KR101834974B1 - Control method of electrically-drive tool - Google Patents

Abstract

The present invention relates to a control method of an electrically driven tool for a hammer rotating by an electric motor to hit an anvil and, more specifically, to a control method of an electrically driven tool, comprising: a first step of grasping joint characteristics with respect to a coupling member before the hammer hits the anvil at first; a second step of controlling the rotational speed of the electric motor to gradually increase hitting torque applied to the anvil; and a third step of reducing the rotational speed to zero when the hitting torque reaches predetermined target torque. Moreover, the rotational speed is controlled for each measurement torque with respect to the hitting torque to be variably controlled in accordance with the joint characteristics in the second step.

Description

[0001] CONTROL METHOD OF ELECTRICALLY-DRIVE TOOL [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a control method for an electric power tool, and more particularly, to a control method for a power tool that generates an impact due to a hammer depending on a size of a load acting on a coupling member in a fastening process.

The electric power tool can drive the electric motor by a power source such as a battery and rotate the tool tool which is selectively coupled according to the kind of the electric work or the application, so that the work can be performed by tightening the screw or drilling the hole.

Among these power tools, particularly the power tools that provide the impact include a hammer coupled to the electric motor side and an anvil struck by the hammer. In this case, the hitting force by the hammer, that is, the magnitude of the impact, depends on the weight of the hammer and the rotational speed of the hammer just before hitting the anvil.

However, the power tool providing the conventional impact has a problem that the hammer is designed to strike the anvil at the same speed so that the size of the impact can not be precisely controlled. In other words, since the size of the impact can not be calculated in advance, an impact of a magnitude exceeding the target torque is applied to the fastening member, resulting in poor fastening.

In addition, there is a problem in that the power tool that provides the conventional impact does not have a structure capable of judging the joint characteristics with respect to the fastening member itself, and the fastening accuracy is lowered in performing the electric operation such as tightening the fastening member.

Korean Patent No. 10-1453891 Japanese Patent Laid-Open No. 06190741 Japanese Laid-Open Patent No. 11138459

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a control method of a power tool capable of precisely controlling the impact torque applied to an anvil, that is, the impact, thereby improving the tightening accuracy.

Further, it is an object of the present invention to provide a control method capable of grasping joint characteristics with respect to a coupling member in an electric power tool providing an impact. It is another object of the present invention to provide a control method capable of preventing an increase in the total time required for tightening by precise control over the magnitude of impact.

In order to solve the above problems, an embodiment of the present invention provides a control method of a power tool in which a hammer pivoted by an electric motor strikes an anvil, the hammer including a joint to a fastening member before the hammer hits the anvil for the first time, A first step of identifying characteristics; A second step of controlling the rotational speed of the electric motor so that the striking torque applied to the anvil is sequentially increased; And a third step of decelerating the rotational speed to zero when the striking torque reaches a predetermined target torque, wherein in the second step, each measured torque for the striking torque varies in accordance with the characteristic of the joint And controlling the rotation speed so as to control the rotation speed of the power tool.

In the first step, the joint characteristic may be determined as a first torque ratio which is an increase rate with respect to time of the measurement torque applied to the anvil.

It is preferable that in the second step, the rate of increase with respect to the maximum value of the measured torque is controlled to coincide with the first torque rate.

And a fourth step of correcting the increase rate when the increase rate is inconsistent with the first torque rate.

The second step may start when the magnitude of the measured torque reaches a range within 70 to 90 percent of the target torque value.

2. The method according to claim 1, wherein in the second step, when the magnitude of the measured torque is less than 70 to 90 percent of the target torque value, each increment of the striking torque is smaller than an increment of the immediately striking torque It is preferable to control the rotation speed.

It is preferable that the striking torque increases nonlinearly and gradually converges to the target torque.

As described above, according to the present invention, various effects including the following can be expected. However, the present invention does not necessarily achieve the following effects.

