JP2013066961A - Power tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance safety with respect to a rise in motor temperature without lowering working efficiency.SOLUTION: This power tool includes a temperature detecting means 10 detecting a temperature of a motor M as a driving source, a control circuit 12 controlling the rotation of the motor in accordance with an output of the temperature detecting means, and a voltage detecting means 13 detecting a voltage of a battery as an electric source. When a -ΔV value indicating a reduction per unit time of the battery voltage during work exceeds a set value, the control circuit controls the subsequent rotation of the rotating motor to be forcefully stopped after a prescribed time Mmax, or forcefully reduced in the number of revolutions, and moreover, limits a subsequent restart of the motor by a prescribed time Smin.

Description

  The present invention relates to prevention of overheating of a power tool, particularly a motor as a power source.

  In a power tool using a motor as a power source, if it is a normal operation, the motor temperature does not rise until reaching a temperature limit at which the motor emits smoke or smells even if it is continuously used as shown in FIG. If the high load work is continuously performed, the temperature limit is reached, and if the work is severe such that the motor is frequently locked, the temperature limit is reached at an early stage to generate smoke, odor, or a motor drive element. Will be destroyed.

  For this reason, a temperature detection element such as a thermistor is installed in the motor or in the vicinity of the motor to monitor the motor temperature, and the motor is stopped when the motor temperature reaches a predetermined temperature (see Patent Document 1). . In this case, the motor does not rotate even if the trigger switch is turned off and then on until the detected motor temperature falls below the predetermined temperature.

  By the way, a thermistor that is commonly used as a temperature detection element has a thermal time constant, and therefore temperature detection involves a delay of about several tens of seconds. Although the limit is exceeded, there is a case where energization of the motor is continued with a delay in temperature detection.

  If the predetermined temperature is set to be considerably lower than the temperature limit in consideration of a delay in temperature detection, the motor stops and the workability is remarkably lowered even though the motor temperature is not so high. Further, if the motor is forcibly turned off due to a temperature rise, a considerable amount of time is required until the motor can be restarted.

JP 2010-110882 A

  This invention is made | formed in view of such a point, and makes it a subject to provide the electric tool which can improve the safety | security with respect to a motor temperature rise, without reducing workability | operativity.

The present invention provides a power tool including a temperature detection unit that detects a temperature of a motor as a drive source, and a control circuit that controls the rotation of the motor according to an output of the temperature detection unit.
Voltage detecting means for detecting the voltage of the battery as a power source is provided, and when the value of the battery voltage during operation decreases per unit time -ΔV exceeds the set value, the control circuit performs the subsequent operation of the rotating motor. It is characterized in that the rotation is forcibly stopped after a predetermined time Mmax or is forced to a low rotation speed, and the subsequent restart of the motor is limited for a predetermined time Smin.

  The control circuit preferably changes the set value and the predetermined times Mmax and Smin according to the motor temperature at the start of work.

  Further, when the motor is forcibly stopped after a predetermined time Mmax or in a state where the motor is forcibly set to a low rotation speed, the control circuit reduces the battery voltage during operation per unit time -ΔV is set to another set value. If it exceeds, the predetermined time Mmax for forcibly stopping or forcibly reducing the rotation speed may be shortened. It is preferable to lengthen the predetermined time Smin for limiting the restart of the motor.

  Further, the control circuit may change the set value or the predetermined times Mmax and Smin according to the remaining capacity of the battery.

When the control circuit is in a state where the motor is forcibly stopped or forcibly set to a low rotational speed after a predetermined time Mmax, and when the restart of the motor is restricted, a notification is issued to notify the user of these. It is also preferable to provide means.
This was made to further reduce the delay in detecting the motor temperature without impairing the user's convenience, and to prevent smoke, odor, and destruction of the control element due to the motor temperature rise.

  In the present invention, even if the motor temperature detected by the temperature detecting element cannot reflect the actual motor temperature, the motor temperature is predicted to be increased from the battery voltage decrease, and the motor operation is restricted. Moreover, instead of immediately stopping the motor or reducing the rotational speed, it is possible to stop the motor after a predetermined time or to reduce the rotational speed. In addition, the motor restart limit may be within the predetermined time Smin, and therefore, it is possible to prevent smoke / odor generation and to prevent the motor drive element from being destroyed, and at the same time, reduce workability. It is nothing.

