JPH05176574A - Power tool - Google Patents

Abstract

PURPOSE:To obtain a power tool capable of being used while speed is fixed at arbitrary speed by providing a speed control means controlling motor speed in the storage speed of a storage means regardless of the state of operation of a trigger switch. CONSTITUTION:A power tool constitutes a storage means by a memory 4 and a timing means transmitting a timing signal over the memory 4 by a set switch S1 and a timing circuit 5 while a sped control means controlling the speed of a motor M by the storage means is composed of a comparison circuit 3 and a control circuit 1 regardless of the state of operation of a trigger switch during a time when motor speed is stored in the memory 4. When the quantity of push-in of a trigger is changed and speed is adjusted so as to reach desired speed and the set switch S1 is depressed when sped reaches desired speed at the time of usage, a timing signal is output from the timing circuit 5, and the timing signal is received and the detecting speed of a speed detector 2 is taken and stored in the memory 4. Outputs corresponding to detecting speed are transmitted over the comparison circuit 3 from the memory 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to speed control for fixing the drive speed of an electric tool such as an electric screwdriver or an electric drill.

[0002]

2. Description of the Related Art In an electric screwdriver or an electric drill as an electric power tool, a trigger of a trigger switch which can be operated by a finger is attached to a portion having an electric power tool, and the electric tool is driven by adjusting the retracted amount of the trigger. There are things that allow you to change the speed. Here, the trigger switch is spring-biased so as to project (becomes an off position) when the trigger is not performing a pressing operation,
The resistance value of the variable resistor is changed according to the amount of pushing of the trigger.

[0003]

However, this type of trigger-operated power tool has a problem in that it is necessary to keep pressing the trigger for a long time during work. Therefore, as a method of improving this point, there is a method of providing a lock structure for fixing the pushed state of the trigger on the trigger switch so that it is not necessary to keep pushing the trigger for a long time.

However, in this type of electric tool with a lock function, the drive speed can be fixed only when the amount of pushing of the trigger is at a maximum, so that the electric tool cannot be set to an arbitrary speed for use. was there. The present invention has been made in view of the above points, and an object thereof is to provide an electric power tool that can be used while being fixed at an arbitrary speed.

[0005]

In the present invention, in order to achieve the above object, a motor as a drive source, a speed detecting means for detecting the speed of the motor, and a storing means for storing the detected motor speed. And timing means for giving a timing signal for storing the motor speed in the storage means,
Speed control means for controlling the motor speed to the storage speed of the storage means regardless of the operating state of the trigger switch while the motor speed is stored in the storage means.

Further, in order to automatically fix the drive speed, the timing means may give a timing signal to the storage means when the motor speed remains substantially constant for a certain period.

[0007]

The present invention has the above-mentioned configuration,
When a timing signal is given to the storage means by the timing means in a state where the desired speed is set by the trigger operation, the motor speed is fixed to the speed stored in the storage means at that time. Further, when the timing means automatically gives the timing signal to the storage means when the state where the motor speed is substantially constant continues for a certain period, the motor speed is automatically fixed to the substantially constant speed at that time.

[0008]

FIG. 1 shows an embodiment of the present invention. The electric power tool of this embodiment includes a control circuit 1 for controlling the drive of the motor M,
A frequency generator FG such as a rotary encoder attached to the motor M, a speed detection circuit 2 for detecting the rotation speed of the motor M from the output of the frequency generator FG, and a rotation of the motor M detected by the speed detection circuit 2. The comparison circuit 3 for comparing the speed with the set speed is provided, and the control circuit 1 performs drive control according to the output of the comparison circuit 3 so that the speed of the motor M matches the set speed. That is, in this electric tool, the rotation speed of the motor M can be automatically adjusted to the set speed by detecting the rotation of the motor M and feeding it back to the control circuit 1. Here, in the present embodiment, the frequency generator FG and the speed detection circuit 2 constitute speed detection means for detecting the speed of the motor M. Then, a reference voltage V _ref that varies according to the amount of _pushing is given to the comparison circuit 3 from the variable resistance VR of the trigger switch, and the control circuit compares the reference voltage V _ref with the output of the speed detection circuit 2. The output corresponding to the difference between the set speed and the actual rotation speed of the motor M is given to 1.