The control method of the power tool according to the embodiment can control the rotation speed of the electric motor so that the magnitude of the striking torque applied to the anvil is sequentially increased, thereby improving the tightening accuracy.

In this case, the control of the rotational speed of the electric motor is controlled so as to be started after a certain portion is engaged, thereby reducing the time required for fastening by preventing the number of impacts from being increased. In addition, the striking torque generated before the control of the rotational speed of the electric motor is started can be rapidly increased by nonlinearly increasing the striking torque.

Further, a power tool that provides impact through a hammer can improve the fastening accuracy because the joint characteristics with respect to the fastening member can be grasped. Further, the magnitude of each measured torque with respect to the striking torque can reflect the joint characteristics that have been grasped in advance before the impact is generated for the first time, so that the tightening accuracy can be improved.

1 is a flowchart showing a control method of a power tool according to an embodiment of the present invention;
2 is a schematic perspective view of the hammer and anvil included in the power tool of FIG. 1;
3 is a graph of striking torque according to one embodiment.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a schematic perspective view of a hammer and an anvil included in the power tool of FIG. 1, and FIG. 3 is a cross-sectional view of a power tool according to an embodiment of the present invention. A graph of striking torque.

1 to 3, the control method of the electric power tool includes: 1) a first step (s10) of grasping joint characteristics; 2) a second step (s20) of controlling the rotational speed of the electric motor; 3) A fourth step s40 for correcting the rate of increase b, and a fifth step s50 for storing the incremental rate b in the removable memory device.

The control method according to an embodiment can be applied to a power tool using an electric motor as a means for providing torque. At this time, the power tool further includes a current control unit dedicated to control of the current, so that the tightening accuracy can be improved. The electric power tool may further include a speed sensor for detecting the rotational speed of the electric motor, a torque sensor for detecting a measurement torque actually applied to the fastening member by the striking torque, an encoder for detecting a rotation angle of the fastening member, .

Referring to Fig. 2, in the power tool, the anvil 20 is struck by the hammer 10 rotating by the electric motor. A power tool that provides impact by the hammer 10 can provide a striking torque to the fastening member, such as, for example, a bolt, thereby tightening the fastening member more firmly.

Specifically, in a power tool, a tool tool suitable for a work purpose is fastened to the tip of the tool axis. On the other hand, the anvil 20 is coupled to the other end of the tool shaft. The anvil 20 can be struck in the rotational direction of the tool axis to provide an impact on the workpiece.

The hammer 10 strikes the anvil 20 in the rotational direction of the tool axis. The amount of the striking torque applied to the anvil 20 by the hammer 10 depends on the elastic force of the spring disposed on the hammer 10 side and the rotational speed of the hammer 10. Here, the elastic force is constant, and the magnitude of the striking torque depends mainly on the rotational speed of the electric motor, which provides the torque to the hammer 10, with respect to the drive shaft. At this time, the control of the rotational speed of the drive shaft can be implemented by controlling the current supplied to the electric motor.

On the other hand, the tightening of the fastening member is influenced by the joint characteristics with respect to the fastening member. These joint characteristics are specified by the International Organization for Standardization. For example, when a hard joint is seated, the head portion of the coupling member rotates further within 30 degrees, and the soft joint is considered to be normally engaged, while the soft joint is considered to be normally engaged when the angle further rotates within 360 degrees or 720 degrees. do. However, the target torque is set in advance regardless of such joint characteristics.

Herein, the term 'sitting' means that as the nut moves forward along the thread of the bolt, especially when the head of the nut comes into contact with the workpiece and the rotation speed of the nut starts to decrease due to the increase of the friction coefficient It refers to the arrangement of the nuts. On the other hand, the fastening process is completed only after the nut is further tightened after being seated.

The joint characteristics depend on the frictional coefficient between the fastening surface and the tightening member that is tightened in contact with the fastening surface. And, it is desirable that such a joint characteristic is grasped before the hammer 10 hits the anvil 20 for the first time.

