houses a motor control circuit device (circuit board) 104 described later and a motor control circuit device (circuit board) 104 to a commercial AC power source 101 (see FIG. 2). Power cord 7. Although not shown, a pair of bevel gears (pinion gears) attached to the rotation output shaft of the commutator motor 103 are accommodated in the gear cover portion 3. It is converted from the direction to the vertical direction and transmitted to the spindle 4. A grinder (grinding stone) 5 is attached to the spindle 4 as a tip tool so that grinding or cutting work can be performed. The semicircular portion of the circular grinder 5 is covered with a protective cover 6. The changeover switch 132 is a switch that functions as overcurrent set value switching means that can set an overcurrent set value according to the use condition of the grinder (tip tool) 5 provided in accordance with the present invention. In the case of this embodiment, since it is designed so that the overcurrent set value can be switched in two stages, it is constituted by a slide-type on / off switch. The changeover switch 132 may be configured by a tial type switch mechanism.

  The motor control circuit device (rotational speed control circuit device) 104 always maintains a predetermined rotational speed so that the rotational speed of the motor 103 that applies rotational force to the grinder 5 that is the tip tool varies even when the load state by the tip tool 5 fluctuates. Control to be. Further, when the motor control circuit device 104 detects a large motor current I with respect to a predetermined overcurrent set value I1 or I2 (see FIG. 7), the overload protection for stopping the operation of the motor 103 or reducing the rotation thereof. It also functions as a means. FIG. 2 shows a circuit block diagram of the motor control circuit device 104.

  As shown in FIG. 2, the motor control circuit device 104 includes a rotation speed sensor 106 for detecting the rotation speed of the motor and a rotation speed signal amplification circuit 105 for amplifying the rotation speed signal from the rotation speed sensor 106. A microcomputer 123, a power supply circuit 107 for supplying drive power in the control circuit device 104 including the microcomputer 123, a zero-cross detection circuit 108 for detecting a zero-cross point from the AC power supply (commercial power supply) 101, a main In order to detect ON or OFF of the switch 102, a resistor 124 for inputting an ON or OFF signal of the main switch 102 to the microcomputer 123, a triac 125 for controlling the phase of the motor 103, and a gate signal of the triac 125 are obtained. A resistor 126 for input and a shunt for detecting the load current of the motor A load current detection circuit 140 including a resistor 127 and an input resistor 128; a start-up time setting circuit 141 including a pair of resistors 129 and 130 for setting the start-up time of the motor 103; and an overcurrent of the motor 103 An overcurrent set value switching circuit 142 composed of a resistor 131 and a changeover switch 132 for setting a set value and inputting an overcurrent set signal to the microcomputer 123, and a resistor for setting the rotational speed of the motor 103 133, and a rotation speed setting circuit 143 including a pair of variable resistors 134 and 135. The AC power supply 101 supplies DC power to the power supply circuit 107 of the motor control circuit device 104, and supplies drive power to the motor 103 via the main switch 102 and the triac 125.

  The rotation speed signal amplifying circuit 105 constituting the motor control circuit device 104 includes electrolytic capacitors 109 and 115, resistors 110, 111, 112 and 114, and a transistor 113. As shown in FIG. The rotation speed signal S 1 from the number sensor 106 is amplified in the range of 0 V to Vcc, and the rotation speed signal S 2 is input to the microcomputer 123. Thereby, the microcomputer 123 detects the number of rotations of the motor 103.

The zero-cross detection circuit 108 includes resistors 120 and 121 and a photocoupler 122. As shown in FIG. 5, the alternating current applied to the photocoupler 122 from the commercial power supply 101 via the resistor 120 is included. A zero cross point is detected from the signal S 3, and a zero cross signal S 4 for controlling the phase of the triac 125 is input to the microcomputer 123.
Furthermore, the power supply circuit 107 is a constant voltage power supply circuit including a diode 116, a resistor 117, a Zener diode 118, and an electrolytic capacitor 119, which converts an AC voltage of the commercial power supply 101 into a DC voltage, and includes a motor including a microcomputer 123. A constant voltage Vcc is supplied into the control circuit device 104.

[Operation of the power tool]
Next, the operation of the motor control circuit device 104 will be described along the control flowchart shown in FIG. First, when an AC voltage is input from the AC power supply (commercial power supply) 101 to the electric power tool 100, the power supply circuit 107 supplies a constant voltage DC power supply (−Vcc) into the control circuit 104 including the microcomputer 123.