It is a time chart which shows operation | movement of an example of embodiment of this invention. It is a block circuit diagram same as the above. It is a flowchart which shows operation | movement same as the above. It is a time chart which shows operation | movement of another example. It is explanatory drawing about the temperature rise of a motor.

  The present invention will be described in detail based on an example of an embodiment. FIG. 2 shows a block circuit diagram of an electric tool according to the present invention. In the figure, reference numeral 1 denotes a tool body using a motor M as a power source, 2 denotes a battery pack including a secondary battery B as a power source, and the battery pack 2 that is detachable from the tool body 1 includes: A battery state monitoring unit 20 is provided.

  The motor M disposed in the tool body 1 is provided with a temperature detection element 10 composed of a thermistor for detecting the temperature of the motor M. The temperature detected by the temperature detection element 10 is used for driving the motor M. It is sent to a control circuit 12 consisting of a microcomputer for controlling the operation of the drive element 11 consisting of FET.

  The control circuit 12 to which the on / off information of the trigger switch 3 connected in series to the motor M is input through the trigger switch detection block 14 is connected to the battery voltage detection circuit 13 and also receives the battery voltage VB information. It is like that. In the figure, reference numeral 15 denotes a display circuit for displaying an operation.

  In this electric power tool, when the trigger switch 3 is turned on, the control circuit 12 turns on the driving element 11 and energizes the motor M to operate the motor M. In order to prevent the motor temperature Tm detected by the temperature detection element 10 from rising and resulting in smoke or odor exceeding the temperature limit, or the drive element 11 being destroyed, it is a power source here. The following control is performed on the basis of the value −ΔV of the battery voltage of the secondary battery 20 per unit time.

  That is, when the motor temperature Tm detected by the temperature detection element 10 becomes equal to or higher than a certain set value (for example, 80 ° C.), the voltage decrease per unit time of the battery voltage VB detected by the battery voltage detection circuit 13 −ΔV When the value exceeds a preset value, the control circuit 12 turns off the drive element 11 to forcibly stop the motor M at the moment when the drive time from this point exceeds the preset drive upper limit time Mmax. In addition, when the forced stop time exceeds a preset lower stop lower limit time Smin, the forced stop of the motor M is canceled. If the trigger switch 3 is turned on at that time, the motor M is rotated.

  Further, since the larger the work load, the larger the current flows and the value of the decrease in the battery voltage VB per unit time becomes larger. Therefore, the upper limit of the drive according to the value of the decrease in the battery voltage VB per unit time −ΔV. It is preferable to change the values of the time Mmax and the pause lower limit time Smin. In the example shown in Table 1, the drive upper limit time Mmax is shortened and the suspension lower limit time Smin is lengthened as the value of the decrease in battery voltage VB per unit time −ΔV increases. The time chart shown in FIG. 1 shows changes in motor temperature and battery voltage when control based on Table 1 is performed.

  In addition, although the motor temperature Tm detected by the temperature detection element 10 is described as an initial condition for limiting the driving time of the motor M, the embodiment has been described, this motor has been described. Regardless of the temperature Tm, the drive limitation may be performed only on the condition of the voltage drop −ΔV.

  On the contrary, the drive upper limit time Mmax and the stop lower limit time Smin are set according to the motor temperature Tm at the start of the operation detected by the temperature detection element 10 and the value of the decrease in battery voltage VB per unit time -ΔV May be. Table 2 shows an example. Of course, the higher the motor temperature at the start of the work, the shorter the drive upper limit time Mmax and the pause lower limit time Smin. FIG. 3 is a time chart showing changes in motor temperature and battery voltage when such control is performed.

  By the way, when the operation is continued in a state where the drive upper limit time Mmax is set because the value of the decrease in battery voltage VB per unit time -ΔV exceeds a predetermined value, the load suddenly increases. In addition, the motor temperature rises suddenly, and the motor temperature may exceed the temperature limit before reaching the drive upper limit time Mmax.

