JP2624970B2 - Electric tool - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric tool such as an electric screwdriver, an electric drill, and an electric jigsaw.

[Background Art] Conventionally, an electric driver using a motor as a driving source can detect a motor current, calculate a torque of an output shaft based on the detected value, and stop the motor with a preset torque value. Met. This has a substantially proportional relationship between the motor current Im and the generated torque Tm,
Further, between the output torque Tm of the motor and the output shaft torque To of the driver, there is a complete proportional relationship between the motor and the output shaft because the speed reducer is formed by a combination of fixed gears. As shown in FIG. 4, a proportional relationship To = aIm +
This is because b.

However, this proportional relationship changes as shown in FIG. 5, for example, when the temperature changes. This is because the viscous resistance of the reduction gear increases and the load increases. FIG. 5 shows a case where Ta = 0 ° C., Ta = 20 ° C., and Ta = 40 ° C. When a predetermined value of the motor current Im is set as a set value,
This shows that the output shaft torque To changes with a change in temperature. Further, if the pressing force of the electric screwdriver increases, the load increases as in FIG. 5, so that the load changes as shown in FIG. In FIG. 6, the pressing force is
The cases of 0 kg, 20 kg and 40 kg are shown.

Therefore, the motor stops at an incorrect torque value due to the pressing force with respect to the preset torque value,
There have been problems that the screw thread is destroyed, the object to be tightened is destroyed, and the screw cannot be completely tightened.

[Object of the invention] The present invention has been provided in view of the above points,
Even if the pressing force changes, the power tool automatically corrects the calculated value of the torque of the output shaft by the motor current, calculates the correct torque value, and always provides a power tool that stops the motor at a preset torque value. It is intended.

[Disclosure of the Invention] (Configuration) The present invention calculates a torque of an output shaft by detecting a motor current, compares a preset torque value with the detected torque value, and sets the detected torque value to a preset value. A power tool having control means for stopping the motor when the torque value exceeds a predetermined torque value, a pressure sensor for detecting a force pressing the tool is provided, and the control means calculates an output shaft torque based on a motor current and an output of the pressure sensor. Is automatically corrected to stop the motor with a constant torque even if the pressing force of the tool changes.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of the electric screwdriver, and FIG. 2 is a diagram showing the arrangement of components of the electric screwdriver. Second
In the figure, a motor 2 and a speed reducer 3 are arranged in a cylindrical housing 1 in the axial direction, and the motor 2 and the speed reducer 3 are motors as shown in FIG. The convex portion 1a of the housing 1 is fitted and fixed to the second concave portion 2a. Further, the motor 2 and the speed reducer 3 are fixed to the housing 1 through a pressure sensor 4 abutting on the partition 1b of the housing 1 in the thrust direction. A chuck 5 is attached to an output shaft of the speed reducer 3, and a printed board 6 on which an electronic circuit described later is mounted is disposed at a rear portion of the housing 1. The upper surface of the rear part of the housing 1 is provided with a volume 7 for setting a torque in advance. A grip portion 8 is integrally provided below the housing 1, and a power supply on / off switch 9 is arranged on an upper front surface of the grip portion 8. A battery pack having a built-in battery serving as a drive source for the motor 2 is provided below the grip portion 8.
10 is detachably mounted.

In FIG. 1 showing a block diagram, a current sensor 12 such as a shunt resistor is inserted and connected in series with the motor 2, and a pressure sensor 4 such as a strain gauge for detecting a pressing force of a tool, a thermistor for detecting an ambient temperature, and the like. The output from the temperature sensor 13 is input to the amplifier circuit 17. The amplification circuit 17 corrects the amplification factor, the bias voltage, and the like by a preset ratio in accordance with the change in the pressing force and the temperature. The amplifying circuit 17 constitutes a correcting means for automatically correcting the calculation of the output shaft torque in response to the change of the situation. The reference voltage generation circuit 16 generates a reference voltage corresponding to the torque at which the motor 2 is to be stopped by the torque setting volume 7. Then, the respective outputs from the amplifier circuit 17 and the reference voltage generation circuit 16 are compared by the comparison circuit 15, and the output of the comparison circuit 15 drives the electronic switch 14 to cut off the power supply from the battery 11 to the motor 2. Like that. Note that the reference voltage generation circuit
The control circuit 18 for stopping the motor 2 when the detected torque value exceeds a preset torque value is constituted by the amplification circuit 17, the amplification circuit 17, and the comparison circuit 15.

Next, the operation will be described. First, when the switch 9 is turned on, the motor 2 rotates because the electronic switch 14 is on in the initial state. The temperature, pressure and current at that time are detected by the sensors 13, 4, and 12, respectively. Amplifier circuit 1 in control circuit 18
In 7, the output from the current sensor 12 is amplified and the comparison circuit 1
The amplification factor and the bias voltage of the amplification circuit 17 are corrected by a preset ratio by the outputs of the temperature sensor 13 and the pressure sensor 4. Accordingly, the signal amplified by the amplifier circuit 17 is proportional to the output shaft torque of the driver even when the temperature or the pressing force changes. This signal is compared with a reference voltage corresponding to the torque at which the motor 2 is to be stopped by the torque setting volume 7 from the reference voltage generating circuit 16 in advance, and the signal from the amplifier circuit 17 reaches the reference voltage. Then, the comparison circuit
A signal is output from 15 to the electronic switch 14, which turns off the electronic switch 14 and stops the motor 2. Thereafter, when the switch 9 is turned off, the electronic switch 14 is turned off.
Turns on. The screw tightened by the driver by this series of operations is not always tightened with a torque equal to or higher than a certain value, and the tightening can be completed. In the above embodiment, the electric screwdriver has been described. However, it is needless to say that the present invention can be applied to a drill, a jigsaw, and the like.

[Effects of the Invention] As described above, the present invention calculates the torque of the output shaft by detecting the motor current, compares the preset torque value with the detected torque value, and determines whether the detected torque value is In a power tool having control means for stopping a motor when a set torque value is exceeded, a pressure sensor for detecting a force pressing the tool is provided. Since the correction means for automatically correcting the calculation is provided, with this correction means, the calculation of the output shaft torque is automatically corrected in accordance with the pressing force of the tool, and even if the pressing force of the tool changes. The motor can be stopped with a constant torque, so, for example, when used as an electric screwdriver, poor tightening or excessive tightening This has the effect of preventing the breakage of the screw thread and the breakage of the tightened object.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a sectional view of the same, FIG. 3 is a BB sectional view of FIG. 2 of the same, and FIG. FIG. 5 is a characteristic diagram showing the relationship between the current and the output shaft torque, FIG. 5 is a characteristic diagram when the temperature is changed, and FIG. 6 is a characteristic diagram when the pressing force is changed. 2 is a motor.

Claims (1)

(57) [Claims] An output shaft torque is calculated by detecting a motor current, a preset torque value is compared with the detected torque value, and when the detected torque value exceeds a preset torque value. In a power tool having control means for stopping a motor, a pressure sensor for detecting a force pressing the tool is provided, and the control means automatically corrects calculation of an output shaft torque based on a motor current and an output of the pressure sensor. An electric tool characterized by comprising means.