  In step 201, the microcomputer 123 detects the start time setting voltage of the motor 103 set by the resistors 129 and 130 of the start time setting circuit 141, and sets the start time. This start-up time is a so-called soft start set time in which the rotational speed is gradually increased to a target set rotational speed after a predetermined period in order to suppress a reaction when the motor 103 is suddenly rotated. is there. More specifically, the drive voltage −Vcc with respect to the ground GND is divided into five stages and set according to the motor size (output capacity). That is, when the start time setting voltage is set to the first voltage range (0 to 1/5 × Vcc), the start time is set to 0 second, and the second voltage range (1/5 × Vcc to 2 / When set to 5 × Vcc), the startup time is 1 second, and when the third voltage range (2/5 × Vcc to 3/5 × Vcc) is set, the startup time is 2 seconds, When the voltage range is set to (3/5 × Vcc to 4/5 × Vcc), the startup time is set to 3 seconds, and when the fifth voltage range (4/5 × Vcc to Vcc) is set, Each time is set to 4 seconds. The starting time is set to a longer time as the size of the motor to be used is larger, and the reaction speed at the time of starting is suppressed by gradually increasing the rotational speed.

Next, in step 202, the microcomputer 123 detects an overcurrent setting signal set by the resistor 131 and the changeover switch 132 of the overcurrent set value switching circuit 142.
In step 202, if the changeover switch 132 is in the OFF state, the process proceeds to step 203, and the overcurrent setting signal input to the microcomputer 123 becomes L (low signal). Setting is made as “weak” (for example, 15A). If the changeover switch 132 is in the ON state, the process proceeds to step 204, and the overcurrent setting signal input to the microcomputer 123 becomes H (high signal), so the microcomputer 123 sets the overcurrent setting value to “strong” (for example, , 30A). As this overcurrent set value “strong”, a current value is set in advance so that the motor 103 does not burn out due to overload.

  Next, in step 205, the microcomputer 123 detects the target rotational speed setting voltage of the motor 103 set by the resistor 133 and the variable resistors 134 and 135 of the rotational speed setting circuit 143, and sets the target rotational speed. Do. The variable resistor 134 constitutes a potentiometer, and the user can freely set the rotational speed from the outside depending on the work application by adjusting the sliding piece of the variable resistor 134. The variable resistor 135 is used as an adjusting resistor for suppressing variations in circuit constants and the like of the rotation speed setting circuit 143.

  Next, in step 206, when the main switch 102 of the motor 103 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 the gate terminal of the triac 125. Input a gate signal (trigger signal) to. Thereafter, the process proceeds to step 206, where the triac 125 is turned on to start supplying current to the motor 103, and the motor 103 starts to rotate. At this time, the microcomputer 123 gradually increases the conduction angle (θ) 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 rotation of the motor 103. The soft start operation is performed so that the number reaches the target rotational speed set by the resistor 133 and the variable resistors 134 and 135.

  Subsequently, in step 207, 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 sets the rotational speed of the motor 103 by the rotational speed setting circuit 143. The phase control is performed by adjusting the magnitude of the gate signal input to the gate of the triac 125 so that the rotational speed (N) of the motor 103 becomes constant at a predetermined value as compared with the rotational speed. That is, if the microcomputer 123 determines that the rotation speed of the motor 103 is lower than the predetermined rotation speed, the microcomputer 123 controls the conduction angle of the triac 125 to a large conduction angle θ1 as shown in FIG. When it is determined that the rotation speed of the motor 103 is higher than the predetermined rotation speed, the triac 125 is controlled so that the conduction angle of the triac 125 is controlled to a smaller conduction angle θ2, as shown in FIG. The gate signal corresponding to the conduction angle is input to the gate (gate resistor 126).

  Next, in step 208, the microcomputer 124 detects the load current value flowing through the motor 103 by the load current detection circuit 140, and is set by the resistor 131 and the changeover switch 132 of the overcurrent set value switching circuit 142. Monitor whether the overcurrent value is exceeded. The load current detection circuit 140 converts the current flowing through the motor 103 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 averages the input voltage signal and compares it with the overcurrent set value set by the overcurrent set value switching circuit 142.

  In step 208, if the detected current value exceeds the overcurrent value set by the overcurrent set value switching circuit 142 (resistor 131, changeover switch 132), the process proceeds to step 209, where the gate of the triac 125 is set. The input signal is stopped or the conduction angle is made extremely small to protect the motor 103 from overload.

  In step 208, if the detected current value does not exceed the overcurrent set value set by the overcurrent set value switching circuit 142 (resistor 131, changeover switch 132), the process returns to step 202, and the motor continues. 103 constant rotation control and overcurrent monitoring.