However, the above-mentioned structure is also equipped with a conventional electric power tool, and in the case of this embodiment as well, it is used in the same manner when a normal trigger is operated. The characteristic configuration of this embodiment will be described below. In the case of the present embodiment, a memory 4 for storing the speed of the motor M detected by the speed detection circuit 2, and a timing circuit 5 for giving a timing signal for reading the rotation speed in this memory 4,
A set switch S ₁ operated when fixing the speed at an arbitrary speed and a reset switch S ₂ operated when releasing the fixed state of the speed are provided. Here, the memory 4 constitutes a storage means, and the set switch S ₁ and the timing circuit 5 constitute a timing means for giving a timing signal to the memory 4. Further, while the motor speed is stored in the memory 4, speed control means for controlling the speed of the motor M to the storage speed of the memory 4 is constituted by the comparison circuit 3 and the control circuit 1 regardless of the operation state of the trigger switch. I am doing it.

The operation of fixing the speed in this embodiment will be described below. When using this electric power tool, the amount of pushing of the trigger is changed to drive the electric power tool to a desired speed. Then, when the desired speed is reached, the set switch S ₁ is pressed. At this time, a timing signal is output from the timing circuit 5,
The memory 4 receiving this output captures and stores the detected speed of the speed detecting circuit 2. Then, an output corresponding to the detected speed is given from the memory 4 to the comparison circuit 3.
Here, when the output from the memory 4 is given in this way, the comparison circuit 3 does not accept the reference voltage V _ref of the trigger switch. Therefore, thereafter, speed control is performed using the output of the memory 4 as a reference voltage. That is, the speed of the motor M is maintained at a desired speed regardless of the operation on the trigger switch side.

Then, the fixed state of the speed of the electric tool is released.
Reset switch S ₂push. This and
This reset switch S₂Of the memory 4
The stored contents are erased and the output of the memory 4 is given to the comparison circuit 3.
Therefore, the reference voltage on the trigger switch side cannot be obtained.
V_refIs canceled, and after that, the
Speed control is performed according to the pushing amount of the rig.

According to this embodiment, when the speed of the electric tool reaches a desired speed, the set switch S ₁
By pressing, the speed of the motor M at that time can be fixed, and thus the speed of the electric tool can be fixed to an arbitrary speed for use. Therefore, even when the power tool is used at a constant speed, it is not necessary to keep pressing the trigger for a long time, which makes the work easier and is particularly effective for a long work.

By the way, in the above case, the speed is the desired speed.
Set switch S ₁I was pressing
With the configuration shown in FIG. 2, the set switch S₁The operation of
It may be unnecessary. In FIG.
Switch S₁Instead of, the speed of the motor M is almost constant
The timer 6 that detects that the state of
The output of this timer 6 causes timing from the timing circuit 5.
To generate a ringing signal.

In the case of fixing at an arbitrary speed in FIG. 2, the trigger switch is operated to drive the electric tool at an arbitrary speed to keep the driving state. Then, the timer 6 detects a state in which the speed is substantially constant, and it is determined whether or not this state continues for a certain period or more. When the state of the constant speed continues for a certain period or more, the timing signal is output from the timer 6. The output for generating is given to the timing circuit 5.

As a result, the above-mentioned set switch S ₁
Similarly to the case of pressing, the rotation speed of the motor M detected by the speed detection circuit 2 at that time is stored in the memory 4, and thereafter the speed of the electric tool is fixed. By doing so, the operation of the set switch S ₁ can be dispensed with. By the way, in the electric tools shown in FIGS. 1 and 2, there may be a case where the electric tool is temporarily stopped but it is desired to use the electric tool at the set speed at the time of subsequent use. Therefore,
In order to cope with such a case, a stop switch S ₃ is provided to stop the power tool without canceling the speed setting state. That is, when the stop switch S ₃ is turned on, the drive control of the motor M by the control circuit 1 is stopped by making the control circuit 1 inoperative, for example. By doing so, the stored contents of the memory 4 are retained as they are, and when the stop switch S ₃ is turned on again to operate the control circuit 1, the speed control is performed based on the output of the memory 4, so that the previous use is possible. Work can be resumed at the set speed.