The first step s10 is a step for grasping the joint characteristics of the fastening member before the hammer 10 hits the anvil 20 for the first time. The joint characteristic is expressed by a value obtained by dividing the measurement torque by the rotation angle of the fastening member by the measurement torque. At this time, the maximum value of the measured torque is used. However, the joint characteristic according to one embodiment is determined as the first torque ratio (a), which is an increase rate with respect to the time of the measured torque applied to the anvil 20.

Theoretically, the joint properties remain constant until the fastening process for each fastening site is completed. However, the actual joint characteristics may be variable due to changes in the friction coefficient and the like as the rotation angle of the nut increases. Accordingly, when the first torque ratio a is calculated, it is possible to judge whether the fastening member used in the power tool is a hard joint or a soft joint.

On the other hand, it is desirable to grasp the joint characteristics before the hitting by the hammer 10 is started for the first time because the load applied to the fastening member increases.

Next, the second step s20 is a step of controlling the rotation speed of the electric motor so that the striking torque applied to the anvil 20 is sequentially increased. A plurality of striking torques are set in advance so as to be sequentially increased in consideration of the target torque. Here, the target torque refers to the striking torque which is finally applied to the fastening member or the like in the process of tightly tightening the fastening member.

According to one embodiment, it is preferable to control the rotational speed of the electric motor such that each measured torque applied to the actual anvil 20 by the striking torque is variably controlled in accordance with the joint characteristics.

To detect the measured torque, for example, a torque sensor or the like may be disposed at the tip of the anvil 20 to detect the striking torque continuously or discontinuously. The power tool can provide impact to the workpiece through the striking torque.

Specifically, the rate of increase (b) with respect to the maximum value of each measured torque is controlled to coincide with the first torque rate (a). That is, the first torque ratio (a) may provide a reference to at least one or more measurement torque that sequentially increases so that the target torque is applied to the coupling member. Therefore, if the fastening member is tightened by reflecting the joint characteristics as described above, the fastening accuracy is improved.

Alternatively, it may further include a fourth step (s40) of correcting the increase rate b if the increase rate b is inconsistent with the first torque rate a. The specific correction method can be implemented by a method of variably controlling the increase of the current supplied to the electric motor.

On the other hand, the second step s20 may be started only when the magnitude of the measured torque reaches a range within 70 to 90 percent of the target torque value. This is to prevent an increase in the time required for fastening because the number of times of providing the impact is increased if the impact torque that generates impact is provided from the beginning of the fastening process. Thus, in this early stage of the fastening process, the rotational speed of the electric motor is controlled irrespective of the joint characteristics.

If the magnitude of the measured torque is less than the range of 70 to 90 percent of the target torque value in the second step s20, each increment of the striking torque that is sequentially increased becomes smaller than the increment of the immediately striking torque It is preferable to control the rotational speed of the motor. Looking at the graph, d1 is greater than d2. Also, d2 is larger than d3. That is, the striking torque preset in the second step s20 may increase nonlinearly and gradually converge to the target torque. Here, d1, d2 and d3 correspond to increments between neighboring striking torques.

That is, when the graph of the striking torque is viewed, the increment gradually decreases from the early half to the latter half. The magnitude of the initial striking torque provided in the early stage may be set differently considering the magnitude of the target torque. For example, the magnitude of the initial striking torque may be proportional to the magnitude of the target torque.

Therefore, as in the preferred embodiment of the present invention, the striking torque can be reached to the target torque more quickly through the control method of increasing the measurement torque in the beginning and gradually increasing the amount of increase.

At this time, if the detected striking torque is smaller than or greater than the preset striking torque, the rotation speed of the next electric motor can be changed. As a result, the striking torque immediately applied next may be closer to the next striking torque preset. That is, the accuracy of the striking torque provided by the power tool can be improved through the step of controlling the magnitude of the striking torque by reflecting the error.