  From this point of view, even when the drive upper limit time Mmax is set, the battery voltage VB is monitored for a decrease per unit time -ΔV, and when this value reaches a larger threshold value, the drive upper limit is reached. It is preferable to change the time Mmax to a shorter value. Table 3 shows the contents of a table for performing such control.

  Not only changing the drive upper limit time Mmax to a shorter value but also changing the lower limit stop time Smin to a longer value as shown in Table 4 can prevent the motor temperature from rising excessively. it can.

  In each of the above examples, the determination value of the value of the decrease in battery voltage VB per unit time −ΔV is the same regardless of the motor temperature at the start of work, but depending on the motor temperature at the start of work, You may make it change the determination value of the value of the fall of the battery voltage VB per unit time-(DELTA) V. Moreover, although -0.5V / 1 second, -0.75V / 1 second, and -1V / 1 second are shown in each table as judgment values, these are examples and are limited to these numerical values. Is not to be done. The same applies to the values of the drive upper limit time Mmax and the stop lower limit time Smin and other numerical values.

  Further, the determination value of the value of the decrease in battery voltage VB per unit time −ΔV, the driving upper limit time Mmax and the stop lower limit time Smin after stopping may be changed depending on the remaining capacity of the battery. An example of the case where the remaining battery capacity is reflected in the table 2 is shown in Table 5 and FIG. Based on the battery voltage VB at the start of the operation, the full, normal, and air regions are determined, and the −ΔV value, the drive upper limit time Mmax, and the stop lower limit time Smin are set to different set values for each region. Of course, the remaining battery capacity may be reflected in the ones shown in Tables 3 and 4.

  In addition, it is preferable to notify the user of the operation of the motor M within the forced upper limit time Max or the forced stop within the suspension lower limit time Smin using the display circuit 15. As the display circuit 15, for example, lighting or blinking of an LED can be used. Regarding the operation within the drive upper limit time Mmax, if the blinking speed increases as the drive upper limit time Mmax is approached, in addition to the operation within the drive upper limit time Mmax for the user, the drive upper limit time Mmax It is possible to easily determine the time to reach

M Motor 1 Tool body 2 Battery pack 10 Temperature detection element 11 Drive element 12 Control circuit 13 Battery voltage detection circuit

Claims (6)

In an electric tool comprising temperature detection means for detecting the temperature of a motor as a drive source, and a control circuit for controlling the rotation of the motor according to the output of the temperature detection means,
Voltage detecting means for detecting the voltage of the battery as a power source is provided, and when the value of the battery voltage during operation decreases per unit time -ΔV exceeds the set value, the control circuit performs the subsequent operation of the rotating motor. An electric tool characterized in that the rotation is forcibly stopped after a predetermined time Mmax or the rotation speed is forcibly reduced, and the subsequent restart of the motor is limited by a predetermined time Smin.   2. The electric tool according to claim 1, wherein the control circuit changes the set value and the predetermined times Mmax and Smin in accordance with a motor temperature at the start of work.   When the motor is forcibly stopped or forcibly set to a low rotation speed after a predetermined time Mmax, the control circuit reduces the battery voltage during operation per unit time -ΔV exceeds the other set value. Then, the electric power tool according to claim 2, wherein the predetermined time Mmax in which the forced stop or the low rotational speed is forced is shortened.   When the motor is forcibly stopped after a predetermined time or in a state where the motor is forcibly set to a low rotation speed, the control circuit determines that the battery voltage during operation is decreased per unit time -ΔV exceeds another set value. 4. The electric power tool according to claim 2, wherein the predetermined time Smin for limiting the restart of the motor is lengthened.   5. The electric tool according to claim 1, wherein the control circuit changes the set value or the predetermined times Mmax and Smin according to a remaining capacity of the battery.   When the control circuit is in a state where the motor is forcibly stopped or forcibly set to a low rotational speed after a predetermined time Mmax, and when the restart of the motor is restricted, a notification is issued to notify the user of these. The electric tool according to any one of claims 1 to 5, further comprising means.

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