By the way, depending on the case, it may be convenient to set the speed to an arbitrary speed each time the work is restarted. Therefore, in the case of the power tool used in this way, the stop switch S ₃ is provided with the function as the reset switch S ₂ as shown in FIG. 3, and when the stop switch S ₃ is operated, the memory 4 is stored. The stored contents may be erased.

Furthermore, if the state in which the speed of the electric power tool is fixed as described above is continued indefinitely, the electric power tool may be left rotating and unfavorable from the viewpoint of safety. It is not preferable for the motor M to rotate the motor M for a too long time. Therefore, FIG.
As shown in FIG. 3, a timer 7 for counting a fixed time from the time when the set switch S ₁ is operated is provided, and the output of the timer 7 is given to the control circuit 1 as a stop signal of the motor M. By doing so, it is possible to prevent the motor M from being driven for a long time. Further, in FIG. 4, the output of the timer 7 is given to the memory 4 through the reset circuit 8 to erase the stored contents of the memory 4 when the motor M is stopped.

Furthermore, the storage state of the memory 4 may be released by the trigger switch 9. In this case, as shown in FIG. 5, the reset switch S ₂ may be incorporated in the trigger switch 9 so that the stored contents of the memory 4 are erased when the trigger 9a of the trigger switch 9 is pushed. Here, as the reset switch S ₂ , it is sufficient to use a structure which is turned on only when the trigger 9a is pushed in and is not turned on when the trigger 9a returns to the off position.

[0019]

As described above, the present invention provides a motor as a drive source, a speed detecting means for detecting the speed of the motor, a storage means for storing the detected motor speed, and a motor speed for the storing means. And timing control means for controlling the motor speed to the storage speed of the storage means regardless of the operation state of the trigger switch while the motor speed is stored in the storage means. Therefore, when the timing signal is given to the storage means by the timing means in the state where the speed is set to the desired speed by the trigger operation, the motor speed can be fixed to the speed stored in the storage means at that time, and therefore the electric tool Can be fixed and used at any speed.

Further, when the timing means gives the timing signal to the storage means when the motor speed is kept substantially constant for a certain period, the motor speed is kept substantially constant when the motor speed is kept for a certain period. The motor speed can be automatically fixed to the speed. For example, the timing means can be configured without using a switch or the like, the operation of turning on the switch or the like can be unnecessary, and the speed fixing operation can be performed easily.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of an embodiment when it is not necessary to operate a set switch in the above.

FIG. 3 is a block diagram showing a circuit configuration of an embodiment in which a stop switch has a function of a reset switch.

FIG. 4 is a block diagram showing a circuit configuration of an embodiment having a function of prohibiting use for a long time.

FIG. 5 is a block diagram showing a circuit configuration of an embodiment in which a fixed speed state can be released by a trigger switch.

[Explanation of symbols]

1 Control Circuit 2 Speed Detection Circuit 3 Comparison Circuit 4 Memory 5 Timing Circuit 6,7 Timer 9 Trigger Switch 9a Trigger M Motor FG Frequency Generator S ₁ Set Switch S ₂ Reset Switch S ₃ Stop Switch

Claims (2)

[Claims] 1. In a power tool whose drive speed changes in accordance with the amount of pressing of a trigger of a trigger switch, a motor as a drive source, speed detection means for detecting the speed of this motor, and the detected motor speed are stored. Storage means, timing means for giving a timing signal for storing the motor speed in the storage means, and storage of the motor speed in the storage means regardless of the operation state of the trigger switch while the motor speed is stored in the storage means. An electric power tool, comprising: speed control means for controlling the speed. 2. The electric tool according to claim 1, wherein the timing means provides a timing signal to the storage means when the motor speed is kept substantially constant for a certain period.