Since the striking torque is proportional to the square of the rotational speed of the electric motor, the rotational speed is determined in consideration of the magnitude of the striking torque to be set. That is, each rotation speed has a large value in the early half and a gradually decreasing increment. At this time, the time at which the set rotational speed is reached may be variable. This can be varied considering the magnitude of the current supplied to the electric motor and the like.

Next, the third step (s30) is a step of decelerating the rotational speed of the electric motor to zero when the striking torque reaches a predetermined target torque. To this end, the electric current supplied to the electric motor is cut off. Alternatively, it is also possible to provide a reverse current to the electric motor so that the driving shaft of the electric motor rotating by the inertial force can be decelerated to zero more quickly.

It is preferable to control the rotational speed of the electric motor so that any one of the striking torques does not exceed the target torque. Therefore, when the striking torque to be measured exceeds the target torque, the electric operation for applying the striking torque can be immediately terminated. In other words, it is preferable to control the striking torque so that the striking torque does not exceed the target torque in order that the power transmission providing the impact can be normally completed without failures.

At this time, if the striking torque falls within 95% to 105% of the target torque, the striking torque can be regarded as having reached the target torque. This is because, when the striking torque reaches within a predetermined range of the target torque, it is difficult to fine-tune the rotational speed of the electric motor and feedback it.

Next, a fifth step (s50) of storing the respective striking torques and rotational speeds in the removable memory device after the third step (s30) or the fourth step (s40) may be further included. Here, the removable memory includes a USB (USB), SD (SD) card and the like, and is detachably mounted on one side of the power tool. This is to manage work quality by separately storing work history. The work quality depends not only on the final applied striking torque but also on the striking torque actually applied in the middle of the process.

To this end, it is preferable to detect the rotational speed of the electric motor at the same time as detecting the striking torque. As a result, the striking torque detected by the actual anvil 20 and the rotation of the electric motor corresponding to the energy of the striking torque detected by the actual anvil 20, which reflects the energy loss generated in the process of energy transmitted from the electric motor through the hammer 10 to the anvil 20, Speed can be detected together.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention.

a: first torque ratio b: increase rate

Claims (7)

A control method for a power tool in which a hammer rotating by an electric motor strikes an anvil,
A first step of grasping a joint characteristic of the fastening member before the hammer strikes the anvil for the first time;
A second step of controlling the rotational speed of the electric motor so that the measured torque for the striking torque is variably controlled according to the characteristics of the joint so that the striking torque applied to the anvil is sequentially increased; And
And a third step of decelerating the rotation speed to zero when the striking torque reaches a predetermined target torque,
And the second step starts when the magnitude of the measured torque reaches a range within 70 to 90 percent of the target torque value.
The method according to claim 1,
If the magnitude of the measured torque in the second step falls within a range of 70 to 90 percent of the target torque value,
And the rotation speed is controlled so that each increment of the striking torque becomes smaller than an increment of the immediately striking torque.
3. The method of claim 2,
Wherein the striking torque increases nonlinearly and gradually converges to the target torque.
A control method for a power tool in which a hammer rotating by an electric motor strikes an anvil,
A first step of grasping a joint characteristic with respect to a fastening member at a first torque rate which is an increase rate with respect to time of a measurement torque applied to the anvil before the hammer hits the anvil for the first time;
A second step of controlling the rotation speed of the electric motor such that the striking torque is sequentially increased by making the rate of increase with respect to the maximum value of the measured torque with respect to the striking torque applied to the anvil equal to the first torque rate;
A third step of decelerating the rotation speed to zero when the striking torque reaches a preset target torque; And
And a fourth step of correcting the increase rate when the increase rate is inconsistent with the first torque rate,
And controlling the rotation speed such that the measured torque for the striking torque is variably controlled in accordance with the joint characteristic in the second step. delete delete delete

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