  As will be apparent from the above description of the embodiment, according to the present invention, the changeover switch 132 of the overcurrent set value switching circuit 142 corresponds to the load state (working use) of the tip tool (grinder) 5. The overcurrent set value can be switched. For example, when using a circular grinder having a larger diameter or polishing a harder workpiece, the overcurrent set value is set to a large value by switching the changeover switch 132 to ON. The maximum performance can be utilized within the range below the overcurrent set value.

  FIG. 7 is a characteristic diagram showing the relationship between the motor current I and the motor rotation speed N when the load state of the tip tool is varied in the electric tool according to the present embodiment. The overcurrent set value switching circuit (142) according to the present invention can set the overcurrent set values I1 and I2 corresponding to the load states L1 and L2 (when L2 is heavier than L1) by the tip tool. it can. When the load state is changed from light load L1 to heavy load L2 as a tip tool, the motor performance is maximized by changing the overcurrent set value from I1 to I2 (I2> I1) according to the load state. Can be used. Moreover, since the overcurrent set value is set to a small value I1 for the light load state L1, excessive use can be prohibited and a long life can be maintained.

  In the above embodiment, the overcurrent set value switching circuit (142) is set with two stages of “low” and “strong” overcurrent set values by using the resistor 131 and the changeover switch 132. As described above, the overcurrent set value switching circuit may be changed to output three or more stages of set potentials to set three or more stages of overcurrent set values. For example, by configuring the changeover switch 132 with a variable resistor (potentiometer), the overcurrent set value can be configured to be switched in three or more stages. In this case, the microcomputer 123 is configured to set an overcurrent set value according to the input overcurrent set voltage value. Further, the overcurrent set value switching means attached to the outer peripheral portion of the electric tool is not limited to the slide type switch, but may be a dial type change switch.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. .

The schematic side view of the electric tool which concerns on one Embodiment of this invention. The functional block diagram of the motor control circuit apparatus in the electric tool shown in FIG. The control flowchart in the motor control circuit apparatus of FIG. FIG. 3 is an input / output waveform diagram of a rotation speed signal amplification circuit in the motor control circuit device of FIG. 2. FIG. 3 is an input / output waveform diagram of a zero cross detection circuit in the motor control circuit device of FIG. 2. The characteristic view which shows the conduction angle of the triac in the motor control circuit apparatus of FIG. The characteristic view which shows the relationship between the motor current and motor rotation speed in the electric tool shown in FIG.

Explanation of symbols

1: Motor housing part 2: Switch handle part 3: Gear cover part 4: Spindle 5: Tip tool (grinder) 6: Protective cover 7: Power cord 100: Electric tool (disc grinder)
DESCRIPTION OF SYMBOLS 101: AC power supply (commercial power supply) 102: Main switch 103: Motor 104: Motor control circuit device 105: Revolution signal amplification circuit 106: Revolution sensor 107: Power supply circuit 108: Zero cross detection circuit 123: Microcomputer 124, 126, 128 129, 130, 131, 133: Resistor 125: Triac 127: Shunt resistor 132: Changeover switch 134, 135: Variable resistor 140: Load current detection circuit 141: Start-up time setting circuit 142: Overcurrent set value switching circuit 143 : Speed setting circuit

Claims (3)

  A motor for driving the tip tool, and overload protection means for stopping the motor or reducing the rotational speed of the motor when a load current flowing through the motor exceeds an overcurrent set value. An electric power tool, wherein the overload protection means includes an overcurrent set value switching means capable of setting the overcurrent set value according to a use condition of the tip tool.   A motor for driving the tip tool, a semiconductor element for controlling a voltage applied to the motor, a rotational speed detecting means for detecting the rotational speed of the motor, and a rotational speed setting means for setting the rotational speed of the motor; And a control means for controlling a conduction angle of the semiconductor element, and a flow through 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 Current detection means for detecting current, overcurrent value setting means for setting the overcurrent value of the motor, overcurrent set value set by the overcurrent value setting means, and detection current output from the current detection means And an overload protection means for stopping the motor or reducing the rotation speed of the motor when the detected current value exceeds the overcurrent set value for a certain period of time. The overcurrent value setting means includes an overcurrent set value switching means capable of setting an overcurrent set value of the motor in accordance with a use condition of the tip tool. .   3. The overcurrent set value switching means is constituted by a switch means, and the overcurrent set value can be switched in a plurality of stages by the switch means. Power tool.

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